WO2010059812A1 - Surface-modified metal phosphate nanoparticles - Google Patents

Abstract

Provided are compositions that comprise surface-modified nanoparticles of at least one metal phosphate. The nanoparticles bear, on at least a portion of their surfaces, a surface modification comprising at least one organocarboxylate surface modifier comprising at least one organic moiety comprising at least about six carbon atoms. Also provided are methods of making said compositions and articles derived therefrom.

Description

SURFACE-MODIFIED METAL PHOSPHATE NANOPARTICLES

Field

Provided are compositions that include surface-modified metal phosphate nanoparticles, articles comprising said compositions, and methods of making said compositions.

Background

Metal phosphates (for example, alkaline earth phosphates such as magnesium phosphate and calcium phosphate) have numerous applications. Alkaline earth phosphates are used in anti-rust coatings, in flame retardants, in antacids, and in producing fluorescent particles. Iron phosphates find application in cathode material for lithium ion batteries. Aluminum, manganese, cobalt, tin, and nickel phosphates are used in heterogeneous catalysis. Zinc phosphate is commonly used as a pigment in anti-corrosion protection. Zirconium phosphates are used as solid acid catalysts. Various lanthanide phosphates are useful as fluorescent and laser materials.

Calcium phosphates are particularly useful, however, due to their classification as biocompatible materials. Under physiological conditions, calcium phosphates can dissolve, and the resulting dissolution products can be readily assimilated by the human body. Biocompatible calcium phosphates include hydroxyapatite (HAP; [Ca₅(PO₄)SOH]), dicalcium phosphate (DCP; [Ca(HPO₄).2H₂O]), tricalcium phosphate (TCP; [Ca₃(PO₄)₂]), tetracalcium phosphate (TTCP, [Ca₄O(PO₄)₂]), and amorphous calcium phosphate. Bioresorbable and biocompatible calcium phosphate materials have wide spread applications in clinical and aesthetic medicine. Some useful applications of these materials include use in dental cements, gene/drug delivery, vaccine/protein adjuvants and allergen desensitization. In addition, other metal phosphates also offer interesting properties. For example, aluminum phosphate coatings are known to provide corrosion inhibition for various metallic substrates (Ni, Ti alloys), zirconium phosphates are used as solid acid catalysts, rare earth metal phosphates and rare earth metal doped calcium phosphate materials find applications as luminescent probes. Metal phosphate encapsulated lithium ion battery cathode materials (LiCoO₂) exhibit enhanced electrochemical performances.

Of the biocompatible calcium phosphates, hydroxyapatite can be more stable under physiological conditions. Thus, hydroxyapatite has been used for bone repair after major trauma or surgery (for example, in coatings for titanium and titanium alloys). Hydroxyapatite has also been used in the separation and purification of proteins and in drug delivery systems. Other calcium phosphates have been used as dietary supplements in breakfast cereals, as tableting agents in some pharmaceutical preparations, in feed for poultry, as anti-caking agents in powdered spices, as raw materials for the production of phosphoric acid and fertilizers, in porcelain and dental powders, as antacids, and as calcium supplements.

For some of these applications (for example, adjuvants for vaccines, cores or carriers for biologically active molecules, controlled release matrices, coating implant materials, protein purification, and dental applications) non-agglomerated nanoparticles of calcium phosphate can be desired. The preferred sizes, morphologies, and/or degrees of crystallinity of the nanoparticles vary according to the nature of each specific application.

Numerous methods have been used for the synthesis of hydroxyapatite nanoparticles including chemical precipitation, hydrothermal reactions, freeze drying, sol- gel formation, phase transformation, mechanochemical synthesis, spray drying, microwave sintering, plasma synthesis, and the like. Hydroxyapatite nanoparticles have often been synthesized by the reaction of aqueous solutions of calcium ion-containing and phosphate ion-containing salts (the so-called "wet process"), followed by thermal treatment. Nanoparticles obtained by this method generally have had a needle-like (acicular) morphology with varying degrees of crystallinity, depending upon the nature of the thermal treatment. Such acicular nanoparticles can be used as coating implant materials but have limited or no use in some of the other applications mentioned above.

Various additives have been used to control hydroxyapatite particle growth and/or to alter hydroxyapatite particle morphology but with only limited success. For example, polymers and solvent combinations have been used in the above-described wet process to suppress crystal growth along one axis, but only a few approaches have provided particles with decreased aspect ratios or particles of spherical morphology but relatively large particle size.

Solid-state reaction of precursors, plasma spraying, pulsed laser deposition, and flame spray pyrolysis methods have resulted in hydroxyapatite nanoparticles of different morphologies (for example, spherical or oblong), but these have often been in the form of micron-sized agglomerates of nanoparticles that have been of limited use in certain applications. Numerous researchers have carried out post- synthesis surface modification of hydroxyapatite to de-agglomerate the particles.

Generally, the synthesis of spherical hydroxyapatite nanoparticles has involved the use of either surfactants or polymers to control the morphology and the size of the resulting particles. The capability of such methods to provide nanoparticles in the form of redispersible dry powders (for example, dry powders that can be redispersed in an appropriate solvent to provide a non-agglomerated nanoparticle dispersions), however, has generally not been demonstrated.

Summary

Metal phosphate nanoparticles, such as for example, calcium or magnesium phosphate nanoparticles and methods of making them are known. Depending on applications like vaccine adjuvants, as cores or carriers for biologically active molecules, coating implant materials and dental applications, unaggregated nanoparticles of calcium phosphate of varying composition, size, morphology and crystallinity are desired. In addition, it is desirable to have very small (< 20nm) core particles, which are bioresorbable and can be used effectively used as an inhalable aerosol delivery system for the delivery of therapeutic proteins or peptides.

Thus, it is desirable to have metal phosphate nanoparticles, for example, calcium phosphate nanoparticles) of primary particle sizes and/or particle morphologies that are surface-modified so as to be compatible with (and therefore dispersible in) a variety of media (for example, solvents, polymers, paints, coatings, cosmetic formulations, pharmaceutical formulations, and the like). In particular, it is desirable to have very small nanoparticles (for example, having average primary particle diameters of less than about 20 nm) that are biocompatible and preferably of spherical morphology, which can be effectively used in, for example, inhalable aerosol drug delivery systems. In order to facilitate industrial use, such nanoparticles typically can be provided in the form of a redispersible powder.

Briefly, in one aspect, this invention provides such a composition, which comprises surface-modified nanoparticles of at least one metal phosphate (typically, calcium phosphate). The nanoparticles bear, on at least a portion of their surfaces, a surface modification comprising at least one organocarboxylate surface modifier that include at least one organic moiety that has at least about six carbon atoms. Typically, the organic moiety has from about 6 to about 24 carbon atoms. We have been discovered that use of the above-described relatively long-chain organocarboxylate surface modifiers can enable the preparation of substantially non- agglomerated metal phosphate nanoparticles. The provided nanoparticles can be relatively simply prepared from relatively inexpensive metal phosphate precursors (for example, from a metal cation source such as a metal salt, and a phosphate anion source such as phosphoric acid) and can be grown to average primary particle sizes (for example, average primary particle diameters of about 1 nanometers (nm) to about 50 nm). By varying the nature of the organocarboxylate surface modifier (for example, the carbon chain length of its organic moiety and/or the presence or absence of various functional groups) and/or its amount, the surface characteristics of the nanoparticles can be controllab Iy tailored and their compatibility with a particular medium can be enhanced.

Surprisingly, the use of relatively long-chain organocarboxylate surface modifier(s) can provide nanoparticles that are also redispersible and typically of substantially spherical morphology. This can be especially advantageous for the production of calcium phosphate nanoparticles having average primary particle diameters in the range of about 1 nm to about 20 nm. Such nanoparticles can be well-suited for use in various pharmaceutical, medical, and dental applications, particularly those (for example, inhalable aerosol drug delivery systems) requiring or desiring relatively small, redispersible, biocompatible nanoparticles of spherical morphology.

Thus, in at least preferred embodiments, the composition of the invention can meet the above-mentioned desire for redispersible metal phosphate nanoparticles (typically, calcium phosphate nanoparticles) of desired primary particle sizes and/or morphologies that are surface-modified so as to be compatible with (and therefore dispersible in) a variety of media, and/or that can be easily tailored to fit the characteristics of a particular medium. The composition can therefore further comprise, for example, at least one carrier material or medium (for example, a material or mixture of materials in the form of a gas, a liquid, a bulk solid, a powder, an oil, a gel, or a dispersion).

In this document the articles "a", "an", and "the" are used interchangeably with "at least one" to mean one or more of the elements being described;

"agglomeration" refers an association of primary particles, which can range from relatively weak (based upon, for example, charge or polarity) to relatively strong (based upon, for example, chemical bonding);

"nanoparticles" refers to particles having a diameter of less than 100 nm; "organocarboxylate(s)" refer to any carboxylate or the conjugate acid of any carboxylate that include at least one organic moiety and have at least 6 and up to 24 carbon atoms in the organic moiety; "primary particle size or diameter" refers to the size or diameter of a non-associated single nanoparticle;

"redispersible" (in regard to nanoparticles) refers to nanoparticles that can be "dried" or precipitated from an original dispersion of the nanoparticles in aqueous or organic solvent or a combination thereof (for example, by removal of the solvent and/or by a change in solvent polarity) to form a powder or a wet precipitate or gel that can be dispersed again in the original dispersion solvent (or a solvent of essentially the same polarity as that of the original dispersion solvent) to provide a nanoparticle dispersion (preferably, without substantial change in primary particle size (and/or average particle size as measured by dynamic light scattering) relative to the original dispersion and/or without substantial sedimentation of the nanoparticles over a period of at least four hours (for example, with size change and/or sedimentation of less than 25 percent (preferably, less than 20 percent; more preferably, less than 15 percent; most preferably, less than 10 percent), where the sedimentation percentage is by weight, based upon the total weight of nanoparticles in the dispersion)); "sol" refers to a dispersion or suspension of colloidal particles in a liquid phase; and "substantially spherical" (in regard to nanoparticles) refers to wherein at least a major portion of the nanoparticles have an aspect ratio less than or equal to 2.0 (preferably, less than or equal to 1.5; more preferably, less than or equal to 1.25; most preferably, 1.0).

In another aspect, articles are provided that comprise the composition of the invention. The articles can include a medicament and the medicament can be a powder.

In addition the articles can include dry powder inhalers.

In yet another aspect, a process is provided that includes combining at least one metal cation source, at least one phosphate anion source, at least one organic base comprising at least one organic moiety comprising at least five carbon atoms, and at least one organocarboxylate comprising at least one organic moiety comprising at least eight carbon atoms, and allowing said metal cation source and said phosphate anion source to react in the presence of said organic base and said organocarboxylate.

The above summary is not intended to describe each disclosed embodiment of every implementation of the present invention. The brief description of the drawing and the detailed description which follows more particularly exemplify illustrative embodiments.

Brief Description of the Drawings

Fig. 1 is a graph of particle size distribution determined by dynamic light scattering for Examples 1-3.

Fig. 2 is a graph of particle size distribution determined by dynamic light scattering for Examples 5-7 and 9-11.

Fig. 3 is a graph of particle size distribution determined by dynamic light scattering for Example 12. Fig. 4 is a transmission electron micrograph (TEM) of Example 3.

Fig. 5 is a transmission electron micrograph (TEM) of Example 5. Fig. 6 is a graph of a Fourier Transform Infrared Spectrum (FTIR) of Example 12.

Detailed Description In the following description, reference is made to the accompanying set of drawings that form a part of the description hereof and in which are shown by way of illustration several specific embodiments. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense. Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. The use of numerical ranges by endpoints includes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range.

The surface-modified metal phosphate nanoparticles of the provided compositions can be prepared by any of a variety of known or hereafter developed particle surface modification methods. Typical preparative methods include those that can provide the desired surface modification while maintaining or producing substantially non- agglomerated nanoparticles. Typical preparative methods include surface modification during nanoparticle synthesis, post-synthesis surface modification, and combinations thereof. For example, in post-synthesis surface modification, starting metal phosphate nanoparticles can be prepared by essentially any method that can provide nanosized particles (for a range of applications, having average primary particle diameters of from about 1 nm, from about 2 nm, or from about 3 nm, to about 50 nm, to about 30 nm; or to about 20 nm, where any lower limit can be paired with any upper limit of the size range) that are capable of then being surface modified with organocarboxylates. Useful methods for producing such starting metal phosphate nanoparticles include those described, for example, in U. S. Pat. Appl. Publ. Nos. 2004/0170699 (Chane-ching et al), 2006/0257306 (Yamamoto et al.), and 2007/0196509 (Riman et al.).

The starting metal phosphate nanoparticles can be dispersed in a liquid medium (for example, alcohol, ether, or a polar aprotic solvent) and, optionally, any water residues removed. The organocarboxylate surface modification agent can then be added to the resulting dispersion (typically, by mixing in an organic solvent and/or water; optionally, a catalyst can be present to facilitate hydrolysis of the organocarboxylate) and the resulting mixture can be heated under reflux to a temperature between room temperature and the boiling point of the liquid medium (at atmospheric pressure). Optionally, any resulting water can be removed. The resulting surface-modified nanoparticles can be separated (for example, by filtration or by precipitation followed by centrifugation), washed, and, optionally, dried.

A typical process comprises (a) combining (preferably, in at least one solvent) (1) at least one metal cation source, (2) at least one phosphate anion source, (3) at least one organic base comprising at least one organic moiety comprising at least about five carbon atoms, and (4) at least one organocarboxylate comprising at least one organic moiety comprising at least about six carbon atoms; and (b) allowing the metal cation source and the phosphate anion source to react in the presence of the organic base and the organocarboxylate (for example, to form surface-modified metal phosphate nanoparticles). Typically, the metal cation source is a metal salt comprising at least one metal cation and at least one anion that is capable of being displaced by phosphate anion, and/or the phosphate anion source is selected from phosphorus-containing compounds (for example, phosphoric acid or an organoammonium phosphate salt) that are capable of providing phosphate anion either directly or upon dissolution or dispersion (for example, in aqueous or non-aqueous solvent), oxidation, or hydrolysis, and combinations thereof.

Use of the above-described metal phosphate precursors including an organic base and a relatively long-chain organocarboxylate can enable the preparation of substantially non-agglomerated metal phosphate nanoparticles that are redispersible and preferably of substantially spherical morphology. The nanoparticles can be grown to preferred average primary particle sizes (for example, average primary particle diameters of about 1 nm to about 50 nm). Preferred embodiments of the process can enable control of average primary particle size and/or particle morphology by varying, for example, the reaction temperature, time, pH, choice and/or amounts of reactants, and/or the order and/or manner of combination of reactants. Metal cation sources suitable for use in making the provided nanoparticles include metal salts comprising at least one metal cation and at least one anion that can be displaced by phosphate anion. Such salts can be prepared, if desired, by the reaction of a metal hydroxide, a metal carbonate, or a metal oxide with a mineral acid. Useful metal cations include those of transition metals, alkaline earth metals, alkali metals, post-transition metals, and combinations thereof. Useful transition metals include titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, ruthenium, cadmium, hafnium, tantalum, tungsten, and combinations thereof. Useful post-transition metals include aluminum, gallium, indium, tin, lead, antimony, bismuth, and combinations thereof. Useful alkaline earth metals include beryllium, calcium, strontium, magnesium, barium, and combinations thereof. Useful alkali metals include lithium, sodium, potassium, rubidium, cesium, and combinations. Typically, the metal cation can be a divalent metal cation such as a divalent alkaline earth metal cation. In some embodiments, divalent earth metal cations include divalent calcium or magnesium.

Useful anions include halide, nitrate, acetate, carbonate, alkanoate (for example, formate, propionate, hexanoate, neodecanoate, and the like), alkoxide, lactate, oleate, acetylacetonate, sulfate, thiosulfate, sulfonate, bromate, perchlorate, tribromoacetate, trichloroacetate, trifluoroacetate, sulfide, hydroxide, oxide, and the like, and combinations thereof. Typical anions include halide, nitrate, sulfate, carbonate, acetate, hydroxide, oxide, and combinations thereof. Mixed metal salts, mixed anion salts, and/or mixtures of salts can be utilized, if desired. The salts can include other metal cations (for example, at levels up to about 10 mole percent, based upon the total number of moles of metal cation), but usually all metals in the salts are selected from those described above. Similarly, the salts can comprise other anions (for example, at levels up to about 10 mole percent, based upon the total number of moles of anion), but usually all anions in the salts are selected from those described above.

Representative examples of useful metal salts include calcium chloride hexahydrate, calcium chloride dihydrate, calcium chloride (anhydrous), calcium bromide hexahydrate, calcium nitrate tetrahydrate, calcium acetate monohydrate, calcium propionate, calcium lactate pentahydrate, calcium 2-ethylhexanoate, calcium methoxyethoxide, calcium carbonate, magnesium chloride hexahydrate, magnesium bromide hexahydrate, magnesium ethoxide, magnesium hydroxide, magnesium nitrate hexahydrate, magnesium acetate tetrahydrate, magnesium oleate, magnesium sulfate heptahydrate, zinc chloride (anhydrous), zinc acetate dihydrate, zinc carbonate hydroxide, zinc bromide dihydrate, zinc nitrate hexahydrate, zinc neodecanoate, zinc oxide, zinc sulfate heptahydrate, cobalt chloride hexahydrate, manganese (II) chloride tetrahydrate, manganese (II) bromide tetrahydrate, manganese (II) nitrate tetrahydrate, manganese (II) acetate tetrahydrate, manganese (III) acetylacetonate, and combinations thereof. Exemplary metal salts include those having anions selected from halide, nitrate, acetate, and combinations thereof. Hydrated metal salts can also be utilized (for example, to facilitate hydrolysis of the organocarboxylate). Useful metal salts can be prepared by known methods. Many of such salts are commercially available.

Phosphate anion sources suitable useful in the provided compositions include phosphorus-containing compounds that provide phosphate anion either directly or upon dissolution or dispersion (for example, in aqueous or non-aqueous solvent), oxidation, or hydrolysis, and combinations thereof. Such compounds include phosphoric acid (H₃PO₄); phosphorous acid (H3PO3); hypophosphorous acid (H3PO2); thiophosphoric acid; phosphoric acid esters; thiophosphoric acid esters (for example, diethylchlorothiophosphate, diethyl dithiophosphate, ethyl dichlorothiophosphate, or trimethyl thiophosphate); phosphite esters (for example, dimethyl phosphite, trimethyl phosphite, diisopropyl phosphite, diethyl hydrogenphosphite, diisobutyl phosphite, dioleyl hydrogenphosphite, diphenyl hydrogenphosphite, triphenyl phosphite, ethylenechlorophosphite, and tris(trimethylsilyl) phosphite); thiophosphite esters (for example, trilauryl trithiophosphite and triethyl trithiophosphite); phosphate salts of alkali metal cations, ammonium cation, or organoammonium cations; thiophosphate salts of alkali metal cations, ammonium cation, and organoammonium cations (for example, ammonium diethyldithiophosphate, potassium diethyldithiophosphate, sodium dithiophosphatetrihydrate); phosphite salts of alkali metal cations, ammonium cation, or organoammonium cations (for example, disodium hydrogenphosphite pentahydrate); hypophosphite salts of alkali metal cations, ammonium cation, or organoammonium cations (for example, sodium hypophosphite hydrate, potassium hypophosphite, ammonium hypophosphite, ethylpiperidiniumhypophosphite, and tetrabutylammonium hypophosphite); phosphorus oxides (for example, P₂O₅); phosphorus halides and/or oxyhalides (for example, POCl₃, PCl₅, PCl₃, POBr₃, PBr₅, PBr₃, difiuorophosphoric acid, and fluorophosphoric acid); phosphorus sulfides (for example, P₂S₅, P₂S₃, and P₄S₃); phosphorus halosulfides (for example, PSCl₃ and PSBr₃); polyphosphoric acid; polyphosphoric acid esters; polyphosphate salts of alkali metal cations, ammonium cation, and organoammonium cations; and combinations thereof. In some embodiments, phosphate anion sources include phosphoric acid, phosphoric acid esters, organoammonium phosphate salts, and combinations thereof.

Useful phosphoric acid esters include alkylphosphates. Representative examples of useful alkylphosphates include mono-, di-, and trialkyl phosphates comprising alkyl moieties having from one to about 12 carbon atoms such as methyl phosphate, ethyl phosphate, propyl phosphate, butyl phosphate, pentyl phosphate, hexyl phosphate, dimethyl phosphate, diethyl phosphate, dipropyl phosphate, dibutyl phosphate, dipentyl phosphate, dihexyl phosphate, di-2-ethylhexyl phosphate, methylethyl phosphate, ethylbutyl phosphate, ethylpropyl phosphate, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, tri-2- ethylhexyl phosphate, ethyldimethyl phosphate, ethyldibuty phosphate, and combinations thereof. Also useful are arylphosphates such as triphenyl phosphate; alkyl phosphate salts such as ammonium dilaurylphosphate; aminoethanoldihydrogenphosphate; and combinations thereof.

Useful polyphosphoric acid esters include esters of di-, tri-, terra-, and pentaphosphoric acid and a monohydric alcohol and/or polyhydric alcohol, and combinations thereof. Representative examples of polyphosphoric acid esters include polyphosphoric acid methyl ester, polyphosphoric acid ethyl ester, polyphosphoric acid propyl ester, polyphosphoric acid butyl ester, polyphosphoric acid pentyl ester, polyphosphoric acid dimethyl ester, polyphosphoric acid diethyl ester, polyphosphoric acid dipropyl ester, polyphosphoric acid dibutyl ester, diphosphoric acid methyethyl ester, diphosphoric acid ethybutyl ester, diphosphoric acid ethylpropyl ester, diphosphoric acid ethylhexyl ester, trialkyl esters of di-, tri-, terra-, and penta-phosphoric acids, tetraalkyl esters of di-, tri-, terra-, and penta-phosphoric acids, pentaalkyl esters of di-, tri-, terra-, and penta-phosphoric acids, hexaalkyl esters of di-, tri-, terra-, and penta-phosphoric acids, and combinations thereof. In some embodiments, polyphosphoric acid esters include those having an ester group containing one to about four carbon atoms (for example, polyphosphoric acid methyl ester, polyphosphoric acid ethyl ester, polyphosphoric acid propyl ester, and polyphosphoric acid butyl ester), and combinations thereof. Useful salts include alkali metal (for example, sodium or potassium) phosphates and polyphosphates, ammonium phosphates and polyphosphates, organoammonium (for example, mono-, di-, tri-, and tetraalkylammonium) phosphates and polyphosphates (including hydroxylamine phosphate), and combinations thereof. Representative examples of useful alkali metal phosphates include sodium dihydrogen phosphate (monobasic), sodium hydrogen phosphate (dibasic), trisodium phosphate (tribasic), potassium dihydrogen phosphate, lithium dihydrogenphosphate, sodium tripolyphosphate, sodium hexametaphosphate, potassium pyrophosphate, and combinations thereof.

Representative examples of useful organoammonium phosphates and polyphosphates include ethylammonium phosphate, diethylammonium phosphate, trimethylammonium phosphate, triethylammonium phosphate, tributylammonium pyrophosphate, methyltriethylammonium dibutylphosphate, pentyltriethylammonium phosphate, hexyltriethylammonium phosphate, octyltriethylammonium phosphate, dodecyltrimethylammonium phosphate, hexadecyltrimethylammonium dihydrogen phosphate, tetramethylammonium dihydrogen phosphate, tetraethylammonium dihydrogenphosphate, tetrabutylammonium phosphate, tetrahexylammonium dihydrogen phosphate, di-2-ethylhexylammonium hexafluorophosphate, tetramethylammonium hexafluorophosphate, tetraethylammonium hexafluorophosphate, tetrapropylammonium hexafluorophosphate, tetrabutylammonium hexafluorophosphate, tetrahexylammonium hexafluorophosphate, phenyltrimethylammonium hexafluorophosphate, benzyltrimethylammonium hexafluorophosphate, and combinations thereof. In some embodiments, organoammonium phosphate salts include pentyltriethylammonium phosphate, hexyltriethylammonium phosphate, octyltriethylammonium phosphate, dodecyltrimethylammonium phosphate, hexadecyltrimethylammonium dihydrogen phosphate, tetrahexylammonium dihydrogen phosphate, di-2-ethylhexylammonium hexafluorophosphate, tetrahexylammonium hexafluorophosphate, phenyltrimethylammonium hexafluorophosphate, benzyltrimethylammonium hexafluorophosphate, and combinations thereof. Useful phosphate salts include organoammonium phosphates, and combinations thereof. In some embodiments, useful salts comprise at least one organic moiety comprising at least about five carbon atoms. Such phosphate anion sources can be prepared by known methods. Many of such sources (for example, phosphoric acid, alkylphosphates, and polyphosphoric acid esters) are commercially available.

Organic bases suitable for use in making the provided nanoparticles compositions include those organic amines and organoammonium hydroxides that include at least one organic moiety comprising at least about five carbon atoms, at least about six carbon atom, or even at least about eight carbon atoms, and combinations thereof (typically, an organic amine). The organic moiety can be linear, branched, alicyclic, aromatic, or a combination thereof (preferably, linear or branched), with the proviso that carbon atoms in a cyclic moiety count only as half their number toward the requisite minimum of five (for example, a phenyl ring counts as three carbon atoms rather than six and must be supplemented by, for example, an attached ethyl moiety). Representative examples of suitable organic amines include monoalkylamines such as hexylamine, heptylamine, octylamine, nonylamine, decylamine, dodecylamine, hexadecylamine, and octadecylamine; dialkylamines such as dihexylamine, di-n-heptylamine, di-n-octylamine, bis(2- ethylhexyl)amine, di-sec-octylamine, di-n-nonylamine, di-n-decylamine, di-n- undecylamine, di-n-tridecylamine, and dicyclooctylamine; trialkylamines such as trihexylamine, triheptylamine, triisooctylamine, trioctylamine, tridodecylamine, tris(4- methylcyclohexyl)amine, tri-n-heptylamine, trinonylamine, N, N-didecylmethylamine, N, N-dimethylcyclohexylamine, N, N-dimethyldodecylamine, N, N-dimethyloctylamine, and tris(2-ethylhexyl)amine; arylamines such as diphenylstearylamine; polyethylene glycol mono- and diamines; and combinations thereof.

Representative examples of suitable organoammonium hydroxides include benzyltriethylammonium hydroxide, benzyltrimethylammonium hydroxide, hexane-1,6- bis(tributylammonium)dihydroxide, 3-(trifluoromethyl)phenyltrimethylammonium hydroxide, dodecyldimethylethylammonium hydroxide, phenyltrimethylammonium hydroxide, cetyltrimethylammonium hydroxide, triethylphenylammonium hydroxide, tetradecylammonium hydroxide, tetrabutylammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrahexylammonium hydroxide, tetraoctylammonium hydroxide, tetrapentylammonium hydroxide, methyltriethylammonium hydroxide, tetraoctadecylammonium hydroxide, dimethyldiethylammonium hydroxide, methyltripropylammonium hydroxide, tetradecyltrihexylammonium hydroxide, ethyltrimethylammonium hydroxide, tris(2- hydroxyethyl)methylammonium hydroxide, and combinations thereof. In some embodiments, organoammonium hydroxides include benzyltriethylammonium hydroxide, benzyltrimethylammonium hydroxide, dodecyldimethylethylammonium hydroxide, cetyltrimethylammonium hydroxide, triethylphenylammonium hydroxide, tetradecylammonium hydroxide, tetrahexylammonium hydroxide, tetraoctylammonium hydroxide, tetrapentylammonium hydroxide, tetraoctadecylammonium hydroxide, tetradecyltrihexylammonium hydroxide, and combinations thereof. Such organic bases can be prepared by known methods. Many of such bases (for example, dodecyldimethylethylammonium hydroxide, cetyltrimethylammonium hydroxide, tetradecylammonium hydroxide, tetrahexylammonium hydroxide, and tetraoctylammonium hydroxide) are commercially available.

The organic bases (as well as the phosphate anion sources) can be used in neat solid or liquid form or can be used in the form of a solution in organic solvent (for example, an alkanol such as methanol). A wide range of concentrations can be useful (for example, from about 5 to about 90 weight percent in alkanol, based upon the total weight of the solution).

In some embodiments, the organic base can be combined with the phosphate anion source (for example, phosphoric acid), dissolved in a polar organic solvent or in at least a portion of the organocarboxylate, and used in the form of the resulting solution. Polar organic solvents useful for dissolving the organic base include acetone, alkanols (for example, methanol, ethanol, and isopropanol), dimethylsulfoxide (DMSO), dimethylformamide (DMF), tetrahydrofuran (THF), and mixtures thereof. In some embodiments the organic solvent includes alkanols and methanol. When the phosphate anion source is an organoammonium phosphate or polyphosphate including at least one organic moiety that includes at least about five carbon atoms, the organoammonium phosphate or polyphosphate can serve as both the phosphate anion source and the organic base, without the need for addition of a separate organic base. Such dual functionality is not limited to these components, however, as other materials can simultaneously serve as more than one of the four reaction mixture components.

Organocarboxylates suitable for use in the preferred in situ process include those organocarboxylates that comprise at least one organic moiety comprising at least about 6 carbon atoms, at least about 8 carbon atoms, at least about 12 carbon atoms, at least about 14 carbon atoms, at least about 16 carbon atoms, or even at least about 18 carbon atoms, and combinations thereof. The organic moiety can be linear, branched, alicyclic, aromatic, or a combination thereof, with the proviso that carbon atoms in a cyclic moiety count only as half their number toward the requisite minimum of 6 (for example, a phenyl ring counts as three carbon atoms rather than six and must be supplemented by, for example, an attached propyl moiety). In some embodiments, the organic moiety comprises from about 6 to about 24 carbon atoms, from about 12 to about 20 carbon atoms; or even from about 16 to about 18 carbon atoms. In some embodiments, the organic moiety has about 18 carbon atoms and can be straight-chained, branched, saturated, monounsaturated, polyunsaturated or a combination thereof. In some embodiments the organocarboxylate can include more than one carboxyl group.

Useful organocarboxylates include straight-chain organomonocarboxylates that have from about 8 to about 24 carbon atoms. These organomonocarboxylates include the conjugate base of organomonocarboxylic acids such as, for example, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, anachidic acid, and eicosonoic acid. In some embodiments, organomonocarboxylates include the conjugate bases of unsaturated straight chain organic acids such as, for example, palmitoleic acid, oleic acid, linoleic acid, and trilinolenic acid. Organocarboxylates derived from branched monocarboxylates such as, for example, 3,5,5-trimethylhexanoic acid, 3-methylhexanoic acid, 3-ethyl5-methylhexanoic acid, 3,3-dimethylhexanoic acid, 5,5-dimethylhexanoic acid, 2-ethylhexanoic acid, 6-methylheptanoic acid, 2-butyloctanoic acid, 7,7-dimethyloctanoic acid can also be useful to make the provided nanoparticle compositions. In other embodiments, useful organocarboxylates can further comprise at least one functional group selected from heterocyclic, acryloxy, methacryloxy, cyano, isocyano, cyanato, isocyanato, phosphino, amino, amido, hydroxyl, vinyl, epoxy, glycidoxy, alkyl, carbon-carbon triple bond-containing, mercapto, siloxy, halocarbon (for example, fluorocarbon), carbon-nitrogen double bond-containing, and carbon-carbon double bond-containing groups, and combinations thereof. Examples of these organocarboxylates include biotin, abeitic acid, cholic acid, to name a few. When a functional group -containing organocarboxylate is utilized, the particular functional group can be selected so as to be compatible with a material to which the resulting metal phosphate nanoparticles are to be added. Representative examples of heterocyclic functional groups include substituted and unsubstituted pyrroles, pyrazoles, imidazoles, pyrrolidines, pyridines, pyrimidines, oxazoles, thiazoles, furans, thiophenes, dithianes, isocyanurates, and the like, and combinations thereof. Representative examples of acryloxy functional groups include acryloxy, alkylacryloxy groups such as methacryloxy, and the like, and combinations thereof. Representative examples of carbon- carbon double bond-containing functional groups include alkenyl, cyclopentadienyl, styryl, phenyl, and the like, and combinations thereof. Solvents can be used in making the provided nanoparticle compositions. Suitable solvents include those in which the various metal phosphate precursors or reaction mixture components can be substantially soluble or dispersible. Most preferably, the solvent will be capable of dissolving the reactants and products of the process, while keeping the desired metal phosphate nanoparticles well-dispersed. Useful solvents for dissolving or dispersing less polar components such as the long-chain organocarboxylates include non- polar organic solvents such as alkanes (for example, hexane, heptane, octane, and the like, and combinations thereof) and aromatic hydrocarbons (for example, toluene, benzene, xylene, and combinations thereof), as well as more polar solvents such as esters (for example, ethyl acetate and combinations thereof), ethers (for example, tetrahydrofuran (THF), diethylether, and combinations thereof), and halocarbons (for example, carbon tetrachloride and combinations thereof), and combinations thereof. Useful non-polar organic solvents include hexane, heptane, octane, toluene, and combinations thereof, due to their boiling points.

Mixtures of the polar and non-polar solvents can advantageously be utilized to facilitate separation of the resulting metal phosphate nanoparticles from reaction byproducts. Water in relatively small amounts can speed the kinetics of growth of the metal phosphate nanoparticles and/or facilitate hydrolysis of the organocarboxylate surface modifier, but the presence of water in relatively larger amounts (for example, a water to metal ratio of greater than about 25) can cause nanoparticle agglomeration and/or loss of substantially spherical morphology. In another aspect, a process is provided to make metal phosphate nanoparticles according to this disclosure. The process can be carried out by combining at least one metal cation source, at least one phosphate anion source, at least one organic base comprising at least one organic moiety comprising at least about five carbon atoms, and at least one organocarboxylate comprising at least one organic moiety comprising at least about six carbon atoms (typically, in at least one solvent). In some embodiments, the metal cation source and the organocarboxylate are commercially available as a salt and can be added as such. Examples of these organocarboxylate salts are calcium stearate, calcium 2-ethylhexanoate, and magnesium stearate. When the salts are utilized as a combination of the metal cation source and the organocarboxylate it is typical to an additional amount of the conjugate organocarboxylic acid to the process mixture. For example, when calcium stearate is used as the metal source, typically additional stearic acid is included in the reaction mixture. Generally, any order and manner of combination of the reaction mixture components can be utilized, although in some embodiments it is useful to dissolve or disperse one or more components (for example, the phosphate anion source and the organic base) separately in solvent prior to combination with the other components.

Depending upon the specific chemical natures of the selected components and the amount of water present, certain orders and manners of combination can assist in minimizing agglomeration and enabling the formation of nanoparticles. For example, it can be preferable (for example, when using relatively more reactive phosphate anion sources such as phosphoric acid) to separately form a mixture of the phosphate anion source and the organic base and a mixture of the metal cation source and the organocarboxylate. These two mixtures can then be combined.

The metal cation source and the phosphate anion source can be combined in generally stoichiometric amounts, based upon the moles of metal cation and the moles of phosphate anion. For example, these components can be combined in amounts such that the metal to phosphorus molar ratio ranges from about 0.8/n to about 6.0/n, where n is the valence of the metal cation. Typically, the molar ratio ranges from about 1.0/n to about 4.0/n (more preferably, from about 1.4/n to about 3.4/n).

The metal cation source (for example, a metal salt comprising a metal cation and counter anion(s)) and the organic base can be combined in generally stoichiometric amounts, based upon the moles of basic groups and the moles of counter anion. For example, these components can be combined in amounts such that the organic base to metal molar ratio ranges from about 0.5n/b to about 3.0n/b, where n is the valance of the metal and b is the number of basic groups per mole of organic base. Typically, the molar ratio ranges from about 0.6n/b to about 2.0n/b (typically, from about 0.7n/b to about 1.5n/b).

The metal cation source and the organocarboxylate can be combined in amounts such that the molar ratio of metal to silicon ranges from about 0.1 to about 20 (preferably, from about 0.2 to about 15; more preferably, from about 0.3 to about 10). If desired, however, the organocarboxylate can be used in larger amounts, so as to function as a reaction solvent. Generally less than 100 percent of the combined organocarboxylate attaches (for example, physically or chemically) to the metal phosphate nanoparticles to provide surface modification.

Mechanical agitation or stirring can be used, if desired, to facilitate mixing. Optionally, heating can be used to facilitate dissolution, reaction, and/or primary particle size growth. The reaction mixture components can be combined in a pressure vessel, if desired (for example, this can be useful for reactions carried out at temperatures above the boiling point of a selected solvent). An inert atmosphere (for example, nitrogen) can optionally be utilized (for example, to minimize the presence of moisture or air).

To influence, for example, the morphology, magnetic properties, conductivity, light absorption or emission characteristics, and/or the crystallinity of the resulting nanoparticles, various compounds (foreign ions) can be added before, during, or after nanoparticle precipitation. Typical additive compounds include 2nd-5th main group and transition metal compounds (typically, magnesium, strontium, barium, aluminum, indium, tin, lead, antimony, bismuth, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, zinc, yttrium, zirconium, niobium, molybdenum, cadmium, hafnium, tantalum, and tungsten compounds, and combinations thereof; typically, magnesium, strontium, aluminum, tin, antimony, titanium, manganese, iron, zinc, yttrium, zirconium, niobium, and tantalum compounds, and combinations thereof) including lanthanide compounds (typically, europium, terbium, dysprosium, samarium, erbium, praseodymium, and cerium compounds, and combinations thereof; most preferably, cerium, europium, terbium, and dysprosium compounds, and combinations thereof). Such additive compounds typically can be added to the reaction mixture in dissolved form and/or typically can be used in an amount from about 0.01 to about 20 mole percent, based on the total number of moles of metal (present, for example, in the form of metal phosphate).

Other common additives (for example, dyes, pigments, catalysts, and the like) can also be utilized. Monomer(s), oligomer(s), and/or polymer(s) of various types can be present in the reaction mixture (for example, in order to form a polymeric composite comprising the resulting metal phosphate nanoparticles).

The resulting nanoparticles can be isolated (for example, from a resulting sol) and/or purified by using standard techniques such as decantation (for example, following centrifugation or settling optionally induced by cosolvent addition), filtration, rotary evaporation for solvent removal, dialysis, diafϊltration, and combinations thereof. The characteristics of the resulting product can be evaluated by ultraviolet- visible spectroscopy (absorption characteristics), X-ray diffraction (crystalline particle size, crystalline phase, and particle size distribution), transmission electron microscopy (particle sizes, crystalline phase, and particle size distributions), and dynamic light scattering (degree of agglomeration).

Upon solvent removal (for example, by rotary evaporation, air or oven drying, centrifugation and decantation, a change in solvent polarity followed by gravitational settling and decantation, or the like), the resulting nanoparticles can be in the form of a powder or gel that can be re-dispersed in solvent (for example, a polar or a non-polar solvent, depending upon the specific chemical nature of the organocarboxylate). The resulting nanoparticles can range in average primary particle diameter from about 1 nm to about 50 nm or more, from about 1 nm to about 30 nm, from about 1 nm to about 20 nm, from about 1 nm to about 15 nm, or even from about 2 nm to about 10 nm, where any lower limit can be paired with any upper limit of the size ranges as explained above. The nanoparticles can be used in various different applications (for example, calcium phosphate nanoparticles can be used in various pharmaceutical, medical, and dental applications). Preferred embodiments of the provided process can provide substantially spherical nanoparticles (for example, substantially spherical calcium phosphate nanoparticles useful in inhalable aerosol drug delivery systems).

The above-described preparative methods can produce metal phosphate (most preferably, calcium phosphate) nanoparticles bearing, on at least a portion of their surfaces, a surface modification comprising at least one organocarboxylate surface modifier comprising at least one organic moiety comprising at least about six carbon atoms. Preferably, the organic moiety has from about 6 to about 24 carbon atoms, from about 12 to about 20 carbon atoms; or even from about 16 to about 18 carbon atoms. The surface modifier can be attached or bonded to the surface of the nanoparticle by a relatively strong physical bond or by a chemical bond (for example, a covalent or ionic bond). For example, organocarboxylate surface modifiers can be derived from organocarboxylate esters through hydrolysis of the organocarboxylate ester and formation of a carbon-oxygen-metal or carbon-oxygen-phosphorus covalent attachment to the metal phosphate nanoparticle. Typically, the organocarboxylate surface modifier is derived from a precursor organocarboxylate compound selected from straight-chain carboxylic acids that are saturated, or unsaturated. For use in at least some applications, the surface-modified nanoparticles preferably have average primary particle diameters of from about 1 nm, from about 2 nm, from about 3 nm, to about 20 nanometers, to about 15 nm, or even to about 10 nm, and/or preferably comprise from about 1 weight percent, from about 2 weight percent, or from about 10 weight percent to about 90 weight percent, to about 70 weight percent, or even to about 50 weight percent of surface-modifier, based upon the total weight of the surface-modified nanoparticles (where any lower limit of a range can be paired with any upper limit of the range).

The composition of the invention can consist or consist essentially of the surface- modified nanoparticles or can further comprise a carrier material or medium (for example, a material or mixture of materials in the form of a gas, a liquid, a bulk solid, a powder, an oil, a gel, a dispersion, and the like). When the composition is in the form of, for example, a dispersion of the surface-modified nanoparticles in a liquid carrier, unreacted and/or polymerized organocarboxylate can also be present (and can be removed, if desired, by various methods such as solvent washing and/or dialysis).

The nature (and amount) of the carrier material can vary widely, depending upon the particular application, as is known in the art. The surface-modified nanoparticles can be used, for example, in biomedical applications (including as adjuvants or excipients for drugs and vaccines, as carriers for various proteins and other growth factors, as components of dental hygiene agents such as mouthwashes and toothpastes, as artificial prosthetic fillers, as drug delivery and gene therapy vectors, and the like), as adsorption materials for chromatography columns, as catalysts, in fluorescent materials, in flame retardants, and in anti-corrosion coatings. Preferred embodiments can be useful, for example, in making dental hygiene products and cements, as carriers and/or aerosolization aids for drugs, in dietary formulations, and in fluorescent materials.

Due to the biocompatibility of the surface modifier, however, exemplary uses for the surface-modified nanoparticles (particularly, calcium phosphate) include use in dietary, cosmetic, and pharmaceutical formulations. The nanoparticles can be used in oral or dental care compositions and nutritional supplements. In such cases, useful carrier materials can include water, water-based liquids, oils, gels, emulsions, microemulsions, dispersions, and the like, and mixtures thereof. The compositions can further comprise, for example, additives commonly used in cosmetics and/or dietary formulations such as fragrances, emulsifϊers, thickeners, flavorings, solubilizers, dyes, antibiotics, moisturizers, and the like, and mixtures thereof. The formulation can be borne on a paper or fabric carrier (for example, a woven or non-woven material) to provide a means of delivery other than by application of a powder or dispersion (for example, in the form of a wipe, an adhesive tape, or a flame-retardant web).

In one embodiment, the provided nanoparticle compositions can find use in pharmaceutical formulations comprising any of a variety of medicaments. For example, the surface-modified nanoparticles can be used to enhance the mixing and/or delivery of medicaments including antiallergics, analgesics, glucocorticoids, bronchodilators, antihistamines, therapeutic proteins and peptides, antitussives, anginal preparations, antibiotics, anti-inflammatory preparations, diuretics, hormones, and combinations of any two or more of these. Noted categories include beta-agonists, bronchodilators, anticholinergics, anti-leukotrienes, mediator release inhibitors, 5-lipoxyoxygenase inhibitors, and phosphodiesterase inhibitors.

The pharmaceutical formulations can further comprise one or more excipients. Suitable excipients include those listed in the Handbook of Pharmaceutical Excipients

(Rowe, et al., APhA Publications, 2003), which include microcrystalline cellulose, dicalcium phosphate, lactose monohydrate (a preferred sugar), mannose, sorbitol, calcium carbonate, starches, and magnesium or zinc stearates. The surface-modified nanoparticles can aid in the preparation of excipient/medicament blends (for example, by reducing mixing times, reducing attrition during processing, and improving the homogeneity of the blends).

The surface-modified nanoparticles can be particularly useful in pharmaceutical inhalation powder formulations (for example, comprising a medicament and optional excipient(s) such as sugar(s) for use in nasal or oral inhalation drug delivery) to enhance the flow characteristics of the powder. The nanoparticles can be present in the formulations in an amount that is at least sufficient to improve the flowability or floodability of the powder relative to corresponding powder that is substantially free of the nanoparticles (for example, the nanoparticles can be used in an amount less than or equal to about 10 weight percent, less than or equal to about 5 weight percent, less than or equal to about 1 weight percent, less than or equal to about 0.1 weight percent, or even less than or equal to about 0.01 weight percent (such as 0.001 weight percent), based upon the total weight of the formulation). Such formulations can generally be prepared by mixing one or more powders (for example, having an average particle size, generally measured as an effective diameter, of less than or equal to about 1,000 microns, more typically less than or equal to about 100 microns) with the surface-modified nanoparticles using any suitable, conventional mixing or blending process.

For example, the surface-modified nanoparticles can be added to an organic solvent so as to form a dispersion, and the powder(s) can be added to the dispersion and the resulting combination stirred or agitated for a period of time to facilitate mixing. The solvent can then be removed by evaporation, with or without the aid of vacuum. Useful solvents include toluene, isopropanol, heptane, hexane, octane, and the like, and mixtures thereof. Preferably, the nanoparticles are calcium phosphate nanoparticles, and the solvent is heptane. In an alternative method, the surface-modified nanoparticles and the powder(s) can be dry blended, if desired.

The surface-modified nanoparticles can be selected to provide the pharmaceutical inhalation powder formulations with a degree of flowability. The hydrophobic or hydrophilic character of the organocarboxylate surface modifier can be varied (for example, by varying the length of the carbon chain of the organic moiety and/or by varying the chemical nature of other moieties present). If desired, the organocarboxylate surface modifiers can also be used in combination with other hydrophobic or hydrophilic surface modifiers, so that, depending upon the character of the processing solvent or the powder(s), the resulting formulation can exhibit substantially free-flowing properties.

Suitable surface modifiers can thus be selected based upon the nature of the processing solvents and powder(s) used and the properties desired in the resulting formulation. When a processing solvent is hydrophobic, for example, one skilled in the art can select from among various hydrophobic surface modifiers to achieve a surface- modified nanoparticle that is compatible with the hydrophobic solvent; when the processing solvent is hydrophilic, one skilled in the art can select from various hydrophilic surface modifiers; and, when the solvent is a hydrofluorocarbon, one skilled in the art can select from among various compatible surface modifiers; and so forth. The nature of the powder(s) and the desired final properties can also affect the selection of the surface modifiers. The nanoparticle can have a plurality of different surface modifiers (for example, a combination of hydrophilic and hydrophobic modifiers) that combine to provide nanoparticles having a desired set of characteristics. The surface modifiers can generally be selected to provide a statistically averaged, randomly surface-modified nanoparticle.

The surface modifiers can be present on the surface of the nanoparticles in an amount sufficient to provide surface-modified nanoparticles with the properties necessary for compatibility with the powder(s). For example, the surface modifiers can be present in an amount sufficient to form a discontinuous or continuous monolayer on the surface of at least a portion (preferably, a substantial portion) of the nanoparticle. The resulting pharmaceutical inhalation powder formulations can be stored in a storage article or device (preferably, a dry powder inhaler comprising a mouthpiece and a powder containment system) prior to dosing. This storage article or device can comprise, for example, a reservoir, capsule, blister, or dimpled tape and can be a multi-dose or single-dose device.

Objects and advantages of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention.

Examples

Materials

Calcium hydroxide (95% percent (%) purity), zinc acetate, tris [2-(2-methoxy ethoxy)-ethyl] amine and crystalline phosphoric acid (99 % purity; Fluka) were obtained from Sigma-Aldrich Chemical Company, St. Louis, MO. Magnesium stearate, Oleic acid (90 % purity), and tri-n-octylamine (98 % purity) were obtained from Alfa Aesar, Ward Hill, Massachusetts.

Calcium stearate (95 % purity) and 3,5,5-Trimethylhexanoic acid were obtained from TCI America, Portland, Oregon.

Magnesium stearate chloride hexahydrate (99 % purity) was obtained from EM Science, Gibbstown, NJ.

Calcium Acetate and Calcium acetate monohydrate were obtained from MP Biomedicals LLC Aurora, OH.

Methanol (ACS grade; BDH) was obtained from VWR, West Chester, PA. Stearic acid, Heptane and hexanes were obtained from EMD Chemicals, Gibbstown, NJ.

Example 1

Calcium hydroxide (1.48 g) was mixed with deionized water (1 g), oleic acid (16.92 g) and heptane (50 g). the mixture was heated at 120⁰C under a stream of nitrogen in an oil bath for 20 minutes. At this temperature a previously made solution of phosphoric acid (1.16 g) and 11.1 tri-n-octylamine (11.1 g) in methanol (3 g) prepared using a vortex mixer was added. Additional heptane (75 g) was added to the reaction flask. The reaction mixture was heated under stirring at 120⁰C under nitrogen atmosphere for 16 hours.

The heating was stopped and the warm reaction mixture was poured in polypropylene bottles, to which a three-fold excess of methanol was added leading to the precipitation of a white solid. Centrifugation of this solution followed by subsequent washes with methanol led to a wet precipitate which was dried under flowing air. The dried precipitate was dispersed in heptane using a vortex mixer. The resulting mixture was centrifuged to remove any solid which did not disperse in heptane. The precipitate was discarded and the supernatant was an optically clear stable dispersion. The dispersion was characterized by Dynamic Light Scattering and Transmission Electron Microscopy (TEM). An optically clear dispersion in heptane from the synthesis was concentrated under a vaccum using a rotary evaporator. To the concentrated dispersion excess methanol was added leading to the precipitation of white solid. The white solid was centrifuged out. The supernatant was discarded. The precipitate was dried in flowing air. This sample was analyzed by X-ray diffraction.

Example 2

Calcium hydroxide (1.48 g) was mixed with 1 g of deionized water (1 g), oleic acid (112 g) and heptane (50 g). The mixture was heated at 120⁰C under a stream of nitrogen in an oil bath for 20 minutes. At this temperature a previously made solution of phosphoric acid (1.32 g) and tri-n-octylamine (9.5 g) in methanol (3g) prepared using a vortex mixer was added. Additional heptane (75 g) was added to the reaction flask. The reaction mixture was heated under stirring at 120⁰C under nitrogen atmosphere for 16 hours. The rest of the workup of the reaction was the same as Example 1.

Example 3

Calcium hydroxide (1.48 g) was mixed with deionized water (1 g), 3,5,5- trimethylhexanoic acid (31.6 g), and heptane (50 g). The mixture was heated at 120⁰C under a stream of nitrogen in an oil bath for 20 minutes. At this temperature a previously made solution of phosphoric acid (1.34 g) and tri-n-octylamine (9.52 g) in methanol (3 g) prepared using a vortex mixer was added. Additional heptane (75 g) was added to the reaction flask. The reaction mixture was heated under stirring at 120⁰C under nitrogen atmosphere for 16 hours.

The rest of the workup of the reaction was the same as Example 1.

Example 4

Calcium acetate (0.79 g) was mixed with stearic acid (22.4 g) and heptane (50 g). The mixture was heated at 120⁰C under a stream of nitrogen in an oil bath for 20 minutes. At this temperature a previously made solution of phosphoric acid (0.37 g) and tri-n- octylamine

(2.5 g) in methanol (2 g) prepared using a vortex mixer was added. Additional heptane (50 g) was added to the reaction flask. The reaction mixture was heated under stirring at 120⁰C under nitrogen atmosphere for 15 hours. The rest of the workup of the reaction was the same as Example 1.

Example 5

Calcium acetate (4.5 g) was mixed with stearic acid (22 g) and heptane (50 g). The mixture was heated at 120⁰C under a stream of nitrogen in an oil bath for 20 minutes. During the stirring process additional stearic acid (44 g) was added in 4 parts of 11 g each. After 20 minutes at this temperature a previously made solution of phosphoric acid (1.84 g) and tri-n-octylamine (13.25 g) in methanol (3 g) prepared using a vortex mixer was added. Additional heptane (75 g) was added to the reaction flask. The reaction mixture was heated under stirring at 120⁰C under nitrogen atmosphere for 3 hours. The rest of the workup of the reaction was the same as Example 1.

Example 6

Calcium acetate (4.5 g) was mixed with stearic acid (66 g) and heptane (50 g). The mixture and heated at 120⁰C under a stream of nitrogen in an oil bath for 20 minutes. At this temperature a solution of phosphoric acid and tri-n-octylamine in 3 g of methanol prepared using a vortex mixer was added. Another 75 g of heptane was added to the reaction flask. The reaction mixture was heated under stirring at

120⁰C under nitrogen atmosphere for 3 hours. The rest of the workup of the reaction was the same as Example 1.

Example 7

Calcium stearate (12.08 g) was mixed with stearic acid (16.8 g) and heptane (50 g). The mixture was heated at 120⁰C under a stream of nitrogen in an oil bath for 20 minutes. At this temperature a solution of phosphoric acid (1.4 g) and of tri-n-octylamine (10.14 g) in 3 methanol (3 g) prepared using a vortex mixer was added. Additonal heptane (75 g) was added to the reaction flask. The reaction mixture was heated under stirring at 120⁰C under nitrogen atmosphere for 3 hours. The rest of the workup of the reaction was the same as Example 1.

Example 8

Calcium stearate (24.28 g) was mixed with stearic acid (28 g) and heptane (100 g). The mixture was heated at 120⁰C under a stream of nitrogen in an oil bath for 20 minutes. At this temperature a solution of phosphoric acid (2.68 g) and tri-n-octylamine (19.0 g) in methanol (6 g) prepared using a vortex mixer was added. Additional heptane (100 g) was added to the reaction flask. The reaction mixture was heated under stirring at 120⁰C under nitrogen atmosphere for 8 hours. The rest of the workup of the reaction was the same as Example 1. To obtain a dry powder of nanoparticles an optically clear dispersion in hexane from the synthesis was concentrated using a rotary evaporator. To the concentrated dispersion excess methanol was added leading to the precipitation of white solid. The white solid was centrifuged out. The supernatant was discarded. The precipitate was dried in flowing air to obtain a waxy powder. Example 9

Calcium acetate monohydrate (3.52 g) was mixed with oleic acid (68.2 g) and heptane (50 g). The mixture was heated at 120⁰C under a stream of nitrogen in an oil bath for 20 minutes. At this temperature a solution of phosphoric acid (1.34 g) and tri-n- octylamine (9.52 g) in methanol (3 g) prepared using a vortex mixer was added.

Additional heptane (75 g) was added to the reaction flask. The reaction mixture was heated under stirring at 120⁰C under nitrogen atmosphere for 4 hours. The rest of the workup of the reaction was the same as Example 1.

To obtain a dry powder of calcium phosphate nanoparticles modified by oleate groups a workup similar to that in Example 8 was followed.

Example 10

Calcium acetate monohydrate (3.52 g) was mixed with 3,5,5-trimethylhexanoic acid (37.9 g) and heptane (50 g). The mixture was heated at 120⁰C under a stream of nitrogen in an oil bath for 20 minutes. At this temperature a solution of phosphoric acid

(1.34 g) and of tri-n-octylamine (9.52 g) in methanol (3 g) prepared using a vortex mixer was added. Additional heptane (75 g) was added to the reaction flask. The reaction mixture was heated under stirring at 120⁰C under nitrogen atmosphere for 4 hours. The rest of the workup of the reaction was the same as Example 1. To obtain a dry powder of calcium phosphate nanoparticles modified by trimethylhexanoate groups a workup similar to that in Example 8 was followed.

Example 11

Magnesium stearate (17.72 g) was mixed with stearic acid (22.45 g) and heptane (50 g). The mixture was heated at 120⁰C under a stream of nitrogen in an oil bath for 20 minutes. At this temperature a solution of phosphoric acid (2.1 g) and of tri-n-octylamine (14.83 g) in methanol (3 g) prepared using a vortex mixer was added. Additonal heptane (75 g) was added to the reaction flask. The reaction mixture was heated under stirring at 120⁰C under nitrogen atmosphere for 3 hours. The rest of the workup of the reaction was the same as Example 1. To obtain a dry powder of magnesium phosphate nanoparticles modified by stearate groups a workup similar to that in Example 8 was followed.

Example 12

Zinc acetate dihydrate (1.10 g) dissolved in methanol (10 mL) was mixed with oleic acid (14.4 g) in hexane. The mixture was heated at 120⁰C under a stream of nitrogen in an oil bath. After 30 minutes a premixed solution of phosphoric acid (0.32 g) and tris- [2-(2-methoxy ethoxy)-ethyl] amine (3.2 g) were dissolved in methanol (4 g) and hexane (20 g) was added to the aforementioned reaction mixture and the heating was continued at 120⁰C for another 2 hrs. Zinc phosphate nanoparticles dispersed in hexane were obtained from this reaction mixture using a similar workup described in Example 1.

X-ray Diffraction (XRD)

Reflection geometry X-ray diffraction data were collected using a BRUKER D8 Advance diffractometer (Bruker-AXS, Madison, Wisconsin, USA), copper IQ_x radiation, and VANTEC detector registry of the scattered radiation. The diffractometer was fitted with variable incident beam slits and fixed diffracted beam slits. The survey scan was conducted in coupled continuous mode from 5 to 80 degrees (2Θ) using a 0.015 degree step size and 2 second dwell time. X-ray generator settings of 40 kV and 40 mA were employed. Tested samples were first milled to produce a fine powder and applied as dry powders to specimen holders containing glass inserts.

X-ray diffraction patterns for Example 7 show that the materials shows broad peaks indicative of nanocrystalline nature of the material. The peaks are too broad to attribute to any crystalline calcium phosphate. The material is indeed X-ray amorphous.

Particle Size Determination in Dispersion

Particle size distribution was measured by Dynamic Light Scattering (DLS) using a Malvern Instruments ZETASIZER-NANO ZS, Model No. ZEN3600 particle size analyzer (available from Malvern Instruments, Malvern, U.K.). 10 weight percent (wt%) dispersions of sample compositions were prepared in hexane/heptane for DLS measurements. A small (50 mg) aliquot was taken from the dispersion and diluted with 2.5 g of hexane. The resulting diluted sample was mixed well and then transferred to a glass cuvette. Light scattering data was recorded with the sample temperature set at 25°C. For all measurements, the solvent (hexane/heptane) and the dispersions were filtered using

0.2 micrometer (μ) polytetrafluoroethylene (PTFE) filter. For transforming autocorrelation function into particle size, standard values for the viscosity (0.294 X lO^" Pa-s; 0.294 cp) and refractive index (1.375) of hexane and the viscosity (0.39 X 10^"3 Pa-s; 0.39 cp) and refractive index (1.39) of heptane at 25⁰C were used. Refractive index values of 1.63 for calcium phosphate , 1.51 for magnesium phosphate and 1.572 for zinc phosphate were used. The reported Z-average diameter (average agglomerated particle diameter, d, in nm) was based upon an intensity weighted distribution. Figs. 1 and 2 show the particle size distribution by volume for Examples 1, 2, 9-1 l(heptane) and 3, 5-7 (hexane) in dispersion. The Z-average diameters for Example 1, 2 and 3 are 99nm, 76nm and 86nm respectively. Nearly all the particles have size less than lOOnm. The Z-average sizes for the calcium phosphate nanoparticles functionalized with stearate groups is 33 nm, 16 nm and 44 nm respectively (see Examples 5-7). For calcium phosphate nanoparticles functionalized with oleate and 3,5,5-trimethylhexanoate groups; (Examples 9 and 10) the Z-average sizes are 20 and 53nm respectively. For Magnesium phosphate nanoparticles functionalized with stearate molecules Example 11 the Z-average size is 54nm. The Z-average diameter for the zinc phosphate nanoparticles surface modified with oleic acid (example 12) was found to be 91 nm (Fig. 4).

Transmission Electron Microscopy (TEM) Samples were prepared by placing a drop of a 2 weight percent heptane or hexane colloidal suspension onto the carbon side of a carbon grid sample holder (type 01801, from Ted Pella Inc., Redding CA, USA). Excess solvent was wicked from the sample holder, and the remaining slurry was air dried for 5 minutes before use. The samples were examined in a JEOL JSM 200CX transmission electron microscope (TEM) (JEOL, Tokyo, Japan) at 200KV. Pictures of the particulate material were imaged at 50 and 100 Kx and Selected Area Diffraction (SAD) was used to determine crystal type and size. Some dark field imaging was conducted to illuminate the crystal phases and again determine crystal size. The images and SAD patterns were captured and digitized for image analysis. TEM images for Examples 3 and 5 shown in Figs. 4 and 5 respectively show that nearly all the nanoparticles are less than 20 nm in size with most of the nanoparticles sizes are between 3-5 nm.

FT-IR Spectroscopy:

The FTIR measurements were performed using a Thermo Nicolet Avatar 370 durascope instrument in the reflectance mode (64 scans and resolution at 8 cm^"1). The FTIR spectrum of the zinc phosphate nanoparticles (Fig. 6) shows characteristic peaks due to (PO₄)^3" at 1010 cm^"1, and peaks due to the C-H stretching (2921, 2851 cm^"1), carboxylate anion (peaks at 1547, 1526 and 1455, 1396 cm^"1) of oleic acid could be observed.

Various modifications and alterations to this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention. It should be understood that this invention is not intended to be unduly limited by the illustrative embodiments and examples set forth herein and that such examples and embodiments are presented by way of example only with the scope of the invention intended to be limited only by the claims set forth herein as follows. All references cited within are herein incorporated by reference in their entirety.

Claims

What is claimed is:

1. A composition comprising surface-modified nanoparticles of at least one metal phosphate, said nanoparticles bearing, on at least a portion of their surfaces, a surface modification comprising at least one organocarboxylate surface modifier comprising at least one organic moiety comprising at least six carbon atoms.

2. A composition according to claim 1 , wherein the metal of said metal phosphate is selected from transition metals, alkaline earth metals, alkali metals, post- transition metals, and combinations thereof.

3. A composition according to claim 1 , wherein the metal of said metal phosphate is divalent.

4. A composition according to claim 1 , wherein the metal of said metal phosphate is selected from alkaline earth metals and combinations thereof.

5. A composition according to claim 1, wherein said organocarboxylate surface modifier comprises at least one organic moiety having from about 6 to about 24 carbon atoms.

6. A composition according to claim 5, wherein said organocarboxylate surface modifier comprises at least one organic moiety having from 16 to 18 carbon atoms.

7. A composition according to claim 5, wherein said organocarboxylate surface modifier is derived from a precursor organocarboxylate compound selected from at least one saturated, monounsaturated, and polyunsaturated carboxylic acids.

8. A composition according to claim 1, wherein said surface-modified nanoparticles have average primary particle diameters of 1 nm to 50 nm.

9. A composition according to claim 1, wherein said surface-modified nanoparticles comprise from 1 weight percent to 90 weight percent of said surface modifier, based upon the total weight of said surface-modified nanoparticles.

10. A composition according to claim 1, wherein said surface-modified nanoparticles are redispersible.

11. A composition according to claim 1 , wherein said surface-modified nanoparticles are substantially spherical.

12. A composition according to claim 1, wherein said composition is in a pharmaceutical formulation comprising a medicament.

13. A composition according to claim 12, wherein said medicament is a powder.

14. An article comprising a composition according to claim 1.

15. An article according to claim 14, wherein said article is a dry powder inhaler.

16. A process comprising : combining at least one metal cation source, at least one phosphate anion source, at least one organic base comprising at least one organic moiety comprising at least five carbon atoms, and at least one organocarboxylate comprising at least one organic moiety comprising at least six carbon atoms in a liquid medium; and allowing said metal cation source and said phosphate anion source to react in the presence of said organic base and said organocarboxylate.

17. A process according to claim 16, wherein said metal cation is selected from cations of transition metals, alkaline earth metals, alkali metals, post-transition metals, and combinations thereof.

18. A process according to claim 16 wherein the at least one metal cation source and the at least one organocarboxylate comprise a metal organocarboxylate salt.

19. A process according to claim 16 further comprising heating said metal cation source and said phosphate anion source in a liquid medium to a temperature between room temperature and the boiling point of the liquid medium to react in the presence of said organic base and said organocarboxylate.

20. A process according to claim 16 further comprising isolating metal phosphate nanoparticles.