Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
  • C07F7/00—Compounds containing elements of Groups 4 or 14 of the Periodic Table
  • C07F7/02—Silicon compounds
  • C07F7/08—Compounds having one or more C—Si linkages
  • C07F7/18—Compounds having one or more C—Si linkages as well as one or more C—O—Si linkages
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/30—Processes for preparing, regenerating, or reactivating
  • B01J20/32—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating
  • B01J20/3231—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating characterised by the coating or impregnating layer
  • B01J20/3242—Layers with a functional group, e.g. an affinity material, a ligand, a reactant or a complexing group
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/281—Sorbents specially adapted for preparative, analytical or investigative chromatography
  • B01J20/286—Phases chemically bonded to a substrate, e.g. to silica or to polymers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/281—Sorbents specially adapted for preparative, analytical or investigative chromatography
  • B01J20/286—Phases chemically bonded to a substrate, e.g. to silica or to polymers
  • B01J20/287—Non-polar phases; Reversed phases
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
  • C07F7/00—Compounds containing elements of Groups 4 or 14 of the Periodic Table
  • C07F7/02—Silicon compounds
  • C07F7/08—Compounds having one or more C—Si linkages
  • C07F7/18—Compounds having one or more C—Si linkages as well as one or more C—O—Si linkages
  • C07F7/1804—Compounds having Si-O-C linkages
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
  • G01N30/02—Column chromatography
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2220/00—Aspects relating to sorbent materials
  • B01J2220/50—Aspects relating to the use of sorbent or filter aid materials
  • B01J2220/54—Sorbents specially adapted for analytical or investigative chromatography
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31652—Of asbestos
  • Y10T428/31663—As siloxane, silicone or silane

Definitions

• This invention relates to polyfunctional silicon compounds and to binding such compounds to substrates for uses such as a separation media.
• Conventional CI 8 (ODS) silica columns are widely accepted as general-purpose stationary phases.
• ODS organic chemical vapor deposition
• some drawbacks impede the use of these columns for certain applications, including the peak tailing of basic analytes and "phase collapse" (or "de-wetting") in a highly aqueous environment.
• Recent advances in silica synthesis and bonding technology provide solutions to minimize the base tailing using high-density bonding followed by exhaustive end-capping of high purity silica. Densely bonded and highly hydrophobic ODS columns cannot be used in 100% water, since the "phase collapse” usually occurs, causing greatly reduced or irreproducible retention.
• Polar-embedded phases were introduced in order to improve the peak shape of basic analytes and to make RP columns fully operational in highly aqueous environment. These phases are primarily hydrophobic but have hydrophilic groups incorporated near the silica surface. The commonly used polar groups are amide, urea, ether and carbamate functionalities. In general, the polar-embedded phases have the following benefits in comparison to conventional C18 packings: they provide good peak shapes of basic analytes, good compatibility with highly aqueous mobile phases, and selectivities that differ from those exhibited by general purpose C18 columns.
• the polar-embedded phases have their own drawbacks such as significantly decreased retention of basic and non-polar compounds and inferior hydrolytic stability, as compared to conventional C18 columns. Therefore, they are often complementary to C18 columns and operated in a narrower pH range.
• An objective of this invention is to provide polyfunctional silylating agents with built-in polar fragments, which provide bonded silica phases with the benefits of the polar-embedded packings, and enhance their longevity. There is a need to provide improved polyfunctional silica compounds which can be used for HPLC stationary phase development.
• One embodiment of the invention is a polyfunctional silicon compound having one of the following structures:
• R l5 R 2 and R 3 is a leaving group which, after leaving, permits the Si in one of said structures to form a Si-O-Si or Si-O-Zr bond
• N - PG, N - PGi and N - PG 2 are mtrogen-containing polar groups
• each of E, Ei, and E 2 comprise alkyl, substituted alkyl, aryl, or substituted aryl groups, comprising 1-50 carbon atoms, and exclude functional groups selected from the group consisting of hydroxyl, carboxyl, amino, thio, halo and sulfonate moieties.
• Another embodiment of the invention is a composition comprising a silicon compound covalently bound to a substrate having one of the following structures:
• R ! and R 2 are independently an alkyl or substituted alkyl group or a leaving group which, after leaving, permits the Si in one of said structures to form a Si-O-Si or Si-O-Zr bond,
• Li, L 2 , and L 3 comprise alkyl or substituted alkyl chains from
• N - PG, N - 1?G ⁇ and N - PG 2 are nitrogen-containing polar groups
• each of E, Ei, and E comprise alkyl, substitute alkyl or aryl or substituted aryl groups, comprising 1-50 carbon atoms, and exclude functional groups selected from the group consisting of hydroxyl, carboxyl, amino, thio, halo and sulfonate moieties.
• analytes in a liquid sample are separated by flowing through medium comprising the composition of the previous paragraph.
• FIG. 1 illustrates the polar selectivity test comparison using conventional C18 phase and newly developed amide-embedded C18 phase.
• FIG. 2 illustrates the amitriptyline test using newly developed amide- embedded C18 phase.
• FIG. 3 illustrates the polarity test using newly developed amide-embedded C18 phase.
• FIG. 4 illustrates the phase collapse test using newly developed amide- embedded C18 phase in comparison to a conventional C18 column.
• FIG. 5 illustrates the hydrolytic stability test at pHl and 50 °C using newly developed amide-embedded C18 column and a well-known polar-embedded commercial phase (brand B).
• FIG. 6 illustrates the hydrolytic stability test at pH 11.5 and 30 °C using newly developed amide-embedded C18 column and high-density conventional CI 8 phase (brand C).
• silicon compounds which are commercially available, or which can be synthesized as disclosed herein, can be used in the methods disclosed herein to react with the surfaces of substrates to form functionalized substrates for a wide range of applications.
• the silicon compounds are covalently attached to the surfaces of the substrates in order to modify those substrates with various functional groups.
• the silicon compounds may be attached to the surface of silica gel to provide the functionalized silica particles for chromatographic packings.
• sicon compound refers to a compound comprising at least two silicon atoms and a polar-embedded functionality, such as amide, carbamate, sulfonamide, or urea.
• the silicon compound is a silylating agent comprising at least two activated silicon groups, such as hydroxy, alkoxy, halo, or aminosilane. These groups are capable of reacting with a functional group, for example, on a surface of a substrate, to form a covalent bond with a surface.
• the activated silicon groups of silicon compound can react with the surface of a substrate such as silica or zirconia, comprising the Si-OH or Zr-OH groups, respectively, to create the Si-O-Si or Si-O-Zr bonds between the silicon compound and a substrate.
• Exemplary activated silicon groups include but are not limited to - Si(OMe) 3 ; -SiMe(OMe) 2 ; -SiMe 2 (OMe); -Si(OEt) 3 ; -SiMe(OEt) 2 ; -SiMe 2 (OEt) and -SiCl 3 ,-SiMe 2 N(Me) 2 .
• the term 'polyfunctional silicon compound refers to a compound comprising at least two activated silyl groups and a polar-embedded functionality, such as amide, carbamate, sulfonamide, or urea.
• polar-embedded functionality such as amide, carbamate, sulfonamide, or urea.
• R ls R 2 and R 3 is a leaving group which, after leaving, permits the Si in one of said structures to form a Si-O-Si or Si-O-Zr bond,
• L ls L 2 and L 3 comprise alkyl or substituted alkyl chains from
• N - PG, N - PGi and N - PG are nitrogen-containing polar groups
• each of E, Ei, and E 2 comprise alkyl, substituted alkyl, aryl, and substituted aryl groups and exclude functional groups selected from the group consisting of hydroxyl, carboxyl, amino, thio, halo and sulfonate moieties.
• E, E ⁇ and E 2 comprise 1 to 50 carbon atoms, preferably 1 to 30 carbon atoms, and more preferably 1 to 20 carbon atoms.
• R l3 R , and R 3 is a leaving group which, after leaving, permits the Si in one of said structures to form a Si-O-Si or Si-O-Zr bond.
• Suitable leaving groups include hydroxy, alkoxy, halide, or amino group, for example, -OMe, or OEt.
• Ri, R 2 , R 3 are all -OMe.
• K and R 2 are independently a reactive group, such as hydroxy, alkoxy, halide, or amino group.
• -OMe, or OEt, and R 3 may be an alkyl group, such as Me, or substituted alkyl group.
• R] may be a reactive group, such as hydroxy, alkoxy, halide, or amino group.
• -OMe, and R and R may be independently alkyl group, such as Me, or substituted alkyl group.
• Lj, Q. and L 3 are independently alkyl or substituted alkyl chains, preferably -(CH ) n-) of a carbon chain length of 1 to 100, preferably 1 to 50 in length.
• Groups Li, L 2 and L 3 may contain heteroatoms such as nitrogen, oxygen, silicon, and sulfur.
• L 3 may contain aromatic and heteroaromatic fragments such as phenyl and pyridyl, respectively.
• N-PG is a nitrogen-containing polar-embedded functionality, also referred to as a polar group. Suitable polar groups include amide, carbamate, sulfonamide, or urea groups.
• E, Ei and E 2 comprise a non-derivatizable functional group, specifically alkyl, substituted alkyl, aryl, substituted aryl groups, excluding functional groups selected from the group consisting of hydroxyl, carboxyl, amino, thio, halo, and sulfonate moieties.
• E, E ⁇ and E 2 comprise a cyano terminal moiety.
• E, B and E 2 may comprise an alkyl chain of sufficient length so that when said silicon compound is bound to a substrate, it is capable of use as a reverse phase chromatography medium.
• E, E] and E are molecular fragments consisting of 1 to 50 carbon atoms, preferably of 1 to 30 carbon atoms, and more preferably of 1 to 20 carbon atoms.
• m 1 to 100, preferably 1 to 10.
• the Formula U results in compounds 10 or 11 containing specific substituents.
• One method for synthesizing polyfunctional silicon compounds of Formula I is as follows: Diallyl a ine is first allowed to react with a reagent, such as acyl chloride, carbamoyl chloride, sulfonyl chloride, or isocyanate, containing a proper functionality. The resulting polar-embedded diallyl compound is then subjected to a hydrosilylation in presence of the silicon compound of formula SiHR ⁇ R 2 R 3 and a Pt catalyst to generate a polyfunctional silicon compound of Formula I.
• a reagent such as acyl chloride, carbamoyl chloride, sulfonyl chloride, or isocyanate
• Scheme 1 below provides an example of synthesizing the polyfunctional silicon compound of Formula I.
• Scheme 1 shows the synthesis of silicon compound 1.
• the silicon compounds of Formulas I or II are bound to a substrate, preferably for use as a chromatography separation medium as in a packed bed form.
• the substrate comprises a silica surface.
• R ⁇ and R 2 are independently an alkyl or substituted alkyl group or a leaving group which, after leaving, permits the Si in one of said structures to form a Si-O-Si or Si-O-Zr bond,
• Li, - , and L 3 comprise alkyl or substituted alkyl chains from
• N - PG, N - PG ⁇ and N - PG 2 are nitrogen-containing polar groups
• each of E, Ei, and E 2 comprise alkyl, substituted alkyl, aryl, substituted aryl groups and exclude functional groups selected from the group consisting of hydroxyl, carboxyl, amino, thio, halo and sulfonate moieties.
• E, Ei, and E 2 are molecular fragments comprising 1 to 50 carbon atoms.
• the silicon compound is covalently bound to a substrate, wherein the Si groups attached to L ⁇ and L 2 are covalently bound to the substrate by reaction of Ri, R 2 or R 3 of Si of said L ⁇ - Si or L - Si linkages with reactive groups on said substrate selected from the group consisting of silanol, alkoxysilane, halosilane and aminosilane moieties.
• the polyfunctional silicon compounds can be covalently attached to a variety of substrates.
• Exemplary substrates include materials that comprise a functional group that is capable of reacting with the polyfunctional silicon compounds containing activated silyl groups.
• the polyfunctional silicon compounds can be attached, for example, to the silica based materials such as glass surfaces, or the surfaces of other silicon oxide, titanium oxide, germanium oxide, zirconium oxide, and aluminum oxide based materials; and also to the surfaces of various carbonized materials, metals, crosslinked and non-crosslinked polymers, which contain suitable functional groups for reacting with the invented silicon compounds.
• suitable functional groups are silanols, alkoxysilanes, titanium hydroxides, zirconium hydroxides, etc.
• Developed silicon compounds can also be incorporated into the polymeric or sol-gel networks by utilizing the reactive silicon functionalities.
• the mono- and multi-layered surfaces are prepared by treating silica substrates with the polyfunctional silicon compounds of Formulas I and II.
• silicon compounds can be covalently attached to a variety of substrates, such as silica gel, zirconia, hybrid sol-gel/polymers or glass plates.
• Suitable silica gels comprise non-porous, or porous silica particles of different pore sizes, preferably from 20 A to 3000 A, and more preferably from 60 A to 2000 A; and of different particle sizes, preferably from 0.2um tolOOO urn, and more preferably from 2um to 50um.
• the treatment reaction can be carried out in a slurry of silica gel in an inert solvent, such as toluene, at elevated temperature.
• Water, acid or base catalyst can be applied to enhance the surface coverage, depending on the type of properties desired for the separation media.
• an aminosilane compound such as bis(trimethoxysilylpropyl)amine can be used for modifying the underivatized silica gel by incorporating the reactive amino group onto a surface.
• a reagent such as acyl chloride, carbamyl chloride, sulfonyl chloride, or isocyanate, containing a proper functional group, can be reacted with the animated silica gel to form the corresponding bonded phase.
• Scheme 3 illustrates an alternative procedure (two-step synthesis) for modification of silica support with new polar-embedded ligands.
• This invention provides a simple and versatile approach to produce a variety of novel solid supports with excellent hydrolytic stability.
• the method of synthesis allows for efficient incorporation of different functionalities onto the surfaces of the substrates and silica substrates, in particular.
• the resulting materials can be applied for development of adsorbents, membranes, filters, microfluidic devices, microchips, and functionalized surfaces for various types of separation, detection and analysis.
• This invention can be applied to a development of new stationary phases for various chromatographic separations and reversed phase chromatography, in particular.
• This example illustrates a process for the synthesis of novel polyfunctional silicon compounds.
• Diallyl amine was mixed with the excess of Et 3 N (2.0 equiv.) in CH C1 2 and kept at 0°C for 20 min. Then, a solution of acyl chloride, sulfonyl chloride or isocyanate (1.0 equiv) in CH C1 2 was slowly added and the reaction mixture was stirred at ambient temperature for 12 hours. The reaction mixture was washed with water and dried over Na 2 SO . After removal of all volatiles under reduced pressure, the corresponding N,N-bis(allyl) polar-embedded precursor was obtained.
• N, JV-bis(allyl) urea-embedded precursor was obtained by mixing an isocyanate with diallyl amine in toluene.
• the structures of synthesized compounds were confirmed by 1H NMR spectroscopy and mass spectrometry
• This example illustrates an alternative process for the synthesis of novel polyfunctional silicon compounds when N,N-bis(silyl)amines, such as bis(trimethoxysilylpropyl)amine or bis[(3-trimethoxysilyl)propyl]ethylene diamine were used as starting materials.
• N,N-bis(silyl)amines such as bis(trimethoxysilylpropyl)amine or bis[(3-trimethoxysilyl)propyl]ethylene diamine were used as starting materials.
• N,N-bis(silyl)amine such as bis(1ximethoxysilylpropyl)amine or bis[(3- trimethoxysilyl)propyl]ethylene diamine was mixed with the excess of Et 3 N (2.0 equiv.) in CH 2 C1 2 and was kept at 0°C for 20 min. Then, a solution of acyl chloride, sulfonyl chloride or isocyanate (1.0 equiv) in CH 2 C1 was slowly added and the reaction mixture was stirred at ambient temperature for 4 hours. The reaction mixture was washed with water and dried over Na 2 SO 4 . After removal of all volatiles under reduced pressure, the corresponding polyfunctional silicon compound was obtained.
• acyl chloride, sulfonyl chloride or isocyanate 1.0 equiv
• This example illustrates a process for silica functionalization using novel polyfunctional silicon compounds.
• the reaction was carried out in the slurry of selected silica gel and a polyfunctional silicon compound in the inert solvent such as toluene, at elevated temperature.
• Water, acid or base catalyst can be applied to control the surface coverage of the functionalized silica gel, depending on a particular application.
• an appropriate end-capping or other type of post-derivatization reaction can be used if necessary.
• This example describes the chromatographic evaluation of octadecylamide functionalized silica produced from the polyfunctional silicon compound 3.
• Synthesized samples were prepared from high-purity raw silica gel with the following physical properties: average particle size, 5.0 ⁇ m; specific surface area, 295 m 2 /g; mean pore size, 136 A; pore volume, 1.00 mL/g; Bonded silica was packed into 4.6 x 150 mm stainless steel columns using traditional high-pressure slurry techniques.
• the test standard was a mixture of uracil, dimethylphthalate, butylparaben, toluene and phenanthrene.
• the test conditions were: eluent, CH 3 CN H 2 O (70:30 v/v); flow rate, 1 mL/min; injection volume, 5 ⁇ L; temperature, 30°C; and detection, 254 nrn.
• FIG. 1 shows that the new phase has different selectivity as compared to conventional RP C18 materials, displaying different elution order for toluene and butylparaben analytes.
• the test mix contained uracil, toluene, ethylbenzene, amitriptyline and quinizarin.
• the test conditions were: eluent, MeOH 20 mM K 2 HPO 4 /KH 2 PO 4 (80:20 v/v); flow rate, 1 mL/min; injection volume, 5 ⁇ L; temperature, 30°C; and detection, 254 nm.
• Aminotriptyline (pKa 9.3) test conducted with pH 7 mobile phase, is a sensitive method for monitoring silanol activity. At this pH, many of the residual silanols are negatively charged, and the basic probes are completely protonated. The protonated base molecules interact with the ionized silanols via ion-exchange mechanism, thus the degree of tailing is a direct measure of silanol activity. As shown in FIG. 2, the new phase provides excellent peak shape and low asymmetry for amitriptyline (As am jtriptyKne ⁇ 1 -2), which indicates that the polar moiety incorporated into the new phase reduces the interaction between bases and residual silanols quite effectively.
• the test mixture contained uracil (void marker), pyridine (basic), phenol (acidic), N,N-dirnethyl aniline (basic), -butylbenzoic acid (acidic), and toluene (non- polar).
• the test conditions were: eluent, CH 3 CN/50 mM K 2 HPO 4 /KH 2 PO 4 (60:40 v/v); flow rate, 1 mL/min; injection volume, 5 ⁇ L; temperature, 30°C; and detection, 254 nm.
• the test results are shown in FIG. 3. It was shown that excellent peak shapes for all acid, basic, and non-polar analytes, can be achieved on the new amide- embedded phase, suggesting good overall column performance.
• the bonded phase was tested in a 10 mM H 3 PO 4 , pH 2.4 mobile phase at 30°C.
• a freshly packed column was washed with 50 column volumes of CH 3 CN, and then equilibrated with 100 column volumes of a mobile phase.
• the sample solution contained cytosine, uracil and thymine.
• each test cycle consisted of two steps. Step one: the column was equilibrated with a mobile phase for 20 min, then the sample was injected and the data acquisition was conducted for another 10 min. Step two: flow was stopped for 30 min before starting the next cycle. Fifty cycles were performed for each bonded phase.
• a newly developed amide-embedded phase was compared against a fresh commercial high-density C18 phase ( Brand A) using the "stop-flow" test in a 100% aqueous eluent (FIG. 4). It was found that the high-density C18 column suffered a sudden loss of retention for cytosine, uracil and thymine after the first stop-flow cycle (FIG. 4). Further gradual decrease of retention was observed in the following cycles. In comparison, the newly developed amide-embedded phase performed consistently well under the same conditions. The only negligible loss of retention was observed after fifty stop-flow cycles for all three analytes (less than 1.0, 1.0, and 5.0 % retention drops for cytosine, uracil, and thymine, respectively).
• the new amide phase and a well-known polar-embedded commercial phase were subjected to low pH stability test at pH 1 and 50°C. During a 30-day testing period, less than 1% drop of toluene k was observed for a new phase, while nearly 20% drop of A: value occurred when brand B column was tested under the same conditions (FIG. 5). The increased number of covalent bonds between the functional silicon compound and a silica surface is believed to be the main reason for an excellent stability of the new amide polar-embedded phase described in this invention.
• a new amide polar-embedded phase was compared against a high-density CI 8 phase prepared on a base of the same raw silica gel, using high pH stability test at pH 11.5, 30°C (FIG. 6). It was found that the high-density CI 8 phase failed after ten days of continuous purging, due to column bed collapse. In comparison, the new amide phase was stable for sixteen days under the same conditions, which is translated into approximately 60% increase of stability.
• the functional layer of the developed amide-embedded phase had a stabilizing effect, preventing a rapid dissolution of the silica backbone at elevated pHs.

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