JP3731603B2 - Thermally developed silver salt photographic light-sensitive material and silver image forming method - Google Patents

Description

  The present invention relates to a heat-developable silver salt photographic light-sensitive material for forming a silver image (hereinafter also referred to as a heat-developable silver salt photographic light-sensitive material) and an image forming method thereof. Relates to a heat-developable silver halide photographic light-sensitive material and an image forming method thereof.

  In order to generate a final image, a so-called dry photosensitive material that does not use a liquid developer is desired from the viewpoint of workability without liquid preparation and environmental protection without waste liquid. Such an image-forming material basically contains a non-photosensitive reducible silver source, a photosensitive material that produces silver when irradiated, and a reducing agent for the silver source. In general, the photosensitive material needs to be in catalytic proximity to the non-photosensitive silver source. Catalytic proximity refers to these two types so that when silver specks or nuclei are produced by photographic silver halide irradiation or exposure, these nuclei can catalyze the reduction of the silver source by the reducing agent. This material has a close physical relationship. Silver is a catalyst for the reduction of silver ions, and the photosensitive silver halide catalyst precursor that produces silver is provided in catalytic proximity to the silver source in many different ways.

  Silver halide emulsions used for heat-developed silver salt photographic light-sensitive materials have many problems such as fogging during storage. As the shelf life of the material increases, such as one year at room temperature (ambient conditions), the level of fog increases gradually. What makes it more difficult to control the fog during the storage period is the fact that a developer (reducing agent) is contained in the heat-developable silver salt photographic light-sensitive material, which is another silver halide photographic light-sensitive material. It is different from the material. Therefore, in the heat-developable silver salt photographic light-sensitive material, the requirement for extending the shelf life is very important. The fog level of the newly prepared heat-developable silver halide photographic material is referred to as initial fog. Great efforts have been made to minimize initial fogging and to stabilize the level of fogging during storage. US Pat. No. 3,589,903 describes mercury salts as antifogging agents. U.S. Pat. No. 4,152,160 is an organic carboxylic acid such as benzoic acid and phthalic acid, U.S. Pat. No. 4,784,939 is a benzoylbenzoic acid compound, and U.S. Pat. No. 4,569,906 is indane or tetralin. Carboxylic acids, dicarboxylic acids in US Pat. No. 4,820,617, and heteroaromatic carboxylic acids in US Pat. No. 4,626,500 are described for fog reduction. Halogenated compounds have also been shown as strong antifoggants and are disclosed in U.S. Pat. Nos. 4,546,075, 4,756,999, 4,452,885, and 3,874,946. And U.S. Pat. No. 3,955,982. Halogen molecules or halogen molecules having a heterocyclic ring are also useful antifoggants and are described in US Pat. No. 5,028,523. However, even with these individual compounds or a combination of these compounds, the fog stability during the storage period of the heat-developable silver salt photographic light-sensitive material is still insufficient, and further improvement is desired.

  Further, the silver image obtained from the heat-developable silver salt photographic light-sensitive material has a lower blackness than the silver image obtained from the silver halide photographic light-sensitive material obtained by liquid development, and the storage stability of the obtained image is inferior.

  SUMMARY OF THE INVENTION The present invention provides a heat-developable silver salt photographic light-sensitive material in which heat fog, silver tone, and image storage are solved without deteriorating sensitivity and an image forming method thereof.

  The above object of the present invention has been achieved by the following.

(Claim 1) A photothermographic material containing at least a photosensitive silver halide, an organic silver salt, and a reducing agent, containing at least one thermally decomposable precursor selected from a heterocyclic sulfoamino compound and a heterocyclic carbonylthio compound. A heat-developable silver salt photographic light-sensitive material for forming a silver image.

(2) A method for forming a silver image using a heat-developable light-sensitive material containing at least light-sensitive silver halide, an organic silver salt and a reducing agent, wherein the heat-developable light-sensitive material is a heterocyclic sulfoamino compound And a silver image forming method for a heat-developable silver salt photographic material, comprising at least one heat-decomposable precursor selected from a heterocyclic carbonylthio compound .

  According to the present invention, it is possible to provide a heat-developable silver salt photographic light-sensitive material in which heat fog, silver tone, and image storage are solved without lowering the sensitivity and an image forming method thereof.

  The photosensitive silver halide of the present invention is prepared in advance as an emulsion such as a Lippmann emulsion, an ammonia method emulsion, a thiocyanate or a thioether ripened emulsion by any method known in the field of photographic technology such as a single jet method or a double jet method. It can then be mixed with the other ingredients of the invention and introduced into the composition used in the invention. In this case, in order to sufficiently contact the organic silver salt and the photosensitive silver halide, for example, U.S. Pat. Nos. 3,706,564 and 3, as protective polymers for preparing a photosensitive silver halide emulsion. Polymers other than gelatin such as polyvinyl acetals described in 706,565, 3,713,833, 3,748,143 and British Patent 1,362,970 are used. Means, means for enzymatically degrading gelatin of photosensitive silver halide emulsions as described in British Patent 1,354,186, or as described in US Pat. No. 4,076,539. Thus, each means such as a means for omitting the use of a protective polymer can be applied by preparing photosensitive silver halide grains in the presence of a surfactant.

  The photosensitive silver halide used in the present invention is also prepared by mixing a halogenated agent and an organic silver salt-forming component in a mixed solution as described in British Patent No. 1,447,454. By injecting a silver ion solution, the organic silver salt can be produced almost simultaneously.

As another method, a photosensitive silver halide forming component is allowed to act on a solution or dispersion of an organic silver salt prepared in advance or a sheet material containing the organic silver salt, so that a part of the organic silver salt is converted to a photosensitive halogen. It can also be converted to silver fossil. The photosensitive silver halide thus formed is in effective contact with the organic silver salt and exhibits a preferable action. The above-mentioned photosensitive silver halide forming component is a compound that can react with an organic silver salt to form a photosensitive silver halide, and what kind of compound is applicable and effective is as follows. Can be determined by testing. That is, the organic silver salt and the compound to be tested are mixed, and after heating, if necessary, the presence of a diffraction peak peculiar to silver halide is examined by an X-ray diffraction method. Examples of photosensitive silver halide forming components that have been confirmed to be effective by such tests include inorganic halides, onium halides, halogenated hydrocarbons, N-halogen compounds, and other halogen-containing compounds. For examples, U.S. Pat. Nos. 4,009,039, 3,457,075, 4,003,749, British Patents 1,498,956 and 1,498,956. Detailed description will be given in the specification and in Japanese Patent Application Laid-Open Nos. 53-27027 and 53-25420. Examples thereof are shown below. (1) Inorganic silver halide: a halide represented by, for example, MXn (where M represents H, NH ₄ and a metal atom, X represents Cl, Br and I, n represents M represents H and NH ₄₎ 1 represents the valence when M is a metal atom, and the metal atom includes lithium, sodium, potassium, cesium, magnesium, calcium, strontium, barium, zinc, cadmium, mercury, tin, antimony, Chrome, manganese, iron, cobalt, nickel, rhodium, cerium, etc.). Halogen molecules such as bromine water are also effective.
(2) Onium halides: quaternary ammonium halides such as trimethylphenylammonium bromide, cetylethyldimethylammonium bromide, trimethylbenzylammonium bromide: quaternary phosphonium halides such as tetraethylphosphonium bromide; trimethyl There are tertiary sulfonium halides such as sulfonium iodide.
(3) Halogenated hydrocarbons: for example, iodoform, bromoform, carbon tetrabromide, 2-bromo-2-methylpropane and the like.
(4) N-halogen compounds: for example N-chlorosuccinimide, N-bromosuccinimide, N-bromophthalimide, N-bromoacetamide, N-iodosuccinimide, N-bromophthalazone, N-bromooxazolinone N-chlorophthalazone, N-bromoacetanilide, N, N-dibromobenzenesulfonamide, N-bromo-N-methylbenzenesulfonamide, 1,3-dibromo-4,4-dimethylhydantoin, N-bromourazole, etc. is there.
(5) Other contained halogen compounds: for example, triphenylmethyl chloride, triphenylmethyl bromide, 2-bromoacetic acid, 2-bromoethanol, benzophenone dichloride and the like.

  These photosensitive silver halide forming components are used in a stoichiometrically small amount with respect to the organic silver salt. Usually, the range is set to about 0.001 mol to about 0.7 mol, preferably about 0.03 mol to about 0.5 mol, per mol of the organic silver salt. Two or more photosensitive silver halide forming components may be used in the above ranges. Various conditions such as reaction temperature, reaction time, reaction pressure, etc. in the process of converting a part of the organic silver salt to photosensitive silver halide using a photosensitive silver halide forming component can be used for preparation purposes. The reaction temperature is usually about -20 ° C to about 70 ° C, the reaction time is about 0.1 seconds to about 72 hours, and the reaction pressure is set to atmospheric pressure. Is preferred. Further, this reaction is preferably carried out in the presence of a polymer used as a binder described later. In this case, the polymer is used in an amount of about 0.01 to 100 parts by weight, preferably about 0.1 to about 10 parts by weight per part by weight of the organic silver salt.

  The photosensitive silver halide prepared by the various methods described above can be chemically sensitized by, for example, a sulfur-containing compound, a gold compound, a platinum compound, a palladium compound, a silver compound, a tin compound, a chromium compound, or a combination thereof. . With respect to this chemical sensitization procedure, for example, US Pat. No. 4,036,650, British Patent No. 1,518,850, JP-A Nos. 51-22430, 51-78319, 51- No. 81124. In an embodiment in which a part of the organic silver salt is converted to photosensitive silver halide by the photosensitive silver halide forming component, the low molecular weight amide compound as described in US Pat. No. 3,980,482 is used. Sensitization can be achieved by coexisting with each other.

As the organic silver salt of the present invention,
(1) Examples of silver salts of organic compounds having an imino group include saccharin silver salts, benzotriazole silver salts, phthalazinone silver salts, benzoxadione silver salts, imidazole silver salts, Tetraazaindene silver salt, pentaazaindene silver salt, etc.
(2) Examples of silver salts of organic compounds having a mercapto group or thione group include silver salts of 2-mercaptobenzoxazoles, silver salts of mercaptooxadiazoles, silver salts of 2-mercaptobenzothiazoles, 2 -Silver salt of mercaptobenzimidazoles, silver salt of 2-mercaptobenzimidazoles, silver salt of 3-mercapto-4-phenyl-1,2,4-triazoles, etc.
(3) Examples of silver salts of organic compounds having a carboxyl group include silver salts of aliphatic carboxylic acids and silver salts of aromatic carboxylic acids (for example, silver benzoate, silver phthalate, silver phenylacetate, 4′-n -Silver salt of octadecyloxydiphenyl-4-carboxylic acid) and the like.

  For more specific examples of these organic silver salts and examples of organic silver salts other than those described herein, for example, U.S. Pat. Nos. 3,457,075, 3,549,379, and 3,785. No. 830, No. 3,933,507, No. 4,009,039 and British Patent No. 1,230,642 or JP-A-50-93139, No. 50-99719, No. 52-141222 and No. 53-36224 are known, and in the present invention, they can be appropriately selected from these known organic silver salts. For example, when using a silver halide or a silver dye photosensitive complex as a photocatalyst, a light-stable one selected from the above known organic silver salts is used. Preferred examples thereof include silver salts of long-chain aliphatic carboxylic acids having 10 to 40 carbon atoms, particularly 18 to 33, and specifically, silver laurate, silver myristate, silver palmitate, silver stearate, arachidine. Illustrative examples include silver oxide, silver behenate, silver lignocerate, silver pentacosanoate, silver serinate, silver heptacosinate, silver montanate, silver melicinate, and silver lactate.

Such organic silver salts are synthesized by, for example, US Pat. Nos. 3,457,075, 3,458,544, 3,700,458, 3,839,049, 960, 908, British Patent Nos. 1,173,426 and JP-A-49-52626, 51-122011, and 52-14122. Is done. In particular, the polymers described in US Pat. No. 3,700,458 or JP-A No. 53-32015, US Pat. No. 3,887,597 or JP-A No. The presence of the metal-containing compound described in Japanese Patent No. 49-13224 is preferable because the particle form, particle size and / or photographic properties of the organic silver salt can be improved. The preferred range of the amount of these coexisting components is about 0.1 g to 1000 g, particularly about 1 g to about 500 g in the case of polymers and about 10 ^{-6 in} the case of metal-containing compounds with respect to 1 mol of the organic silver salt produced. Mol to 10 ⁻¹ mol.

  Among the organic silver salts prepared as described above, those having a major axis having a particle size of about 0.01 to 10 microns, particularly about 0.1 to about 5 microns are preferably used.

In the present invention, the organic silver salt is used in the range of about 0.1 g to about 4 g, preferably about 0.2 g to about 2.5 g in terms of silver amount per 1 m ² of the support. This is a range of an amount necessary and sufficient to give an appropriate image density, and if it is used below this range, the pixel density will be insufficient, and if it is used above this range, the image density will not increase. High cost.

  Examples of the reducing agent used in the heat-developable silver salt photographic light-sensitive material of the present invention include generally known reducing agents such as monophenols, polyphenols having two or more phenol groups, mononaphthols, and bis. Naphthols, polyhydroxybenzenes having two or more hydroxyl groups, polyhydroxynaphthalenes having two or more hydroxyl groups, ascorbic acids, 3-pyrazolidones, pyrazolin-5-ones, pyrazolines, phenylenediamines, hydroxyl Examples thereof include amines, hydroquinone monoethers, hydroxamic acids, hydrazides, amide oximes, N-hydroxyureas, and the like, and more specifically, for example, U.S. Pat. Nos. 3,615,533 and 3,679,426. No. 3,672,904, No. 3,751,252 3,782,949, 3,801,321, 3,794,488, 3,893,863, 3,887,376, 3,770 No. 4,448, No. 3,819,382, No. 3,773,512, No. 3,839,048, No. 3,887,378, No. 4,009,039, No. No. 4,021,240, British Patent No. 1,486,148 or Belgian Patent No. 786,086 and JP-A-50-36143, No. 50-36110, No. 50-11603, 50-99719, 50-140113, 51-51933, 51-23721, 52-84727 or JP-B-51-35851, there are specific reducing agents. The invention is like this It can be appropriately selected from known reducing agents. As the selection method, it is considered that the simplest method is to examine the superiority or inferiority of the reducing agent used by actually producing a heat-developable photographic light-sensitive material and evaluating its photographic properties.

  Among the reducing agents described above, when an aliphatic silver carboxylate is used as the organic silver salt, preferred reducing agents include polyphenols in which two or more phenol groups are linked by an alkylene group or sulfur, particularly the phenol. Alkyl group (for example, methyl group, ethyl group, propyl group, t-butyl group, cyclohexyl group, etc.) or acyl group (for example, acetyl group, propionyl group, etc.) is substituted at at least one of the substitution positions adjacent to the hydroxy substitution position of the group Polyphenols in which two or more of the selected phenol groups are linked by an alkylene group or sulfur, such as 1,1-bis (2-hydroxy-3,5-dimethylphenyl) -3,5,5-trimethylhexane, 1,1 -Bis (2-hydroxy-3-tert-butyl-5-methylphenyl) methane, 1,1-bis ( -Hydroxy-3,5-di-tert-butylphenyl) methane, 2,6-methylenebis (2-hydroxy-3-tert-butyl-5-methylphenyl-4-methylphenol, 6,6'-pentylidene-bis (2,4-di-t-butylphenol), 6,6'-pentylidene-bis- (2-t-butyl-4-methylphenol), 6,6'-pentylidene-bis (2,4-dimethylphenol) 1,1-bis (2-hydroxy-3,5-dimethylphenyl) -2-methylpropane, 1,1,5,5-tetrakis (2-hydroxy-3,5-dimethylphenyl) -2,4- US patents such as ethylpentane, 2,2-bis (4-hydroxy-3,5-dimethyl) propane, 2,2-bis (4-hydroxy-3,5-di-t-butylphenyl) propane 3,589,903, 4,021,249 or British Patent 1,486,148 and JP-A-51-51933, 50-36110, 50-11603, 52-84727 or JP-B-51-35727); bis-β-naphthols described in US Pat. No. 3,672,904 (for example, 2,2′-dihydroxy- 1,1'-binaphthyl, 6,6'-dibromo-2,2'-dihydroxy-1,1'-binaphthyl, 6,6'-dinitro-2,2'-dihydroxy-1,1'-binaphthyl, bis (2-hydroxy-1-naphthyl) methane, 4,4'-dimethoxy-1,1'-dihydroxy-2,2'-binaphthyl, etc.); U.S. Pat. No. 3,801,321 Sulfonamidophenols or sulfonamidonaphthols as described in the literature (eg 4-benzenesulfonamidophenol, 2-benzenesulfonamidophenol, 2,6-dichloro-4-benzenesulfonamidophenol, 4-benzenesulfonamide) Naphthol).

  The amount of the reducing agent used in the present invention varies depending on the type of organic silver salt, the reducing agent, and other additives, but is generally about 0.05 mol to about 10 mol per mol of the organic silver salt. From about 0.1 to about 3 moles is preferred. Within this range, two or more of the reducing agents described above may be used in combination, and are incorporated in the heat-developable silver salt photographic light-sensitive material.

Next, the pyrolysis precursor of the present invention will be described. Pyrolysis of precursors of the present invention, 70 ° C. or higher, preferably by 100 ° C. or more heat, compound der which decompose to form a silver halide inhibitor, include heterocyclic sulfoamino compound or heterocyclic carbonyl thio compound Specific examples of these are shown below. (Reference compounds are also exemplified)

Synthesis of Thermally Decomposable Precursor c-5 The following compound a-27 is dissolved in 300 g of 10 g water: methanol = 1: 1 solution, and 1.5 times mole hydrogen peroxide water of a-27 is added and heated for 1 hour. Refluxed to disulfide. Yield 7.5g.

In the heat-developable silver salt photographic light-sensitive material of the present invention, the above-described heat-decomposable precursor of the present invention is preferably added by the following method.
(1) A method in which a compound is added to a layer separate from the photosensitive layer containing silver halide. (2) If the compound is in the same layer, coat it with a thermosoftening resin (3) Organic silver (4) When transferred from a different material, transferred in a salt crystal, and transferred from another material, contacted with the photosensitive material during heat development, and transferred and diffused (5) Silver and a complex ligand such as Co and Ni Coordination of the complex-forming substance is released by thermal development.

  In the present invention, it is desirable to use an additive called a color tone, a color tone imparting agent or an activator toner (hereinafter referred to as a color tone agent) together with the above-described components. The toning agent is involved in the redox silver (image) formation reaction between the organic silver salt and the reducing agent, and has a function of making the resulting image dark, especially black. As the color toning agent, a very wide variety of compounds are already known, but most of them are compounds having an imino group, a mercapto group or a thione group. Among them, an appropriate color tone is selected according to the type of organic silver salt and reducing agent to be used. Examples of those that give a preferable color tone effect in the present invention include phthalazinones (for example, phthalazinone, 2-acetylphthalazine). Non-, 2-carbamoylphthalazinone, etc.), 2-pyrazolin-5-ones (such as 3-methyl-2-pyrazolin-5-one) or quinazolinones (such as quinazolinone, 4-methylquinazolinone) pyrimidines ( For example, 6-methyl-2,4-dihydroxypyrimidines) or 1,2,5-triazines (for example, 3-methyl-4,6-dihydroxy-1,2,5-triazines), phthalazinediones (for example) Such as phthalazinedione), cyclic imides (eg succinimides, phthalimides or Tetrazole compounds, benzoxazine diones, benzothiazine diones, and a heterocyclic compound having an imino group such as naphthalimides). These colorants may be used in combination of two or more. For example, as described in JP-A Nos. 53-1020 and 53-55115, benzoxazinediones and benzothiazines are combined with phthalazinone. By using diones or phthalimides in combination, it is possible to prevent deterioration of the color tone effect resulting from storage under high temperature and high humidity.

  Further, as described in U.S. Pat. Nos. 3,847,612 and 3,994,732, phthalic acid, naphthoic acid or phthalamic acid and imidazoles or phthalazines are used as a color toning agent. It can also be used.

  When a color tone is used, the amount used is preferably in the range of about 0.0001 mol to about 2 mol, particularly about 0.0005 mol to about 1 mol, per mol of the organic silver salt.

  Each component used in the present invention is dispersed in at least one colloid as a binder. A suitable binder may include a hydrophobic polymer material, but in some cases, a hydrophilic polymer material may be used in combination or singly. The polymer material used as the binder is preferably a transparent or translucent and colorless, white or light colored layer or layer when applied or cast. For example, there are proteins such as gelatin, cellulose derivatives, polysaccharides such as dextran, natural polymer materials such as gum arabic, and synthetic polymer materials. Among them, polyvinyl butyral, polyvinyl acetate, ethyl cellulose, vinylidene chloride-chloride Vinyl copolymers, polymethyl methacrylate, vinyl chloride-vinyl acetate copolymers, cellulose acetate butyrate, gelatin or polyvinyl alcohol are particularly preferably used. If necessary, two or more of these polymer materials may be used in combination. The polymer material is used in an amount sufficient to support the component dispersed therein, that is, an amount effective as a binder. The range can be appropriately determined by those skilled in the art. For example, when at least the organic silver salt is dispersed and supported, the weight ratio with respect to the organic silver salt is about 10: 1 to 1:10, especially about 4: 1 to It is used in the range of 1: 4.

  The composition containing each component of the present invention may be formed as a film supporting each component according to a known casting method when the binder used gives a film having a self-supporting property, but is usually preferable. Is completed as a photothermographic material coated on a variety of supports selected from a wide range of materials in a single layer or in two or more layers. Examples of the material of the support include various polymer materials, glass, wool cloth, cotton cloth, paper, metal (for example, aluminum), etc., but are processed into a flexible sheet or call as an information recording material. What can be done is preferred. Therefore, as a support in the present invention, a plastic film (for example, a cellulose acetate film, a polyester film, a polyethylene terephthalate film, a polyamide film, a polyimide film, a triacetate film or a polycarbonate film) or paper (for example, for photographic use) Base paper, base paper for printing such as coated paper or art paper, baryta paper, resin (coated) paper, paper sized with a polysaccharide as described in Belgian Patent No. 784,615, titanium dioxide Pigment paper containing pigments such as, and paper sizing polyvinyl alcohol) are particularly preferred.

Next, although this invention is demonstrated based on an Example, the embodiment of this invention is not limited to this.
Example 1
Preparation of Photosensitive Material 1 A silver halide / silver behenate complete soap was prepared by the method described in US Pat. No. 3,839,049. To 50 g of the above silver behenate, 200 g of methyl ethyl ketone, 100 g of toluene, 25 g of polyvinyl butyral (PVB), and 200 ml of isopropanol were added and stirred at 3000 rpm for 30 minutes to prepare a dispersion. 30 ml of calcium bromide (5% MeOH solution) and 10 g of polyvinylpyrrolidone were added and stirred for 1 hr. Furthermore, 10 ml of a 10% acetone solution of 2,2′-methylenebis- (6-tert-butyl-4-ethylphenol) was used as a reducing agent in 2 ml of sensitizing dye A in 0.025% methanol solution, 2 ml of phthalazinone, 0.5% methanol solution. The added coating solution was coated and dried on a subtracted 180 μPET support made of vinyl chloride / vinyl acetate copolymer so that the amount of silver was 1 g / m ² to obtain Photosensitive Material 1.

Preparation of Photosensitive Material 5 The compound of the present invention shown in Table 1 was added in an amount of 1.0 g / m ^{2 to} the coating solution for photosensitive material 1 and then applied and dried in the same manner as photosensitive material 1 to obtain photosensitive material 5.

  The obtained photosensitive materials 1 and 5 were sensitometrically exposed and thermally developed at 120 ° C. for 10 seconds with a heat roller. Sensitivity was determined by the relative value of the amount of light with a density of 2.5, and the fog of the unexposed area at that time was measured. Further, the color tone of the blackened silver having a density of 1.5 at that time was visually evaluated. Further, irradiation with 10000 lux Xe light for 5 hours was performed to measure the rise in fog, and the evaluation of image stability was shown in Table 1.

  From Table 1, the sample using the light-sensitive material of the present invention was stable in heat fog, silver tone and image storage without lowering the sensitivity.

Claims (2)

A heat-developable photosensitive material containing at least a photosensitive silver halide, an organic silver salt, and a reducing agent, characterized by containing at least one thermally decomposable precursor selected from a heterocyclic sulfoamino compound and a heterocyclic carbonylthio compound. A heat-developable silver salt photographic material for silver image formation. In a silver image forming method for obtaining a silver image using a heat-developable photosensitive material containing at least photosensitive silver halide, an organic silver salt, and a reducing agent, the heat-developable photosensitive material comprises a heterocyclic sulfoamino compound and a heterocyclic carbonylthio. A silver image forming method for a heat-developable silver salt photographic light-sensitive material, comprising at least one heat-decomposable precursor selected from compounds .