Abstract: A silver halide color photographic light-sensitive material has a support provided thereon a photographic constitutional layer including at least one photographic light-sensitive layer that contains a light-sensitive silver halide, an organosilver salt having a nitrogen-containing heterocycle, a compound capable of forming a dye by coupling reaction with an oxidized developing agent, and a binder,

Abstract: Photothermographic materials have increased photospeed provided by gold(III)-containing chemical sensitizers that are used combination with sulfur- and/or tellurium-containing chemical sensitizers. Increased photographic speed is achieved with minimal increase in Dmin. The gold(III)-containing chemical sensitizers are represented by the following Structure GOLD: Au(III)L′rYq GOLD wherein L′ represents the same or different ligands, each ligand comprising at least one heteroatom that is capable of forming a bond with gold, Y is an anion, r is an integer of from 1 to 8, and q is an integer of from 0 to 3.

Abstract: A thermographic recording element having an image forming layer contains an organic silver salt, a reducing agent, an optional photosensitive silver halide, and a specific nucleating agent. The element has high Dmax, high sensitivity, satisfactory contrast, low fog, and minimal dependency of photographic properties on developing temperature.

Abstract: A color photographic element comprises a support and at least one dye image forming layer unit comprising gelatin-peptized radiation-sensitive silver halide grains, a fragmentable electron donating compound; and an electron transfer agent releasing compound.

Abstract: Photothermographic emulsions and materials that are highly sensitive to imaging radiation and that provide high contrast images are provided by making the emulsions with photosensitive silver halide grains that have been formed in the presence of a hydroxytetrazaindene or an N-heterocyclic compound comprising at least one mercapto group, such as a mercapto tetrazole. Such grains can then be chemically sensitized before or after mixing with an organic silver salt using a sulfur-, tellurium-containing, or gold-containing chemical sensitizing compound, or mixtures thereof.

Abstract: The present invention is to provide a silver halide photographic light-sensitive material comprising a support having thereon a light-sensitive silver halide emulsion layer comprising a compound represented by Formula,

Abstract: A silver halide color photographic light sensitive material is disclosed, comprising a support having thereon a blue-sensitive silver halide emulsion layer, a green-sensitive silver halide emulsion layer and a red-sensitive silver halide emulsion layers, wherein at least one of the silver halide emulsion layers contains a coupler represented by the following formula:

Abstract: A silver halide photographic material is disclosed, comprising a support having thereon at least one silver halide emulsion layer, wherein said silver halide emulsion comprises a metal complex in which a majority of coordination sites of the metal ion is occupied by ligands containing a chain or cyclic hydrocarbon as a parent compound, or ligands in which carbon atoms or hydrogen atoms in the chain or cyclic hydrocarbon as a parent compound are partially replaced by other atoms or atomic groups.

Abstract: Novel co-developer compounds are useful in combination with hindered phenol developers to produce high contrast black-and-white photothermographic elements. The co-developer compounds have the formula wherein: Y is H, a metal (preferably, an alkali metal), or an alkyl group (preferably, an alkyl group having from 1 to 4 carbon atoms), and the solid curved line represents the atoms and bonds necessary to complete a ring structure (preferably a 5 or 6 membered ring structure). The photothermographic elements may be used as a photomask in a process where there is a subsequent exposure of an ultraviolet or short wavelength visible radiation-sensitive imageable medium.

Abstract: A silver halide photographic material comprising a support having provided thereon at least a silver halide emulsion layer, wherein the material contains at least one metal complex contained in any of groups A, B and C: group A: an optically active metal complex; group B: a metal complex comprising a metal ion selected from the group consisting of transition metallic elements belonging to period 4 to 6 and group III to XI of the Periodic Table, and typical metallic elements belonging to period 4 to 6 and group XII to XIV of the Periodic Table, and at least one ligand represented by the following formula (I): wherein Z represents an atomic group to form a 5- or 6-membered ring; A represents a carbon atom or a nitrogen atom; X represents O31, S31 , NR1R2 or COO−; R1 and R2 each represents a hydrogen atom or an alkyl group; R represents a substituent; and n represents 0 or an integer of from 1 to 6; group C: a metal complex selected from a porphyrin complex, a porphycene complex, a pht

Abstract: Disclosed is a color photographic element comprising at least one of (1) a light sensitive silver halide emulsion layer and (2) a non-silver containing light insensitive layer, said at least one layer containing a compound with a minimum of three heteroatoms that does not react with oxidized developer and that has a ClogP sufficient to increase the photographic speed of said element compared to the same element without the compound. The invention provides improved light sensitivity.

Abstract: Photothermographic materials have increased photospeed provided by certain organic solvent-soluble thiourea compounds that can be represented by the following Structure I, II, or III: wherein in Structure I, R1, R2, R3 and R4 are independently alkyl, cycloalkyl, allyl, alkenyl, alkynyl, aryl or heterocyclic groups, or R1 and R2 taken together, R3 and R4 taken together, R1 and R3 taken together or R2 and R4 taken together, can form a 5- to 7-membered heterocyclic ring, in Structure II, R1, R2, R3, R4 and R5 are independently alkyl, cycloalkyl, allyl, alkenyl, alkynyl, aryl or heterocyclic groups, or R3 and R5 taken together, R4 and R5 taken together, R1 and R3 taken together or R2 and R4 taken together, can form a substituted or unsubstituted 5- to 7-membered heterocyclic ring, and in Structure III, R1, R2, R3, R4, R5, and R6 are independently alkyl, cycloalkyl, allyl, alkenyl, alkynyl, aryl or heterocyclic groups, or R3 and R6 taken together, R4 and R5 taken together, R1 and R3 taken togethe

Abstract: The present invention provides a silver halide photographic material free of cyanide ions but having a higher photographic speed than ever. A novel silver halide photographic material is provided comprising a support having thereon at least one silver halide emulsion layer, wherein there is contained a complex in which an organic compound having no electric charge which doesn't form coordinate bond with metals or metal ions other than the central metals or metal ions occupies more than half of the central metals or metal ions as coordination site.

Abstract: A heat-developable photographic material which contains a particular class of polyhalogenated organic compound having a water-soluble group in one or more layers on the side of the image-forming layer. The heat-developable photographic material can be obtained at a low cost and has much reduced fog and excellent storage stability.

Abstract: A silver halide photographic element comprising a silver halide emulsion which is greater than 50 mole-% silver chloride, said emulsion containing an isothiazolone compound represented by the formula wherein R1 is a substituent; and Z contains the carbon atoms necessary to form a substituted or unsubstituted non-aromatic ring, wherein the isothiazolone compound was added before or during precipitation of the emulsion.

Abstract: Disclosed is a color silver halide photographic element comprising a support bearing: (1) a light sensitive silver halide emulsion layer; (2) a nitrogen heterocycle with a minimum of three heteroatoms that does not react with oxidized developer, does not contain free thiol substituents, and has a ClogP sufficient to increase the photographic speed of said element compared to the same element without the compound, said heterocycle compound located either in said light sensitive layer or in a layer adjacent to it; and (3) a light reflecting silver halide material; provided that the heterocycle compound and the light reflecting material are located either (a) in different layers of the element located close enough to each other so that a super-additive speed increase is realized or (b) in the same light sensitive layer. The invention provides improved light sensitivity.

Abstract: A silver halide photographic light-sensitive material is disclosed, comprising a support having thereon at least one silver halide emulsion layer, which contains at least one compound represented by formula (1) or (A-1).

Abstract: Image recording materials, especially photothermographic light-sensitive image recording materials, that comprise a compound of formula (1) to acquire excellent image storage stability: 1

Abstract: A silver halide photographic lightsensitive material comprises at least one lightsensitive silver halide emulsion layer on a support. The lightsensitive material exhibits a speed at 3×10−9 sec exposure time being lower than a speed at 10−5 sec exposure time by 30 or more in terms of speed unit.

Abstract: A silver halide photographic material is disclosed, comprising a support having thereon at least one silver halide emulsion layer, wherein said silver halide emulsion comprises a metal complex in which a majority of coordination sites of the metal ion is occupied by ligands containing a chain or cyclic hydrocarbon as a parent compound, or ligands in which carbon atoms or hydrogen atoms in the chain or cyclic hydrocarbon as a parent compound are partially replaced by other atoms or atomic groups.

Abstract: A silver halide photothermographic material is disclosed, comprising a support having thereon a light-sensitive layer and light-insensitive layer, wherein the light-sensitive layer or the light-insensitive layer comprises a heteroatom-containing macrocyclic compound, and the light-sensitive layer comprising a sensitizing dye exhibiting maximum sensitivity at a wavelength of 600 nm or more.

Abstract: This invention concerns a non-spectral sensitized radiographic product for exposure to ionizing radiation of energy equal to at least 40 keV containing at least 50 mg/dm2, which comprises a support covered with on at least one of its sides with a layer of silver halide emulsion in which at least 50% of the grains are tabular grains, and at least 0.05 mmol/mol Ag of a compound of formula wherein R1 and R2 are each independently an atom of hydrogen, an alkyl group comprising from 1 to 5 atoms of carbon, substituted or not, a hydroxyl group, or a benzyl group; R3 and R4 are each independently a hydrogen, or an alkyl group from 1 to 5 atoms of carbon, or jointly comprise the atoms necessary to form a heterocycle of 4 to 6 atoms, substituted or not. The product for industrial radiography of the invention provides an improved keeping of the latent image and higher speed.

Abstract: Disclosed is a silver halide photographic material comprising a silver halide emulsion layer containing at least one specific compound, with examples including compounds represented by formula (I), wherein an average aspect ratio of silver halide emulsion grains constituting said silver halide emulsion layer is from 8 to 100: wherein Z1 represents atoms completing a 5- or 6-membered nitrogen-containing heterocyclic ring, L1, L2, L3 and L4 each represent a methine group, V1 represents a monovalent substituent, l1 is an integer of from 0 to 4, p1 is 0 or 1, n1 is 0, 1, 2 or 3, R1 represents a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group, M1 represents a counter ion for adjusting the electric charge balance, m1 is the number of counter ions necessary to render the molecule electrically neutral and ranges from 0 to 10, and La represents a methylene group.

Abstract: Disclosed is a color photographic element comprising at least one of (1) a light sensitive silver halide emulsion layer and (2) a non-silver containing light insensitive layer, said at least one layer containing a compound with a minimum of three heteroatoms that does not react with oxidized developer and that has a ClogP sufficient to increase the photographic speed of said element compared to the same element without the compound. The invention provides improved light sensitivity.

Abstract: This invention relates to an imaging element comprising an imaging layer having associated therewith a compound of Structure I: In the above Structure I, the substituents are as defined in the application. Such compounds have good reactivity and can by used to block photographically useful compounds such as developing agents until thermally activated under preselected conditions. Compounds according to the present invention are especially useful in color photothermographic imaging elements.

Abstract: A method has been described of chemically sensitizing a silver halide emulsion having silver halide grains and a binder, comprising the steps of adding thereto, besides a chemically sensitizing agent providing sulphur, an organo-tellurium sensitizing compound providing tellurium in a molar ratio amount versus sulphur of less than 0.30. A light-sensitive silver halide photographic element has also been described which has been made highly sensitive by chemically sensitizing a silver halide emulsion which has been made highly sensitive by the method described hereinbefore.

Abstract: Disclosed is a color silver halide photographic element comprising a light-sensitive silver halide emulsion layer or a non-silver containing light-insensitive layer, said light-sensitive or light-insensitive layer containing a polymer compound comprising a heterocycle unit derived from: (a) a heterocycle monomer (1) comprising two or more annulated rings containing, in total, a minimum of three ring heteroatoms of which no more than two of the heteroatoms are connected in sequence to each other and (2) having a ClogP less than 6.2; or (b) a monocyclic heterocycle monomer having exactly three ring heteroatoms and having a ClogP less than 8.75; with the proviso that the heterocycle unit does not contain a hydroxy or mercapto group (or their tautomeric equivalent), and does not react with oxidized developer; and the amount of the polymer compound in the element being sufficient to increase the photographic speed of the element compared to the same element without the compound.

Abstract: A thermographic recording element having an image forming layer contains an organic silver salt, a reducing agent, an optional photosensitive silver halide, and a specific nucleating agent. The element has high Dmax, high sensitivity, satisfactory contrast, low fog, and minimal dependency of photographic properties on developing temperature.

Abstract: Disclosed is a color photographic element comprising: a) a first light sensitive silver halide emulsion layer containing a compound with an aromatic bicyclic nitrogen nucleus of which at least one ring is six-membered and with two nitrogen ring atoms in each ring and with at least one N—H bond provided that the ClogP for the compound is at least 2.0 and less than 7.2; and (b) a second light sensitive silver halide emulsion layer, having a spectral sensitivity different from that of the first light sensitive silver halide emulsion layer, containing a compound of Formula III: COUP-(TIME)j-INH  III  wherein: COUP is a coupler parent group capable of forming a dye upon reaction with an oxidized developer; TIME is a timing group and j is 0,1 or 2; and INH is a mild silver development inhibitor fragment. The invention provides improved color reproduction.

Abstract: A photographic element comprising at least one silver halide emulsion layer in which the silver halide is sensitized with a compound of the formula: wherein A is a silver halide adsorptive group that contains at least one atom of N, S, Se, or Te that promotes adsorption to silver halide, and Z is a light absorbing group including for example cyanine dyes, complex cyanine dyes, merocyanine dyes, complex merocyanine dyes, homopolar cyanine dyes, styryl dyes, oxonol dyes, hemioxonol dyes, and hemicyanine dyes, and XY is an fragmentable electron donor moiety in which X is an electron donor group and Y is a leaving group other than hydrogen, and wherein: 1) XY has an oxidation potential between 0 and about 1.4 V; and 2) the oxidized form of XY undergoes a bond cleavage reaction to give the radical X• and the leaving fragment Y. In a preferred embodiment of the invention, the radical X• has an oxidation potential ≦−0.7 V.

Abstract: This invention relates to an imaging element comprising an imaging layer having associated therewith a compound of Structure I: wherein the substituents are as defined in the specification.

Abstract: A photothermographic material is disclosed, comprising a non-photosensitive organic silver salt, a photosensitive silver halide, a reducing agent a binder and a cross-linking agent; the photothermographic material further comprising a compound capable of generating a labile species other than a halogen atom upon exposure to ultraviolet radiation or visible radiation to deactivate the reducing agent.

Abstract: A silver halide photographic material comprising a support having thereon at least one silver halide emulsion layer, wherein the material is contained at least one complex selected from complexes having a compound represented by the following formula (I) as at least one of their respective ligands or complexes having a diketone compound as at least one of their respective ligands: 1

Abstract: A photothermographic element comprising on a support (a) a photosensitive silver halide, (b) a reducible silver salt, (c) a reducing agent, (d) an ultrahigh contrast-providing agent, (e) a binder, (f) a specific salicylic acid type antifoggant, and optionally (g) phosphoric acid or a salt thereof has a low fog, high sensitivity, high contrast, and storage stability.

Abstract: Disclosed is a color photographic element comprising:

Abstract: An image forming method for a thermally processable photosensitive material is disclosed, comprising exposing a thermally processable photosensitive material to light using a laser light source, and subjecting the exposed photosensitive material to thermal processing, wherein the thermally processable photosensitive material comprises a support having thereon an organic silver salt, a binder, a photosensitive silver halide, and a compound containing nitrogen covalently bonded to halogen represented by the following formula or a nitrogen-containing acyclic compound associated with a pair of halogen atoms represented by the following formula

Abstract: A photographic element comprises a support bearing a cyan dye image-forming unit comprising at least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye-forming coupler, a magenta dye image-forming unit comprising at least one green-sensitive silver halide emulsion layer having associated therewith at least one magenta dye-forming coupler, a yellow dye image-forming unit comprising at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler, wherein at least one of said emulsion layers comprises a) an emulsion with 3D, core/shell grains of at least 0.

Abstract: This invention provides a multicolor photographic element comprising a support bearing a cyan dye image-forming unit comprising at least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye-forming coupler, a magenta dye image-forming unit comprising at least one green-sensitive silver halide emulsion layer having associated therewith at least one magenta dye-forming coupler, a yellow dye image-forming unit comprising at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler, wherein at least one of said emulsion layers comprises large tabular grains having an average equivalent circular diameter of greater than 3 &mgr;m and contains a one equivalent image dye-forming coupler and a fragmentable electron donating compound of the formula: X—Y′ or a compound which contains a moiety of the formula —X—Y′; wherein X is an electron donor moiety, Y′ is a leaving proton H

Abstract: The present invention relates to a process for manufacturing a silver halide photographic element comprising the step of adding to a silver halide emulsion (1) an aryl compound having at least two hydroxyl groups and at least one additional substituent represented by a sulfonic group, an alkali metal sulfonate group, a hydroxyl group, a carboxy group or a hydroxymethyl group, and (2) a polyhydroxyalkyl derivative selected from the group consisting of non-hydrogenated polysaccharides having an average molecular weight higher than 10,000 and hydrogenated polysaccharides having an average molecular weight equal to or lower than 10,000. The use of such a combination to increase the speed to Dmin ratio of a silver halide photographic element and a silver halide element comprising such a combination is also claimed.

Abstract: The invention provides a color photographic element comprising: a) a first light sensitive silver halide emulsion layer containing a compound of Formula 1:  wherein: M is hydrogen, an alkali metal cation or an ammonium cation, X is oxygen, sulfur or selenium, and Q represents a ballasting moiety; provided further that the ClogP for the compound of Formula I is at least 1.0 and less than 7.6; and b) a second light sensitive silver halide emulsion layer, having a spectral sensitivity different from that of the first light sensitive silver halide emulsion layer, containing a compound of Formula II: COUP—(TIME)j—INH  II  wherein: 1) COUP is a coupler parent group capable of forming a dye upon reaction with an oxidized developer; 2) TIME is a timing group and j is 0 or 1; and 3) INH is a mild silver development inhibitor fragment. The invention provides improved color reproduction.

Abstract: A multicolor photographic element comprising a support bearing a cyan dye image-forming unit comprising at least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye-forming coupler, a magenta dye image-forming unit comprising at least one green-sensitive silver halide emulsion layer having associated therewith at least one magenta dye-forming coupler, a yellow dye image-forming unit comprising at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler, wherein at least one of said emulsion layers comprises tabular grains having {111} major faces containing greater than 50 mole percent bromide, and accounting for greater than 50 percent total grain projected area precipitated in a peptizer that is a water dispersible cationic starch, and contains a fragmentable electron donating sensitizer.

Abstract: Disclosed is a silver halide photographic light-sensitive material comprising at least one photosensitive silver halide emulsion layer on a support, and containing a Pd(II) complex represented by formula (I-1): where Z1 represents an alkylene group, an arylene group, or a divalent heterocyclic group, Q represents an ion which neutralizes electric charge of the Pd complex, m represents an integer of from 0 to 4, R1 represents a hydrogen atom, an alkyl group, an aryl group, a heterocyclic group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a carbamoyl group, an alkylsulfonyl group, or an arylsulfonyl group, each of X1 and X2 represents a hydrogen atom, an alkyl group, an aryl group, or a heterocyclic group, and each of Y1 and Y2 represents an organic or inorganic ligand wherein Y1 and Y2 may be combined to form a ring together with Pd.

Abstract: A silver halide photographic material comprising a support having thereon at least one silver halide emulsion layer, wherein said emulsion contains as a dopant a metal complex represented by the following formula (I) or (II): [MLXLI(4−x)]n  (I) wherein M represents a metal or a metal ion, L represents an imidazole compound which is bonded to M, x represents 1, 2, 3 or 4, n represents an integer of from −6 to +5, and LI represents a chemical species bonded to M and LI(4−x) may be the same or different chemical species when x is 1 or 2; [MXnL(6−n)]m  (II) wherein M represents a metal ion, L represents an imidazole compound, X represents a halogen ion, n represents 3, 4 or 5, and m represents −5, −4, −3, −2, −1, 0, +1 or +2.

Abstract: The invention provides a color photographic element comprising: a) a first light sensitive silver halide emulsion layer containing a compound of Formula I: wherein Q represents the atoms necessary to form a triazole ring and the associated bonds, provided that the ring members may be substituted and that two of such members may join to form a fused ring; provided further that the ClogP for the compound of Formula I is from 4.75 to 9.0; and b) a second light sensitive silver halide emulsion layer, having a spectral sensitivity different from that of the first light sensitive silver halide emulsion layer, containing a compound of Formula II: COUP-(TIME)j-INH  II wherein: 1) COUP is a coupler parent group capable of forming a dye upon reaction with an oxidized developer; 2) TIME is a timing group and j is 0 or 1; and 3) INH is a mild silver development inhibitor fragment. The invention provides improved color reproduction.

Abstract: The invention provides a color photographic element comprising: a) a first light sensitive silver halide emulsion layer containing a tetrazole compound of Formula I:  wherein when R1 is hydrogen, then R2 is an alkyl, aryl, alkoxy , aryloxy, alkylthio or arylthio, sulfoxyl, sulfonyl, sulfamoyl, —O—CO—, —O—SO2—, a heterocyclic group, a carbonyl group or an amino group or when R2 is a thiol (—SH) group, then R1 is an alkyl, aryl or heterocyclic group provided further that the ClogP for the compound of Formula I is at least 2.0 and less than 7.

Abstract: There is disclosed a silver halide photographic light-sensitive material, which comprises a support having thereon at least one spectrally sensitized light-sensitive silver halide emulsion layer, wherein the silver halide emulsion layer contains at least two kinds of silver halide emulsions, which are different in the concentration of at least one nitrogen-containing heterocyclic compound capable of forming a complex with silver, and wherein the emulsion layer or another hydrophilic colloid layer contains at least one hydrazine derivative, as a nucleating agent, and at least one of amine derivatives, onium salts, disulfide derivatives, or hydroxymethyl derivatives, as a nucleating accelerator. The light-sensitive material is high in sensitivity, extremely high in contrast, and high in blackening density; it makes both saving of a sensitizing dye and low dye stain possible; and the change in sensitivity is small in the production thereof.

Abstract: An image-forming material comprising a support and a constituent layer(s) comprising at least (a) a thermographic image-forming layer containing a reducible silver salt, a reducing agent of the reducible silver salt and a binder or (b) a photothermographic image-forming layer containing a light-sensitive silver halide as a photocatalyst, reducible silver salt, a reducing agent of the reducible silver salt and a binder, wherein the image-forming material comprises a compound represented by formula (I-1) or (II-1) in at least one constituent layer: ##STR1## wherein R represents a secondary alkyl group or a cycloalkyl group; and M.sup.1 and M.sup.2 each represents a hydrogen atom, a metal ion or an ammonium ion; ##STR2## wherein R.sup.1 represents a secondary alkyl group, a cycloalkyl group, an aryl group, or a primary alkyl group substituted with a substituent bonded via a hetero atom; and M.sup.1 and M.sup.2 each represents a hydrogen atom, a metal ion or an ammonium ion.

Abstract: There is disclosed a silver halide photographic light-sensitive material which contains, on a support, a specific nitrogen-containing heterocyclic compound, and a divalent metal cation that is an acid with intermediate hardness/softness classified in accordance with the HSAB principle, in an amount 1 to 300 times the number of moles of the nitrogen-containing heterocyclic compound. The light-sensitive material can form an image with high sensitivity and low fogging, both in heat-development processing characterized by its ease and rapidness, and in usual liquid-developing processing that is widely used.

Abstract: There is disclosed a light-sensitive silver halide photographic emulsion, which comprises light-sensitive silver halide grains mainly composed of (100) planes and (111) planes, at least one compound that is adsorbed selectively on the (100) planes of the silver halide grains, and at least one spectrally sensitizing dye. There is also disclosed a light-sensitive material using the emulsion. The emulsion is high in sensitivity and excellent in graininess.

Abstract: This invention comprises a photographic element comprising a support and at least one silver halide emulsion layer in which the silver halide is sensitized with a compound of the formula:Q-XYwherein Q represents the atoms necessary to form a chromophore comprising an amidinium-ion, a carboxyl-ion or dipolar-amidic chromophoric system when conjugated with XY, and XY is a fragmentable electron donor moiety in which X is an electron donor group and Y is a leaving group other than hydrogen, and wherein:1) XY has an oxidation potential between 0 and about 1.4 V;2) the oxidized form of XY undergoes a bond cleavage reaction to give the radical X.sup..cndot. and the leaving fragment Y.In a preferred embodiment of the invention, the radical X.cndot. has an oxidation potential <-0.7V.