Publications

1990
Mandler D, Bard AJ. Hole injection and etching studies of gallium arsenide using the scanning electrochemical microscope. LangmuirLangmuir. 1990;6 (9) :1489 - 94.Abstract
A scanning electrochem. microscope (SECM) was used as an anal. tool to study the etching of GaAs surfaces. Hole injection from several electrogenerated oxidants to n-type, p-type, and undoped GaAs was examd. by the feedback mode of the SECM. Assignment of the process as a hole injection from the oxidized form of the redox couple into the valence band and assignment of the energy of the valence band edge in the semiconductor were made by studying the behavior of the feedback current at various pHs and with different redox couples. The nature of the dopant strongly affected the etching process. Both n-GaAs and undoped GaAs were etched by using the feedback mode while p-GaAs was completely resistive toward etching. The differences between n-GaAs and p-GaAs are explained in terms of semiconductor-electrolyte interactions. [on SciFinder(R)]
Mandler D, Bard AJ. A new approach to the high resolution electrodeposition of metals via the feedback mode of the scanning electrochemical microscope. J. Electrochem. Soc.Journal of the Electrochemical Society. 1990;137 (4) :1079 - 86.Abstract
Au and Pd electrodeposition in polymer films immersed in soln. with high resoln. has been accomplished using the scanning electrochem. microscope (SECM). The SECM was used in the feedback mode, where Ru(NH3)63+ was reduced at an ultramicroelectrode (UME) and diffused to a protonated polyvinylpyridine-coated surface. When metal anions e.g., AuCl4- or PdCl42-, were incorporated in the polymeric matrix, the diffusion of reduced mediator, Ru(NH3)2+, from the UME to the polymer film resulted in metal deposition. The different factors that det. the size and pattern of deposited metal were examd. The difference between Au and Pd deposition was studied by several techniques and interpreted in terms of kinetic and thermodn. properties of the mediator and the metal complex. [on SciFinder(R)]
Bard AJ, Denuault G, Lee C, Mandler D, Wipf DO. Scanning electrochemical microscopy - a new technique for the characterization and modification of surfaces. Acc. Chem. Res.Accounts of Chemical Research. 1990;23 (11) :357 - 63.Abstract
A review on the technique of electrochem. imaging of a substrate surface by monitoring the tip current when the substrate and tip are part of an electrochem. cell and the tip is scanned in a rastered pattern across the substrate surface. Samples include electrodes, polymer films on electrodes, and biol. materials. The method can be used to control microstructure fabrication by deposition or etching. 28 Refs. [on SciFinder(R)]
1989
Willner I, Mandler D. Characterization of palladium-β-cyclodextrin colloids as catalysts in the photosensitized reduction of bicarbonate to formate. J. Am. Chem. Soc.Journal of the American Chemical Society. 1989;111 (4) :1330 - 6.Abstract
Photosensitized redn. of HCO3- to HCO2- proceeds in an aq. system composed of deazariboflavin, dRFl, as photosensitizer, N,N'-dimethyl-4,4'-bipyridinium, MV2+, as primary electron acceptor, sodium oxalate as sacrificial electron donor, and in the presence of a Pd colloid stabilized by β-cyclodextrin, Pd-β-CD. The reaction proceeds with a quantum efficiency of 1.1. Kinetic characterization of the Pd-β-CD catalyst activity reveals the presence of active sites for bicarbonate activation and redn. as well as catalytic sites for H2 evolution. The HCO3- activation sites are specifically inhibited by thiols. The catalytic redn. of HCO3- to HCO2- and the resp. inhibition processes exhibit enzyme-like kinetic properties. The Pd-β-CD colloid shows reversible activities and effects the redn. of MV2+ by formate. Kinetic characterization of the catalyzed redn. of HCO3- to HCO2- and the reverse oxidn. of HCO2- provides a sequential mechanism for the reactions. [on SciFinder(R)]
Willner I, Mandler D. Enzyme-catalyzed biotransformations through photochemical regeneration of nicotinamide cofactors. Enzyme Microb. Technol.Enzyme and Microbial Technology. 1989;11 (8) :467 - 83.Abstract
A review with 110 refs. on photosensitized regeneration of NAD(P)H cofactors by photochem. means. Reductive regeneration of NAD(P)H cofactors proceeds through coupling of photogenerated N,N'-dimethyl-4,4'-bipyridinium radical cation, which acts as electron carrier, to the enzymes lipoamide dehydrogenase, LipDH and ferredoxin reductase, FDR, resp. Regeneration of NAD(P)H is also accomplished by substitution of the enzymes and electron carrier by synthetic rhodium complexes acting as H-donors for the regeneration of NAD(P)H. Oxidn. of NAD(P)H proceeds either by reductive quenching of the excited photosensitizer by NAD(P)H or dark oxidn. of NAD(P)H by the oxidized photoproduct formed in the photosensitized electron-transfer process. The systems are applied in the dehydrogenation of alcs., hydroxy acids, and amino acids. [on SciFinder(R)]
Mandler D, Bard AJ. Scanning electrochemical microscopy: the application of the feedback mode for high resolution copper etching. J. Electrochem. Soc.Journal of the Electrochemical Society. 1989;136 (10) :3143 - 4.Abstract
The etching is described of Cu circuit paths using a scanning electrochem. microscope supplied with a redox couple to induce feedback. Very small dimensions (<0.6 μm) are achieved. [on SciFinder(R)]
1988
Mandler D, Willner I. Photochemical fixation of carbon dioxide: enzymic photosynthesis of malic, aspartic, isocitric, and formic acids in artificial media. J. Chem. Soc., Perkin Trans. 2Journal of the Chemical Society, Perkin Transactions 2: Physical Organic Chemistry (1972-1999). 1988;(6) :997 - 1003.Abstract
Photosensitized regeneration of 1,4-dihydronicotinamide adenine dinucleotide phosphate (NADPH) with an artificial photosystem allows the enzymic fixation of CO2 through carboxylation of α-oxo acids using sacrificial electron donors. Pyruvic acid is carboxylated to malic acid and α-oxoglutaric acid is carboxylated to isocitric acid with the malic enzyme and isocitrate dehydrogenase (ICDH) as biocatalysts, ϕ = 1.9%. Malic acid formed through the photosensitized process is used as a synthetic building block for subsequent sequestered enzymic transformations, and its conversion into aspartic acid is accomplished with fumarase and aspartase as biocatalysts. Photoredn. of CO2 to formate is accomplished in the presence of formate dehydrogenase (FDH) as catalyst. Photosensitized redn. of different bipyridinium relay systems, i.e. N,N'-dimethyl-4,4'-bipyridinium (MV2+), N,N'-dimethyl-2,2'-bipyridinium (DM2+), N,N'-trimethylene-2,2'-bipyridinium (DT2+), and N,N'-tetramethylene-2,2'-bipyridinium (DQ2+) to the corresponding radical cations yields reduced relays that act as cofactors for FDH, which mediates the redn. of CO2 to formate. The quantum yield for formate formation is in the range ϕ = 0.5-1.6%. [on SciFinder(R)]
1987
Willner I, Mandler D, Maidan R. Biomodels and artificial models for photosynthesis. New J. Chem.New Journal of Chemistry. 1987;11 (2) :109 - 21.Abstract
A review with 33 refs. discussing biomodels of photosynthesis (composites of artificial photosystems linked to biocatalysts) and artificial models of photosynthesis (artificially tailored systems that mimic natural photosynthesis). [on SciFinder(R)]
Mandler D, Willner I. Effective photoreduction of carbon dioxide/bicarbonate to formate using visible light. J. Am. Chem. Soc.Journal of the American Chemical Society. 1987;109 (25) :7884 - 5.Abstract
The photoredn. of CO2/HCO3- in aq. soln. contg. deazariboflavin as photosensitizer, Me viologen as primary electron acceptor, and oxalate as electron donor is studied. Visible light was used to induce photoredn., and Pd colloid stabilized by β-cyclodextrin was used as redn. catalyst. Examn. of the mechanism of CO2/HCO3- photoredn. to formate indicates that Pd-β-cyclodextrin is extremely important as catalyst in the redn. and appears to activate bicarbonate toward the photoredn. process. [on SciFinder(R)]
Mandler D, Willner I. Photohydrogenation of acetylenes in water-oil two-phase systems: application of novel metal colloids and mechanistic aspects of the process. J. Phys. Chem.Journal of Physical Chemistry. 1987;91 (13) :3600 - 5.Abstract
Photohydrogenation of phenylacetylene and methylphenylacetylene was accomplished in a H2O-cyclohexane system, using tris(bipyridine)ruthenium Ru(bpy)32+ (bpy = 2,2'- bipyridine) as a photosensitizer, N,N'-dialkyl-4,4'-bipyridinium (viologen), CnV2+, as a charge relay, Na2EDTA as a sacrificial electron donor, and a Pt or Pd colloid stabilized in the org. phase as a hydrogenation catalyst. The photogenerated bipyridinium radical cations undergo induced disproportionation in the water-oil two-phase system, and the 2-electron charge relay CnV: is the active photoproduct that charges the metal colloid and generates metal-bound H atoms that are active in the hydrogenation of the substrate. The Pt and Pd colloids differ in their effectiveness in the generation of metal-bound H atoms. While Pt is a superior catalyst in this function, Pd is superior to Pt in the activation of the substrate toward hydrogenation. Use of a mixt. of Pt and Pd colloids in a water-oil 2-phase system shows a synergetic catalytic activity in the photohydrogenation of the acetylenic substrates. [on SciFinder(R)]
1986
Willner I, Mandler D, Riklin A. Photoinduced carbon dioxide fixation forming malic and isocitric acid. J. Chem. Soc., Chem. Commun.Journal of the Chemical Society, Chemical Communications. 1986;(13) :1022 - 4.Abstract
CO2 was successfully fixed in vitro as malic acid and isocitric acid using NADPH-dependent enzymes coupled to a photosensitized NADPH regeneration system. For the formation of malic acid, the enzymes involved were ferredoxin-NADP reductase (E.C. 1.18.1.2) (I) and the malic enzyme (E.C. 1.1.1.40); for isocitric acid formation, I and isocitrate dehydrogenase (E.C. 1.1.1.42) were used. [on SciFinder(R)]
Mandler D, Willner I. Photoinduced enzyme-catalyzed synthesis of amino acids by visible light. J. Chem. Soc., Chem. Commun.Journal of the Chemical Society, Chemical Communications. 1986;(11) :851 - 3.Abstract
Visible light-induced NADPH regeneration effects the prodn. of glutamic acid that mediates transamination and formation of aspartic acid and alanine in the presence of enzymes. [on SciFinder(R)]
Mandler D, Willner I. Photosensitized NAD(P)H regeneration systems. Application in the reduction of butan-2-one, pyruvic, and acetoacetic acids and in the reductive amination of pyruvic and oxoglutaric acid to amino acid. J. Chem. Soc., Perkin Trans. 2Journal of the Chemical Society, Perkin Transactions 2: Physical Organic Chemistry (1972-1999). 1986;(6) :805 - 11.Abstract
NADH and NADPH were formed by a photosensitized enzyme-catalyzed process. NADPH was formed in the presence of ferredoxin NADP-reductase with Ru(bpy)32+ (bpy = 2,2'-bipyridine) as photosensitizer, Me viologen as primary electron acceptor, and (NH4)3 EDTA or 2-mercaptoethanol. Zn(II) meso-tetramethylpyridiniumporphyrin was used as photosensitizer for the photoinduced prodn. of NADH with the same reaction components but with lipoamide dehydrogenase as the enzyme catalyst. The photoinduced NADH/NADPH regeneration systems were coupled to secondary enzyme-catalyzed processes, e.g. the redn. of butan-2-one to butan-2-ol, pyruvic acid to lactic acid, or acetoacetic acid to β-hydroxybytyric acid; coupling to the reductive amination of pyruvic acid to alanine and of α-oxoglutaric acid to glutamic acid was also possible. The products showed high optical purity and the enzymes and coenzymes showed high turnover nos. and stability. [on SciFinder(R)]
1985
Willner I, Goren Z, Mandler D, Maidan R, Degani Y. Transformation of single-electron transfer photoproducts into multielectron charge relays: the functions of water-oil two-phase systems and enzyme catalysis. J. Photochem.Journal of Photochemistry. 1985;28 (2) :215 - 28.Abstract
Water-in-oil microemulsions provide an organized environment that effectively controls photosensitized electron transfer processes. Effective charge sepn. and stabilization of the intermediate photoproducts against back electron transfer processes are achieved by means of hydrophobic and hydrophilic interactions of the photoproducts with the water-oil phases. Water-oil 2-phase systems also provide a means for induced disproportionation of a photogenerated 1-electron transfer product to the corresponding 2-electron charge relay. This induced disproportionation can be achieved by design of opposite soly. properties of the comproportionation products in the 2 phases. The 2-electron charge relay mediates the redn. of meso-1,2-dibromostilbene to trans-stilbene. An alternative route for generating multielectron charge relays involves the enzyme-catalyzed prodn. of NADPH using the 4,4'-bipyridinium radical cation as an electron carrier. NADPH is subsequently utilized in the redn. of 2-butanone to (-)-2-butanol in the presence of the enzyme alc. dehydrogenase. [on SciFinder(R)]
1984
Mandler D, Degani Y, Willner I. Photoredox reactions in water-in-oil microemulsions. The functions of amphiphilic viologens in charge separation and electron transfer across a water-oil boundary. J. Phys. Chem.Journal of Physical Chemistry. 1984;88 (19) :4366 - 70.Abstract
Photosensitized redn. of a series of dialkyl-4,4'-bipyridinium salts, CnV2+, with Cn alkyl of n = 1, 4, 6, 8, 14, and 18 was examd. in water-in-oil microemulsions, by using Ru(bpy)32+ (bpy = 2,2'-bipyridine) [15158-62-0] as sensitizer and (NH4)3 EDTA [15934-01-7] as electron donor. With the amphiphilic electron acceptors (n = 8-18) the water-in-oil microemulsion media effect the charge sepn. of the initial encounter cage complex, and stabilize the photoproducts, CnV+ and Ru(bpy)33+, against the recombination process. Consequently, enhanced quantum yields for CnV+. formation are obsd. under continuous illumination. [on SciFinder(R)]
Mandler D, Willner I. Solar light induced formation of chiral 2-butanol in an enzyme-catalyzed chemical system. J. Am. Chem. Soc.Journal of the American Chemical Society. 1984;106 (18) :5352 - 3.Abstract
The photosensitized prodn. of chiral (-)-2-butanol is accomplished in a chem.-enzyme catalyzed-system in which ruthenium-tris-bipyridine, Ru(bipy)32+, photosensitizes the redn. of dimethyl-4,4'-bipyridinium (methylviologen, MV2+), and the sensitizer is recycled by oxidn. of (NH4)3EDTA. The primary reduced photoproduct, MV+·, mediates the redn. of NADP to NADPH in the presence of ferredoxin-NADP reductase. The final step in the cycle involves the redn. of 2-butanone by NADPH in the presence of alc. dehydrogenase. The optical purity of the formed (-)-2-butanol is 100%. The net reaction that corresponds to the redn. of 2-butanone by (NH4)3EDTA is an endoergic process by ∼33 kcal/mol EDTA consumed. [on SciFinder(R)]

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