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)]

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)]

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)]

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)]

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)]

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)]

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)]

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)]

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)]