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Biomedical subjects

J I Brauman

Publications and source records attributed to J I Brauman.

10 recordsLinked to original sources
PubMed1993

Regioselective and enantioselective epoxidation catalyzed by metalloporphyrins.

Recent progress in regioselective and enantioselective epoxidations catalyzed by metalloporphyrins is discussed here, with an explanation of the biomimetic antecedents of this area and its relevance to synthetic applications. Classification of the catalysts that have been studied allows useful conclusions to be drawn about the development of this field. In particular, both the most promising biomimetic and practical catalysts have arisen from systems that can be systematically modified by convenient synthetic methodology.

Alkenes↗
PubMed1984

Epoxidation of olefins by cytochrome P-450 model compounds: mechanism of oxygen atom transfer.

The mechanism of the Mn(III) porphyrin-catalyzed epoxidation of olefins by lithium hypochlorite is examined. The active oxidant is thought to be a high-valent manganese-oxo complex. It is shown that a relatively stable intermediate is reversibly formed upon interaction of the olefin and the oxo complex. The decomposition of this intermediate to Mn(III) porphyrin and epoxide is the rate-determining step of the catalytic cycle. Some analogies to the biochemical epoxidation of olefins catalyzed by cytochrome P-450 are discussed.

Alkenes↗
PubMed1979

Carbon monoxide binding to iron porphyrins.

The carbon monoxide affinities of iron complexes of meso-tetra (alpha, alpha, alpha, alpha-o-pivalamidophenyl)porphyrin (the "picket fence" porphyrin) and of a "picket fence" porphyrin derivative with an appended axial base have been measured in solution and compared with the CO affinities of various hemoproteins. The model complexes bind CO with much greater affinity than normal hemoproteins; the role of the steric bulk of distal residues in lowering the CO affinities of the hemoproteins is discussed. The significance of this lowered CO affinity is described with regard to endogenous CO. A discussion of mutant hemoglobins lacking distal residues that sterically inhibit the binding of CO is presented. The use of pressure units versus concentration units in equilibrium expressions is analyzed.

Animals↗
PubMed1978

Model compounds for the T state of hemoglobin.

O2 binding to a series of ferrous and cobaltous "picket fence" porphyrins is reported. N-Methylimidazole and covalently attached imidazoles gives O2 binding to ferrous porphyrins with deltaH degrees =-16.2 kcal/mol (-67.7 kJ/mol) and deltaS degrees =-40 eu (standard state, 1 atmosphere O2). Similar studies with cobaltous porphyrins yield deltaH degrees =- 12.8 kcal/mol (-53.5 kJ/mol) and deltaS degrees =- 39 eu. These values match well those of myoglobin and isolated subunits of hemoglobin and their cobalt reconstituted analogues. 1,2-Dimethylimidazole has been successfully used to mimic the presumed restraint of T state hemoglobin. In direct analogy to the decreased cooperativity shown by cobalt-substituted hemoglobin, model cobalt porphyrins show a smaller decrease in O2 affinity than the analogous iron porphyrins when the axial base is hindered. Thermodynamic data are presented. The molecular mechanism of cooperativity in hemoglobin is discussed.

Cobalt↗
PubMed1978

Cooperativity in O2 binding to iron porphyrins.

The solid-gas O2 binding equilibrium has been studied for for ferrous "picket fence" porphyrinates with sterically hindered axial imidazoles. Such systems show significant cooperativity in their binding of O2: at low O2 pressures a low O2 affinity form exists, and at high O2 pressures a higher O2 affinity form develops. Direct analogies are drawn to the cooperativity shown in O2 binding by hemoglobin. These model systems mimic hemoglobin quantitatively.

Chemical Phenomena↗
PubMed1976

Nature of O2 and CO binding to metalloporphyrins and heme proteins.

The O2 vibration of dioxygen adducts of Fe and Co model complexes of alpha,alpha,alpha,alpha-tetrapivalamidophenylporphyrin ("picket fence" porphyrin, TpivPP) with 1-methylimidazole and 1-tritylimidazole as axial bases are reported, obtained with difference techniques between 16O2, 18O2, 169-18O, and NO with a Fourier transform infrared spectrometer. Assignments of upsilono2 are (O2)Fe(TpivPP) 1-methylimidazole, 1159 cm-1 in Nujol; (O2)Fe(TpivPP) 1-tritylimidazole, 1163 in benzene; (O2)Co(TpivPP) 1-methylimidazole, 1150 in Nujol; (O2)Co(TpivPP) 1-tritylimidazole, 1153 in benzene. Comparisons with other known Fe, Co, Cr, and Ti dioxygen complexes are made, and it is concluded that the bent dioxygen ligand is best viewed as bound superoxide, O2-. The CO affinities of various hemoproteins and model systems are discussed. A correlation between the CO stretching frequency and its binding constant is described. The drastically lowered affinity of hemoproteins for CO compared with unencumbered models is attributed to steric hindrance in the distal binding site, which allows discrimination between the already bent FeIII-O2- and the normally linear FeII-CO systems. If the affinity of hemoproteins in living systems for CO relative to O2 were not decreased, then massive poisoning would result from endogenous CO.

Binding Sites↗