ISSN:0021-2148    

DOI:10.1002/ijch.198800001

出版商:WILEY‐VCH Verlag    

年代:1987

数据来源: WILEY

ISSN:0021-2148    

DOI:10.1002/ijch.198800002

出版商:WILEY‐VCH Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractAddition of [FeII(MeCN)24+(ClO−4)2to solutions of hydrogen peroxide in dry acetonitrile (MeCN) catalyzes a rapid disproportionation of H2O2via the initial formation of an adduct, [FeII(HOOH)↔Fe(O)(OH2)]2+, which oxidizes a second H2O2to dioxygen. This intermediate also cleanly oxidizes substituted hydrazines, alcohols, aldehydes, and thioethers by a two‐electron process. The products for these H2O2oxidations are consistent with those that result from catalase‐ and some peroxidase‐catalyzed processes. In the same aprotic medium (MeCN) anhydrous FeIIICl3catalyzes the demethylation ofN,N‐dimethylaniline, the epoxidation of olefins, and the oxidative cleavage of 1‐phenyl‐1,2‐ethanediol (and other 1,2‐diols) by hydrogen peroxide. A mechanism is proposed in which an initial Lewis acid‐base interaction of FeIIICl3with H2O2generates a highly electrophilic FeIII‐oxene species as the reactive intermediate. For each class of substrate the products closely parallel those that result from their enzymatic oxidation by cytochrome P‐450. Because of (a) the close congruence of products, (b) the catalytic nature of the FeIIICl3/H2O2reaction mimic, and (c) the similarity of the dipolar aprotic solvent (acetonitrile) to the proteinaceous lipid matrix of the biomembrane, the form of the reactive intermediate may be the same in each case. This is in contrast to the prevailing view that cytochrome P‐450 acts as a redox catalyst to generate an Fe(V)‐oxo species or an Fe(IV)‐oxo cation radic

ISSN:0021-2148    

DOI:10.1002/ijch.198800003

出版商:WILEY‐VCH Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractMagnitude of cooperativity of a hypotheticalm‐subunit allosteric system of hemoglobin type is discussed, based on computation of the amount of O2to be transferred to the corresponding monomeric nonallosteric system of myoglobin type. For quantitative discussion, “allosteric gain” is defined as the difference between the amount of O2to be transferred from the allosteric to the nonallosteric system and that from the hypothetical system of average O2affinity to the nonallosteric system. These two quantities, allosteric gain and amount of O2transfer, are quite sensitive to equilibrium constant ratio, especiallyKm/K1, (Ki+1/Ki)max, andi.Hill's coefficient appropriately describes neither the amount of O2transferred nor allosteric gain. Allosteric gain or the amount of O2transfer which is best characterized by the total cooperativity index (Km/K1) and the local cooperativity indices (Ki+1/Ki) seem to be appropriate measures of the magnitude of cooperat

ISSN:0021-2148    

DOI:10.1002/ijch.198800004

出版商:WILEY‐VCH Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractA few examples of (multi)enzymatic reactions in reversed micellar media are described and discussed. The key enzymes in these examples are 20β‐hydroxy‐steroid dehydrogenase, enoate reductase, and an NAD+‐independent hydrogenase, catalyzing the reactions of interest, viz., the site‐ and stereo‐specific reduction of 20‐ketosteroids to their corresponding 20β‐hydroxy form, the chiral hydrogenation of α,β‐unsaturated carboxylates, and the production of hydrogen, respectively. These cofactor‐requiring enzymes are coupled to variousin situcofactor‐regenerating systems, powered either by light, electricity, or hydrogen. The performance of all

ISSN:0021-2148    

DOI:10.1002/ijch.198800005

出版商:WILEY‐VCH Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractThe transamination reaction of l‐phenylalanine with pyruvate as catalyzed by the artificial transaminase formed with synthetic bilayer aggregates was examined in aqueous media under mild kinetic conditions. Each catalyst system was constructed with a combination of a synthetic peptide lipid, a hydrophobic vitamin B6derivative, and metal ions. Modification of the active site in the present artificial transaminase was performed by changing a combination of molecular components constituting the catalytic system. While the catalytic activity was scarcely influenced by differences in aggregate structure, single‐ or multi‐walled bilayer, and in copper‐(II) concentration, molecular structures of the hydrophobic vitamin B6and an amino acid residue of the peptide lipid had significant effects on the rea

ISSN:0021-2148    

DOI:10.1002/ijch.198800006

出版商:WILEY‐VCH Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractThe protons of silanol groups on a silica or silica‐alumina surface are replaced by metal(III) porphyrin cations, FeTPP+, MnTPP+, and CoTPP+(TPP = tetraphenylporphyrin). The heterogenized iron(III) or manganese(III) porphyrin supported on silica thus prepared can activate dioxygen in the presence of excess amounts of NaBH4and cyclohexene, affording cyclohexanol and cyclohex‐2‐ene‐1‐ol in a 4:1 ratio, which is the same as the ratio observed in the known P‐450 type oxidation of cyclohexene catalyzed by a homogeneous manganese porphyrin (MnTPPCl) in the presence of NaBH4used as an electron source. The heterogenized iron(III) porphyrin shows a reactivity comparable with that of the corresponding heterogenized manganese(III) porphyrin. On the other hand, substitution of the heterogenized iron(III) porphyrin by the corresponding homogeneous catalyst, FeTPPCl, results in drastic change in the product ratio; the ratio of cyclohexanol to cyclohex‐2‐ene‐l‐ol is reversed, suggesting that the oxidation of cyclohexene proceeds via radical chain autoxidation reactions. The catalytic activity for the P‐450 type oxidation is diminished while FeTPPCl is converted to the μ‐oxo‐dimer (FeTPP)2O. Cobalt(III) porphyrin in a homogeneous system also affords the autoxidation products. Such a mechanistic difference between the homogeneous and heterogeneous metal porphyrins in the oxidation of cyclohexene by dioxygen has been confirmed by kinetic studies in which the P‐450 type oxidation and autoxida

ISSN:0021-2148    

DOI:10.1002/ijch.198800007

出版商:WILEY‐VCH Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractA study of intra‐ and intermolecular charge transfer interactions with organic reagents which can be solubilized in micelles and vesicles is reported. The first part of the paper details the study on the formation of intermolecular charge transfer complexes between aromatic hydrocarbons (“enes”) and the methyl viologen dication; these complexes show a weak charge transfer transition which is dependent on solvent polarity. A study of the charge transfer transition in homogeneous solutions and microheterogeneous media shows that the complexes occur for micelles at a reasonably polar “interfacial” site. A quantitative study of complex formation for several different substrates and different surfactant media reveals that the precise micropolarity for various combinations varies and hence indicates that the solubilization site provided for a given set of reagents in a given detergent is variable and cannot be too precisely defined. Studies of two polyenes containing electron donor and electron acceptor substituents within the same molecule have also been carried out. In the case of 4‐nitro‐4′‐methoxystilbene (NMS) it has been found that the triplet‐triplet absorption spectrum observed following laser flash excitation is sensitive to both solvent polarity and viscosity; in micelles, NMS exhibits a single moderately polar solubilization site in good agreement with that reported for the aforementioned charge transfer complexes. In contrast, it has been found that vesicles solubilize NMS in two distinctively different solubilization sites. One of the solubilization sites is attributed to an “interfacial” location while the other appears less polar but more viscous. Studies of the analogous diene, NND, have focused on its fluorescence and indicate the presence once again of a site which is sensitive to the hydrocarbon chains in bilayer vesicles. The hydrocarbon‐sensitive site in vesicles for both NMS and NND could be associated with a “wedge”‐shaped or cleft site in the vesicles which exists most prominently below the phase transi

ISSN:0021-2148    

DOI:10.1002/ijch.198800008

出版商:WILEY‐VCH Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractReduction ofn‐C5H11N3by Na2S2O4was performed in the presence of (n‐Bu4N)3[Mo2Fe6S8(OMe)3(SC6H4‐p‐n‐C8H17)6] ((n‐Bu4N)3[Mo‐Fe]) as a catalyst in aqueous Triton X‐100 micellar solutions. The rate of the reduction is enhanced efficiently by the addition of methyl viologen (MV2+). The methyl viologen radical cation (MV+) produced by the reaction of MV2+with Na2S2O4undergoes a disproportionation reaction to afford MV2+and MV° in the micellar solution. The resultant MV° formed in the micelle transfers two electrons to [Mo‐Fe]3−effectively to give [Mo‐Fe]5−, which reducesn‐C5H11N3with two electrons

ISSN:0021-2148    

DOI:10.1002/ijch.198800009

出版商:WILEY‐VCH Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractUsing a chiral 1,4‐dihydronicotinamide derivative,N‐α‐methylbenzyl‐1‐propyl‐2,4‐dimethyl‐1,4‐dihydronicotinamide (Me2PNPH), we have studied the reduction of various α‐keto esters that have a chiral center in the acid‐moiety. All of the four possible diastereomers of the corresponding α‐hydroxy esters were afforded. A detailed investigation into the diastereomeric composition of the product has revealed that the molecular arrangement and the conformations of the substrate at the transition state of the reduction are controlled by the polarity and/or the polarizability of the substituents. The 2R,3R‐isomer is the most predominant product when 4R,9R‐Me2PNP

ISSN:0021-2148    

DOI:10.1002/ijch.198800010

出版商:WILEY‐VCH Verlag    

年代:1987

数据来源: WILEY