Investigation of the electron-transfer mechanism by cross-linking between Zn-substituted myoglobin and cytochrome b(5)

We have investigated the photoinduced electron transfer (ET) in the 1:1 cross-linked complex (CL-ZnMb/b(5)) formed by a cross-linking reagent, EDC, between Zn-substituted myoglobin (ZnMb) and cytochrome b(5) (Cytb(5)) to reveal the mechanism of the inter-protein ET reactions under the condition of multiple encounter complexes. A variety of the ZnMb-Cytb(5) orientations was suggested because of failure to identify the single and specific cross-linking site on Cytb(5) by the peptide-mapping analysis using mass spectrometry. In CL-ZnMb/b(5), a laser pulse generates the triplet excited state of the ZnMb domain ((3)ZnMb()), which can transfer one electron to the Cytb(5) domain. The decay kinetics of (3)ZnMb() in CL-ZnMb/b(5) consists of a facile power-law ET phase to Cytb(5) domain ( approximately 30%) and a slower single-exponential phase ( approximately 70%). The application of the Marcus equation to this power-law phase indicates that CL-ZnMb/b(5) has a variety of ZnMb-Cytb(5) orientations for the facile ET in which the distance between the redox centers (D-A distance) is distributed over 13-20 A. The single-exponential phase in the (3)ZnMb() decay kinetics of CL-ZnMb/b(5) is similar to the intrinsic decay of (3)ZnMb() in its rate constant, 65 s(-)(1). This implies that the ET is impeded in about 70% of the total ZnMb-Cytb(5) orientations due to the D-A distance larger than 20 A. Combined with the results of the Brownian dynamics simulations for the encounter complexes, the overall bimolecular ET rate, k(app), can be reproduced by the sum of the ET rates for the minor encounter complexes of which D-A distance is less than 20 A. On the other hand, the encounter complexes with longer D-A distance, which are the majority of the encounter complexes between ZnMb and Cytb(5), have little contribution to the overall bimolecular ET rate. These observations experimentally demonstrate that ZnMb forms a variety of encounter complexes with Cytb(5), among which a minor set of the complexes with the shorter D-A distance (< approximately 20 A) regulates the overall bimolecular ET between the proteins.     

Porphyrins bearing arylphosphonic acid tethers for attachment to oxide surfaces

Synthetic molecules bearing phosphonic acid groups can be readily attached to oxide surfaces. As part of a program in molecular-based information storage, we have developed routes for the synthesis of diverse porphyrinic compounds bearing phenylphosphonic acid tethers. The routes enable (1) incorporation of masked phosphonic acid groups in precursors for use in the rational synthesis of porphyrinic compounds and (2) derivatization of porphyrins with masked phosphonic acid groups. The precursors include dipyrromethanes, monoacyldipyrromethanes, and diacyldipyrromethanes. The tert-butyl group has been used to mask the dihydroxyphosphoryl substituent. The di-tert-butyloxyphosphoryl unit is stable to the range of conditions employed in syntheses of porphyrins and multiporphyrin arrays yet can be deprotected under mild conditions (TMS-Cl/TEA or TMS-Br/TEA in refluxing CHCl(3)) that do not cause demetalation of zinc or magnesium porphyrins. The porphyrinic compounds that have been prepared include (1) A(3)B-, trans-AB(2)C-, and ABCD-porphyrins that bear a single phenylphosphonic acid group, (2) a trans-A(2)B(2)-porphyrin bearing two phenylphosphonic acid groups, (3) a chlorin that bears a single phenylphosphonic acid group, and (4) a porphyrin dyad bearing a single phenylphosphonic acid group. For selected porphyrin-phosphonic acids, the electrochemical characteristics have been investigated for molecules tethered to SiO(2) surfaces grown on doped Si. The voltammetric behavior indicates that the porphyrin-phosphonic acids form robust, electrically well-behaved monolayers on the oxide surface.     

Asymmetric synthesis of 2-substituted cycloalkanecarboxaldehydes

The 1,4-addition of Grignard reagents to chiral α,β-unsaturated cyclic aldimines ($\text{3}$), prepared from the corresponding cycloalkenecarboxaldehydes ($\text{1}$) and optically active α-amino acid tert-butyl esters ($\text{2}$, was found to give, after hydrolysis, trans-2-substituted cycloalkanecarboxaldehydes ($\text{5}$) in reasonably high enantiomeric purities.     

Flourescence quenching in aqueous solution of Amphiphilic copolymers: a kinetic model for downward curvature in a stern—volmer-type plot

A kinetic model is presented for downward curvature in a Stern—Volmer-type plot for flourescence quenching of flourophores in hydrophobic microdomains of amphiphilic copolymers in aqueous media. In the extreme case where quenchers were rigorously associated with the microdomains, the association constant and the aggregation number of the chromophores in the microdomains could be estimated.     

Hologram Recording in Various Glass Plates by Corona Charging

We propose techniques of hologram replication in glass plates and reconstruction on another film by corona charging. A surface relief hologram on an azobenzene polymer film was recorded in the form of electric polarization in glass plates that include alkali cations by corona charging at high temperature. The hologram recorded in the glass plate is stable for more than 1 month at room temperature. After removal of the azobenzene polymer film from the plate, poly(methyl methacrylate) (PMMA) film was spin-coated onto the plate. The hologram recorded in the plate was reconstructed with the same surface relief structure on the PMMA film by corona charging again at 110°C.     

CC bond formation from schiff base and vinyloxyborane: Synthesis of β-amino acid derivatives

An efficient methodology for the preparation of β-amino acid derivatives ($\text{3}$) by CC bond formation from Schiff bases ($\text{1}$) and vinyloxyborane ($\text{2}$) and their utilization in the synthesis of the pyrimidine moiety ($\text{3f}$) of bleomycin are described.     

Kurzkettenverzweigung von Polyvinylalkohol. 1. Mitt. Synthese von Modell-Polymeren

Ohne Zusammenfassung     

The sum rule for dipolar absorptions and rotational kinetic energy of wate and some dipolar molecules in condensed phases

Another form of the sum rule for dipolar absorptions has been derived by means of quantum statistics. The difference between this and usually used form results from a quantum effect on the molecular rotational motion. By the joint use of the two forms, average rotational kinetic energies of water molec in the liquid and solid phases and some dipolar molecules in solutions have been estimated. It has been shown that the average rotational kinetic energ larger than the value expected from the classical equipartition rule, with an increase in the hindering potential for the rotational motion of the mole The dipole moments of water molecules in liquid and solid water have been estimated. These are considerably smaller than the gas-phase value.