Structural change of a cofactor binding site of flavoprotein detected by single-protein fluorescence spectroscopy at 1.5 k

The visible fluorescence spectrum of single flavoprotein at a temperature of 1.5 K has been measured by one-photon excitation. The flavoprotein studied was a photoswitchable enzyme, photoactivated adenylyl cyclase. The time course of the spectrum revealed a structural change occurring at a rate of 10(-3) s(-1) around hydrogen bonds at the flavin cofactor binding site.     

AM1 calculation of hydration to aldehyde group in nitro-substituted benzaldehydes

Hydration to the aldehyde group in nitro-substituted benzaldehydes was studied theoretically by using an AM 1 method. The calculated values of activation energy and heat of reaction showed good correlations with the experimental values of rate constants and equilibrium constants, respectively. To examine the hydration mechanism, localized molecular orbitals were calculated. Furthermore, expression of the molecular orbitals of supermolecular complexes in terms of occupied and vacant orbitals of the component molecules elucidated that the interaction between the lonepair orbital of water and the antibonding C? O π-orbital of aldehyde was important. 2,6-DNBAl was concluded to be less reactive toward water than was 2.4-DNBAl. This is consistent with the experimental result that the mutagenic activity of 2,4-DNBAl depends not only on the reduction of the nitro group by a bacterial enzyme but also on the acetyl conjugation, but that in the case of 2,6-DNBAl the mutagenic activity is manifested through the reduction by a bacterial enzyme. © 1993 John Wiley & Sons, Inc.     

OXIDATION OF THE ALKYL-, ARYL-, AND AMINO-SULFONIUM IONS TO THE SULFOXONIUM IONS AND ITS REACTION MECHANISM

Abstract

Hitherto, the preparative method of the sulfoxonium ions has been practically limited to thealkylation of the sulfoxides with methyliodide. The yields of the desired sulfoxonium salts by this method are usually poor except that of trimethylsulfoxonium iodide, Diarylalkyl- or triaryl-sulfoxonium ions can not be prepared by this alkylation.     

Mechanism of Reaction of Polyvinyl Chloride) with Triethylaluminum

Polyvinyl chloride) was treated with triethylaluminum in 1,2-dichloroethane solution. Negligibly small amounts of hydrogen chloride are evolved from the modified polyvinyl chloride) in decomposition at 180°C for 150 min in nitrogen. Quantitative analysis of the rate of dehydrochlorination of the modified polymer gave a calculated activation energy for the alkylation of 8.3 kcal/mole in 1,2-dichloroethane solution; the concentration of the labile chlorines in the original polyvinyl chloride) was less than 0.25 mole % Furthermore, the fact that the average polyene length of the modified polymer for the thermal decomposition was much shorter than that of the starting material suggests that the labile chlorines inherent in the polymer exist not only in the chain end but also in the polymer chain.     

An efficient synthesis of indane-derived bis(oxazoline) and its application to hetero Diels-Alder reactions on polymer support

Indane-derived bis(oxazolines) were synthesized in two steps and 93% overall yield starting from commercially available substrates. This ligand is as effective as tert-butyl bis(oxazoline) in hetero Diels-Alder reaction both in solution and on polymer support.     

Thermal carbosilylation of endohedral dimetallofullerene La(2)@I(h)-C(80) with silirane

Thermal carbosilylation of endohedral dimetallofullerene La(2)@I(h)-C(80) with silirane (silacyclopropane) is reported herein for the first time. Two diastereomers of the carbosilylated La(2)@I(h)-C(80) have been isolated and characterized. The fascinating molecular structure of one diastereomer of the carbosilylated derivatives has been determined unambiguously using X-ray crystallographic analysis. Detailed characteristics of the molecular structures including their metal atom movements have also been revealed using NMR spectroscopic studies and computational calculations. Results revealed that two La atoms move dynamically inside the carbon sphere. Furthermore, electrochemical study has demonstrated that carbosilylation is effective to fine-tune the La(2)@I(h)-C(80) electronic properties.     

Generation of a triplet diradical from a donor-acceptor cross conjugate upon acid-induced electron transfer

Enhancement of the electron acceptor ability of a para-quinodiimine unit by double protonation leads to the proton-induced intramolecular electron transfer from the donor unit to the cross-conjugated acceptor, giving rise to ground state triplet diradical reversibly.     

Location of the metal atoms in Ce2@C78 and its bis-silylated derivative

Dimetallofullerene Ce(2)@C(78) and its bis-silylated derivative (1) were successfully prepared and fully characterized.     

Structural, magnetic, and electronic properties of phenolic oxime complexes of Cu and Ni

Square planar complexes of the type Ni(L(1))(2), Ni(L(2))(2), Cu(L(1))(2), and Cu(L(2))(2), where L(1)H = 2-hydroxy-5-t-octylacetophenone oxime and L(2)H = 2-hydroxy-5-n-propylacetophenone oxime, have been prepared and characterized by single-crystal X-ray diffraction, cyclic voltammetry, UV/vis spectroscopy, field-effect-transistor measurements, density functional theory (DFT) and time-dependent DFT (TDDFT) calculations, and, in the case of the paramagnetic species, electron paramagnetic resonance (EPR) and magnetic susceptibility. Variation of alkyl groups on the ligand from t-octyl to n-propyl enabled electronic isolation of the complexes in the crystal structures of M(L(1))(2) contrasting with π-stacking interactions for M(L(2))(2) (M = Ni, Cu). This was evidenced by a one-dimensional antiferromagnetic chain for Cu(L(2))(2) but ideal paramagnetic behavior for Cu(L(1))(2) down to 1.8 K. Despite isostructural single crystal structures for M(L(2))(2), thin-film X-ray diffraction and scanning electron microscopy (SEM) revealed different morphologies depending on the metal and the deposition method (vapor or solution). The Cu complexes displayed limited electronic interaction between the central metal and the delocalized ligands, with more mixing in the case of Ni(II), as shown by electrochemistry and UV/vis spectroscopy. The complexes M(L(2))(2) showed poor charge transport in a field-effect transistor (FET) device despite the ability to form π-stacking structures, and this provides design insights for metal complexes to be used in conductive thin-film devices.     

Preparation and characterization of thin films of monomeric and polymeric octacyanophthalocyanines

Thin films were prepared on substrates, cleavage surface of KCl single crystal, and metallic copper, by reaction of 1,2,4,5-tetracyanobenzene with the substrate at various temperatures. The films were characterized by elemental analysis, IR, and UV/VIS spectroscopies. The films were observed by scanning electron microscopy. The films produced on copper at temperatures between 300 and 400°C consisted of copper octacyanophthalocyanine and its polymer with ladder structure. The ratio of polymer to monomer increased with elevating the reaction temperature. The films were composed of ribbon-like crystals. The film produced on copper above 450°C was composed of an amorphous and continuous layer of polymeric copper phthalocyanine. The film produced on KCl at temperatures between 250 and 350°C consisted of potassium octacyanophthalocyanine and its polymer with ladder structure. The film produced on KCl above 450°C was polymeric potassium phthalocyanine. Those films contained more metal content than that required stoichiometrical.