Electron transfer reactions of cytochrome c at metal electrodes

The heterogeneous electron transfer reactions of cytochromec occurring at platinum, gold and mercury electrodes are shown to be quasi-reversible. In each case the electrodes have not been modified and the cytochromec samples are native. This work extends previous work and demonstrates that biological molecule electron transfer reactions can be studied at clean metal surfaces to gain fundamental knowledge of the mechanisms of these reactions.     

Fractionally colouring total graphs

Bchzad and Vizing have conjectured that given any simple graph of maximum degree , one can colour its edges and vertices with +2 colours so that no two adjacent vertices, or two incident edges, or an edge and either of its ends receive the same colour. We show that for any simple graphG, V(G)E(G) can be fractionally coloured with +2 colours.     

Proton-ionizable crown compounds. 4. New macrocyclic polyether ligands containing a triazole subcyclic unit

A series of macrocyclic polyether (crown) ligands containing the proton-ionizable s-triazole subcyclic unit were prepared by reacting the 1-THP blocked 3,5-bis(chloromethyl)-1H-1,2,4-triazole with various oligoethylene glycols. The starting bis(chloromethyl)triazole is a vessicant and must be used with caution. Triazolo-18-crown-6 ( 5 ) formed stable complexes with barium, strontium, copper and benzylammonium cations but not with potassium or lithium. The crystal structure of 5 showed the triazole proton to be on nitrogen 3 which is outside the macroring cavity.     

Synthesis of two new crown ethers containing selenium and the complexation of one of them with silver and lead

Two new macrocyclic crown ethers containing one or two selenium donor atoms have been prepared. Diselena-18-crown-6 (2) was found to transport silver ions through a methylene chloride bulk membrane at about the same rate as the analogous dithia- (3) and diaza-18-crown-6 (4) compounds and transported lead ions about the same as dithia-18-crown-6 but better than diaza-18-crown-6.     

Proton-ionizable crown compounds. 11. Synthesis of macrocyclic ligands containing two sulfonamide groups and chloro substituents or pyridine subcyclic units and a preliminary study of cation transport by three of these ligands

Five new macrocyclic ligands each containing two sulfonamide groups have been prepared. Three of these compounds contain one or two chloro substituents and the other two have one or two pyridine subcyclic units. A seventeen-membered ring ligand (4) was found to be an excellent transport agent for all alkali metal cations in a water-methylene chloride-water bulk liquid membrane system when the pH of the source phase was 13 or higher. The chlorine-substituted analog (5) was a poor transport agent for the alkali metal cations possibly because the chlorine atom blocked entry to the macrocycle cavity. An open-chain analog containing two sulfonamide groups was particularly effective in transporting cesium ions.     

Modeling the gel electrophoresis of short duplex DNA by Brownian dynamics: cubic gel lattice with direct interaction

The technique of Brownian dynamics is used to model the electrophoretic mobility of spherical and rod-like particles in a three-dimensional cubic gel lattice. In addition to excluded volume interactions between the migrating particle and the gel, direct interactions are also included. The methodology is first applied to spherical particles in the absence of direct interactions and the resulting mobilities are shown to agree with independent studies. The methodology is then applied to rod-like models of short duplex DNA fragments 10-50 base pairs in length. In the absence of direct interactions between gel and DNA, calculated mobilities show a much weaker dependence on gel concentration than observed in experiments of DNA in Tris-acetate buffer and polyacrylamide gels. When an attractive interaction between gel and DNA of approximately -0.3 k(B)T per base pair at contact is included, good agreement between calculated and experimental mobilities is achieved.     

Etude de la fragmentation de semi-carbazones terpeniques

Terpene semicarbazones have been investigated using high resolution mass spectrometry. We have studied correlations between rings and functional semicarbazone degradations. The mass spectra are more complicated than the mass spectra of oximes, methyloximes and hydrazones. Cleavages are explained by known mechanisms. An interpretation of almost all the peaks is offered. The fragmentation of the semicarbazone skeleton is less marked than in the oximes. Fragmentation processes induced by the functional group are numerous. Ions obtained are concerned in secondary cleavages. Thus it is not surprising that the predominant feature is localisation of charge upon the imino nitrogen atom. Other centres may, however, be responsible for the appearance of several peaks.     

Enantioreversal in the sharpless asymmetric epoxidation reaction controlled by the molecular weight of a covalently appended achiral polymer

Polymers such as poly(ethylene glycol) (PEG) have proven use in a variety of applications including organic synthesis. We now disclose our investigations into the recently disputed report that PEG tartrate esters can reverse the enantioselectivity of the Sharpless asymmetric epoxidation reaction. The results presented herein have clarified that the enantioselectivity of this reaction can be reproducibly reversed solely as a function of the molecular weight of the appended PEG. By preparing a range of tartrate ligands with varying PEG chains lengths, the reversal was found to occur within a molecular weight change of only 800. As the PEG chain did not affect the inherent chirality of the ligand, the enantioreversal was proposed to occur as a result of two Ti-ligand complexes which differ in their molecularity of ligand, one monomeric in ligand and the other dimeric. Support for this hypothesis was given through equilibrium measurements which revealed that the predominant species in Ti/PEG tartrate ester mixtures is a distinct 2:1 Ti-ligand complex, as opposed to the 2:2 Ti-ligand complex of traditional Sharpless asymmetric epoxidations. In total, these data represent an unrecognized property of PEG-supported catalysts that could open up new venues in the control of asymmetric reactions by means of achiral appended polymers.     

New pyrimidino-crown ether ligands

Eight new macrocyclic ligands containing the pyrimidine subcyclic unit ( 3-10 , Figure 1) have been prepared. Two of these new crown ethers are chiral. Pyrimidino-crowns 3-8 were prepared by treating the di-tosylate derivative of the appropriate oligoethylene glycol with 4-methoxy-5-raethyl-2,6-pyrimidinedimeth-anol in basic conditions. The yields were in the 30-50% range giving the crowns as viscous oils. Chiral dimethyl-substituted pyrimidino-crown 9 was prepared from 4-methoxy-5-methyl-2,6-pyrimidinedimethyl di-tosylate and chiral dimethyl-substituted tetraethylene glycol. Treatment of dimethyl 4-methoxy-5-methyl-2,6-pyrimidinedicarboxylate with the diamine derivative of chiral dibenzyl-substituted tetraethylene glycol gave the chiral dibenzyl-substituted pyrimidino-crown diamide 10. Starting 4-methoxy-5-methyl-2,6-pyrimidinedi-methanol was prepared by a six step process from acetamidine hydrochloride and diethyl oxalpropionate.