Q2 Dependence of quadrupole strength in the gamma*p --> Delta(+)(1232) --> p pi(0) transition

Models of baryon structure predict a small quadrupole deformation of the nucleon due to residual tensor forces between quarks or distortions from the pion cloud. Sensitivity to quark versus pion degrees of freedom occurs through the Q2 dependence of the magnetic (M1+), electric (E1+), and scalar (S1+) multipoles in the gamma*p-->Delta(+)-->p pi(0) transition. We report new experimental values for the ratios E(1+)/M(1+) and S(1+)/M(1+) over the range Q2 = 0.4-1.8 GeV2, extracted from precision p(e,e(')p)pi(0) data using a truncated multipole expansion. Results are best described by recent unitary models in which the pion cloud plays a dominant role.     

NMR studies on natural and synthetic Amavadin

The stereochemistry of isolated natural product Amavadin, which contains a 1:2 complex of V(IV) with N-hydroxyimino-2,2'-dipropionic acid (HIDPAH(3)), and some synthetic complexes have been investigated. Amavadin was isolated from Amanita muscaria and oxidized with [NH(4)](2)[Ce(NO(3))(6)]. H(2)[Delta-V(S,S-HIDPA)(2)].3H(2)O, H(2)[Delta,Lambda-V(S,S-HIDPA)(2)].3H(2)O and their equivalent oxidized species have been synthesized and characterized spectroscopically. A combination of COSY, NOE, (1)H, (13)C-NMR and CD spectroscopy have been used to prove that the isolated natural product Amavadin consists of an almost equal mixture of the Delta- and Lambda-isomers of [V(S,S-HIDPA)(2)](2-).     

Fast voltammetric studies of the kinetics and energetics of coupled electron-transfer reactions in proteins

A wealth of information on the reactions of redox-active sites in proteins can be obtained by voltammetric studies in which the protein sample is arranged as a layer on an electrode surface. By carrying out cyclic voltammetry over a wide range of scan rates and exploiting the ability to poise or pulse the electrode potential between cycles, data are obtained that are conveniently (albeit simplistically) analysed in terms of plots of peak potentials against scan rate. A simple reversible electron-transfer process gives rise to a 'trumpet'-shaped plot because the oxidation and reduction peaks separate increasingly at high scan rate; the electrochemical kinetics are then determined by fitting to Butler-Volmer or Marcus models. Much more interesting though are the ways in which this 'trumpet plot' is altered, often dramatically, when electron transfer is coupled to biologically important processes such as proton transfer, ligand exchange, or a change in conformation. It is then possible to derive particularly detailed information on the kinetics, energetics and mechanism of reactions that may not revealed clearly or even at all by other methods. In order to interpret the voltammetry of coupled systems, it is important to be able to define 'ideal behaviour' for systems that are expected to show simple and uncoupled electron transfer. Accordingly, this paper describes results we have obtained for several proteins that are expected to show such behaviour, and compares these results with theoretical predictions.     

Hysteretic magnetic moment of YBa2Cu3O7?δ: An angular study

The hysteretic magnetization of an YBa₂Cu₃O_7−δ crystal containing a high density of Y₂BaCuO_x precipitates was investigated by two-axis, quasistatic, de magnetometry. As the eff-axis applied magnetic fieldH was increased and the magnetization magnitude, decreased, its orientation approached a direction near the crystallinec axis. The bulk persistent currentsJ _p predominately flowed parallel to the Cu−O planes for a wide range of temperature and applied field. Even forH almost perpendicular toc, where the deduced irreversibility line maximized as commonly observed, the resulting magnetization was observed to be within 15° of [001]. Managed by Lockheed Martin Energy Research Corp, under contract AC05-96OR22464 with the U. S. Dept. of Energy.     

Preparation and properties of a soluble polymeric aquo ion of molybdenum(V)

An orange/brown ionic and polymeric Mo(V) ion (Mo to Na ratio 2.3:1), soluble in H₂O to give stable solutions at pH～6, with UV visible spectrum λ_max 318nm, ?(per Mo) 330OM^?1 cm^?1, has been prepared and partially characterised. Various properties are described, including the conversion to the well established Mo(V) aquo dimer, MO₂O₄²⁺, on adjustment of [H⁺] to 0.17–0.50 M, I=0.50 M (H/LiClO₄). First-order rate constants, k_obs(25°C), determined by conventional spectrophotometry give a good fit to the empirical rate law,     

Investigation of the electronic structures of vinyl silicon compounds by the free electron method

The two compounds, Me₄Si₂ (C₂H₃)₂ and Me₈Si₂ (C₂H₃)₂ have been studied by the anti-symmetrized free electron molecular orbital method. Electron delocalisation over the whole chain via the silicon atoms occurs and a satisfactory account of the electronic spectra may be obtained.

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Zusammenfassung Me₄Si₂ (C₂H₃)₂ und Me₈Si₄ (C₂H₃)₂ wurden nach der MO-Methode des freien Elektronengases behandelt. Delokalisierung der Elektronen über die Si-Atome der Kette wird festgestellt. Die berechneten Spektren sind zufriedenstellend.

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Résumé On a étudié par la méthode des orbitales moléculaires d'électrons libres avec antisymétrisation les composés Me₄Si₂(C₂H₃)₂ et Me₈Si₄(C₂H₃)₂. Il se produit une délocalisation électronique le long de toute la chaÎne par l'intermédiaire des atomes de silicium, et l'on peut rendre compte d'une manière satisfaisante des spectres électroniques.

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We wish to thank the S.R.C. for a maintenance grant to one of us (D.R.A.).     

The single basis filter diagonalization method: a rapid multidimensional data processing scheme

A new way to apply the filter diagonalization method (FDM) that results in a large increase in the speed of calculation of multidimensional NMR spectra is presented. The speed increase is accompanied by slight differences in spectral lineshapes, although frequency estimates remain essentially identical. For contoured spectra, the method does not result in appreciable differences from the full FDM calculation. Optimal parameter sets for an FDM calculation can be estimated far more rapidly, which makes the FDM more straightforward to employ in practice. The performance of the method versus the full FDM was investigated for both model and experimental signals. The effect of noise on the method was also studied.