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摘要

ISSN 0306-001 2 CSRVBR 23(2) 75-146 (1994) Chemical Society Reviews Volume 23 Issue 2 Pages 75-146 April 1994 Carrier-mediated Transport through Liquid Membranes By Herman C. Visser, David N.Reinhoudt, and Feike de Jong (pp. 75-81 ) A review is presented of work on carrier-mediated transport of (organic) salts and neutral molecules through liquid membranes. Attention is focused on recent studies of diffusion-limited transport through BLM's and SLM's, the description of which is guided by simple mathematical equations. Finally, developments in the direction of ultra-thin membranes are outlined. The Colourless 'Chameleon' or the Peculiar Properties of Zn2+ in Complexes in Solution By Helmut Sigel and R. Bruce Martin (pp. 83-91 ) The adaptability of the coordination sphere of Zn2 + in biological systems is well known.Less appreciated is the fact that equilibria between Zn2 + species with coordination numbers 6 and (5 or) 4 are indeed quite common in solution in the presence of low-molecular-weight ligands. In this essay ways are described that allow a quantification of these equilibria in binary and in ternary (mixed ligand) complexes. For example, the 1:1 and 1:2 complexes formed by Zn2 + and ethylenediamine exist in aqueous solution to about 50 and 90, respectively, as tetrahedral species; the remaining parts being octahedral. The Diagnosis of Concerted Organic Mechanisms By A. Williams (pp. 93-1 00) The concept of concertedness is paramount in all discussions of reaction mechanisms. The criterion that a concerted mechanism has a single transition state and hence possesses no intermediates enables the unambiguous diagnosis of these mechanisms.This review describes current experimental techniques which provide unequivocal evidence against processes involving intermediates; such techniques therefore indicate concertedness. Contemporary evidence is discussed for reactions, such as displacements at unsaturated centres, not hitherto regarded as capable of supporting concerted mechanisms. I MELDOLA LECTURE. The Role of Aromatic Interactions in Molecular Recognition By Christopher A. Hunter (pp. 101-1 09) Studies of T-T interactions in covalently linked porphyrin dimers have been used to develop a simple electrostatic model for understanding and computing non-covalent interactions between aromatic molecules.The model has been tested on experimental data from protein X-ray crystal structures and by the successful design and synthesis of a molecular receptor for p-benzoquinone. Applications of the model to sequence- dependent DNA structure show that ideas derived from simple chemical systems can be useful for understanding more complex molecular assemblies. Non-Bonding Molecular Orbitals and the Chemistry of Non-Classical Organic Molecules By Christopher A. Ramsden (pp. 1 1 1-1 1 8) Professor Ramsden explores common features of the bonding and modes of reaction of a large and diverse family of 'non-classical' organic molecules, which includes 1,3-dipoles, hypervalent compounds, betaines, and ylides, and discusses their relationship to the transition states of SN2 reactions. All these molecules can be considered to contain three-centre, four-election bonds and the associated non-bonding molecular orbitals influence structure and reactivity.Two common modes of reaction, which are described as ligand coupling and syn-addition, are recognized and examples of these transformations are discussed. TILDEN LECTURE. Studies on Thymidylate Synthase and Dihydrofolate Reductase -Two Enzymes Involved in the Synthesis of Thymidine By Douglas W. Young (pp. 11 9-1 28) The review describes the author's work on thymidylate synthase and dihydrofolate reductase. A chemical model for the synthesis of thymine followed the biological labelling results more closely than expected. Work on the enzyme dihydrofolate reductase showed a difference in docking at the active site of the enzyme between the natural substrate and the drug methotrexate.Synthesis of stereospecifically deuteriated leucine and incorporation into the enzyme allowed assignment of the diastereotopic methyl groups of the leucine residues of the enzyme in the 'H-NMR spectrum. This will be generally applicable to other proteins. Structure and Dynamics of Electrolyte Solutions. A NMR Relaxation Approach By Antonio Sacco (pp. 1 29-1 36) Investigations on the dynamical and structural properties of electrolyte solutions based on NMR relaxation methods are reported. Using selected examples of electrolytes in pure solvents, the behaviour of the solvent molecules in the first coordination sphere of ions is highlighted.Moreover, by splitting intra- and inter- molecular contributions to the relaxation for some electrolytes in DMSO, the influence of the salts on the reorientational and translational properties of the solvent molecules is shown. Finally, NMR relaxation by quadrupolar interactions to probe the preferential solvation of ionic species in binary solvent mixtures is reported. The Electrophoresis of Semiconductor Particles By Colin Boxall (pp. 137-1 45) The role of colloidal semiconductor particles as photocatalysts in some environmentally important reactions, and the importance of the nature of the particle surface during such reactions is discussed. A summary of semicondutor particle-related electrochemical concepts is presented and the potential of electrophoresis for in situ non-perturbative interrogation of particle surface behaviour is described.The new technique of photoelectrophoresis and its utility in photocolloidal systems is also described. Finally, some recent advances in the field of semiconductor colloid chemistry are presented, with emphasis on those systems for which particle surface charge-related information would prove most useful. Articles that will appear in forthcoming issues include Homo- and Hetero-metallic Alkoxides of Groups 1, 2, and 12 Metals R. C. Mehrotra, A. Singh, and S. Sogani Towards a Laboratory Strategy for the Study of Heterogeneous Catalysis in Stratospheric Ozone Depletion Martin R.S. McCoustra and Andrew B. Horn Trimetallic Units as Building Blocks in Cluster Chemistry D. Imhof and L. M. Venanzi Chemistry in Near-critical Fluids Roberto Fernandez-Prini and M. Laura Japas Polyradicals: Synthesis, Spectroscopy, and Catalysis Joe A. Crayston, Ahmed Iraqi, and John C. Walton Affinity Biosensors Dbnal Leech The Hydrides of Aluminium, Gallium, Indium, and Thallium: A Re-evaluation Anthony J. Downs and Colin R. Pulham Electrophoretic NMR Manfred Hob Protein Structure from Linear Dichroism Spectroscopy and Transient Electric Birefringence Michael Bloemendal Chemical Society Reviews (ISSN 0306-00 12) is published bi-monthly by The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge, CB4 4WF, England.All orders accompanied with payment should be sent directly to The Royal Society of Chemistry, Turpin Distribution Services Ltd., Blackhorse Road, Letchworth, Herts., SG6 IHN, U.K. NB Turpin Distribution Services Ltd., distributors, is wholly owned by The Royal Society of Chemistry. 1994 annual subscription rate E.C. E99.00, U.S.A. $186.00, Canada €1 1l.OO+ GST, Rest of World €106.00. 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