In the past twenty years, the X-ray crystallography of organic molecules has expanded rapidly in two opposite directions. One is towards larger and larger biological macromolecules and the other is towards the fine details of the electronic structure of small molecules. Both advances required the development of more sophisticated methodologies. Both were made possible by the rapid development of computer technology. X-ray diffraction equipment has responded to these demands, in the one case by the ability to measure quickly many thousands of diffraction spectra, in the other by providing instruments capable of very high precision. Molecules interact through their electrostatic potentials and therefore their experimental and theoretical measurement and calculation is an essential component to understanding the electronic structure of chemical and biochemical reactions. In this ASI, we have brought together experts and their students from both the experimental and theoretical sides of this field, in order that they better understand the philosophy and complexity of these two complementary approaches. George A. Jeffrey Department of Crystallography University of Pittsburgh Pittsburgh, Pennsylvania 15260 USA vii CONTENTS LECTURES General Considerations on Methods for Studying Molecular Structures and Electron Density Distributions ..

Proceedings of a NATO ASI, held in Sant Feluide Guixols, Costa Brava, Spain, April 17--27, 1990

Zusammenfassung
Proceedings of a NATO ASI, held in Sant Feluide Guixols, Costa Brava, Spain, April 17--27, 1990

Inhalt
Lectures.- General Considerations on Methods for Studying Molecular Structures and Electron Density Distributions.- The Past and Future of Experimental Charge Density Analysis.- Determination of Atomic and Structural Properties from Experimental Charge Distributions.- Electrostatic Properties of Molecules from Diffraction Data.- X-ray Diffraction and Charge Distribution. Application to the Electron Density Distribution in the Hydrogen Bond.- Electron Density Models: Description and Comparison.- Experimental Requirements for Charge Density Analysis.- Necessity and Pitfalls of Low-Temperature Measurements.- The Use of Synchrotron Radiation and Its Promise in Charge Density Research.- The Use of Neutron Diffraction in Charge Density Analysis.- Structural Chemistry and Drug Design.- Correlation of Crystal Data and Charge Density with the Reactivity and Activity of Molecules: Towards a Description of Elementary Steps in Enzyme Reactions.- Charge Density Studies of Drug Molecules.- Posters.- Charge Density Distribution of Dimethyl-1,3-amino-4-uracil.- Structure and Electron Density of Trans-dichloro-bis(creatinine)platinum(II) Dihydrate.- A Low-Temperature (23 K) Study of L-Alanine: Topological Properties of Experimental and Theoretical Charge Distributions.- Electrostatic Properties and Topological Analysis of the Charge Density of Syn-1,6:8,13-biscarbonyl[14]annulene Derived from X-ray Diffraction Data at 16 K.- Electron Density Analysis of the Antimicrobial Drug and Radiosensitizer Dimetridazole at 105 K.- The Influence of Packing at a Molecular Level: Conformation, Geometry, Spectroscopy (IR, Raman).- The Experimental Electron Density Distribution of a CH?Co Bridged Complex.- Transferable Atom Equivalents. Molecular Electrostatic Potentials from the Electric Multipoles of PROAIMS Atomic Basins.- An Ab Initio Study of Clavulanic Acid and the Relation to Its Chemical Reactivity.- UHF Calculations of the g Tensor in Metal-Carbonyles Radicals.- Magnetostriction in NiF2: Combined ?-Ray and Neutron Diffraction.- The Conformation of Some Neuromuscular Blocking Agents.- A Structural Comparison of Potential HIV Inhibitors: 2?,3?-Didesoxinucleosides and 2?,3?-Didesoxicarbonucleosides.- Experimental Observation of Intermolecular ?-Electron Interactions in Photoreactive Crystals.- The Metal-Nitroxyl Interaction in MNO Metallacycles (M = Cu, Pd): An Ab Initio SCF/CI Study.- First-Principles Theoretical Methods for the Calculation of Electronic Charge Densities and Electrostatic Potentials.- Comparison of Precise Electronic Charge Densities and Electrostatic Potentials Obtained from Different Ab Initio Approaches.- Theoretical and Experimental Study of Dimerization of Substituted Phenylacetylenes.- Electron Deformation Density of Metal Carbyne Complexes.- The Potential Function in Short O H???O Bonds. Experimental Evidence and Ab Initio Modelling.- The Effect of Conformational Changes on the Polarizability of PNA.- Charge Density in Adeninium Hydrochloride Hemihydrate and 1H+-Adeniniumtrichlorozinc(II): The Effects of Metal Binding to a Nucleobase.- Participants.