I An Investigation Of Hydrogen Nitrogen Lone Pair Interactions

X-ray diffraction is a useful method for studying the absolute structure of a molecule or complex in crystalline form. Analysis and determination by this technique provides information on atomic positions within the molecule as well as bond lengths, angles, unit cell, space group and symmetry. We used X-ray analysis to study hydrogen-bonding interactions in a number of molecules. A hydrogen bond occurs between a hydrogen atom covalently bonded to a first row electronegative atom and weakly bonded to another first-row electronegative atom having at least one lone pair of electrons. Hydrogen-bonding interactions affect the coordination and complexation of molecular compounds. In this paper, we examine a structural anomaly of a far-too-short hydrogen bond in H5O2+cation and describe the various methods employed to resolve this issue. We also investigate intra- and inter-molecular hydrogen bonding in an oligosaccharide, as well as sulfate ion coordination due to hydrogen bonding in two different macrocycles.

Hydrogen bond (H-bond) effects are known: it makes sea water liquid, joins cellulose microfibrils in trees, shapes DNA into genes and polypeptide chains into wool, hair, muscles or enzymes. Its true nature is less known and we may still wonder why O-H...O bond energies range from less than 1 to more than 30 kcal/mol without apparent reason. This H-bond puzzle is re-examined here from its very beginning and presented as an inclusive compilation of experimental H-bond energies and geometries. New concepts emerge from this analysis: new classes of systematically strong H-bonds (CAHBs and RAHBs: charge- and resonance-assisted H-bonds); full H-bond classification in six classes (the six chemical leitmotifs); and assessment of the covalent nature of strong H-bonds. This leads to three distinct but inter-consistent models able to rationalize the H-bond and predict its strength, based on classical VB theory, matching of donor-acceptor acid-base parameters (PA or pKa), or shape of the H-bond proton-transfer pathway. Applications survey a number of systems where strong H-bonds play an important functional role, namely drug-receptor binding, enzymatic catalysis, ion-transport through cell membranes, crystal design and molecular mechanisms of functional materials.

Water and Biological Macromolecules presents an excellent description of the structural aspects of water molecules around biological macromolecules. Topics discussed include the properties of water in solid and liquid states; proteins, nucleic acids, polysaccharides, and lipids; and theoretical approaches for understanding the macroscopic observations and integrating microscopic descriptions. The nature and roles of hydration forces in macromolecular complexation and cell-cell interactions are explained, in addition to phenomena such as entropy-enthalpy compensation and the thermodynamic treatment of water bridging. Water and Biological Macromolecules will be a valuable reference for biophysicists, biochemists, and macromolecular biologists.

This book gives an extensive description of the state-of-the-art in research on excited-state hydrogen bonding and hydrogen transfer in recent years. Initial chapters present both the experimental and theoretical investigations on the excited-state hydrogen bonding structures and dynamics of many organic and biological chromophores. Following this, several chapters describe the influences of the excited-state hydrogen bonding on various photophysical processes and photochemical reactions, for example: hydrogen bonding effects on fluorescence emission behaviors and photoisomerization; the role of hydrogen bonding in photosynthetic water splitting; photoinduced electron transfer and solvation dynamics in room temperature ionic liquids; and hydrogen bonding barrier crossing dynamics at bio-mimicking surfaces. Finally, the book examines experimental and theoretical studies on the nature and control of excited-state hydrogen transfer in various systems. Hydrogen Bonding and Transfer in the Excited State is an essential overview of this increasingly important field of study, surveying the entire field over 2 volumes, 40 chapters and 1200 pages. It will find a place on the bookshelves of researchers in photochemistry, photobiology, photophysics, physical chemistry and chemical physics.

This book describes unconventional noncovalent interactions and analyzes their importance for crystal growth in organic and hybrid organic–inorganic systems. Several examples illustrate how the combination of theory and experiment allows rationalizing the strength and directionality of noncovalent interactions. This book elegantly describes the results of a survey of X-ray structures of main group element compounds (M = Sn, Pb As, Sb, Bi, and Te) exhibiting intermolecular M•••Se noncovalent interactions in one of its chapters. Moreover, it provides a consistent description of noncovalent interactions, covering most groups of the periodic table. The interactions are described and discussed using their trivial names. That is, a comprehensive and accurate description is provided for alkali, alkaline earth, regium, spodium, triel, tetrel, pnictogen, chalcogen, halogen, and aerogen bonding interactions. No other book is available covering such an extensive number of interactions and examples where these interactions are relevant. relevant.

This book explores chemical bonds, their intrinsic energies, and the corresponding dissociation energies which are relevant in reactivity problems. It offers the first book on conceptual quantum chemistry, a key area for understanding chemical principles and predicting chemical properties. It presents NBO mathematical algorithms embedded in a well-tested and widely used computer program (currently, NBO 5.9). While encouraging a "look under the hood" (Appendix A), this book mainly enables students to gain proficiency in using the NBO program to re-express complex wavefunctions in terms of intuitive chemical concepts and orbital imagery.

A significant contributing factor to the evolution in drug discovery was the methodological and technological revolution with the advent of combinatorial chemistry. This volume summarizes discussions of three aspects of modern drug discovery, that is, priority for targets, early ADMET assessment, and in silico screening.