Study Of Hydrogen Bonding Interactions Via X Ray Analysis

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.

This book uses examples from experimental studies to illustrate theoretical investigations, allowing greater understanding of hydrogen bonding phenomena. The most important topics in recent studies are covered. This volume is an invaluable resource that will be of particular interest to physical and theoretical chemists, spectroscopists, crystallographers and those involved with chemical physics.

Hydrogen bonded systems play an important role in all aspects of science but particularly chemistry and biology. Notably, the helical structure of DNA is heavily reliant on the hydrogens bonds between the DNA base pairs. Although the area of hydrogen bonding is one that is well established, our understanding has continued to develop as the power of both computational and experimental techniques has improved. Understanding Hydrogen Bonds presents an up-to-date overview of our theoretical and experimental understanding of the hydrogen bond. Well-established and novel approaches are discussed, including quantum theory of ‘atoms in molecules’ (QTAIM); the electron localization function (ELF) method and Car–Parinnello molecular dynamics; the natural bond orbital (NBO) approach; and X-ray and neutron diffraction and spectroscopy. The mechanism of hydrogen bond formation is described and comparisons are made between hydrogen bonds and other types of interaction. The author also takes a look at new types of interaction that may be classified as hydrogen bonds with a focus on those with multicentre proton acceptors or with multicentre proton donors. Understanding Hydrogen Bonds is a valuable reference for experimentalists and theoreticians interested in updating their understanding of the types of hydrogen bonds, their role in chemistry and biology, and how they can be studied.

This book comprises seven chapters. In chapter 1 an overview of chemistry, biological functions and literature studies of hydroxamic acids (HA) and its isosteres is presented. The principles of quantum mechanics underlying the computational methods employed to study HAs are given in brief. Chapter 2 describes intra- and intermolecular H-bonding interactions between formohydoxamic acid (FHA) and single water molecule and the dimerization among the isomeric forms. Chapter 3 involves the comparative study of H-bonding abilities of thioformohydoxamic acid (TFHA) and FHA. The deprotonation enthalpies of different sites of FHA and TFHA, probable pathways for interconversion among anions and their H-bonding with water are explored in chapter 4. The Effect of aqueous medium on deprotonation by using solvation methods is also discussed. Further insight into H-bonded aggregates and dimers of HAs is gained through the analysis of calculated stabilization energies and their comparison to similar H-bonded functionalities. The reasons behind the H-bond cooperativity in the aggregates and dimers are explored in chapter 5. Chapter 6 deals with the study of properties of formylphosphinous acid (FPA) isostere of FHA and a comparative study is carried out. In chapter 7, the aggregation of the most stable keto and enol conformer of FHA and TFHA with five amino acid side chain groups occurring at active sites of enzymes is studied.

This book is a printed edition of the Special Issue "Analysis of Hydrogen Bonds in Crystals" that was published in Crystals

The main focuses of this project have been investigations of a variety of hydrogen bonding systems for unusual behaviour such as disordered or migrating hydrogens/protons with both single crystal X-ray and neutron diffraction, crystallisation of a large number of molecular complexes of the chloranilic acid molecule, and examining the bifurcated hydrogen bond motif found in many of the chloranilic acid co-crystals discovered. The neutron single crystal diffraction instruments SXD and VIVALDI have been used to provide conclusive results in cases of suspected unusual hydrogen bond behaviour in molecular materials. 2,4-dihydroxybenzoic acid and its isomer 2,5-dihydroxybenzoic acid have been examined using X-ray and neutron diffraction to investigate possible disordered cooperative hydrogen bond systems. The energy difference of the three possible tautomers of 2,4-dihydroxybenzoic acid in different environments have been calculated in theoretical computations which concur with the neutron results. Single crystal neutron diffraction experiments were also carried out on isonicotinamidium formate, 2-iodoaniliium picrate, chloranilic acid 2,4-lutidine and malonic acid, where unusual behaviour in the hydrogen systems was also suspected. The molecular complexes of chloranilic acid with various pyridine-based molecules have been the main focus of the X-ray diffraction work of this thesis. Multiple crystallisations over a range of different conditions were set up for chloranilic acid with various series of molecules including lutidines (dimethylpyridines) and picolines (methylpyridines). This resulted in a large number of new crystal structures, determined by X-ray diffraction and all found to contain a bifurcated hydrogen bond motif producing two robust hydrogen-bonded supramolecular synthons. The investigation examines the bifurcated hydrogen bond interactions and the suitability of chloranilic acid complexes for crystal engineering. The two related supramolecular synthon units are discussed and difference Fourier maps and Hirshfeld surfaces used to examine the hydrogen bond architecture. Bromanilic acid co-crystals are also studied to examine the effect of the halogen in the crystal structures.

Hydrogen bonds are weak attractions, with a binding strength less than one-tenth that of a normal covalent bond. However, hydrogen bonds are of extraordinary importance; without them all wooden structures would collapse, cement would crumble, oceans would vaporize, and all living things would disintegrate into random dispersions of inert matter. Hydrogen Bonding in Biological Structures is informative and eminently usable. It is, in a sense, a Rosetta stone that unlocks a wealth of information from the language of crystallography and makes it accessible to all scientists. (From a book review of Kenneth M. Harmon, Science 1992)

Hydrogen Bonding covers the papers presented at the Symposium on Hydrogen Bonding, held at Ljubljana on July 29 to August 3, 1957. The book focuses on the developments, processes, approaches, methodologies, and reactions involved in hydrogen bonding. The selection first offers information on the structure of water; function of hydrogen bond in solids and liquids; and study of hydrogen bonds by neutron diffraction. The text then takes a look at x-ray and neutron studies of hydrogen bonding; x-ray studies of ammonium bifluoride, potassium hydrogen maleate, theophylline, and caffeine; and isotope effect in relation to bond length in hydrogen bonds in crystals. The publication ponders on proton magnetic resonance measurements of hydrogen bonding; interpretation of nuclear magnetic resonance shifts in hydrogen bonding; nuclear resonance investigation of hydrogen bonding; and infrared spectroscopy and hydrogen bonding — band-widths and frequency shifts. The book then examines the tunneling of protons as a cause of the splitting of hydroxyl stretching bands; infrared spectroscopic study of H-bonding and of metal-element bonding; and effect of hydrogen bond formation on the electronic spectra of phenolic substances. The selection is a vital source of information for readers interested in hydrogen bonding.

Crystal engineering is an interdisciplinary area that cuts across the traditional subdivisions of chemistry. Fuelled by our increasingly precise understanding of the chemistry and properties of supramolecular systems, interest in the potential of the field has increased rapidly. The topics discussed in the 28 contributions in this book provide a state-of-the-art description of the field and offer new research ideas that, if pursued, will serve to strengthen the field at the interface between supramolecular chemistry and materials science.