Hydrogen bond

About: Hydrogen bond is a research topic. Over the lifetime, 57701 publications have been published within this topic receiving 1306326 citations.

Polarization and Experimental Configuration Analysis of Sum Frequency Generation Vibrational Spectra of Air/Water Interface

Abstract: Here we report a detailed study on spectroscopy, structure and dynamics of water molecules at air/water interface, investigated with Sum Frequency Generation Vibrational Spectroscopy (SFG-VS). Quantitative polarization and experimental configuration analysis of the SFG data in different polarizations with four sets of experimental configurations can shed new lights on our present understanding of the air/water interface. Firstly, we concluded that the motion of the interfacial water molecules can only be in a limited angular range, instead rapidly varying over a broad angular range in the vibrational relaxation time suggested previously. Secondly, because different vibrational modes of different molecular species at the interface has different symmetry properties, polarization and symmetry analysis of the SFG-VS spectral features can help assignment of the SFG-VS spectra peaks to different interfacial species. These analysis concluded that the narrow 3693cm-1 and broad 3550cm-1 peaks belong to C_ v symmetry, while the broad 3250cm-1 and 3450cm-1 peaks belong to the symmetric stretching modes with C_2v symmetry. Thus, the 3693cm-1 peak is assigned to the free OH, the 3550cm-1 peak is assigned to the single hydrogen bonded OH stretching mode, and the 3250cm-1 and 3450cm-1 peaks are assigned to interfacial water molecules as two hydrogen donors for hydrogen bonding (with C_2v symmetry), respectively. Thirdly, analysis of the SFG-VS spectra concluded that the singly hydrogen bonded water molecules at the air/water interface have their dipole vector direct almost parallel to the interface, and is with a very narrow orientational distribution. The doubly hydrogen bond donor water molecules have their dipole vector point away from the liquid phase.

Structural components of alginic acid. II. The crystalline structure of poly-alpha-L-guluronic acid. Results of x-ray diffraction and polarized infrared studies.

Abstract: A structural investigation of the marine algal polysaccharide poly-α-L-guluronic acid is described. The molecular chains consist of 1 4 diaxially linked L-guluronic acid residues in the 1C chair conformation and are stabilized in a twofold helix conformation by an intra-molecular O(2)H … O(6)D hydrogen-bond. The X-ray fiber diffraction photograph has been indexed to an orthorhombic unit cell in which a = 8.6 A, b (fiber axis) = 8.7 A, c = 10.7 A. A structure corresponding to the space group P212121 is proposed, in which all intermolecular hydrogen bonds interact with water molecules and in which all oxygen atoms except for the inaccessible bridge oxygens are involed. The relationship between the shape and structure of the polyguluronic acid molecule and its biological function is discussed.

Experimental Evidence for Hydrogen Bonding in Polyaniline: Mechanism of Aggregate Formation and Dependency on Oxidation State

Abstract: Aggregation in the nondoped polyaniline, emeraldine base (EB), as observed by GPC in a N-methyl-2-pyrrolidinone (NMP) solution, was found to be closely related to the fraction of the imine nitrogen atoms in the nondoped polymer, i.e., to the oxidation state of the polymer. As EB was reduced to leucoemeraldine base (LEB), the degree of aggregation was significantly reduced. The results of gel permeation chromatography (GPC) and infrared studies suggest that the aggregation of the polymer is due to interchain hydrogen bonding between the imine and amine nitrogen sites on adjacent polymer molecules. The degree of hydrogen bonding and, thus, aggregation found in the polymer is greatly affected by solvents, LiCl, and the oxidation state of the polymer.

The effect of an external magnetic field on the structure of liquid water using molecular dynamics simulation

Abstract: Through a series of molecular dynamics simulations based on the flexible three-centered water model, this study analyzes the structural changes induced in liquid water by the application of a magnetic field with a strength ranging from 1to10T. It is found that the number of hydrogen bonds increases slightly as the strength of the magnetic field is increased. This implies that the size of a water cluster can be controlled by the application of an external magnetic field. The structure of the water is analyzed by calculating the radial distribution function of the water molecules. The results reveal that the structure of the water is more stable and the ability of the water molecules to form hydrogen bonds is enhanced when a magnetic field is applied. In addition, the behavior of the water molecules changes under the influence of a magnetic field; for example, the self-diffusion coefficient of the water molecules decreases.