Orientation Of OH Groups Research Articles

Orientation of OH groups in kaolinite and dickite: Ab initio molecular dynamics study

Ab-initio density-functional molecular dynamics simulations and full relaxation of all atomic positions are used to reconcile the crystal structures with IR spectra of dickite and kaolinite. The relaxation of atomic positions preserves the accepted space group symmetries. A pair of two hydroxyl groups oriented parallel to the layer is formed in structures of both dickite and kaolinite producing the high-frequency components of the OH-stretching frequencies. Other hydroxyls make relatively strong interlayer hydrogen bonds and produce down-shifted stretching bands. All hydroxyl groups are involved in effective hydrogen bonds. The OH-stretching frequencies depend linearly on the strength of the hydrogen bond.

The plastically crystalline phase of NaOH, NaOD, KOH and KOD

The high-temperature cubic phases of sodium hydroxide and potassium hydroxide have been investigated using X-ray, elastic and inelastic neutron scattering from single crystals. As a special feature of these experiments the crystals had to be kept at temperatures of around 550 K as grown from melt, since they are destroyed when passing through the structural phase transition. In these compounds the OH or OD groups are known to undergo rapid reorientational motions. The X-ray diffraction results are characterized by a rapid decrease in the Bragg intensities with increasing diffraction angle and diffuse rods passing through the Bragg reflections. By neutron diffraction, about 20 symmetrically non-equivalent reflections have been observed. Different means of analysis will be presented; one obtains the probability distribution of H+ or D+ around oxygen, and the OH distance. This is of interest in the context of possible H bonding and proton conductivity. The disorder of H or D gives rise to diffuse scattering of neutrons as an approximately spherical halo around the origin in Q-space. The orientations of OH groups at different sites being correlated cannot be excluded from the experimental findings; a 2D correlation model, however, does not predict a dramatic narrowing of this halo. Inelastic scattering yielded rather ill-defined phonon groups in constant-Q scans. In particular, the shear modes showed strong overdamping. The observed features can be explained by treating the OH groups as elastic dipoles coupled to the lattice distortions, with the dynamics of a relaxator, and by extending conventional soft-mode theory to allow for the mixing of several softened modes. The softened modes also explain the diffuse rods in X-ray photographs.

Conformational analysis of substituted 1-cycloheptene-5,6- and 1-cycloheptene-6,7-diols from ir, raman, and pmr spectra

For a number of substituted vic-cycloheptenediols the chair conformation with a transdiequatorial orientation of hydroxyl groups is suggested by the data of PMR in CDCl3. The data of IR and Raman spectra of dilute solutions of these compounds in CCl4, indicate the possibility of multiple conformations due to the different orientation of OH groups forming intramolecular hydrogen bonds or, depending on the nature of substitution, in ‘twist boat’ forms.

糖の親水性と疎水性 脂質膜に与える効果

Saccharides have been regarded as the strong hydrophilic solutes by virtue of their hydrogen bonding with water molecules. The oxygen positions of equatorial OH groups almost fit the oxygen positions of tridymite structure of water. Therefore, the degree of hydrophilicity is different from each saccharide, because of the different orientation of OH groups. On the contrary, the hydrophobic plane formed by the CH- and CH2-groups is also different from each saccharide molecule and different hydrophobicities are observed for various monosaccharides, though they are considerably weak. The amphipathic character of saccharide molecule, that is, strong hydrophilicity and weak hydrophobicity, has been demonstrated by the studies of the interaction of lipid membranes with monosaccharides and cyclodextrins. The most hydrophilic monosaccharides stabilize the liposome membrane in frozen state, while the most hydrophobic cyclodextrins destruct the liposome membrane at room temperature by recognizing the lipid molecule and forming the inclusion complexes. Bile salts are also included in the cavity of, β-cyclodextrin and liberate the guest molecule by the exchange reaction.

Relation between the orientation of OH groups in stereoisomers of derivatives of 3,4-dioxy-1-methylpiperdine and their IR absorption

Relation between the orientation of OH groups in stereoisomers of derivatives of 3,4-dioxy-1-methylpiperdine and their IR absorption

X-ray and infrared investigations of a synthetic dioctahedral vermiculite saturated with alkali and alkaline earth cations

AbstractA synthetic dioctahedral vermiculite was saturated with Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr and Ba, and examined by X-ray diffraction and infrared spectroscopy under various dehydration conditions. Cations which were larger than the ditrigonal hole (Cs, Rb, Ba) increased the b-dimension by forcing the oxygen triads open. With small cations the b-dimension decreased as a function of the residual water content rather than of cation size. The OH stretching vibration did not change in position, probably due to the inclined orientation of OH groups. The cations perturbed the lattice vibrations when they caused a change in the tetrahedral rotation angle, i.e. in b-dimension. With the small cations Be, Li and Mg, librations below 450 cm−1 shifted towards higher frequencies indicating cation migration into the empty octahedral sites.