Proton dynamics in ferroelectric colemanite

1970 ◽  
Vol 48 (9) ◽  
pp. 1081-1085 ◽  
Author(s):  
A. Watton ◽  
H. E. Petch ◽  
M. M. Pintar
Keyword(s):  
Temperature Dependence ◽  
Line Width ◽  
Hydroxyl Group ◽  
Water Molecules ◽  
Kcal Mole ◽  
Hydrogen Atoms ◽  
Second Moment ◽  
Diffraction Model ◽  
Proton Dynamics ◽  
Good Agreement

A reexamination of the proton second moment in powdered colemanite, CaB3O4(OH)3∙H2O, over the range 4.2–450 °K has shown that the temperature dependence is in qualitative agreement with earlier work but that the magnitudes of the changes occurring at the two line-width transitions are substantially different. The observed values of the second moment have been compared with values calculated on the basis of models in which the hydrogen-containing molecular groups reorient. The line-width transition at about 130 °K is attributed to a motion in which the water molecules undergo 180° flips about the bisectrix of the H—O—H angle. The activation energy for this motion has been determined as 5.3 ± 0.3 kcal/mole from the temperature dependence of T1. The observed change in the second moment at the ferroelectric transition (270 °K) is in good agreement with the value calculated on the basis of the neutron diffraction model, in which a cooperative motion involving one of the hydrogen atoms of the water molecule and the hydrogen of an adjacent hydroxyl group is active above the transition.

About the degree of hydration in potassiumtrisoxalatochromate hydrate

2005 ◽  
Vol 220 (11) ◽  
Author(s):  
Chunhua Hu ◽  
Gernot Heger ◽  
Irmgard Kalf ◽  
Ullrich Englert
Keyword(s):  
Neutron Diffraction ◽  
Water Molecules ◽  
Structure Model ◽  
Hydrogen Atoms ◽  
Neutron Data ◽  
X Ray ◽  
Degree Of Hydration ◽  
Thermogravimetric Data ◽  
Hydration Model ◽  
Good Agreement

AbstractData obtained from single crystal X-ray and neutron diffraction experiments have been combined with results from thermogravimetry in order to derive an improved structure model for potassium tris(oxalato)chromate hydrate. The degree of hydration for this compound has been reinvestigated: Earlier work assumed a trihydrate stoichiometry and had to accept an unusually short K···O distance of 2.3 Å. Our neutron data reveal the position of the hydrogen atoms in the water molecules; they prove that abnormally short separations between a cation and atoms of a water molecule can only occur between sites of mutually exclusive occupancy and hence remain without chemical relevance. Closest K···O distances in our revised hydration model amount to 2.6 Å, in good agreement with expectation. Both diffraction experiments and thermogravimetric data agree with the stoichiometry K

Towards clathrates. 2. The frozen states of hydration of tert-butanol

2018 ◽  
Vol 233 (1) ◽  
pp. 41-49 ◽  
Author(s):  
Lukasz Dobrzycki
Keyword(s):  
Single Crystal ◽  
Crystalline Phase ◽  
Ambient Pressure ◽  
Water System ◽  
Hydroxyl Group ◽  
Molar Ratio ◽  
Water Molecules ◽  
Hydroxyl Groups ◽  
Hydrogen Atoms ◽  
Ir Laser

AbstractA new crystal structure oftert-butanol and water crystallizing as the decahydrate is reported. The crystallization of the mixture in the desired molar ratio was performed in a capillary placed directly on a goniometer of a single crystal diffractometer at 200 K and ambient pressure using focused IR laser radiation. The crystals were grown while the melting zone formed by the IR laser was moved along the capillary. Usually the crystallization process should be long enough (hours) in order to obtain a good quality single crystal. However, in the case oftert-butanol decahydrate, such a long process led to separation of the ice and alcohol. Only fast crystallization taking tens of seconds allowed crystallization of the desired crystalline phase. In the decahydratetert-butanol molecules are located in channels formed by water molecules. Hydroxyl groups are anchored to the water framework via hydrogen bonds. All water molecules in the structure have hydrogen atoms disordered equally over two sites; the hydroxyl group is likewise disordered. This effect is observed at both, 200 K and 100 K. Raman spectra recorded for the crystalline phase suggest dynamic disorder at higher temperature, converting to static at lowerT. The decahydrate oftert-butanol, together with already known itsdi- andhepta-hydrates, display similar features to those observed for series oftert-butylamine hydrates. The latter structures behave as frozen steps of amine hydration observed as crystal structures leading, at maximum dilution, to hexagonal ice. Hydrates oftert-butanol nicely follow this tendency completing the relationship found for thetert-butylamine: water system.

Proton Rotating Frame Relaxation in Lithium Hydrazinium Sulfate, Li(N2H5)SO4

1971 ◽  
Vol 49 (7) ◽  
pp. 870-875 ◽  
Author(s):  
R. R. Knispel ◽  
H. E. Petch
Keyword(s):  
Activation Energy ◽  
Relaxation Time ◽  
Temperature Dependence ◽  
Rotating Frame ◽  
Kcal Mole ◽  
Second Moment ◽  
Rotating Frame Relaxation ◽  
And Diffusion

The temperature dependence of the rotating frame relaxation time T1ρ for protons in powdered lithium hydrazinium sulfate, Li(N2H5)SO4, has been determined from 140 to 495 °K. These measurements indicate that the –NH2 part of the N2H5+ ion executes 180° flips about the bisectrix of the H–N–H angle with activation energy of 10.7 ± 0.5 kcal/mole. Evidence for motion of the entire N2H5+ ion with activation energy of 17.4 ± 1.1 kcal/mole was also obtained. Separate reorientation and diffusion motions of the N2H5+ ion could not be distinguished, although evidence that the N2H5+ motion detected in the T1ρ measurements includes diffusion is obtained by comparing the T1ρ results with the temperature dependence of the proton second moment.

Temperature Dependence of the Air/Water Interface Revealed by Polarization Sensitive Sum-Frequency Generation Spectroscopy

2018 ◽  
Author(s):  
Daniel R. Moberg ◽  
Shelby C. Straight ◽  
Francesco Paesani
Keyword(s):  
Temperature Dependence ◽  
Low Frequency ◽  
Potential Energy Function ◽  
Md Simulations ◽  
Sum Frequency Generation ◽  
Water Molecules ◽  
Water Interface ◽  
Sum Frequency ◽  
Air Water Interface ◽  
Frequency Generation

<div> <div> <div> <p>The temperature dependence of the vibrational sum-frequency generation (vSFG) spectra of the the air/water interface is investigated using many-body molecular dynamics (MB-MD) simulations performed with the MB-pol potential energy function. The total vSFG spectra calculated for different polarization combinations are then analyzed in terms of molecular auto-correlation and cross-correlation contributions. To provide molecular-level insights into interfacial hydrogen-bonding topologies, which give rise to specific spectroscopic features, the vSFG spectra are further investigated by separating contributions associated with water molecules donating 0, 1, or 2 hydrogen bonds to neighboring water molecules. This analysis suggests that the low frequency shoulder of the free OH peak which appears at ∼3600 cm−1 is primarily due to intermolecular couplings between both singly and doubly hydrogen-bonded molecules. </p> </div> </div> </div>

The Influence of Hydrogen atoms on the Performance of Radial Distribution Function Based Descriptors in the Chemoinformatic Studies of HIV-1 Prote-ase Complexes with Inhibitors.

2020 ◽  
Vol 17 ◽  
Author(s):  
Jurica Novak ◽  
Maria A. Grishina ◽  
Vladimir A. Potemkin
Keyword(s):  
Distribution Function ◽  
Radial Distribution Function ◽  
Radial Distribution ◽  
Current Model ◽  
Direct Interaction ◽  
Hydroxyl Group ◽  
Linear Regression Method ◽  
Hydrogen Atoms ◽  
Protease Enzyme ◽  
Hiv 1

: In this letter the newly introduced approach based on the radial distribution function (RDF) weighted by the number of va-lence shell electrons is applied for a series of HIV-1 protease enzyme and its complexes with inhibitors to evaluate the influ-ence of hydrogen atoms on the performance of the model. The multiple linear regression method was used for the selection of the relevant descriptors. Two groups of residues having dominant contribution to the RDF descriptor are identified as relevant for the inhibition. In the first group are residues like Arg8, Asp25, Thr26, Gly27 and Asp29, which establish direct interaction with the inhibitor, while the second group consists of the amino acids at the interface of the two homodimer sub-units or with the solvent. The crucial motif pointed out by our approach as the most important for inhibition of the enzyme’s activity and present in all inhibitors is hydroxyl group that establish hydrogen bond with Asp25 side chain. Additionally, the comparison to the model without hydrogen showed that both models are of similar quality, but the downside of the current model is the need for the determination of residues’ protonation states.

Temperature dependence of the EPR line width and a relaxation of Cr3+ ions in ZnWo4

1971 ◽  
Vol 44 (1) ◽  
pp. 199-202
Author(s):  
A. A. Bugai ◽  
M. D. Glinchuk ◽  
M. F. Deigen ◽  
V. M. Maksimenko
Keyword(s):  
Temperature Dependence ◽  
Line Width

Line-width temperature dependence of selected R-branch transitions in the ν3 fundamental of 14N216O between 135 and 295 K

1992 ◽  
Vol 48 (9) ◽  
pp. 1243-1248 ◽  
Author(s):  
Max Loewenstein ◽  
H.William Wilson
Keyword(s):  
Temperature Dependence ◽  
Line Width

Dielectric and nuclear magnetic resonance study of the hydrate of sulphur hexafluoride

1968 ◽  
Vol 46 (10) ◽  
pp. 1683-1690 ◽  
Author(s):  
Y. A. Majid ◽  
S. K. Garg ◽  
D. W. Davidson
Keyword(s):  
Magnetic Resonance ◽  
Lattice Structure ◽  
Nuclear Magnetic Resonance Study ◽  
Water Molecules ◽  
Activation Entropy ◽  
Sulphur Hexafluoride ◽  
Rigid Lattice ◽  
Second Moment ◽  
Resonance Behavior ◽  
Arrhenius Energy

In its dielectric and proton magnetic resonance behavior (except T1) the clathrate hydrate of SF6 is similar to ice I. Reorientation of water molecules appears to be little affected by the guest SF6 molecules and probably depends on the diffusion of rotational Bjerrum defects formed in numbers intrinsic to the lattice structure. The Arrhenius energy and activation entropy for dielectric relaxation are 12.3 + 0.5 kcal mole−1 and 6.8 + 2.0 cal deg−1 mole−1, respectively. The proton rigid-lattice second moment is 32.8 ± 0.5 G2 at −180 °C. The 19F second moment agrees with the value calculated for rapid isotropic rotation of SF6 molecules in the large cages only. Diffusion of water molecules in the hydrate is slower than in ice, which suggests that diffusion in ice occurs by migration of interstitial molecules through the channels in ice rather than by migration of lattice vacancies.

Vulcanization of Elastomers. 23. The Chemical Kinetics of Vulcanization Reactions and The Physical Properties of The Vulcanizates. I

1960 ◽  
Vol 33 (2) ◽  
pp. 335-341
Author(s):  
Walter Scheele ◽  
Karl-Heinz Hillmer
Keyword(s):  
Activation Energy ◽  
Physical Properties ◽  
Chemical Kinetics ◽  
Kcal Mole ◽  
First Order ◽  
Equilibrium Swelling ◽  
Kinetics Of ◽  
Kinetics Of Vulcanization ◽  
Limiting Value ◽  
Good Agreement

Abstract As a complement to earlier investigations, and in order to examine more closely the connection between the chemical kinetics and the changes with vulcanization time of the physical properties in the case of vulcanization reactions, we used thiuram vulcanizations as an example, and concerned ourselves with the dependence of stress values (moduli) at different degrees of elongation and different vulcanization temperatures. We found: 1. Stress values attain a limiting value, dependent on the degree of elongation, but independent of the vulcanization temperature at constant elongation. 2. The rise in stress values with the vulcanization time is characterized by an initial delay, which, however, is practically nonexistent at higher temperatures. 3. The kinetics of the increase in stress values with vulcanization time are both qualitatively and quantitatively in accord with the dependence of the reciprocal equilibrium swelling on the vulcanization time; both processes, after a retardation, go according to the first order law and at the same rate. 4. From the temperature dependence of the rate constants of reciprocal equilibrium swelling, as well as of the increase in stress, an activation energy of 22 kcal/mole can be calculated, in good agreement with the activation energy of dithiocarbamate formation in thiuram vulcanizations.

13C NMR-spektroskopische Untersuchungen an Äthylaluminiumverbindungen / 13C NMR Spectroscopic Investigations of Ethylaluminium Compounds

1976 ◽  
Vol 31 (6) ◽  
pp. 730-736 ◽  
Author(s):  
R. Rottler ◽  
C. G. Kreiter ◽  
G. Fink
Keyword(s):  
Temperature Dependence ◽  
Exchange Reaction ◽  
13C Nmr ◽  
Line Shape ◽  
Nmr Spectra ◽  
Exchange Process ◽  
Kcal Mole ◽  
Line Shapes ◽  
Calculated Line ◽  
C Nmr

The 13C NMR spectra of the ethylaluminium compounds [Al(C2H5)xCl3_x]2 x = 1, 1,5, 2 and 3 are presented and factors governing the temperature dependence of the line shape are discussed. The exchange reaction of terminal ethyl groups for chlorine ligands and ethyl ligands, resp., in ethylaluminium-sesquichloride was investigated by fitting the calculated line shapes to the observed spectra.The energy of activation of this exchange process was determined as to be 12,3 ‡ 1,5 kcal/mole. The synthesis of 13C2-[Al(C2H5)Cl2]2 is described.

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