THE STRUCTURAL BASIS OF FERROELECTRICITY IN COLEMANITE

1966 ◽  
Vol 44 (12) ◽  
pp. 3083-3107 ◽  
Author(s):  
F. N. Hainsworth ◽  
H. E. Petch
Keyword(s):  
Neutron Diffraction ◽  
Water Molecule ◽  
Ferroelectric Phase ◽  
The Other ◽  
Hydroxyl Group ◽  
Structural Basis ◽  
Hydrogen Atoms ◽  
Complete Structure ◽  
Ferroelectric State ◽  
Order Of Magnitude

The complete structure of colemanite, CaB3O4(OH)3∙H2O, in both its nonpolar and ferroelectric phases, has been determined by neutron diffraction. This work shows that one of the hydrogen atoms of the water molecule and the hydrogen of an adjacent hydroxyl group, which are in a state of dynamic disorder in the nonpolar phase, settle into ordered noncentric positions in the ferroelectric phase. The ordering of the hydrogen atoms is accompanied by small displacements of the other atoms from the positions they occupy in the nonpolar phase. Assuming reasonable charge assignments, the magnitude of the spontaneous polarization calculated from the observed positional changes is of the same order of magnitude as the experimental value. On the basis of these results, a model for the atomistic mechanism of the transition to the ferroelectric state is advanced.

A study of α -resorcinol by neutron diffraction

1956 ◽  
Vol 235 (1203) ◽  
pp. 552-559 ◽  
Keyword(s):  
Hydrogen Bonds ◽  
Neutron Diffraction ◽  
Oxygen Atom ◽  
Neutron Scattering ◽  
Benzene Ring ◽  
Unit Cell ◽  
The Other ◽  
Aromatic Molecule ◽  
Hydrogen Atoms ◽  
A Value

The first study of an aromatic molecule by neutron diffraction, leading to a Fourier projection of the neutron scattering density in the unit cell, gives a value of 1·08 ± 0·04 Å for the length of the C—H bonds which link hydrogen atoms to the benzene ring. The spirals of hydrogen bonds which bind together neighbouring molecules are found to consist of typical ‘long bonds’, with the proton much closer to one oxygen atom than to the other. The O—H distance is 1·02 Å, and it appears that the O, H, O atoms are not collinear.

NEUTRON DIFFRACTION DETERMINATION OF THE HYDROGEN POSITIONS IN NATROLITE

1964 ◽  
Vol 42 (2) ◽  
pp. 229-240 ◽  
Author(s):  
B. H. Torrie ◽  
I. D. Brown ◽  
H. E. Petch
Keyword(s):  
Hydrogen Bonds ◽  
Neutron Diffraction ◽  
Oxygen Atom ◽  
Water Molecule ◽  
Neutron Diffraction Data ◽  
X Ray Diffraction ◽  
Hydrogen Atoms ◽  
X Ray ◽  
Diffraction Determination

Neutron diffraction data obtained with single crystals of natrolite, Na2Al2Si3O10.2H20, have been analyzed using Fourier difference synthesis arid least squares methods. The details of the aluminosilicate framework were found to be in agreement with the results of earlier X-ray diffraction studies. The oxygen atom of the water molecule is linked by bent hydrogen bonds to two oxygen atoms in the framework, making an O—O—O angle of 134°. Lying almost in the O—O—O plane, the hydrogen atoms are located at distances of 0.94 ± 0.03 and 0.98 ± 0.02 Å from the oxygen of the water molecule and make with it an H—O—H angle of 108°. Natrolite thus provides an excellent example of the ability of the water molecule to resist the influence of the environment in opening the H—O—H angle.

The structure of chromium potassium alum

1958 ◽  
Vol 246 (1244) ◽  
pp. 78-90 ◽  
Keyword(s):  
Hydrogen Bonds ◽  
Neutron Diffraction ◽  
Water Molecule ◽  
Water Molecules ◽  
Hydrogen Atoms ◽  
Potassium Alum ◽  
X Ray ◽  
Single Crystal Study ◽  
Thermal Vibrations ◽  
Oxygen Atoms

A single-crystal study of chromium potassium alum has been made by neutron diffraction, thus completing the structure first indicated by the X-ray investigations of Lipson & Beevers (1935). Hydrogen bonds link the oxygen atoms within the water molecules to other oxygen atoms in the structure. In each case the angle HOH for a water molecule is about 106°, although this sometimes entails appreciable displacement of the hydrogen atoms from the direct O—O line. Large thermal vibrations of the oxygen atoms in the sulphate groups are noteworthy.

scholarly journals Crystal structure of ipratropium bromide monohydrate, C20H30NO3Br(H2O)

2020 ◽  
Vol 35 (1) ◽  
pp. 61-66
Author(s):  
Shivang Bhaskar ◽  
Joseph T. Golab ◽  
James A. Kaduk ◽  
Amy M. Gindhart ◽  
Thomas N. Blanton
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Water Molecule ◽  
Powder Diffraction ◽  
Density Functional ◽  
Ipratropium Bromide ◽  
Hydroxyl Group ◽  
Methyl Groups ◽  
Hydrogen Atoms ◽  
Methylene Group

The crystal structure of ipratropium bromide monohydrate has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional techniques. Ipratropium bromide monohydrate crystallizes in the space group P21/c (#14) with a = 8.21420(7) Å, b = 10.54617(13) Å, c = 24.0761(39) Å, β = 99.9063(7) °, V = 2054.574(22) Å3, and Z = 4. Both hydrogen atoms of the water molecule act as donors to the bromide cation, forming a ring with the graph set R2,4(8). The hydroxyl group also acts as a donor to Br. Several C–H⋯Br hydrogen bonds are present. The water molecule acts as an acceptor in two C–H⋯O hydrogen bonds from methyl groups. The ketone acts as an acceptor in C–H⋯O hydrogen bonds from methyl groups, a methylene group, and a methyne group. The hydroxyl group acts as an acceptor in a C–H⋯O hydrogen bond from a phenyl carbon atom. The powder pattern is included in the Powder Diffraction File™ as entry 00-066-1611.

Hydrogen positions in potassium pentaborate tetrahydrate as determined by neutron diffraction

1970 ◽  
Vol 48 (9) ◽  
pp. 1091-1097 ◽  
Author(s):  
J. P. Ashmore ◽  
H. E. Petch
Keyword(s):  
Neutron Diffraction ◽  
Water Molecule ◽  
Least Squares ◽  
Single Crystals ◽  
Diffraction Data ◽  
Hydroxyl Groups ◽  
Neutron Diffraction Data ◽  
Hydrogen Atoms ◽  
X Ray ◽  
Atomic Coordinates

Neutron diffraction data obtained with single crystals of potassium pentaborate tetrahydrate have been analyzed using least squares methods. Apart from significant differences in the atomic coordinates of the hydrogen atoms, the structure is in agreement with recent X-ray work. The O—H distances in the hydroxyl groups are 1.012 ± 0.018 and 0.955 ± 0.020 Å. In contrast to the X-ray results, the geometry of the water molecule is normal for an inorganic hydrate with O—H distances of 0.954 ± 0.026 and 1.004 ± 0.018 Å and an H—O—H angle of 108 ± 2°.

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.

Comparison of the Potency of 8-L-Arginine, 8-D-Arginine and 8-D-Homoarginine Vasopressin Analogs with Substituted Phenylalanine in Position 2

1994 ◽  
Vol 59 (6) ◽  
pp. 1439-1450 ◽  
Author(s):  
Miroslava Žertová ◽  
Jiřina Slaninová ◽  
Zdenko Procházka
Keyword(s):  
Amino Acid ◽  
Solid Phase Synthesis ◽  
Solid Phase ◽  
Basic Amino Acid ◽  
The Other ◽  
Side Chain ◽  
Inhibitory Potency ◽  
Phase Synthesis ◽  
Other Hand ◽  
Order Of Magnitude

An analysis of the uterotonic potencies of all analogs having substituted L- or D-tyrosine or -phenylalanine in position 2 and L-arginine, D-arginine or D-homoarginine in position 8 was made. The series of analogs already published was completed by the solid phase synthesis of ten new analogs having L- or D-Phe, L- or D-Phe(2-Et), L- or D-Phe(2,4,6-triMe) or D-Tyr(Me) in position 2 and either L- or D-arginine in position 8. All newly synthesized analogs were found to be uterotonic inhibitors. Deamination increases both the agonistic and antagonistic potency. In the case of phenylalanine analogs the change of configuration from L to D in position 2 enhances the uterotonic inhibition for more than 1 order of magnitude. The L to D change in position 8 enhances the inhibitory potency negligibly. Prolongation of the side chain of the D-basic amino acid in position 8 seems to decrease slightly the inhibitory potency if there is L-substituted amino acid in position 2. On the other hand there is a tendency to the increase of the inhibitory potency if there is D-substituted amino acid in position 2.

Local pseudosymmetry of the water molecule in BaBr2 · 2H2O, a neutron diffraction study

1991 ◽  
Vol 197 (3-4) ◽  
Author(s):  
Th. Kellersohn ◽  
B. Engelen ◽  
H. D. Lutz ◽  
H. Bartl ◽  
B. P. Schweiss ◽  
...  
Keyword(s):  
Neutron Diffraction ◽  
Water Molecule ◽  
Diffraction Study ◽  
Neutron Diffraction Study

AbstractBarium bromide dihydrate, BaBr

scholarly journals Amide-Type Substrates in the Synthesis of N-Protected 1-Aminomethylphosphonium Salts

Catalysts ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 552
Author(s):  
Dominika Kozicka ◽  
Paulina Zieleźny ◽  
Karol Erfurt ◽  
Jakub Adamek
Keyword(s):  
Reaction Times ◽  
The Other ◽  
Hydroxyl Group ◽  
Other Hand ◽  
Step Procedure ◽  
Higher Temperature ◽  
Short Time ◽  
Work Up

Herein we describe the development and optimization of a two-step procedure for the synthesis of N-protected 1-aminomethylphosphonium salts from imides, amides, carbamates, or lactams. Our “step-by-step” methodology involves the transformation of amide-type substrates to the corresponding hydroxymethyl derivatives, followed by the substitution of the hydroxyl group with a phosphonium moiety. The first step of the described synthesis was conducted based on well-known protocols for hydroxymethylation with formaldehyde or paraformaldehyde. In turn, the second (substitution) stage required optimization studies. In general, reactions of amide, carbamate, and lactam derivatives occurred at a temperature of 70 °C in a relatively short time (1 h). On the other hand, N-hydroxymethylimides reacted with triarylphosphonium salts at a much higher temperature (135 °C) and over longer reaction times (as much as 30 h). However, the proposed strategy is very efficient, especially when NaBr is used as a catalyst. Moreover, a simple work-up procedure involving only crystallization afforded good to excellent yields (up to 99%).

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