Influence of hydrogen bonds on charge distribution and conformation of l-arginine

It is shown that one of the main reasons for most failures of the methods for calculating distance-dependent bond strengths is related to the distortion of the coordination polyhedra. The charge distribution (CD) method which depends on only one universal empirical parameter (contraction parameter) is modified to include: (i) an iterative calculation of the effective coordination number (ECoN), to deal with structures containing very distorted coordination polyhedra; (ii) a specific contraction parameter to treat structures containing any type of hydrogen bond; (iii) scale factors for coordination subshells, to treat structures with hetero-ligand polyhedra. The contraction parameter for the hydrogen bonds was obtained from 119 well refined structures based on neutron diffraction data. Examples of the application of the iterative charge distribution (CD-IT) are presented to show the efficiency of the new method in dealing with distorted (including hydrogen bonding) and hetero-ligand polyhedra. In particular, analysis of a series of 74 structures with pentacoordinated cations shows that deviations from overall trends are related to structure instability. The possible failure of the method with polyionic structures and `dynamic' structures is discussed.

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Simple amidinium carboxylates - An MO treatment of molecular geometry and electronic structure

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19890673 ◽

1989 ◽

Vol 54 (3) ◽

pp. 673-683 ◽

Cited By ~ 11

Author(s):

Jiří Krechl ◽

Stanislav Böhm ◽

Svatava Smrčková ◽

Josef Kuthan

Keyword(s):

Electronic Structure ◽

Hydrogen Bonds ◽

Charge Distribution ◽

Chemical Treatment ◽

Quantum Chemical ◽

Geometry Optimization ◽

Molecular Geometry ◽

Chemical Data ◽

Molecular Geometry Optimization ◽

Physico Chemical

Carboxylates of amidines (I, II), substituted guanidine (III) and iso(thio)ureas (IV, V) were prepared. Nonempirical quantum chemical treatment of the electronic structure of simple compounds I-V, based on total molecular geometry optimization, their preparation and physico-chemical data are reported. Interaction between the two amidinium nitrogens and carboxylate oxygens is mediated by hydrogen bonds and alternation of charge distribution.

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Does electron density in bond critical point reflect the formal charge distribution in H-bridges? The case of charge-assisted hydrogen bonds (CAHBs)

Computational and Theoretical Chemistry ◽

10.1016/j.comptc.2011.02.021 ◽

2011 ◽

Vol 966 (1-3) ◽

pp. 113-119 ◽

Cited By ~ 24

Author(s):

Barbara Bankiewicz ◽

Marcin Palusiak

Keyword(s):

Hydrogen Bonds ◽

Critical Point ◽

Charge Distribution ◽

Electron Density ◽

Bond Critical Point ◽

Formal Charge

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Study of charge transfer in FeTi

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100075270 ◽

1983 ◽

Vol 41 ◽

pp. 296-297

Author(s):

J. Taft∅

Keyword(s):

Charge Transfer ◽

Charge Distribution ◽

Electron Scattering ◽

Periodic System ◽

Electron Distribution ◽

Scattering Amplitude ◽

Transition Elements ◽

Hartree Fock ◽

Cscl Structure ◽

The Right

It is well known that for reflections corresponding to large interplanar spacings (i.e., sin θ/λ small), the electron scattering amplitude, f, is sensitive to the ionicity and to the charge distribution around the atoms. We have used this in order to obtain information about the charge distribution in FeTi, which is a candidate for storage of hydrogen. Our goal is to study the changes in electron distribution in the presence of hydrogen, and also the ionicity of hydrogen in metals, but so far our study has been limited to pure FeTi. FeTi has the CsCl structure and thus Fe and Ti scatter with a phase difference of π into the 100-ref lections. Because Fe (Z = 26) is higher in the periodic system than Ti (Z = 22), an immediate “guess” would be that Fe has a larger scattering amplitude than Ti. However, relativistic Hartree-Fock calculations show that the opposite is the case for the 100-reflection. An explanation for this may be sought in the stronger localization of the d-electrons of the first row transition elements when moving to the right in the periodic table. The tabulated difference between fTi (100) and ffe (100) is small, however, and based on the values of the scattering amplitude for isolated atoms, the kinematical intensity of the 100-reflection is only 5.10-4 of the intensity of the 200-reflection.

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