On applicability of EHT method for study of interactions of pyridinium ions with anions. Calculations of pyridine hydrochloride

1979 ◽  
Vol 44 (1) ◽  
pp. 99-109 ◽  
Author(s):  
Josef Kuthan ◽  
Stanislav Böhm ◽  
Vratislav Skála
Keyword(s):  
Ion Pair ◽  
Chloride Anion ◽  
Stabilization Energy ◽  
Mutual Orientation ◽  
Energy Minimum ◽  
Ionic Bond ◽  
Local Minima ◽  
Orbital Symmetry ◽  
Pyridine Hydrochloride ◽  
Pyridinium Cation

EHT calculations of the ion-pair I do not give, according to what is expected, the overall energy minimum corresponding to stabilization energy of ionic bond between the both partners. However, position of local minima at some energy curves corresponds to mutual orientation of pyridinium cation and chloride anion in the crystal. Orbital symmetry and interaction between the both mentioned ions are discussed.

The Stabilization Energy of the GLU-LYS Salt Bridge in the Protein/Water Environment: Correlated Quantum Chemical ab initio, DFT and Empirical Potential Studies

2008 ◽  
Vol 73 (6-7) ◽  
pp. 921-936 ◽  
Author(s):  
Jan Řezáč ◽  
Karel Berka ◽  
Dominik Horinek ◽  
Pavel Hobza ◽  
Jiří Vondrášek
Keyword(s):  
Quantum Chemical ◽  
Ion Pairs ◽  
Water Environment ◽  
Salt Bridge ◽  
Ion Pair ◽  
Stabilization Energy ◽  
Basis Set ◽  
Salt Bridges ◽  
Empirical Potential ◽  
Stabilization Energies

The stabilization energies of Glu-Lys salt bridges are calculated at the CCSD(T) complete basis set limit to provide a reasonable description of the strength of the ion-pair bond in the gas phase. The effect of the environment (protein with ε = 4 and water with ε = 80) on the stabilization energy was introduced via a modification of the quantum chemical DFT energy, for which the COSMO methodology was adopted. The other (standard) approach was based on incorporating a dielectric constant into the Coulomb electrostatic term of the Amber empirical potential function and utilizing the generalized Born model implemented in the Amber program. The environment affects the stabilization energy of the salt bridge dramatically: The protein reduces the energy to less than one half of the original value, whereas water sometimes changes stabilization to destabilization. Both theoretical procedures, based on completely different theoretical backgrounds, yield very similar results, which strongly support their validity. An ion pair is converted to an ion-neutral pair when its pH is changed. This transformation is connected with a strong reduction of the stabilization energy regardless of the environment. The substantial differences in the stabilization energies of ion pairs and ion-neutral pairs contradict the negligible changes of free energy detected experimentally. Evidently, the contribution of formation and hydration entropy is significant and compensates for the large stabilization energies.

Oligoether-Strapped Calix[4]pyrrole: An Ion-Pair Receptor Displaying Cation-Dependent Chloride Anion Transport

2012 ◽  
Vol 18 (9) ◽  
pp. 2514-2523 ◽  
Author(s):  
In-Won Park ◽  
Jaeduk Yoo ◽  
Bohyang Kim ◽  
Suman Adhikari ◽  
Sung Kuk Kim ◽  
...  
Keyword(s):  
Anion Transport ◽  
Ion Pair ◽  
Chloride Anion

scholarly journals The Effect of Substitution Pattern on Binding Ability in Regioisomeric Ion Pair Receptors Based on an Aminobenzoic Platform

Molecules ◽  
2019 ◽  
Vol 24 (16) ◽  
pp. 2990 ◽  
Author(s):  
Damian Jagleniec ◽  
Krzysztof Ziach ◽  
Kajetan Dąbrowa ◽  
Jan Romański
Keyword(s):  
1H Nmr ◽  
Ion Pairs ◽  
Ion Pair ◽  
Mutual Orientation ◽  
Substitution Pattern ◽  
X Ray ◽  
Binding Domains ◽  
Sodium Cations ◽  
Solution Studies ◽  
Intramolecular Hydrogen

A series of ditopic ion pair receptors equipped with 4-nitrophenylurea and 1-aza-18-crown-6-ether linked by ortho-(1), meta-(2), and para-(3) substituted benzoic acid were readily synthesized in three steps from commercially available materials. The binding properties of these regioisomeric receptors were determined using UV-vis and 1H NMR spectroscopy in MeCN and in the solid state by single-crystal X-ray diffraction crystallography. The solution studies revealed that, apart from carboxylates, all the anions tested formed stronger complexes in the presence of sodium cations. Receptors 2 and 3 were found to interact with ion pairs with remarkably higher affinity than ortho-substituted 1. 1H NMR titration experiments showed that both urea NH protons interacted with anions with comparable strength in the case of receptors 2 and 3, but only one of the NHs was effective in anion binding in the case of receptor 1. X-ray analysis of the crystal structure of receptor 1 and 1·NaPF6 complex showed that binding was hampered due to the formation of an intramolecular hydrogen bond. Analysis of the crystal structures of 2·NaBr and 3·NaBr complexes revealed that proper mutual orientation of binding domains was responsible for the improved binding of the sodium salts.

Role of the Small (40S) Subunits in the Structure of the Interface of Eukaryotic Ribosomes

1980 ◽  
Vol 38 ◽  
pp. 548-549
Author(s):  
M. Boublik ◽  
N. Robakis ◽  
W. Hellmann ◽  
F. Jenkins
Keyword(s):  
Structural Similarity ◽  
High Resolution Electron Microscopy ◽  
Peptide Bond ◽  
Uranyl Acetate ◽  
Mutual Orientation ◽  
Mutual Position ◽  
Peptide Bond Formation ◽  
Resolution Electron ◽  
Direct Technique ◽  
Structural Details

Ribosomes are ribonucleoprotein particles which process the genetic information coded in mRNA into protein synthesis. The analogy in function and composition of ribosomes from various sources, both prokaryotic and eukaryo-tic, imply a structural similarity. At present, high resolution electron microscopy is the most direct technique with a potential to resolve the extent of the structural homology of ribosomal particles at a macromolecular level. The structure of ribosomes is highly complex as a result of the large number of their constituents. In general, 80S eukaryotic monosomes consist of two uneven subunits - large (60S) and small (40S) - accomodating four different RNAs and approximately 80 different proteins. Mutual orientation of both subunits on the monosome is of particular interest because it determines the interface, the supposed site of interactions of ribosomes with other macro-molecules involved in peptide bond formation. Since entrapping of the contrasting solution (0.5% aqueous uranyl acetate) obscures all structural details in the interface, information on its architecture is limited to an indirect reconstruction based on the established 3-D structure of both sub-units and their mutual position after association.

National primary standard of air kerma, air kerma rate, exposure, exposure rate and energy flux for X-rays and gamma radiation GET 8-2019

2020 ◽  
pp. 8-12
Author(s):  
Alexandr V. Oborin ◽  
Anna Y. Villevalde ◽  
Sergey G. Trofimchuk
Keyword(s):  
Gamma Radiation ◽  
Energy Flux ◽  
Primary Standard ◽  
Average Energy ◽  
Ion Pair ◽  
X Rays ◽  
Exposure Rate ◽  
Ionization Chambers ◽  
Air Kerma ◽  
Air Kerma Rate

The results of development of the national primary standard of air kerma, air kerma rate, exposure, exposure rate and energy flux for X-rays and gamma radiation GET 8-2011 in 2019 are presented according to the recommendations of the ICRU Report No. 90 “Key Data for Ionizing-Radiation Dosimetry: Measurement Standards and Applications”. The following changes are made to the equations for the units determination with the standard: in the field of X-rays, new correction coefficients of the free-air ionization chambers are introduced and the relative standard uncertainty of the average energy to create an ion pair in air is changed; in the field of gamma radiation, the product of the average energy to create an ion pair in air and the electron stopping-power graphite to air ratio for the cavity ionization chambers is changed. More accurate values of the units reproduced by GET 8-2019 are obtained and new metrological characteristics of the standard are stated.

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