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Int. J. Mol. Sci., Volume 3, Issue 2 (February 2002) – 4 articles , Pages 56-113

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172 KiB  
Article
Theoretical Calculation of Absolute Radii of Atoms and Ions. Part 1. The Atomic Radii
by Dulal C. Ghosh and Raka Biswas
Int. J. Mol. Sci. 2002, 3(2), 87-113; https://doi.org/10.3390/i3020087 - 28 Feb 2002
Cited by 176 | Viewed by 28977
Abstract
A set of theoretical atomic radii corresponding to the principal maximum in the radial distribution function, 4πr2R2 for the outermost orbital has been calculated for the ground state of 103 elements of the periodic table using Slater orbitals. The set [...] Read more.
A set of theoretical atomic radii corresponding to the principal maximum in the radial distribution function, 4πr2R2 for the outermost orbital has been calculated for the ground state of 103 elements of the periodic table using Slater orbitals. The set of theoretical radii are found to reproduce the periodic law and the Lother Meyer’s atomic volume curve and reproduce the expected vertical and horizontal trend of variation in atomic size in the periodic table. The d-block and f-block contractions are distinct in the calculated sizes. The computed sizes qualitatively correlate with the absolute size dependent properties like ionization potentials and electronegativity of elements. The radii are used to calculate a number of size dependent periodic physical properties of isolated atoms viz., the diamagnetic part of the atomic susceptibility, atomic polarizability and the chemical hardness. The calculated global hardness and atomic polarizability of a number of atoms are found to be close to the available experimental values and the profiles of the physical properties computed in terms of the theoretical atomic radii exhibit their inherent periodicity. A simple method of computing the absolute size of atoms has been explored and a large body of known material has been brought together to reveal how many different properties correlate with atomic size. Full article
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109 KiB  
Article
Conservation Equations for Chemical Elements in Fluids with Chemical Reactions
by E. Piña and S.M.T. De la Selva
Int. J. Mol. Sci. 2002, 3(2), 76-86; https://doi.org/10.3390/i3020076 - 28 Feb 2002
Viewed by 10518
Abstract
It is well known that when chemical reactions occur, the masses of the participating molecules are not conserved, whereas the masses of the nuclei of the chemical elements constituting these same molecules, are conserved. Within the context of non-equilibrium thermodynamics, the first fact [...] Read more.
It is well known that when chemical reactions occur, the masses of the participating molecules are not conserved, whereas the masses of the nuclei of the chemical elements constituting these same molecules, are conserved. Within the context of non-equilibrium thermodynamics, the first fact is expressed by the differential balance equations, for the densities of the chemically reacting molecules, having a non zero source term. At the same time the conserved quantities like the total mass, charge and energy obey differential conservation equations, i.e with zero source term. In this paper, we show that in fluids with chemical reactions occurring in them, there are additional conserved quantities, namely densities associated to the fact that the masses of the chemical elements are conserved. The corresponding differential conservation equations are derived. The found out conserved densities, one for each involved chemical element are shown to be linear combinations of the densities of those reacting molecules containing the element, weighted with the number of atoms of the element in the species. It is shown that in order to find the conserved densities, it is not necessary to know explicitly the reactions taking place. Some examples are provided. Full article
108 KiB  
Article
Dynamical Effects in the Optical Response of Carbon Chains
by T. Berkus, P.-G. Reinhard and E. Suraud
Int. J. Mol. Sci. 2002, 3(2), 69-75; https://doi.org/10.3390/i3020069 - 28 Feb 2002
Cited by 6 | Viewed by 9141
Abstract
We discuss the optical response of small carbon chains from the linear to the non linear domain in the framework of Time Dependent Local Density Approximation. We show that even for moderate ionizations, corresponding to a moderately intense excitation, the optical response exhibits [...] Read more.
We discuss the optical response of small carbon chains from the linear to the non linear domain in the framework of Time Dependent Local Density Approximation. We show that even for moderate ionizations, corresponding to a moderately intense excitation, the optical response exhibits significant alteration with respect to the truly linear domain response. This reflects non trivial dynamical effects at the level of electrons. Full article
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129 KiB  
Article
Three-Dimensional Common-Feature Hypotheses for Octopamine Agonist 1-Arylimidazolidine-2-Thiones
by Akinori Hirashima, Masako Morimoto, Hiroto Ohta, Eiichi Kuwano, Eiji Taniguchi and Morifusa Eto
Int. J. Mol. Sci. 2002, 3(2), 56-68; https://doi.org/10.3390/i3020056 - 28 Feb 2002
Cited by 12 | Viewed by 6846
Abstract
Three-dimensional pharmacophore hypotheses were built from a set of 10 octopamine (OA) agonist 1-arylimidazole-2(3H)-thiones (AIHTs) and 1-arylimidazolidine-2-thiones (AITs). Among the ten common-featured models generated by program Catalyst/HipHop, a hypothesis including a hydrophobic aromatic (HpAr), three hydrophobic aliphatic (HpAl) and a hydrogen-bond acceptor lipid [...] Read more.
Three-dimensional pharmacophore hypotheses were built from a set of 10 octopamine (OA) agonist 1-arylimidazole-2(3H)-thiones (AIHTs) and 1-arylimidazolidine-2-thiones (AITs). Among the ten common-featured models generated by program Catalyst/HipHop, a hypothesis including a hydrophobic aromatic (HpAr), three hydrophobic aliphatic (HpAl) and a hydrogen-bond acceptor lipid (HBAl) features was considered to be important in evaluating the OA-agonist activity. Active OA agonist 2,6-Et2 AIT mapped well onto all the HpAr, HpAl and HBAl features of the hypothesis. On the other hand, inactive compound 2,6-Et2 AIHT was shown to be difficult to achieve the energetically favorable conformation which is found in the active molecules in order to fit the 3D common-feature pharmacophore models. The present studies on OA agonists demonstrate that an HpAr, three HpAls and an HBAl sites located on the molecule seem to be essential for OA-agonist activity. Full article
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