Smectogenic Behaviour of 7O.6 at it's Phase Transition Temperature: A Computational Analysis Reprint request to

2001 ◽  
Vol 56 (12) ◽  
pp. 873-878
Author(s):  
Durga Prasad Ojha ◽  
Devesh Kumar ◽  
V. G. K. M. Pisipati
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Perturbation Method ◽  
Phase Transition Temperature ◽  
Computational Analysis ◽  
Atomic Charge ◽  
Configurational Energy ◽  
Schrödinger Perturbation ◽  
Atomic Centre

Abstract A computational analysis has been carried out to determine the configurational preference of a pair of Ar-(4-n-heptyloxybenzylidine)-4-hexylaniline (70.6) molecules with respect to translatory and orien­ tational motions. The CNDO/2 method has been employed to evaluate the net atomic charge and atom ic dipole components at each atomic centre of the molecule. The configurational energy has been com­ puted using the modified Rayleigh-Schrödinger perturbation method. The obtained energies were used to calculate the probability of each configuration at phase transition temperature, using Maxwell-Boltz-mann's formula. The flexibility of various configurations has been studied in terms of variations of the probability due to small departures from the most probable configuration. The results are discussed in the light of experimental as well as other theoretical observations. The smectogenic character of the molecule has been correlated with the parameters introduced in this paper.

Nematic Behaviour of a Compound EBBA – A Compuational Analysis

2002 ◽  
Vol 57 (12) ◽  
pp. 977-981 ◽  
Author(s):  
V. G. K. M. Pisipati ◽  
Durga Prasad Ojha
Keyword(s):  
Perturbation Method ◽  
Computational Analysis ◽  
Atomic Charge ◽  
Interaction Energies ◽  
Configurational Energy ◽  
Molecular Pair ◽  
Atomic Dipole ◽  
Schrödinger Perturbation ◽  
Atomic Centre ◽  
Theoretical Results

EBBAA computational analysis has been carried out to determine the configurational preferences of a pair of p-ethoxybenzylidine-p-n-butylaniline () molecules with respect to translatory and orientational motions. The CNDO/2 method has been employed to evaluate the net atomic charge and atomic dipole components at each atomic centre of the molecule. The configurational energy has been computed using the Rayleigh-Schrödinger perturbation method. The interaction energies obtained through these computations were used to calculate the probability of each configuration at 300 K. The energy of a molecular pair during stacking, in-plane, and terminal interaction has been calculated. The results are discussed in the light of other experimental and theoretical results.

Role of Dielectric Medium on a Nematogen. A Statistical Approach Based on Quantum Mechanics and Computer Aided Modelling

2002 ◽  
Vol 57 (8) ◽  
pp. 645-649
Author(s):  
Durga Prasad Ojha ◽  
V. G. K. M. Pisipati
Keyword(s):  
Molecular Model ◽  
Atomic Charge ◽  
Dielectric Medium ◽  
Liquid Crystallinity ◽  
Configurational Energy ◽  
Atomic Dipole ◽  
Total Interaction ◽  
Schrödinger Perturbation ◽  
Atomic Centre

ECCPA statistical analysis has been carried out to determine the configurational preferences of a pair of 5-(4-ethylcyclohexyl)-2-(4-cyanophenyl) pyrimidine () molecules. The CNDO/2 method has been employed to evaluate the net atomic charge and atomic dipole components at each atomic centre of the molecule. The configurational energy has been computed using the Rayleigh-Schrödinger perturbation theory. The total interaction energies obtained by these computations were used to calculate the probability of each configuration in vacuum and in a dielectric medium (benzene) at the phase transition temperature using the Maxwell-Boltzmann formula. On the basis of stacking, in-plane and terminal interaction energy calculations, all possible geometrical arrangements of the molecular pair have been considered. An attempt has been made to explain the nematogenic behavior of liquid crystals and thereby develop a molecular model for liquid crystallinity.

ORDERING IN HIGHER HOMOLOGOUS SERIES OF nBAC — A COMPARATIVE COMPUTATIONAL ANALYSIS

2005 ◽  
Vol 04 (04) ◽  
pp. 1015-1028 ◽  
Author(s):  
DURGA PRASAD OJHA
Keyword(s):  
Dipole Moment ◽  
Transition Temperature ◽  
Homologous Series ◽  
Computational Analysis ◽  
Atomic Charge ◽  
Expansion Method ◽  
Multipole Expansion ◽  
Intermolecular Forces ◽  
Multipole Expansion Method ◽  
Schrödinger Perturbation

A Comparative computational analysis of ordering in higher homologous series of p-n-alkylbenzoic acids (nBAC), having 7(7BAC); 8(8BAC) and 9(9BAC) carbon atoms in the alkyl chain, has been carried out based on quantum mechanics and intermolecular forces. The evaluation of atomic charge and dipole moment at each atomic centre has been carried out through an all-valence electron (CNDO/2) method. The modified Rayleigh-Schrodinger perturbation theory, along with multicentered-multipole expansion method, has been employed to evaluate long-range intermolecular interactions, while a "6-exp" potential function has been assumed for short-range interactions. The total interaction energy values obtained through these computations were used to calculate the probability of each configuration at room temperature, nematic-isotropic transition temperature and above transition temperature using the Maxwell-Boltzmann formula. A comparative picture of molecular parameters such as total energy, binding energy and total dipole moment has been given. A model has been developed to describe the nematogenicity of these acids in terms of their relative order with molecular parameter introduced in this paper.

scholarly journals Molecular Organization in a Nematogen: PBPCN -A Computational Analysis Based on Quantum Mechanics

2001 ◽  
Vol 56 (11) ◽  
pp. 730-734
Author(s):  
Durga Prasad Ojha ◽  
Devesh Kumar ◽  
V. G. K. M. Pisipati
Keyword(s):  
Computational Analysis ◽  
Atomic Charge ◽  
Expansion Method ◽  
Multipole Expansion ◽  
The Other ◽  
Molecular Organization ◽  
Multipole Expansion Method ◽  
Atomic Dipole ◽  
Schrödinger Perturbation ◽  
Atomic Centre

Abstract A computational analysis has been carried out to determine the configurational preference of a pair of 4'-n-pentyloxy-4-biphenylcarbonitrile (PBPCN) molecules with respect to translatory and orientational motions. The CNDO/2 method has been employed to evaluate the net atomic charge and atomic dipole components at each atomic centre of the molecule. Modified Rayleigh-Schrödinger perturbation theory along with multicentered-multipole expansion method has been employed to evaluate long-range intermolecular interactions, while a '6-exp' potential function has been assumed for short-range interactions. On the basis of stacking, in-plane and terminal interaction energy calculations, all possible geometrical arrangements of molecular pair have been considered. It has been observed that the molecule has a strong preference for stacking through a particular face, while the other configurations, such as stacking through the other face, in-plane and terminal interactions show, in general, an aligned structure along molecular axis. The results are discussed in the light of experimental as well as other theoretical observations.

Nematogenic Behaviour of a Cyano-Compound Using Quantum Mechanics and Computer Simulations

2001 ◽  
Vol 56 (3-4) ◽  
pp. 319-325 ◽  
Author(s):  
Durga Prasad Ojha
Keyword(s):  
Quantum Mechanics ◽  
Perturbation Method ◽  
Computer Simulations ◽  
Atomic Charge ◽  
Intermolecular Forces ◽  
Relative Order ◽  
Configuration Energy ◽  
Molecular Ordering ◽  
Schrödinger Perturbation ◽  
Atomic Centre

Abstract Using quantum mechanics and intermolecular forces, the molecular ordering of a nematogenic cya-no-compound, 5-(frans-4-ethylcyclohexyl)-2-(4-cyanophenyl)-pyrimidine (ECCPP), has been exam­ ined. The CNDO/2 method has been employed to evaluate the net atomic charge and the dipole mo­ ment components at each atomic centre of the molecule. The configuration energy has been computed using the modified Rayleigh-Schrödinger perturbation method at intervals of 1Ä in translation and 10P in rotations, and corresponding probabilities have been calculated using Maxwell-Boltzmann statistics. The flexibility of various configurations has been studied in terms of the variation of the probability due to small departures from the most probable configuration. All possible geometrical arrangements between a molecular pair have been considered during stacking, in-plane and terminal interactions, and the most favourable configuration of pairing has been obtained. An attempt has been made to under­ stand the behaviour of the molecules in terms of their relative order. The results have been compared with those obtained for other nematogens like DPAB [4,4'-di-n-propoxy-azoxybenzene] and EMBAC [ethyl 4-(4'-methoxybenzylidene amino) cinnamate].

ORDERING OF A THERMOTROPIC MESOGEN AT PHASE TRANSITION TEMPERATURE — A STATISTICAL APPROACH BASED ON QUANTUM MECHANICS

2005 ◽  
Vol 04 (03) ◽  
pp. 803-810 ◽  
Author(s):  
DURGA PRASAD OJHA
Keyword(s):  
Phase Transition ◽  
Quantum Mechanics ◽  
Transition Temperature ◽  
Phase Transition Temperature ◽  
Intermolecular Forces ◽  
Dielectric Medium ◽  
Theoretical Support ◽  
Molecular Ordering ◽  
Complete Neglect ◽  
Schrödinger Perturbation

The molecular ordering of a thermotropic mesogen, 4-alkenyl bicyclohexylnitrile (ALKBCHN), has been carried out on the basis of quantum mechanics and intermolecular forces. The evaluation of atomic charges and dipole moment at each atomic centre has been done through the Complete Neglect Differential Overlap (CNDO/2) method. The configurational energy has been computed using the Rayleigh-Schrodinger perturbation method. The total interaction energy values obtained through these computations were used to calculate the probability of each configuration in a dielectric medium (i.e. non-interacting and non-mesogenic solvent, benzene) at phase transition temperature (364.7 K) using the Maxwell–Boltzmann formula. It has been observed that in dielectric medium the energies/probabilities are redistributed and there is a considerable rise in the probability of interactions, although the order of preference remains the same. An attempt has been made to develop a new and interesting model of mesogen in a dielectric medium. The present article offers a theoretical support to the experimental observations.

The structure of membranes and membrane proteins embedded in amorphous ice

1992 ◽  
Vol 50 (1) ◽  
pp. 432-433
Author(s):  
Uwe Lücken ◽  
Joachim Jäger
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Membrane Proteins ◽  
Phase Transition Temperature ◽  
Lipid Vesicles ◽  
Freezing Stress ◽  
Amorphous Ice ◽  
Different Temperatures ◽  
Band Pass ◽  
Lipid Polymorphism

TEM imaging of frozen-hydrated lipid vesicles has been done by several groups Thermotrophic and lyotrophic polymorphism has been reported. By using image processing, computer simulation and tilt experiments, we tried to learn about the influence of freezing-stress and defocus artifacts on the lipid polymorphism and fine structure of the bilayer profile. We show integrated membrane proteins do modulate the bilayer structure and the morphology of the vesicles.Phase transitions of DMPC vesicles were visualized after freezing under equilibrium conditions at different temperatures in a controlled-environment vitrification system. Below the main phase transition temperature of 24°C (Fig. 1), vesicles show a facetted appearance due to the quasicrystalline areas. A gradual increase in temperature leads to melting processes with different morphology in the bilayer profile. Far above the phase transition temperature the bilayer profile is still present. In the band-pass-filtered images (Fig. 2) no significant change in the width of the bilayer profile is visible.

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