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2000 (2)
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1Author    Prasad Durga, B. Ojha, V.G K M Raja Rajeswari, PisipatiRequires cookie*
 Title    Molecular Ordering of a Nematic Liquid Crystal in a Dielectric Medium  
 Abstract    A computational analysis of the molecular ordering of 4-(4'-ethoxyphenylazo) phenyl hexanoate (EPPH) has ben carried out on the basis of intermolecular interaction energy calculations. The CNDO/2 method has been employed to evaluate the net atomic charge ad atomic dipole moment components at each atomic centre of the molecule. A modified Rayleigh-Schrödinger perturbation theory alongwith a 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, and cor-responding probabilities have been calculated in a dielectric medium (benzene) using the Maxwell-Boltzmann formula. Further, the flexibility of various configurations has been studied in terms of vari-ations of the probability due to departure from the most probable configuration. All possible geometri-cal arrangements between molecular pairs have been considered during stacking, in-plane and terminal interactions, and the most favourable configuration of the paring has been obtained. It has been observed that in a dielectric medium the probabilities are redistributed and there is a considerable rise in the prob-ability of interactions although the order of preference remains the same. An attempt has been made to explain the nematogenic behaviour of liquid crystals and thereby develop a molecular model for liquid crystallinity. Results have been discussed in the light of those obtained for other nematogens like EPPV [4-(4'-ethoxyphenylazo) phenyl valerate] and DPAB [4-4'-di-n-propoxy-azoxybenzene], 
  Reference    Z. Naturforsch. 55a, 929—935 (2000); received November 3 2000 
  Published    2000 
  Keywords    CNDO/2 Method, Intermolecular Interactions, Statistical Analysis, Computer Simulation 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0929.pdf 
 Identifier    ZNA-2000-55a-0929 
 Volume    55 
2Author    D. Schiel, W. Richter, G. DögeRequires cookie*
 Title    CH3F/CD3F System  
 Abstract    It has been proved with the aid of CH3F/CD3F mixtures that the remarkably large non-coincidence effect in the Raman scattering spectrum of the v 3 mode of liquid methyl fluoride is due to intermolecular vibrational coupling medi-ated mainly by transition dipole interaction. The amount of the effect and its temperature and mole fraction dependence are -at least qualitatively -in agreement with Logan's theoretical concept. The rather different behaviour of the isotopic species and the asymmetry and narrow width of the isotropic band, however, raise new questions which require further investigations. 
  Reference    Z. Naturforsch. 45a, 1381—1382 (1990); received September 26 1990 
  Published    1990 
  Keywords    Raman spectroscopy, Liquids, Intermolecular interactions, Isotopic dilution, Band shift 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-1381_n.pdf 
 Identifier    ZNA-1990-45a-1381_n 
 Volume    45 
3Author    DurgaPrasad OjhaRequires cookie*
 Title    Molecular Ordering in Liquid Crystalline EMBAC. A Quantum Mechanical Study  
 Abstract    Molecular ordering in a liquid crystal, ethyl 4-(4'-methoxybenzylidene amino) cinnamate (EMBAC) has been studied by intermolecular interaction energy calculations. The CNDO/2 method has been employed to compute the atomic charge and atomic dipole at each atomic centre. The modified Rayleigh-Schrödinger perturbation theory along with the multicentered-multipole expansion method have been employed to evaluate the long-range intermolecular interactions, while a '6-exp' potential function has been assumed for the short-range interactions. On the basis of stacking, in-plane, and terminal interac-tion energy calculations all possible geometrical arrangements of a molecular pair have been considered, and the most favourable configuration of the pair has been obtained. Molecular parameters like total ener-gy, binding energy and total dipole moment have been given. Results are discussed in the light of those obtained for the nematogens 4-(4'-ethoxyphenylazo) phenyl valerate (EPPV) and 4,4'-di-n-propoxy-azoxybenzene (DPAB). An attempt is made to explain the liquid crystalline behavior of these liquid crys-tals and thereby develop a molecular model for liquid crystallinity. 
  Reference    Z. Naturforsch. 55a, 923—928 (2000); received September 28 2000 
  Published    2000 
  Keywords    Liquid Crystal, Multicentered-multipole, CNDO/2 Method, Intermolecular Interactions, EMBAC 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0923.pdf 
 Identifier    ZNA-2000-55a-0923 
 Volume    55 
4Author    KlausP. Hofmann, Georg ZundelRequires cookie*
 Title    Effect of the Protons Arising in Aqueous Hydrolysing ATP Solutions, IR Investigations  
 Abstract    IR spectra of 0.3 m aqueous solutions of Mgo.5K3_ nH w ATP were plotted. The dependence of the spectra on the hydrolysis was investigated for three different K/H ratios of the nonhydrolysed system. Changes to bands provide information as to the protons added to the phosphate groups and base residues as a function of the initial protonation and degree of hydrolysis. More and more proton addition to the — P 0 3__ groups is observed as the initial protonation increases and as the degree of hydrolysis rises. The same applies as far as the addition of protons to the base residues is concerned to the systems with a higher initial protonation. At low degrees of hydrolysis the P 0 43' ions which occur do not bind the two hydrolysis protons completely. 150% protonated P 0 43" ions first form which cross-like via 0 H +--'0 hydrogen bonds, which only become more strongly protonated in the systems with a higher initial protonation at large degrees of hydrolysis. The 0 H +---0 bonds between the 150% protonated hydrogen phosphate ions as well as the N H +,--N hydrogen bonds between the base residues cause an IR continuum and are thus easily polarizable. An extremely large change to the hydrate structure within narrow hydrolysis ranges is indicated by changes to the bands of the water molecules. The biological relevance of these findings is briefly discussed in the conclusions. Intermolecular Interaction in Systems with Energy-Rich Phosphates, II 
  Reference    (Z. Naturforsch. 29c, 29—35 [1974]; received July 10 1973) 
  Published    1974 
  Keywords    Energy-Rich Phosphate, ATP Hydrolysis, Hydrogen Bonds Polarizable, Intermolecular Interaction, Proton Addition 
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 TEI-XML for    default:Reihe_C/29/ZNC-1974-29c-0029.pdf 
 Identifier    ZNC-1974-29c-0029 
 Volume    29