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'Molecular dynamics' in keywords Facet   Publication Year 1998  [X]
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Publication Year
1998[X]
1Author    Lucia Calucci, Claudia Forte, Marco Geppi, CarloAlberto VeraciniRequires cookie*
 Title    Dynamics of Liquid Crystals by Means of 2 H-NMR: a Comparison between 4,4'-bis(hexyloxy)azoxybenzene and the Derivative Pd(II) Complex AZPAC  
 Abstract    In the present work we report a molecular dynamics investigation of the two mesogens 4,4'-bis(hexyloxy)azoxybenzene (HL) and its Pd(II) acetylacetonate derivative Azpac in their nematic phases. Deuterium Zeeman and quadrupolar spin-lattice relaxation times have been measured at 46.04 MHz on two isotopomers of Azpac (Azpac-d 4 and Azpac-c/ 26 > deuteriated on the aromatic core and on the alkoxy chains, respectively) and on HL-d 4 , an isotopomer of HL partially deuteri-ated on the aromatic core, by means of the Wimperis pulse sequence. The spectral densities obtained from the measured relaxation times are discussed in terms of internal and overall molecular motions. A small step rotational diffusion model for the overall molecular motions, superimposed on a free rotational model for internal motions, allowed diffusion coefficients for molecular spinning and tumbling and for phenyl ring rotations to be derived for HL; the same models were used in describing the dynamics of Azpac. 
  Reference    Z. Naturforsch. 53a, 427—435 (1998); received October 31 1997 
  Published    1998 
  Keywords    Liquid Crystals, Deuterium Relaxation, Molecular Dynamics, Metallomesogens, NMR 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0427.pdf 
 Identifier    ZNA-1998-53a-0427 
 Volume    53 
2Author    Martin Jäger1, Paul Schuler1, HartmutB. Stegmann, Antal RockenbauerbRequires cookie*
 Title    Molecular Recognition Analyzed by Observing Intramolecular Interconversion with E PR Spectroscopy  
 Abstract    Molecular recognition between Rebek's cleft R and 4-(2-benzimidazolyl)-aminomethyl-2,6-di-rm-butyl-phenol (Bi) is investigated by means of EPR spectroscopy. Their specific inter-molecular interactions are distinguished from non-specific interactions represented by mere protonation on addition of benzoic acid. Both interactions are related to intramolecular in­ terconversions at the CQ-atom of Bi*, where a two-jump mechanism is found for free and protonated Bi* and a two-site exchange for the complexed ligand. While NMR spectroscopy indicates the existence of 1:1 and 1:2 receptor-substrate complexes, the faster time scale of EPR spectroscopy allows to identify one 1 : 2 as well as three 1 : 1 associates and to elucidate their formation conditions. Based upon the corresponding hf parameters, binding modes and sites are proposed for the key-in-the-lock system. 
  Reference    Z. Naturforsch. 53b, 1511—1519 (1998); received July 22 1998 
  Published    1998 
  Keywords    Rock-Key-Equilibria, Spin Labeling, Molecular Dynamics 
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 TEI-XML for    default:Reihe_B/53/ZNB-1998-53b-1511.pdf 
 Identifier    ZNB-1998-53b-1511 
 Volume    53 
3Author    C. Cruz, P. J. Sebastião, J. Figueirinhas, A. C. Ribeiro, H. T. Nguyen, C. Destrade, F. NoackRequires cookie*
 Title    NMR Study of Molecular Dynamics in a D ho Columnar Mesophase  
 Abstract    In this paper we report the first molecular dynamics study combining fast field-cycling and conven-tional NMR techniques in a thermotropic liquid crystal of discotic molecules exhibiting an ordered columnar hexagonal mesophase. Using the association of these techniques we obtained proton T { data over a very large domain of Larmor frequencies (u/2n from 500 Hz to 85 MHz). The proton spin-lattice relaxation results were analysed considering the structure of the mesophase and the types of movements which are expected to influence significantly the relaxation rate, namely local molecu-lar rotational reorientations, inter-columnar self-diffusion and collective movements corresponding to bending and compression of the columns. We verified that these mechanisms dominate the relaxation respectively for high, medium and low Larmor frequencies. 
  Reference    Z. Naturforsch. 53a, 823—827 (1998); received July 16 1998 
  Published    1998 
  Keywords    NMR, Proton Relaxation, Molecular Dynamics, Columnar Hexagonal Mesophases (D ho ), Discotic Molecules 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0823.pdf 
 Identifier    ZNA-1998-53a-0823 
 Volume    53 
4Author    IgorZbigniew ZubrzyckiRequires cookie*
 Title    Conformational Studies of the Emp-AKH Peptide Using Molecular and Langevin Dynamics Methods  
 Abstract    The secondary structure of the member of the A K H/RPCH family has been studied by Molecular Dynamics and Langevin Dynamics methods. Molecular dynamics simulation were performed in vacuum, m odel aqueous solution and simulated membrane. Langevin dynamics simulation was performed using the friction factor y equal to 2 ps_1. Molecular dynamics as well as Langevin Dynam ics simulation were conducted at 300 K. All minimum energy con-formers have similar backbone structure characterised by the turn consisted out of 3 amino acids, Thr, Pro and A sn7. Structures obtained from Molecular Dynamics simulation are char­ acterised by the lack o f hydrogen bonds whereas the structure obtained form Langevin D y­ namics simulation is stabilised by the web of hydrogen bonds. 
  Reference    Z. Naturforsch. 53c, 857 (1998); received April 29/June 12 1998 
  Published    1998 
  Keywords    Molecular Dynamics, Langevin Dynamics, Adipokinetic Hormones, Em p-AKH, 3D-Structure 
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 TEI-XML for    default:Reihe_C/53/ZNC-1998-53c-0857.pdf 
 Identifier    ZNC-1998-53c-0857 
 Volume    53