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1Author    Amelia Thereza, Roberto Soares3, Ricardo Dias Lins3, RichardG. Longo3, Ricardo Arrattb, Ferreira3Requires cookie*
 Title    Plural Origins of Molecular Homochirality in Our Biota Part II. The Relative Stabilities of Homochiral and Mixed Oligoribotides and Peptides  
 Abstract    By computer simulations -molecular mechanics and molecular dynamics with the amber force field (Weiner et al., (1986), J. Comp. Chem. 7, 2 3 0 -2 5 2) -we have determined the stabilities of oligoribotide strands built with d -and L-riboses, and of peptide chains with d -and L-amino acid residues. In particular, complementary double-chains of oligoribotides were studied, since they are an important feature of the growing mechanism o f modern nucleic acids. Peptide chains on the other hand, grow without need of a template. We found that mixed oligoribotides are less stable than homochiral ones, and that this chiral effect is less noticeable in peptide chains. The results support the interpretation that L-riboses act as termi­ nators to the template-assisted growth of oligo-r-GD (enantiomeric cross-inhibition; Joyce et al., (1987), Proc. Natl. Acad. Sei. U S A 84, 4 398-4402). Based on this effect, a chemical pathway is proposed which could, under assumed prebiotic conditions, bypass the hindrance of homochiral growth. 
  Reference    Z. Naturforsch. 52c, 89 (1997); received July 10/September 4 1996 
  Published    1997 
  Keywords    Chirality, Peptides, Oligoribotides, Computer Simulations 
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 TEI-XML for    default:Reihe_C/52/ZNC-1997-52c-0089.pdf 
 Identifier    ZNC-1997-52c-0089 
 Volume    52 
2Author    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 
3Author    DurgaPrasad OjhaRequires cookie*
 Title    Nematogenic Behaviour of a Cyano-Compound Using Quantum Mechanics and Computer Simulations  
 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 o f 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]. 
  Reference    Z. Naturforsch. 56a, 319—325 (2001); received February 6 2000 
  Published    2001 
  Keywords    ECCPP, CNDO/2 Method, Intermolecular Forces, Computer Simulation 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0319.pdf 
 Identifier    ZNA-2001-56a-0319 
 Volume    56 
4Author    Prasad Durga, Devesh Ojha, V.G K M Kumar, PisipatiRequires cookie*
 Title    Molecular Organization in a Nematogen: PBPCN -A Computational Analysis Based on Quantum Mechanics  
 Abstract    A computational analysis has been carried out to determine the configurational preference of a pair o f 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 o f 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 o f experimental as well as other theoretical observations. 
  Reference    Z. Naturforsch. 56a, 730—734 (2001); received September 7 2001 
  Published    2001 
  Keywords    PBPCN, Nematogen, Interaction Energy, Computer Simulation 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0730.pdf 
 Identifier    ZNA-2001-56a-0730 
 Volume    56 
5Author    Prasad Durga, Devesh Ojha, V.G K M Kumar, PisipatiRequires cookie*
 Title    Smectogenic Behaviour of 70.6 at it's Phase Transition Temperature: A Computational Analysis Reprint request to  
 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 o f 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. 
  Reference    Z. Naturforsch. 56a, 873—878 (2001); received October 12 2001 
  Published    2001 
  Keywords    706, CNDO/2 Method, Quantum Chemistry, Computer Simulation 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0873.pdf 
 Identifier    ZNA-2001-56a-0873 
 Volume    56 
6Author    Reiner Memmer, Folkert JanssenRequires cookie*
 Title    Computer Simulation of Chiral Liquid Crystal Phases IX. Chiral Induction in Guest-host Systems - Calculation of the Helical Twisting Power  
 Abstract    The chiral induction in liquid crystalline phases was studied by Monte Carlo simulation of the chiral Lebwohl-Lasher model. Binary guest-host systems composed of achiral and chiral molecules as well as of different chiral molecules were investigated in dependence on the composition. A cholesteric phase was induced by dissolving a small fraction of chiral molecules in a nematic phase. For dilute solutions the equilibrium pitch was found to be a linear function of the chiral dopant concentration. Independent of system size effects the application of self-determined boundary conditions enabled the determination of the symmetry adapted quantities for the chiral induction, the helical twisting power (HTP) and the achiral helical twisting power (AHTP). Additionally, a different orientational behaviour of enantiomer-ic dopants in the chiral surroundings of a cholesteric host phase has been determined. 
  Reference    Z. Naturforsch. 54a, 747—754 (1999); received October 29 1999 
  Published    1999 
  Keywords    Chirality, Liquid Crystals, Computer Simulation, Induced Cholesteric Phases, Helical Twisting Power 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0747.pdf 
 Identifier    ZNA-1999-54a-0747 
 Volume    54 
7Author    Christian Holzapfel, Robert BauerRequires cookie*
 Title    Computer Simulation of Primary Photosynthetic Reactions — Compared with Experimental Results on 0 2-Exchange and Chlorophyll Fluorescence of Green Plants  
 Abstract    A computer model describing the "Z-scheme" of photosynthetic electron transport in terms of reduction and oxydation of coupled redox pools was built up. Starting from a certain initial state corresponding to the dark adapted state of the photosynthetic system the reduction and reoxidation levels of the pools were calculated during adaptation of the system to a steady state in the light. The changes of calculated redox levels were compared with experimental results of fluorescence and oxygen evolution induction curves. It is shown that the transients in prompt fluorescence and oxygen evolution can be described by reduction and reoxidation of the primary electron acceptor pool and the electron donor pool of photosystem II due to reduction and oxidation of the other pools during adaptation to light. The first depression D in the fluorescence induction curve is explained by the existence of a redox pool X between the primary electron acceptor pool Q of photosystem II and plastoquinone. It is shown that DCMU blocks the electron flow between Q and X. Furthermore, it is shown that the inhibitor DBMIB probably not only blocks the electron flow but also causes a successive disconnection of the plastoquinone pool from the electron transport chain. 
  Reference    (Z. Naturforsch. 30c, 489—498 [1975]; received March 3/April 18 1975) 
  Published    1975 
  Keywords    Primary Photosynthetic Electron Transport, Computer Simulation, Fluorescence Induction, Oxygen Exchange Transient 
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 TEI-XML for    default:Reihe_C/30/ZNC-1975-30c-0489.pdf 
 Identifier    ZNC-1975-30c-0489 
 Volume    30 
8Author    Christoph GierschRequires cookie*
 Title    A Kinetic Model for Translocators in the Chloroplast Envelope as an Element of Computersimulation of the Dark Reaction of Photosynthesis  
 Abstract    A kinetic model for the chloroplast translocators (mediating equal and opposite exchange fluxes between the external medium and the stroma) is derived. This model is a modification of the clas­ sical Widdas model corresponding to the exchange of an arbitrary number of compounds with no contribution to net transport. It describes the rate of transport of each compound in simple terms and with a minimum number of kinetic constants. Predictions from the model agree with ex­ perimental data as recorded in the literature. From the experimental apparent kinetic constants FmaX and K m those in terms of the model are calculated. These constants complete the model and make it applicable to the study of metabo­ lism of photosynthesis by means of computer simulation. The set of differential equations describing the operation of the phosphate translocator is solved numerically for some illustrative examples. 
  Reference    (Z. Naturforsch. 32c, 263 [1977]; received November 22 1976) 
  Published    1977 
  Keywords    Chloroplast, Phosphate Translocator, Computer Simulation, Metabolite Exchange, Kinetic Model 
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 TEI-XML for    default:Reihe_C/32/ZNC-1977-32c-0263.pdf 
 Identifier    ZNC-1977-32c-0263 
 Volume    32 
9Author    Christian HolzapfelRequires cookie*
 Title    Analysis of the Prompt Fluorescence Induction by Means of Computer Simulation of the Primary Photosynthetic Reactions  
 Abstract    The induction phenomenon of prompt fluorescence of the photosynthetic system in green plants reflects the adaptation of the electron transport system from a dark adapted state to a steady state under light condition. The appearance of the P-peak in the prompt fluorescence induction curve is explained by the decay of the electrochemical gradient across the thylakoid membrane in the dark. The decay of the electrochemical gradient in the dark is calculated using measured fluorescence induction curves with different times of dark adaptation. The influence of photophosphorylation inhibitors is discussed and the threshold effect of ATP-formation depending on the electrochemical gradient is explained by the coupling of the ATP-formation with the electron transport in the thylakoid membrane. 
  Reference    Z. Naturforsch. 33c, 402—2 (1978); received April 17 1978 
  Published    1978 
  Keywords    Primary Photosynthetic Electron Transport, Computer Simulation, Fluorescence Induction, ATP-Formation 
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 TEI-XML for    default:Reihe_C/33/ZNC-1978-33c-0402.pdf 
 Identifier    ZNC-1978-33c-0402 
 Volume    33 
10Author    N. E. Ainbinderl, G. A. Volgina, E. A. Kravchenko, A. N. Osipenko, \.A A Gippius, SuanHai Fam, A. A. Bush3Requires cookie*
 Title    209Bi N Q R Powder Spectra Influenced by Local and Applied Magnetic Fields  
 Abstract    Several experimental techniques have shown evidence for the existence of internal magnetic fields of the order of 200 G in oc-Bi20 3 [1]. The asymmetrical 209Bi N Q R lineshapes in Bi30 4Br also point to a source of poorly resolved splitting present in this compound. In order to obtain further insight into the origin of the local magnetic fields in these compounds the 209Bi N Q R lineshapes of polycrystalline a-Bi20 3 and Bi30 4Br were recorded in weak (below 500 G) static magnetic fields. A calculation of the expected powder lineshapes in a-Bi20 3 under the influence of the internal and applied magnetic fields up to 1 kG was made. The results of the computer simulation are compared with the lineshapes recorded. From the 209Bi lineshapes ob­ served in the experiment, the local magnetic field at one of the two Bi-sites in Bi30 4Br was estimated. 
  Reference    Z. Naturforsch. 49a, 425—432 (1994); received December 15 1993 
  Published    1994 
  Keywords    209Bi N Q R, Internal magnetic field, Lineshape, Applied magnetic field, Computer simulation 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0425.pdf 
 Identifier    ZNA-1994-49a-0425 
 Volume    49 
11Author    E. A. Kravchenko, V. G. Orlov, SuanHai Fam, YuF. KarginRequires cookie*
 Title    Bi NQR and Magnetic Properties of Bismuth Oxide-Based Compounds  
 Abstract    The NQR line shapes of 209 Bi in the a-Bi 2 0 3 -based mixed oxides Bi 2 0 3 • 2M 2 0 3 (M = Al, Ga). Bi 2 0 3 • 3Ge0 2 , and 2Bi 2 0 3 • 3Ge0 2 are recorded in zero and weak magnetic fields (// ext < 500 Oe) and compared with the results of computer simulation. Splittings and line shape asymmetry, exhibited by the resonances, suggest that internal magnetic fields, similar to those earlier reported for a-Bi 2 0 3 and Bi 3 0 4 Br, may exist in these compounds. In the spectra of single crystal Bi 4 Ge 3 0 12 , the line multiplicity in external magnetic fields is higher than simulated, which might results from domains in the crystal. In external magnetic fields a notable increase in the line intensity was observed, the effect depend-ing on the mutual orientation of the EFG axes and the fields perturbing the nuclear spin system. 
  Reference    Z. Naturforsch. 53a, 504—513 (1998); received January 26 1998 
  Published    1998 
  Keywords    209 Bi NQR, Internal Magnetic Field, Line Shape, Applied Magnetic Field, Computer Simulation 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0504.pdf 
 Identifier    ZNA-1998-53a-0504 
 Volume    53 
12Author    AshokK. Adya, Ryuzo Takagi, Marcelle Gaune-EscardRequires cookie*
 Title    Unravelling the Internal Complexities of Molten Salts  
 Abstract    Much experimental and theoretical effort has gone into revealing the internal complexities of molten salts for the past two decades. In this paper we shall show how neutron diffraction and computer sim-ulation techniques have helped in gaining a better understanding of these systems at the microscopic level. Firstly, a short review on the structure of molten halide systems as revealed by these techniques will be presented. Complementarity of using X-rays with neutrons and, some recent results on the struc-ture of molten DyCl 3 obtained by combining neutron and X-ray diffraction with molecular dynamic simulations will be discussed. Neutron diffraction isotopic substitution techniques have played an im-portant role in elucidating the interatomic structure of a diversity of molten salts. Pair distribution func-tions (PDFs), determined for a number of 1:1 and 2 :1 halide melts, provided theorists with a critical test of their model potentials. It is now clear that for 1:1 molten systems theoretical models based on Fumi-Tosi potentials can adequately describe many of the structural features. Nevertheless, the chal-lenge is two fold: (i) to determine real interatomic potentials for 2:1 and 3 :1 molten systems capable of reproducing not only the microscopic structural details obtained at the partial PDF, g a ß (r) level, but also their macroscopic behaviour and, (ii) to characterise the structure in binary molten salt mixtures. 
  Reference    Z. Naturforsch. 53a, 1037—1048 (1998); received November 18 1998 
  Published    1998 
  Keywords    Molten Salts, Structure, Neutron and X-ray Diffraction, Computer Simulations, Liquid State Structural Theory, Molten Halides 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-1037.pdf 
 Identifier    ZNA-1998-53a-1037 
 Volume    53