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  • 1
    Digitale Medien
    Digitale Medien
    Influence of substituents on the reorientational motion of 9-anthracene derivatives studied by depolarized light scattering and fluorescence anisotropy decay (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 813-819 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The influence of substituents on the reorientational motion of 9-anthroates is studied by depolarized light scattering (DLS) and fluorescence anisotropy decay (FAD). We investigate the dependence of the reorientational relaxation times on the length of flexible chains of 9-alkylanthroates and on the size of rigid substituents such as t-butyl, cyclohexyl, and adamantyl. Temperature-dependent measurements are performed in CCl4 and paraffin, respectively, with the two methods, which monitor the reorientation of different axes. Our results are discussed taking into consideration models for alkyl chain dynamics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.461087
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  • 2
    Digitale Medien
    Digitale Medien
    Reorientational motion of diphenylpolyenes in simple solvents as studied by depolarized light scattering and fluorescence anisotropy decay (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 6008-6017 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The reorientational motion of diphenylpolyenes and related molecules in simple solvents is studied by depolarized light scattering and fluorescence anisotropy decay. The viscosity dependence of the reorientational correlation times obtained by the two techniques shows remarkable differences, although the Stokes–Einstein–Debye equation applies to all data. The light scattering results are consistent with hydrodynamic models and slip boundary conditions. The reorientation about an axis perpendicular to the long molecular axis is monitored. With the fluorescence anisotropy decay measurements of the diphenylpolyenes on the other hand, a much smaller viscosity dependence is found. The influence of photophysical processes in the excited state on the fluorescence depolarization is discussed and it is shown that the fluorescence anisotropy measurements are sensitive to reorientation about a perpendicular axis as well as about the long molecular axis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.456366
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  • 3
    Digitale Medien
    Digitale Medien
    Molecular dynamics simulations of the depolarized light scattering spectra of liquid OCS in comparison with experiment and simulations of CO2 and CS2 (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 6318-6330 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Molecular dynamics computer simulation was used to study depolarized light scattering in liquid OCS at temperatures of 170, 243, and 298 K. Applying the first-order dipole-induced dipole model for the interaction-induced polarizabilities, the time correlation functions and spectral line shapes corresponding to the depolarized Rayleigh and nonvibrational contributions to the symmetric stretch (ν1) mode Raman spectra were calculated. The results were compared with experimental findings and simulations on the liquids CO2 and CS2. We find that the OCS simulations reflect the main spectral features in satisfactory agreement with experiment and that an intermediate position concerning all the studied particularities is assigned to liquid OCS between CO2 and CS2. For these three liquids the difference correlation functions between Rayleigh and Raman light scattering were computed and discussed in terms of their component many-body contributions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.467094
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  • 4
    Digitale Medien
    Digitale Medien
    Line shape analysis of the depolarized Rayleigh spectra of CS2/PS mixtures (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 9370-9376 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Mixtures of carbon disulfide and polystyrene with the composition 0, 5%, 20%, 40%, 60%, 80%, 100% by weight of CS2 have been studied using depolarized Rayleigh scattering experiments within the temperature range of 263–313 K. The spectral ranges between 20 and 150 cm−1 were described in the reduced representation by the 3-parameter-Mori-function, indicating that most of the spectral features depend more on the CS2 compound than on the polymer matrix. The concept of analyzing the line shapes of liquid systems by separating the logarithmic spectrum into various distinct regions with characteristic slope parameters was successfully applied to the CS2/polystyrene mixtures and indicates the existence of liquid CS2 microstructures in the mixtures and the applicability of the dipole-induced dipole mechanism to the investigated system. © 1994 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.467967
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  • 5
    Digitale Medien
    Digitale Medien
    Rotational diffusion in polyacrylamide gels as a function of solvent quality (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 11052-11059 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We have investigated the rotational motion of the dianion polyphenyl 2 (PP2) in polyacrylamide (PAA) gels by fluorescence anisotropy decay. A comparison of the dynamics of the probe molecule in various solvent mixtures of water–glycerol and water–methanol in solution as well as in the presence of the polymer matrix revealed a significant retardation of the reorientation with increasing PAA concentration. Having excluded specific interactions of PP2 with the gel matrix, we suggest that a modification of the solvent viscosity in the presence of the polymer is responsible for the alteration of the probe dynamics. The effect is strongly dependent on the solvent quality for the polymer component, i.e., more distinct under good solvent conditions (in pure water) than in a poor solvent (increasing glycerol content). Changing the crosslinker concentration from 0% to 4% we obtained fluid-like solutions as well as viscoelastic gels. However, the reorientational motion of PP2 was independent of the macroscopic constitution of the samples which means that on a microscopic scale the local environment for the probe molecule that determines its dynamics appears similar. © 1994 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.468480
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  • 6
    Digitale Medien
    Digitale Medien
    Rotational motion of charged molecules in aqueous solutions. A change in the diffusion mechanism (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 11044-11051 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The rotational motion of the anions polyphenyl 2 (PP2) and pyrene tetrasulfonate (PTS) was studied as a function of the solvent viscosity by time-resolved fluorescence depolarization spectroscopy using the single photon counting technique. The viscosity was varied by changing the temperature and the composition of the water–glycerol mixtures, respectively. At low viscosity the reorientational behavior of PP2 and PTS is well described by the Stokes–Einstein–Debye (SED) equation under stick boundary conditions. With increasing viscosity (η≥25 cP) however the rotational motion did no longer follow the SED predictions. Instead, we observed a much faster relaxation time, approaching an asymptotic value at very high viscosities. It seems that in the high viscosity regime microscopic collisional effects rather than the macroscopic hydrodynamic drag of the solvent determines the reorientational dynamics of the solute molecules. © 1994 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.467856
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  • 7
    Digitale Medien
    Digitale Medien
    Normal mode dynamics in simple liquids (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 1912-1919 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A dynamical generalization of the instantaneous normal mode (INM) theory of liquid state dynamics is presented. Due to anharmonicities the eigenvalues and eigenvectors of the Hessian matrix change with time. Therefore, regular INM theory gives a description of molecular dynamics valid only for short times. Starting out from the classical equations of motion the velocity correlation function is expressed in terms of a series of propagation matrices. These are calculated by diagonalizing the Hessian matrix at configurations equidistant in time along a short piece of trajectory. Correlation functions calculated by this normal mode propagation (NMP) for a representative selection of atomic systems agree quantitatively with results from molecular-dynamics simulation. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.476768
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  • 8
    Digitale Medien
    Digitale Medien
    Effect of pressure and temperature on the dynamics of bulk polyethylacrylate and polyethylmethacrylate polymers studied by photon correlation spectroscopy (1982)
    Springer
    Colloid & polymer science 260 (1982), S. 949-955 
    Details
    ISSN: 1435-1536
    Schlagwort(e): Light scattering ; high pressure ; α-relaxation ; β-relaxation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract Photon correlation spectroscopy has been used to study relaxation processes in bulk polymers: PEA and PEMA, above the glass transition temperature under high pressure. In the case of PEA one relaxation process was observed over the whole pressure range of 1–2000 bar. This process is assigned to the localized backbone motion of the polymer chain. In PEMA two overlaping relaxation modes have been found. Quantitative characterization of these two modes was possible after their separation in the time domain, which was achieved by applying high pressure to the sample. It was found that an additionalα-methyl group in PEMA (in comparison with PEA) causes an appearance of an additional relaxation mode which can be assigned to the side group motion. Moreover, the localized backbone motion in PEMA is more cooperative because of a hindrance effect due to the presence of the additionalα-methyl side group. The obtained results are in a good agreement with the previous dielectric relaxations studies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01413129
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  • 9
    Digitale Medien
    Digitale Medien
    Size and shape parameter of the actin-binding protein profilin in solution: A depolarized and polarized dynamic light scattering study (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 219-222 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.360300123
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  • 10
    Digitale Medien
    Digitale Medien
    Internal dynamics of tRNAPhe studied by depolarized dynamic light scattering (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 975-983 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The collective internal dynamics of transfer RNAphe from brewer's yeast in solution was studied by depolarized dynamic light scattering (DDLS). Within the melting region of tRNA the depolarized spectra consist of two Lorentzian, where the narrow (slow) component describes the overall rotation of the macromolecule. The broad component is attributed to the collective reorientation of the bases within the biopolymer. At high temperature only this relaxation process is observed in the spectrum. The viscosity dependence of the collective internal relaxation process is described by the Stokes-Einstein-Debye equation for rotational diffusion. Estimates of the internal orientational pair correlation factor from the integral depolarized intensities of tRNAPhe solutions indicates that the observed dynamics correspond to the collective reorientation of approximately 5 bases. A comparison of the results presented with DDLS studies on the aggregation of the mononucleotide guanosine-5′-monophosphate confirms this result. For a further characterization of the relaxation process we studied the effect of hydrostatic pressure (1-1000 bar) on the depolarized spectra of tRNA. While other spectroscopic methods like nmr, fluorescence polarization anisotropy decay, or ESR give information about the very local motion of a single base within the DNA or RNA, this study shows that by DDLS one can characterize collective internal motions of macromolecules.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.360300912
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