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  • 1
    Electronic Resource
    Electronic Resource
    Dodecylphosphocholine micelles as a membrane-like environment: new results from NMR relaxation and paramagnetic relaxation enhancement analysis (1998)
    Springer
    European biophysics journal 28 (1998), S. 48-58 
    Details
    ISSN: 1432-1017
    Keywords: Key words Dodecylphosphocholine ; Peptide-lipid interaction ; Paramagnetic probe ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract To further examine to what extent a dodecylphosphocholine (DPC) micelle mimics a phosphatidylcholine bilayer environment, we performed 13C, 2H, and 31P NMR relaxation measurements. Our data show that the dynamic behavior of DPC phosphocholine groups at low temperature (12 °C) corresponds to that of a phosphatidylcholine interface at high temperature (51 °C). In the presence of helical peptides, a PMP1 fragment, or an annexin fragment, the DPC local dynamics are not affected whereas the DPC aggregation number is increased to match an appropriate area/volume ratio for accommodating the bound peptides. We also show that quantitative measurements of paramagnetic relaxation enhancements induced by small amounts of spin-labeled phospholipids on peptide proton signals provide a meaningful insight on the location of both PMP1 and annexin fragments in DPC micelles. The paramagnetic contributions to the relaxation were extracted from intra-residue cross-peaks of NOESY spectra for both peptides. The location of each peptide in the micelles was found consistent with the corresponding relaxation data. As illustrated by the study of the PMP1 fragment, paramagnetic relaxation data also allow us to supply the missing medium-range NOEs and therefore to complete a standard conformational analysis of peptides in micelles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002490050182
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  • 2
    Electronic Resource
    Electronic Resource
    Three-dimensional quantum mechanical study of Ne⋅⋅⋅Cl2 vibrational predissociation (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 3966-3975 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Three-dimensional quantum mechanical calculations for vibrational predissociation of the Ne⋅⋅⋅Cl2 van der Waals complex are presented and compared with experiments. Lifetimes and final rotational state distributions were obtained for the two processes: (i) Ne⋅⋅⋅Cl2(X,v=1) →Ne+Cl2(X,v=0) and (ii) Ne⋅⋅⋅Cl2(B,v=11) →Ne +Cl2(B,v=10,9) where v denotes the vibrational quantum number of Cl2 and X and B specify electronic states of Ne⋅⋅⋅Cl2 which correlate with the X 1∑+0g and B 3∏+0u states of the free Cl2 molecule, respectively. The van der Waals interaction potential was taken to have the same form in the X and B states. At short distances, it is described by a sum of Morse pairwise potentials between the Ne atom and each of the Cl atoms, and between the neon atom and the center of mass of Cl2. At large distances the potential switches to an anisotropic van der Waals interaction with R−6 and R−8 dependence. The parameters were adjusted so that the T-shaped configuration the potential matched the one determined from scattering experiments. The initial quasibound state wave function of the complex was calculated variationally, while the final continuum wave functions were obtained by integration of the rotational close coupled Schrödinger equations. Finally, the lifetime and the final rotational state distribution were calculated using the Fermi golden rule. A line shape calculation verified the validity of the golden rule approximation for this system. The lifetimes obtained for the X and the B states differ by several orders of magnitude, the X state being the longest lived as observed experimentally. The calculated lifetimes and rotational distributions of the Cl2 fragments agree qualitatively with the experimental values. The rotational distribution is compared to that obtained from a decomposition of the initial quasibound state in terms of free rotor states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452950
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  • 3
    Electronic Resource
    Electronic Resource
    On the possibility of nonadiabatic transitions in the photodissociation of I2M clusters excited above the dissociation limit of the B state (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 3965-3967 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction I2M→hν I2(B,v', j')+M has been studied experimentally for excitation above the dissociation limit of the I2M B state. A surprisingly large amount of the available energy is found as relative translational energy of the I2 and M products. These results have been interpreted in terms of a one atom "cage effect,'' where the iodine atoms are prevented from dissociating by the presence of the rare gas atom M. A purely kinematic cage effect could occur on a single electronically excited potential energy surface, namely the one correlating to the I2(B) state plus M in its electronic ground state. In this paper we discuss another possible mechanism for a pathway leading to bound I2, which involves an electronic nonadiabatic transition. Above the I2M(B) threshold the 1Π1u electronic state can also be excited. Since the 1Π1u and the B states can be coupled by the presence of the rare gas atom, there is a finite probability for an electronic transition from 1Π1u to B, with the energy difference being transformed into relative kinetic energy of the rare gas atom with respect to I2 after a fraction of the available energy has been used to break the van der Waals bond. The relationship between this mechanism and the electronic predissociation of I2M(B) van der Waals molecules at much lower energies, as well as the collision induced electronic predissociation of I2(B), are also mentioned. Finally the possibility of observing similar transitions in other halogen–rare gas clusters is considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451906
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  • 4
    Electronic Resource
    Electronic Resource
    A wave packet Golden Rule treatment of vibrational predissociation (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 4230-4233 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The time-dependent wave packet technique is applied to the Golden Rule treatment of vibrational predissociation. The wave packet at time zero is taken as the product of the quasibound wave function and the coupling inducing predissociation. The rate for vibrational predissociation can then be obtained by Fourier transform into the energy domain of the time-dependent wave packet autocorrelation function. The method has been applied to a model triatomic van der Waals molecule. It is shown that when the bound-state components of the wave packet are projected out, the time-dependent version of the Golden Rule approximation provides an alternative efficient technique to treat intramolecular decay.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460631
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  • 5
    Electronic Resource
    Electronic Resource
    Photofragmentation of the Ne⋅⋅⋅ICl complex: A three-dimensional quantum mechanical study (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 3348-3358 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Converged three-dimensional quantum mechanical calculations for photofragmentation of the Ne⋅⋅ICl van der Waals molecule in the energy region of the electronically excited B(3∏0+) state of ICl are presented and compared with experiments. Lifetimes and final state distributions for the ICl fragments were determined for vibrational predissociation from the lowest van der Waals level in the B(v'=2) channel. Good agreement between theory and experiment was achieved using a sum of atom–atom pairwise potentials. This potential energy surface predicts the equilibrium geometry of the complex to be bent at 140° with the Ne atom towards the Cl end of ICl. The diabatic vibrational golden rule (DVGR) approximation, as well as the rotational infinite order sudden approximation (RIOSA), have been tested again the full 3D calculations. Analysis of the quasibound wave function reveals that the highly inverted rotational distribution of the ICl fragments observed in the experiment, is not due to zero-point bending motion. It is more likely to be due to a rotational rainbow effect enhanced by the favorable initial geometry of the complex. The effect of the excitation of the bending van der Waals mode in the complex has also been studied. As compared with the lowest level, a longer lifetime and a different rotational distribution of the fragments is predicted. The results presented in this work not only elucidates many dynamical aspects of vibrational predissociation for the Ne⋅⋅⋅ICl complex, but also provide benchmark data for the study of other theoretical methods and approximations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458578
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  • 6
    Electronic Resource
    Electronic Resource
    A theoretical study of the Ar2HCl van der Waals cluster (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1337-1344 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theoretical method for treating the dynamics of polymeric van der Waals clusters is developed, based on an adiabatic separation of the heavy atom motions. The method is applied to the calculation of spectroscopic parameters for the complex Ar2HCl, and the results are compared with experimental data from high-resolution microwave studies. Potentials based on pairwise additivity and the known Ar–HCl pair potential are used. Small discrepancies between experiment and theory are observed, and it seems likely that these are attributable to the effects of three-body forces rather than to deficiencies of the pair potentials used. High-resolution spectroscopy of van der Waals clusters shows great promise as a tool for investigating nonadditive intermolecular forces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456075
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  • 7
    Electronic Resource
    Electronic Resource
    A quantum mechanical treatment of vibrational mixing in ethylene dimer and rare gas–ethylene complexes (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 3970-3982 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An approximate description of the van der Waals vibrations of ethylene dimer and rare gas–ethylene complexes is presented. Using a model atom–atom potential, this calculation examines the mixing of the ethylene ν7 vibration with a set of background vibrational levels, consisting of combinations of the van der Waals vibrations and the ethylene ν10 vibration. The ethylene dimer exhibits extensive vibrational mixing, while the rare gas–ethylene molecules do not. For the ethylene dimer, calculated line strengths produce a complex spectrum of vibrational lines that span a 10 cm−1 region, in agreement with the experimental spectrum. This result suggests new explanations for the coexistence of broad and narrow lines in the ethylene dimer ν7 dissociation spectrum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454830
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  • 8
    Electronic Resource
    Electronic Resource
    Fine-structure electronic predissociation in van der Waals molecules. I. Theory (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 5500-5508 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A quantum-mechanical model for fine-structure predissociation in van der Waals molecules is presented. The process corresponds to: A(2S+1LJA )⋅⋅⋅M→A(2S+1LJ′A) +M where A is an atom and M an atom or a diatomic molecule A(2S+1LJA) ⋅⋅⋅M represents the van der Waals complex in a state which correlates to the 2S+1LJA electronic manifold of A. The general formalism based on close-coupling equations is presented first. The limiting case of slow predissociation is then considered and treated by perturbation theory. Finally, the application to the atom–atom and the atom–diatom van der Waals complexes for L=1 and S=1/2 or S=1 is discussed. This simple analysis allows predictions to be made for predissociation rates and lifetimes in cases where the spin–orbit interaction is larger than the van der Waals binding energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452522
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  • 9
    Electronic Resource
    Electronic Resource
    Quantum-classical dynamics including continuum states using quantum trajectories (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 8-13 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We apply the MQCB (mixed quantum/classical mechanics based on Bohmian trajectories) [E. Gindensperger, C. Meier, and J. A. Beswick, J. Chem. Phys. 113, 9369 (2000)] to the case where the quantum degree of freedom contains both bound and continuum states. The quantum degree of freedom is treated by a wave packet that is propagated on a spatial grid with a Hamiltonian that depends parametrically on the classical degrees of freedom, while the classical degrees of freedom themselves are coupled to the wave function via quantum trajectories. The method is applied to a simple model of a light particle colliding with a heavy (classical) particle absorbed on a surface, which has been used by other authors to develop methods to combine quantum degrees of freedom including continuum states with classical mechanics. The results are compared to the Ehrenfest mean-field method as well as to full quantum results. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1415452
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  • 10
    Electronic Resource
    Electronic Resource
    Mixing quantum and classical dynamics using Bohmian trajectories (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 9369-9372 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A novel time-dependent hybrid quantum/classical propagation scheme based on Bohmian quantum trajectories is presented. The quantum subsystem is described by a wave packet depending on the quantum variables x and, via the total potential energy of the system, parametrically on the classical trajectories X(t). The wave packet is used to calculate de Broglie–Bohm quantum trajectories x(t) which are used to calculate the force acting on the classical variables. Quantum corrections of the classical equation of motion are also included. The method is applied to a simple case of two coupled oscillators. Comparison between exact quantum and approximate results demonstrates that these MQCB (Mixed Quantum/Classical Bohmian) trajectories provide a good description of the energy exchange between the two oscillators. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1328759
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