K. Stark

Northwestern University

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Hans‐Joachim Werner

University of Stuttgart

F. J. Aoiz

Universidad Complutense de Madrid

Luis Bañares

Universidad Complutense de Madrid

Vı́ctor J. Herrero

Instituto de Estructura de la Materia

V. Sáez Rábanos

Universidad Politécnica de Madrid

G. Zając

Argonne National Laboratory

George Fitzgerald

Waterford Institute

David E. Manolopoulos

University of Oxford

Joseph T. Golab

Illinois Mathematics and Science Academy

James M. Gallas

The University of Texas at San Antonio

Cooperative Institutions

Institute of Virology of the Slovak Academy of Sciences

Goethe University Frankfurt

German Center for Infection Research

Simulations Plus (United States)

University Hospital Frankfurt

Universität Hamburg

Heidelberg University

Institute of Medical Microbiology and Hygiene

Freie Universität Berlin

Charité - Universitätsmedizin Berlin

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Spectroscopic Study and Simulation from Recent Structural Models for Eumelanin: II. Oligomers

The Journal of Physical Chemistry B (2003)

K. Stark James M. Gallas G. Zając M. Eisner Joseph T. Golab

Spectroscopic simulations of a leading structural model for melanin, which is the pigment responsible for coloration and photo protection in humans and animals, were conducted. In direct continuation of an earlier study on possible monomer and dimer subunits of eumelanin, we have performed density functional theory (DFT) calculations on a recent structural model for eumelanin based on higher oligomers of neutral 5,6-indolequinone. This paper further reports on our semiempirical spectroscopic simulations for the higher oligomer (tetramers through hexamers) energy-minimized structures. A linear combination of the oligomeric spectra reproduces several features of the experimental spectrum. This result strongly supports the assumption that melanin is constituted of substructures such as those considered in this study.

Oligomer

10.1021/jp034965r

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Citations (78)

A Spectroscopic and Computational Investigation of the Vanadomolybdate Local Structure in the Lyonsite Phase Mg_2.5VMoO₈.

ChemInform (2007)

Jared P. Smit Hacksung Kim Ian Saratovsky K. Stark George Fitzgerald

Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

10.1002/chin.200742006

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Citations (0)

Spectroscopic Study and Simulation from Recent Structural Models for Eumelanin: I. Monomer, Dimers

The Journal of Physical Chemistry B (2003)

K. Stark James M. Gallas G. Zając M. Eisner Joseph T. Golab

Spectroscopic simulations of a leading structural model for melanin, the pigment responsible for coloration and photoprotection in humans and animals, were done. We performed density functional theory (DFT) calculations using both the local density approximation (LDA) and the generalized gradient approximation (GGA) on a recent structural model for eumelanin based on higher oligomers of the monomer of neutral 5,6-indolequinone and its reduced forms, semiquinone and hydroquinone. This paper reports on our semiempirical spectroscopic simulations for the monomer and dimer energy-minimized structures. Our second study (part II) extends this approach to higher oligomers (tetramers through hexamers) and points out that the known optical spectra of eumelanins can be adequately explained on this basis.

Semiquinone

Photoprotection

Hydroquinone

10.1021/jp0266594

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Citations (84)

Effect of Stacking and Redox State on Optical Absorption Spectra of Melanins−Comparison of Theoretical and Experimental Results

The Journal of Physical Chemistry B (2005)

K. Stark James M. Gallas G. Zając Joseph T. Golab Shirley Gidanian

In this work the effect of aggregation and oxidation on the optical absorption of eumelanin oligomeric sheets is investigated by applying quantum mechanics and atomistic simulation studies to a simplified eumelanin structural model that includes 1−3 sheets of hexameric oligomer sheets. The oligomeric hypothesis is supported by AFM characterizations of synthetic eumelanins, formed by auto-oxidation or electrochemical oxidation of dihydroxyindole (DHI). Comparison of calculated absorption spectra to experimental spectra demonstrates a red shift in absorption with oxidation and stacking of the eumelanin and validates the theoretical results.

Oligomer

10.1021/jp046710z

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Citations (102)

Automatisches Fahren von Schiffen längs eines Leitkabels

Ernst Dieter Gilles K. Stark

Source

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Citations (2)

Ab Initio Simulation of Molecular Beam Experiments for the F + H₂ → HF + H Reaction

The Journal of Physical Chemistry A (1997)

F. J. Aoiz Luis Bañares Bruno Martı́nez−Haya J. F. Castillo David E. Manolopoulos

The celebrated 1985 molecular beam measurements for the F + H2 reaction of Lee and co-workers, consisting of time-of-flight (TOF) spectra and angular distributions (AD) at several collision energies, have been directly simulated using fully resolved differential cross-sections (DCS) obtained in accurate quantum mechanical (QM) and quasi-classical trajectory (QCT) calculations on the most recent ab initio potential energy surface (PES) by Stark and Werner. The simulations performed using the QM calculations show an unprecedentedly good agreement with the experimental results for all final vibrational states of the HF product. In particular, the height of the peak in the experimental laboratory angular distribution corresponding to HF(v'=3) forward scattering is quite well reproduced by the simulation using the QM theoretical data at all three experimental collision energies for both para and normal hydrogen. The most important discrepancies between theory and experiment are found in the HF(v'=3) sideways and backward scattering. The simulations carried out with the QCT data, although accounting correctly for the backward scattering, fail to account for most of the v' = 3 forward scattering. The analysis performed in this work indicates that an unbiased comparison between theoretical and experimental results in the laboratory frame (as opposed to the center-of-mass frame) is required to assess the quality of a theoretical calculation on a given ab initio PES.

Crossed molecular beam

Potential energy surface

Molecular beam

10.1021/jp970695z

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Citations (60)

Quantum mechanical angular distributions for the F+H2 reaction

The Journal of Chemical Physics (1996)

J. F. Castillo David E. Manolopoulos K. Stark Hans‐Joachim Werner

Quantum mechanical integral and differential cross sections have been calculated for the title reaction at the three collision energies studied in the 1985 molecular beam experiment of Lee and co-workers, using the new ab initio potential energy surface of Stark and Werner (preceding paper). Although the overall agreement between the calculated and experimental center-of-mass frame angular distributions is satisfactory, there are still some noticeable differences. In particular, the forward scattering of HF(v′=3) is more pronounced in the present calculations than it is in the experiment and the calculations also predict some forward scattering of HF(v′=2). A comparison with the quasiclassical trajectory results of Aoiz and co-workers on the same potential energy surface shows that the forward scattering is largely a quantum mechanical effect in both cases, being dominated by high orbital angular momenta in the tunneling region where the combined centrifugal and potential energy barrier prevents classical trajectories from reacting. The possible role of a reactive scattering resonance in contributing to the quantum mechanical forward scattering is also discussed in some detail.

Potential energy surface

10.1063/1.471373

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Citations (249)

Classical dynamics for the F + H2 → HF + H reaction on a new ab initio potential energy surface. A direct comparison with experiment

Chemical Physics Letters (1994)

F. J. Aoiz Luis Bañares Vı́ctor J. Herrero V. Sáez Rábanos K. Stark

Potential energy surface

10.1016/0009-2614(94)00435-8

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Citations (120)

Heterogeneous catalysis: looking forward with molecular simulation