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  • Aidas, Kestutis, et al. (författare)
  • A quantum mechanics/molecular dynamics study of electric field gradient fluctuations in the liquid phase. The case of Na+ in aqueous solution
  • 2013
  • Ingår i: Physical Chemistry, Chemical Physics - PCCP. - 1463-9076. ; 15:5, s. 1621-1631
  • Tidskriftsartikel (refereegranskat)abstract
    • The Na-23 quadrupolar coupling constant of the Na+ ion in aqueous solution has been predicted using molecular dynamics simulations and hybrid quantum mechanics/molecular mechanics methods for the calculation of electric field gradients. The developed computational approach is generally expected to provide reliable estimates of the quadrupolar coupling constants of monoatomic species in condensed phases, and we show here that intermolecular polarization and non-electrostatic interactions are of crucial importance as they result in a 100% increased quadrupolar coupling constant of the ion as compared to a simpler pure electrostatic picture. These findings question the reliability of the commonly applied classical Sternheimer approximation for the calculations of the electric field gradient. As it can be expected from symmetry considerations, the quadrupolar coupling constants of the 5- and 6-coordinated Na+ ions in solution are found to differ significantly.
  • Aidas, Kestutis, et al. (författare)
  • Photoabsorption of Acridine Yellow and Proflavin Bound to Human Serum Albumin Studied by Means of Quantum Mechanics/Molecular Dynamics
  • 2013
  • Ingår i: Journal of Physical Chemistry B. - 1520-6106. ; 117:7, s. 2069-2080
  • Tidskriftsartikel (refereegranskat)abstract
    • Attempting to unravel mechanisms in optical probing of proteins, we have performed pilot calculations of two cationic chromophores-acridine yellow and proflavin-located at different binding sites within human serum albumin, including the two primary drug binding sites as well as a heme binding site. The computational scheme adopted involves classical molecular dynamics simulations of the ligands bound to the protein and subsequent linear response polarizable embedding density functional theory calculations of the excitation energies. A polarizable embedding potential consisting of point charges fitted to reproduce the electrostatic potential and isotropic atomic polarizabilities computed individually for every residue of the protein was used in the linear response calculations. Comparing the calculated aqueous solution-to-protein shifts of maximum absorption energies to available experimental data, we concluded that the cationic proflavin chromophore is likely not to bind albumin at its drug binding site I nor at its heme binding site. Although agreement with experimental data could only be obtained in qualitative terms, our results clearly indicate that the difference in optical response of the two probes is due to deprotonation, and not, as earlier suggested, to different binding sites. The ramifications of this finding for design of molecular probes targeting albumin or other proteins is briefly discussed.
  • Aklillu, Eleni, et al. (författare)
  • Association of MAOA gene functional promoter polymorphism with CSF dopamine turnover and atypical depression.
  • 2009
  • Ingår i: Pharmacogenetics and genomics. - 1744-6872. ; 19:4, s. 267-75
  • Tidskriftsartikel (refereegranskat)abstract
    • OBJECTIVE: Monoamine oxidase-A (MAO-A) is a key mitochondrial enzyme that metabolizes biogenic amine neurotransmitters such as dopamine and serotonin. Individuals with atypical depression (AD) are particularly responsive to treatment with MAO inhibitors (MAOIs). Biomarker tests are essential for prompt diagnosis of AD, and to identify those with an altered brain neurotransmitter metabolism who may selectively respond to MAOI therapy. METHODS: In a sample of 118 Scandinavian patients with treatment-resistant depression who are naive to MAOI therapy, we investigated the associations between a common MAOA functional promoter polymorphism (MAOA-uVNTR), cerebrospinal fluid (CSF) neurotransmitter metabolites, and AD susceptibility. The metabolites for dopamine (homovanillic acid, HVA), serotonin (5-hydroxyindoleacetic acid) and noradrenaline (3-methoxy-4-hydroxyphenylglycol) were measured in the CSF. RESULTS: AD was associated with the female sex and a higher HVA in CSF (P=0.008). The carriers of the MAOA-uVNTR short allele were significantly overrepresented among women with AD (P=0.005; odds ratio=4.76; 95% confidence interval=1.5-13.1; statistical power=80.0%). Moreover, the MAOA-uVNTR genotype significantly influenced the HVA concentration (P=0.01) and showed a strong trend in relation to 5-hydroxyindoleacetic acid concentration (P=0.057) in women. The mediational statistical analyses showed the CSF-HVA concentration as a key driver of the relationship between MAOA-uVNTR genotype and AD. CONCLUSION: The association of the MAOA-uVNTR with both susceptibility to AD and dopamine metabolite (HVA) concentration lends further biological plausibility for high MAO-A enzyme activity as a mechanistic factor for genetic predisposition to AD through altered dopamine turnover. Our observations provide new evidence on the in-vivo functional significance of the MAOA-uVNTR short allele as a high activity variant.
  • Andersson, E., et al. (författare)
  • Core-valence double photoionization of the CS2 molecule
  • 2010
  • Ingår i: Journal of Chemical Physics. - 0021-9606. ; 133:9, s. 094305
  • Tidskriftsartikel (refereegranskat)abstract
    • Double photoionization spectra of the CS2 molecule have been recorded using the TOF-PEPECO technique in combination with synchrotron radiation at the photon energies h nu=220, 230, 240, 243, and 362.7 eV. The spectra were recorded in the S 2p and C 1s inner-shell ionization regions and reflect dicationic states formed out of one inner-shell vacancy and one vacancy in the valence region. MCSCF calculations were performed to model the energies of the dicationic states. The spectra associated with a S 2p vacancy are well structured and have been interpreted in some detail by comparison to conventional S 2p and valence photoelectron spectra. The lowest inner-shell-valence dicationic state is observed at the vertical double ionization energy 188.45 eV and is associated with a (2p(3/2))(-1)(2 pi(g))(-1) double vacancy. The spectrum connected to the C 1s vacancy shows a distinct line at 310.8 eV, accompanied by additional broad features at higher double ionization energies. This line is associated with a (C 1s)(-1)(2 pi(g))(-1) double vacancy.
  • Andersson, E., et al. (författare)
  • Single-photon core-valence double ionization of molecular oxygen
  • 2008
  • Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947. ; 78:2, s. 023409
  • Tidskriftsartikel (refereegranskat)abstract
    • Single-photon core-valence double ionization of molecular oxygen has been studied using a magnetic bottle time-of-flight electron coincidence spectrometer. The K-1V-1 double ionization electron spectrum of O-2 is reported and is assigned with the aid of ab initio calculations. A direct comparison of the core-valence double ionization electron spectra with the conventional valence band photoelectron spectrum is made. The lowest core-valence double ionization energy is found to be 571.6 eV and is associated with a (3)Pi dicationic state.
  • Backlund, Lena, et al. (författare)
  • Identifying predictors for good lithium response - A retrospective analysis of 100 patients with bipolar disorder using a life-charting method.
  • 2009
  • Ingår i: European psychiatry : the journal of the Association of European Psychiatrists. - 0924-9338. ; 24:3, s. 171-7
  • Tidskriftsartikel (refereegranskat)abstract
    • PURPOSE: Our aim was to investigate bipolar patients in order to test the validity of various outcome measures and to identify prognostic predictors for pharmacological treatment. MATERIAL AND METHOD: One hundred patients were interviewed using a computerized life-charting program in a descriptive, retrospective analysis. The concept "Burden of illness" was defined as a combination of severity and duration of episodes. Response to treatment was defined as the difference in burden before and after treatment, a low burden during treatment, and freedom of episodes for at least 3 years after insertion of treatment. RESULTS: The absence of mixed episodes and a high initial burden predicted a good response measured as the difference in burden. If remission for 3 years or a low burden during lithium treatment was used, the absence of rapid cycling and of mixed episodes were the most important predictors. The severity of illness before treatment had no impact. DISCUSSION AND CONCLUSION: We suggest the use of absolute measures of severity during treatment as the most appropriate measure of the outcome. Furthermore, our data provide corroboration that treatment with lithium ameliorates the prognosis of the illness, but that mixed episodes and rapid cycling predict a poorer response to lithium.
  • Baev, Alexander, et al. (författare)
  • A quantum mechanical - Electrodynamical approach to nonlinear properties : Application to optical power limiting with platinum-organic compounds
  • 2007
  • Ingår i: Journal of nonlinear optical physics and materials. - 0218-8635. ; 16:2, s. 157-169
  • Tidskriftsartikel (refereegranskat)abstract
    • Light propagation in a medium is sensitively dependent on the shape and intensity of the optical pulse as well as on the electronic and vibrational structure of the basic molecular units. We review in this paper the results of systematic studies of this problem for isotropic media. Our theoretical approach-the quantum mechanical-electrodynamical ( QMED) approach-is based on a quantum mechanical account of the many-level electron-nuclear medium coupled to a numerical solution of the density matrix and Maxwell's equations. This allows us to accommodate a variety of nonlinear effects which accomplish the propagation of strong light pulses. Particular attention is paid to the understanding of the role of coherent and sequential excitations of electron-nuclear degrees of freedom. The QMED combination of quantum chemistry with classical pulse propagation enables us to estimate the optical transmission from cross sections of multi-photon absorption processes and from considerations of propagation effects, saturation and pulse effects. Results of the theory suggest that in the nonlinear regime, it is often necessary to simultaneously account for coherent one-step and incoherent step-wise multi-photon absorption, as well as for off-resonant excitations even when resonance conditions prevail. The dynamic theory of nonlinear propagation of a few interacting intense light pulses is highlighted here in a study of the optical power limiting with platinum-organic molecular compounds.
  • Baev, A., et al. (författare)
  • Bi-directional description of amplified spontaneous emission induced by three-photon absorption
  • 2005
  • Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224. ; 22:2, s. 385-393
  • Tidskriftsartikel (refereegranskat)abstract
    •  A semiclassical dynamic theory of the nonlinear propagation of a few interacting intense light pulses is applied to study the nonlinear counterpropagation of amplified spontaneous emission (ASE) induced by three-photon absorption of short intense laser pulses in a chromophore solution. Several important results from the modeling are reached for the ASE process developing in the regime of strong saturation. Accounting for ASE in both forward and backward directions with respect to the pump pulse results in a smaller efficiency of nonlinear conversion for the forward ASE compared with the case in which forward emission is considered alone, something that results from the partial repump of the absorbed energy to the backward ASE component; the overall efficiency is nevertheless higher than for the forward emission considered alone. The efficiency of nonlinear conversion of the pump energy to the counterpropagating ASE pulses is strongly dependent on the concentration of active molecules so that a particular combination of concentration versus cell length optimizes the conversion coefficient. Under certain specified conditions, the ASE effect is found to be oscillatory; the origin of oscillations is dynamical competition between stimulated emission and off-resonant absorption. This result can be considered one of the possible explanations of the temporal fluctuations of the forward ASE pulse [Nature 415, 767 (2002)].
  • Baev, A., et al. (författare)
  • Doppler interference in dissociative resonant photoemission
  • 2002
  • Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947. ; 66:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Resonant photoemission involving dissociative core excited states has been the subject of a great number of experimental and theoretical investigations in recent time. The resonant decay of such dissociating systems has been shown to lead to semiatomic Auger electron emission spectra, with particular angular behavior. In the present paper a detailed theoretical analysis of dissociative resonant photoemission spectra of homonuclear diatomic molecules is presented. The theory addresses both fixed in space and randomly oriented homonuclear molecules and emphasizes the Doppler effect and the role of the interference between channels referring to the Doppler split atomic fragments. It is shown that peaks originating from decay in the atomic fragments can be asymmetric and structured due to the Doppler interference effect. The predicted strong non-Lorentzian behavior of the substructure on the top of the Doppler broadened atomiclike contribution is traced to the interplay between decay channels leading to gerade and ungerade final states. Simulations based on wave-packet theory are compared with experimental data for molecular oxygen. Our numerical simulations of the atomiclike resonance of fixed in space molecules show that the spectral profile is very sensitive to the shape of interatomic potentials of core excited and final states. It is shown that the Doppler effect in the decay spectra depends upon the symmetry of the core excited state.
  • Baev, A., et al. (författare)
  • General theory for pulse propagation in two-photon active media
  • 2002
  • Ingår i: Journal of Chemical Physics. - 0021-9606. ; 117:13, s. 6214-6220
  • Tidskriftsartikel (refereegranskat)abstract
    • The propagation of laser pulses of different lengths in nonlinear media of organic absorbers is described starting out from a recently suggested dynamical theory for two-photon absorption (TPA) of molecules in solutions [J. Opt. Soc. Am. B 19, 937 (2002)]. The roles of saturation effects and pulse duration on the suppression of TPA are emphasized. The numerical simulations of the pulse propagation are performed for a two-photon active charge transfer molecule using molecular parameters obtained from first principle calculations.
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