| 1. |
- Velkov, Zhivko A., et al.
(författare)
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Melatonin : Quantum-chemical and biochemical investigation of antioxidant activity
- 2009
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Ingår i: European Journal of Medicinal Chemistry. - : Elsevier. - 0223-5234 .- 1768-3254. ; 44:7, s. 2834-2839
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Tidskriftsartikel (refereegranskat)abstract
- Experimental and theoretical investigation of the antioxidant activity of melatonin is carried out. The theoretical approach comprises the evaluation of several appropriate descriptors of scavenging activity with the help of quantum-chemistry methods. The values obtained are compared with available data for substances with established antioxidant properties. One of the most widely used markers for in vivo free radical oxidation processes is malondialdehyde (MDA) as an end product of membrane lipid peroxidation. Experimental support of the computed scavenging parameters is provided by estimation of the effect of supplementary melatonin therapy on the plasma levels of MDA in CRF patients on maintenance HD therapy. Different reaction paths have been considered and related to the obtained data, allowing speculations about the reaction mechanism and the antioxidant potential of melatonin for practical purposes.
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| 2. |
- Velkov, Yasen, et al.
(författare)
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Origin of fine structures on the dissociative 1s ->sigma* resonance in X-ray absorption spectra of O-2
- 2009
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 476:4-6, s. 147-150
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Tidskriftsartikel (refereegranskat)abstract
- We attempt to explain a puzzling long-tailed peak shape of the X-ray absorption spectrum of the oxygen molecule in the energy region around 539 eV taking into account the Rydberg-valence and vibronic couplings. The long-tailed feature is found to arise from two dissociative sigma* states and the sudden drop in intensity is related to decrease in transition dipole near the crossing point between the repulsive sigma* and weak 3s Rydberg states with the quartet ion cores. This is supported by numerical wave-packet simulations allowing for all interchannel couplings between the Rydberg and valence manifolds with the quartet and doublet ion cores in a diabatic representation of the core-excited states.
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| 3. |
- Velkov, Yasen, et al.
(författare)
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X-ray-absorption spectroscopy beyond the natural width measured in partial Auger yield mode
- 2009
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 79:2
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Tidskriftsartikel (refereegranskat)abstract
- We report both experimental and theoretical studies on x-ray absorption measured using partial Auger yields of gas phase nitrogen, carbon monoxide, and oxygen molecules near the N 1s ->pi(*), O 1s ->pi(*), and O 1s ->pi(*) regions, respectively. The main tool of our study is a two-dimensional map in which resonant Auger yields are plotted as a function of photon and kinetic energy. The partial yields of the three molecules are analyzed in detail by extracting profiles along various directions in the map. Narrowing of the absorption resonances is observed along the direction of constant kinetic energy. It is shown that such profiles are similar to the conventional x-ray-absorption spectrum for a broad class of molecules whose potential energy surfaces of the final and core-excited states are almost parallel. However, substantial differences with the conventional x-ray-absorption profiles are observed in the general case of nonparallel surfaces due to the lifetime vibrational interference. Here, we suggest a systematic way to eliminate the lifetime vibrational interference.
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