Browsing by Author "Makarov, Vladimir, I"
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- Analysis of quantum coherence in biologyPublication . Khmelinskii, Igor; Makarov, Vladimir, IWe reviewed the tools of quantum physics used in modeling of quantum coherence (QC) effects in different systems, including biological systems, which behave as quantum objects in some of their degrees of freedom. In particular, we considered the usage of the effective Hamiltonian (EH), Green's function (GF) and density matrix (DM) methods in the analysis of QC, focusing on QC in biological systems. We discussed the two main mechanisms of loss of quantum state coherence: (i) dephasing of the originally prepared coherent wave package and (ii) population relaxation in the same wave package. Dephasing does not affect the quantum state population, e.g. as in spin-spin relaxation, where dephasing is described by the tau(2) relaxation time. On the other hand, the state population relaxation of the spin wavepackage is attributed to spin-lattice relaxation and is described by the tau(1) relaxation time. Presently we discussed EH and GF formalisms in terms of the complex energy, dependent on intra- and intersystem interactions that induce state population relaxation. We provided a detailed analysis of these approaches for the exciton relaxation dynamics in a glycine polypeptide chain. The same phenomena were described in the DM formalism using the relaxation matrix. We discussed QC in different biological systems, showing that QC is conserved when the interactions of the coherent wavepackage with other degrees of freedom are weak, as otherwise population relaxation causes loss of QC. We believe that our results will be useful for the researchers in the area of quantum biology.
- Energy propagation along polypeptide alpha-helix: experimental data and ab initio zone structurePublication . Khmelinskii, Igor; Makarov, Vladimir, IWe report new theoretical and experimental results that may significantly change our ideas on the workings of life. We performed ab initio analysis of the band structure of periodic α-helix polypeptides (PP) in function of the chain length. Three different calculation approaches were tested: (a) PP described semiempirically as a onedimensional object, with the amino acids substituted by effective atoms; (b) density functional theory (DFT) as implemented in WIEN2k approach, and (c) CRYSTAL-17 software package. The approach (c) was used for the detailed ab initio analysis, as it provided better accuracy in less computation time. We found that the bandgap was weakly dependent on the PP composition, with the asymptotic values in the 0.43 – 0.63 eV range. We estimated the effective electron and hole masses, their mean free path and mobility for the glycine-PP. The electron mobility in the PP conductive band was about half of that in polycrystalline silicon. The PP zone structure was used to study the mechanism of energy transfer along the PP. The current-voltage (I/V) characteristics of Müller cell (MC) intermediate filaments (IFs) from porcine retina were experimentally measured. The measured I/V characteristics show that the IFs behave as semiconductors. These results were discussed in light of the presently reported PP zone structure theory. The results obtained may open new areas in biomedical research and applications.
- Nonlinear optical effects in one- and two-layer metal structuresPublication . Khmelinskii, Igor; Makarov, Vladimir, IIn this study, we determined the spectral properties and frequency summing that induced superemission (SE) in two assemblies (A and B) built from a Co nanolayer and a Co nanotrack, which differed in terms of their topography. We found that homogeneous Co films with layer thicknesses of 7.101 and 11.755 nm produced discrete absorption spectra, which originated from the transverse quantum confinement operating in these metal films. The surface plasmon resonance in these films appeared at energies over 50000 cm(-1) where a longer wavelength tail was readily observable. All of the nanolayers considered had discrete emission spectra and the emission bands strongly overlapped due to the large bandwidths. Their emission decay was described by a single-exponential function with lifetimes of 167 +/- 5 and 231 +/- 7 ns for assemblies A and B, respectively. Similarly, the absorption spectrum for the two-layer sandwich assembly comprised the superposition of the respective spectra for the individual Co nanolayers. We found that these assemblies could sum the pumping radiation photons to produce photons with higher energy. After exciting the 11.755 nm Co nanolayer to a given transition, the Co nanotrack produced emission at close to double the energy. We identified this emission as SE and the bandwidths were only about 32 +/- 0.5 and 21 +/- 3 cm(-1) for assemblies A and B, respectively. The SE band appeared with the build-up time of 32 +/- 2 ns for assembly A and 21 +/- 1 ns for assembly B, and disappeared with decay times of 143 +/- 5 and 113 +/- 4 ns, respectively. We analyzed the energy transfer in detail based on the exchange mechanism, and the eventual contribution of the electric dipole-dipole mechanism was also estimated.
- Reaction coupling in ADH1A alcohol dehydrogenase enzyme by exciplex formation with adenosine diphosphate moderated by low-energy electronic excited statesPublication . Khmelinskii, Igor; Makarov, Vladimir, ITwo commonly accepted theories about enzymes were revisited. The first states that adenosine triphosphate (ATP)-stored energy is only released when the substrate is in place, because the substrate changes the enzyme structure when it is bound to the enzyme. In fact, as demonstrated and discussed presently, no structural changes are required, and ATP-stored energy is released when it can be used. The second states that ATP-released energy moves along the enzyme molecule in the form of molecular vibrations (Davydov's vibrational solitons). In fact, as reported presently, energy released upon ATP hydrolysis moves in the form of excited-state electrons (excitons), with no molecular vibrations involved. The relevant experimental evidence was obtained for the human ADH1A alcohol dehydrogenase enzyme. Spontaneous ATP hydrolysis in the absence of substrate was apparently prevented by electronically excited enzyme + adenosine diphosphate (ADP) + inorganic phosphate (P) complex (exciplex) formed upon ATP hydrolysis. This exciplex kept ADP + P bound and in place for the inverse reaction, until the excess energy was dissipated in the enzyme-catalyzed reaction or by energy transfer to a suitable acceptor. Additionally, and contrary to textbooks, ADH1A has required ATP, working orders of magnitude faster in its presence.
- Superluminescence and macroscopic exciton propagation in freestanding ZnO thin filmsPublication . Khmelinskii, Igor; Makarov, Vladimir, IRecently we have reported properties of ZnO semiconductor films attached to CaF2 substrate. Presently we characterized absorption, emission and superluminescence of freestanding ZnO films, comparing these to the attached films with the same thickness values. The absorption spectra of the freestanding films had resolved bands, with the band density increasing with the nanofilm thickness. Additionally, the spectral transitions in these films were blue-shifted as compared to attached films. The absorption and emission spectra of freestanding films were resolved better than those of attached films, with the difference traceable to the surface roughness of the substrate used for deposition. We also explored exciton dynamics and propagation over macroscopic distances in freestanding films. The excitons lived longer and propagated further in freestanding films as compared to attached films. The superluminescence yield in freestanding 9.3 nm film of 0.43 +/- 0.05 was significantly larger than 0.17 +/- 0.03 in an equivalent attached film. We provided a detailed analysis of the results obtained. The reported data are unique, demonstrating significant difference in the optical properties of attached and freestanding ZnO thin films. Freestanding ZnO films are promising for optoelectmnic applications.