Calculation of three-center nuclear attraction integral over Slater type orbitals in molecular coordinate system using Löwdin <Emphasis Type="Italic">α</Emphasis>-radial function and Guseinov’s two-center charge density expansion formulae

Using Löwdin α-radial function and the Guseinov’s charge density expansion formulae, the calculation of the three-center nuclear attraction integrals over Slater type orbitals in molecular coordinate system is performed. The proposed algorithm is especially useful for computation of multicenter-multielectron integrals that arise in the Hartree-Fock-Roothaan approximation, which plays a significant role for the study of electronic structure and electron-nuclei interaction properties of atoms, molecules and solids. The algorithm described in the present work is valid for the arbitrary values of quantum numbers, screening constants and internuclear distances. The calculation results are in good agreement with those obtained using the alternative evaluation procedure.     

Benzimidazoles and related heterocycles

3-Aryl-1’H-spiro[2-pyrazoline-5,2’-quinoxalin]-3’(4’H)-ones, easily available by the reaction of 3-(2-aryl-2-oxoethylidene)-3,4-dihydroquinoxalin-2(1H)-ones with hydrazine hydrate (and phenylhydrazine), in boiling acetic acid undergo new acid-catalyzed rearrangement with the contraction of pyrazine ring of the quinoxaline system to form 2-(pyrazol-3-yl)benzimidazoles. Possible mechanisms of this rearrangement are considered.     

Alteration of the Axial Met Ligand to Electron Acceptor A0 in Photosystem I: Effect on the Generation of P 700 ·+ A 1 ·− Radical Pairs as Studied by W-band Transient EPR

Photosystem I (PS I) mutants from the cyanobacterium Synechocystis sp. PCC 6803 bearing point mutations to the axial ligands of A_0A (M688N_PsaA) and A_0B (M668N_PsaB) were studied by high-field W-band electron paramagnetic resonance (EPR) spectroscopy. It was found that the EPR observables of PS I from the M668N_PsaB mutant were virtual identical to that of the wild type (WT), and are clearly distinct from the M688N_PsaA mutant. In particular, the P ₇₀₀ ^·+ decay kinetics in the M688N_PsaA mutant is significantly slower than in the WT or the M668N_PsaB mutant. The analysis of the out-of-phase electron–electron dipolar electron spin echo envelope modulation shows that in the M668N_PsaB mutant, the estimated distance of 26.0 ± 0.3 Å agrees well with the 25.8 Å distance for the P ₇₀₀ ^·+ A _1A ^·? radical pair measured in the X-ray crystal structure. In the M688N_PsaA mutant, two populations are found with estimated distances of 26.0 ± 0.3 and 25.0 ± 0.3 Å in a ratio of 0.7–0.3, which agree well with the 25.8 Å distance for the P ₇₀₀ ^·+ A _1A ^·? radical pair and the 24.6 Å distance for the P ₇₀₀ ^·+ A _1B ^·? radical pair measured in the X-ray crystal structure. The data confirm that under the experimental conditions employed in this work, which involve dark-adapted samples without the pre-reduction of the iron–sulfur clusters, electron transport in cyanobacterial PS I is asymmetrical at 100 K, with the majority of electron transfer taking place through the A-branch of cofactors.     

Nonlinear absorption in undoped and Ge doped layered GaSe semiconductor crystals

P type-GaSe and 0.01 at% Ge doped GaSe crystal were grown using the conventional Bridgman–Stochbarger method from a stoichiometric mixture of starting materials in quartz ampoules, and the nonlinear absorption properties of both crystals have been studied by using an open aperture Z-scan technique under 1064 nm wavelength with 4 ns or 65 ps pulse durations. GaSe crystal exhibits two-photon absorption (TPA) at all input irradiances. On the other hand, at low input irradiance the Ge doped GaSe crystal exhibits saturable absorption (SA). At higher input irradiances TPA becomes dominant. A monotonic increase of the nonlinear absorption coefficient with increasing laser pulse duration from 65 ps to 4 ns is observed for the GaSe and Ge doped GaSe crystals.     

Macrocycles,derivatives of nitrogen-containing heterocycles 2. Synthesis and electrochemical properties of diindolizinadiquinoxalinacyclooxaalkaphanes

Phenylindolizinylquinoxalinomonopodands, obtained by the reaction of 1-(phenylindolizin-2-yl)quinoxalin-2(1H)-one with corresponding dibromotrioxa- and dibromopentaoxaalkanes, undergo oxidative dehydrocyclization assisted by molecular iodine to yield new redox-active diindolizinadiquinoxalinacyclooxaalkaphanes. Using CVA, the indolizine fragments of the heterocyclophanes in acetonitrile are found to undergo three-step oxidation with transfer of one electron in each step. The first and the third steps are reversible, whereas the second is irreversible. The oxidation at potentials of the first peak leads to the stable radical cations registered by ESR (g = 2.0024, a _2N = 0.26 mT).     

Cation binding by 2<Superscript>1</Superscript>,3<Superscript>1</Superscript>-diphenyl-l <Superscript>2</Superscript>,4<Superscript>2</Superscript>-dioxo-7,10,13-trioxa-1,4(3,1)-diquinoxalina-2 (2,3),3(3,2)-diindolizinacyclopentadecaphane and its acyclic analog

The binding of cations Li⁺, Na⁺, K⁺, Cs⁺, Ag⁺, Zn²⁺, Ni²⁺, Co²⁺, NH₄ ⁺ (group I), H⁺, Mg²⁺, Al³⁺, Ga³⁺ (group II), and Ca²⁺, Pb²⁺ (group III) by 2¹,3¹-diphenyl-l ²,4²-dioxo- 7,10,13-trioxa-l,4(3,1)-diquinoxalina-2(2,3),3(3,2)-diindolizinacyclopentadecaphane (1), which contains two indolizine and two quinoxaline fragments and 3,6,9-trioxaundecanes spacer, and by its acyclic analog (2) was studied using cyclic voltammetry in MeCN/0.1 M Bu₄NBF₄. It was concluded that the ions of group I are not bound by these compounds, the ions of group II exhibit the reversible redox-switched binding by the carbamoyl groups of the quinoxaline fragments, whereas the ions of group III are bound not only by the initial compounds and radical cations 1 and 2, but also by dication 1. This binding of the Ca²⁺ and Pb²⁺ ions stabilizes dication 1.     

Synthesis of esters by addition of chloroacetic acid to cage-like cyclic olefins

Thermal addition of chloroacetic acid to bicyclo[2.2.1]hept-2-ene, its 5-alkyl-substituted derivatives, and tricyclo[5.2.1.0^2,6]deca-3,8-diene gave the corresponding chloroacetic acid esters which attract interest as potential insecticides for plant protection.     

Phase equilibrium in the PbSnS2-PbSb2S4 system

The PbSnS₂-PbSb₂S₄ system was studied by physicochemical methods, and its phase diagram was plotted. The system is quasi-binary; solid solutions regions based on PbSnS₂ (6 mol % PbSb₂S₄) and PbSb₂S₄ (12 mol % PbSnS₂) were revealed. At a component ratio of 1: 1, a congruently melting compound Pb₂SnSb₂S₆ is formed. Pb₂SnSb₂S₆ single crystals were obtained by chemical transport. The unit cell parameters of Pb₂SnSb₂S₆, which crystallizes in orthorhombic system, were determined: a = 15.22 ?, b = 10.68 ?, c = 3.90 ?.     

Long-lived coherent oscillations of the femtosecond transients in cyanobacterial photosystem I

The pulsed excitation of electronic levels coupled to specific nuclear modes by a 26 fs laser pulse at 706 nm creates a wavepacket in the nuclear space of photopystem I (PS I) of Synechocystis sp. strain PCC 6803 both in the ground state and in the one-exciton manifold. Fourier transform of transient decay curves shows several low frequency peaks. The most prominent Power Spectral Density (PSD) peaks are at omega = 49 cm(-1) and omega = 88 cm(-1). The peculiarity of the coherent wavepacket in the PS I of S. sp. strain PCC 6803 is the unique, long-lived 49 cm(-1) and 88 cm(-1) oscillations with decay times up to 10 ps. It was suggested that such a long-lived coherence is determined by a contribution of the ground state wavepacket. The dependence of these two PSD peaks on the probe wavelength resembles the profile of the transient absorption spectra of PS I. The pump-probe signal in the Soret region reflects the dynamics of the ground state wavepacket created by pulsed excitation of the Q(y)-band. It was shown that the multimode Brownian oscillator model allows a quantitative fit of the oscillatory patterns of the pump-probe signal to be obtained.     

Synthesis of epitaxial layers of zinc oxide on nonorienting substrates

The first experiments on the growth of single-crystal layers of zinc oxide on nonorienting substrates (crystalline leucosapphire and fused quartz) by chemical transport reactions in a reduced-pressure flow-through reactor in a hydrogen atmosphere is reported. To ensure autoepitaxy on a surface of a nonorienting substrate, an optimized intermediate layer of zinc oxide of thickness 200–1000 Å, which provides a texture of basal orientation regardless of the orienting properties of the substrate, is preliminarily deposited by magnetron sputtering. It is shown that the subsequent growth of layers on such a surface by a chemical transport reaction to a thickness of 1–5 ensures high structural perfection, uniformity, and a very smooth surface, while polycrystalline films are deposited on the portion of the surface without a buffer layer. The proposed method can be used to grow heteroepitaxial structures and other electronic materials on nonorienting substrates using chemical transport reactions.