Publications by authors named "Sidorkin V"

Electrochemical oxidation of 1-R-substituted silatranes (R = Me, vinyl, (CH)CN, CHPh, CH(CH), Ph, CHMe, -Cl-CH, Cl)-classical representatives of pentacoordinated silicon compounds-and the formation of their short living cation radicals upon reversible or quasi-reversible one-electron withdrawal were studied by means of cyclic and square-wave voltammetry, faradaic impedance spectroscopy and real-time temperature-dependent EPR spectroelectrochemistry supported by DFT B3PW91/6-311++G(d,p) (C-PCM, acetonitrile) calculations. The main reaction responsible for the decay of is shown to be their deprotonation, and ways of increasing the stability of these species are proposed.

View Article and Find Full Text PDF

Covalent immobilization of TEMPO at carbon and gold an aliphatic -(CH)- linker was achieved cathodic grafting of a diamagnetic precursor, tetramethylpiperidine, with subsequent >NH to >NO oxidation to give TEMPO-capped paramagnetic interfaces ( = 5.2 × 10 mol cm); catalytic and spin switching potential of the thus prepared systems was demonstrated.

View Article and Find Full Text PDF

The effective use of photochromic systems based on azo compounds in a number of applications, especially biomedical and pharmacological ones, is impeded by the unresolved problem of their E⇆Z isomerization in the near-IR region, NIR (780-1400 nm). We have demonstrated at the TD-DFT, STEOM-DLPNO-CCSD and CASSCF-NEVPT2 levels of theory that the presence of a silylated diazene core -Si-N=N-Si- with three-, tetra- or five-coordinated silicon atoms practically guarantees the absorption of the E and Z forms of such derivatives in NIR and the amazing (185-400 nm) separation of their first absorption bands. In particular, the maximum λ of the first n→π* band of the E isomer of azosilabenzene ASiB is at ∼1030 nm, while for the Z isomer λ ≅1340 nm.

View Article and Find Full Text PDF

In the series of silatranes XSi(OCH2CH2)3N, 1 (X = Me, 1a; H, 1b; F, 1c) with the known gas electron diffraction (GED) structures, the problematic geometry of 1-methylsilatrane 1a has been revised. In particular, the new value of the SiN distance (dSiN) in 1a turned out to be ∼0.06 Å longer than the generally accepted one.

View Article and Find Full Text PDF

Using the example of silatranes XSi(OCHCH)N (X = Me, H, F, Cl), , it was found that the effect of the dipole-bound (DB) electron on the cage intramolecular complexes does not fit into the standard views. Upon the transition from to the DB anions , the unusual shortening of the internuclear Si···N distance is always observed. For X = Cl, it is equal to 0.

View Article and Find Full Text PDF

The problematic experimental photoelectron spectra of silatranes XSi[OCHCH]N (X = vinyl and Ph) were theoretically studied. The ab initio electron propagator theory, many-body methods, and model vibrational Hamiltonian were employed to establish the nature of bands in the energetically lowest part of the photoelectron spectrum of these intramolecular silicon complexes. The first vertical ionization energy corresponds to a nitrogen atom lone pair, n, in 1-vinylsilatrane, and the essentially doubly degenerate π-orbitals π and π' of the aromatic ring in 1-phenylsilatrane.

View Article and Find Full Text PDF

Dipole-bound molecular anions are often envisioned as unperturbed neutral, polar molecules with single excess electrons. We report the observation of intramolecular structural distortions within silatrane molecules due to the formation of their dipole-bound anions. The combination of Rydberg electron transfer-anion photoelectron spectroscopy (RET-PES) and ab initio computational methodologies (CCSD and MP2) was used to study 1-hydro- (HS) and 1-fluoro- (FS) silatranes and their dipole bound anions, HS and FS.

View Article and Find Full Text PDF

Electrochemical oxidation of phenylsilatrane (1) in CHCN/0.1 M BuNPF has been studied by voltammetry, UV-Vis and EPR-coupled spectroelectrochemistry supported by DFT calculations. One-electron withdrawal from the HOMO of 1, formed with a predominant contribution of the atrane N atom to the 3c-4e system, results in a short lived radical cation, in which the atrane nitrogen atom is almost planar and carries most of the spin density showing strong coupling with the protons of the axially directed C-H bonds of the three adjacent α-methylene groups (g = 2.

View Article and Find Full Text PDF

Using 18 silatranes XSi(OCH CH ) N (1) as examples, the potentials of electrochemical oxidation E of the hypervalent compounds of Si were calculated for the first time at the ab initio and DFT levels. The experimental peak potentials E (acetonitrile) show an excellent agreement (MAE=0.03) with the MP2//B3PW91 calculated E (C-PCM).

View Article and Find Full Text PDF

The problematic experimental photoelectron spectra of fluoro- and ethoxy-silatranes, XSi[OCH2CH2]3N (X = F and OEt), were assigned using theoretical spectra obtained by combining the OVGF//CCSD vertical ionization energies with the vibrational widths of the electronic transitions (linear vibronic coupling formalism, LVC). Taking into account the overlapping of the silatrane bands with the bands of probable impurities, bicyclic amines, (OH)XSi(OCH2CH2)2NCH2CH2OH, allowed us to reliably determine the position of the low-energy bands (at ∼9.7 eV for F- and at ∼9.

View Article and Find Full Text PDF

The first representatives of the radical anions of silatranes XSi(OCH2CH2)3N – organic derivatives of the pentacoordinate silicon atom (X = Ph, 1; p-NO2PhO, 2a; m-NO2PhO, 2b; o-NO2PhO, 2c) – were obtained and characterized by EPR spectroscopy. The structure of 1(−˙), 2a(−˙), 2b(−˙), and 2c(−˙) in polar solvents (C-PCM and COSMO models) was studied at the UMP2 and UB3PW91 levels of theory. The variation of structural characteristics and pentacoordinate character of the silicon atom in 1, 2 upon the attachment of an additional electron to them is discussed.

View Article and Find Full Text PDF

Theoretical investigation of the phenomenon of hypersensitivity of the (29)Si NMR chemical shift, δ, in the pentacoordinate silicon compounds to the temperature effect has been performed by the example of N-(silylmethyl)acetamides MeC(O)NMeCH2SiX3 (X = Me, 1; OMe, 2; F, 3) and MeC(O)NMeCH2SiMe2F (4) with the use of experimental dynamic NMR (DNMR) (29)Si data. It is based on the following: (i) the analysis of the potential energy surface of molecules 1-4 in polar solvents and the energetics of interconversion between their possible isomeric forms; (ii) the calculations of δ at different temperatures taking into account the dependence of the dielectric constant (ε) of the medium on T, and (iii) the isolation of dynamic, geometrical, and polar contributions to the temperature drift of δ. The results obtained allowed us to give a consistent explanation of the DNMR (29)Si spectra of acetamides 1-4 and to elucidate the nature of an unusual effect of T on δ.

View Article and Find Full Text PDF

DFT (B3LYP, M06-2X) and MP2 methods are applied to the design of a wide series of the potentially 10-C-5 neutral compounds based on 6-azabicyclotetradecanes: XC(1)(YCH2CH2CH2)3N 1-3, XC(1)(YC6H4CH2)3N 4-6, XC(1)[Y(tBuC6 H3)CH2]3N 7-9 and carbatranophanes C6H3[XC(1)(YC6H3CH2)3N] 10-25 (X = Me, F, Cl; Y = O, NH, CH2, SiH2; Z = O, CH2, (CH2)2, (CH2)3). Carbatranophanes 10-25 are characterized by a sterical compression of their axial 3c-4e XC(1)←N fragment with respect to that in the parent molecules 4-6. A magnitude of the revealed effect depends on a valence surrounding of the central carbon atom C(1), the size and the nature of the side chains (Z) that link the "π-electron cap" with a tetradecane backbone.

View Article and Find Full Text PDF

Silatranes XSi(OCH2CH2)3N exhibit a good linear relationship between their experimental and calculated (IGLO and GIAO) values of the NMR chemical shifts of (15)N, δN, and the lengths of dative bonds Si←N, dSiN, determined in the gas phase (ED, CCSD), solutions (COSMO PBE0, B3PW91), and crystals (X-ray). An aggregate of the obtained data provides strong evidence that the gas-phase value of dSiN in MeSi(OCH2CH2)3N should be greater by ∼0.05 Å than that determined in the electron diffraction (ED) experiment (2.

View Article and Find Full Text PDF

Substituted isobenzofuranone derivatives 1a-3a and bindone 4 are characterized by the presence of an intramolecular C(Ar)-H···O hydrogen bond in the crystal (X-ray), solution ((1)H NMR and specific and nonspecific IEF-PCM solvation model combined with MP2 and B3LYP methods), and gas (MP2 and B3LYP) phases. According to geometric and AIM criteria, the C(Ar)-H···O interaction weakens in 1a-3a (independent of substituent nature) and in 4 with the change in media in the following order: gas phase > CHCl(3) solution > DMSO solution > crystal. The maximum value of hydrogen bond energy is 4.

View Article and Find Full Text PDF

In this work, we used a preparation of diminazene, which belongs to the group of aromatic diamidines. This compound acts on the causative agents of blood protozoan diseases produced by both flagellated protozoa (Trypanosoma) and members of the class Piroplasmida (Babesia, Theileria, and Cytauxzoon) in various domestic and wild animals, and it is widely used in veterinary medicine. We examined the behavior of water-disperse diminazene (immobilized in Tween 80 micelles) at the cellular and organismal levels.

View Article and Find Full Text PDF

The structure and the hydrogen bonding in the systems formed by the intramolecularly H-bonded systems, namely, maltol (3-hydroxy-2-methyl-4-pyrone), 5, 2,4,6-trinitrophenol, 6, acetylacetone enol, 7, with Lewis bases, phosgene, 8, dioxane, 9, and DMSO, 10, have been studied by density functional theory (B3LYP) and MP2 using the 6-311G* basis set. The continuum solvent effect was simulated by IEF-PCM model. The hydrogen bond analysis using the atoms in molecules (AIM) method was applied by using the MP2(full)/6-311++G** electron density to establish the nature of the bifurcate hydrogen bond (BHB) in these systems as well as contributory factors for its stabilization.

View Article and Find Full Text PDF

The study was aimed at evaluating the effectiveness of liposomal, micellar, and water-soluble drug forms of diminazene for its localization in cells and selective accumulation at the sites of aggregation of pathogenic organisms. Pharmacological and dynamic properties of a new injection micellar diminazene preparation were experimentally determined. These properties were compared with the same parameters obtained for the water-soluble and liposomal diminazene aceturate drug forms.

View Article and Find Full Text PDF

B3LYP and MP2 computations have been performed on a variety of Si,Si'-substituted N,N'-bis(silylmethyl)propylene ureas. According to electron-density atoms-in-molecules (AIM) and electron localization function (ELF) quantum-topological analyses, a transition from the unstable non-chelate forms of these compounds to mono- and bis-chelate forms results in the successive interaction of one and two tetracoordinate silicon atoms with the carbonyl oxygen and the formation, respectively, of one and two covalent, polar Si..

View Article and Find Full Text PDF

Silicon-nitrogen bonding and the photoelectron spectra of hydro-silatrane and methyl-silatrane, XSi[OCH2CH2]3N (X = H and Me), were studied with ab initio electron propagator theory, many-body methods, and density functional models. A linear vibronic coupling (LVC) model was employed to estimate vibrational widths of the ionization bands and to study the dependence of the ionization energies on the molecular geometry. Particular attention was given to coordinates that change the Si-N distance and the strength of the donor-acceptor interaction between these two atoms.

View Article and Find Full Text PDF

We have studied radiative pion decays pi(+)-->e(+)nugamma in three broad kinematic regions using the PIBETA detector and a stopped pion beam. Based on Dalitz distributions of 41 601 events we have evaluated absolute pi-->enugamma branching ratios in the three regions. Minimum chi(2) fits to the integral and differential (E(e(+)),E(gamma)) distributions result in the axial-to-vector weak form factor ratio of gamma identical with F(A)/F(V)=0.

View Article and Find Full Text PDF

Using a large acceptance calorimeter and a stopped pion beam we have made a precise measurement of the rare pi(+)-->pi(0)e(+)nu (pi(beta)) decay branching ratio. We have evaluated the branching ratio by normalizing the number of observed pi(beta) decays to the number of observed pi(+)-->e(+)nu (pi(e2)) decays. We find the value of Gamma(pi(+)-->pi(0)e(+)nu)/Gamma(total)=[1.

View Article and Find Full Text PDF

The prophylactic and therapeutic action of immunotropic preparations in different doses on the development of Pseudomonas infection of experimental animals with thermal burns was evaluated. Natural marrow and thymic regulatory peptides (myelopid, tactivin and thymalin), as well as the synthetic immunopreparation polyoxydonium, were used for immunocorrection. The study revealed that the injection of these immunomodulators in doses recommended by instructions for use did not affect the course of the infectious process, antibody production by immunocompetent cells and the death rate of experimental animals.

View Article and Find Full Text PDF