Potential function of the internal rotation of a methacrolein molecule in the ground (<Emphasis Type="Italic">S</Emphasis> <Subscript>0</Subscript>) electronic state

The structural parameters of s-trans- and s-cis-isomers of a methacrolein molecule in the ground (S₀) electronic state are determined by means of MP2 method with the cc-pVTZ basis set. Kinematic factor F(φ) is expanded in a Fourier series. The potential function of internal rotation (PFIR) of methacrolein in this state is built using experimental frequencies of transitions of the torsional vibration of both isomers, obtained from an analysis of the vibrational structure of the high-resolution UV spectrum with allowance for the geometry and difference between the energy (ΔH) of the isomers. It is shown that the V_n parameters of the potential function of internal rotation of the molecule, built using the frequencies of the transition of the torsional vibrations of s-trans- and s-cis-isomers of the methacrolein molecule, determined from vibrational structure of the high-resolution UV spectrum and the FTIR spectrum, are close.     

Comparative reactivity of substituted 1,3-and 1,4-thiasilinane <Emphasis Type="Italic">S</Emphasis>-oxides in the sila-Pummerer rearrangement and inversion of the thiocarbonyl group

The thermal sila-Pummerer rearrangement of diastereomeric 2,3,3-trimethyl-1,3-thiasilinane S-oxides was studied. Introduction of the methyl group in the 2 position of 3,3-trimethyl-3-thiasilinane S-oxide slows down the rearrangement. When heated in CCl₄, the trans isomer (2-Me_eq, SO_eq) converts into the cis isomer (2-Me_eq, SO_ax) which rapidly rearranges into 2,2,7-trimethyl-1,6,2-oxathiasilepane. On the contrary, the isomeric 2,4,4-trimethyl-1,4-thiasilinane S-oxide is thermally stable up to 160°C in DMSO. The inversion at the sulfur atom in 2,3,3-trimethyl-1,3-thiasilinane S-oxides and 2,4,4-trimethyl-1,4-thiasilinane S-oxides under the action of triethyloxonium tetrafluoroborate was studied. The trans isomer of 2,3,3-trimethyl-1,3-thiasilinane S-oxide (2-Me_eq, SO_eq) forms with Et₃O⁺BF ₄ ^? a salt which decomposes in two ways. The first involves recovery of the starting sulfoxide due to Sn2 substitution at the carbon atom of the ethoxy group, and the second, convertion into the cis isomer (2-Me_eq, SO_ax) which rearranges into 2,2,7-trimethyl-1,6,2-oxathiasilepane. Under the same conditions, the cis isomer of 2,3,3-trimethyl-1,3-thiasilinane S-oxide (2-Me_eq, SO_eq) decomposes to form siloxanes. trans-2,4,4-Trimethyl-4-thiasilinane S-oxide (2-Me_eq, SO_eq) under the action of Et₃O⁺BF ₄ ^? convers into the cis isomer (2-Me_eq, SO_ax). The B3LYP/6-311G(d,p) theoretical analysis showed that the thermal inversion at the sulfur atom in the compounds studied has a high energy barrier.     

Synthesis of <Emphasis Type="Italic">ortho</Emphasis>-carboranyl derivatives of (<Emphasis Type="Italic">S</Emphasis>)-asparagine and (<Emphasis Type="Italic">S</Emphasis>)-glutamine

(S)-Asparagine and (S)-glutamine ortho-carboranyl derivatives with free amino and carboxy groups in the α-position were synthesized. By an example of N ^γ-(1,2-dicarba-closo-dodecarboran-3-yl)-(S)-glutamine it was demonstrated that the developed synthetic approach carboranyl derivatives of amino acids allowed the preparation of optically pure isomers.     

Comparative analysis of the vibrational structure of the absorption spectra of acrolein in the excited (<Emphasis Type="Italic">S</Emphasis><Subscript>1</Subscript>) electronic state

The assignments of absorption bands of the vibrational structure of the UV spectrum are compared with the assignments of bands obtained by the CRDS method in a supersonic jet from the time of laser radiation damping for the trans isomer of acrolein in the excited (S ₁) electronic state. The ν_00trans = 25861 cm⁻¹ values and fundamental frequencies, including torsional vibration frequency, obtained by the two methods were found to coincide in the excited electronic state (S ₁) for this isomer. The assignments of several absorption bands of the vibrational structure of the spectrum obtained by the CRDS method were changed. Changes in the assignment of (0-v′) transition bands of the torsional vibration of the trans isomer in the Deslandres table from the ν_00trans trans origin allowed the table to be extended to high quantum numbers v′. The torsional vibration frequencies up to v′ = 5 were found to be close to the frequencies found by analyzing the vibrational structure of the UV spectrum and calculated quantum-mechanically. The coincidence of the barrier to internal rotation (the cis-trans transition) in the one-dimensional model with that calculated quantum-mechanically using the two-dimensional model corresponds to a planar structure of the acrolein molecule in the excited (S ₁) electronic state.     

The dynamics of nonadiabatic transitions in collisions between the I<Subscript>2</Subscript>(<Emphasis Type="Italic">E</Emphasis>) and I<Subscript>2</Subscript>(<Emphasis Type="Italic">X</Emphasis>) molecules

The paper presents the results of a theoretical study of the dynamics of nonadiabatic transitions between the ion-pair states E0 _g ⁺ and D0 _u ⁺ of the I₂ molecule induced by collisions with the I₂ molecule in the ground electronic state X0 _g ⁺ . The potential energy surfaces and diabatic coupling matrix elements of electronic states were obtained using a model based on the diatomics-in-molecule approximation. Special perturbation theory for intermolecular interaction was used to show that the large transition dipole moment between the E0 _g ⁺ and D0 _u ⁺ states caused the appearance of additional long-range corrections, an electrostatic dipole-quadrupole correction to the diabatic coupling matrix elements and induction dipole-dipole correction to the potential energy surface. The influence of these corrections on nonadiabatic dynamics was studied at the level of the semiclassical approximation. The electrostatic correction was found to sharply increase the contribution of resonance (accompanied by minimum kinetic energy changes) vibronic transitions at large distances between the colliding molecules. The induction correction had the opposite effect because of the high transition probability at short distances. The results obtained were in qualitative agreement with experimental data. The conclusion was drawn that obtaining quantitative agreement required a more balanced inclusion of interactions at short and long distances.     

The internal rotation potential functions of the methacryloyl chloride molecule in the ground and excited electronic states

The systems of torsional vibration levels of the trans and cis methacryloyl chloride isomers in the ground (S ₀) and excited (S ₁) electronic states obtained by analyzing the vibrational structure of the gas-phase UV spectrum were used to reproduce the internal rotation potential functions of the molecule in both electronic states. The kinematic F factor in the S ₀ and S ₁ electronic states was calculated taking into account the relaxation of geometric parameters depending on the internal rotation angle. The internal rotation potential function parameters in the S ₀ state are substantially different from the parameters obtained using the torsional levels of the IR Fourier transform spectrum; at the same time, they are substantiated by quantum-mechanical calculations.     

<Emphasis Type="Italic">S</Emphasis>-functional derivatives of 3,4-dihydro-2<Emphasis Type="Italic">H</Emphasis>-1,4-thiasilines

The first cyclic unsaturated S-functional derivatives of 4,4-diphenyl-3,4-dihydro-2H-1,4-thiasiline, S-oxide, S,S-dioxide, and S-sulfonimide, were prepared. Oxidation of the hydrolytically less stable 4,4-dimethyl-3,4-dihydro-2H-1,4-thiasiline leads to the corresponding sulfoxide and sulfone along with the ring opening products, siloxanes containing the sulfoxide or sulfonyl group.     

Solution Thermodynamics of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis><Superscript>/</Superscript>-Ethylenebis-(salicylideneiminato)-diaquochromium(III) Chloride in Aqueous Dimethylsulphoxide

The densities, viscosities and refractive indices of N,N ^/-ethylene-bis(salicylideneiminato)-diaquochromium(III) chloride, [Cr(salen)(H₂O)₂]Cl, in aqueous dimethylsulfoxide (DMSO) with different mass fractions (w ₂ = 0.20, 0.40, 0.60, 0.80 and 1.00) of DMSO were determined at 298.15, 308.15 and 318.15 K under atmospheric pressure. From measured densities, viscosities and refractive indices the apparent molar volumes (V _φ ), standard partial molar volume (V _φ ⁰ ), the slope (S _V ^* ), standard isobaric partial molar expansibility (φ _E ⁰ ) and its temperature dependence (?φ _E ⁰ /?T) _p , the viscosity B-coefficient, its temperature dependence (?B/?T), solvation number (S _n ) and apparent molar refractivity (R _D ^φ ), etc., were calculated and discussed on the basis of ion–ion and ion–solvent interactions. These results revealed that the solutions are characterized by ion–solvent interactions rather than by ion–ion interactions and the complex behaves as a long range structure maker. Thermodynamics of viscous flow was discussed in terms of transition state theory.     

Potential functions of internal rotation in <Emphasis Type="Italic">n</Emphasis>-alkanes and its contribution to thermodynamic properties

The potential functions of braked internal rotation V(?) in n-alkanes (ethane, propane, butane, n-pentane, n-hexane, n-heptane) were calculated by ab initio and DFT methods with the 6-311++G(3df,3pd) basis set. The functions were approximated as a series of six cosines. The dependences of V(?) on the length of the hydrocarbon chain in n-alkanes were analyzed. The heights of the trans-cis and trans-gauche barriers and the differences between the energies of the trans and gauche conformers were calculated and compared with the experimental data. From the calculated geometric parameters and V(?), the contributions of the braked internal rotation to the enthalpy, entropy, heat capacity, and Gibbs free energy at 298 K were determined. The contributions of internal rotations are transferable within the framework of additive approaches. The generalized function V _av(?) for n-alkanes and averaged contributions of internal rotation of the C-C bonds and CH₃- and -CH₂- tops to the thermodynamic properties were suggested.     

Bischelated complexes of a dithiocarbazate <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">S</Emphasis> Schiff base ligand: synthesis,characterization and antimicrobial activities

The N,S bidentate proligand S-hexyl-β-N-(4-methoxybenzylidene)dithiocarbazate (HL), obtained by condensation of S-hexyldithiocarbazate with 4-methoxybenzaldehyde, has been used to synthesize six metal complexes, namely NiL₂, CuL₂, ZnL₂, CdL₂, PdL₂ and PbL₂, which have been characterized by physicochemical techniques and spectroscopic methods. Single crystal structural analyses for NiL₂, CuL₂ and PdL₂ show that these are square-planar complexes with each metal bischelated by the Schiff base in its deprotonated monoanionic form. In all three cases, the ligands show a trans configuration, although they crystallize in different space groups. All the metal complexes with the exception of the nickel derivative show a significant decrease in fluorescence intensity with respect to the free proligand HL. Free HL and all six complexes were tested for antibacterial activity against three pathogenic gram-negative organisms. The metal complexes show moderate although diverse activities; however, free HL as well as the copper(II) complex did not reveal any antibacterial activity against the tested organisms.     

Synthesis of (2<Emphasis Type="Italic">S</Emphasis>,3<Emphasis Type="Italic">S</Emphasis>,4<Emphasis Type="Italic">S</Emphasis>)-2,3-<Emphasis Type="Italic">O</Emphasis>-isopropylidene-4-(methoxycarbonylmethyl)cyclopentan-1-one

(2S,3S,4S)-2,3-O-Isopropylidene-4-(methoxycarbonylmethyl)cyclopentan-1-one was synthesized starting from D-ribose through methyl (Z)-3-(5-acetyl-2,2-acetoxyacetyl-2,2-dimethyl-1,3-dioxolan-4-yl)prop-2-enoate which was subjected to cyclization in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene, followed by decarboxylation.     

Catalytic multimolecular reactions of 1,3-dicarbonyl CH acids with CH<Subscript>2</Subscript>O and <Emphasis Type="Italic">S</Emphasis>- and <Emphasis Type="Italic">N</Emphasis>-nucleophiles

The literature data on the synthesis and properties of oxo-functionalized acyclic and cyclic sulfides obtained by the catalytic multicomponent reactions of 1,3-dicarbonyl compounds with formaldehyde and S-nucleophiles are summarized. An approach to the multimolecular four-component heterocyclization of 1,3-dicarbonyl compounds with CH₂O and S- and N-nucleophiles in the synthesis of sulfanyl-substituted azaheterocycles is discussed.     

Compositions and structures of nanoparticles of pentagonal axial symmetry <Emphasis Type="Italic">D</Emphasis><Subscript>5<Emphasis Type="Italic">d</Emphasis></Subscript>: Nanotubes

The method of determination of the structure and the number of atoms in the shells of nanoparticles as a function of the arrangement of atoms at the symmetry elements of a symmetry group has been developed. The formulas for the calculation of the number of particles with symmetry group D _5d are reported. The number of particles in these shells is determined by three structurally invariant numbers and the “quantum number” of the group order n. The classification of all possible nanostructures with symmetry group D _5d is given: C _θ+10z , z = 0, 1, 2, …, where the basic shells are C _θ = C ₂, C ₁₀, C ₁₂. The sum rule has been obtained for the coordination numbers of shell sites located at symmetry axes. Pentagonal axial nanoparticles are shown to be the initial shells for obtaining (5,5) and (10,10) armchair nanotubes or (5,0) and (10,0) zigzag nanotubes. The general formula of these nanotubes closed with icosahedral and dodecahedral caps is N _20+10p , N _60+10p (p = 1, 2, …). The graphical constructions of all classes of nanoparticles and nanotubes of the pentagonal axial type are reported.     

Splitting of the <Emphasis Type="Italic">d</Emphasis><Superscript><Emphasis Type="Italic">N</Emphasis></Superscript> atomic states in icosahedral 3<Emphasis Type="Italic">d</Emphasis> metal endofullerenes M@C<Subscript>60</Subscript>

Group-theoretical and quantum-chemical investigations of the spectrum of low-lying excited states have been performed by the ROHF and FCI-RAS (Full CI in Restricted Active Space) methods for 3d metal endofullerenes (MEFs) M@C₆₀ (M =Mn, Cr, and Fe) in different charged states. The major purpose of this study is quantum-chemical verification of the anomalous (“non-Bethe’s”) character of splitting of the d ^N atomic states in an electrostatic field with icosahedral symmetry, predicted previously within the theory of integral invariants theory. The interrelation between the integral invariants theory and the quantumchemical methods applied in this work is considered in detail. Our calculations suggest that the d ^N atomic states in the icosahedral field generated by fullerene C60 (I _h ) on a metal atom (ion) remain non-split for different charged states of the metal and C₆₀. Reasons for this phenomenon and other possible approaches to verification of the prediction are discussed. It is demonstrated that the d ^N states of the encapsulated metal are split in icosahedral 3d MEFs only under very strong compression of these structures.     

Compositions and structures of nanoparticles of trigonal symmetry <Emphasis Type="Italic">D</Emphasis><Subscript>3<Emphasis Type="Italic">d</Emphasis></Subscript>: Nanotubes

A method has been developed for the determination of the structure and number of atoms in the shells of nanoparticles as a function of the arrangement of atoms at the symmetry elements of a symmetry group. The formulas for calculation of the number of particles of symmetry D _3d have been reported. It has been shown that the number of atoms in trigonal shells is determined by three structurally invariant numbers and the quantum number of the group order n. All possible nanostructures of symmetry D _3d have been classified: C_{θ + 6z} , z = 0, 1, 2, ..., where the basic shells are C_θ = C₆, C₈, and C₁₄. A sum rule has been obtained for the coordination numbers of the shell sites located on symmetry axes. Trigonal nanoparticles are parent ones for obtaining (3,0), (6,0), and (9,0) nanotubes of trigonal type. The general formulas of these nanotubes with icosahedral, dodecahedral, and cubic caps are N_{8 + 12p} , N_{20 + 24p} , and N_{60 + 36p} (p = 1, 2, ...), respectively. The graphical constructions of all classes of trigonal nanoparticles and nanotubes are reported.     

Stability of <Emphasis Type="Italic">s</Emphasis>-, <Emphasis Type="Italic">p</Emphasis>-, and <Emphasis Type="Italic">d</Emphasis>-element diphosphates in water

The mean atomic Gibbs energies of formation of (Δ _f ? _at ⁰ ) of s-, p-, and d-element diphosphates have been calculated using ion increments of the Gibbs energy (Δ _f G ⁰). The diphosphate hydrolysis kinetics is considered, and a correlation between the Δ _f ? _at ⁰ values and the hydrolysis rate constants is presented.     

Nitrosative Stress Response in <Emphasis Type="Italic">Vibrio cholerae</Emphasis>: Role of <Emphasis Type="Italic">S</Emphasis>-Nitrosoglutathione Reductase

Vibrio cholerae, the causative agent of cholera, poses serious threats to humans worldwide. V. cholerae faces host inflammatory response and encounters nitrosative stress before establishing successful colonization. It is not clear how V. cholerae combats nitric oxide and reactive nitrogen species. In the present study, we used three clinical strains of V. cholerae and tested their nitrosative stress response pattern towards sodium nitroprusside (SNP) and S-Nitrosoglutathione (GSNO). Among them, V. cholerae, belonging to both O1 and O139 serotypes, showed moderate resistance to SNP and GSNO. However, a V. cholerae strain belonging to non O1 and non O139 showed sensitivity to SNP but resistance towards GSNO. Reduced glutathione and glutathione reductase play a significant role to combat nitrosative stress in V. cholerae. This is the first report where we show the presence of GSNO reductase activity in V. cholerae and that it plays an important role to detoxify S-Nitrosoglutathione. GSNO reductase activity of V. cholerae was regulated by posttranslational modification through S-nitrosylation under in vitro conditions which could be reversed by dithiothreitol (DTT). In addition, we show that biofilm formation remained unaffected under nitrosative stress in V. cholerae.     

Direct electrochemistry and electrocatalysis of cytochrome <Emphasis Type="Italic">c</Emphasis> based on dandelion-like Bi<Subscript>2</Subscript>S<Subscript>3</Subscript> nanoflowers

The direct electrochemistry and electrocatalysis of cytochrome c (Cyt c) based on dandelion-like bismuth sulfide (d-Bi₂S₃) nanoflowers have been developed. The morphologies and composition of the d-Bi₂S₃ were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). Then, the electrochemical behaviors of Cyt c immobilized within the d-Bi₂S₃/chitosan film and its electrocatalytic ability toward hydrogen peroxide (H₂O₂) reduction were investigated by cyclic voltammetry. The electron transfer rate constant was estimated to be 13.1 s^?1, suggesting that a fast direct electron transfer was realized. The prepared Cyt c/d-Bi₂S₃/chitosan nanobiocomposite-modified electrode possessed excellent electrocatalytic ability toward H₂O₂ reduction that showed linearity in the range from 0.5 μM to 1.56 mM with a correlation coefficient of 0.9993. The detection limit was 0.2 μM on signal-to-noise ratio of 3. In addition, the d-Bi₂S₃ nanoflowers may be also applied to direct electron transfer of other redox proteins.     

Crystallographic and conformational analysis of (<Emphasis Type="Italic">E</Emphasis>)-2-isopropyl-4-(<Emphasis Type="Italic">p</Emphasis>-tolyldiazenyl)phenol

The molecular and crystal structures of the title compound, C₁₆H₁₈N₂O, were characterized and determined by single crystal X-ray diffraction method in addition to spectroscopic means such as IR, UV–VIS and ¹H NMR. The compound crystallizes in orthorhombic space group P bca, with a = 9.3350(5) Å, b = 23.4878(13) Å, c = 26.5871(12) Å, Z = 16, D _calc. = 1.1591(1) g/cm³, μ (MoK_α) = 0.073 mm^?1. Monomers of the compound in the crystal structure are linked into C(7) and C(8) chains generated by translation along the [1 0 0] direction with the aid of O–H···N type H-bonds which serve to the stabilization of periodic organization of the molecules beside major and minor component in the disordered azo fragment. In order to describe conformational flexibility and the crystal packing effects on the molecular conformation, potential barriers regarding the rotation along both Ar–N bonds were calculated by varying the related torsional degrees of freedom in every 10° ranging from ?180° to +180° via quantum chemical calculations at DFT/B3LYP level.     

<Emphasis Type="Italic">S</Emphasis>- to <Emphasis Type="Italic">N</Emphasis>-Palmitoyl Transfer During Proteomic Sample Preparation

N-palmitoylation has been reported in a number of proteins and suggested to play an important role in protein localization and functions. However, it remains unclear whether N-palmitoylation is a direct enzyme-catalyzed process, or results from intramolecular S- to N-palmitoyl transfer. Here, using the S-palmitoyl peptide standard, GC_palmLGNAK, as the model system, we observed palmitoyl migration from the cysteine residue to either the peptide N-terminus or the lysine side chain during incubation in both neutral and slightly basic buffers commonly used in proteomic sample preparation. Palmitoyl transfer can take place either intra- or inter-molecularly, with the peptide N-terminus being the preferred migration site, presumably because of its lower basicity. The extent of intramolecular palmitoyl migration was low in the system studied, as it required the formation of an entropically unfavored macrocycle intermediate. Intermolecular palmitoyl transfer, however, remained a tangible problem, and may lead to erroneous reporting of in vivo N-palmitoylation. It was found that addition of the MS-compatible detergent RapiGest could significantly inhibit intermolecular palmitoyl transfer, as well as thioester hydrolysis and DTT-induced thioester cleavage. Finally, palmitoyl transfer from the cysteine residue to the peptide N-terminus can also occur in the gas phase, during collision-induced dissociation, and result in false identification of N-palmitoylation. Therefore, one must be careful with both sample preparation and interpretation of tandem mass spectra in the study of N-palmitoylation.

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