Indo calculation of electronic spectra for transition metal complexes in the extended approximation of singly excited configurations

Semiempirical INDO-E/S calculations of [RuX₆]^q (X=NH₃, q=+2, +3; X=CN⁻, q=−4, −3) complexes are performed to demonstrate that the MO relaxation in the electronically excited state can be taken into account by introducing certain double excitations into the configuration interaction matrix; the principles of selection of the excitations are discussed. The calculation results are compared with the experimental electronic absorption spectra. St. Petersburg State University. Translated fromZhurnal Struktumoi Khimii, Vol. 37, No. 2, pp. 195–205, March–April, 1996. Translated by I. Izvekova     

121,123Sb NQR study of solid phases formed in systems (MF)1−x −(M′F) x −SbF3−H2O (M, M′=Na, K, Rb, Cs, and NH4)

Crystalline substances formed in the (MF)_1−x −(M′F) _x −SbF₃−H₂O systems (M, M′=Na, K, Rb, Cs, and NH₄;x=0 to 1) were investigated by^121,123Sb NQR spectroscopy at 77 K. The formation of individual Sb^III complexes NaCs₃Sb₄F₁₆·H₂O and NaKSbF₅·1.5H₂O, and statistically disordered mixed crystals M_1−x −M′ _x −SbF₄ (M, M′=K, Rb, Cs, and NH₄) was established. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 109–112, January, 1999.     

Semiempirical calculations of the electronic spectra of organometallic compounds: Estimation of solvent and counterion effects

The electronic spectra of the [Ru(NH₃)₅pz]²⁺, [Ru(NH₃)₅pz]³⁺, and [Ru(CN)₅pz]³⁻ complexes are calculated by the CI INDO method. The effect of solvation on the spectra is considered in a point charge approximation and in terms of the parametric model of a charged sphere enveloping the metal fragment. Interrelation of these approaches is discussed. Data on the molecular electrostatic potentials created by the complexes are presented to substantiate the models. St. Petersburg State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 4, pp. 603–618, July–August, 1996. Translated by I. Izvekova     

Processes of dissociative electron capture by 20-hydroxyecdysone molecules

The peculiarities of dissociative electron capture by 20-hydroxyecdysone molecules with the formation of fragment negative ions were studied. In the region of high electron energies (5–10 eV), processes of skeleton bond rupture are accompanied by the elimination of H₂O and H₂ molecules. In the region of thermal energies of electrons (≈0 eV), the mass spectrum is formed mainly by the [M−nH₂O]^.− (n=1–3) and [M−H₂−nH₂O]^.− (n=0−3) ions that are generated exclusively by the rearrangement. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 709–712, April, 2000.     

Effect of obligatory replacement and conformational restriction on psychotropic activity of thyroliberin analogs

Easy lactamization of Gln(Asn)−Pro−NH₂ with the formation of cyclic dipeptides with the diketopiperazine structure (mimetics of the conformational fragments of linear tripeptides with the X−Protrans-bond) was observed in the synthesis of tripeptide Glp−Gln−Pro−NH₂ modified by the replacement of histidine with obligatory similar glutamine in thyroliberin (Glp−His−Pro−NH₂, TRH) and in the synthesis of its structural analog [Asn²]TRH. Ion peaks corresponding to the Glp and Pro amino acid residues were revealed in the mass spectra of the peptides synthesized. The biological properties of the compounds obtained were determined indicating that the obligatory replacement resulted in an increased physiological specificity of [Gln²]TRH. The enhanced activity of conformationally restricted cyclic peptides compared to linear ones suggests that the biologically active conformation responsible for the antidepressant activity of linear TRH analogs is the conformation with X−Protrans-bond. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2015–2020, October, 1998.     

Probing the structural effects on the intrinsic electronic and redox properties of [2Fe–2S]<Superscript>+</Superscript> clusters,a broken-symmetry density functional theory study

In biological electron transport chains, [2Fe–2S] clusters have versatile electrochemical properties and serve as important electron carriers in a wide variety of biological processes. To understand structural effects on the variation in reduction potentials in [2Fe–2S] proteins, a series of [2Fe–2S] protein analogs with bidentate ligands ( − SC ₂ H ₄ NH ₂) were recently produced by collision-induced dissociation of [Fe ₄ S ₄(L)₄]²⁻ (L = SC ₂ H ₄ NH ₂). Combined with photoelectron spectroscopy findings, the reaction mechanisms of [Fe ₄ S ₄(L)₄]²⁻ to [Fe ₂ S ₂(L)₂]⁻ and the structural effects of ligands on the electronic and redox properties of the [2Fe–2S] clusters are investigated here using broken-symmetry density functional theory method. Our calculations suggest that [Fe ₂ S ₂(η² − L)(cis − L)]⁻ and [Fe ₂ S ₂(η² − L)₂]⁻ are the experimentally observed [2Fe–2S] products, which are generated via a fission process of [Fe ₄ S ₄(L)₄]²⁻ followed by rearrangement of ligands of [Fe ₂ S ₂(L)₂]⁻. Moreover, structural variation of the ferrous center may dramatically affect the oxidation energy of the [2Fe–2S] clusters.     

Clathrate formation in the liquid phase of (C4H9)4NF−NH4F−H2O

At a certain concentration of NH₄F, the solid allocyric solutions of the (C₄H₉)₄NF−NH₄F−H₂O system stratify into two liquid phases in the process of melting. The mutual solubility of the liquids decreases at elevated temperatures. The boundary surface of the stratification region was determined The solubility isotherms (27 and 30°C) of the stratification region are investigated by the solubility method This relatively rare mutual sulubility of liquids (retrograde solubility) is associated with clathrate formation in the liquid phase. Near the melting points of the solid clathrate solutions, both in the liquid and solid phases the tetrabutylammonium cation evidently forms surrounding cavities bounded by water and ammonium fluoride molecules linked by hydrogen bonds. The clathrate-like components of the solution are structurally compatible with “water-like” and “organic” components, i.e., they are homogenizing components. At higher temperatures, the homogenizing clathrate-like structures break down, and the structurally incompatible solution components stratify into two phases. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol 35, No. 6, pp. 122–128, November–December, 1994. Translated by L. Smolina     

Manifestation of electron-nuclear motions in the123Sb NQR spectra of pentafluoroantimonites

A dependence between the quadrupole coupling constants (e ² Qq _zz ) and the asymmetry parameters of the electric field gradient (η) for the antimony atoms in the complex [SbF₅]²⁻ anions of M₂SbF₅ pentafluoroantimonites (M=Na, K, Rb, Cs, NH₄, Ti, and Et₂NH₂) was revealed from the¹²³Sb NQR spectra at 77 K. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1988–1990, October, 1998.     

Crystallochemical features of the anion varieties of aluminum and lithium binary hydroxide

Crystallochemical features of anion (Cl⁻, Br⁻, I⁻, NO ₃ ⁻ , CO ₃ ²⁻ , SO ₄ ²⁻ ) varieties of the aluminum and lithium hydroxide were studied by using the aluminum and lithium binary hydroxide (LiOH·2Al(OH)₃·2H₂O) model in space group P6₃cm with the tetrahedral coordination of lithium. Atomic coordinates corresponding to the lowered lattice symmetry were refined. Institute of Solid State Chemistry and Processing of Mineral Raw Materials, Siberian Branch, Russian Academy of Sciences. Novosibirsk State Pedagogical University. Translated fromZhurnal Struktumoi Khimii, Vol. 35, No. 5, pp. 158–170, September–October, 1994. Translated by T. Yudanova     

Hydration and protonation ofO-vinylacetoxime in the gas phase: anab initio study

Ab initio HF/6–31G^* calculations ofO-vinylacetoxime monohydrates and cations were performed. Each conformer forms two stable H-complexes with participation of N and O atoms. The former have planar heavy-atom skeletons, whereas the water molecule in the latter is located above the plane of the proton-acceptor complex. The complexes stabilized by N...HO and O...HO bonds have different dipole moments and frequencies of the OH stretching vibrations. The most energetically favorable cation is formed by adding a proton to the C_β atom of the vinyl group ofO-vinylacetoxime. Theap,ap-conformer (ap is antiperiplanar) of this cation is 6.5 and 34.9 kcal mol⁻¹ more stable than the onium cations with the NH⁺ and OH⁺ fragments, respectively, and is characterized by polarization and appreciable lengthening of the N−O and C=C bonds. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 597–600, April, 2000.     

Reactions of 1,1,3,3-tetramethyldisilazane with dicobalt octacarbonyl and iron pentacarbonyl. Thermal decomposition of the cobalt and iron carbonyl silazane complexes

The reaction of (HMe₂Si)₂NH with Co₂(CO)₈ gives the complex [Co₂(CO)₇(SiMe₂)₂NH₂]⁺[Co(CO)₄]⁻. Its thermal decomposition starts with dissociation into the “acid” HCo(CO)₄ and the “base” Co₂(CO)₇(SiMe₂)₂NH. After that, the base and the initial complex decompose further under the action of HCo(CO)₄. The final products of this reaction are CO, NH₃, Co, volatile dimethylcyclosilazane, and a solid residue consisting of cobalt particles encapsulated into a polymethylsiloxane matrix and possessing properties of mixed para- and ferromagnetics with an ultimate specific magnetization of 64–74 G g⁻¹. Tetramethyldisilazane reacts with iron pentacarbonyl under UV irradiation to give relatively stable 1,3-bis(tetracarbonylthydrideiron)-1,1,3,3-tetramethyldisilazane. This product contains Fe−H…N hydrogen bonds, which stabilize it against dehydrogenation and cyclization to diironcyclodisilazane. Thermal decomposition of this product was investigated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2537–2544, December, 1998.     

Five coordination modes of 4-aminopyrimidine with N-hydroxy-ethylethylenediaminetriacetatoruthenate(II)

Summary The complex [Ru^II(hedta)(4NH₂pym)]⁻, hedta³⁻ = N-hydroxyethylethylenediaminetriacetate, 4NH₂pym = 4-aminopyrimidine, exists at pH 7 as five different coordination isomers, which are most readily distinguished by their electrochemical waves in comparison with the 2-aminopyridine (2NH₂py) complex. The 2NH₂py complex exhibits N(1) (pyridine bound), exo-NH₂ (amine bound) and N(1), NH₂-chelated species. The 4NH₂pym complex forms N(1), exo-amine and N(3), NH₂-chelated isomers analogues to the 2NH₂py species, but also engages in η² (olefin bound) coordination of the dearomatized 4NH₂pym ring in C(5)–C(6), and another η² type of complex involving electron density between N(1) and N(3) of the ring (η³ form). N(1), η² and η³ isomers have also been detected for unsubstituted pyrimidine (pym), 4-methylprimidine (4CH₃pym) and 2-aminopyrimidine (2NH₂pym). Electrochemical waves (V versus NHE) for the five isomers are assigned as follows: (Ru^II/III) exo-NH₂ (0.06 V), N(1) (0.29 V), η² (0.49 V); (Ru^II/III) η³ (0.76 V); N(3), NH₂-chelated (1.09 V).     

Kinetics of the thermal decomposition of dinitramide

The kinetic regularities of the heat release during the thermal decomposition of liquid NH₄N(NO₂)₂ at 102.4–138.9 °C were studied. Kinetic data for decomposition of different forms of dinitramide and the influence of water on the rate of decomposition of NH₄N(NO₂)₂ show that the contributions of the decomposition of N(NO₂)₂ ⁻ and HN(NO₂)₂ to the initial decomposition rate of the reaction at temperatures about 100 °C are approximately equal. The decomposition has an autocatalytic character. The analysis of the effect of additives of HNO₃ solutions and the dependence of the autocatalytic reaction rate constant on the gas volume in the system shows that the self-acceleration is due to an increase in the acidity of the NH₄N(NO₂)₂ melt owing to the accumulation of HNO₃ and the corresponding increase in the contribution of the HN(NO₂)₂ decomposition to the overall rate. The self-acceleration ceases due to the accumulation of NO₃ ⁻ ions decreasing the equilibrium concentration of HN(NO₂)₂ in the melt. For Part 2, see Ref. 1. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 395–401 March 1998.     

Probing the Interaction Between a Surfactant–Cobalt(III) Complex and Bovine Serum Albumin

The mechanism of binding of the surfactant–cobalt(III) complex, cis-[Co(phen)₂(C₁₄H₂₉NH₂)Cl](ClO₄)₂⋅3H₂O (phen = 1,10-phenanthroline, C₁₄H₂₉NH₂ = tetradecylamine) with bovine serum albumin (BSA) was investigated by UV–vis absorption, circular dichroism (CD) and fluorescence spectroscopic techniques. The results of fluorescence titration revealed that the surfactant–cobalt(III) complex quenched the intrinsic fluorescence of BSA through a combination of static and dynamic quenching. The apparent binding constant (K _a) and number of binding sites (n) were calculated below and above the critical micelle concentration (CMC). The thermodynamic parameters determined by the van’t Hoff analysis of the constants (ΔH ^∘=14.87 kJ⋅mol⁻¹; ΔS ^∘=152.88 J⋅mol⁻¹⋅K⁻¹ below the CMC and 25.70 kJ⋅mol⁻¹ and 243.14 J⋅mol⁻¹⋅K⁻¹, respectively, above the CMC) clearly indicate that the binding is entropy-driven and enthalpically disfavored. Based on F?rster’s theory of non-radiation energy transfer, the binding distance, r, between donor (BSA) and the acceptor (surfactant–cobalt(III) complex) was evaluated. UV–vis, CD and synchronous fluorescence spectral results showed that the binding of the surfactant–cobalt(III) complex to BSA induced conformational changes in BSA.     

Li+/H+ ion exchange in Li3 ? 2xNbxM2 ? x(PO4)3 (M = In, Fe) materials with a NASICON structure

H_{3 − 2x} Nb _x M_{2 − x} (PO₄)₃ (M = In, Fe) acid phosphates have been obtained by ion exchange from their lithium forms and X-ray powder diffraction, impedance measurements, and ⁷Li and ¹H NMR spectroscopy. The parameters of the hexagonal unit cell of the proton-exchanged forms differ only slightly from those of the initial lithium compounds. According to ¹H NMR data, the proton in the acid phosphates is not hydrated. The conductivity of the acid phosphates at high temperatures depends weakly on their composition and is ∼1.7 × 10⁻⁷ S cm⁻¹ at 620 K. The activation energy of conduction is 30–33 kJ/mol (430–770 K).     

Determination of hemoglobin at a novel NH2/ITO ion implantation modified electrode

A novel electrode was prepared by implanting NH₂ ⁺ into an ITO film (NH₂/ITO). Gold nanoparticles were deposited on the surface of NH₂/ITO electrode. The NH₂/ITO and Au/NH₂/ITO electrodes were used to determine hemoglobin (Hb) immobilized on the electrodes surfaces. The relationship of the reductive peak current value of Hb among different electrodes was: Hb/ITO:Hb/Au/ITO:Hb/NH₂/ITO:Hb/Au/NH₂/ITO=1:1.5:2:4. The linkage between the –NH₂ implanted into ITO film and the –COOH of Hb was recognized to be the reason for the increase of active Hb coverage on NH₂/ITO electrode compared with the ITO electrode. Increase of active Hb coverage on Au/NH₂/ITO compared with Au/ITO was attributed to the different amount of gold nanoparticles deposited. The determination of Hb at an Au/NH₂/ITO electrode was optimized. Calibration curve was obtained over the range of 1.0 × 10⁻⁸ – 1.0 × 10⁻⁶ mol · L⁻¹ with a detection limit of 1.0 × 10⁻⁸ mol · L⁻¹. Results showed that the novel NH₂/ITO and Au/NH₂/ITO electrodes exhibited good stability, reproducibility besides better electrochemical performance. Correspondence: Jing Bo Hu, Department of Chemistry, Beijing Normal University, Beijing 100875, China     

Mild template synthesis in the CoII-dithiooxamide-glyoxal system in cobalt(II) hexacyanoferrate(II) gelatin-immobilized matrices

Complexation processes in a cobalt(II) hexacyanoferrate(II) gelatin-immobilized matrix under the action of aqueous solutions containing dithiooxamide H₂N−C(S)−C(S)−NH₂ and glyoxal HOC−CHO at pH>10 were studied. Under these conditions, mild template synthesis occurs to form a Co^III chelate with the (N,N,S,S)-ligand,viz. 2,7-dithio-3,6-diazaoctadiene-3,5-dithioamide-1,8, with a metal to ligand ratio of 1∶1, where dithiooxamide and glyoxal act as ligand synthons. The reaction mechanism is discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1999–2004, October, 1999.     

The state of metals in the supported bimetallic Pt−Pd/SO4/ZrO2 system

The behavior of the metals in the Pt−Pd/ZrO₂ and Pt−Pd/SO₄/ZrO₂ systems was studied by DRIFT spectroscopy. After reduction of Pt−Pd/ZrO₂ at 100 °C, the states of the metals are mainly Pt⁰ and Pd⁰ with a minor admixture of positively charged forms of Pt⁺ or Pd²⁺. An increase in the temperature of reduction leads to the formation of a bimetallic alloy. In the Pt−Pd/SO₄/ZrO₂ system, the effects of alloy formation and the interaction of the surface SO₄ groups superimpose. At low reduction temperatures, the surface SO₄ groups interact mainly with palladium. The influence of the surface sites on both supported metals increases with increasing reduction temperature. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1265–1270, July, 1999.     

Blue and green centers in natural apatites by ERS and optical spectroscopy data

Using ESR and optical spectroscopy we showed that the blue coloring is imparted to natural apatites by SO ₃ ⁻ radicals and the green coloring is due to SiO ₃ ⁻ radicals complexed with rare earth ions, SiO ₃ ⁻ -(Ce³⁺+K). The role of U⁴⁺ and Th⁴⁺ isomorphous actinide ions in the process of color center formation is investigated. United Institute of Geology, Geophysics, and Mineralogy, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Struktumoi Khimii, Vol. 36, No. 1, pp. 89–101, January–February, 1995. Translated by L. Smolina     

Molecular architecture and conformation of macromolecules of novel polysilanes

Molecular-weight parameters of new silane homo- and copolymers were analyzed. For all polymers, theM _w values are close ((6.0–8.6)·10⁴), the curves of molecular weight distribution are unimodal, andM _w/M _n=2−2.5. Cyclic fragments or those containing the −C=C− groups make the major contribution to the polysilane chain rigidity. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2430–2433, December, 1998.