Halodiazirines and halodiazo compounds: a computational study of their thermochemistry and isomerization reaction

A computational study of the isomerization reaction of a series of halodiazirines to halodiazo compounds (cyclic to open-chain RXCN₂ species) has been carried out in order to establish the effect of the substituent groups on the isomerization rates and to obtain computational evidence of reaction mechanisms. Fluorine and chlorine were present as the halogen (X) atom, and the groups R=H, CH₃, C₂H₅, n-C₃H₇, i-C₃H₇, cyclo-C₃H₅, phenyl, OCH₃ and OH were used. Thermochemical calculations and natural bond orbital analyses were carried out at the B3LYP/6-31+G(d,p) level of theory. The results allowed us to discuss a reaction mechanism that proceeds in two steps: The first is the extrusion of nitrogen and formation of a carbene through a cyclic transition state that promotes the simultaneous breaking of the two C–N bonds, and the second one is described as the rebounding between the carbene and one of the nitrogen atoms of molecular nitrogen, both formed in the first step. The enthalpies of formation of halodiazirines and halodiazoalkanes have been calculated at the G3 level of theory.     

Study of the complexation and precipitation equilibria in the system Cr(VI)-Fe(III)-H2O

Potentiometric and spectrophotometric studies of the systems Cr(VI)-Fe(III)-H₂O and Fe(III)-H₂O systems have been performed. The formation of the complex FeCrO ₄ ⁺ is suggested and the corresponding thermodynamic formation constant has been calculated (log₁₁ = 7.77 ± 0.02) . In order to understand the cation-anion interactions, a study of the precipitation equilibrium between Cr(VI) and Fe(III) has been carried out. The results indicate the formation of FeOHCrO₄·2Fe(OH)₃, a mixed precipitate whose thermodynamic solubility product is pK_so=99.8±0.2.     

The Formation of OH*(<Superscript>2</Superscript>Σ<Superscript>+</Superscript>) Radical in the Reaction of Hydrogen with Oxygen behind a Shock Wave in Nonequilibrium Conditions

The mechanism of formation of the electronically excited radical OH*(A²Σ⁺) has been studied by analyzing calculations quantitatively describing the results of shock wave experiments carried out in order to determine the moment of maximum OH* radiation at temperatures T < 1500 K and pressures P ≤ 2 atm in the H₂ + O₂ mixtures diluted by argon when the vibrational nonequilibrium is a factor determining the mechanism and rate of the overall process. In kinetic calculations, the vibrational nonequilibrium of the initial H₂ and O₂ components, the HO₂, OH(X²Π), O₂*(¹Δ) intermediates, and the reaction product H₂O were taken into account. The analysis showed that under these conditions the main contribution to the overall process of OH* formation is caused by the reactions OH + Ar → OH* + Ar, H₂ + HO₂ → OH* + H₂O, H₂ + O*(¹D) → OH* + H, HO² + O → OH* + O² and H + H²O → OH* + H², which occur in the vibrational nonequilibrium mode (their activation barrier is overcome due to the vibrational excitation of reactants), and by H + O₃ → OH* + O₂ and H + H₂O₂ → OH* + H₂O, which are reverse to the reactions of chemical quenching.     

The formation of flouride complexes of titanium(IV)

The complex formation equilibria between titanium(IV) and fluoride ions have been studied at 25°C in 3 M(Na)Cl ionic medium by measuring, with an ion selective electrode for F^?, the free HF concentration in acid Ti(IV) solutions. The [H⁺] was kept within 0.25 and I M where the predominant form of uncomplexed metal is the dihydroxotitanium(IV) ion, Ti(OH)²⁺₂. The potentiometric data have been explained by assuming Ti(OH)₂F⁺, TiF₄ and HTiF^?₆, with equilibrium constants given in Table 3. Within the accuracy of the present e.m.f. study, ±0.2 mV, no evidence for intermediate complexes bearing 2, 3 and 5 F^? was found.From a special series of measurements, carried out by replacing a large part of the Cl^? with ClO^?₄, it is concluded that no appreciable amount of Ti(IV)Cl complexes is formed at the 3 M level employed as ionic medium.     

Formation pathways of DMSO2 in the addition channel of the OH‐initiated DMS oxidation: A theoretical study

The production of dimethyl sulfoxide (DMSO) and dimethyl sulfone (DMSO₂) in the dimethyl sulfide (DMS) degradation scheme initiated by the hydroxyl (OH) radical has been shown to be very sensitive to nitrogen oxides (NO_x) levels. In the present work we have explored the potential energy surfaces corresponding to several reaction pathways which yield DMSO₂ from the CH₃S(O)(OH)CH₃ adduct [including the formation of CH₃S(O)(OH)CH₃ from the reaction of DMSO with OH] and the reaction channels that yield DMSO or/and DMSO₂ from the CH₃S(O₂)(OH)CH₃ adduct are also studied. The formation of the CH₃S(O₂)(OH)CH₃ adduct from CH₃S(OH)CH₃ (DMS‐OH) and O₂ was analyzed in our previous work. All these pathways due to the presence of NO_x (NO and NO₂) and also due to the reactions with O₂, OH and HO₂ are compared with the objective of inferring their kinetic relevance in the laboratory experiments that measure DMSO₂ (and DMSO) formation yields. In particular, our theoretical results clearly show the existence of NO_x‐dependent pathways leading to the formation of DMSO₂, which could explain some of these experimental results in comparison with experimental measurements carried out in NO_x‐free conditions. Our results indicate that the relative importance of the addition channel in the DMS oxidation process can be dependent on the NO_x content of chamber experiments and of atmospheric conditions. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009     

Os and Pd Modified Tin Oxide Films for Sensors by the Sol Gel Process

Pure, Pd and Os modified SnO₂ films were prepared by the sol gel process and used as active materials in gas sensing devices. The films have been prepared starting from tin tetrachloride in alcoholic solution hydrolysed with water. The modifier was added to the sol as inorganic salt. Pd acetate and Os chloride were the Pd and Os precursors respectively. A structural and morphological study was carried out by means of Atomic Force Microscope (AFM), Secondary Ion Mass Spectrometer (SIMS) and x-ray Diffraction (XRD). The electrical resistance variations as a function of various gaseous atmospheres and temperature were measured to evaluate the sensing properties of the films. CO, CH₄, CH₃OH and C₂H₅OH gases were used for the tests. Following results were obtained: Pd is present in the form of PdO nanoclusters in the polycrystalline SnO₂ matrix as evidenced by XRD spectra whereas Os is a cationic modifier uniformly dispersed as evidenced in SIMS studies. Optimum sensing temperature and the sensitivity variations, with respect to the undoped films, differ according to the gaseous species. It looks therefore promising to use inexpensive, sol-gel derived, array of films in smart gas sensing devices that are able to recognise gas species and concentration.     

Vanadium(III) Complexes with Picolinic Acid and Dipicolinic Acid in Aqueous Solution

The complex species formed in aqueous solution (25 ^∘C, I = 3.0 mol-dm⁻³ KCl ionic medium) between V³⁺ cation and the ligands: picolinic acid (Hpic, HL) and dipicolinic acid (H₂dipic, H₂L), have been studied potentiometrically and by spectrophotometric measurements. The application of the least-squares computer program LETAGROP to the experimental emf (H) data, taking into account the hydrolytic species of V³⁺ ion, indicates that under the employed experimental conditions, the formation of the complexes [VL]²⁺, [V(OH)L]⁺, [VL₂]⁺, [VL₃], [V₂OL₄] with picolinic acid and the complexes [VL]⁺, [V(OH)L], [V(OH)₂L]⁻, [V(HL)(L)], and [VL₂]⁻ with dipicolinic acid were observed. The stability constants of the complexes formed were determined by potentiometric measurements, and spectrophotometric measurements were done in order to perform a qualitative characterization of the complexes formed in aqueous solution.     

Synthesis,characterization, DNA binding,DNA cleavage,antioxidant and in vitro cytotoxicity studies of ruthenium(II) complexes containing hydrazone ligands

The synthesis, spectral characterization, and biological studies of ruthenium(II) hydrazone complexes [RuCl(CO)(PPh₃)₂L] (where L = hydrazone ligands) have been carried out. The hydrazones are monobasic bidentate ligands with O and N as the donors and are preferably found in the enol form in all the complexes. The molecular structure of the ligands HL¹, HL²_, and HL³ were determined by single-crystal X-ray diffraction. The DNA binding studies of the ligands and complexes were carried out by absorption spectroscopic and viscosity measurements. The results revealed that the ligands and complexes bind to DNA via intercalation. The DNA cleavage activity of the complexes, evaluated by gel electrophoresis assay, revealed that the complexes are good DNA cleaving agents. The antioxidant properties of the complexes were evaluated against DPPH, OH, and NO radicals, which showed that the complexes have strong radical-scavenging. Further, the in vitro cytotoxic effect of the complexes examined on HeLa and MCF-7 cancer cell lines showed that the complexes exhibited significant anticancer activity.     

The hydrolysis of the cerium(III) ion,Ce3+, in aqueous perchlorate solutions at 50°C

The hydrolysis equilibria of the Ce³⁺ ion have been studied at 50°C by measuring, with a glass electrode, the hydrogen ion concentration of Ce(ClO₄)₃ solutions. The Ce(III) concentration ranged from 0.1 to 1 m, while the ClO⁻₄ level was kept constant at 3 m by adding LiClO₄. Solutions containing hydrolysed species, in which at the most 0.4% of the Ce³⁺ can be transformed into reaction products without the formation of a precipitate, were prepared by constant-current coulometry. The potentiometric data have been explained in terms of Ce(OH)²⁺, Ce₂(OH)⁵⁺ and Ce₃(OH)⁴⁺₅ complexes. Their formation constants in the inert 3 m LiClO₄ medium are reported.     

Organoboron(III) and organolead(IV) complexes as antimicrobial and antimycobacterial agents: Synthetic,structural, and biological aspects

Phenylboron(III) and triorganolead(IV) derivatives of the types PhB(OH)(DTCZ), PhB(DTCZ)₂, and Ph₃Pb(DTCZ) (where DTCZ⁻ is the anion of a S-benzyldithiocarbazate ligand) have been synthesized by the substitution reactions of phenylboronic acid and triphenyllead chloride with S-benzyldithiocarbazate. The resulting complexes have been characterized by elemental analyses, molecular weight determinations, and conductivity measurements. The mode of bonding has been established on the basis of infrared and ¹H, ¹³C, and ¹¹B NMR spectroscopic studies. Probable tetrahedral and trigonal bipyramidal structures for the resulting derivatives have been proposed. The X-ray powder diffraction study of the compound [PhB(OH)(L¹)] was carried out in order to have an idea about the molecular symmetry of the compound. The results show that the compound belongs to the orthorhombic crystal system. In the quest for better fungicides and bactericides, the studies were conducted to assess the growth inhibiting potential of the synthesized complexes against various fungal and bacterial strains. The studies demonstrate the concentration reached levels which are sufficient to inhibit and kill the pathogens. The antimycobacterial effects of the organolead(IV) compounds were also examined. The results obtained indicated that the compounds display antimycobacterial activity. The article is published in the original.     

Oxidative addition of an imidazolium cation to an anionic gallium(I) N-heterocyclic carbene analogue: Synthesis and characterisation of novel gallium hydride complexes

The reactions of N-heterocyclic carbenes and imidazolium salts towards an anionic gallium(I) heterocycle, [:Ga{[N(Ar)C(H)]₂}]⁻, , have been studied. No reactions with N-heterocyclic carbenes were observed, though the reaction of the gallium heterocycle with the imidazolium salt, [HC{N(Mes)C(H)}₂]Cl, IMesHCl, Mes = C₆H₂Me₃-2,4,6, led to oxidative insertion of the Ga(I) centre into the imidazolium C-H bond and formation of the gallium hydride complex, [HGa{[N(Ar)C(H)]₂}(IMes)]. When this reaction was carried out in the presence of traces of water, partial hydrolysis of [HGa{[N(Ar)C(H)]₂}(IMes)] resulted in the formation of the hydroxy-bridged, anionic gallium hydride complex, [{HGa[N(Ar)C(H)]₂}₂OH][(IMes)₂H]. Both compounds have been spectroscopically and structurally characterised.     

Nitrosyl Rhenium Complexes: Iodonitrosyl derivatives

The anionic Re(NO)I₅^2? has been isolated as salts of Cs⁺, Rb⁺, and dipyH⁺. The nonelectrolytic Re(NO)I₃L (L stands for 1,10-phenanthroline and 2,2′-dipyridyl) and cationic [Re(NO)IL₂]PtCl₆ have also been prepared. From a solution of Re(NO)(OH)₃ in HI, compound of formula Re(H₂O)(NO)(OH)I₂ has been isolated, pyrolysis of which yielded Re(H₂O)_0.5(NO)(OH)₂I. Measurements of electronic and i.r. spectra and magnetic moments have been carried out. The properties of the iodo derivatives have been compared with those of the corresponding fluoro, chloro and bromo complexes.     

Kinetic study of surface reactions of O2 and H2 on polycrystalline copper

Adsorption and transformation of O₂, H₂, water and methanol on polycrystalline copper in the 300–400 K range have been studied by surface potential variations. In particular, O₂ reacts with H(a) to form OH(a) with a first order kinetic law, whereas OH(a) reacts with H₂ to form water which desorbs and restores H(a) with an Elovich kinetic law.     

Study of Equilibria in the Aluminium(III)-Glycine and -Alanine Systems

The formation of various hydrolytic and mixed hydrolytic complexes of the aluminium(III) ion in the presence of glycine and L-alanine, has been studied in 0.5 mol dm^?3 (Na)NO₃ medium at 25deg;C, by emf method. The concentration ratios of amine acids to aluminium(III) were varied from 1 : 1 to 10 : 1. The least-squares treatment of the data obtained, in the absence of the amino acids, indicates the formation of the dimer, [Al₂(OH)₂]⁴⁺, and monomer, [AlOH]²⁺, with the stability constants log β₂₂ = ?7.03 ± 0.03 and log β₁₁ = ?5.65 ± 0.09, respectively. At pH values higher then ～4.0 formation of the trimer [Al₃(OH)₄]⁵⁺ (log β₃₄ = ?12.60 ± 0.08) becomes significant. In the presence of amino acids the evidence has been found for the formation of [Al₂(OH)₄]²⁺ (log β₂₄ = ?15.65 ± 0.09). Besides the formation of the pure hydrolytic complexes, equilibria in the title systems can be explained by assuming the main reaction products to have the compositions [Al(OH)₃Gly] (log β₁₃₁ = ?7.53 ± 0.04), [Al₂(OH)₂(Gly)₂] (log β₂₂₂ = 6.56 ± 0.09) and [Al(OH)₃Ala] (log β₁₃₁ = ?7.70 ± 0.03), [Al₂(OH)₂Ala₂] (log β₂₂₂ = 7.23 ± 0.07).     

Thermal analysis of β-Co2(OH)3Cl and Zn5(OH)5Cl2 · H2O

Samples of β-Co₂(OH)₃Cl and Zn₅(OH)₈Cl₂ · H₂O have been prepared and their thermal decomposition studied in air and N₂ by DTA and TG up to 1000°C. X-Ray diffraction analysis of the thermal treatment products in air at various temperatures from 100 to 100°C was also carried out. The results obtained made it possible to establish the steps through which the pyrolysis of both compounds proceeds.     

Synthesis of carbon nanofibers by catalytic pyrolysis of ethylene in the presence of vapors of volatile components

Catalytic pyrolysis of ethylene was carried out at 700 °C in the presence of vapors of H₂O, EtOH, NH₄OH, PCl₃, (MeO)₃P, Me₂SO₄, (MeO)₃B, and HCl. The composition of solid pyrolysis products was studied using the elemental analysis, X-ray diffraction analysis, and electron microscopy. The composition of the gaseous pyrolysis products was studied using mass spectrometry. The processes in the gas phase were characterized, and the relationship between conditions of ethylene pyrolysis and the structure of formed carbon nanofibers was revealed. The introduction of gaseous additives has a substantial effect on the formation, growth, and structure of the carbon nanofibers formed.     

Solvent-free synthesis of reactive inorganic precursors for preparation of organic/inorganic hybrid materials

Prehydrolyzed-condensed precursors containing amino or glycido groups were prepared via sol gel process using various alkoxysilanes in the bulk, without addition of solvent in any step of their preparation. The influence of the experimental set-up, the functionality and ratio of alkoxysilanes, and type of catalyst, on the structure buildup was studied. In the case of amino precursors, the sol–gel process was carried out at weak basic conditions while in the case of glycido precursors the sol–gel process was catalyzed by acid or neutral pH. The sol–gel process was monitored by ²⁹Si NMR in solution and the structure of the prehydrolysed-condensed precursors was characterized by small-angle X-Ray scattering. The systems with high content of tetraethoxysilane led to the fast gel formation. In weak acid medium tetraethoxysilane formed larger, more condensed species as well as small structures (based on Q ₁, Q ₂ and Q ₃ species) with silanol groups. Strong acidic conditions led to the fast formation of insoluble silica particles in liquid (sol) phase containing monomeric alkoxysilanes. The most suitable precursor formulations based on the alkoxysilanes with amino groups, as well as the most efficient set-up, were selected and used to prepare hybrid organic/inorganic networks based on an epoxy matrix. These networks were characterized using dynamic mechanical analysis.     

Mechanism of the radiolytic transformation of cellulose

The formation under -irradiation of volatile products in cellulose preparations with different degrees of crystallinity has been studied. The volatile products of the radiolysis of cellulose have been found to contain H₂, CH₄, H₂O, CO, and C0₂. According to the results obtained, these products can be divided into two groups, the first of which (H₂, H₂O, and CO) is formed as the result of the splitting out of hydrogen atoms and of —OH and —CH₂OH groups from the macromolecule, while the second (CH₄ and CO₂) is the result of radiation-chemical reactions between the components of the volatile products of the first group.Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 921–927, November-December, 1996. Original article submitted February 26, 1996.     

Grafting onto Cellulose. VI. Graft Copolymerization of Vinyl Acetate by Use of Metal Chelates as Initiators

Graft copolymerization of vinyl acetate (VAc) onto cellulose has been studied in an aqueous medium in the presence of Fe(acac)₃, Al(acac)₃, and Zn(acac)₂ as initiators. Percentage of grafting has been determined as a function of concentration of initiators and monomer, reaction time, and temperature. The reactivities of different metal chelates toward grafting of VAc on cellulose have been determined and were found to follow the order: Zn(acac)₂ > Al(acac)₃ > Fe(acac)₃. A plausible mechanism for grafting involving complex formation between metal chelates and vinyl monomer has been suggested. Several grafting experiments were carried out in presence of CCl₄, CHCl₃, CH₃CH₂CH₂SH and Et₃N. All these additives with the exception of Et₃N were found to suppress grafting.     

An unusual isotopic fractionation of boron in synthetic calcium carbonate precipitated from seawater and saline water

Inorganic calcium carbonate precipitation from natural seawater and saline water at various pH values was carried out experimentally. The results show the clear positive relationships between boron concentration and δ11B of inorganic calcium carbonate with the pH of natural seawater and saline water. However, the variations of boron isotopic fractionation between inorganic calcite and seawater/saline water with pH are inconsistent with the hypothesis that B(OH)4- is the dominant spe-cies incorporated into the biogenic calcite structure. The isotopic fractionation factors α between synthetic calcium carbonate precipitate and parent solutions increase systematically as pH increases, from 0.9884 at pH 7.60 to 1.0072 at pH 8.60 for seawater and from 0.9826 at pH 7.60 to 1.0178 at pH 8.75 for saline water. An unusual boron isotopic fractionation factor of larger than 1 in synthetic calcium carbonate precipitated from seawater/saline water at higher pH is observed, which implies that a substantial amount of the isotopically heavier B(OH)3 species must be incorporated preferentially into synthetic inorganic carbonate. The results propose that the incorporation of B(OH)3 is attributed to the formation of Mg(OH)2 at higher pH of calcifying microenvironment during the synthetic calcium carbonate precipitation. The preliminary experiment of Mg(OH)2 precipitated from artificial seawater shows that heavier 11B is enriched in Mg(OH)2 precipitation, which suggests that isotopically heavier B(OH)3 species incorporated preferentially into Mg(OH)2 precipitation. This result cannot be applied to explain the boron isotopic fractionation of marine bio-carbonate because of the possibility that the unusual environment in this study appears in formation of marine bio-carbonate is infinitesimal. We, however, must pay more attention to this phenomenon observed in this study, which accidentally appears in especially natural environment.