PVA networks grafted with PDMS branches

We describe a simple and efficient synthesis of poly(vinyl alcohol) (PVA) networks fitted with polydimethylsiloxane (PDMS) branches (PVA_netw‐g‐PDMS). The syntheses were achieved in two steps: (1) Grafting by urethane linking PDMS carrying ? NCO termini (PDMS‐NCO) onto PVA fitted with a few (～4) photoreactive acryl amide groups (PVA_AA), followed by (2) Photocrosslinking the PVA_AA‐g‐PDMS to PVA_netw‐g‐PDMS. The use of the binary N‐methyl‐2‐pyrrolidone/tetrahydrofuran (NMP/THF, 67/33) solvent system enabled the thermodynamically unfavorable mixing of hydrophobic PDMS branches with hydrophilic PVA_AA backbones. The amphiphilic graft, PVA_AA‐g‐PDMS, was characterized by ¹H NMR spectroscopy, and the final graft network, PVA_netw‐g‐PDMS, by FTIR spectroscopy, DSC, and equilibrium swelling. The grafting of sufficient volumes of PDMS branches onto PVA_AA yields cocontinuous hydrophilic/hydrophobic PVA/PDMS domains, whose existence was demonstrated by swelling in both water and hexanes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5272–5277, 2009     

Quantitative analysis of phosphoric acid esters in aqueous samples by isotope dilution stir-bar sorptive extraction combined with direct analysis in real time (DART)-Orbitrap mass spectrometry

A novel hyphenated technique, namely the combination of stir bar sorptive extraction (SBSE) with isotope dilution direct analysis in real time (DART) Orbitrap™ mass spectrometry (OT-MS) is presented for the extraction of phosphoric acid alkyl esters (tri- (TnBP), di- (HDBP), and mono-butyl phosphate (H2MBP)) from aqueous samples. First, SBSE of phosphate esters was performed using a Twister™ coated with 24 μL of polydimethylsiloxane (PDMS) as the extracting phase. SBSE was optimized for extraction pH, phase ratio (PDMS volume/aqueous phase volume), stirring speed, extraction time and temperature. Then, coupling of SBSE to DART/Orbitrap-MS was achieved by placing the Twister™ in the middle of an open-ended glass tube between the DART and the Orbitrap™. The DART mass spectrometric response of phosphate esters was probed using commercially available and synthesized alkyl phosphate ester standards. The positive ion full scan spectra of alkyl phosphate triesters (TnBP) was characterized by the product of self-protonation [M + H]⁺ and, during collision-induced dissociation (CID), the major fragmentation ions corresponded to consecutive loss of alkyl chains. Negative ionization gave abundant [M − H]⁻ ions for both HDnBP and H2MnBP. Twisters™ coated with PDMS successfully extracted phosphate acid esters (tri-, di- and mono-esters) granted that the analytes are present in the aqueous solution in the neutral form. SBSE/DART/Orbitrap-MS results show a good linearity between the concentrations and relative peak areas for the analytes in the concentration range studied (0.1–750 ng mL⁻¹). Reproducibility of this SBSE/DART/Orbitrap-MS method was evaluated in terms of %RSD by extracting a sample of water fortified with the analytes. The %RSDs for TnBP, HDnBP and H₂MnBP were 4, 3 and 3% (n = 5) using the respective perdeuterated internal standards. Matrix effects were investigated by matrix matched calibration standards using underground water samples (UWS) and river water samples (RWS). Matrix effects were effectively compensated by the addition of the perdeuterated internal standards. The application of this new SBSE/DART/Orbitrap-MS method should be very valuable for on-site sampling/monitoring, limiting the transport of large volumes of water samples from the sampling site to the laboratory.     

Stir-bar-sorptive extraction and liquid desorption combined with large-volume injection gas chromatography–mass spectrometry for ultra-trace analysis of musk compounds in environmental water matrices

Stir-bar-sorptive extraction with liquid desorption followed by large-volume injection and capillary gas chromatography coupled to mass spectrometry in selected ion monitoring acquisition mode (SBSE–LD/LVI-GC–MS(SIM)) has been developed to monitor ultra-traces of four musks (celestolide (ADBI), galaxolide (HHCB), tonalide (AHTN) and musk ketone (MK)) in environmental water matrices. Instrumental calibration (LVI-GC–MS(SIM)) and experimental conditions that could affect the SBSE-LD efficiency are discussed. Assays performed on 30-mL water samples spiked at 200 ng L^?1 under optimized experimental conditions yielded recoveries ranging from 83.7?±?8.1% (MK) to 107.6?±?10.8% (HHCB). Furthermore, the experimental data were in very good agreement with predicted theoretical equilibria described by octanol–water partition coefficients (K _PDMS/W?≈?K _O/W). The methodology also showed excellent linear dynamic ranges for the four musks studied, with correlation coefficients higher than 0.9961, limits of detection and quantification between 12 and 19 ng L^?1 and between 41 and 62 ng L^?1, respectively, and suitable precision (< 20%). Application of this method for analysis of the musks in real water matrices such as tap, river, sea, and urban wastewater samples resulted in convenient selectivity, high sensitivity and accuracy using the standard addition methodology. The proposed method (SBSE–LD/LVI-GC–MS(SIM)) was shown to be feasible and sensitive, with a low-sample volume requirement, for determination of musk compounds in environmental water matrices at the ultra-trace level, overcoming several disadvantages presented by other sample-preparation techniques.     

Enhanced Microchip Electrophoresis of Neurotransmitters on Glucose Oxidase Modified Poly(dimethylsiloxane) Microfluidic Devices

In this paper, glucose oxidase (GOx) was employed to construct a functional film on the poly(dimethylsiloxane) (PDMS) microfluidic channel surface and apply to perform electrophoresis coupled with in‐channel electrochemical detection. The film was formed by sequentially immobilizing poly(diallyldimethylammonium chloride) (PDDA) and GOx to the microfluidic channel surface via layer‐by‐layer (LBL) assembly. A group of neurotransmitters (5‐hydroxytryptamine, 5‐HT; dopamine, DA; epinephrine, EP; dobuamine, DBA) as a group of separation model was used to evaluate the effect of the functional PDMS microfluidic devices. Electroosmotic flow (EOF) in the modified PDMS microchannel was well suppressed compared with that in the native one. Experimental conditions were optimized in detail. As expected, these analytes were efficiently separated within 110 s in a 3.7 cm long separation channel and successfully detected at a single carbon fiber electrode. Good performances were attributed to the decreased EOF and the interactions of analytes with the immobilized GOx on the PDMS surface. The theoretical plate numbers were 2.19×10⁵, 1.89×10⁵, 1.76×10⁵, and 1.51×10⁵ N/m at the separation voltage of 1000 V with the detection limits of 1.6, 2.0, 2.5 and 6.8 μM (S/N=3) for DA, 5‐HT, EP and DBA, respectively. In addition, the modified PDMS channels had long‐term stability and excellent reproducibility.     

Polydimethylsiloxane/polypyrrole stir bar sorptive extraction and liquid chromatography (SBSE/LC-UV) analysis of antidepressants in plasma samples

A new polymeric coating consisting of a dual-phase, polydimethylsiloxane (PDMS) and polypyrrole (PPY) was developed for the stir bar sorptive extraction (SBSE) of antidepressants (mirtazapine, citalopram, paroxetine, duloxetine, fluoxetine and sertraline) from plasma samples, followed by liquid chromatography analysis (SBSE/LC-UV). The extractions were based on both adsorption (PPY) and sorption (PDMS) mechanisms. SBSE variables, such as extraction time, temperature, pH of the matrix, and desorption time were optimized, in order to achieve suitable analytical sensitivity in a short time period. The PDMS/PPY coated stir bar showed high extraction efficiency (sensitivity and selectivity) toward the target analytes. The quantification limits (LOQ) of the SBSE/LC-UV method ranged from 20 ng mL⁻¹ to 50 ng mL⁻¹, and the linear range was from LOQ to 500 ng mL⁻¹, with a determination coefficient higher than 0.99. The inter-day precision of the SBSE/LC-UV method presented a variation coefficient lower than 15%. The efficiency of the SBSE/LC-UV method was proved by analysis of plasma samples from elderly depressed patients.     

Study of Activation and Inhibition of Certain Metal Ions to Amylase Catalyzed Reaction by Microcalorimetry

IntroductionMostcomplicatedreactionshappenedinlivingcrea tures ,amongthemenzymecatalyzedreactionisanimpor tantclass .Itissignificantinboththeoryandpracticetoinvestigateenzymecatalyzedreaction .Therearemanyex perimentalmethodssuchasspectrophotometry ,titrimetry ,isotopemethod ,microcalorimetryandsoon ,inwhichmi crocalorimetryisanewoneduetoitshighsensitivityandaccuracy .Wecanstudythewholeprocessoftheheatef fectusingamicrocalorimeter .Sincetheabsorptionorpro ductionofheatisanintrinsicpropertyofe…     

Graphene oxide coated capillary for the analysis of endocrine‐disrupting chemicals by open‐tubular capillary electrochromatography with amperometric detection

A graphene oxide‐coated capillary was fabricated by using 3‐aminopropyltriethoxysilane as the cross‐linking agent. It was used for the separation and detection of three endocrine‐disrupting chemicals, including bisphenol A, 4‐nonylphenol, and 4‐octylphenol by capillary electrochromatography. Due to the hydrophobicity, hydrogen bonding, and π–π interaction between graphene oxide and the analytes, the three analytes could be well separated in pH = 11.0, 20 mmol/L Na₂B₄O₇‐NaOH/methanol mobile phase (50:50, v/v) within 950 s. After preconcentration, the detection limits were 6.7 × 10^?10, 3.3 × 10^?9, and 6.7 × 10^?10 mol/L (S/N = 3) for bisphenol A, nonylphenol, and octylphenol, respectively. The developed method was successfully applied to the determination of the above analytes in water samples. The satisfactory result demonstrated that the graphene oxide coated capillary used in capillary electrochromatography with amperometric detection was convenient to prepare, highly stable, and had good reproducibility.     

One-pot synthesis,characterization, DNA binding and enzymatic studies of 4-methyl trans-cinnamate zinc(II)-mixed ligand complexes

Four new zinc(II) complexes formulated as [Zn(L)₂] (1), [Zn(L)₂(phen)] (2), [Zn(L)₂(bipy)H₂O] (3), and [Zn(en)₂(H₂O)₂](L)₂(H₂O)₂ (4), where HL = 4-methyl trans-cinnamic acid, bipy = 2,2′-bipyridine, phen = 1,10-phenanthroline, and en = ethylenediamine, have been synthesized and characterized by FT-IR and NMR spectroscopy. Single-crystal XRD revealed distorted square-pyramidal structure for 3 and octahedral for 4. The complexes were screened for DNA interaction via viscommetry and UV–visible spectroscopy. The apparent binding constants were calculated to be 1.18 × 10⁴, 1.26 × 10⁵, 4.64 × 10⁴_, and 1.89 × 10⁴ for 1–4, respectively. The binding propensity to salmon sperm DNA was in the order: K₂ > K₃ > K₄ > K₁. Furthermore, these complexes demonstrated efficient inhibition of alkaline phosphatase, which was attributed to the binding of zinc(II) to the enzyme’s active site.     

Effects of molecular weight of nitrocellulose on structure and properties of polyurethane/nitrocellulose IPNs

Semi‐interpenetrating polymer network (semi‐IPN) coatings were prepared by using castor oil‐based polyurethane (PU) and nitrocellulose (NC) with various viscosity‐average molecular weights (M_η) from 6 × 10⁴ to 42 × 10⁴, and coated on a regenerated cellulose (RC) film to obtain water‐resistant film. The PU/NC coatings and coated films, which were cured at 80°C for 5 min and 2 min, respectively, were investigated by infrared (IR) and ultraviolet (UV) spectroscopy, X‐ray diffraction, swelling test, strength test, dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The results show that the crosslink densities of the PU/NC semi‐IPNs were smaller than that of pure PU, and decreased with the decrease of M_η of nitrocellulose (NC M_η), indicating NC molecules cohered intimately with PU, and hindered the PU network formation. The physical and mechanical properties of the films coated with PU/NC coatings were significantly improved. With the increase of NC M_η, the strength and thermal stability of the coated films increased, but the pliability, water resistivity, and optical transmission decreased slowly. The PU/NC coating with low NC M_η more readily penetrated into the RC film, and reacted with cellulose, resulting in a strong interfacial bonding and dense surface caused by intimate blend of PU/NC in the coated films. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1623–1631, 1999     

Selective Determination of Zn2+ Ion in Various Environmental,Biological and Medicinal Plant Samples Using a Novel Coated Graphite Electrode

Novel Zn²⁺ ion‐selective PVC based coated graphite electrodes were fabricated using the ionophores N‐((1H‐indol‐3‐yl)methylene)thiazol‐2‐amine (I₁), N‐((1H‐indol‐3‐yl)methyl)‐thiazol‐2‐amine (I₂) and 1‐((1H‐indol‐3‐yl)methylene)urea (I₃). Their potentiometric performance was examined in dependence of the addition of plasticizers and anion excluders and compared. It is found that the coated graphite electrode with the composition I₁:KTpClPB:o‐NPOE:PVC=9 : 1.5 : 51 : 38.5 is the best with respect to the wide working concentration range (4.2×10^?8–1.0×10^?1 mol L^?1), low detection limit (1.6×10^?8 mol L^?1) and wide pH range of 3.0–8.0. The proposed electrode was successfully applied to quantify Zn²⁺ in various environmental, biological and medicinal plant samples and used as indicator electrode.     

Multilayer Assembly of Hemoglobin and Colloidal Gold Nanoparticles on Multiwall Carbon Nanotubes/Chitosan Composite for Detecting Hydrogen Peroxide

Chitosan (CS) was chosen for dispersing multi‐wall carbon nanotubes (MWNTs) to form a stable CS‐MWNTs composite, which was first coated on the surface of a glassy carbon electrode to provide a containing amino groups interface for assembling colloidal gold nanoparticles (GNPs), followed by the adsorption of hemoglobin (Hb). Repeating the assembly step of GNPs and Hb resulted in {Hb/GNPs}_n multilayers. The assembly of GNPs onto CS‐MWNTs composites was confirmed by transmission electron microscopy. The consecutive growth of {Hb/GNPs}_n multilayers was confirmed by cyclic voltammetry and UV‐vis absorption spectroscopy. The resulting system brings a new platform for electrochemical devices by using the synergistic action of the electrocatalytic activity of GNPs and MWNTs. The resulting biosensor displays an excellent electrocatalytic activity and rapid response for hydrogen peroxide. The linear range for the determination of H₂O₂ was from 5.0×10^?7 to 2.0×10^?3 M with a detection limit of 2.1×10^?7 M at 3σ and a Michaelis–Menten constant K_M^app value of 0.19 mM.     

Development and validation of stir bar sorptive extraction of polar phenols in water followed by HPLC separation in poly(vinylpyrrolididone‐divinylbenzene) monolith

An effective and simple method for polar phenols in water matrix was developed by using stir bar sorptive extraction (SBSE) based on a hydrophilic poly(vinylpyrrolididone‐divinylbenzene) (VPDB) monolithic material and HPLC analysis. To achieve optimum extraction performance for phenols, several parameters, including extraction and desorption time, desorption solvent, pH value, and ionic strength of sample matrix, were investigated. Under the optimized experimental conditions, eight phenols were directly enriched from water samples and analyzed by HPLC‐DAD. The detection limits (S/N = 3) and quantification limits (S/N = 10) of the proposed method for the target compounds were achieved within the range of 0.72–1.37 and 2.40–4.27 ng/mL from spiked water, respectively. Recoveries of eight phenolic compounds were found in the range of 55.2–95.9%. The calibration curves showed the linearity ranging from 5 to 150 ng/mL with linear regression coefficient R² values above 0.98. Method repeatability presented as intra‐ and interday precisions were also found with the RSDs less than 4.10 and 7.61%, respectively. The distribution coefficients between VPDB and water (K_VPDB/W) for phenolic compounds were also calculated and compared with K_O/W. Finally, the proposed method was successfully applied to the determination of the target compounds in tap water, sea water and wastewater samples.     

Regulation of α‐Chymotrypsin Catalysis by Ferric Porphyrins and Cyclodextrins

Positively charged α‐chymotrypsin (ChT) formed a 1:1 complex with negatively charged 5,10,15,20‐tetrakis(4‐sulfonatophenyl)porphyrinato iron(III) (FeTPPS) in phosphate buffer at pH 7.4 through electrostatic interaction. In spite of the large binding constant (K=4.8×10⁵ M ^?1), FeTPPS could not completely inhibit the catalysis of ChT in the hydrolysis of the model substrate, N‐succinyl‐L ‐phenylalanine p‐nitroanilide (SPNA). The degree of inhibition (60 %) was saturated at 1.6 equivalents of FeTPPS, which indicates that covering of the active site of ChT by FeTPPS was insufficient. The enzymatic activity lowered by FeTPPS was entirely recovered for the freshly prepared sample when the porphyrin on the protein surface was detached by per‐O‐methylated β‐cyclodextrin (TMe‐β‐CD), which formed a stable 1:2 inclusion complex with FeTPPS (K₁=1.26×10⁶ M ^?1, K₂=6.3×10⁴ M ^?1). FeTPPS gradually induced irreversible denaturation of ChT, and the denatured ChT further lost its catalytic ability. No repairing effect of TMe‐β‐CD was observed with irreversibly denatured ChT. A new reversible inhibitor, 5,10,15,20‐tetrakis[4‐(3,5‐dicarboxyphenylmethoxy)phenyl]porphyrinato iron(III) (FeP8M), was then designed, and its inhibitory behavior was examined. FeP8M formed very stable 1:1 and 1:2 FeP8M/ChT complexes with ChT, the K₁ and K₂ values being 2.0×10⁸ and 1.0×10⁶ M ^?1, respectively. FeP8M effectively inhibited the ChT‐catalyzed hydrolysis of SPNA (maximum degree of inhibition=85 %), and the activity of ChT was recovered by per‐O‐methylated γ‐cyclodextrin. No irreversible denaturation of ChT occurred upon binding with FeP8M. The kinetic data support the observation that, for nonincubated samples, both inhibitors did not cause significant conformational change in ChT and inhibited the ChT activity by covering the active site of the enzyme.     

Study and Application of Polarographic Catalytic Wave of Chlordiazepoxide in the Presence of Persulfate

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Evaluation of the Oxo‐bridged Dinuclear Ruthenium Ammine Complex as Redox Mediator in an Electrochemical Biosensor

The mediation of electron‐transfer by oxo‐bridged dinuclear ruthenium ammine [(bpy)₂(NH₃)Ru^III(µ‐O)Ru^III(NH₃)(bpy)₂]⁴⁺ for the oxidation of glucose was investigated by cyclic voltammetry. These ruthenium (III) complexes exhibit appropriate redox potentials of 0.131–0.09 V vs. SCE to act as electron‐transfer mediators. The plot of anodic current vs. the glucose concentration was linear in the concentration range between 2.52×10^?5 and 1.00×10^?4 mol L^?1. Moreover, the apparent Michaelis‐Menten kinetic (K_M^app) and the catalytic (K_cat) constants were 8.757×10^?6 mol L^?1 and 1,956 s^?1, respectively, demonstrating the efficiency of the ruthenium dinuclear oxo‐complex [(bpy)₂(NH₃)Ru^III(µ‐O)Ru^III(NH₃)(bpy)₂]⁴⁺ as mediator of redox electron‐transfer.     

New barium,strontium and strontium‐doped barium squarates: synthesis,crystal structures and DNA/BSA binding,antioxidant and in vitro cytotoxicity studies

A new set of differently hydrated barium and strontium squarates, namely poly[[triaqua(μ‐1,2‐dioxocyclobut‐3‐ene‐1,2‐diolato)barium] monohydrate], {[Ba(C₄O₄)(H₂O)₃]·H₂O}_n ( 1 ), poly[[diaqua(μ‐1,2‐dioxocyclobut‐3‐ene‐1,2‐diolato)strontium] monohydrate], {[Sr(C₄O₄)(H₂O)₂]·H₂O}_n ( 2 ), and poly[[triaqua(μ‐1,2‐dioxocyclobut‐3‐ene‐1,2‐diolato)barium/strontium(0.85/0.15)] monohydrate], {[Ba_0.85Sr_0.15(C₄O₄)(H₂O)₃]·H₂O}_n ( 3 ), is reported. The study of their crystal structures indicates that all the complexes crystallize in the triclinic space group P. Complexes 1 and 3 have a rare combination of squarate units coordinated through monodentate O atoms to two different metal atoms and through two bidentate O atoms to three different metal atoms. Furthermore, they have three coordinated water molecules to give a coordination number of nine. The squarate ligands in complex 2 exhibit two different coordination modes: (i) monodentate O atoms coordinated to four different Sr atoms and (ii) two monodentate O atoms coordinated to two different metal atoms with the other two O atoms bidentate to four different Sr atoms. All the compounds decompose to give the respective carbonates when heated to 800 °C, as evidenced by thermogravimetry/differential thermal analysis (TG‐DTA), which are clusters of nanoparticles. Complexes 1 and 3 show additional endothermic peaks at 811 and 820 °C, respectively, indicating the phase transition of BaCO₃ from an orthorhombic (α‐Pmcn) to a trigonal phase (β‐R3m). All three complexes have significant DNA‐binding constants, ranging from 2.45 × 10⁴ to 9.41 × 10⁴ M^?1 against EB‐CT (ethidium bromide–calf thymus) DNA and protein binding constants ranging from 1.1 × 10⁵ to 8.6 × 10⁵ with bovine serum albumin. The in vitro cytotoxicity of the complexes is indicated by the IC₅₀ values, which range from 128.8 to 261.3 µg ml^?1. Complex 3 shows better BSA binding, antioxidant activity against the DPPH radical and cytotoxicity than complexes 1 and 2 .     

Curing kinetics,thermal, mechanical,and dielectric properties based on o‐cresol formaldehyde epoxy resin with polyhedral oligomeric (N‐aminoethyl‐γ‐amino propyl)silsesquioxane

The curing reaction and kinetics of o‐cresol formaldehyde epoxy resin (o‐CFER) with polyhedral oligomeric silsesquioxane of N‐aminoethyl‐γ‐amino propyl group (AEAP‐POSS) were investigated by differential scanning calorimetry (DSC). The thermal, mechanical, and dielectric properties of o‐CFER/AEAP‐POSS nanocomposites were investigated with thermogravimetric analysis (TGA), torsional braid analysis (TBA), tensile tester, impact tester, and electric analyzer, respectively. The results show that the activation energy (E) of curing reaction is 58.08 kJ/mol, and the curing reaction well followed the ?esták‐Berggren (S‐B) autocatalytic model. The glass transition temperature (T_g) increases with the increase in AEAP‐POSS content, and reaches the maximum, 107°C, when the molar ratio (N_s) of amino group to epoxy group is 0.5. The nanocomposites containing a higher percentage of AEAP‐POSS exhibited a higher thermostability. The AEAP‐POSS can effectively increase the mechanical properties of epoxy resin, and the tensile and impact strengths are 2.84 MPa and 143.25 kJ m^?2, respectively, when N_s is 0.5. The dielectric constant (ε), dielectric loss factor (tan δ), volume resistivity (ρ_v), and surface resistivity (ρ_s) are 4.98, 3.11 × 10^?4, 3.17 × 10¹² Ω cm³, and 1.41 × 10¹² Ω cm², respectively, similarly at N_s 0.5. Copyright © 2009 John Wiley & Sons, Ltd.     

Triangular telluride complexes containing a cluster fragment [M3(µ3-Te)(µ2-Te2)3]4+ (M = Mo, W): Study of specific non-valence interactions

Various synthetic approaches are used to obtain new triangular complexes with rare cluster nuclei M₃Te₇ ⁴⁺ (M = Mo, W), as well as with partial substitution for chalcogen W₃Te_3.8Se _3.2 ⁴⁺ . The crystalline structure has been identified for K₅{[Mo₃Te₇(CN)₆]₂I}·2.5H₂O (I), K₃{[Mo₃Te₇(CN)₆]SeCN}·3.25H₂O (II), Cs₂K{ [W₃Te₇(CN)₆]Br_0.8Cl_0.2}·2.5H₂O (III), Cs₃{ [W₃Te₇(CN)₆]Br}·2H₂O (IV), Cs_1.59K_1.41{[W₃Te_3.8Se_3.2× ×(CN)₆]Br}·1,5H₂O (V), [W₃Te₇((EtO)₂PS₂)₃]Br (VI). The compounds are characterized by IR methods and electronic spectroscopy, electrospray-mass-spectrometry. The crystalline structure of this class of compounds is analyzed. Specific non-valence interactions in these systems are considered in detail.     

Study of the reactions of oxygen atoms with carbonothioicdichloride,carbonothioicdifluoride, and tetrafluoro-1,3-dithietane

The reactions of ground-state oxygen atoms with carbonothioicdichloride, carbonothioicdifluoride, and tetrafluoro-1,3-dithietane have been studied in a crossed molecular jet reactor in order to determine the initial reaction products and in a fast-flow reactor in order to determine their overall rate constants at temperatures between 250 and 500 K. These rate constants are??(O + C₂CS) =(3.09 ± 0.54) × 10^?11 exp(+115 ± 106 cal/mol/RT),??(O + F₂CS) = (1.22 ± 0.19) × 10^?11 exp(-747 ± 95 cal/mol/RT), and??(O + F₄C₂S₂) = (2.36 ± 0.52) × 10^?11 exp(-1700 ± 128 cal/mol/RT) cm³/molec˙sec. The detected reaction products and their rate constants indicate that the primary reaction mechanism is the electrophilic addition of the oxygen atom to the sulfur atom contained in the reactant molecule to form an energy-rich adduct which then decomposes by C-S bond cleavage.     

Rate coefficients for the gas‐phase reactions of OH radicals with methylbutenols at 298 K

The relative‐rate method has been used to determine the rate coefficients for the reactions of OH radicals with three C₅ biogenic alcohols, 2‐methyl‐3‐buten‐2‐ol (k₁), 3‐methyl‐3‐buten‐1‐ol (k₂), and 3‐methyl‐2‐buten‐1‐ol (k₃), in the gas phase. OH radicals were produced by the photolysis of CH₃ONO in the presence of NO. Di‐n‐butyl ether and propene were used as the reference compounds. The absolute rate coefficients obtained with the two reference compounds agreed well with each other. The O₃ and O‐atom reactions with the target alcohols were confirmed to have a negligible contribution to their total losses by using two kinds of light sources with different relative rates of CH₃ONO and NO₂ photolysis. The absolute rate coefficients were obtained as the weighted mean values for the two reference compound systems and were k₁ = (6.6 ± 0.5) × 10^?11, k₂ = (9.7 ± 0.7) × 10^?11, and k₃ = (1.5 ± 0.1) × 10^?10 cm³ molecule^?1 s^?1 at 298 ± 2 K and 760 torr of air. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 379–385 2004