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There is a growing body of evidence that a substantial number of protein domains identified as DNA-binding also interact with RNA to regulate biological processes. Several recent studies have revealed that the Sox2 transcription factor binds RNA through its high-mobility group box (HMGB) domain

Quantifying the local pH of a gas diffusion electrode undergoing CO2 reduction is a complicated problem owing to a multitude of competing processes, both electrochemical- and transport-related, pos...

Bioelectrochemical CO2 reduction is a promising method for biogas upgrading. However, the CO2 reduction efficiency in these bioelectrical systems is always relatively low and limits their applicati...

Chemical activation experiments and computational methods have been used to study the unimolecular reactions of C2H5CH2Br and C2D5CHFBr with 90 and 93 kcal mol–1 of vibrational energy, respectively...

By mimicking iron(Fe)-based phosphorus (P) immobilization in natural environments, an Fe-retrofitted UCT-MBR involving in situ vivianite crystallization for removing and recovering P from sewage was developed, and its performance was examined in this work. We show that dosing of ferrihydrite, once biological P uptake reached its limit, enabled effective ongoing P removal; whereas conventional conditions in the anaerobic chamber of the University of Cape Town (UCT) system (i.e., a sludge retention time of hours and a completely mixed sludge phase) was insufficient for a satisfactory Fe(III) bioreduction, with the overaccumulation of Fe(III) as fine particles finally resulting in severe membrane fouling and collapse in P removal. The enhancement of reductive conditions in the anaerobic chamber by lowering agitation and adding biocarriers to favor Fe(III) reduction was found to be effective in enabling ongoing P removal and recovery. The average level of effluent P was as low as 0.18 mg/L for a period of 258 d under this condition. Using chemical and spectroscopic methods, the P product was identified as primarily vivianite: Fe

The gas-phase unimolecular reactions of C2D5CHFCl molecules with 94 kcal mol-1 of vibrational energy have been studied by the chemical-activation experimental technique and by electronic-structure computations. Products from the reaction of C2D5CHFCl molecules, formed by the recombination of C2D5 and CHFCl radicals in a room temperature bath gas, were measured by gas chromatography-mass spectrometry. The 2,1-DCl (81%) and 1,1-HCl (17%) elimination reactions are the principal processes, but 2,1-DF and 1,1-HF elimination reactions also are observed. Comparison of experimental rate constants to calculated statistical rate constants provides threshold energies. The potential surfaces associated with C2D5(F)C: + HCl and C2D5(Cl)C: + HF reactions are of special interest because hydrogen-bonded adducts with HCl and HF with dissociation energies of 6.4 and 9.3 kcal mol-1, respectively, are predicted by calculations. The relationship between the geometries and threshold energies of transition states for 1,1-HCl elimination and carbene:HCl adducts is complex, and previous studies of related molecules, such as CD3CHFCl, CD2ClCHFCl, C2D5CHCl2, and halogenated methanes are included in the computational analysis. Extensive calculations for CH3CHFCl as a model for 1,1-HCl reactions illustrate properties of the exit-channel potential energy surface. Since the 1,1-HCl transition state is submerged relative to dissociation of the adduct, inner and outer transition states should be considered for analysis of rate constants describing 1,1-HCl elimination and addition reactions of carbenes to HCl.

Anaerobically treated leachate from municipal solid waste incineration plants contains extremely high free ammonia (FA) concentrations, which can hinder short-cut nitrification. pH adjustments made...

The five unimolecular HX and DX (X = F, Cl) elimination pathways of CD2ClCHFCl* were examined using a chemical activation technique; the molecules were generated with 92 kcal mol–1 of vibrational energy in a room-temperature bath gas by a combination of CD2Cl and CHFCl radicals. The total unimolecular rate constant was 9.7 × 107 s–1, and branching fractions for each channel were 0.52 (2,1-DCl), 0.29 (1,1-HCl), 0.10 (2,1-DF), 0.07 (1,1-HF), and 0.02 (1,2-HCl). Comparison of the individual experimental rate constants to calculated statistical rate constants gave threshold energies for each process as 63, 72, 66, 73, and 70 kcal mol–1, listed in the same order as the branching fractions. The 1,1-HCl and 1,1-HF reactions gave carbenes, CD2Cl(F)C: and CD2Cl(Cl)C:, respectively, as products, which have hydrogen-bonded complexes with HCl or HF in the exit channel of the potential energy surface. These carbenes have energy in excess of the threshold energy for D atom migration to give CDCl═CDF and CDCl═CDCl, and ...

Solid supported colorimetric sensing arrays have the advantage of portability and ease of use when deployed in the field, such as crime scenes, disaster zones, or in war zones, but many sensor arrays require complex fabrication methods. Here, we report a practical method for the fabrication of 4 × 4 colorimetric sensor arrays, which are printed on nylon membranes, using a commercially available inkjet printer. In order to test the efficacy of the printed arrays, they were exposed to 43 analytes at concentrations ranging from 0.001 to 3.0 M for a total of 559 samples of inorganic and organic acids or bases including hydrochloric, acetic, phthalic, malonic, picric, and trifluoroacetic acid, ammonium hydroxide, sodium hydroxide, lysine, and water as the control. Colorimetric data from the imaged arrays was analyzed with linear discriminant analysis and k-nearest neighbors to determine the analyte and concentration with ∼88-90% accuracy. Overall, the arrays have impressive analytical power to identify a variety of analytes at different concentrations while being simple to fabricate.

The recombination of CF3 and CHF2 radicals in a room-temperature bath gas was used to prepare vibrationally excited CF3CHF2* molecules with 101 kcal mol–1 of vibrational energy. The subsequent 1,2-H atom transfer and 1,1-HF and 1,2-HF elimination reactions were observed as a function of bath gas pressure by following the CHF3, CF3(F)C: and C2F4 product concentrations by gas chromatography using a mass spectrometer as the detector. The singlet CF3(F)C: concentration was measured by trapping the carbene with trans-2-butene. The experimental rate constants are 3.6 × 104, 4.7 × 104, and 1.1 × 104 s–1 for the 1,2-H atom transfer and 1,1-HF and 1,2-HF elimination reactions, respectively. These experimental rate constants were matched to statistical RRKM calculated rate constants to assign threshold energies (E0) of 88 ± 2, 88 ± 2, and 87 ± 2 kcal mol–1 to the three reactions. Pentafluoroethane is the only fluoroethane that has a competitive H atom transfer decomposition reaction, and it is the only example with...

Methane (CH4)-producing bioelectrochemical systems (BES) are an attractive way to store excess renewable electricity and captured CO2. Studies have suggested that methanogenesis via direct electron uptake from a biocathode is more energetically efficient than hydrogenotrophic methanogenesis. However, mechanisms and key microorganisms involved in direct electron uptake remain unclear, primarily because of H2 produced by bacteria or extracellular hydrogenases in the system. In an attempt to minimize biological H2 production and enrich for methanogens that could efficiently convert electrons from the cathode surface to CH4, cathode chambers were pretreated with antibiotics targeting bacteria. We found that antibiotics pretreatment effectively reduced the proportion of H2-producing bacteria and H2-utilizing methanogens associated with the biocathode biofilm, and significantly promoted growth of acetoclastic methanogens from the genera Methanosarcina and Methanosaeta, several of which are known to participate ...

The recombination of ·CHF2 radicals in a room-temperature bath gas was used to generate CHF2CHF2* (where * indicates vibrational excitation) molecules with 96 kcal mol–1 of vibrational energy. The CHF2CHF2* molecules decompose by four-centered 1,2-HF elimination and by three-centered 1,1-HF elimination reactions to give HF and either CHF═CF2 or :CFCHF2, respectively. The 1,1-HF component was identified by trapping the :CFCHF2 carbene with trans-2-butene that forms 1-fluoro-1-difluoromethyl-2,3-dimethylcyclopropane. The total rate constant for the decomposition of CHF2CHF2* was 6.0 × 105 s–1, and the rate constant for the 1,1-HF pathway forming the carbene, as measured by the 1-fluoro-1-difluoromethyl-2,3-dimethylcyclopropane yield, was 1.4 × 105 s–1. On the basis of matching the experimental rate constants to calculated statistical rate constants, the threshold energies for the four-centered and three-centered reactions are 78 and ≤85 kcal mol–1, respectively.

Chemically activated C2D5CHCl2 molecules were generated with 88 kcal mol–1 of vibrational energy by the recombination of C2D5 and CHCl2 radicals in a room temperature bath gas. The competing 2,1-DCl and 1,1-HCl unimolecular reactions were identified by the observation of the CD3CD═CHCl and CD3CD═CDCl products. The initial CD3CD2C—Cl carbene product from 1,1-HCl elimination rearranges to CD3CD═CDCl under the conditions of the experiments. The experimental rate constants were 2.7 × 107 and 0.47 × 107 s–1 for 2,1-DCl and 1,1-HCl elimination reactions, respectively, which corresponds to branching fractions of 0.84 and 0.16. The experimental rate constants were compared to calculated statistical rate constants to assign threshold energies of 54 and ≈66 kcal mol–1 for the 1,2-DCl and 1,1-HCl reactions, respectively. The statistical rate constants were obtained from models developed from electronic-structure calculations for the molecule and its transition states. The rate constant (5.3 × 107 s–1) for the unimol...

The recombination of CHF2 and C2D5 radicals was used to produce CD3CD2CHF2* molecules with 96 kcal mol(-1) of vibrational energy in a room temperature bath gas. The formation of CD3CD═CHF and CD3CD═CDF was used to identify the 1,2-DF and 1,1-HF unimolecular elimination channels; CD3CD═CDF is formed by isomerization of the singlet-state CD3CD2CF carbene. The total unimolecular rate constant is 1.6 × 10(6) s(-1), and the branching ratio for 1,1-HF elimination is 0.25. Threshold energies of 64 ± 2 and 73 ± 2 kcal mol(-1) were assigned to the 1,2-DF and 1,1-HF reaction channels. The E and Z isomers of 1-fluoropropene were observed for each reaction; approximately 30% of the CD3CD═CDF molecules derived from 1,1-HF elimination retained enough energy to undergo cis-trans isomerization. Electronic structure calculations with density-functional theory were used to characterize the transition-state structures and the H atom migration barrier for CD3CD2CF. Adjustment of the rate constants to account for kinetic-isotope effects suggest that the branching ratio would be 0.20 for 1,1-HF elimination from C2H5CHF2. The results from an earlier study of CD3CHF2 and CH3CHF2 are also reinterpreted to assign a threshold energy of 74 kcal mol(-1) for the 1,1-HF elimination reaction. Because CHF2CHF2* is generated in the photolysis system, the 1,1-and 1,2-HF-elimination reactions of CHF2CHF2* are discussed. The 1,1-HF channel was identified by trapping the CF2HCF carbene with cis-butene-2.

The recombination of CCl3 radicals with CH3, CH3CH2, and CF3CH2 radicals was used to generate CH3CCl3, CH3CH2CCl3, and CF3CH2CCl3 molecules with approximately 87 kcal mol(-1) of vibrational energy in a bath gas at room temperature. The competition between collisional deactivation and unimolecular reaction by HCl elimination was used to obtain the experimental rate constants for each molecule. These experimental rate constants were matched to calculated statistical unimolecular rate constants to assign threshold energies to the three HCl elimination reactions. The models needed for the calculations of the rate constants were obtained from molecular structure calculations using density functional theory (DFT) with the hybrid density-functional MO6-2X recommended by Truhlar for transition states. The assigned threshold energies are 52 ± 2, 50 ± 2, and 52 ± 2 kcal mol(-1) for CH3CCl3, CH3CH2CCl3, and CF3CH2CCl3, respectively, and the CH3 and CF3 groups have only a minor effect on the threshold energies for HCl elimination. The DFT calculated threshold energies are in agreement with the experimentally assigned values. The addition of Cl atoms to the same carbon atom lowers the threshold energy for HCl elimination in the CH3CH2Cl, CH3CHCl2, and CH3CCl3 series. This trend, which is the opposite of that for CH3CH2F, CH3CHF2, and CH3CF3, is discussed in terms of transition-state structure and correlated with the relative stabilities of CH3CH2(+), CH3CHCl(+), and CH3CCl2(+) ions; the relative stabilities are based on the hydride affinities obtained from calculations. Comparison of the reactions of CH3CCl3 and CH2ClCHCl2 shows that the threshold energy is much higher for the isomer with chlorine atoms on both carbon atoms.

The recombination reactions of CH2Cl radicals with CF3CHF and with CH3CHF radicals were used to generate CF3CHFCH2Cl and CH3CHFCH2Cl molecules with 90-92 kcal mol(-1) of vibrational energy. The experimental rate constants for elimination of HCl and HF and the interchange of Cl and F atoms were measured and compared to RRKM calculated rate constants to assign the threshold energy for each unimolecular reaction channel. The Cl/F interchange reaction is approximately 18% of the total unimolecular reaction for both molecules. The product branching ratios and some rate constants also could be measured for the unimolecular reactions of the rearranged molecules, CF3CHClCH2F and CH3CHClCH2F. The most important result is that the CH3 group lowers the threshold for Cl/F interchange relative to CH2FCD2Cl, as expected for an electron-density donating group, and the CF3 group, an electron-density withdrawing group, increases the threshold energy relative to CH2FCD2Cl. The CH3 and CF3 groups alter the threshold energies of the HCl and HF elimination reactions in such a way so as to maintain the same branching fraction for the interchange reaction. The results from density functional theory using the B3PW91 method with the 6311+G(2d,p) and G-31G(d',p') basis sets are used to discuss the trends in threshold energies for the Cl/F interchange and the HF and HCl elimination reactions.

The room-temperature gas-phase recombination of CH2F and CD2Cl radicals was used to prepare CH2FCD2Cl molecules with 91 kcal mol(-1) of vibrational energy. Three unimolecular processes are in competition with collisional deactivation of CH2FCD2Cl; HCl and DF elimination to give CHF═CD2 and CH2═CDCl plus isomerization to give CH2ClCD2F by the interchange of F and Cl atoms. The Cl/F interchange reaction was observed, and the rate constant was assigned from measurement of CHCl═CD2 as a product, which is formed by HF elimination from CH2ClCD2F. These experiments plus previously published results from chemically activated CH2ClCH2F and electronic structure and RRKM calculations for the kinetic-isotope effects permit assignment of the three rate constants for CH2FCD2Cl (and for CH2ClCD2F). The product branching ratio for the interchange reaction versus elimination is 0.24 ± 0.04. Comparison of the experimental rate constant with the RRKM calculated rate constant permitted the assignment of a threshold energy of 62 ± 3 kcal mol(-1) for this type-1 dyotropic rearrangement. On the basis of electronic structure calculations, the nature of the transition state for the rearrangement reaction is discussed. The radical recombination reactions in the chemical system also generate vibrationally excited CD2ClCD2Cl and CH2FCH2F molecules, and the rate constants for DCl and HF elimination were measured in order to confirm that the photolysis of CD2ClI and (CH2F)2CO mixtures was giving reliable data for CH2FCD2Cl.

The 1,2-HX elimination reaction (where X = F, Cl, Br, OH) has been established as an important reaction in the degradation of compounds introduced into the upper atmosphere, including common CFC replacement compounds. By analyzing the electron densities of the transition state geometries of these reactions using QTAIM, we see that we can divide these reactions into two types. For HF and HOH elimination, the transition state is a complete ring of bonds, and neither the C-H nor the C-X bonds have been broken at the maximum of energy. There is very little accumulation of electron density on the X atom, with the majority of charge being lost by the hydrogen atom undergoing elimination, being transferred on to the two carbon atoms. In HCl and HBr elimination, a similar loss of electron density of the hydrogen atom is accompanied by significant accumulation of electron density on the X atom and a smaller change in electron density on the carbon atoms. The C-X bond is broken in the transition state geometry, with no ring critical point being present. This may explain the relative stabilities of halohydrocarbons and haloalcohols with respect to loss of H-X.

A recent photofragment translational spectroscopy study of 1,1-dichloroacetone at 193 nm reported two primary unimolecular decomposition channels: C-Cl bond cleavage and elimination of HCl in a 9:1 ratio, respectively. The HCl translational energy distribution was bimodal suggesting two distinct decomposition pathways that were assumed to be 1,1-HCl loss forming a carbene and a 1,3-HCl elimination reaction forming a biradical ( Butler , L. J. ; Liu , Y. ; Lau , K. ; McCunn , L. R. ; Fitzpatrick , B. L. ; Bell , J. M. ; Krisch , M. J. J. Phys. Chem. A 2007 , 111 , 5968. ). An alternative two-step mechanism for HCl loss has been proposed involving interchange of a chlorine atom and a CH(3) group converting 1,1-dichloroacetone into 2-chloropropanoyl chloride followed by either a 1,2-HCl or 2,3-HCl elimination reaction. This alternative mechanism was computationally explored with density functional theory using B3PW91/6-31G(d',p') and unimolecular rate constants were calculated. The theoretical rate constant ratio for loss of HCl and the mean HCl translation energy for each elimination channel were in excellent agreement with the experimental results.

The recombination of chloromethyl and t-butyl radicals at room temperature was used to generate neopentyl chloride molecules with 89 kcal mol(-1) of internal energy. The observed unimolecular reactions, which give 2-methyl-2-butene and 2-methyl-1-butene plus HCl, as products, are explained by a mechanism that involves the interchange of a methyl group and the chlorine atom to yield 2-chloro-2-methylbutane, which subsequently eliminates hydrogen chloride by the usual four-centered mechanism to give the observed products. The interchange isomerization process is the rate-limiting step. Similar experiments were done with CD(2)Cl and C(CH(3))(3) radicals to measure the kinetic-isotope effect to help corroborate the proposed mechanism. Density functional theory was employed at the B3PW91/6-31G(d',p') level to verify the Cl/CH(3) interchange mechanism and to characterize the interchange transition state. These calculations, which provide vibrational frequencies and moments of inertia of the molecule and transition state, were used to evaluate the statistical unimolecular rate constants. Matching the calculated and experimental rate constants, gave 62 ± 2 kcal mol(-1) as the threshold energy for interchange of the Cl atom and a methyl group. The calculated models also were used to reinterpret the thermal unimolecular reactions of neopentyl chloride and neopentyl bromide. The previously assumed Wagner-Meerwein rearrangement mechanism for these reactions can be replaced by a mechanism that involves the interchange of the halogen atom and a methyl group followed by HCl or HBr elimination from 2-chloro-2-methylbutane and 2-bromo-2-methylbutane. Electronic structure calculations also were done to find threshold energies for several related molecules, including 2-chloro-3,3-dimethylbutane, 1-chloro-2-methyl-2-phenylpropane, and 1-chloro-2-methyl-2-vinylpropane, to demonstrate the generality of the interchange reaction involving a methyl, or other hydrocarbon groups, and a chlorine atom. The interchange of a halogen atom and a methyl group located on adjacent carbon atoms can be viewed as an extension of the halogen atom interchange mechanisms that is common in 1,2-dihaloalkanes.

The recombination of CH(2)Cl and CH(2)F radicals generates vibrationally excited CH(2)ClCH(2)Cl, CH(2)FCH(2)F, and CH(2)ClCH(2)F molecules with about 90 kcal mol(-1) of energy in a room temperature bath gas. New experimental data for CH(2)ClCH(2)F have been obtained that are combined with previously published studies for C(2)H(4)Cl(2) and C(2)H(4)F(2) to define reliable rate constants of 3.0 x 10(8) (C(2)H(4)F(2)), 2.4 x 10(8) (C(2)H(4)Cl(2)), and 1.9 x 10(8) (CH(2)ClCH(2)F) s(-1) for HCl and HF elimination. The product branching ratio for CH(2)ClCH(2)F is approximately 1. These experimental rate constants are compared to calculated statistical rate constants (RRKM) to assign threshold energies for HF and HCl elimination. The calculated rate constants are based on transition-state models obtained from calculations of electronic structures; the energy levels of the asymmetric, hindered, internal rotation were directly included in the state counting to obtain a more realistic measure for the density of internal states for the molecules. The assigned threshold energies for C(2)H(4)F(2) and C(2)H(4)Cl(2) are both 63 +/- 2 kcal mol(-1). The threshold energies for CH(2)ClCH(2)F are 65 +/- 2 (HCl) and 63 +/- 2 (HF) kcal mol(-1). These threshold energies are 5-7 kcal mol(-1) higher than the corresponding values for C(2)H(5)Cl or C(2)H(5)F, and beta-substitution of F or Cl atoms raises threshold energies for HF or HCl elimination reactions. The treatment presented here for obtaining the densities of states and the entropy of activation from models with asymmetric internal rotations with high barriers can be used to judge the validity of using a symmetric internal-rotor approximation for other cases. Finally, threshold energies for the 1,2-fluorochloroethanes are compared to those of the 1,1-fluorochloroethanes to illustrate substituent effects on the relative energies of the isomeric transition states.

Vibrationally excited CF(2)ClCHFC(2)H(5)(CF(2)ClCHFC(2)D(5)) molecules were prepared in the gas phase at 300 K with approximately 93 kcal mol(-1) of energy by recombination of CF(2)ClCHF and C(2)H(5) or C(2)D(5) radicals. Three unimolecular reactions were observed. 1,2-ClF interchange converts CF(2)ClCHFC(2)H(5)(CF(2)ClCHFC(2)D(5)) into CF(3)CHClC(2)H(5)(CF(3)CHClC(2)D(5)), and subsequent 2,3-ClH (ClD) elimination gives CF(3)CH=CHCH(3) (CF(3)CH=CDCD(3)). 2,3-FH(FD) elimination gives cis- and trans-CF(2)ClCH=CHCH(3) (CF(2)ClCH=CDCD(3)), and 1,2-ClH elimination gives CF(2)=CFCH(2)CH(3) (CF(2)=CFCD(2)CD(3)). The experimental rate constants for CF(2)ClCHFC(2)H(5) (CF(2)ClCHFC(2)D(5)) were 1.3 x 10(4) (0.63 x 10(4)) s(-1) for 1,2-FCl interchange and 2.1 x 10(4) (0.61 x 10(4)) s(-1) with a trans/cis ratio of 3.7 for 2,3-FH(FD) elimination. The 1,2-ClH process was the least important with a branching fraction of only 0.08 +/- 0.04. The rate constants for 2,3-ClH (ClD) elimination from CF(3)CHClC(2)H(5) (CF(3)CHClC(2)D(5)) were 1.8 x 10(6) (0.49 x 10(6)) s(-1) with a trans/cis ratio of 2.4. Density functional theory was used to compute vibrational frequencies and structures needed to obtain rate constants from RRKM theory. Matching theoretical and experimental rate constants provides estimates of the threshold energies, E0, for the three reaction pathways; 1,2-FCl interchange has the lowest E0. The unimolecular reactions of CF(2)ClCHFC(2)H(5) are compared to those of CF(2)ClCHFCH(3). Both of these systems are compared to CH(3)CHFC(2)H(5) to illustrate the influence of a CF(2)Cl group on the E0 for FH elimination.

The combination of CF(3)CHF and CH(3) or CD(3) radicals was used to prepare vibrationally excited CF(3)CHFCH(3) or CF(3)CHFCD(3) molecules with 97 kcal mol(-1) of internal energy. The experimental unimolecular rate constants were 3.7 x 10(6) s(-1) for 2,3-FH elimination from CF(3)CHFCH(3) and 1.3 x 10(6) s(-1) for 2,3-DF elimination from CF(3)CHFCD(3). Unimolecular rate constants for 1,2-FH elimination reaction were approximately 230 and 98 times smaller for CF(3)CHFCH(3) and CF(3)CHFCD(3), respectively, than the corresponding rate constants for 2,3-FH elimination. Density functional theory (DFT) was used to calculate the structures and vibrational frequencies of the molecules and transition states; this information was subsequently employed for calculations of RRKM rate constants. Comparison of the experimental and calculated rate constants gave a threshold energy of 73 +/- 2 kcal mol(-1) for the 1,2-FH elimination process and 60.5 +/- 1.5 kcal mol(-1) for the 2,3-FH elimination reaction from CF(3)CHFCH(3). The calculated kinetic-isotope effects agree with the experimental results. The experimentally derived threshold energies for 1,2-FH and 2,3-FH elimination reactions from several fluoropropanes and fluorochloropropanes are summarized and compared to those from DFT calculations.

Chemically activated CF(3)CFClCH(3), CF(3)CFClCD(3), CF(3)CFClCH(2)D, and CF(3)CFClCHD(2) molecules with 94 kcal mol(-1) of internal energy were formed by the combination of CF(3)CFCl radicals with CH(3), CD(3), CH(2)D, and CHD(2) radicals, which were generated from UV photolysis of CF(3)CFClI and CH(3)I, CD(3)I, CH(2)DI, or CHD(2)I. The total (HF + HCl) elimination rate constants for CF(3)CFClCH(3) and CF(3)CFClCD(3) were 5.3 x 10(6) and 1.7 x 10(6) s(-1) with product branching ratios of 8.7 +/- 0.6 in favor of HCl (or DCl). The intermolecular kinetic isotope effects were 3.22 and 3.18 for the HCl and HF channels, respectively. The product branching ratios were 10.3 +/- 1.9 and 11.8 +/- 1.8 (10.8 +/- 3.8 and 11.6 +/- 1.7) for HCl/HF and DCl/DF, respectively, from CF(3)CFClCH(2)D (CF(3)CFClCHD(2)). The intramolecular kinetic-isotope effects (without correction for reaction path degeneracy) for HCl/DCl and HF/DF elimination from CF(3)CFClCH(2)D (CF(3)CFClCHD(2)) were 2.78 +/- 0.16 and 2.98 +/- 0.12 (0.82 +/- 0.04 and 0.91 +/- 0.03), respectively. Density function theory at the B3PW91/6-311+G(2d,p) and B3PW91/6-31G(d',p') levels was investigated, and the latter was chosen to calculate frequencies and moments of inertia for the molecules and transition states. Rate constants, branching ratios and kinetic-isotope effects then were calculated using RRKM theory with torsional motions treated as hindered internal rotations. Threshold energies for HF and HCl elimination from CF(3)CFClCH(3) were assigned as 61.3 +/- 1.5 and 58.5 +/- 1.5 kcal mol(-1), respectively. The threshold energy for Cl-F interchange was estimated as 67 kcal mol(-1). The difference between the transition states for HCl and HF elimination is discussed.

Vibrationally activated CF3CH2CH2Cl molecules were prepared with 94 kcal mol-1 of vibrational energy by the combination of CF3CH2 and CH2Cl radicals and with 101 kcal mol-1 of energy by the combination of CF3 and CH2CH2Cl radicals at room temperature. The unimolecular rate constants for elimination of HCl from CF3CH2CH2Cl were 1.2 × 107 and 0.24 × 107 s-1 with 101 and 94 kcal mol-1, respectively. The product branching ratio, kHCl/kHF, was 80 ± 25. Activated CH3CH2CH2Cl and CD3CD2CH2Cl molecules with 90 kcal mol-1 of energy were prepared by recombination of C2H5 (or C2D5) radicals with CH2Cl radicals. The unimolecular rate constant for HCl elimination was 8.7 × 107 s-1, and the kinetic isotope effect was 4.0. Unified transition-state models obtained from density-functional theory calculations, with treatment of torsions as hindered internal rotors for the molecules and the transition states, were employed in the calculation of the RRKM rate constants for CF3CH2CH2Cl and CH3CH2CH2Cl. Fitting the calculated ...

Pt(IV)-mediated addition of the sulfimide Ph2S = NH and the mixed sulfide/sulfimides o- and p-[PhS(=NH)](PhS)-C6H4 by the S=NH group to the metal-bound nitriles in the platinum(IV) complexes [PtCl4(RCN)2] proceeds smoothly at room temperature in CH2Cl2 and results in the formation of the heterodiazadiene compounds [PtCl4[NH=C(R)N=SR'Ph]2] (R' = Ph, R = Me, Et, CH2Ph, Ph; R' = o- and p-(PhS)C6H4; R = Et). While trans-[PtCl4(RCN)2] (R = Et, CH2Ph, Ph) reacting with Ph2S=NH leads exclusively to trans-[PtCl4[NH=C(R)N=SPh2]2], cis/trans-[PtCl4(MeCN)2] leads to cis/trans mixtures of [PtCl4[NH=C(Me)N=SPh2]2] and the latter have been separated by column chromatography. Theoretical calculations at both HF/HF and MP2//HF levels for the cis and trans isomers of [PtCl4[NH=C(Me)N=SMe2]2] indicate a higher stability for the latter. Compounds trans-[PtCl4[E-NH=C(R)N=SPh2]2] (R = Me, Et) and cis-[PtCl4[E-NH=C(Me)N=SPh2][Z-NH=C(Me)N=SPh2]] have been characterized by X-ray crystallography. The complexes [PtCl4[NH=C(R)N=SPh2]2] undergo hydrolysis when treated with HCl in nondried CH2Cl2 to achieve the amidines [PtCl4[NH=C(NH2)R]2] the compound with R = Et has been structurally characterized) and Ph2SO. The heterodiazadiene ligands, formed upon Pt(IV)-mediated RCN/sulfimide coupling, can be liberated from their platinum(IV) complexes [PtCl4[NH=C(R)N=SR'Ph]2] by reaction with Ph2PCH2CH2PPh2 (dppe) giving free NH=C(R)=SR'Ph and the dppe oxides, which constitutes a novel route for such rare types of heterodiazadienes whose number has also been extended. The hybrid sulfide/sulfimide species o- and p-[PhS(=NH)](PhS)C6H4 also react with the Pt(II) nitrile complex [PtCl2(MeCN)2] but the coupling--in contrast to the Pt(IV) species--gives the chelates [PtCl2[M-I=C(Me)N=S(Ph)C6H4SPh]]. The X-ray crystal structure of [PtCl2[M-I=C(Me)N=S(Ph)C6H4SPh-o]] reveals the bond parameters within the metallacycle and shows an unusual close interaction of the sulfide sulfur atom with the platinum.

Density functional theory, DFT, and high-level conventional ab initio calculations, together with RRKM calculations, have been employed to study the nature of the transition state geometry for 1,2 elimination of HF from 1,1,1-trifluoroethane-d0,-d3; these serve as test cases for 1,2-HF elimination from fluorocarbons. Quantities calculated include structural parameters, bond indices, energies, atomic charges, vibrational frequencies, and moments of inertia for the reactant and the transition state geometry. The threshold energies for HF and DF elimination were computed and the vibrational frequencies and moments of inertia data were used with the RRKM theory to calculate the entropies of activation, preexponential factors for thermal activation, and also rate constants and the kinetic isotope effect for both thermally and chemically activated 1,1,1-trifluoroethane-d0,-d3. Of all the methods employed, the hybrid DFT methods incorporating either the three-parameter exchange functional of Becke with the corre...

The type of chemistry instruments funded as part of the Research in Undergraduate Institutions (RUI) Program at the National Science Foundation is summarized for proposals funded in 2006-2010. The data provided report on the success rate of RUI proposals, the average size of awards, the average duration of awards, and the percentage of the budget allocated to instruments. Information is given both for new and for experienced principle investigators.

Proposals submitted by chemistry departments over the past five years to the Major Research Instrumentation (MRI) Program at NSF have been analyzed to determine the types of instruments funded by MRI, and the success rate of MRI proposals submitted to NSF from undergraduate institutions. We have also compared MRI with the Course, Curriculum and Laboratory Improvement (CCLI) Program in terms of the funding rate and types of instruments supported by each so that faculty may determine which program is more suitable for them.

Calculations at the B3PW91/6-311+G(2d,p) level of theory have been performed on a series of chlorofluoropropanes in order to account for the chemistry of the molecules CF2ClCF2CH3 and CF2ClCF2CD3, chemically activated in the gas phase, which form novel elimination products, CF3CFCH2 or CF3CFCD2, formally a 1,3-HCl or DCl elimination together with a 1,2-fluorine migration. The proposed mechanism involves an initial 1,2-FCl rearrangement, with an activation energy of 62.5 kcal/mol, giving CF3CFClCH3, which is 3.3 kcal/mol lower in energy than CF2ClCF2CH3. Subsequently CF3CFClCH3 eliminates HCl with a barrier height of 55.4 kcal/mol. This mechanism accounts for both the unimolecular kinetics and the small kinetic isotope effect. A concerted transition geometry has been characterized for the 1,2-FCl rearrangement of each molecule of the type CF2ClCXFCY3, where X and Y are H, D, or F; in each case the rearrangement leads to a more thermodynamically stable rearrangement product CF3CXClCY3.

Chemically activated CF2ClCF2CH3 and CF2ClCF2CD3, containing 98.5 and 100 kcal/mol of internal energy, respectively, were formed in the gas phase from the combination of CF2ClCF2 and CH3 or CD3 radicals, respectively. These radicals were generated from the UV photolysis of CF2ClCF2I and CH3I or CD3I. The decomposition products were CF2ClCFCH2 (CF2ClCFCD2) from a 2,3-HF (DF) elimination and CF3CFCH2 (CF3CFCD2) suggesting a 1,3-HCl (DCl) elimination reaction. The 1,3-HCl elimination mechanism appears to be a two-step process; a 1,2-FCl rearrangement, producing CF3ClCFClCH3 (CF3CFClCD3), followed by a 2,3-HCl (DCl) elimination. Unimolecular rate constants for CF2ClCF2CH3 (CF2ClCF2CD3) were 5.3 ± 2.1 × 105 s-1 (1.8 ± 0.7 × 105 s-1) for 2,3-HF (DF) loss and 3.6 ± 1.4 × 104 s-1 (2.3 ± 0.9 × 104 s-1) for the 1,2-FCl rearrangement. The branching ratio was 13.5 ± 3 (7.8 ± 1.6) favoring the HF (DF) process. The isotope effect for 2,3-HF/DF was 2.9 ± 0.6, while for the FCl rearrangement, it was considerably smaller ...

This organic laboratory experiment introduces students to stereoselective enzyme reactions, resolution of enantiomers, and NMR analysis of diastereomers. The reaction between racemic 1-phenylethanol and vinyl acetate in hexane to form an ester is catalyzed by acylase I. The unreacted alcohol is then treated with a chiral acid and the resulting ester diastereomer is analyzed by NMR. This experiment is suitable for group work in the laboratory as several diastereomers are synthesized and compared to determine which enantiomer of 1-phenylethanol reacts with the enzyme.

Proposals submitted by chemistry departments to the Course Curriculum and Laboratory Improvement (CCLI) Program at NSF over the past five years have been analyzed to explore whether there have been changes in the percentage of proposals requesting an instrument or the types of instruments requested. We have also conducted a 10-year comparison of the Instrument and Laboratory Improvement Program for 1996−1998 versus the CCLI Program data for 2006−2009.

A method was developed to determine the concentrations of the ionic species present in the CO2−NH3−H2O system. The 13C NMR spectra of these solutions contain two peaks, one for the carbamate and one for the carbonate and bicarbonate. The method uses the area ratio and the position of the latter peak to determine concentrations. Ion concentrations were determined at 17 different concentrations for total NH3 and CO2 and at two different temperatures, 25 and 35 °C. All measurements were for solutions in which the total concentration of NH3 was greater than that of CO2. A comparison of three different thermodynamic models showed that although the models overpredicted the amount of carbonate, all were in reasonable agreement with experiment when the total ammonia concentration was less than 3 mol/L of solvent. At the higher concentrations, all the models badly underpredicted the amount of carbamate formed and overpredicted the amount of carbonate.

Chemically activated CF3CH2CF3 was prepared with 104 kcal/mol of internal energy by the combination of CF3CH2 and CF3 radicals, and chemically activated CF3CH2CH3 was prepared with 101 and 95 kcal/mol by combination of CF3 and CH2CH3 radicals and by combination of CF3CH2 and CH3 radicals, respectively. The experimental rate constants for unimolecular 1,2-dehydrofluorination were 1.2 × 105 s-1 for CF3CH2CF3 and 3.2 × 106 s-1 for CF3CH2CH3 with 95 kcal/mol and 2.0 × 107 s-1 with 101 kcal/mol of energy. Fitting the calculated rate constants for HF elimination from RRKM theory to the experimental values provided threshold energies, E0, of 73 kcal/mol for CF3CH2CF3 and 62 kcal/mol for CF3CH2CH3. Comparing these threshold energies to those for CF3CH3 and CF3CH2Cl illustrates that replacing the hydrogen of CF3CH3 with CH3 lowers the E0 by 6 kcal/mol and replacing with CF3 or Cl raises the E0 by 5 and 8 kcal/mol, respectively. The CF3 substituent, an electron acceptor, increases the E0 an amount similar to Cl, su...

Methyl and CF3CF2 radicals were combined to form chemically activated CF3CF2CH3 with 104 kcal/mol of internal energy, and the experimental rate constant for unimolecular 1,2-dehydrofluorination was 4.5 × 105 s-1. Fitting the calculated rate constant for HF elimination from RRKM theory to the experimental value provided a threshold energy, Eo, of 68.5 kcal/mol. Comparing this threshold energy to those for CF2HCH3, CH3CF2CH3, CF2ClCH3, and CF3CH3 shows that replacing the α-H of CF2HCH3 with CH3 lowered the Eo by 7 kcal/mol and replacing with CF3, Cl, or F raises the Eo about 8 kcal/mol. The CF3 substituent, an electron acceptor, increased the Eo by an amount nearly equal to that with F and Cl substituents, suggesting that halogen substituents exert a similar inductive effect at the α-carbon that loses electron density as the transition state forms. These proposals will be compared to recent calculations of the carbon's atomic charges in the reactant and transition state.

Combination of CFCl2 and methyl-d0 and -d3 radicals form CFCl2CH3-d0 and -d3 with 100 and 101 kcal/mol of internal energy, respectively. An upper limit for the rate constant ratio of disproportionation to combination, kd/kc, for Cl transfer is 0.07 ± 0.03 for collision of two CFCl2 radicals and 0.015 ± 0.005 for CH3 and CFCl2 radicals. The chemically activated CFCl2CH3 undergoes 1,2-dehydrochlorination and 1,2-dehydrofluorination with rate constants of 3.9 × 109 and 4.9 × 107 s-1, respectively. For CFCl2CD3 the rate constants are 8.7 × 108 s-1 for loss of DCl and 1.1 × 107 s-1 for DF. The kinetic isotope effect is 4.4 ± 0.9 for HCl/DCl and appears to be identical for HF/DF. Threshold energies are 54 kcal/mol for loss of HCl and 68 kcal/mol for HF; the E0's for the deuterated channels are 1.4 kcal/mol higher. Comparison of these threshold energies with other haloethanes suggests that for HF and HCl elimination the transition states are developing charges of different signs on the carbon containing the depa...

A threshold energy barrier of 29±4 kcal/mol was estimated for the 1,2-fluorine migration reaction converting 1,1,1-trifluoromethylcarbene, CF 3 CH, into CF 2 =CHF in the gas phase. The CF 3 CH was formed by the 1,1-elimination of HCl from chemically activated CF 3 CH 2 Cl containing 97.5 kcal/mol of internal energy. RRKM theory was used to calculate rate constants for the 1,2-fluorine shift that were fitted to the experimental pressure dependence to determine the threshold barrier

Chemically activated CF 3 CH 2 Cl was prepared with 97.5 kcal/mol of internal energy by the combination of CF 3 and CH 2 Cl radicals. The total unimolecular decomposition rate constant was measured by using two internal standard methods and the average was (7.5±2.6/1.5)×10 6 s −1 . The rate constant for four-centered elimination of HF was measured as (2.8±0.1)×10 6 s −1 , for C-Cl bond homolysis the rate constant was (0.8±5.6/0.1)×10 6 s −1 , and by difference the three-centered HCl elimination rate constant was (3.9±2.6/3.0)×10 6 s −1 . These rate constants were compared to predictions from RRKM theory, and threshold energies were assigned for loss of HF (76 kcal/mol), for C-Cl bond rupture (83 kcal/mol), and for HCl elimination (72 kcal/mol). Product distributions from three activation methods (chemical, multiphoton laser, and thermal) were analyzed to develop a self-consistent view of this complex reaction system

Chemically activated CF 2 ClCH 3 -d 0 and -d 3 were prepared with 101 and 102 kcal/mol of internal energy, respectively, by the combination of CF 2 Cl with methyl-do and -d 3 radicals at 300 K. The CF 2 ClCH 3 reacts by loss of HCl and HF with rate constants of (2.5±0.4)×10 9 and (0.10±0.02)×10 9 s -1 , respectively, a branching ratio of 25:1 in favor of HCl

In this interdisciplinary laboratory course, groups of beginning students complete semester-long projects studying soil chemistry, plant uptake of metals, and environmental analysis while applying their knowledge to the research area of phytoremediation. Phytoremediation is the use of plants capable of accumulating pollutants to reduce levels in contaminated soils or water. In a series of short experiments, students learn methods for sample collection and preparation including collection of an aqueous runoff sample and digestion of soil and plants. Chemical analysis methods presented include the determination of soil pH, potentiometric titration of carbonates, determination of anions by ion chromatography, measurement of cation-exchange capacity of soil using an ammonium ion selective electrode, and trace-metal analysis using ion chromatography or atomic absorption spectrometry. Students begin reviews of scientific literature early in the course that are relevant to their projects, use computer software t...

Human alpha 2-antiplasmin (alpha 2AP) has been expressed in Chinese hamster ovary cells and purified from conditioned media. The recombinant protein (r alpha 2AP) is immunologically identical with natural alpha 2AP and indistinguishable with respect to plasmin(ogen) binding properties. Second-order rate constants (k1) for the interaction of alpha 2AP and r alpha 2AP with plasmin are both (1-2) X 10(7) M-1 s-1. In order to examine the effects of alterations within the reactive site of alpha 2AP, deletions of the P1 residue Arg-364 (r alpha 2AP-delta Arg364) or the P'1 residue Met-365 (r alpha 2AP-delta Met365) were introduced by in vitro site-directed mutagenesis. r alpha 2AP-delta Met365 completely retains its ability to inhibit both plasmin and trypsin, indicating that alpha 2AP has no absolute requirement for Met in the P'1 position. Unexpectedly, no increase in antithrombin activity was observed. r alpha 2AP-delta Arg364 has lost the ability to inhibit plasmin, trypsin, and thrombin, but unlike the wild-type protein, this variant is an effective elastase inhibitor (k1 = 1.5 X 10(5) M-1 s-1).