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Here, we report the kinetic energy distributions (KEDs) of the fragment ions produced from multiply ionized ethane (C₂H₆) molecules in single electron capture collisions with 1.2 MeV C²⁺. To systematically investigate the fragmentation dynamics, the KEDs were obtained as functions of the charge state of the intermediate C₂H₆r⁺* ions r transiently generated prior to fragmentation. r was determined from coincidence measurement of the fragment ions and the number of emitted electrons. The KEDs are drastically different depending on the number of broken C–H bonds. The underlying causes are explained by the variation of the relative contributions of the multiply ionized states and preferential fragmentation pathways. For instance, CHn⁺ fragment ions with smaller n exhibit lower KEs because they are likely to be correlated with H⁺ emission, which carries away a large portion of the KE release. In addition, we report the KEDs of H₃⁺ produced from doubly and triply charged states., Special Issue: Proceedings of the 19th International Conference on the Physics of Highly Charged Ions (HCI 2018), Caparica, Lisboa, Portugal, 3‐7 September 2018

A novel dynamic fugacity-based model is described, developed, and tested that simulates the uptake of narcotic organic chemicals in fish from water as occurs in aquatic bioconcentration and toxicity tests. The physiologically based toxicokinetic model treats the time course of chemical distribution in 4 compartments (tissue groups) in the fish, including the liver, in which biotransformation may occur. In addition to calculating bioconcentration and toxicokinetics, 5 possible toxic endpoints are defined corresponding to chemical concentration, fugacity, or activity reaching a critical value that causes 50% mortality. The mathematical description of multicompartment uptake is simplified by expressing the equations in the fugacity format. The model is parameterized and tested against reported empirical data for the bioconcentration of pentachloroethane in rainbow trout and for uptake and mortality from aquatic exposures to naphthalene and 1,2,4-trichlorobenzene in fathead minnows. Model performance is evaluated, and it is concluded that with suitable parameterization it has potential for application for assessment of both bioconcentration and toxicity expressed as median lethal concentrations, critical body residues, and chemical activity as a function of time to death.

The straightforward solid-state grinding of a mixture of Ni nitrate and Nb oxalate crystals led to, after mild calcination (T

A designed bis(dithienyl) dicyanoethene-based, strictly E/Z photoswitch (4TCE) operates through state-selective (E and Z isomer) photoactivation with visible light. The E and Z isomers of 4TCE exhibit remarkably different spectroscopic characteristics, including a large separation (70 nm) in their absorption maxima (λ(max)) and a 2.5-fold increase in molar extinction coefficient from cis to trans. The energetically stable trans form can be completely converted to the cis form within minutes when exposed to white light, whereas the reverse isomerization occurs readily upon irradiation by blue light (λ480 nm) or completely by thermal conversion at elevated temperatures. These features together with excellent thermal stability and photostability of both isomers make this new E/Z photoswitch a promising building block for photoswitchable materials that operate without the need for UV light.

A new type of high‐pressure reactor based on liquid‐flow pressurisation using a HPLC pump has been developed. This high‐pressure reactor allows the easy and safe performance of reactions with gaseous alkanes under high‐pressures up to 10 MPa (100 atm), without the need for high‐pressure gas cylinders. The amount of substrate gas required for a single reaction is very small compared with reactions using a conventional autoclave, which, when using expensive substrate gasses, such as 13C‐labelled ethane, becomes critical. Employing this high‐pressure reactor in conjunction with cytochrome P450BM3 and the assistance of decoy molecules, the direct hydroxylation of gaseous alkanes was drastically improved. At 5 MPa the TOF of propane hydroxylation increased 10‐fold, reaching 2200 min^−1. Hydroxylation of ethane was also substantially accelerated at 5 MPa, reaching a TOF of 28 min^−1., ファイル公開：2020-10-07

The flavoprotein nitroalkane oxidase catalyzes the oxidative denitrification of a broad range of primary and secondary nitroalkanes to yield the respective aldehydes or ketones, hydrogen peroxide and nitrite. With nitroethane as substrate the D2O(k(cat)/K(M)) value is 0.6 and the D2Ok(cat) value is 2.4. The k(cat) proton inventory is consistent with a single exchangeable proton in flight, while the k(cat)/K(M) is consistent with either a single proton in flight in the transition state or a medium effect. Increasing the solvent viscosity did not affect the k(cat) or k(cat)/K(M) value significantly, establishing that nitroethane binding is at equilibrium and that product release does not limit k(cat).

Pd-doped propyl sulfonic acid-functionalized hollow nanospheres proved to be efficient bifunctionalized catalysts for the one-pot synthesis of methyl isobutyl ketone (MIBK) from acetone and hydrogen in liquid phase. These hollow nanospheres exhibited a higher activity than their bulk mesoporous counterparts (SBA-15 or FDU-12), mainly due to the short diffusion resistance of hollow nanospheres. Hollow nanospheres with silica frameworks showed higher activity and selectivity for MIBK than those with ethane-bridged frameworks, suggesting that hollow nanospheres with hydrophilic surface properties favor the formation of MIBK. This is probably due to the increased affinity of the hydrophilic surface towards acetone and its decreased affinity towards MIBK, which precludes deep condensation of MIBK with acetone. Under optimal conditions, up to 90 % selectivity for MIBK can be obtained with conversions of acetone as high as 43 %. This result is among the best reported so far for mesoporous silica-based catalysts. The control/fine-tuning of morphology and surface properties provides an efficient strategy for improving the catalytic performance of solid catalysts.

Ruthenium alkynyl dendrimers up to second generation in size have been prepared by a divergent route and exploiting Sonogashira coupling. The cubic NLO properties have been examined by wide spectral range fs Z-scan studies, revealing an NLO dendritic effect. The significant increase in NLO properties seen on generation increase is maintained when the coefficients are scaled by the number of metal atoms, the dendrimer molecular weights, or the number of "effective" (delocalizable π) electrons in the dendritic structures.

12 not so angry men: Hexaphenylethane is unstable, a phenomenon traditionally attributed to steric repulsion between the six phenyl rings. However, adding 12 bulky tert-butyl groups, one to each of the 12 meta positions, gives a stabile ethane derivative (see space-filling model and potential energy curve for the dissociation of the central C-C bond). This unexpected stabilization is shown to result from attractive dispersion interactions between the substituents.

Geometry optimization of ethane clusters (C(2)H(6))(n) in the range of n ≤ 25 is carried out with a Morse potential. A heuristic method based on perturbations of geometries is used to locate global minima of the clusters. The following perturbations are carried out: (1) the molecule or group with the highest energy is moved to the interior of a cluster, (2) it is moved to stable positions on the surface of a cluster, and (3) orientations of one and two molecules are randomly modified. The geometry obtained after each perturbation is optimized by a quasi-Newton method. The global minimum of the dimer is consistent with that previously reported. The putative global minima of the clusters with 3 ≤ n ≤ 25 are first proposed and their building-up principle is discussed.

(r)-(+)-binol-functionalized chiral periodic mesoporous organosilicas (pmos) with different framework compositions were successfully synthesized by cocondensation of (r)-2,2'-di(methoxymethyl)oxy-6,6'-di(1-propyl-trimethoxysilyl)-1,1'-binaphthyl (bsbinol) with 1,2-bis(trimethoxysilyl)ethane (btme) and tetramethoxysilane (tmos) using triblock copolymer p123 as a template in acidic solution. the mixture of btme and bsbinol can result in a highly ordered mesostructure in an acidic medium but the mesoporous materials synthesized using a mixture of tmos and bsbinol can only be obtained in a weak acidic buffer solution. all the materials are efficient catalysts (coordinated with ti) for asymmetric addition of diethylzinc to aldehydes. the chiral pmo with ethane and (r)-(+)-binol in the framework exhibits an enantioselectivity as high as 90% with a turnover frequency (tof) of 104 h(-1), which is even higher than the homogeneous (r)-(+)-binol catalyst (83% ee with tof of 96 h(-1)) using toluene as solvent under similar conditions. this work demonstrates the positive effect of the rigid pore wall in increasing the enantioselectivity of the chiral pmos.

The effect of the incorporation of either ester or ester and ether functions into the side chain of an 1-alkyl-3-methylimidazolium cation on the physico-chemical properties of ionic liquids containing bis(trifluoromethylsulfonyl)imide or octylsulfate anions is studied. It is believed that the introduction of an ester function into the cation of the ionic liquids greatly increases their biodegradability. The density of three such ionic liquids is measured as a function of temperature, and the solubility of four gases-carbon dioxide, ethane, methane, and hydrogen-is determined between 303 K and 343 K and at pressures close to atmospheric level. Carbon dioxide is the most soluble gas, followed by ethane and methane; the mole fraction solubilities vary from 1.8 x 10(-3) to 3.7 x 10(-2). These solubilities are of the same order of magnitude as those determined for alkylimidazolium-based ionic liquids. The chemical modification of the alkyl side chain does not result in a significant change of the solvation properties of the ionic liquid. All of the solubilities decrease with increasing temperature, corresponding to an exothermal solvation process. From the variation of this property with temperature, the thermodynamic functions of solvation (Gibbs energy, enthalpy, and entropy) are calculated and provide information about the solute-solvent interactions and the molecular structure of the solutions.

Monolithic poly(1,2-bis(p-vinylphenyl)ethane (BVPE)) capillary columns were prepared by thermally initiated free radical polymerisation of 1,2-bis(p-vinylphenyl)ethane in the presence of inert diluents (porogens) and alpha,alpha'-azoisobutyronitrile (AIBN) as initiator. Polymerisations were accomplished in 200 microm ID fused silica capillaries at 65 degrees C and for 60 min. Mercury intrusion porosimetry measurements of the polymeric RP support showed a broad bimodal pore-size-distribution of mesopores and small macropores in the range of 5-400 nm and flow-channels in the mum range. N(2)-adsorption (BET) analysis resulted in a tremendous enhancement of surface area (101 m(2)/g) of BVPE stationary phases compared to typical organic monoliths (approximately 20 m(2)/g), indicating the presence of a considerable amount of mesopores. Consequently, the adequate proportion of both meso- and (small) macropores allowed the rapid and high-resolution separation of low-molecular-weight compounds as well as biomolecules on the same monolithic support. At the same time, the high fraction of flow-channels provided enhanced column permeability. The chromatographic performance of poly(1,2-bis(p-vinylphenyl)ethane) capillary columns for the separation of biomolecules (proteins, oligonucleotides) and small molecules (alkyl benzenes, phenols, phenons) are demonstrated in this article. Additionally, pressure drop versus flow rate measurements of novel poly(1,2-bis(p-vinylphenyl)ethane) capillary columns confirmed high mechanical robustness, low swelling in organic solvents and high permeability. Due to the simplicity of monolith fabrication, comprehensive studies of the retention and separation behaviour of monolithic BVPE columns resulted in high run-to-run and batch-to-batch reproducibilities. All these attributes prove the excellent applicability of monolithic poly(1,2-bis(p-vinylphenyl)ethane) capillary columns for micro-HPLC towards a huge range of analytes of different chemistries and molecular sizes.

Spectra of the N-phenyl-5,6-dihydro-2,4-diphenylbenzo[h]quinolinium tetrafluoroborate (1) and of the N-phenyl-5,6,8,9-tetrahydro-7-phenyldibenzo[c,h]acridinium tetrafluoroborate (2) were recorded in various solvents and temperatures. The analysis of the (1)H-NMR spectra of the tetrafluoroborate salt 1, recorded in acetone, acetonitrile, 1,1,2,2-tetrachloroethane and chloroform, revealed the existence of an equilibrium between two conformers in solution. Tight ion-pairing in chloroform led to a smaller barrier for interconversion between the two conformers. In more polar solvents, where the dihydrobenzoquinolinium exists as a free cation, theoretical calculations predicted larger barriers. The spectra of 1 in 1,1,2,2-tetrachloroethane also varied with temperature, resembling at higher temperatures the spectrum in CDCl(3) and at 300K spectra in more polar media. Spectra of 2 did not vary with the solvent or the temperature, in an indication of a much higher barrier to conformational interconversion, because of a greater steric hindrance between the N-phenyl substituent and the dihydrobenzo rings.

The ability to process and purify engineered nanomaterials using near critical or supercritical fluids (NcFs or ScFs) has enormous potential for the application at various stages of the development of green nanomaterials. The dispersibility of octanethiol-stabilized gold nanocrystals of different core sizes is explored, which were chosen to serve as model nanomaterials of general interest in compressed ethane and propane over a wide range of fluid conditions. Both solvents have enormous potential for the environmentally benign processing and transport of engineered nanomaterials due to their nominal toxicity and high degree of tunability and processability that can essentially eliminate solvent waste. The dispersibility is determined by measuring the absorption spectra of dispersions of various sizes of nanocrystals in NcFs. To better understand the obtained results three models, the total interaction theory, the sedimentation coefficient equation, and the Chrastil method, are discussed. Nanoparticle dispersibility versus density plots are strongly dependent on nanoparticle size and solvent conditions, with the dispersion of larger nanocrystals more dependent on changes of pressure or density at a given temperature. For the range of nanoparticle sizes studied, compressed ethane at 25 degrees C leads to a greater tunability of nanoparticle dispersion when compared with compressed propane at 65 degrees C. For equivalent pressures, compressed propane is found to provide better solubility than ethane due to its higher density. The results quantitatively demonstrate that NcFs can offer pressure-tunable, size-selective control of nanoparticle solvation and transport at easily obtainable temperature and pressure conditions. These capabilities provide clear advantages over conventional solvents and direct application to various nanomaterials processes, such as synthesis, separation, transport, and purification of nanocrystals.

In vivo lipid peroxidation was studied in phenobarbital pretreated rats exposed for chloroform. Lipid peroxidation was monitored as ethane exhalation or malondialdehyde (MDA) excretion in urine. A single oral dose of chloroform (0.7 ml/kg b. wt.) showed a marked increase in ethane exhalation in animals starved for 48 hours prior to chloroform treatment. This increase became evident after a lag-period of about 100 min. Pretreatment with diethylmaleate (1 ml/kg b. wt.) 1 hour prior to chloroform treatment gave a similar result. MDA excretion in urine from non-starved animals, exposed to chloroform, markedly increased after 4 hours and after 24 hours 115 nmol/kg had been excreted. In animals starved for 48 hours prior to chloroform treatment about 270 nmol/kg excreted within 24 hours. Small molecular weight thiols were measured in liver, kidneys and lungs. Chloroform decreased the thiol content of the liver by 43.2% within 100 min. while the concentration in the kidneys and the lungs were less affected. It is suggested that chloroform may act as a potent inducer of lipid peroxidation in vivo. The synergistic effects of the pretreatments and the lag phase indicate that glutathione depletion in the liver was an essential factor in this response.

The molecular-dynamics-based calculation of accurate free energy differences for biomolecular systems is a challenging task. Accordingly, convergence and accuracy of established equilibrium methods has been subject of many studies, often focusing at small test systems. In contrast, the potential of more recently proposed nonequilibrium methods, derived from the Jarzynski and Crooks equalities, has not yet fully been explored. Here, we compare the performance of these methods by calculating free energy differences for test systems at different levels of complexity and varying extent of the involved perturbations. We consider the interconversion of ethane into methanol, the switching of a tryptophane-sidechain in a tripeptide, and the binding of two different ligands to the globular protein snurportin 1. On the basis of our results, we suggest and assess a new nonequilibrium free energy method, Crooks Gaussian Intersection (CGI), which combines the advantages of existing methods. CGI is highly parallelizable and, for the test systems considered here, is shown to outperform the other studied equilibrium and nonequilibrium methods. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009

Summary • Recent studies demonstrating an in situ formation of methane (CH4) within foliage and separate observations that soil-derived CH4 can be released from the stems of trees have continued the debate about the role of vegetation in CH4 emissions to the atmosphere. Here, a study of the role of ultraviolet (UV) radiation in the formation of CH4 and other trace gases from plant pectins in vitro and from leaves of tobacco (Nicotiana tabacum) in planta is reported. • Plant pectins were investigated for CH4 production under UV irradiation before and after de-methylesterification and with and without the singlet oxygen scavenger 1,4-diazabicyclo[2.2.2]octane (DABCO). Leaves of tobacco were also investigated under UV irradiation and following leaf infiltration with the singlet oxygen generator rose bengal or the bacterial pathogen Pseudomonas syringae. • Results demonstrated production of CH4, ethane and ethylene from pectins and from tobacco leaves following all treatments, that methyl-ester groups of pectin are a source of CH4, and that reactive oxygen species (ROS) arising from environmental stresses have a potential role in mechanisms of CH4 formation. • Rates of CH4 production were lower than those previously reported for intact plants in sunlight but the results clearly show that foliage can emit CH4 under aerobic conditions.

Synthetic amavadin Ca[V{ON[CH(CH(3))COO](2)}(2)] and its models Ca[V{ON(CH(2)COO)(2)}(2)] and [VO{N(CH(2)CH(2)O)(3)}], in the presence of K(2)S(2)O(8) in trifluoroacetic acid (TFA), exhibit remarkable catalytic activity for the one-pot carboxylation of ethane to propionic and acetic acids with the former as the main product (overall yields up to 93 %, catalyst turnover numbers (TONs) up to 2.0 x 10(4)). The simpler V complexes [VO(CF(3)SO(3))(2)], [VO(acac)(2)] and VOSO(4) are less active. The effects of various factors, namely, C(2)H(6) and CO pressures, time, temperature, and amounts of catalyst, TFA and K(2)S(2)O(8), have been investigated, and this allowed optimisation of the process and control of selectivity. (13)C-labelling experiments indicated that the formation of acetic acid follows two pathways, the dominant one via oxidation of ethane with preservation of the C--C bond, and the other via rupture of this bond and carbonylation of the methyl group by CO; the C--C bond is retained in the formation of propionic acid upon carbonylation of ethane. The reactions proceed via both C- and O-centred radicals, as shown by experiments with radical traps. On the basis of detailed DFT calculations, plausible reaction mechanisms are discussed. The carboxylation of ethane in the presence of CO follows the sequential formation of C(2)H(5) (*), C(2)H(5)CO(*), C(2)H(5)COO(*) and C(2)H(5)COOH. The C(2)H(5)COO(*) radical is easily formed on reaction of C(2)H(5)CO(*) with a peroxo V catalyst via a V{eta(1)-OOC(O)C(2)H(5)} intermediate. In the absence of CO, carboxylation proceeds by reaction of C(2)H(5) (*) with TFA. For the oxidation of ethane to acetic acid, either with preservation or cleavage of the C-C bond, metal-assisted and purely organic pathways are also proposed and discussed.

An anaerobic microcosm set up with aquifer material from a 1,1,2,2-tetrachloroethane (TeCA) contaminated site and amended with butyrate showed a complete TeCA dechlorination to ethene. A structure analysis of the microbial community was performed by fluorescence in situ hybridization (FISH) with already available and on purpose designed probes from sequences retrieved through 16S rDNA clone library construction. FISH was chosen as identification tool to evaluate in situ whether the retrieved sequences belong to primary bacteria responsible for the biodegradative reactions. FISH probes identified up to 80% of total bacteria and revealed the absence or the marginal presence of known TeCA degraders and the abundance of two well-known H(2)-utilizing halorespiring bacteria, Sulfurospirillum (32.4 +/- 8.6% of total bacteria) and Dehalococcoides spp. (14.8 +/- 2.8), thereby providing a strong indication of their involvement in the dechlorination processes. These results were supported by the kinetic and thermodynamic analysis which provided indications that hydrogen was the actual electron donor for TeCA dechlorination. The specific probes, developed in this study, for known dechlorinators (i.e., Geobacter, Dehalobacter, and Sulfurospirillum species) represent a valuable tool for any future in situ bioremediation study as well as a quick and specific investigation tool for tracking their distribution in the field.

Effects of 2-nitro-1-propanol, 2-nitroethanol, nitroethane, and 2-nitro-methyl-propionate (0, 10, and 20 mM) on growth of Campylobacter jejuni were tested during culture in Bolton broth adjusted to pH 5.6, 7.0, or 8.2. The nitrocompounds were similarly tested against C. coli but at pH 8.2 only. Viable cell counts measured during incubation revealed main effects (P < 0.05) of all nitrocompounds on the survivability of C. jejuni. An effect of pH (P < 0.05) on the survivability of C. Jejuni during incubation with nitrocompounds was observed, with greater inhibition observed at pH 8.2 than at pH 5.6 or 7.0 for nitroethane, 2-nitro-l-propanol, and 2-nitroethanol, but not for 2-nitro-methyl-propionate, which showed greatest inhibition at pH 5.6. Except for 2-nitro-methyl-propionate, which was ineffective, all nitrocompounds elicited similar effects on C. coli. The effect of nitroethane and 2-nitro-l-propanol (10 mM) on naturally occurring Campylobacter was investigated during incubation of porcine fecal suspensions, where Campylobacter concentrations decreased more rapidly (P < 0.05) in suspensions with added 2-nitro-l-propanol than in unsupplemented or nitroethane-supplemented suspensions, thus reiterating the superior inhibitory effect of 2-nitro-l-propanol.

The thermodynamic properties of three halocarbon molecules relevant in atmospheric and public health applications are presented from ab initio calculations. Our technique makes use of a reaction path-like Hamiltonian to couple all the vibrational modes to a large-amplitude torsion for 1,2-difluoroethane, 1,2-dichloroethane, and 1,2-dibromoethane, each of which possesses a heavy asymmetric rotor. Optimized ab initio energies and Hessians were calculated at the CCSD(T) and MP2 levels of theory, respectively. In addition, to investigate the contribution of electronically excited states to thermodynamic properties, several excited singlet and triplet states for each of the halocarbons were computed at the CASSCF/MRCI level. Using the resulting potentials and projected frequencies, the couplings of all the vibrational modes to the large-amplitude torsion are calculated using the new STAR-P 2.4.0 software platform that automatically parallelizes our codes with distributed memory via a familiar MATLAB interface. Utilizing the efficient parallelization scheme of STAR-P, we obtain thermodynamic properties for each of the halocarbons, with temperatures ranging from 298.15 to 1000 K. We propose that the free energies, entropies, and heat capacities obtained from our methods be used to supplement theoretical and experimental values found in current thermodynamic tables.

Guest–host interac-tions play a crucial role in the crystal structure, and thusclathrate hydrates are thermodynamically stable only whenguestmoleculesareencagedinthehostcages.Therelationbetween structural type of clathrate hydrate and guestmolecule is categorized according to the size of the guestmolecule.

Picking on someone smaller. Cytochromes P450 catalyze the hydroxylation of thousands of substrates, including alkanes. No naturally occurring P450, however, is known to oxidize the smallest alkanes, ethane and methane. Here we report the direct and selective oxidation of ethane to ethanol using dioxygen, catalyzed by a cytochrome P450 BM‐3 variant engineered for high activity towards small alkanes (see scheme). Achieving P450‐catalyzed oxidation of ethane is a key step in the pathway to P450‐catalyzed methane oxidation and opens new opportunities for the bioconversion of natural gas to fuels and chemicals.

A novel continuous high-pressure biphasic bioreactor was designed to investigate the toxicity of compressed and supercritical fluids on the thermophilic bacterium Clostridium thermocellum. Cultures were conducted at 1.8 and 7.0 MPa hydrostatic pressure and in the presence of compressed N(2) (7.0 MPa), gaseous (1.8 MPa) and supercritical ethane (7.0 MPa), and gaseous (1.8 MPa) and liquid (7.0 MPa) propane at a single dilution rate. No significant changes in metabolism or growth were observed in the presence of compressed N(2) relative to 7.0 MPa hydrostatic pressure, indicating that it acted as an inert fluid. However, dramatic inhibitions of growth and metabolism occurred in the presence of ethane and propane at 7.0 MPa. These inhibitions were reversed by depressurization from the supercritical (ethane) or liquid (propane) to gaseous state. Solvent toxicity by compressed and supercritical fluids was attributed to phase toxicity and was correlated with fluid density rather than conventional measures of toxicity (log P(o/w)). This biphasic reactor system facilitates investigations of solvent toxicity and dissolved gas effects on whole cells under elevated pressures.

The interactions of nitric oxide (NO) and organic nitroso compounds with heme proteins are biologically important, and adduct formation between NO-containing compounds and myoglobin (Mb) have served as prototypical systems for studies of these interactions. We have prepared crystals of horse heart (hh) MbNO from nitrosylation of aqua-metMb crystals, and we have determined the crystal structure of hh MbNO at a resolution of 1.9 A. The Fe-N-O angle of 147° in hh MbNO is larger than the corresponding 112° angle previously determined from the crystal structure of sperm whale MbNO (Brucker et al., Proteins 1998;30:352–356) but is similar to the 150° angle determined from a MS XAFS study of a frozen solution of hh MbNO (Rich et al., J Am Chem Soc 1998;120:10827–10836). The Fe-N(O) bond length of 2.0 A (this work) is longer than the 1.75 A distance determined from the XAFS study and suggests distal pocket influences on FeNO geometry. The nitrosyl N atom is located 3.0 A from the imidazole Nϵ atom of the distal His64 residue, suggesting electrostatic stabilization of the FeNO moiety by His64. The crystal structure of the nitrosoethane adduct of ferrous hh Mb was determined at a resolution of 1.7 A. The nitroso O atom of the EtNO ligand is located 2.7 A from the imidazole Nϵ atom of His64, suggesting a hydrogen bond interaction between these groups. To the best of our knowledge, the crystal structure of hh Mb(EtNO) is the first such determination of a nitrosoalkane adduct of a heme protein. Proteins 2003. © 2003 Wiley-Liss, Inc.

International audience; It is proposed to revisit the problem of gas - liquid crystallization in the framework of a two-film model and with the help of experimental data from two experimental systems. Preliminary quantitative discussion of the order of magnitude of different effects makes possible realistic simplifications in the theoretical models. In particular, the role of the interfacial film in the whole process is clearly defined. As previous researchers have done, a formulation in terms of moments of the crystal size distribution is used; however, instead of the numerical solution to the corresponding differential system, a general Procedure to express analytically the asymptotic behavior of the physical system is proposed. With this formulation, the influence of different parameters can be easily identified and validated on the available data from two experimental systems.

Background and Objectives: Cryogen spray cooling (CSC) is used extensively for epidermal protection during laser-induced photothermolysis of port wine stains and other vascular skin lesions. The efficacy of CSC depends critically on the heat transfer coefficient (H) at the skin surface for which, however, no reliable values exist. Reported values for H, based on tissue phantoms, vary from 1,600 to 60,000 W/m 2 K. Study Design/Materials and Methods: A simple experimental model was designed and constructed, consisting of a pure silver-measuring disk (diameter 10 mm, thickness � 1 mm), embedded in a thermal insulator. The disk was covered with a 10 mm thick stratum corneum layer, detached from in vivo human skin. The heat transfer coefficient of the stratum corneum/cryogen interface was measured during CSC with short spurts of atomized tetrafluoroethane. Results:H was found to be dependent on the specific design of the cryogen valve and nozzle. With nozzles used in typical clinical settings,H was 11,500 W/m 2 K, when averaged over a 100 ms spurt, and 8,000 W/m 2 K when averaged over a 200 ms spurt. Conclusions: The presented model enables accurate prediction of H and thus improve control over temperature depth profile and cooling efficiency during laser therapy. Thereby, it may contribute to improvement of therapeutic outcome. Lasers Surg. Med. 32:137–142, 2003. 2003 Wiley-Liss, Inc.

The effect of gestational age on postnatal free-radical-mediated lipid peroxidation was studied in 19 term (gestational age 37-42 weeks) and 21 healthy preterm (gestational age 31-36 weeks) infants by measurement of expired ethane and pentane during the first 7 days of life. Ethane (11.9 versus 5.7 pmol/kg/min; p = 0.0001) and pentane (11.4 versus 7.5 pmol/kg/min; p = 0.01) were significantly higher in preterm than in term infants. Correlations were found between gestational age and ethane (r = 0.60, p = 0.0001) for days 1-7 and pentane (r = 0.54, p = 0.0003) for days 3-7; and between birth weight and ethane (r = 0.58, p = 0.0001) and pentane (r = 0.55, p = 0.0003). These results indicate that during the postnatal period, immaturity is a major factor determining the rate of free-radial-mediated lipid peroxidation.

Formation of free radicals and lipoperoxidation occur at the onset of cellular damage. These effects are produced during normal metabolism and in pathological states. The peroxidation of polyunsaturated fatty acids, i.e. linoleic acid and linolenic acid, which are both cellular membrane compounds, induces ethane and pentane formation in pulmonary air exhalation. These two volatile hydrocarbons can be considered as potential lipoperoxidation markers. Methodological difficulties limit the use of these gases for assessment of free oxygen radical activity but we have developed and validated a non-invasive technique. A study was performed with ten healthy volunteers.

I-TevI, a double-strand DNA endonuclease encoded by the mobile td intron of phage T4, has specificity for the intronless td allele. Genetic and physical studies indicate that the enzyme makes extensive contacts with its DNA substrate over at least three helical turns and around the circumference of the helix. Remarkably, no single nucleotide within a 48 bp region encompassing this interaction domain is essential for cleavage. Although two subdomains (DI and DII) contain preferred sequences, a third domain (DIII), a primary region of contact with the enzyme, displays much lower sequence preference. While DII and DIII suffice for recognition and binding of I-TevI, all three domains are important for formation of a cleavage-competent complex. Mutational, footprinting and interference studies indicate predominant interactions of I-TevI across the minor groove and phosphate backbone of the DNA. Contacts appear not to be at the single nucleotide level; rather, redundant interactions and/or structural recognition are implied. These unusual properties provide a basis for understanding how I-TevI recognizes T-even phage DNA, which is heavily modified in the major groove. These recognition characteristics may increase the range of natural substrates available to the endonuclease, thereby extending the invasive potential of the mobile intron.

In this communication we define electronic symmetry operation and symmetry group measures, eSOM and eSGM, respectively, develop the basic algorithms to obtain them, and give some examples of the possible applications of these new computational tools. These new symmetry measures based on the electron density have been tested in an analysis of (a) the inversion symmetry for heteronuclear diatomic molecules, for the eclipsed and staggered conformations of ethane and tetrafluoroethane, and for a series of octahedral sulfur halides; (b) the reflection symmetry of three different conformers of tetrafluoroethene; and (c) the loss of C6 symmetry along the B2u distortion mode of benzene and an analysis of rotational symmetry for different six-member ring heterocycles. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010

SUMMARY Rapid freezing is the most important step in sample preparation for freeze-fracture and other cryotechniques for electron microscopy. A simple heat transfer model is experimentally validated to show that convection from the cryogen to the specimen is the limiting step in rapid freezing of small samples [Biot modulus, (hd/k) < 1] by measuring cooling rates in a variety of samples, materials, and cryogens. In comparison to the commonly accepted conduction-limited model, the convection-limited model predicts, and our experiments show, that cooling rates are proportional to the surface area to volume ratio, independent of the sample thermal conductivity, and inversely proportional to the product of sample density and heat capacity. We show that almost any material can be frozen at similar rates if the sample thickness, the cryogen, and the method and velocity of contact with cryogen are similar. Liquid ethane or propane cooled to liquid nitrogen temperature are shown to give the best results.

The ortho-alkylation of phenols or aniline by catalytic C-H activation and multifunctional catalysis is described.

[reaction: see text] A variety of furan-2-ylacetates have been prepared by dehydrogenation of monocyclic 2-alkylidenetetrahydrofurans, which are readily available by cyclizations of open-chained 1,3-dicarbonyl dianions with 1-bromo-2-chloroethane. 5'H-[2,3']Bifuranyl-2'-ones are available based on sequential "cyclization/dehydrogenation" reactions of alpha-acetyl-gamma-butyrolactones. A variety of 7-(alkoxycarbonyl)benzofurans and 7-(alkoxycarbonyl)-2,3-dihydrobenzofurans were prepared by a cyclization/dehydrogenation strategy. These reactions rely on cyclizations of 2-oxocycloalkane-1-carboxylate-derived 1,3-dicarbonyl dianions ("free dianions") or 1,3-bis-silyl enol ethers ("masked dianions") with various 1,2-dielectrophiles.

Dramatic solvent effect of nitroethane was observed in the catalytic asymmetric reductions of allenyl ketones and alpha,beta-ynones using the oxazaborolidine cayalyst to yield the corresponding alcohols in high levels of enantioselectivity.

Synthesis of new potential COX-1 and/or COX-2 inhibitors, derivatives of 1,1-di-(3-carboxyphenyl)ethane, their biological activity, docking results on COX-1 enzyme and absorption, distribution, metabolism, excretion (ADME) properties are presented. In addition to known interactions between ketoprofen and ibuprofen, leading NSAID agents and COX-1 active site, the possibility of formation of additional interactions is explored. Interactions with Ala527, and with one of the water molecules situated within the active site are identified. Molecular mechanics and DFT calculations for studied compounds have revealed free rotation around two central bonds (C 1 –C 3′ and C 1 –C 3″ ), making them flexible, thus easier to enter and adjust to the active site. Further modifications of core structure have been undertaken to optimize biological activity and ADME properties. As a result, two of the compounds are indicated as novel COX-1 inhibitors.

Green rusts, mixed Fe(II)/Fe(III) hydroxide minerals present in many suboxic environments, have been shown to reduce a number of organic and inorganic contaminants. The reduction of halogenated ethanes was examined in aqueous suspensions of green rust, both alone and with the addition of Ag(I) (AgGR) and Cu(II) (CuGR). Hexachloroethane (HCA), pentachloroethane (PCA), 1,1,1,2-tetrachloroethane (1,1,1,2-TeCA), 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA), 1,1,1-trichloroethane (1,1,1-TCA), 1,1,2-trichloroethane (1,1,2-TCA), 1,1-dichloroethane (1,1-DCA), and 1,2-dibromoethane were reduced in the presence of green rust alone, AgGR, or CuGR; only 1,2-dichloroethane and chloroethane were nonreactive. The reduction was generally more rapid for more highly substituted ethanes than for ethanes having fewer halogen groups (HCA > PCA > 1,1,1,2-TeCA > 1,1,1-TCA > 1,1,2,2-TeCA > 1,1,2-TCA > 1,1-DCA), and isomers with the more asymmetric distributions of halogen groups were more rapidly reduced than the isomer with greater symmetry (e.g., 1,1,1-TCA > 1,1,2-TCA). The addition of Ag(I) or Cu(II) to green rust suspensions resulted in a substantial increase in the rate of halogenated ethane reduction as well as significant differences in the product distributions with respect to green rust alone.

Infusion of aldehyde such as acetaldehyde, propionaldehyde or benzaldehyde to perfused rat liver leads to an increase in hepatic ethane production. Half-maximal effect was obtained with about 20 microM acetaldehyde, a concentration range found in plasma during ethanol metabolism. Compounds which metabolically generate aldehydes such as monoamines (benzylamine, phenylethylamine) as substrates for monoamine oxidase or ethanol as substrate for alcohol dehydrogenase [A. Müller and H. Sies (1982) Biochem. J. 206, 153-156] are also able to elicit ethane release. Results obtained with inhibitors of hepatic aldehyde metabolism (pargyline or cyanamide) or of monamine oxidase (pargyline or tranylcypromine) suggest that metabolism of the aldehydes is required for ethane production. Radical scavenging by the addition of the flavonoid, cyanidanol, or by pretreatment with vitamin E (alpha-tocopherol) abolished ethane release, in agreement with lipid peroxidation as a source of alkane production during aldehyde metabolism.

SUMMARY The cooling efficiencies of various fluids at low temperature were compared by measuring the temperature decay in 3 μl water samples plunged into them. A simple model of cooling was used in order to discuss the results. Liquid ethane was found to produce a cooling rate of 660 K s−1, about twice that of liquid propane, while ethanol was almost as effective as ethane between 273 to 223 K. The heat-transfer coefficient of liquid ethane was estimated to be between 1500 and 5000 W m−2 K−1, depending on the physical state assumed for the water sample. Samples of flagellated organisms, after being frozen rapidly in the above way, were freeze-substituted by the method of Barlow & Sleigh (1979). Although this fixation did not give good definition of the microtubules of the flagellar axoneme, it exhibited reasonable tissue preservation in thin sections of the cell body. The fixation method resulted in preserved flagellar wave shapes, which were observed under the light microscope and in critical-point dried cells examined by scanning and conventional electron microscopy. It was concluded (a) that methods for preserving the wave shape of the flagellum and for preserving its internal structure may not be compatible, and (b) that although the present cooling method (with ethane) approaches the speed required to arrest a flagellar wave, further improvements in the speed of the method are desirable.

Measurements of pentane and ethane as indices of in vivo lipid peroxidation were made on samples of breath from vitamin C-sufficient and vitamin C-deficient guinea pigs injected with 23 microliters carbon tetrachloride (CCl4)/100 g body wt. Vitamin C-deficient animals produced significantly more pentane and ethane after CCl4 treatment than did vitamin C-sufficient guinea pigs. Pretreatment of vitamin C-deficient animals with 75 mg ascorbic acid/100 g body wt significantly lowered both pentane and ethane evolution. Protection against in vivo lipid peroxidation similar to that provided by ascorbic acid was also found when vitamin C-deficient guinea pigs were pretreated with isoascorbic acid, reduced glutathione, alpha-tocopherol or beta-carotene. When animals were pretreated with the radical scavenger mannitol, a protective effect was also observed as measured by pentane evolution.

An analytical method for the measurement of hydrocarbon gases in the breath of rats is described. The method was used to follow the expiration in rat breath of in vivo formed scission products of hydroperoxides. The major products are pentane from the linoleic acid family and ethane from the linolenic acid family. Rats were fed 0, 11 or 40 i.u. vitamin E acetate/kg diet for 7 wk starting at age 21 days. Data obtained by gas chromatographic analysis of breath samples were analyzed by the Mann-Whitney nonparametricU-test. This statistical analysis showed that pentane evolved by the group of rats not supplemented with vitamin E was significantly higher during the period 1–7 wk than that evolved by either of the two supplemented groups of rats. Ethane from the nonsupplemented group was significantly higher than that from the group supplemented with 40 i.u. vitamin E/kg of diet by 5 wk, and significantly higher than both supplemented groups by 6 wk. By 7 wk, pentane production was tenfold greater in the nonsupplemented group than in either supplemented group, and ethane was about twofold greater. There was no significant difference between the groups supplemented with 11 and 40 i.u. vitamin E/kg diet for either ethane or pentane. This new technique, which measures scission products from in vivo lipid peroxidation, promises to be useful for application to many experimental areas where lipid peroxidation is expected or known to occur.