Proton gradient energy in the catalytic ATP synthesis

ATP synthesis assisted by the F₁F₀-ATP synthase enzyme is considered in the context of chemical thermodynamics. It is shown that the proton gradient itself has no energy. For this reason, ATP synthesis with the participation of protons’ gradient has no privileges in comparison with direct ATP synthesis.     

Fluorescent sensing layer for the determination of<Emphasis Type="SmallCaps"> L</Emphasis>-malic acid in wine

An enzymatic method for determining L-malic acid in wine based on an L-malate sensing layer with nicotinamide adenine dinucleotide (NAD⁺), L-malate dehydrogenase (L-MDH) and diaphorase (DI), immobilized by sol-gel technology, was constructed and evaluated. The sol-gel glass was prepared with tetramethoxysilane (TMOS), water and HCl. L-MDH catalyzes the reaction between L-malate and NAD⁺, producing NADH, whose fluorescence (λ _exc = 340 nm, λ _em = 430 nm) could be directly related to the amount of L-malate. NADH is converted to NAD⁺ by applying hexacyanoferrate(III) as oxidant in the presence of DI. Some parameters affecting sol-gel encapsulation and the pH of the enzymatic reaction were studied. The sensing layer has a dynamic range of 0.1–1.0 g/L of L-malate and a long-term storage stability of 25 days. It exhibits acceptable reproducibility [s _r(%)≈10] and allows six regenerations. The content of L-malic acid was determined for different types of wine, and polyvinylpolypyrrolidone (PVPP) was used as a bleaching agent with red wine. The results obtained for the wine samples using the sensing layer are comparable to those obtained from a reference method based on UV-vis molecular absorption spectrometry, if the matrix effect is corrected for.     

Bioelectrosynthesis as an alternative to photosynthesis

The CO₂ reduction processes have been discussed as a way of designing an ecologically totally closed technology. An electric current and molecular hydrogen are the two related available agents that can be discussed as ecologically pure reductants. The most important products are liquid and gaseous fuels, the products of large-scale organic synthesis, monomers, and amino acids. For CO₂ reduction, the necessary energy consumption and H₂ costs were calculated. For complex organic molecules, amino acids for instance, the energy consumption does not make up the main portion of the costs. The biocatalytic systems of CO₂ reduction based on cryoimmobilized cells are described. Conversion of CO₂ into L-lysine with electrochemical decomposition of water was effected on the laboratory scale. A general unit for diverse technological processes can be a bioelectrosynthetic Index Entries: Bioelectrosynthesis; CO₂ reduction; liquid fuels; amino acids; immobilized cells; economic estimates. modulus, an electrochemical hydrogen generator coupled with a biocatalytic converter of hydrogen and oxygen. The systems for bioelectrosynthesis of motor fuels and essential amino acids have been economically estimated and characterized. The possibilities of combining the solar energy transformation and H₂–CO₂ conversion have been discussed.     

Production of optically pure d-lactic acid by Nannochlorum sp. 26A4

Microalgae were screened from seawater for greenhouse gas CO₂ fixation and d-lactic acid production by self-fermentation and tested for their growth rate, starch content, and conversion rate from starch into d-lactic acid. More than 300 strains were isolated, and some of them were found to have suitable properties for this purpose. One of the best strains, Nannochlorum, sp. 26A4, which was isolated from Sakito Island, had a starch content of 40% (dry weight), and a conversion rate from consumed starch into d-lactic acid of 70% in the dark under anaerobic conditions. The produced d-lactic acid showed a high optical purity compared with the conventional one. The proposed new d-lactic acid production system using Nannochlorum sp. 26A4 should also be an effective technology for greenhouse gas CO₂ fixation and/or conversion into industrial raw materials.     

Electrochemical study of Meldola's blue,methylene blue and toluidine blue immobilized on a SiO<Subscript>2</Subscript>/Sb<Subscript>2</Subscript>O3 binary oxide matrix obtained by the sol-gel processing method

SiO₂/Sb₂O₃ (SiSb), having a specific surface area, S _BET, of 788 m² g⁻¹, an average pore diameter of 1.9 nm and 4.7 wt% of Sb, was prepared by the sol-gel processing method. Meldola's blue (MeB), methylene blue (MB) and toluidine blue (TB) were immobilized on SiSb by an ion exchange reaction. The amounts of the dyes bonded to the substrate surface were 12.49, 14.26 and 22.78 μmol g⁻¹ for MeB, MB and TB, respectively. These materials were used to modify carbon paste electrodes. The midpoint potentials (E _m) of the immobilized dyes were −0.059, −0.17 and −0.18 V vs. SCE for SiSb/MeB, SiSb/MB and SiSb/TB modified carbon paste electrodes, respectively. A solution pH between 3 and 7 practically did not affect the midpoint potential of the immobilized dyes. The electrodes presented reproducible responses and were chemically stable under various oxidation-reduction cycles. Among the immobilized dyes, MeB was the most efficient to mediate the electron transfer for NADH oxidation in aqueous solution at pH 7. In this case, amperometric detection of NADH at an applied potential of 0 mV vs. SCE gives linear responses over the concentration range of 0.1–0.6 mmol L⁻¹, with a detection limit of 7 μmol L⁻¹.     

Photocatalytic Reduction of Greenhouse Gas CO2 to Fuel

Sun is the Earth’s ultimate and inexhaustible energy source. One of the best routes to remedy the CO₂ problem is to convert it to valuable hydrocarbons using solar energy. In this study, CO₂ was photocatalytically reduced to produce methanol, methane and ethylene in a steady-state optical-fiber reactor under artificial light and real sunlight irradiation. The photocatalyst was dip-coated on the optical fibers that enable the light to transmit and spread uniformly inside the reactor. The optical-fiber photoreactor, comprised of nearly 120 photocatalyst-coated fibers, was designed and assembled. The XRD spectra indicated the anatase phase for all photocatalysts. It is found that the methanol yield increased with UV light intensity. A maximum methanol yield of 4.12 μmole/g-cat h is obtained when 1.0 wt% Ag/TiO₂ photocatalyst was used under a light intensity of 10 W/cm². When mixed oxide, TiO₂–SiO₂, is doped with Cu and Fe metals, the resulting photocatalysts show substantial difference in hydrocarbon production as well as product selectivity. Methane and ethylene were produced on Cu–Fe loaded TiO₂–SiO₂ photocatalyst. Since dye-sensitized Cu–Fe/P25 photocatalyst can fully harvest the light energy of 400–800 nm from sunlight, its photoactivity was significantly enhanced. Finally, CO₂ photoreduction was studied by in situ IR spectroscopy and possible mechanism for the photoreaction was proposed.     

Reaction Mechanisms in Both a CCl2F2/O2/Ar and a CCl2F2/H2/Ar RF Plasma Environment

Decomposition of dichlorodifluoromethane (CCl₂F₂ or CFC-12) in aradiofrequency (RF) plasma system is demonstrated. The CCl₂F₂decomposition fractions _{CCl 2 F 2} and mole fractionsof detected products in the effluent gas stream of CCl₂F₂/O₂/Ar andCCl₂F₂/H₂/Ar plasma, respectively, have been determined. The experimentalparameters including input power wattage, O₂/CCl₂F₂ or H₂/CCl₂F₂ ratio,operational pressure, and CCl₂F₂ feeding concentration wereinvestigated. The main carbonaceous product in the CCl₂F₂/O₂/Arplasma system was CO₂, while that in the CCl₂F₂/H₂/Ar plasma systemwas CH₄ and C₂H₂. Furthermore, the possible reaction pathways werebuilt-up and elucidated in this study. The results of the experimentsshowed that the highly electronegative chlorine and fluorine wouldeasily separate from the CCl₂F₂ molecule and combine with the addedreaction gas. This led to the reactions terminated with the CO₂,CH₄, and C₂H₂ formation, because of their high bonding strength. Theaddition of hydrogen would form a preferential pathway for the HCland HF formations, which were thermodynamically stable diatomicspecies that would limit the production of CCl₃F, CClF₃, CF₄, andCCl₄. In addition, the HCl and HF could be removed by neutral orscrubber method. Hence, a hydrogen-based RF plasma system provideda better alternative to decompose CCl₂F₂.     

Radical addition of RFI to alkenylsuccinic anhydrides and gem-substituted alkenyl triesters : Zinc and radical induced, or spontaneous radical cyclization, of the δ-iodoalkanoic esters to γ-lactones

Radical addition of R_FI to alkenylsuccinic anhydrides affords ω-(perfluoroalkyl)-δ-iodoalkyl-2-butane-1,4-dioc acid anhydrides, and these adducts are reductively dehalogenated and esterified by zinc and acid in ethanol without lactonization. However, the R_FI adducts react with KOH in ethanol to give the alkenyl half esters (but no γ-lactone), which convert to the γ-lactones by acid catalysis. When treated with water, ethanol, Zn and 48% HBr, the R_FI adduct from but-3-en-2-yl-succinic anhydride converts to the iodo half ester, R_FCH₂CHICH(CH₃)CH(CO₂H)CH₂CO₂Et, which undergoes Zn induced (S_Hi) conversion to γ-lactone. R_FI (AIBN) and the triester CH₂CHCH₂C(CO₂Et)₂CH₂CO₂Et yield R_FCH₂CHICH₂C(CO₂Et)₂CH₂CO₂Et (95%). When heated to 140 °C, the adduct loses iodoethane.and cyclizes to diester γ-lactones (94%). With benzoyl peroxide, R_FI and the triester at 99 °C, spontaneous radical cyclization of the adduct to lactone occurs. Evidently, the gem-disubstituted triester readily forms a five-membered lactone as a consequence of steric compression in the open chain form.     

Determination of the enthalpy of fusion of K<Subscript>3</Subscript>TaO<Subscript>2</Subscript>F<Subscript>4</Subscript> and KTaF<Subscript>6</Subscript>

Areas of fusion and crystallization peaks of K₃TaO₂F₄ and KTaF₆ were measured using the DSC mode of a high-temperature calorimeter (SETARAM 1800 K). On the basis of these quantities, considering the temperature dependence of the calorimeter sensitivity, values of the fusion enthalpy of K₃TaO₂F₄ at the fusion temperature of 1181 K of (43 ± 4) kJ mol⁻¹ and of KTaF₆ at the fusion temperature of 760 K of (8 ± 1) kJ mol⁻¹ were determined.     

Calorimetric Investigations of Some Phases in the System Sodium Fluoride - Aluminium Fluoride

Beside the two well-known minerals cryolite, Na₃AlF₆, and chiolite, Na₅Al₃F₁₄, the binary system NaF-AlF₃ also contains a third compound, NaAlF₄, sodium tetrafluoroaluminate. Solid NaAlF₄ has been prepared from its vapour under controlled conditions. The stability of NaAlF₄ has been investigated by differential scanning calorimetry. It is shown that the disproportionation of the compound: 5NaAlF_4(s)=Na₅Al₃F_14(s)+2AlF_3(s) takes place at considerable rate between 700 and 900 K. The enthalpy of this reaction is calculated and found to be -66.9 kJ. Enthalpies of the two solid state transitions α-Na₃AlF₆ → β-Na₃AlF₆ and α-AlF₃ → β-AlF₃ have also been measured and new values are reported. The enthalpy of formation of chiolite, Na₅Al₃F₁₄, at 900 K has been recalculated from enthalpy increment data obtained by drop calorimetry. A value of ΔH₉₀₀ ^o = -7513.6±12.0 kJ mol^-1 has been obtained. This value is in disagreement with the recommended value given in JANAF Thermochemical Tables given at 900 K ΔH_f ^o = -7559.2 kJ mol^-1. This revised version was published online in July 2006 with corrections to the Cover Date.     

Encapsulation and Release Characteristics of Carbon Dioxide in α-Cyclodextrin

Encapsulation and release of carbon dioxide (CO₂) into and from α-cyclodextrin (α-CD) was studied. Initial moisture content of α-CD and CO₂ pressure were found to have affected the encapsulation behavior. The increase of CO₂ pressure has constantly accelerated the encapsulation rates and increased the maximum inclusion ratio, whereas the increase of initial moisture content showed no consistent effect. The saturated α-CD solution produced the inclusion complex crystal of similar inclusion ratio to solid α-CD. The release characteristics of inclusion complexes were also monitored at various relative humidities at 25 °C. Predominantly, increase in storage humidity accelerated the release of CO₂. The inclusion complex crystal prepared from saturated α-CD solution showed the most stable release characteristic at all storage humidities investigated. The encapsulation and the release characteristics were analyzed using the first-order reaction equation and the Avrami’s equation respectively, in order to estimate the rate processes of encapsulation and release. The FT-IR spectra of inclusion complexes presented an absorption band at wavenumber around 2338 cm⁻¹, indicating CO₂ molecules resided inside the α-CD cavities in gaseous state rather than being bound to the hydroxyl groups of α-CD. Powder X-ray diffractometry was carried out to investigate the crystal lattice structure of α-CD and inclusion complexes. Scanning electron microscopy was also performed for morphological examination.     

H2‐Fueled ATP Synthesis on an Electrode: Mimicking Cellular Respiration

ATP, the molecule used by living organisms to supply energy to many different metabolic processes, is synthesized mostly by the ATPase synthase using a proton or sodium gradient generated across a lipid membrane. We present evidence that a modified electrode surface integrating a NiFeSe hydrogenase and a F₁F₀‐ATPase in a lipid membrane can couple the electrochemical oxidation of H₂ to the synthesis of ATP. This electrode‐assisted conversion of H₂ gas into ATP could serve to generate this biochemical fuel locally when required in biomedical devices or enzymatic synthesis of valuable products.     

Ab initio and density functional theory study of the enthalpies of formation of F2SOx and FClSOx (x=1, 2)

Enthalpies of formation of F₂SO, F₂SO₂, FClSO and FClSO₂ molecules have been determined using ab initio molecular orbital theory and density functional theory (DFT) calculations. Different DFT approaches and levels of the Gaussian-3 and the complete basis set (CBS) ab initio model chemistries have been employed to calculate enthalpies of formation from both total atomization energies and isodesmic reaction schemes. The best values at 298 K for F₂SO, F₂SO₂, FClSO and FClSO₂ as derived from an average of G3, G3B3, CBS-Q and CBS-QB3 isodesmic energies are −140.6, −181.1, −92.6 and −132.3 kcal mol⁻¹, respectively. The results obtained suggest that the accumulated small component errors found in the DFT-based methods are significantly reduced at the ab initio levels employed. Structural properties, harmonic vibrational frequencies, mode assignations and infrared intensities derived from B3LYP and mPW1PW91 functional with the 6-311+G(3df) basis set are presented.     

A kinetic study of the oxidation of <Emphasis Type="SmallCaps">l</Emphasis>-methionine by water soluble colloidal MnO<Subscript>2</Subscript>

Aqueous solution of water soluble colloidal MnO₂ was prepared by Perez-Benito method. Kinetics of l-methionine oxidation by colloidal MnO₂ in perchloric acid (0.93 × 10⁻⁴ to 3.72 × 10⁻⁴ mol dm⁻³) has been studied spectrophotometrically. The reaction follows first-order kinetics with respect to [H⁺]. The first-order kinetics with respect to l-methionine at low concentration shifts to zero order at higher concentration. The effects of [Mn(II)] and [F⁻] on the reaction rate were also determined. Manganese (II) has sigmoidal effect on the rate reaction and act as auto catalyst. The exact dependence on [Mn(II)] cannot be explained due to its oxidation by colloidal MnO₂. Methionine sulfoxide was formed as the oxidation product of l-methionine. Ammonia and carbon dioxide have not been identified as the reaction products. The mechanism with the observed kinetics has been proposed and discussed.     

Theoretical study on the reaction mechanism of (CH<Subscript>3</Subscript>)<Subscript>3</Subscript>CO<Superscript>.</Superscript> radical with NO

The reaction mechanism of (CH₃)₃CO^. radical with NO is theoretically investigated at the B3LYP/6-31G* level. The results show that the reaction is multi-channel in the single state and triplet state. The potential energy surfaces of reaction paths in the single state are lower than that in the triple state. The balance reaction: (CH₃)₃CONO⇔(CH₃)₃CO^.+NO, whose potential energy surface is the lowest in all the reaction paths, makes the probability of measuring (CH₃)₃CO^. radical increase. So NO may be considered as a stabilizing reagent for the (CH₃)₃CO^. radical.     

Effect of PEG with different <Emphasis Type="Italic">M</Emphasis><Subscript>W</Subscript> as template direction reagent on preparation of porous TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> with assistance of supercritical CO<Subscript>2</Subscript>

Titania–silica composite have been prepared using polyethylene glycol (PEG) with different molecular weights (M _w), PEG20000, PEG10000, and PEG2000, as template in supercritical carbon dioxide (SC CO₂). The composite precursors were dissolved in SC CO₂ and impregnated into PEG templates using SC CO₂ as swelling agent and carrier. After removing the template by calcination at suitable temperature, the titania–silica composite were obtained. The composite were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and nitrogen sorption–desorption experiment. Photocatalytic activity of the samples has been investigated by photodegradation of methyl orange. Results indicate that there are many Si–O–Ti linkages in the TiO₂/SiO₂ composite; the PEG template has a significant influence on the structure of TiO₂/SiO₂. In addition, the TiO₂/SiO₂ prepared with PEG10000 exhibited high photocatalytic efficiency. So this work supplies a clue to control and obtain the TiO₂/SiO₂ composite with different photocatalytic reactivity with the aid of suitable PEG template in supercritical CO₂.     

Generation of carbohydrate-deficient transferrin by enzymatic deglycosylation of human transferrin

Carbohydrate-deficient transferrin (CDT) molecules are transferrin isoforms that lack one or both of the carbohydrate groups attached to a normal human transferrin molecule. CDT has been reported to be a sensitive and specific marker for diagnosing alcoholism. This report demonstrates the in vitro generation of CDT molecules that can potentially be used as the standard in measuring CDT concentrations. This was achieved by deglycosylation of human transferrin with the enzyme Endo-β-N-acetylglucosaminidase F₂ (Endo-F₂). The enzyme was immobilized on sepharose beads, which were packed into a column. The immobilization of the enzyme not only eliminated the Endo-F₂ contamination of CDT, but also rendered the enzyme suitable for repetitive use. In this manner, it was possible to obtain at least 200 mg of CDT over a period of more than 3 mo, without any noticeable decrease of enzyme activity, using only 3.0 μg of enzyme. This proved to be an efficient method for generating CDT.     

The fluorination of scheelite with ammonium bifluoride

The interaction of scheelite with ammonium bifluoride was studied. It was shown that sheelite reacts with NH₄HF₂ at room temperature, in contrast with tungstic oxide and other tungsten compounds. Two complexes are formed (NH₄)₃WO₃F₃ and the previously unknown (NH₄)₂WO₃F₂. The compounds obtained were fluorinated to (NH₄)₃WO₂F₅ (endothermic peaks at 170° and 90°C, respectively).Cubic monocrystals of (NH₄)₃WO₂F₅ were obtained. The cubic form is unstable and underwent a lattice transformation at room temperature to the more stable tetragonal form, which was transformed reversibly into the cubic form at 140°C. The thermal decomposition of (NH₄)₂WO₃F₂ was studied.

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Zusammenfassung Es wird die Wechselwirkung von Scheelit und Ammoniumhydrogenfluorid untersucht. Im Gegensatz zu Wolframoxid und anderen Wolframverbindungen geht Scheelit mit Ammoniumhydrogenfluorid bei Raumtemperatur eine chemische Reaktion ein, wobei zwei verschiedene Komplexe gebildet werden: (NH₄)WO₃F₃ und der bisher unbekannte Komplex (NH₄)₂WO₃F₂. Die erhaltenen Verbindungen werden zu (NH₄)₃WO₂F₅ fluoriert (endotherme Peaks bei 170° bzw. 90°C).Man erhält die kubischen Einkristalle (NH₄)₃WO₂F₅. Die unstabile kubische Form wandelte sich bei Raumtemperatur in die stabilere tetragonale Form um, die bei 140°C reversibel wieder in die kubische Form überführt werden kann.Es wird weiterhin die thermische Zersetzung von (NH₄)₂WO₃F₂. untersucht.

     

Isomerism in OBe3F3 + cation: anab initio study

Ab initio MP2/6-31G^*//HF/6-31G^*+ZPE(HF/6-31G^*) calculations of the potential energy surface in the vicinity of stationary points and the pathways of intramolecular rearrangements between low-lying structures of the OBe₃F₃ ⁺ cation detected in the mass spectra of μ₄-Be₄O(CF₃COO)₆ were carried out. Ten stable isomers with di- and tricoordinate oxygen atoms were localized. The relative energies of six structures lie in the range 0–8 kcal mol⁻¹ and those of the remaining four structures lie in the range 20–40 kcal mol⁻¹. Two most favorable isomers, aC _2v isomer with a dicoordinate oxygen atom, planar six-membered cycle, and one terminal fluorine atom and a pyramidalC _3v isomer with a tricoordinate oxygen atom and three bridging fluorine atoms, are almost degenerate in energy. The barriers to rearrangements with the breaking of one fluorine bridge are no higher than 4 kcal mol⁻¹, except for the pyramidalC _3v isomer (∼16 kcal mol⁻¹). On the contrary, rearrangements with the breaking of the O−Be bond occur with overcoming of a high energy barrier (∼24 kcal mol⁻¹). A planarD _3h isomer with a tricoordinate oxygen atom and linear O−Be−H fragments was found to be the most favorable for the OBe₃H₃ ⁺ cation, a hydride analog of the OBe₃F₃ ⁺ ion; the energies of the remaining five isomers are more than 25 kcal mol⁻¹ higher. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 420–430, March, 1999.     

Negative ion formation in compounds relevant to SF6 decomposition in electrical discharges

Dissociative and nondissociative electron attachment in the electron impact energy range 0–14 eV are reported for SOF₂ SOF₄, SO₂F₂, SF₄, SO₂, and SiF₄ compounds which can be formed by electrical discharges in SF₆. The electron energy dependences of the mass-identified negative ions were determined in a time-of-flight mass spectrometer. The ions studied include F^– and SOF ₂ ^–* from SOF₂; SOF ₃ ^– and F^– from SOF₄; SO₂F ₂ ^–* , SO₂F^–, F ₂ ^– , and F^– from SO₂F₂; SF ₄ ^–* and F^– from SF₄; O^–, SO^–, and S^– from SO₂; and SiF ₃ ^– and F^– from SiF₄. Thermochemical data have been determined from the threshold energies of some of the fragment negative ions. Lifetimes of the anions SOF ₂ ^–* , SO₂F ₂ ^–* , and SF ₄ ^–* are also reported.