Kinetics of CO oxidation on the surface of heterophase catalysts. Modeling by the Monte Carlo method

The Monte Carlo method has been used to simulate CO oxidation on a lattice consisting of various alternating patches: M1, where s(CO)>s(O₂) and M2, where s(CO)2). The reaction is shown to proceed over all the surface at low temperature as CO_ads spillover from M1 to M2 and backwards.     

Modeling of CO oxidation rate oscillations on a chain of surface patches

Autooscillations of CO oxidation rate are considered for a surface, which is a chain of uniform M1–M4 patches differing by their properties. For chain 5333 due to CO_ads diffusion, induced oscillations propagate from oscillating patches M1 (scheme 5) to patches M2–M4 (Scheme 3), which themselves do not sustain the oscillation mode.     

Change of the roginski “control band” in the case of surface diffusion of adsorbed particles

The effect of surface particle migration between different surface patches on the distribution of the catalytic activity of patches of a linearly inhomogenous surface has been studied. It has been shown that the diffusion can result in an equilibrium distribution of particles A_ads on the surface patches and, therefore, shift of the “control band” and significant change of the reaction rate.     

HYDROPHOBIZING EFFECT OF CATIONS ON ACIDIC PHOSPHOLIPID MEMBRANES

By means of contact angle measurements with water and aqueous salt solutions, it is shown that plurivalent cations increase the hydrophobicity of negatively charged phospholipid vesicle membranes (consisting of phosphatidic acid, PA, or of phosphatidylserine, PS), but does not influence the hydrophobicity of neutral phospholipid membranes, (e.g., phosphatidylcholine, PC, at up to 200 mM of CaCl₂). The hydrophobizing action of cations on PA and PS membranes is concomitant with the reduction in (negative) zeta potential with increasing cation concentrations. Trivalent cations, La³⁺, showed more effective in hydrophobizing negatively charged phospholipid membranes than divalent and monovalent cations. Except for hydrogen ions, monovalent cations do not show any appreciable hydrophobizing effect on lipid vesicle membranes at concentrations less than 1 M. The hydrophobizing effect on phospholipid membranes can also be used to explain the induction of lateral phase separation into patches of different phospholipids as well as cell fusion.     

Kinetic model ofCO oxidation on nonuniform surface analyzed regardingCOads spillover, 2. homotopic method. Effect ofm1 surface portion

The homotopic method has been used to analyze the kinetic model of three-stageCO oxidation on two nonuniform surface patches conjugated byCO ₂ spillover. Diagrams of steady states depending on the portion of surface patchm ₁ at various temperatures and pressure ratiosP(O ₂)/P(CO) have been constructed. The ratios of different type patches corresponding to the maximum overall reaction rate have been found.     

Stability of DNA-tethered lipid membranes with mobile tethers

We recently introduced two approaches for tethering planar lipid bilayers as membrane patches to either a supported lipid bilayer or DNA-functionalized surface using DNA hybridization (Chung, M.; Lowe, R. D.; Chan, Y-H. M.; Ganesan, P. V.; Boxer, S. G. J. Struct. Biol.2009, 168, 190-9). When mobile DNA tethers are used, the tethered bilayer patches become unstable, while they are stable if the tethers are fixed on the surface. Because the mobile tethers between a patch and a supported lipid bilayer offer a particularly interesting architecture for studying the dynamics of membrane-membrane interactions, we have investigated the sources of instability, focusing on membrane composition. The most stable patches were made with a mixture of saturated lipids and cholesterol, suggesting an important role for membrane stiffness. Other factors such as the effect of tether length, lateral mobility, and patch membrane edge were also investigated. On the basis of these results, a model for the mechanism of patch destruction is developed.     

Generation of WO3-ZrO2 catalysts from solid solutions of tungsten in zirconia

WO₃-ZrO₂ samples were obtained by precipitating zirconium oxynitrate in presence of WO₄ species in solution from ammonium metatungstate at pH=10.0. Samples were characterized by atomic absorption spectroscopy, thermal analysis, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy and energy filtered-TEM. The ammonia retained in the dried sample produced a reductive atmosphere to generate W⁵⁺ ions coexisting with W⁶⁺ ions to produce a solid solution of tungsten in the zirconia lattice to stabilize the zirconia tetragonal phase when the sample was annealed at 560 °C. When the sample was annealed at 800 °C, the W atoms near crystallite surface were oxidized to W⁶⁺, producing patches of WO₃ on the zirconia crystallite. The HR-TEM analysis confirmed the existence of the solid solution when the sample was annealed at 560 °C, and two types of crystalline regions were identified: One with nearly spherical morphology, an average diameter of 8 nm and the atomic distribution of tetragonal zirconia. The second one had a non-spherical morphology with well-faceted faces and dimensions larger than 30 nm, and the atom distribution of tetragonal zirconia. When samples were annealed at 800 °C two different zirconia crystallites were formed: Those where only part of the dissolved tungsten atoms segregated to crystallite surface producing patches of nanocrystalline WO₃ on the crystallite surface of tetragonal zirconia stabilized with tungsten. The second type corresponded to monoclinic zirconia crystallites with patches of nanocrystalline WO₃ on their surface. The tungsten segregation gave rise to the WO₃-ZrO₂ catalysts.     

On the possible role of adparticles spillover on a heterophase surface in causing superadditive activity

It is shown that for a two-stage reaction on the surface involving two types of surface patches with adsorption heats lower and higher than q_opt migration of adparticles between surface patches (spillover) can both increase and decrease the reaction rate.     

Röntgenographische und schwingungsspektroskopische Untersuchung der Mischkristallreihen Cu3MxM′;1-xX4 (M,M′ = V,Nb, Ta; X = S,Se) mit Sulvanitstruktur

X-ray and Vibrational Spectroscopical Investigation of the Mixed Crystal Series Cu₃M_xM′_1-xX₄ (M, M′ = V, Nb, Ta; X = S, Se) with Sulvanite Structure Solid solutions Cu₃M_xM′_1-xX₄ (M, M′ = V, Nb, Ta; X = S, Se) with Sulvanite structure have been prepared in the range 0 ≤ x ≤ 1 by solid state reaction between 600°C and 900°C. The lattice constants decrease linearly with x. The UR active antisymmetrical as well as the Raman active symmetrical M–X stretching vibrations may be attached to independently vibrating MX₄ and M′X₄ tetrahedrons.     

Reaction between 7,8-dihydropterins and hydrogen peroxide under physiological conditions

In vitiligo, a common skin disorder that produces white patches of depigmentation, 7,8-dihydropterins accumulate in the presence of high concentration of H₂O₂. In this work, we present a study of the reaction between 7,8-dihydropterins and H₂O₂. The rate of the reaction, as well as the products formed, strongly depend on the chemical structure of the substituents. Electron-donor groups as substituents are the most reactive derivatives and undergo oxidation of the pterin moiety. The corresponding bimolecular rate constants at 37 °C in neutral aqueous solutions are reported. The biological implications of the results obtained are also discussed.     

Clinic Pharmacokinetic Profiles of Huperzine A Following Transdermal Administration to Healthy Human Volunteers

To support the rationale behind the development of the huperzine A patches and its pharmacological effects in clinical therapy, an LC?CMS?CMS method was developed and validated for determination of huperzine A in human plasma and then applied to the clinic pharmacokinetics study on transdermal patches of huperzine A. After a simple liquid?Cliquid extraction with ethyl acetate, analytes were separated on a C18 column with isocratic elution. The detection of analytes was performed on a tandem mass system equipped with an electrospray ionization source in positive mode using multiple-reaction monitoring. The MS?CMS ion transitions monitored were m/z 243.2??210.1 for huperzine A and m/z 248.1??128.0 for tinidazole (internal standard). Method validation and sample analysis were performed according to FDA guidelines and the results met the acceptance criteria. The pharmacokinetic profiles of huperzine A following single transdermal administration of 8, 10 and 12 mg huperzine A to healthy human volunteers were depicted using the established method. The results showed that the pharmacokinetic behavior of huperzine A in vivo was present as linear dynamic characteristics with much longer T _max, lower C _max, and relatively constant plasma concentration. No gender difference and obvious adverse effects were observed from all three groups in our study. Our study indicated that the huperzine A transdermal patches could provide continuous drug delivery over 120 h with favorable tolerability. This may allow patients to obtain optimal plasma concentrations of drugs and to benefit from a longer duration of treatment.     

Vibrational spectroscopy of aqueous solutions at high concentrations: Raman and inelastic neutron scattering

We review work performed by our group on vibrational spectroscopy of water and aqueous solutions of strong II-I electrolytes at high concentrations. Evidence shall be presented for the existence of intermediate range, solute-connected, ordered patches, whose collective vibrational modes yield a continuous vibrational density of states, as in amorphous solids. We shall review Raman and inelastic neutron scattering results, obtained for electrolytes such as ZnCl₂, NiCl₂, CuBr₂, CdCl₂. Other results, such as EXAFS, viscosity and ultrasonic attenuation will also be discussed.     

Vesicle formation induced by layered double hydroxides in the catanionic surfactant solution composed of sodium dodecyl sulfate and dodecyltrimethylammonium bromide

In this paper, it is reported that positively charged Mg₃Al layered double hydroxide (LDH) nanoparticles can induce the spontaneous formation of vesicles in micelle solution of sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) with a mass ratio of 8:2. The formation of vesicles was demonstrated by negative-staining transmission electron microscopy observations. The size of the vesicles increased with the increase in the concentration of Mg₃Al-LDH nanoparticles. A composite of LDH nanoparticles encapsulated in vesicles was formed. A possible mechanism of LDH-induced vesicle formation was suggested. The positively charged LDH surface attracts negatively charged micelles or free amphiphilic molecules, which facilitates their aggregation into bilayer patches. These bilayer patches connect to each other and finally close to form vesicles. It was also found that an adsorbed compound layer of SDS and DTAB micelles or molecules on the LDHs surface played a key role in vesicle formation.     

Kinetic model of CO oxidation on heterophase surface analyzed regarding COads spillover, I. Homotopic method. Effect of temperature and CO pressure

The homotopic method has been used to analyze the kinetic models of CO oxidation on two surface patches conjugated by CO_ads spillover. On each patch reaction proceeds via a three-stage mechanism but with different constants. The stability of steady-states solution has been studied. CO_ads spillover from one patch to another changes substantially the bifurcation picture of steady states and produces islands.     

Synthese und XPS-Analyse von nano-skaligen Metall/Metalloxid-Kompositen mit Germanium,Zinn und Blei als metallische Komponente

Synthesis and XPS Analysis of nano-scaled Metal/Metaloxid Composites with Germanium, Tin, and Lead as Metallic Component tert-Butanolates of Germanium(II), tin(II), and lead(II) of the formula {M[O-C(CH₃)₃]₂}_n (M ? Ge, n = 2; M ? Sn, n = 2; M ? Pb, n = 3) as well as the corresponding heterometalalkoxides M′M₂[O? C(CH₃)₃]₆ (M ? Ge, M′ ? Sr, Ba; M ? Sn, M′ ? Ca, Sr, Ba; M ? Pb, M′ ? Ca, Ba) have been subject to a single precursor chemical vapour deposition (CVD) process. In this process the volatile precursor has been pyrolized under reduced pressure (0,1 Torr) on a graphit or metal substrate which has been heated by induction in a microwave field to about 300–500°C. The gases originating from this pyrolisis have been analyzed by means of a quadrupole mass spectrometer whereas the solid coating which contained the micro composite was characterized by X-ray diffraction, electron microscopy, EDX-analysis and XPS-spectra. In all cases the solid material contained two phases, in which the element M ((Ge), Sn, Pb) either had oxidation state 0 or +4 (in the surface of the solids made of germanium containing precursors only Ge^II along with Ge⁰ has been detected by XPS spectroscopy). The group 14-element in the starting material had thus undergone a disproportionation from the +2 oxidation state into a lower and a higher one by two units. The elemental phase and the phase containing the formal +4 cation which is amorphous in most cases and which approaches the formula MO₂ or M′MO³ (M ? (Ge), Sn, Pb; M′ ? Ca, Sr, Ba) are uniformally distributed. The composites consist of ball shaped particles on which other smaller particles are placed in a fractal manner ressembling a black berry. In the case of the composite Sn · BaSnO³ the center of the ball shaped particles has been analyzed as pure elemental tin. The organic substituents of the precursors as well as the dynamic vacuum in the decomposition process seem to be responsible for the ball shaped nature of the solid material. In a test experiment gallium tri-tert-but-oxide has been used as precursor: again ball shaped particles are obtained which have the chemical composition Ga₂O₃ but which contain no elemental gallium.     

Acyl- und Alkylidenarsane. IV [1] Molekül- und Kristallstruktur des 2,4-Di(tert. butyl)-1,3-dimethyl-2,4-bis(trimethylsiloxy)-1,3-diarsetans

Bis-Nitridochloro Complexes Cl₃PO? (Cl₄)M?N? C₂Cl₄? N?M(Cl₄)? OPCl₃ with M = Mo, W, Re By the reaction of cyanogen with tungstenhexachloride, as well as by the reactions of cyanogen and chlorine with molybdenum-, tungsten- and rheniumpentachloride, in POCl₃ solution the POCl₃ solvated bis-nitridochloro complexes Cl₃PO? (Cl₄)M?N? C₂Cl₄? N?M(Cl₄)? OPCl₃ can be obtained. The i.r. spectra indicate that the complexes contain metal nitrogen triple bonds with a linear M?N? C arrangement. The O atoms of the POCl₃ molecules are coordinated in trans-position to the M?N triple bond.     

Influence of Crosslinking Agent on the Release of Drug from the Matrix Transdermal Patches of HPMC/Eudragit RL 100 Polymer Blends

The present work was designed to develop suitable transdermal matrix patches using the polymer blends of hydroxy propyl methyl cellulose (HPMC) and Eudragit RL100 (ERL) with triethyl citrate as a plasticizer in group A and in group B, other than HPMC and ERL, crosslinking agent, succinic acid was added. A 3² full factorial design was employed for both groups. The concentration of HPMC and ERL were used as independent variables, while percentage drug release was selected as dependent variable. Physical evaluation was performed such as moisture content, moisture uptake, tensile strength, flatness and folding endurance. In vitro diffusion studies were performed using cellulose acetate membrane (pore size 0.45 μ) in a Franz's diffusion cell. The concentration of diffused drug was measured using UV-visible spectrophotometer (V-530, Jasco) at λ _max 272 nm. The experimental results shows that the transdermal drug delivery system (TDDS) containing ERL in higher proportion gives sustained the release of drug and patches containing crosslinking agent shows more release than those do not contains succinic acid.     

Superior Performance of a MoS2‐RGO Composite and a Borocarbonitride in the Electrochemical Detection of Dopamine,Uric Acid and Adenine

A MoS₂‐RGO composite and borocarbonitride (BC₅N) have been used as electrodes to selectively detect dopamine and uric acid in the presence of ascorbic acid. Both the electrodes show excellent eletrocatalytic activity towards the detection of dopamine, the detection limits being 0.55 μM and 2.1 μM in the case of MoS₂‐RGO and BCN respectively. MoS₂‐RGO shows a linear range of current over the 1–110 μM concentrations of dopamine, while BCN shows over the 2.3–20 μM range. BCN also exhibits satisfactory performance in the oxidation of uric acid with a detection limit of 3.8 μM and the linear range from 4 to 40 μM. The MoS₂‐RGO has also been used to detect adenine as well.     

A REINVESTIGATION OF THE ACTION OF NITRIC OXIDE ON DIMETHYLZINC AND DIMETHYLCADMIUM

Abstract

The reactions of the dimethylmetals, Me₂ M (M = Zn, Cd), with nitric oxide have been reinvestigated. Two moles of NO are taken up per mole of dimethylmetal in each case. Infrared, laser Raman and mass spectral data indicate that the Me₂M. 2NO adducts are best formulated as MeM[O.N(NO)Me] rather than Me₂M.M[O.N(NO)Me]₂ as had been suggested earlier. On hydrolysis, the methyl(N-methyl-N-nitrosohydroxylamine)metal(II) complexes apparently disproportionate to yield M[O.N(NO)Me]₂ and M(OH)₂.     

Solvation of cobalt-thiocyanate complexes by 2-hexylpyridine from aqueous mineral acid solutions

A study of the distribution of cobalt between mineral acid solutions containing potassium thiocyanate and 0.1M 2-hexylpyridine in benzene has been undertaken. Cobalt can be quantitatively extracted as its thiocyanate complex from very dilute acid solutions containing 0.1–1M KSCN. Variation of the distribution coefficient D_Co in terms of the ligand concentration in the organic phase has allowed the formula of the extracted species to be determined as Co(HPy)₄ (SCN)₂. The effects of oxalate, acetate, fluoride, ascorbate, sulphate and thiosulphate ions on the extraction of cobalt from three mineral acid solutions have been reported. The extraction coefficients of several elements are given for the 0.1M 2-hexylpyridine in three systems containing 0.5M KSCN with 0.25M HNO₃, 0.05M HCl and 0.05M H₂SO₄ respectively; and their factors for separation from cobalt are estimated.