An iterative method for solving nonlinear functional equations

An iterative method for solving nonlinear functional equations, viz. nonlinear Volterra integral equations, algebraic equations and systems of ordinary differential equation, nonlinear algebraic equations and fractional differential equations has been discussed.     

Useful chemical information obtained by use of common counterions as internal calibrants in X-ray photo-electron spectra of inorganic complex ions

It is shown that the accuracy and precision, and hence the value for bonding-structure studies, in relative binding energy measurements can be enhanced if a common counterion is employed. The differences in chemical shifts between the peaks for the atoms under consideration and for a common counterion in twenty-nine compounds are measured. This technique reduces charging effect errors, which otherwise often occur when non-conducting samples (e.g., salts) are measured relative to a traditional external calibrant. The improvements in accuracy and precision are demonstrated by using the cesium salt of twenty-nine heteropoly and isopoly anions in more than seventy-five different runs. Oxygen 1s, tungsten 4d, and molybdenum 3d binding energies are measured relative to the cesium 3d ionization potential. In this work the cesium counterion is assumed to be chemically invariant. For the relative binding energies that are studied, no dependence on the charge of the anion is observed. A linear relation seems to exist between the oxygen Is binding energies (measured relative to Cs) and the oxygen-to-tungsten ratio in five isopoly anions. This latter finding may serve as a useful aid in studies related to the synthesis of new compounds.     

Induced waveguiding in a two-dimensional Λ-configuration atomic medium

We show that induced waveguiding of a cw probe by a spatial soliton pump in a two-dimensional (one longitudinal and one transverse spatial dimension) Λ-configuration atomic medium can be achieved. The effects of probe-pump detuning and the initial probe transverse momentum on waveguiding are also examined.     

Fluorescence Spectral Properties of Indocyanine Green on a Roughened Platinum Electrode: Metal-Enhanced Fluorescence

The interactions of fluorophores with noble metal particles can modify their emission spectral properties, a relatively new phenomenon in fluorescence. We subsequently examined indocyanine green (ICG), which is widely used in medical testing and imaging, in close proximity to an electrically roughened platinum electrode. The emission intensity and lifetimes were decreased about 2-fold on the roughened surface as compared to a smooth Pt surface, and the photostability about the same. Platinum does not appear promising for metal enhanced fluorescence, at least for long wavelength fluorophores.     

o-Phenylenediamine as a New Catalyst in the Highly Regioselective Conversion of Epoxides to Halohydrins with Elemental Halogens

The regioselective ring opening of epoxides using elemental iodine and bromine in the presence of o-phenylenediamine as a new catalyst affords vicinal iodo alcohols and bromo alcohols in high yields. The major advantages of this method are versatility, high regioselectivity, a cheap and commercially available catalyst, mild and neutral reaction conditions, and short reaction times. Fourier transform Raman spectroscopy was used to study the reaction of iodine with o-phenylenediamine. The results indicate that the complex [(Diamine)I]⁺·I₅^– is formed, and we suggest that the major nucleophile is the pentaiodide ion. This bulky nucleophile has a fundamental role in the high regioselectivity observed attacking the less sterically hindered epoxide carbon.     

Excess volumes of the binary mixtures of trichloroethylene withn-alcohols at 30 and 40°C

Volumes of mixing binary systems formed by trichloroethylene with n-alcohols (1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, and 1-octanol) were measured as a function of composition at 30 and 40°C, by dilatometric measurements. All the systems show a change of sign for V ^E from negative to positive as the mole fraction trichloroethylene increases at both temperatures The positive value of the excess volumes increase as carbon chain length increases. The results are explained in terms of depolymerization of hydrogen bonded alcohol aggregates and weak hydrogen-bonding interaction of the type Cl-H–O between unlike molecules.     

The sterepolides: new isolactaranes from stereumpurpureum

Sterepolide and dihydrosterepolide, new sesquiterpenes isolated from the fungus $\text{Stereum}$$\text{purpureum}$, are assigned structures $\text{4}$ and $\text{7}$, respectively. The assignments are based mainly on spectroscopic studies and similarities to isolactarorufin ($\text{5}$). A possible mode of biogenesis of these isolactarane type sesquiterpenes is discussed.     

XPS study of molybdenum sulfide catalyst exposed to CO and H2

Amorphous MoS(3) (air-dried precipitate), crystalline MoS(2) (made in the laboratory under nitrogenous atmosphere), and commercial molybdenum disulfide catalysts have been investigated by X-ray photoelectron spectroscopy (XPS). The chemical species present on the surface and the S/Mo atomic ratios of laboratory catalysts were compared to those present on a commercial molybdenum disulfide catalyst before and after treatment with CO and H(2). Pretreatment of MoS(2) with CO followed by H(2) showed that CO was adsorbed on the surface with no change in the chemical oxidation state of Mo and S. However, the results indicated that CO was not adsorbed when the sequence of gas exposures was reversed.     

A rapid and simple microwave-assisted digestion procedure for spectrophotometric determination of titanium dioxide photocatalyst on activated carbon

Deposition of titanium dioxide (TiO₂) on activated carbon (AC) surface has been widely utilized for the production of TiO₂/AC photocatalyst, which can be used in photo-degradation of pollutants. In this work, a fast and simple digestion procedure has been developed for the spectrophotometric quantitative analysis of TiO₂ in TiO₂/AC photocatalyst. Microwave-assisted digestion was used in the procedure. The microwave-digestion procedure was optimized using the single-variable method. Variables optimized included time of ashing, effective digestion time, volume and concentration of sulfuric acid, effect of adding a digestion catalyst, effect of sample pulverizing and on–off time cycle of the microwave. The analysis was completed spectrophotometrically after addition of hydrogen peroxide to the digested solution. Procedure precision and accuracy was tested by application to photocatalyst samples containing known amounts of TiO₂, and compared with previously published spectrophotometric procedures. The proposed microwave procedure was capable of recovering 98.4–101.1% of TiO₂ in the catalyst in less than 10 min, without the need for sample ashing. Analytical precision is 1.42–2.39% relative standard deviation (R.S.D.). In terms of accuracy and precision, the proposed microwave procedure was comparable with other procedures, but the proposed microwave procedure was superior in terms of shorter procedure duration.     

Characterization of sol-gel immobilized lipases

The immobilization of lipases within a chemically inert hydrophobic sol-gel support, which is prepared by polycondensation of hydrolyzed tetramethoxysilane (TMOS) and methyltrimethoxysilane (MTMS) or iso-butyltrimethoxysilane (iso-BTMS), results in heterocatalysts. The heterocatalysts so prepared showed a dramatically enhanced catalytic activity and stability as measured by the hydrolysis and transesterification of soybean oil. The lipase/sol-gel materials were characterized by nitrogen adsorption to determine their specific surface area. Solid state NMR was used to reveal the degree of cross-linking of the sol-gel materials. Scanning electron microscopy and atomic force microscopy were used to observe the morphology of the biocatalysts. Transmission electron microscopy and confocal microscopy were used to investigate the enzyme distribution within the sol-gel materials. The characterization studies showed that the most active lipase-containing sol-gel was a non-porous amorphous material with enzyme randomly distributed throughout the sol-gel material. The activity of the immobilized enzyme did not correlate to the degree of cross-linking or the specific surface area of the sol-gel materials. The highly retained activity of the immobilized enzyme was more likely attributed to the conformational changes of the enzyme during the immobilization, which result in enzyme's fixation in a more favorable conformation and to the lipophilic environment of the hybrid matrix structure which facilitates the transport of the hydrophobic substrate to the active sites.