FT‐Raman and FTIR spectroscopic characterization of biogenic carbonates from Philippine venus seashell and Porites sp. coral

Some seashells of the Philippine venus species and sea coral of Porites sp. were studied by means of FT‐Raman, Fourier transform infrared spectroscopy (FTIR) and Far‐FTIR spectroscopic methods. The Raman spectra show that both Porites sp. and P. venus are of aragonite‐structured CaCO₃. Detailed spectral analysis, however, reveals some small differences, due to differences in the crystallite size or habit and to different minor element contents. IR spectra show that Porites sp. contains also some small quantities of calcite‐structured carbonates. The ν₂ band (shoulder) of calcite at 875.7 cm⁻¹ is present in the IR spectrum. The separation of the two ν₂ bands (856.4 cm⁻¹ for aragonite and 875.7 cm⁻¹ for calcite) suggests the absence of solid solution of the two polymorphic phases of CaCO₃. Spectroscopic results were confirmed also by X‐ray powder diffraction measurements. Copyright © 2008 John Wiley & Sons, Ltd.     

Applicability of winged bean extracts as organic corrosion inhibitors for reinforced steel in 0.5 ​M HCl electrolyte

Corrosion inhibition properties of winged bean (WB) extracts on reinforced steel in 0.5 ?M HCl solution was studied through experimental and theoretical calculation methods. The electrochemical studies suggested that inhibition efficiency increased with increasing concentration of WB extracts up to 95%. Nyquist diagrams revealed an increase in the charge transfer resistance values and a decrease in the constant phase element as the concentration of WB extracts were increased. The potentiodynamic polarization results revealed that WB extracts behave as mixed-type inhibitors, which physically adsorbed onto the reinforced steel surface. Effect of temperature study demonstrated that the corrosion resistance behaviour of WB extracts decreased with an increase in temperature, yielding a corrosion rate of 3.39 mmpy and 4.02 mmpy at 333 ?K with the incorporation of 1000 ?ppm WBW and WBE extracts, respectively. The thermodynamic study implied that the adsorption process follows the Langmuir isotherm with free energy adsorption of ΔG_ads WBW ?= ?-17.29 ?kJ ?mol^-1 and ΔG_ads WBE ?= ?-16.81 ?kJ ?mol^-1. Corresponding to the molecular modelling study, the semi-empirical method and molecular dynamics (MD) simulation investigated the correlation between the inhibitor compounds and the metal surface. One of the phenolic molecule constituents (gallic acid) was chosen to establish the structural and electronic parameters responsible for the high inhibition efficiency. A greater E_binding of 0.181 (a.u.) indicates that gallic acid in WB extracts can easily bind with the Fe surface, thus projecting a higher inhibitory performance. Surface morphology study affirmed the effective adsorption of WB extracts onto the surface of reinforced steel.     

Preparation of MIP grafts for quercetin by tandem aryl diazonium surface chemistry and photopolymerization

The food antioxidant quercetin was used as a template in an ultrathin molecularly imprinted polymer (MIP) film prepared by photopolymerization. Indium tin oxide (ITO) plates were electrografted with aryl layers via a diazonium salt precursor bearing two terminal hydroxyethyl groups. The latter act as hydrogen donors for the photosensitizer isopropylthioxanthone and enabled the preparation of MIP grafts through radical photopolymerization of methacrylic acid (the functional monomer) and ethylene glycol dimethacrylate (the crosslinker) in the presence of quercetin (the template) on the ITO. The template was extracted, and the remaining ITO electrode used for the amperometric determination of quercetin at a working potential of 0.26 V (vs. SCE). The analytical range is from 5.10⁻⁸ to 10⁻⁴ mol L⁻¹, and the detection limit is 5.10⁻⁸ mol L⁻¹.

This work describes the grafting of a molecularly imprinted polymer (MIP) film by combining diazonium surface chemistry and surface-initiated photopolymerization. The MIP grafts specifically and selectively recognize quercetin in pure solution in THF and in real green tea infusion.

     

Selectivity and thermodynamic characteristics of doubly charged cations on zirconium titanate from aqueous and alcoholic solutions

The ion-exchange isotherms of Ni²⁺/H⁺ and Co²⁺/H⁺ have been determined with a solution of 0.1 ionic strength for both forward and backward reactions at 25^°C by a batch technique. The thermodynamic equilibrium constants for the exchange process have been calculated using the Gains and Thomas equation. The preference Ni²⁺>Co²⁺ has been shown. The ion exchange selectivity for exchange of Ni²⁺ and Co²⁺ ions with hydrogen ions on zirconium titanate has been investigated as a function of [HCl] from aqueous and 25% of methanol and/or ethanol solutions. The values of the thermodynamic functions for the studied systems have been reported. This revised version was published online in July 2006 with corrections to the Cover Date.     

Highly sensitive and selective catalytic determination of formaldehyde and acetaldehyde

A highly sensitive, simple and selective kinetic method was developed for the determination of ultra-trace levels of formaldehyde and acetaldehyde based on their catalytic effect on the oxidation of N,N-diethyl-p-phenylenediamine (DPD) with hydrogen peroxide. The reaction was monitored spectrophotometrically by tracing the formation of the red-colored oxidized product of DPD at 510nm, within 30s of mixing the reagents. The optimum reaction conditions were: 20mmolL(-1) DPD, 250mmolL(-1) H(2)O(2), 150mmolL(-1) phosphate, 150mmolL(-1) citrate and pH 6.60+/-0.05 at 25 degrees C. Following the recommended procedure, formaldehyde and acetaldehyde could be determined with linear calibration graphs up to 0.50 and 1.4microg mL(-1) and detection limits, based on the 3S(b)-criterion, of 0.015 and 0.035microg mL(-1), respectively. In addition, analytical data for other 10 aldehydes were also presented. The high sensitivity and selectivity of the proposed method allowed its successful application to rain water, mainstream smoke (MSS) and disposed tips of smoked cigarettes (DTSC). A sample aliquot was directly analyzed for its total water-soluble aldehyde content. A second sample aliquot was heated at 80 degrees C for 10min to expel acetaldehyde and the aliquot was analyzed for its content of other water-soluble aldehydes (expressed as formaldehyde equivalent), and acetaldehyde was determined by difference. The analytical results were in excellent agreements with those obtained following the standard HPLC method based on pre-column derivatization with 2,4-dinitrophenylhydrazine. Moreover, published catalytic-spectrophotometric methods for the determination of aldehydes were reviewed.     

Application of retention modelling to the simulation of separation of organic anions in suppressed ion chromatography

The ion-exchange separation of organic anions of varying molecular mass has been demonstrated using ion chromatography with isocratic, gradient and multi-step eluent profiles on commercially available columns with UV detection. A retention model derived previously for inorganic ions and based solely on electrostatic interactions between the analytes and the stationary phase was applied. This model was found to accurately describe the observed elution of all the anions under isocratic, gradient and multi-step eluent conditions. Hydrophobic interactions, although likely to be present to varying degrees, did not limit the applicability of the ion-exchange retention model. Various instrumental configurations were investigated to overcome problems associated with the use of organic modifiers in the eluent which caused compatibility issues with the electrolytically derived, and subsequently suppressed, eluent. The preferred configuration allowed the organic modifier stream to bypass the eluent generator, followed by subsequent mixing before entering the injection valve and column. Accurate elution prediction was achieved even when using 5-step eluent profiles with errors in retention time generally being less than 1% relative standard deviation (RSD) and all being less than 5% RSD. Peak widths for linear gradient separations were also modelled and showed good agreement with experimentally determined values.     

Synthesis of a Negative Photochrome with High Switching Quantum Yields and Capable of Singlet-Oxygen Production and Storage

A dimethyldihydropyrene (DHP) photochromic unit has been functionalized by donor (triphenylamine group) and acceptor (methylpyridinium) substituents. This compound was characterized by NMR, absorption and emission spectroscopies as well as cyclic voltammetry, and its properties were rationalized by theoretical calculations. The incorporation of both electron-donor and -withdrawing groups at the photochromic center allows i) an efficient photo-isomerization of the system when illuminated at low energy (quantum yield: Φ_c-o=13.3 % at λ_ex=660 nm), ii) the reversible and quantitative formation of two endoperoxyde isomers when illuminated under aerobic conditions at room temperature, and iii) the storage and production of singlet oxygen. The photo-isomerization mechanism was also investigated by spin-flip TD-DFT (SF-TD-DFT) calculations.     

Preparation of MIP grafts for quercetin by tandem aryl diazonium surface chemistry and photopolymerization

The food antioxidant quercetin was used as a template in an ultrathin molecularly imprinted polymer (MIP) film prepared by photopolymerization. Indium tin oxide (ITO) plates were electrografted with aryl layers via a diazonium salt precursor bearing two terminal hydroxyethyl groups. The latter act as hydrogen donors for the photosensitizer isopropylthioxanthone and enabled the preparation of MIP grafts through radical photopolymerization of methacrylic acid (the functional monomer) and ethylene glycol dimethacrylate (the crosslinker) in the presence of quercetin (the template) on the ITO. The template was extracted, and the remaining ITO electrode used for the amperometric determination of quercetin at a working potential of 0.26 V (vs. SCE). The analytical range is from 5.10^?8 to 10^?4 mol L^?1, and the detection limit is 5.10^?8 mol L^?1.

Sorption and dilation of silicone elastomer composites at high gas pressures: The role of interfacial quality

In elastomers the crosslink density, the presence of filler particles, and the volumetric confinement toward sorptive dilation can influence the extent of gas mass uptake. In this study the effects of filler particles on the high-pressure gas mass sorption and the volumetric dilation of a silicone elastomer matrix has been investigated. Glass beads, ca. 30 μm radii, with different surface treatments were incorporated as inclusions in various specimens at relatively low concentrations of ca. 10% by volume. The high-pressure gases used were N₂ and CO₂ up to a maximum ambient pressure of ca. 25 MPa at ca. 20°C and 42°C, respectively. The gas mass sorption was determined by a vibrating reed technique. The sorptive dilation was measured by an ultrasonic transducer operating as a displacement probe. In certain systems the absorbed CO₂ gas was able to disrupt the internal interfaces. This led to an increased gas mass uptake in the corrupted specimen. The N₂ gas did not affect the interfacial bonds. The amount of penetrant uptake was found generally to be reduced when the internal interfaces were not disrupted. The presence of various internal interfaces restrained the sorptive dilation of the elastomeric matrix. These hindrances to the natural sorptive dilation of the elastomer network suppressed the extent of the gas sorption process. This effect has also been investigated separately in detail using model ‘poker chip’ type of specimens of various aspect ratios. The sorptive dilational characteristics have been correlated with the mechanical properties of similar specimens. The influence of an almost complete volumetric confinement on the gas sorption capacity of the silicone elastomer specimen has also been studied. © 1992 John Wiley & Sons, Inc.