Influence of silanization on voltammetry at electrodes modified with silica films of controlled porosity formed by electrochemically initiated sol-gel processing

Silica sol-gel (SG) films with templated pores were deposited on glassy carbon (GC) electrodes by an electrochemically initiated process. Generation-4 poly(amidoamine), PAMAM, dendrimer was included in the tetraethoxysilane precursor to facilitate pore formation. The PAMAM adsorbs to the GC, which blocks SG formation at those sites on the electrode. The pore size was 10?±?5?nm. After removal of the PAMAM, cyclic voltammetry of Fe(CN)₆ ^3? and Ru(NH₃)₆ ³⁺ at pH?6.2 showed that the residual negative charge on the silica attenuated the current for the former and increased the current for the latter, presumably by electrostatic repulsion and ion-exchange preconcentration, respectively. This premise was supported by repeating the measurements at the isoelectric point. Methylation of the silanol sites was used to eliminate the charge of the SG. At the end-capped SG, the voltammetry of Fe(CN)₆ ^3? and Ru(NH₃)₆ ³⁺ yielded currents that were independent of pH over the range 2.1 to 7.2. Circumventing the need for the silanization by using (3-glycidyloxypropyl)trimethoxysilane as the sol-gel precursor failed because the oxygen plasma treatment to remove the PAMAM attacked the organically modified sol-gel backbone. The resulting modified electrode mitigated the influence of proteins on the voltammetry of test species and stabilized functionalize nanoparticle catalysts under hydrodynamic conditions.     

Niobium oxide solid catalyst: esterification of fatty acids and modeling for biodiesel production

Biodiesel can be obtained from fatty acid raw materials through esterification. The reactivity of lauric, palmitic, stearic, oleic, and linoleic fatty acids with methanol using powdered niobic acid as a heterogeneous catalyst was investigated in this work, both experimentally (in a batch reactor) and theoretically. A 2³ experimental design was used, with methanol/fatty acid molar ratio, catalyst concentration, and temperature as main factors. An empirical model demonstrated that temperature is the most important variable. Fourteen heterogeneous and 56 homogeneous‐like kinetic models were tested. A homogeneous‐like model considering zero order for all species and inhibition by water was the most adequate for experiments without catalyst. A homogeneous‐like model considering a second‐order reaction in relation to the fatty acid and no water inhibition was the most adequate for niobic acid catalyzed reaction. Molecular modeling confirmed the experimental results showing that the reactivity is directly related to the increase of unsaturated bonds and the reduction of carbon chain length. The polarity of the fatty acid is determinant in the reactivity. At the molecular level, reaction occurs between the HOMO orbital of methanol and LUMO orbitals of fatty acids and reactivity is higher when the energy difference between these orbitals is lower. Copyright © 2010 John Wiley & Sons, Ltd.     

The Studies of 13C NMR Chemical Shifts and Induced Lanthanide Shift Reagent Cis-trans Isomerization of N-Cinamylidene-hexyl,t-butyl and Substituted Aryl-Amines

The Carbon-13 chemical shifts of N-Cinamylidenehexyl, t-butyl and sixteen substituted aryl amines were analysed. The lanthanide induced carbon-13 chemical shifts of the cis and trans of four N-cinamylidene substituted anilines were analysed. The spectra N-cinamylidene hexylamine showed only the trans form. The cis/trans ratio of N-cinamylidene aryl amines increased as the LSR concentration increased.     

Monocyclic and Fused 4-Imino(4-Oxo)-1,3,2-Diazaphospholanes and - Phosphorinanes. Synthesis and Some Properties

Abstract

In contrast to the great variety of well known phosphorus heterocycles with exocyclic C=O double bond the number of ones containing exocyclic C=N bond is unusually modest. We elaborated the convenient method of preparation of various N,P,N-heterocycles with exocyclic C=N bond (1–4) from the readily available corresponding amino acid amidines and appropriated dichlorides or diamides of phosphorus (III) acids. Rings' 1–3 with P(III) are easily converted into (thio)phosphoryl derivatives, while the direct phosphorylation of amino amidines by RP(Y)Cl₂ is unusually ineffective. Tricycles 4 - derivatives of 2-(2-amino pheny1)imidazoline - mainly exist in the more conjugated hydrophosphazo tautomeric form 4b (>90 %).     

Estimating Aluminum leaching from Aluminum cook wares in different meat extracts and milk

A method of estimating Al leaching from Al cook ware in some meat extracts and liquid milk was investigated. In the present work four kinds of Al cook wares from four countries were chosen from the local market. Extracts of boiled meat (lamb, chicken, and fish) were used to make 10–50% (w/v) concentrations. In addition liquid fresh milk and long life milk were diluted to make 10–50% (v/v) concentrations. Weight loss (WL) method, atomic absorption, polarization method, and surface study were applied. The “estimated” Al intake per person from WL in 30% meat extract and milk range from 8.16 to 12.75 mg/h with fish extract having the highest leaching and chicken extract having the lowest leaching. Atomic absorption gave comparable results to that of WL. Comparing the present results with the Provisional Tolerance Weekly Intake of Al approved by the FDA/WHO shows that Al leaching from Al cook wares may add high doses of Al into the diet.     

New catalytic approach for nano-sized V(IV), Cr(III), Mn(II) and Fe(III)-triazole complexes: detailed spectral,electrochemical and analytical studies

Research on Chemical Intermediates - A new series of metal ion complexes from a triazole-Schiff base was synthesized and fully characterized. The tridentate mode of coordination was the only mode...     

Microwave synthesis of sulfur-doped α-Fe2O3 and testing in photodegradation of methyl orange

α-Fe₂O₃, as a promising photocatalyst in environmental aspects, was doped by a nonmetal to enhance the optical and electronic properties. Sulfur-doped hematite was synthesized by microwave irradiation. The samples were investigated by X-ray diffraction and energy dispersive X- ray-scanning electron microscopy. Nanostructure particles have a hexagonal structure that did not change after sulfur incorporation. The optical studies via UV–Visible spectroscopy proved the high absorbance of S/α-Fe₂O₃under the visible region. Moreover, the band gap of S/α-Fe₂O₃ was shifted to higher wavelengths. However, nonmetals may exhibit a negative effect and act as recombination centers as the photoactivity of undoped hematite was still higher in the photodegradation of methyl orange as a pollutant. H₂O₂ as an oxidant was fourfold better than O₂, leading to the formation of the active oxygen species. The preparation method plays a crucial role in the shaping of nanostructure particles and its photoactivity.     

1H NMR Study of the Photoisomerization of Cinamylidene-2-Methyl-5-Chloro aniline

Abstract

Cinamylidene-2-methyl-5-chloro-aniline undergoes isomerization from the trans form to the cis form under irradiation with u.v. light at room temperature. The isomerization was studied in three solvents and the % cis was found to be in the following order: in DMSO 〉 CDCl₃ 〉 CCl₄. The rate of the process of isomerization was found to be a first order one.     

Statistically rigorous analysis of imaging SIMS data in the presence of detector saturation

We present a new strategy for analyzing imaging time‐of‐flight SIMS data sets affected by detector saturation. Rather than attempt to correct the measured data to remove saturation, we incorporate the detector behavior into the statistical basis of the analysis. This is performed within the framework of maximum a posteriori reconstruction. The proposed approach has several advantages over previous techniques. No approximations are involved other than the assumed model of the detector. The method performs well even when applied to highly saturated and/or single‐scan data sets. It is statistically rigorous, correctly treating the underlying statistical distribution of the data. It is also compatible with Bayesian methods for incorporating prior knowledge about sample properties. An efficient iterative scheme for solving the proposed equations is presented for the case of the bilinear model commonly used in analyses of SIMS data. The correctness of the approach and its efficacy are demonstrated on synthetic data sets. The method is found to perform better than a widely‐used data‐correction method used in combination with alternating‐least‐squares Multivariate Curve Resolution analysis. Copyright © 2015 John Wiley & Sons, Ltd.