Structures of aliphatic amino acid proton-bound dimers by infrared multiple photon dissociation spectroscopy in the 700-2,000 cm(-1) region

Structural aspects of proton-bound dimers composed of amino acids with aliphatic side chains are investigated using infrared multiple photon dissociation (IRMPD) spectroscopy and electronic structure calculations. Features in the IRMPD spectra in the 700-2,000 cm-1 range are due primarily to C=O stretching, NH2 bending, and COH bending. It was possible to distinguish between isomeric structures by comparing the experimental IRMPD spectra and those predicted using B3LYP/6-31+G(d,p). It was possible, based on the calculations and IRMPD spectra, to assign the experimental spectrum of the glycine proton-bound dimer to a structure which was slightly different from that assigned by previous spectroscopic investigations and in agreement with recent thermochemical studies. Since all proton-bound dimers studied here, composed of the different amino acids, have very similar spectra, it is expected that they also have very similar lowest-energy structures including the mixed alanine/glycine proton-bound dimer. In fact, the spectra are so similar that it would be very challenging to distinguish, for example, the glycine proton-bound dimer from the alanine or valine proton-bound dimers in the 700-2,000 cm-1 range. According to the calculated IR spectra it is shown that in the approximately 2,000-3,200 cm-1 range differentiating between different structures as well as different proton-bound dimers may be possible. This is due mainly to differences in the asymmetric stretch of the binding proton which is predicted to occur in this region.     

Global existence and boundedness of classical solutions for a chemotaxis model with consumption of chemoattractant and logistic source

This paper deals with the following chemotaxis system: under homogeneous Neumann boundary conditions in a bounded domain with smooth boundary. Here, δ and χ are some positive constants and f is a smooth function that satisfies with some constants a ?0,b  > 0, and γ  > 1. We prove that the classical solutions to the preceding system are global and bounded provided that Copyright © 2016 John Wiley & Sons, Ltd.     

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.     

Nanomolar Determination of Penicillamine by Using a Novel Cobalt/Polyaniline/Carbon Paste Nanocomposite Electrode

The fabrication of cobalt/polyaniline nanocomposite was performed using a simple chemical method. It was characterized by using TEM and FTIR techniques. The nanocomposite was applied as a modifier in a carbon paste electrode for selective determination of penicillamine. Penicillamine reacts with emeraldine polyaniline by using 1,4, Michael addition reaction. It can decrease the voltammetric peak current of emeraldine polyaniline. The effects of pH and potential sweep rate on the response of the electrode were investigated. Differential pulse voltammetry was applied for quantitative determination. Dynamic linear ranges were obtained in the ranges of 1.0×10^?8–1.0×10^?7 mol L^?1 and 1.0×10^?9–1.0×10^?8 mol L^?1.     

Simultaneous voltammetric determination of uric acid and ascorbic acid using carbon paste/cobalt Schiff base composite electrode

Differential pulse and cyclic voltammetry were applied for the oxidation of mixture of uric acid and ascorbic acid at the surface of carbon paste/cobalt Schiff base composite electrode. The electrooxidation of these compounds at bare electrode is sluggish, and there is no suitable peak separation between them. However, using cobalt methyl salophen as modifier, two well-defined anodic waves with a considerable enhancement in the peak current and a remarkable peak potential separation near 315 mV are obtained. It can improve the kinetics of electron transfer for both compounds remarkably. All these improvements are created because of the electrocatalytic property of cobalt Schiff base complex. The effect of some parameters such as pH and scan rates were studied. All the anodic peak currents for the oxidation of ascorbic acid and uric acid shifted toward more negative potential with an increase in pH, revealing that protons have taken part in their electrode reaction processes. The best peak separation with appropriate current was obtained for pH 4.0. A linear range of 5.0?×?10^?4 to 1.0?×?10^?8 and 1.0?×?10^?3 to 1.0?×?10^?8 M with detection limit of 8.0?×?10^?9 and 8.0?×?10^?9 M was obtained for ascorbic acid and uric acid using differential pulse voltammetry at the surface of modified electrode, respectively. Analytical utility of the modified electrode has been examined successfully using human urine samples and vitamin C commercial tablets.     

Sonocatalyzed facile and mild one pot synthesis of gem-dichloroaziridine derivatives under alkaline conditions

In this research, rapid and efficient preparation of 2,2-dichloro-1,3-diarylaziridines through the reaction of Schiff base compounds with dichlorocarbene yielded in situ from chloroform and sodium hydroxide without any phase transfer catalyst under ultrasonic irradiation is described. The advantages of this reaction are very short reaction times, excellent product yields, simplicity of the method and high purity of products.     

Facile and efficient method for preparation of schiff bases catalyzed by P2O5/SiO2 under free solvent conditions

A simple and convenient method for the preparation of Schiff bases is developed. In this method, the Schiff base compounds were prepared from the reaction of carbonyl compounds with primary amines. In this reaction, P₂O₅/SiO₂ have catalyzed the Schiff base formation in dry media under solvent‐free conditions. Advantages of this method are use of an inexpensive and efficient catalyst, high yields of products, short reaction times, and simpli‐city of the reaction and workup. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:43–47, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20383