Thin chitosan films as a platform for SPR sensing of ferric ions

Homogeneous chitosan films of various thicknesses (10-65 nm) were deposited on thin gold films through spin coating. The resulting interfaces were characterized using surface plasmon resonance (SPR), AFM, profilometry and cyclic voltammetry. The strong chelating properties of chitosan films to Fe(3+) were investigated using cyclic voltammetry. Through SPR measurements, an affinity constant between chitosan and Fe(3+) of 9.49 x 10(5) M(-1) was determined with a detection limit as low as 250 ppb.     

Structural studies of cyclic ureas: 1. Enthalpies of formation of imidazolidin-2-one and N,N′-trimethyleneurea

A thermophysical and thermochemical study has been carried out for crystalline imidazolidin-2-one and N,N′-trimethyleneurea [tetrahydropyrimidin-2(1H)-one]. The thermophysical study was made by differential scanning calorimetry, d.s.c., in the temperature intervals between T = 268 K and their respective melting temperatures. Several solid–solid transitions have been detected in imidazolidin-2-one. The standard (p^° = 0.1 MPa) molar enthalpies of formation, at T = 298.15 K, for crystalline imidazolidin-2-one and N,N′-trimethyleneurea [tetrahydropyrimidin-2(1H)-one], were determined using static-bomb combustion calorimetry. The standard molar enthalpies of sublimation, at T = 298.15 K, for the two compounds were derived from the variation of their vapour pressures, measured by the Knudsen effusion method, with the temperature. These two thermochemical parameters yielded the standard molar enthalpies of formation of the two cyclic urea compounds studied in the gaseous phase at T = 298.15 K. These values are discussed in terms of molecular structural contributions and interpreted on the bases of the “benzo-condensed effect” and of the ring strain of imidazolidin-2-one.     

Comparison of high performance TLC and HPLC for separation and quantification of chlorogenic acid in green coffee bean extracts

Two chromatographic methods, high-performance TLC (HPTLC) and HPLC, were developed and used for separation and quantitative determination of chlorogenic acid in green coffee bean extracts. For HPTLC silica gel Kieselgel 60 F 254 plates with ethyl acetate/dichlormethane/formic acid/acetic acid/water (100:25:10:10:11, v/v/v/v/v) as mobile phase were used. Densitometric determination of chlorogenic acid by HPTLC was performed at 330 nm. A gradient RP HPLC method was carried out at 330 nm. All necessary validation tests for both methods were developed for their comparison. There were no statistically significant differences between HPLC and HPTLC for quantitative determination of chlorogenic acid according to the test of equality of the means.     

Determination of lead in sediments and sewage sludge by on-line hydride-generation axial-view inductively-coupled plasma optical-emission spectrometry using slurry sampling

Among the “traditional” hydride-forming elements, lead is probably the most difficult, and its determination in this form has rarely been reported in the literature. In this paper a simple and rapid method, axial-view inductively-coupled plasma optical-emission spectrometry using on-line hydride generation (HG–ICP–OES) from samples prepared as slurry, is proposed for determination of lead in environmental samples. The samples (20–50 mg, particle size ≤120 μm) were treated with 1 mL aqua regia in a 40-kHz ultrasonic bath for 60 min. The slurry was diluted to a final volume of 50 mL with a 10% m/v solution of (NH₄)₂S₂O₈. The concentrations of NaBH₄, tartaric acid, and (NH₄)₂S₂O₈, used for on-line plumbane generation were optimized by means of a complete factorial analysis applied to an aqueous standard solution and to the slurry of a sediment certified reference material (CRM). External calibration against aqueous standards in the concentration range 10–100 μg L⁻¹ was used for analysis of six CRM—three marine sediments, one river sediment, and two sewage sludges. Analysis of the filtered slurry showed that Pb was only partially extracted into the liquid phase. Several major concomitants tested did not affect the Pb signal. The detection limit (3s, n = 10) for 20 mg sample in a final volume of 50 mL was 5.0 μg g⁻¹. Tin was the only other hydride-forming analyte that could be determined satisfactorily with Pb; for tin the detection limit was 1.0 μg g⁻¹. The values obtained for Pb and Sn were not significantly different from the certified concentrations, according to the t-test at the 95% confidence level. Nine river sediments collected locally were also analyzed and the concentrations were in agreement with results obtained after total digestion.     

An Optimal Alternative Theorem and Applications to Mathematical Programming

Given a closed convex cone P with nonempty interior in a locally convex vector space, and a set , we provide various equivalences to the implication

An Iodide-Mediated Anodic Amide Coupling

The ubiquity of amide bonds, present in natural products and common pharmaceuticals renders this functional group one of the most prevalent in organic chemistry. Despite its importance and a wide variety of existing methods for its formation, the latter still can be a challenge for classical activating reagents such as chloridating agents or carbodiimides. As the spent reagents often cannot be recycled, the development of more sustainable methods is highly desirable. Herein, we report an operationally simple and mild indirect electrochemical protocol to effect the condensation of carboxylic acids with amines, forming a wide variety of carboxamides.     

Calculation of the convective heat transfer coefficient and cooling kinetics of an individual fig fruit

A methodology for determination of the convective heat transfer coefficient, h _H, is proposed for fruits with spherical shape, using numerical simulation and experimental data of the temperature within the fruit in the course of its cooling. In the proposed methodology, the position of the thermocouple inside the fruit is assumed to be unknown, and can be obtained through several simulations, supposing different positions for this sensor. The position of the thermocouple is then determined through analyses of the chi-squares of the simulations, which enabled to calculate h _H. The proposed methodology was applied for an individual fig fruit, and the cooling kinetics was described in details.