Standard Enthalpies of Formation for Solid Complexes of Chromium Chloride with L—α—Amino Acids

ＩｎｔｒｏｄｕｃｔｉｏｎＧＴＦ ,ｔｈｅｉｎｄｉｓｐｅｎｓａｂｌｅｃｏｆａｃｔｏｒｏｆｉｎｓｕｌｉｎ ,ｉｓａｃｏｍｐｌｅｘｆｏｒｍｅｄｂｅｔｗｅｅｎａｍｉｎｏａｃｉｄ ,ｎｉａｃｉｎａｎｄｃｈｒｏｍｉ ｕｍ .Ｉｎｓｕｌｉｎｄｏｅｓｎｏｔｋｅｅｐｔｈｅｎｏｒｍａｌｓｕｇａｒｍｅｔａｂｏｌｉｃｕｎ ｌｅｓｓＧＴＦｈａｓａｆｆｉｎｉｔｙｆｏｒｉｔｓｃｏｍｐｌｅｘ .1Ｔｈｕｓ ,ｉｔｉｓｄｅｓｉｒ ａｂｌｅｔｏｈａｖｅａｇｏｏｄｕｎｄｅｒｓｔａｎｄｉｎｇｏｆｃｏｏｒｄｉｎａｔｉｏｎｂｅｈａｖｉｏｒｏｆｃｈｒｏｍｉ…     

Standard enthalpy of formation of platinum hydrous oxide

Standard enthalpies of formation of amorphous platinum hydrous oxide PtH_2.76O_3.89 (Adams' catalyst) and dehydrated oxide PtO_2.52 at T=298.15 K were determined to be -519.6±1.0 and -101.3 ±5.2 kJ mol^-1, respectively, by micro-combustion calorimetry. Standard enthalpy of formation of anhydrous PtO₂ was estimated to be -80 kJ mol^-1 based on the calorimetry. A meaningful linear relationship was found between the pseudo-atomization enthalpies of platinum oxides and the coordination number of oxygen surrounding platinum. This relationship indicates that the Pt-O bond dissociation energy is 246 kJ mol^-1 at T=298.15 K which is surprisingly independent of both the coordination number and the valence of platinum atom. This may provide an energetic reason why platinum hydrous oxide is non-stoichiometric. This revised version was published online in August 2006 with corrections to the Cover Date.     

Corner transfer matrices of the eight-vertex model. I. Low-temperature expansions and conjectured properties

A corner transfer matrix (CTM) is defined for the zero-field, eight-vertex model on the square lattice. Its logarithm and its diagonal form are obtained to second order in a perturbation expansion of low-temperature type. They turn out to have a very simple form, apart from certain remainder contributions that can be ignored in the limit of a large lattice. It is conjectured that in this limit the operators have these simple forms for all temperatures less than the critical temperatureT _c. The spontaneous magnetization can then easily be obtained, and agrees with the expression previously proposed. It is intended to prove some of the conjectures in subsequent papers.     

Astragalin identification in graviola pericarp indicates a possible participation in the anticancer activity of pericarp crude extracts: In vitro and in silico approaches

Graviola, soursop, or guanabana (Annona muricata L.), is an ethnomedical fruit consumed to alleviate headache, diarrhea, diabetes, and cancer. Pericarp is the inedible part of graviola least studied in comparison to seeds and leaves, even thought, it contains the highest concentration of graviola total polyphenols. Anticancer effect of graviola pericarp has been demonstrated in crude extracts attributing the effect to acetogenins, however, crude extracts contain several active molecules. Thus, the present work aimed to fractionate and purify an ethanolic crude extract from graviola pericarp. Purified graviola pericarp fraction (PGPF) was evaluated on cancerous and non-cancerous cell lines, and then was identified by NMR, TOF-MS, and HPLC. Finally, an in silico analysis was performed to predict targets cancer-related of the molecule detected. Our results revealed IC₅₀ values for cervix adenocarcinoma (HeLa), hepatocellular carcinoma (HepG2), triple-negative breast cancer (MDA-MB-231), and non-cancerous cell line (HaCaT) of 92.85 ± 1.23, 81.70 ± 1.09, 84.28 ± 1.08, and 170.2 ± 1.12 µg PGPF/mL, respectively. In vitro therapeutic indexes estimated as quantitative relationship between safety and efficacy of PGPF were 1.83, 2.08, and 2.02 for HeLa, HepG2, and MDA-MB-231, respectively. The NMR analysis revealed astragalin (kaempferol-3-O-glucoside) in PGPF, a flavonoid not reported in graviola pericarp until now. Astragalin identity was confirmed by TOF-MS and HPLC. In silico results support previous reports about astragalin modulating proteins such as Bcl-2, CDK2, CDK4, MAPK and RAF1. Also, results suggest that astragalin may interact with other cancer-related proteins not associated previously with astragalin. In conclusion, astragalin may be contributing to the anticancer effect observed in graviola pericarp extracts.     

Electrochemical Properties of Carbon Black AD-100 and AD-100 Promoted with Pyropolymer of Cobalt Tetra(p-methoxyphenyl)porphyrin

Carbon black AD-100: initial, activated, and promoted with pyropolymer of cobalt tetra(p-methoxyphenyl)porphyrin is characterized by a complex of electrochemical (floating electrode, rotating disk electrode, rotating ring-disk electrode, electrochemical impedance) and structural (standard porosimetry, BET) methods of investigation. Procedures for the AD-100 activation and promotion and the preparation of thin layers of the material to be studied and deposited on disk electrodes are described. The effect of the activation and promotion of carbon black on the surface and electrocatalytic activity of materials under study in the reduction of oxygen and hydrogen peroxide is shown. The ratio of constants of oxygen reduction directly to water and through intermediate formation of hydrogen peroxide is determined. A path for the oxygen reduction is discussed.     

水合偏硼酸钾的热化学研究

Hydrated potassium monoborate(KBO₂·4/3H₂O) was obtained from an aqueous solution in a mole ratio of K₂O∶B₂O₃=2∶1 and characterized by powder X-ray diffraction(XRD)， infrared spectroscopy(FT-IR) and Raman spectroscopy. The enthalpy of solution of hydrated potassium monoborate， KBO₂·4/3H₂O， in approximately 1mol·dm^-3 aqueous hydrochloric acid was determined. Together with the previously determined enthalpies of so-lution of H₃BO₃ in approximately 1mol·dm^-3 HCl(aq) ，and of KCl in aqueous(hydrochloric acid+boric acid)， the standard molar enthalpy of formation of -(1411.11±0.84)kJ·mol^-1 for KBO₂·4/3H₂O was obtained from the standard molar enthalpies of formation of KCl(s)， H₃BO₃(s)， and H₂O(l). The standard molar entropy of formation of -422.94J·K^-1·mol^-1 and standard molar entropy of 163.47J·K^-1·mol^-1 for KBO₂·4/3H₂O were calculated from the thermodynamic relations. A group contribution method is applicable to KBO₂·4/3H₂O.     

Dielectric relaxation pattern of dilute colloidal suspensions

An immediate method of analysis of the relaxation characteristics of a colloidal suspension, like of any dielectric, is based on the so-called Cole-Cole representation (imaginary part versus real part) of its complex dielectric constant in a wide frequency range. In this work, we show theoretical plots calculated according to the models developed by DeLacey and White (J Chem Soc Faraday Trans 2 77:2007–2039), and by Rosen et al. (J Chem Phys 98: 4183–4194; this model uses the dynamic Stern layer theory). Both theoretical approaches to the dielectric relaxation pattern of a colloidal suspension are compared to each other, and to experimental data obtained on polystyrene suspensions. Although no significant differences are found between the theoretical predictions of the relaxation patterns (except for the values of the dielectric constant; the DSL model yields higher polarizabilities of the suspensions), none of the models can exactly reproduce the frequency dependence of the dielectric constant of a colloidal system. We propose a modification of DeLacey and White's model to include the possibility that the ionic drag coefficients depend on the ion position in the double layer. The final results show that the general trends of the frequency dependence of the quantities involved are not modified, irregardless of the changes in ionic drag coefficients.     

Preconcentration/preelution ion chromatography for the determination of perchlorate in complex samples

The determination of perchlorate in complex matrices by ion chromatography (IC) with an online preconcentration and preelution technique is discussed. The method was applied to different sample types containing large concentrations of matrix anions that would otherwise interfere with analysis via conventional IC. The present approach was highly effective in removing most of the matrix anions and was thus resistant to the interferences commonly encountered in a high ionic strength background. Method performance was evaluated by analyzing for low-level perchlorate in synthetic high ionic strength solutions, tissue extracts, and hydroponic nitrate fertilizer samples. Not only is it easier to practice the present method compared to USEPA Method 314.0, but for most of these samples the present approach provided equal to or better recovery of perchlorate than Method 314.0. With a sample of specific conductance 12,650 μS cm⁻¹, for example, the present method provided a perchlorate recovery of 101% at the 25 μg L⁻¹ level versus 89% by EPA Method 314.0. Method detection limits of perchlorate in hydroponic fertilizer samples with this method (130-190 μg kg⁻¹) are the lowest thus far reported.     

A new derivatization procedure for the determination of cephalexin with 1,2-naphthoquinone 4-sulphonate in pharmaceutical and urine samples using solid-phase extraction cartridges and UV–visible detection

The present report shows how to derivatize cephalexin with 1,2-naphthoquinone-4-sulphonate (NQS) into solid-phase extraction cartridges (C₁₈) using UV–visible detection. Optimum conditions for this new procedure are: hydrogen carbonate/carbonate buffer pH=10.5, 5 min reaction time at 25°C and NQS concentration of 7.1×10⁻³ mol l⁻¹. The accuracy and the precision of the method were tested. The procedure was used to measure cephalexin in pharmaceutical and urine samples. The results obtained were contrasted with those reported by UV-spectrophotometric and HPLC methods for pharmaceutical samples and with HPLC method for urine samples. The H-point standard additions method was used to measure cephalexin in pharmaceutical samples, and the generalized H-point standard additions method was used to measure cephalexin in urine samples.     

Uncertainties of gas chromatographic measurement of troublesome pesticide residues in apples employing conventional and mass spectrometric detectors

In recent years the declaration of estimated uncertainty of measurement has become an integral part of analytical results. This study presents the assessment of results generated within the analysis of selected pesticides represented by carbamates, pyrethroides and azoles, residues of which may be found in treated apples. Multiresidue method used for analysis of spiked samples (residues at levels 0.040–0.163 mg/kg) consisted of (i) ethyl acetate extraction, (ii) GPC clean-up and (iii) identification/quantification of residues by GC. Procedures utilizing either conventional (electron-capture, nitrogen–phosphorus) or mass-selective detectors (quadrupole and ion trap analyzer) were evaluated. The results generated through alternative strategies of uncertainty estimation (“bottom-up”, “top-down”) were compared.

Using the “bottom-up” approach uncertainty of extraction which comprises two components—(i) repeatability of extraction and (ii) uncertainty of extraction recovery was shown to represent the main source of combined standard uncertainty (values of uncertainty of extraction for tested pesticides ranged from 4.6% to 21.6%). On the other hand, uncertainties associated with the GC calibration (uncertainties of weighing and diluting standards, uncertainties of purity of standards) were not so important (most of them did not exceed 2%). Combined standard uncertainties associated with the described analytical method ranged for individual compounds from 9.3% to 24.3%. Similar values of combined standard uncertainties were obtained using the alternative “top-down” approach.