Molecular volume calculation using AM1 semi-empirical method toward diffusion coefficients and electrophoretic mobility estimates in aqueous solution

Diffusion coefficients and electrophoretic mobility are two important physicochemical parameters used in mass transport phenomenon studies. The volume of the solute is required to determine or estimate these parameters. Classical methods, such as the LeBas method are commonly used. However, although valid, this method may represent a boring and time-consuming task, depending on the nature and number of compounds to be calculated. In this study, the volumes of a series of neutral and charged substances of the main functional groups present in organic molecules, amino acids, drugs and diverse compounds, such as cytosine and glucose, were calculated according to the LeBas method (V_M) and the AM1 semi-empirical method, V_W(AM1). The latter showed to be statistically coincident with the former. Employed as a pure value or corrected by the LeBas molar volume, the AM1 molecular volume was also demonstrated to estimate the diffusion coefficients in infinite aqueous dilution within an acceptable average error, according to the Othmer–Thakar, Wilke–Chang and Hayduk–Laudie methods, as well as the electrophoretic mobility of charged substances, such as carboxylates and protonated amines. According to these results, the AM1 method was seen to be statistically valid to calculate molecular volume. Many advantages in the construction of most diverse structures were noted, as well as a reduction in time and an increase in the quality of the information, when run on molecular modeling software.     

Thermal evaluation of cashew nutshell liquid as new bioadditives for poly(methyl methacrylate)

In this study, the thermal-oxidative stability of poly(methyl methacrylate), PMMA, 1 % additivated with replenishable phenolic lipids is evaluated by thermogravimetric (TG/DTG) analyses and differential scanning calorimetry (DSC) analyses. Since technical cashew nutshell liquid (CNSL), a byproduct from the cashew industry, is composed basically of two phenolic lipids, cardanol and cardol, the utilization of this industrial waste and its main components as a new source of bioadditives for use as antioxidants is evaluated. The TG analyses revealed that addition of the phenolic constituent of CNSL increased the thermal stability of PMMA films considerably. The results obtained were also confirmed by DSC analyses.     

A multiresidual method based on ion-exchange chromatography with conductivity detection for the determination of biogenic amines in food and beverages

In the present work a sensitive and accurate method by ion chromatography and conductimetric detection has been developed for the determination of biogenic amines in food samples at microgram per kilogram levels. The optimized extraction procedure of trimethylamine, triethylamine, putrescine, cadaverine, histamine, agmatine, spermidine, and spermine from real samples, as well as the separation conditions based on a multilinear gradient elution with methanesulfonic acid and the use of a weak ionic exchange column, have provided excellent results in terms of resolution and separation efficiency. Extended calibration curves (up to 200 mg/kg, r?>?0.9995) were obtained for all the analyzed compounds. The method gave detection limits in the range 23–65 μg/kg and quantification limits in spiked blank real samples in the range 65–198 μg/kg. Recovery values ranged from 82 to 103 %, and for all amines, a good repeatability was obtained with precision levels in the range 0.03–0.32 % (n?=?4). The feasibility and potential of the method were tested by the analysis of real samples, such as tinned tuna fish, anchovies, cheese, wine, olives, and salami.

Bridging fluorides and hard/soft mismatch in d6 and d8 complexes: the case of [Tl(mu-F)3Ru(PPh3)3

[RuCl2(PPh3)3] reacts with thallium(I) fluoride to give either [Tl(mu-F)3Ru(PPh3)3] (1) or [Tl(mu3-F)(mu2-Cl)2Ru2(mu2-Cl)(mu2-F)(PPh3)4] (2) depending on the excess of TlF used. Both 1 and 2 were fully characterized, including X-ray structure determinations. Complex 1 reacts with dihydrogen to form the known ruthenium hydride complex [Ru(H)2(H2)(PPh3)3] upon hydrogenolysis of the Ru-F bond. The reaction of 1 with activated alkyl bromides (R-Br) gives the corresponding alkyl fluorides and the trinuclear complex [Tl(mu3-F)(mu2-F)(mu2-X)Ru2(mu2-Br)(mu2-F)(PPh3)4] (X=Br, F) (3), whose structure closely resembles that of 2. However, 1 is not active as catalyst for the nucleophilic fluorination of R-Br in the presence of thallium fluoride. The effect of the bridging coordination mode of fluoride on the Ru-F bond is discussed in terms of the HSAB principle, which suggests a more general model for predicting the stability of d6 and d8 complexes containing hard ligands (such as fluoro, oxo, and amido).     

Synthesis of a cyclic peptide containing norlanthionine: effect of the thioether bridge on peptide conformation

Two diastereomeric analogues of ring C of nisin incorporating a novel norlanthionine residue have been synthesized via a triply orthogonal protecting group strategy. A full structural study was carried out by NMR, which elucidated the conformational properties of the two peptides and enabled the identity of each diastereoisomer to be proposed.     

Co-detection of Copper and Lead in Artisanal Sugarcane Spirit Using Caffeic Acid-modified Graphite Electrodes

Caffeic acid (CA)-modified graphite electrodes [GE/poly(CA)] was applied to the co-detection of copper and lead in artisanal sugarcane spirit using square-wave anodic stripping voltammetry (SWASV). Electrochemical and morphological studies were performed, and a mechanism for polymerization was proposed. Electropolymerization, SWASV, and analysis conditions parameters were optimized. Interferents, repeatability, reproducibility, and addition and recovery tests were carried out. GE/poly(CA) shows a linear range from 15 to 705 μg/L with a limit of detection of 3.01 μg/L for Pb(II) and 4.50 μg/L for Cu(II). Real samples of artisanal sugarcane spirit were used, and the electrochemical results were compared with atomic absorption spectroscopy experiments.     

Simple functionalization of cellulose beads with pre-propargylated chitosan for clickable scaffold substrates

Concerning the increased market for bio-based materials and environmentally safe practices, cellulose-based beads are one of the more attractive alternatives. Thus, this work focuses on the generation of functional cellulose-based beads with a relatively simple and direct method of blending a pre-modified chitosan bearing the targeted functional groups and cellulose, prior to the formation of the beads, as a mean to have functional groups in the formed structure. To this end, chitosan was chemically modified with propargyl bromide in homogenous reaction conditions and then combined with cellulose in sodium hydroxide/urea solution and coagulated in nitric acid to produce spherical shaped beads. The successful chemical modification of chitosan was assessed by elemental analysis, as well as by Fourier-transform infrared spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The alkynyl moieties from the chitosan derivative, served as reactive functional groups for click-chemistry as demonstrated by the tagging of the commercial fluorophore Azide-Fluor 488 via CuI-catalysed alkyne-azide cycloaddition reaction, in aqueous media. This work demonstrates the one-step processing of multiple polysaccharides for functional spherical beads as a template for bio-based scaffolds such as enzyme immobilization for stimuli-response applications and bioconjugations.

     

Osteoarthritis subjects have differentiated lower extremity thermal skin response after the concurrent acute training session

Journal of Thermal Analysis and Calorimetry - This study investigated the thermal skin (Tsk) response of lower limbs in older adults with or without osteoarthritis before and after a concurrent...