Interactions between aminoacids and alcohols in water at 25 °C

The enthalpies of dilution of ternary aqueous solutions containing an alcohol (ethanol,n-propanol,n-butanol or tert-butanol) and an aminoacid or a peptide (glycine, glycyl-glycine or glycyl-glycyl-glycine), were measured at 25 °C. The results were used to calculate pair cross interaction parameters between solutes. The coefficients of virial expansion of the excess enthalpies are compared with those referring to solutions containing the same alcohols and other structure-breaking solutes (urea, thiourea and biuret). The enthalpic pair parameter for the systems glycine-alcohols shows the same trend, as reported in the literature, for similar structure-breaking solutes, with a maximum in the cross coefficients when reported versus the self pair interaction coefficients of alcohols. The results are interpreted in terms of a prevailing release of water from the cospheres of alcohols.

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Zusammenfassung Die Verdünnungsenthalpien ternärer wässeriger Lösungen, die einen Alkohol (Ethanol,n-Propanol,n-Butanol odertert-Bulanol) und eine Aminosäure oder ein Peptid (Glycin, Glycil-glycin oder Glycyl-glycyl-glycin) enthalten, wurden bei 25 °C gemessen. Die erhaltenen Werte wurden zur Berechnung der Parameter der zwischen den Molekülen der verschiedenartigen gelösten Stoffe auftretenden Wechselwirkungen herangezogen. Die Koeffizienten der Virialentwicklung der Überschussenthalpien werden mit denen verglichen, die sich auf die gleichen Alkohole und andere strukturbrechende gelöste Stoffe (Harnstoff, Thioharnstoff und Biuret) enthaltenden Lösungen beziehen. Die Enthalpieparameter der Systeme Glycin-Alkohole zeigen den in der Literatur für ähnliche strukturbrechende gelöste Stoffe mitgeteilten Trend nämlich ein Maximum in der Kurve, die beim Auftragen der Koeffizienten der Wechselwirkung zwischen verschiedenartigen Molekülen gegen die Koeffizienten der Wechselwirkung zwischen den Alkoholmolekülen erhalten wird. Die Ergebnisse werden unter Annahme eines bevorzugten Austritts von Wasser aus der Kosphäre der Alkohole interpretiert.

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This work is financially supported by the Italian Ministry of Public Education and by the Italian National Research Council.     

Four-membered rings family in the Si–O extended rocking IR band from quantum chemistry calculations

We calculate the vibrational modes of four-membered rings family in the Si–O extended rocking infrared for vitreous SiO₂ materials. In particular these species are obtained in the early stages of the sol–gel process. We have performed high quality quantum-mechanical calculations based on cluster models and gradient corrected density functional theory, (GC-DFT). Three possible configurations were obtained, a regular planar, a slightly deformed or quasi-planar, and a deformed ring. According to our result, the more probable one is the slightly deformed configuration. The calculated vibrational frequencies are compared with experimental IR and Raman results obtaining very good agreement. Also, we calculated geometries and vibrational frecuencies for three-membered rings. We found that 3- and 4-fold rings show evidence of decoupled vibrational modes, those modes are compared with a Raman spectrum obtaining very good coincidence.     

Hydrophobic effect in aqueous solutions of nonelectrolytes. II. Cross-interactions of alkylureas

The heats of mixing of the aqueous solutions of monomethylurea, monoethylurea, 1,3-dimethylurea, 1,3-diethylurea were determined at 25°C. The excess enthalpies obtained are expressed in virial form, in terms of pair and triplet interaction coefficients. A method previously discussed for predicting the excess enthalpies and the interaction coefficients of ternary solutions has been applied to the alkylureas. The large deviations between the experimental and calculated values, led to the modification of that method, which better accounts for the marked mixed character of these substances.     

Bacteriostatic Behavior of PLA-BaTiO3 Composite Fibers Synthesized by Centrifugal Spinning and Subjected to Aging Test

The present work investigated the effect of Polylactic acid (PLA) fibers produced by centrifugal spinning with incorporated BaTiO₃ particles to improve their bacteriostatic behavior. The PLA matrix and three composites, presenting three different amounts of fillers, were subjected to UV/O₃ treatment monitoring the possible modifications that occurred over time. The morphological and physical properties of the surfaces were characterized by different microscopic techniques, contact angle, and surface potential measurements. Subsequently, the samples were tested in vitro with human dermal fibroblasts (HDF) to verify the cytotoxicity of the substrates. No significant differences between the PLA matrix and composites emerged; the high hydrophobicity of the fibers, derived by the polymer structure, represented an obstacle limiting the fibroblast attachment. Samples underwent bacterial exposure (Staphylococcus epidermidis) for 12 and 24 h. Increasing the concentration of BT, the number of living bacteria and their distribution decreased in comparison with the PLA matrix suggesting an effect of the inorganic filler, which generates a neutralization effect leading to reactive oxygen species (ROS) generation and subsequently to bacterial damages. These results suggest that the barium titanate (BT) fillers clearly improve the antibacterial properties of PLA fibers after aging tests made before bacterial exposure, representing a potential candidate in the creation of composites for medical applications.     

Detecting exponential dichotomy on the real line: SVD and QR algorithms

In this paper we propose and implement numerical methods to detect exponential dichotomy on the real line. Our algorithms are based on the singular value decomposition and the QR factorization of a fundamental matrix solution. The theoretical justification for our methods was laid down in the companion paper: “Exponential Dichotomy on the real line: SVD and QR methods.”     

Quantum cascade laser-based photoacoustic spectroscopy of volatile chemicals: application to hexamethyldisilazane

The use of photoacoustic spectroscopy and mid-infrared quantum-cascade lasers (QCLs) for the detection of hexamethyldisilazane (HMDS) is reported. A detection limit of 200 parts in 10(9) is found using a Fabry-Perot QCL operated at 8.4 microm in pulsed mode and a photoacoustic cell equipped with four electret microphones. The laser multimode spectrum matches the range of the N-H bending absorption band of HMDS. Further improvements to reach lower detection limits are discussed.