The anomalous melting behavior of water in aqueous PVME solutions

The Wertheim lattice thermodynamic perturbation theory is used to predict the liquid-liquid and solid-liquid coexistence data for a model polymer solution. The theory predicts bimodal LCST phase behavior and an unusual step with composition in the solid-liquid equilibrium of the solvent.The theoretical solid-liquid equilibrium calculations are used to interpret experimental data obtained for aqueous solutions of poly(vinyl methyl ether) (PVME), which is known to show bimodal LCST phase behavior. An experimental method is proposed, employing Fourier transform infrared (FTIR) spectroscopy to determine the equilibrium melting line of water in the presence of PVME. In addition, the complete melting line of water is obtained by partial integration of the melting endotherm observed using modulated temperature differential scanning calorimetry (MTDSC). Both, the FTIR and MTDSC methods are in good agreement, experimentally confirming the predicted step with composition in the solid-liquid equilibrium. This peculiar concentration dependence of the melting curve of ice provides a new explanation for the inhibited crystallization of water in aqueous PVME solutions, since the actual supercooling (at high polymer concentration) is smaller than it could be anticipated for a conventional course of the melting curve. Hence, the vicinity of the glass transition region in these highly concentrated polymer mixtures leads to a dramatic slowing down of the nucleation rate and thus the subsequent crystallization. Moreover, the atypical shape of the equilibrium melting line also provides a new explanation for the double melting endotherm observed in (MT)DSC experiments, which is conventionally attributed to the melting at different temperatures of bound and free water.     

A Bentonitic Clay Assisted Method for the Preparation of 2-(R-Anilino)-1, 4-Naphthoquinones

A new and efficient protocol to prepare 2-(R-anilino)-1,4-naphthoquinones in quantitative yields is presented. This synthesis occurs under mild conditions by reacting the corresponding aniline and 1,4-naphthoquinone in the presence of a bentonitic clay. The role of the clay is explained in terms of a reaction mechanism in which an activated complex is formed by the reaction of 1,4-naphthoquinone with Lewis acid sites of the clay. Based on the chemical composition of the clay, with Fe³⁺ sites, the last step of the mechanism is proposed to involve an oxidation-reduction reaction.     

Irradiation delayed oxidative rancidity in tuna loins

TBA numbers of irradiated and control tuna samples reached a maximum after 25 and 10 days of cold storage, respectively. A decline occurred thereafter for both samples. These changes may be correlated with sensory acceptability scores.     

Adsorption of Arsenic on Activated Charcoal

This study explores the adsorption behavior of As(III) and As(V) on activated charcoal under the various conditions of solution pH and temperature. The adsorption loading of As(III) remains constant in the pH range from 0.16 to 3.5, while that of As(V) shows a maximum value at pH2.35 when the pH varies from 0.86 to 6.33. The isosteric heat of adsorption for As(III) varies from 4 to 0.75 Kcal/mole and that for As(V), from 4 to 2 Kcal/mole with varying surface loading. The magnitude of these values suggests that the adsorption of arsenic is by physisorption and due to weak forces such as Van der Waals forces. Activated charcoal adsorbs As(V) by 2.5% of its own weight while it absorbs As(III) by 1.2% of its own weight when the equilibrium concentration of each species is 22 × 10^?2 molar. Since arsenic has appreciable adsorbability on activated charcoal, this adsorbent may be a viable candidate to be used for removing arsenic from solution. Further studies to determine more information on the selectivity of arsenic over other valuable metal ions and the ones to determine the effects of other cations such as, ferric, calcium, and magnesium ions are suggested as a next step.     

Theory of "frozen waves": modeling the shape of stationary wave fields

In this work, starting by suitable superpositions of equal-frequency Bessel beams, we develop a theoretical and experimental methodology to obtain localized stationary wave fields (with high transverse localization) whose longitudinal intensity pattern can approximately assume any desired shape within a chosen interval 0 < or = z < or = L of the propagation axis z. Their intensity envelope remains static, i.e., with velocity v = 0, so we have named "frozen waves" (FWs) these new solutions to the wave equations (and, in particular, to the Maxwell equation). Inside the envelope of a FW, only the carrier wave propagates. The longitudinal shape, within the interval 0 < or = z < or = L, can be chosen in such a way that no nonnegligible field exists outside the predetermined region (consisting, e.g., in one or more high-intensity peaks). Our solutions are notable also for the different and interesting applications they can have--especially in electromagnetism and acoustics--such as optical tweezers, atom guides, optical or acoustic bistouries, and various important medical apparatuses.     

Engineering thermal stability in RNA phage capsids via disulphide bonds

The RNA bacteriophages, a group that includes phages Qbeta and MS2, have a number of potential bionanotechnological applications, including cell specific drug delivery and as substrates for the formation of novel materials. Despite extensive sequence identity between their coat protein subunits, and an almost identical three-dimensional fold, Qbeta and MS2 capsids have dramatically different thermal stabilities. The increased stability of Qbeta has been correlated with the inter-subunit disulphide bonds present in that capsid and not present in MS2. We have tested this hypothesis directly using mass spectrometry. Analysis of the dissociated coat protein subunits suggests that inter-molecular disulphides are formed at the capsid five-fold but may not be at the three-fold axes. This conclusion has been tested by engineering disulphide cross-links into either the five-fold or three-fold positions of the recombinant MS2 capsid. Five-fold cross-linking results in a mutant with stability properties similar to those of Qbeta. Three-fold cross-linking results in a mutant unable to assemble T = 3 shells, implying that five-fold structures are on pathway to capsid assembly in these phages. The results demonstrate how it is possible to redesign the physical properties of phage shells and may be of general relevance to future applications of viruses and virus-like particles.