Surface properties of poly(N-monoalkylmaleamic acid-alt-styrene) sodium salts: effect of the molecular weight and the side chain length

The surface properties of poly(N-monoalkylmaleamic acid-alt-styrene) sodium salts are studied as a function of the molecular weight and the size of the linear alkyl lateral chain of the polyelectrolyte. The experimental results are well described by the Gibbs-Szyszkowski treatment. Both the surface tension behavior and the standard free energy of adsorption depend on the polyelectrolyte side chain and on the average molecular weight, M(w). An M(w)-dependent contribution to the free energy of adsorption ranging from -1.21 to -1.05 kJ for mole of methylene groups is found. The area covered by monomer units increases with M(w) and the sizes of side chains are similar to those reported in small-molecule systems. The nature of the functional group amide in the side chain has practically no effect on the surface properties as compared with the ester group in this kind of polyelectrolytes.     

Kinetics and mechanism of the anilinolysis of aryl 4-nitrophenyl carbonates in aqueous ethanol

[Chemical reaction: See text] The reactions of anilines with 4-nitrophenyl, 4-methylphenyl, and 4-chlorophenyl 4-nitrophenyl carbonates (BNPC, MPNPC and ClPNPC, respectively) are studied kinetically in 44 wt % ethanol-water, at 25.0 degrees C, with an ionic strength of 0.2 M (KCl). Plots of k(obsd) vs [amine] are linear, with the slopes (kN) independent of pH. The Br?nsted-type plots (log k(N) vs pKa of conjugate acids of anilines) are linear, with slopes beta = 0.65, 0.85, and 0.78 for the reactions of anilines with BNPC, MPNPC, and ClPNPC, respectively. The values of the slopes for the two latter reactions are in accordance with those obtained in stepwise mechanism where breakdown to product of a zwitterionic tetrahedral intermediate is the rate-determining step. On the other hand, the beta value for the reactions of BNPC is at the upper limit of those found for concerted mechanisms. The kinetic results for the reactions of anilines with BNPC correlates well with those for the concerted reactions of the same amines with 4-methylphenyl and 4-chlorophenyl 2,4-dinitrophenyl carbonates: A plot of the calculated log k(N) values (through a multiple parametric equation) vs the experimental log k(N) values is linear with unity slope and zero intercept, which confirms the concerted mechanism for the latter three reactions.     

Siliceous mesoporous material templated with hexadecyltrimethylammonium bromide–sodium dehydrocholate mixed micelles

A mixture of sodium dehydrocholate (NaDHC) and hexadecyltrimethylammonium bromide (HDTAB) was employed as a template to produce mesoporous silica. The obtained material shows the same structure as common MCM-41 sieves, but the pore radius distribution is narrower than that of the material produced with the same concentration of pure HDTAB. The average pore radius is also larger than that of the pure HDTAB-templated material.     

A simple strategy for determining ethanol in all types of alcoholic beverages based on its on-line liquid-liquid extraction with chloroform, using a flow injection system and Fourier transform infrared spectrometric detection in the mid-IR

In this work, a simple strategy for the determination of ethanol in all types of alcoholic beverages using Fourier transform infrared spectrometric detection has been developed. The methodological proposal includes the quantitative on-line liquid-liquid extraction of ethanol with chloroform, through a sandwich type cell equipped with a PTFE membrane, using a two-channel manifold; and direct measurement of the analyte in the organic phase, by means of Fourier transform infrared spectrometry. The quantification was carried out measuring the ethanol absorbance at 877 cm⁻¹_, corrected by means of a baseline established between 844 and 929 cm⁻¹. The procedure, which does not require any sample pretreatment (except for the simple degassing of beer and gassy wine samples, and a simple dilution of spirits with water), was applied to determine ethanol in different alcoholic beverages such as beers, wines and spirits. The results obtained highly agree with those obtained by a derivative FTIR spectrometric procedure, and by head space-gas chromatography with FID detection. The proposed method is simple, fast, precise and accurate. Moreover, it can be easily adapted to any infrared spectrometer equipped with a standard transmission IR cell, and provides attractive analytical features, which are comparable to, or better than those offered by other published methods. In consequence, it represents a valid alternative for the determination of ethanol in alcoholic beverages, and could be suitable for the routine control analysis.     

Melting a Hubbard dimer: benchmarks of ‘ALDA’ for quantum thermodynamics

The competition between evolution time, interaction strength, and temperature challenges our understanding of many-body quantum systems out-of-equilibrium. Here, we consider a benchmark system, the Hubbard dimer, which allows us to explore all the relevant regimes and calculate exactly the related average quantum work. At difference with previous studies, we focus on the effect of increasing temperature, and show how this can turn the competition between many-body interactions and driving field into synergy. We then turn to use recently proposed protocols inspired by density functional theory to explore if these effects could be reproduced by using simple approximations. We find that, up to and including intermediate temperatures, a method which borrows from ground-state adiabatic local density approximation improves dramatically the estimate for the average quantum work, including, in the adiabatic regime, when correlations are strong. However at high temperature and at least when based on the pseudo-LDA, this method fails to capture the counterintuitive qualitative dependence of the quantum work with interaction strength, albeit getting the quantitative estimates relatively close to the exact results.     

Theoretical models to predict the inhibitory effect of ligands of sphingosine kinase 1 using QTAIM calculations and hydrogen bond dynamic propensity analysis

We report here the results of two theoretical models to predict the inhibitory effect of inhibitors of sphingosine kinase 1 that stand on different computational basis. The active site of SphK1 is a complex system and the ligands under the study possess a significant conformational flexibility; therefore for our study we performed extended simulations and proper clusterization process. The two theoretical approaches used here, hydrogen bond dynamics propensity analysis and Quantum Theory of Atoms in Molecules (QTAIM) calculations, exhibit excellent correlations with the experimental data. In the case of the hydrogen bond dynamics propensity analysis, it is remarkable that a rather simple methodology with low computational requirements yields results in excellent accord with experimental data. In turn QTAIM calculations are much more computational demanding and are also more complex and tedious for data analysis than the hydrogen bond dynamic propensity analysis. However, this greater computational effort is justified because the QTAIM study, in addition to giving an excellent correlation with the experimental data, also gives us valuable information about which parts or functional groups of the different ligands are those that should be replaced in order to improve the interactions and thereby to increase the affinity for SphK1. Our results indicate that both approaches can be very useful in order to predict the inhibiting effect of new compounds before they are synthesized.     

4,6‐Dimethyl‐2‐(3‐pyrid­yl)quinolin‐5‐amine

The title compound, C₁₆H₁₅N₃, shows a hindrance effect between adjacent amino and methyl groups that leads to a structural distortion, which is reflected in the non‐planarity of the quinoline entity and in the bond angles and distances. The crystal packing consists of chains along the b axis sustained by an inter­molecular hydrogen bond between the amino group and the N atom of the pyridyl ring.     

Polyelectrolyte complex dispersions with a high colloidal stability controlled by the polyion structure and titrant addition rate

Three ionic/nonionic random copolymers of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS) with either t-butyl acrylamide (TBA) or methyl methacrylate (MM), were used in the preparation of some polyelectrolyte complex dispersions (PCD) with two strong polycations of integral type, poly(diallyldimethylammonium chloride) (PDADMAC), and an ionene type polycation, containing 95 mol% N,N-dimethyl-2-hydroxypropyleneammonium chloride repeat units (PCA₅). The novelty of the paper is that PCDs with a high colloidal stability, both before and after the complex stoichiometry, were obtained even with hydrophilic/hydrophobic polyanions, with a high titrant addition rate (TAR), a less explored parameter, which allows a fine control of PCDs aggregation level, in salt-free aqueous solutions. The characteristics of PCDs were also correlated with the polyanion average charge density and the structure of the nonionic comonomer, at a constant TAR, the polyanion with the lowest charge density leading to the highest turbidities and the lowest colloidal stabilities. A mechanism of the PCDs colloidal stabilization as a function of TAR was suggested in the paper.