Effect of confinement on the collapsing mechanism of a flexible polymer chain

In this paper, Brownian dynamics simulation (BDS) studies are executed to demonstrate the distinctive influences of the extent of confinement on the collapsing mechanism and kinetics of a flexible hydrophobic polymer chain in a poor solvent. The collapsing behavior is quantified by the time of collapse, which below a critical dimension of the confinement (h(c)), encounters a drastic reduction with a further strengthening in the degree of confinement. For dimensions greater than this critical one, the collapse occurs through the well-known hydrodynamic interaction (HI) controlled multiple-globule-mediated mechanisms. However, for channel dimensions less than this critical one, the collapse mechanism is drastically altered. Under such circumstances, the collapse gets predominantly controlled by the confinement effects (with negligible contribution of the HIs) and occurs via the formation of a single central globule. This central globule rapidly engulfs the noncondensed polymer segments, and in the process largely hastens up the collapsing event. Under such circumstances, the collapse time is found to decrease linearly with decrements in the channel height. On the contrary, for channel heights greater than h(c), the multiple-globule-mediated collapse is characterized by a collapse time that shows an exponential dependence on the channel height, rapidly attaining a state in which the confinement effect becomes inconsequential and HIs dictate the entire collapsing behavior. We further propose detailed arguments based on physical reasoning as well as free energy estimations to conclusively support the qualitative and quantitative nature of influences of the confinement on the polymer collapse.     

Formulation of photocleavable liposomes and the mechanism of their content release

In pursuit of designing photocleavable liposomes as drug delivery vehicles, we synthesized several amphiphilic lipids by connecting stearyl amine (as the non-polar tail) and charged amino acids (as polar heads) via the o-nitrobenzyl derivatives. The lipids containing Glu, Asp, and Lys amino acids were subjected to photocleavage reaction by UV light, and the overall spectral changes of the chromophoric o-nitrobenzyl conjugates were determined as a function of time. The experimental data revealed that the feasibility of the cleavage reaction, nature and magnitude of the spectral changes during the course of the cleavage reaction, and their overall kinetic profiles were dictated by the type of amino acid constituting the polar head groups. The cleavage reactions of the Asp and Glu containing lipids were found to be more facile than that of the lysine-containing lipid. Using these lipids, we formulated photocleavable liposomes, and investigated the photo-triggered release of an encapsulated (within the liposomal lumen) dye as a function of time. The kinetic data revealed that the release of the liposomal content conformed to a two-step mechanism, of which the first (fast) step involved the photocleavage of lipids followed by the slow release of the liposomal content during the second step. The overall mechanistic features intrinsic to the photocleavage of Asp, Glu and Lys containing o-nitrobenzyl conjugated lipids, and their potential applications in formulating liposomes (whose contents can be "unloaded" by the UV light) as drug delivery vehicles are discussed.     

Studies on manganese nodule leached residue 4. Physicochemical characterization and catalytic activity of acetic acid treated manganese nodule leached residue

The catalytic activity of water-washed manganese nodule leached residue (WMNLR) samples improved by treating with acetic acid. The effects of acetic acid treatment on the physicochemical properties and catalytic activity of manganese nodule leached residue have been studied. The surface area, surface oxygen, surface hydroxyl groups, surface acidity, electron donating properties, etc., increase gradually with acid treatment up to 0.5 M and thereafter show a decreasing trend. The rate constant of H2O2 decomposition, catalytic activity of CO oxidation, and esterification of acetic acid also show a similar trend to that of surface properties.     

Hydrogen bond and residence dynamics of ion-water and water-water pairs in supercritical aqueous ionic solutions: dependence on ion size and density

We have carried out a series of molecular dynamics simulations to investigate the hydrogen bond and residence dynamics of X(-)-water (X=F, Cl, and I) and pairs in aqueous solutions at a temperature of 673 K. The calculations are done at six different water densities ranging from 1.0 to 0.15 g cm(-3). The hydrogen bonds are defined by using a set of configurational criteria with respect to the anion(oxygen)-oxygen and anion(oxygen)-hydrogen distances and the anion(oxygen)-oxygen-hydrogen angle for an anion(water)-water pair. The F(-)-water hydrogen bonds are found to have a longer lifetime than all other hydrogen bonds considered in the present study. The lifetime of Cl(-)-water hydrogen bonds is shorter than that of F(-)-water hydrogen bonds but longer than the lifetime of water-water hydrogen bonds. The lifetimes of I(-)-water and water-water hydrogen bonds are found to be very similar. Generally, the lifetimes of both anion-water and water-water hydrogen bonds are found to be significantly shorter than those found under ambient conditions. In addition to hydrogen bond lifetimes, we have also calculated the residence times and the orientational relaxation times of water molecules in ion(water) hydration shells and have discussed the correlations of these dynamical quantities with the observed dynamics of anion(water)-water hydrogen bonds as functions of the ion size and density of the supercritical solutions.     

Affinity monolith chromatography

The combined use of monolithic supports with selective affinity ligands as stationary phases has recently given rise to a new method known as affinity monolith chromatography (AMC). This review will discuss the basic principles behind AMC and examine the types of supports and ligands that have been employed in this method. Approaches for placing affinity ligands in monoliths will be considered, including methods based on covalent immobilization, biospecific adsorption, entrapment, and the formation of coordination complexes. Several reported applications will then be presented, such as the use of AMC for bioaffinity chromatography, immunoaffinity chromatography, immobilized metal-ion affinity chromatography, dye-ligand affinity chromatography, and biomimetic chromatography. Other applications that will be discussed are chiral separations and studies of biological interactions based on AMC.     

Shuttling of nickel oxidation states in N4S2 coordination geometry versus donor strength of tridentate N2S donor ligands

Seven bis-Ni(II) complexes of a N(2)S donor set ligand have been synthesized and examined for their ability to stabilize Ni(0), Ni(I), Ni(II) and Ni(III) oxidation states. Compounds 1-5 consist of modifications of the pyridine ring of the tridentate Schiff base ligand, 2-pyridyl-N-(2'-methylthiophenyl)methyleneimine ((X)L1), where X = 6-H, 6-Me, 6-p-ClPh, 6-Br, 5-Br; compound 6 is the reduced amine form (L2); compound 7 is the amide analog (L3). The compounds are perchlorate salts except for 7, which is neutral. Complexes 1 and 3-7 have been structurally characterized. Their coordination geometry is distorted octahedral. In the case of 6, the tridentate ligand coordinates in a facial manner, whereas the remaining complexes display meridional coordination. Due to substitution of the pyridine ring of (X)L1, the Ni-N(py) distances for 1~5 < 3 < 4 increase and UV-vis λ(max) values corresponding to the (3)A(2g)(F)→(3)T(2g)(F) transition show an increasing trend 1~5 < 2 < 3 < 4. Cyclic voltammetry of 1-5 reveals two quasi-reversible reduction waves that correspond to Ni(II)→Ni(I) and Ni(I)→Ni(0) reduction. The E(1/2) for the Ni(II)/Ni(I) couple decreases as 1 > 2 > 3 > 4. Replacement of the central imine N donor in 1 by amine 6 or amide 7 N donors reveals that complex 6 in CH(3)CN exhibits an irreversible reductive response at E(pc) = -1.28 V, E(pa) = +0.25 V vs saturated calomel electrode (SCE). In contrast, complex 7 shows a reversible oxidation wave at E(1/2) = +0.84 V (ΔE(p) = 60 mV) that corresponds to Ni(II)→Ni(III). The electrochemically generated Ni(III) species, [(L3)(2)Ni(III)](+) is stable, showing a new UV-vis band at 470 nm. EPR measurements have also been carried out.     

Thiourea dioxide in water as a recyclable catalyst for the synthesis of structurally diverse dihydropyrido[2,3-d]pyrimidine-2,4-diones

A series of dihydropyrido[2,3-d]pyrimidine-2,4-diones derivatives were synthesized by the three-component reaction of 6-amino-1,3-dimethyl uracil, aromatic aldehydes, and 1,3-dicarbonyl compound catalyzed by thiourea dioxide in aqueous media. Importantly, the aqueous layer containing thiourea dioxide could be reused for several runs without significant loss in catalytic activity. This method provided several advantages such as inexpensive, recyclable catalyst, easier work-up, milder reaction conditions and environmental benign nature.     

Targeted screening of pesticides, veterinary drugs and mycotoxins in bakery ingredients and food commodities by liquid chromatography-high-resolution single-stage Orbitrap mass spectrometry

In the food industry, it is frequently necessary to check the quality of an ingredient to decide whether to use it in production and/or to have an idea of the final possible contamination of the finished product. The current need to quickly separate and identify relevant contaminants within different classes, often with legal residue limits on the order of 1-100?μg?kg(-1) , has led to the need for more effective analytical methods. With thousands of organic compounds present in complex food matrices, the development of new analytical solutions leaned towards simplified extraction/clean-up procedures and chromatography coupled with mass spectrometry. Efforts must also be made regarding the instrumental phase to overcome sensitivity/selectivity limits and interferences. For this purpose, high-resolution full scan analysis in mass spectrometry is an interesting alternative to the traditional tandem mass approach. A fast method for extracting and purifying bakery matrices was therefore developed and combined with the exploitation of ultra-high-pressure liquid chromatography (UHPLC) coupled to a Orbitrap Exactive? high-resolution mass spectrometer (HRMS). Extracts of blank, naturally contaminated and fortified minicakes, prepared through a combined use of industrial and pilot plant production lines, were analyzed at different concentration levels (1-100?μg?kg(-1) ) of various contaminants: a limit of detection at 10?μg?kg(-1) was possible for most of the analytes within all the categories analyzed, including pesticides, aflatoxins, trichothecene toxins and veterinary drugs. The application of accurate mass targeted screening described in this article demonstrates that current single-stage HRMS analytical instrumentation is well equipped to meet the challenges posed by chemical contaminants in the screening of both bakery raw materials and finished products. Copyright ? 2012 John Wiley & Sons, Ltd.     

Magnetic ordering in Ni–Cd ferrite

A series of Ni_1−xCd_xFe₂O₄ (0.0≤x≤0.8) were prepared by conventional double sintering ceramic method and sintered at 1200 °C for 6 h. X-ray diffraction results confirmed the single-phase spinel structures of all the samples. The Curie temperature decreases linearly with increasing Cd content, which is explained due to the weakening of the A–B exchange interaction. The sample with x=0.7 shows re-entrant type of spin glass phase transitions. The magnetic moment and saturation magnetization at 20 K are found to increase with Cd content up to x=0.5 and then tends to decrease for x>0.5. The increase in magnetic moment with cadmium is attributed to Neel's two sublattice (A- and B-sublattice) collinear models according to which the magnetic moment is the vector sum of the lattice magnetic moment. The decrease in magnetization for x>0.5 obeys the Yafet–Kittel (Y–K) model. The increase in Y–K angles for x>0.3 indicates the increased tendency for triangular spin arrangements on B-sites. This suggests the existence of a canted spin structure in the ferrite system with higher content of Cd.