Fluorometric and isothermal titration calorimetric studies on binding interaction of a telechelic polymer with sodium alkyl sulfates of varying chain length

Steady-state fluorescence measurements and isothermal titration calorimetric experiments have been performed to study the interaction between a telechelic polymer, pyrene-end-capped poly(ethylene oxide) (PYPY), and sodium alkyl sulfate surfactants having decyl, dodecyl, and tetradecyl hydrocarbon tails. Fluorometric results suggest polymer-surfactant interaction in the very low range of polymer concentrations. The relative variation in the excimer to monomer pyrene emission intensities with varying surfactant concentration reveals that initial addition of surfactant favors intramolecular preassociation until the surfactant molecules start binding with the ethylene oxide (EO) chain. With the growing number of surfactant aggregates along the EO chain, the association becomes hindered due to the polyelectrolyte effect. The results from microcalorimetric titrations in the low concentration range of PYPY solution (approximately 10(-6) M) with alkyl sulfates suggest two kinds of surfactant-polymer interactions, one with the polymer hydrophobic end groups and the other with the ethylene oxide backbone. The overall polymer-surfactant interaction starts at a much lower surfactant concentration for the hydrophobically modified polymers compared to that in the case of unsubstituted poly(ethylene oxide) homopolymer. From the experiments critical aggregation concentration values and the second critical concentration where free micelles start forming have been determined. An endeavor has been made to unveil the mechanism underlying the corresponding associations of the surfactants with the polymer.     

Improved in‐solution trypsin digestion method for methanol–chloroform precipitated cellular proteomics sample

Methanol–chloroform based protein precipitation is an essential step in many liquid chromatography–tandem mass spectrometry‐based cellular proteomics applications. However, re‐solubilization of the total protein precipitate is difficult using regular in‐solution digestion protocol. Sodium deoxycholate is reported as an efficient surfactant for re‐solubilization of membrane fractions. In this study, we demonstrated an application combining methanol–chloroform based protein precipitations and deoxycholic acid assisted re‐solubilization of pellets to evaluate the improvement of protein identifications in mass spectrometry‐based bottom‐up proteomics. We evaluated the modified method using an equal amount of Raw 264.7 mouse macrophage cell lysate. Detailed in‐solution trypsin digestion studies were presented on methanol–chloroform precipitated samples with or without deoxycholic acid treatments and compared with popular sample digestion methods. A mass spectrometric analysis confirmed an 82% increase in protein identification in deoxycholic acid‐treated samples compared to other established methods. Furthermore, liquid chromatography–tandem mass spectrometry analysis of an equal amount of proteins from methanol–chloroform precipitated, and methanol–chloroform/deoxycholic acid‐treated macrophage cell lysate showed a 14% increase and 27% unique protein identifications. We believe this improved digestion method could be a complementary or alternative method for mammalian cell sample preparations where sodium dodecyl sulfate based lysis buffer is frequently used.     

Effect of nanocavity confinement on the rotational relaxation dynamics: 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine in micelles

In continuation of our recent study on the steady state photophysics of a biologically active beta-carboline derivative, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), in the present article we have investigated the effect of nanocavity confinement on the excited state dynamics and rotational relaxation of the probe using picosecond time resolved fluorescence and fluorescence anisotropy techniques. The polarity dependent intramolecular charge transfer process is responsible for the remarkable sensitivity of this biological fluorophore in micellar environments. The fluorescence anisotropy decay of AODIQ incorporated inside the micelle is biexponential. The rotational motion of the probe was interpreted on the basis of a two step model consisting of a fast restricted rotation of the probe and a slow lateral diffusion of the probe in the micelle; both coupled to the overall rotation of the micelle. Experimental results reveal that micellar environment causes significant retardation of both the wobbling as well as the translational motion of the probe.     

A clay-mediated, regioselective synthesis of 2-(aryl/alkyl)amino-thiazolo[4,5-c]carbazoles

The 3-aminocarbazoles 1a-e were condensed with phenyl and benzyl isothiocyanates on montmorillonite K10 clay or TLC-grade silica gel at room temperature to furnish efficiently the N-phenyl and N-benzylthioureidocarbazoles, 2a-e and 2f, respectively, within minutes. When adsorbed on montmorillonite K10 clay impregnated with para-toluene sulfonic acid (1:1, w/w) and heated at 60-70 °C, 2a-e and 2f furnished the 2-anilino and 2-benzylaminothiazolo[4,5-c]carbazoles, 3a-e and 3f, respectively, regioselectively in high yields. The cyclisation was also effective for the N-methylthioureidocarbazoles 2g-i.     

SEM analysis and gas permeability test to characterize polysulfone membrane prepared with polyethylene glycol as additive

Phase inversion method is applied to prepare flat sheet asymmetric polymeric membranes from homogeneous solution of 12 wt% polysulfone (PSf) with two different solvents--N-methyl-2-pyrrolidone (NMP) and dimethyl acetamide (DMAc). 5.0 wt% polyethylene glycol (PEG) of three different molecular weight (400, 6000, and 20,000 Da) is used as the polymeric additives in the casting solution. Membranes are characterized by two different techniques viz. scanning electron microscopy (SEM) and gas permeation tests. Finally, the results of both the techniques are compared with those calculated from pure water permeation tests using Hagen-Poiseuille equation. It is found that though the values obtained from all the techniques vary from each other, their trend with increase in molecular weight of PEG seems to be the same. It is seen that when molecular weight of PEG increases from 400 to 20,000 Da, the mean pore size of the prepared membranes decreases, while the porosity and pore density show an increasing trend; the pressure normalized gas flux rises significantly and the thickness of the top layer of the prepared membrane sheet increases.     

A mild and expedient one-pot synthesis of substituted benzimidazoles in water using a phase-transfer catalyst

Abstract  1-Alkyl/phenyl-2-arylbenzimidazoles have been synthesized in very good to excellent yields by a one-pot condensation of N-alkyl/phenyl-o-phenylenediamines with aryl aldehydes in water at room temperature using cetylpyridinium bromide as a cheap and eco-friendly catalyst. Graphical abstract        

Polymerization of Acrylonitrile with Ceric lon-2-Propanethiol as Initiator System

The kinetics of the polymerization of arylonitrile with ceric ammonium sulfate in the presence of 2-propanethiol as the redox initiator system in aqueous solution has been investigated. The rate of polymerization was found to be proportional to the square root of both ceric ion and thiol concentrations, and the monomer exponent was close to 1.5. Spectral studies indicated that there is a complex formation between ceric ion and the monomer acrylonitrile. A kinetic scheme, based on initial formation of this complex and its subsequent reaction with the thiol to produce the free radicals (RS.) responsible for initiation has been postulated to account for the observed results. The activation energy and different kinetic and transfer constants for the system have also been evaluated.     

Heavy Meson Spectroscopy

In this article we give a review of certain aspects of the present understanding of spectroscopy of heavy mesons and constituent quark masses in the light of non-relativistic potential model approach motivated by quantum chromodynamics. We find that the one gluon exchange at short distance and colour-confining interaction at large distance which is pure scalar (or scalarvector admixture with dominant scalar interaction) under the Lorentz transformation, can explain only partially the present data on 1 P states of bb and bb states. The S-wave data, that are available at present, however can be understood with both scalar confinement or scalar-vector admixture with scalar-dominant interaction.