Universal consequences of the presence of excluded volume interactions in dilute polymer solutions undergoing shear flow

The role of solvent quality in determining the universal material properties of dilute polymer solutions undergoing steady simple shear flow is examined. A bead-spring chain representation of the polymer molecule is used, and the influence of solvent molecules on polymer conformations is modelled by a narrow Gaussian excluded volume potential that acts pairwise between the beads of the chain. Brownian dynamics simulations data, acquired for chains of finite length, and extrapolated to the limit of infinite chain length, are shown to be model independent. This feature of the narrow Gaussian potential, which leads to results identical to a delta-function repulsive potential, enables the prediction of both universal crossover scaling functions and asymptotic behavior in the excluded volume limit. Universal viscometric functions, obtained by this procedure, are found to exhibit increased shear thinning with increasing solvent quality. In the excluded volume limit, they are found to obey power law scaling with the characteristic shear rate beta, in close agreement with previously obtained renormalization group results. The presence of excluded volume interactions is also shown to lead to a weakening of the alignment of the polymer chain with the flow direction.     

Kinetic studies of nonaqueous polymerization of methyl methacrylate initiated by ferric laurate–n-hexyl amine system

The polymerization of methyl methacrylate was studied in carbon tetrachloride medium with ferric laurate, a metal soap, in combination with n-hexyl amine as the initiator system at 60°C. The rate of polymerization was found to be linear with the monomer concentration and proportional to the square root of both ferric ion and amine concentration. A reaction scheme involving initial complex formation between ferric ion and amine and subsequent reaction of the complex with the solvent molecule to produce free radicals responsible for initiation of polymerization has been postulated to account for the observed results.     

Amino Acid based cationic surfactants in aqueous solution: physicochemical study and application of supramolecular chirality in ketone reduction

The present study provides a molecular understanding of the origin of the chirality in aqueous micelles and its correlation with the proficiency of stereoselective ketone reduction. The effects of varied headgroup architecture on the surface-active properties as well as on other microstructural parameters were studied and correlated to the structural differences of these naturally occurring amino acid containing surfactants (1-4). Micropolarity sensed by pyrene showed that the micelles prepared using 1-4 are mostly hydrated; particularly large headgroup size surfactant produces more polar environment. A theoretical study was done to quantify the varied spatial dissymmetry for all four surfactants. Asymmetric reduction of prochiral ketones was carried out at the aqueous micellar interface of these chiral amphiphiles by exploiting the supramolecular chirality as evidenced from a circular dichroism study. The enantioselectivity of the reduction process is rationally improved through increase in spatial dissymmetry and steric constraint imposed at the micellar interface by the polar head of surfactants.     

Benzoxazine-bismaleimide blends: Curing and thermal properties

A blend of bisphenol A based benzoxazine (Bz-A) and a bismaleimide (2,2-bis[4(4-maleimidophenoxy) phenyl] propane (BMI), was thermally polymerised in varying proportions and their cure and thermal characteristics were investigated. The differential scanning calorimetric analysis, supplemented by rheology confirmed a lowering of the cure temperature of BMI in the blend implying catalysis of the maleimide polymerisation by benzoxazine. FTIR studies provided evidences for the H-bonding between carbonyl group of BMI and -OH group of polybenzoxazine in the cured matrix. The cured matrix manifested a dual phase behaviour in SEM and DMTA with the minor phase constituted by polybenzoxazine dispersed in an interpenetrating polymer network (IPN) of polybenzoxazine and cured BMI. The IPN possessed improved thermal stability over the constituent polybenzoxazine. A benzoxazine monomer possessing allyl functional groups, 2,2′-bis(8-allyl-3-phenyl-3,4-dihydro-2H-1,3-benzoxazinyl) propane (Bz-allyl) was reactively blended with the same bismaleimide in varying stoichiometric ratios (Bz-allyl/BMI), where the curing involved mainly Alder-ene reaction between allyl- and maleimides groups and ring-opening polymerisation of benzoxazine. The rheological analysis showed the absence of catalytic polymerisation of BMI in this case. The overall processing temperature was lowered in the blend owing to the co-reaction of the two systems to form a single-phase matrix. The cured resins of both Bz-A/BMI and Bz-allyl/BMI blends exhibited better thermal stability than the respective polybenzoxazines. The T_g of the IPN was significantly improved over that of polybenzoxazine (Bz-A). However, the co-reaction resulted in a marginal decrease in the T_g of the system in comparison to the polybenzoxazine (Bz-allyl).     

First principles study of small palladium cluster growth and isomerization

Structures and physical properties of small palladium clusters Pd_n up to n = 15 and several selected larger clusters were studied using density functional theory under the generalized gradient approximation. It was found that small Pd_n clusters begin to grow 3‐dimensionally at n = 4 and evolve into symmetric geometric configurations, such as icosahedral and fcc‐like, near n = 15. Several isomers with nearly degenerate average binding energies were found to coexist and the physical properties of these clusters were calculated. For several selected isomers, relatively moderate energy barriers for structural interchange for a given cluster size were found, implying that isomerization could readily occur under ambient conditions. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Tetrahydroepoxides and diol epoxides of benz[c]acridine

The chemical synthesis and NMR characterization of the benzo ring tetrahydro- and diol epoxides of the carcinogen benz[c]acridine are described.     

Partitioning of quencher ions in the micellar microenvironment of polyoxyethylene nonyl phenol

This paper has explored the quenching of fluorescence of the dye safranine T (ST) by the inorganic cations viz Cu2+, Co2+, Ni2+ and Mn2+ in micellar solutions of the surfactant dioxyethylene nonyl phenol (Igepal CO-210), pentaoxyethylene nonyl phenol (Igepal CO-520) and dodecaoxyethylene nonyl phenol (Igepal CO-720). The quenching results have been calculated in light of stern volmer equation (SV) to evaluate the extent of interaction between the fluorophore (ST) and quencher. The average concentration of the quencher ions in the micelle have been determined. The quenching efficiency of ST by inorganic ions in micellar medium is lower than that in aqueous medium. The results show that the ions get partitioned in the micellar medium. The values of the partition coefficient of the ions decrease with increase in HLB value and number of oxyethylene groups in Igepal.     

Superpositions of chiral states in the presence of electric dipole, magnetic dipole, and electric quadrupole interactions

This paper is a straightforward generalization of Maierle-Harris proposal regarding parity implications on the superpositions of chiral states of a molecule. It is shown that the inclusion of electric quadrupole and magnetic dipole interactions removes several of restrictions on the preparation of superpositions of mid R:L and mid R:R states of a chiral molecule. It is also found that the dephasing of mid R:L and mid R:R superpositions, due to the spontaneous emission from the chiral molecule, has opposing contributions from electric quadrupole-magnetic dipole and electric dipole interactions.     

Novel solid-phase extraction and preconcentration technique coupled with ICP-AES for the determination of Cr(III), Ni(II), and Zn(II) in various water samples

Newly synthesized 2-propylpiperidine-1-carbodithioate (2-PPC) was used for the extraction of Cr(III), Ni(II), and Zn(II) from various water samples. In the present investigation, the use of a syringe loaded with sorbent for the separation and enrichment of Cr(III), Ni(II), and Zn(II) prior to their determination by inductively coupled plasma-atomic emission spectrometry (ICP-AES) was proposed to substitute the batch and column techniques. The described method was compared with the column technique with respect to fastness, simplicity, recovery, and risk of contamination. The syringe was loaded with 1.0 g of sorbent in order to retain the analyte elements. Next, 7.0 mL of sample solution (pH 5.0 ± 0.2) was drawn into the syringe in 15 s and discharged over 15 s. Then, an eluent (3.0 M HCl) was drawn into the syringe and ejected back to desorb the analyte elements. At the optimum conditions, the percentage recoveries of Cr(III), Ni(II), and Zn(II) were in the range of 94.50 to 99.62% with a standard deviation (S.D.) of 0.03%. The elements could be concentrated by drawing and discharging several portions of sample successively and eluting only one time. The detailed study of various interferences proved the method to be highly selective. The risk of contamination is less than that with the column technique. The method was successfully applied to the determination of Cr(III), Ni(II), and Zn(II) in spiked and natural water samples. The results obtained are in good agreement with those obtained by the reported methods at the 95% confidence level. The text was submitted by the authors in English.     

New sphingolipids and a sterol from a lobophytum species of the Indian ocean

Chemical investigation of a soft coral species of the genus Lobophytum has resulted in the isolation of three new sphingolipids--(2S,3S,4R)-2-nonadecanoylamino-octadecane-1,3,4-triol (1), (2S,3R,4E,8E)-[(2'R)-2'-hydroxyheptadecanoylamino]-4,8-octadecadiene-1,3-diol (2), 1-O-(beta-D-glucopyranosyl)-(2S,3R,4E,8E)-2-[(2'R)-2'-hydroxynonadecanoylamino]-9-methyl-4,8-octadecadiene-1,3-diol (3) and a sterol--(24S)-ergost-5-en-3beta,7beta-diol (4) along with the known sphingolipid--(2S,3R,4E,8E)-2-hexadecanoylamino-4,8-octadecadien-1,3-diol (5) which showed cytotoxicity against human peripheral blood mononuclear cells (PBMC).