Dissolution and regeneration of cellulose in NaOH/thiourea aqueous solution

A novel cellulose solvent, 1.5 M NaOH/0.65 M thiourea aqueous solution, was used to dissolve cotton linters having a molecular weight of 10.1 × 10⁴ to prepare cellulose solution. Regenerated cellulose (RC) films were obtained from the cellulose solution by coagulating with sulfuric acid (H₂SO₄) aqueous solution with a concentration from 2 to 30 wt %. Solubility of cellulose, structure, and mechanical properties of the RC films were examined by infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, ¹³C NMR, and tensile tests. ¹³C NMR analysis indicated that the novel solvent of cellulose is a nonderivative aqueous solution system. The presence of thiourea enhanced significantly the solubility of cellulose in NaOH aqueous solution and reduced the formation of cellulose gel; as a result, thiourea prevented the association between cellulose molecules, leading to the solvation of cellulose. The RC film obtained by coagulating with 5 wt % H₂SO₄ aqueous solution for 5 min exhibited higher mechanical properties than that with other H₂SO₄ concentrations and a homogenous porous structure with a mean pore size of 186 nm for free surface in the wet state. The RC film plasticized with 10% glycerin for 5 min had a tensile strength of 107 MPa and breaking elongation of 10%, and about 1% glycerin in the RC film plays an important role in the enhancement of the mechanical properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1521–1529, 2002     

Protein side chains facilitate Mg/Al exchange in model protein binding sites.

Among the most frequent protein binding sites served by Mg(II), we identify those which have higher affinity towards Al(III). We also estimate the free energies of metal exchange for all these binding sites taking into account solvent effects explicitly. The obtained results show that thermodynamically favored Mg(II)/Al(III) exchange reactions take place at a number of these metal binding sites, which could possibly be related to some dysfunctions of Mg(II)-dependent biological processes. Additionally, they shed light on the molecular basis of the toxicity of Al(III) in living organisms.     

Solvent‐free cyanosilylation of ketones with (CH3)3SiCN (TMSCN) catalyzed by NbF5

The addition of TMSCN to ketones catalyzed by dispersed NbF₅ gave corresponding cyanohydrin trimethylsilylethers with excellent yield (>90%). Cyano transfer occurs within 30 min at room temperature in the presence of 1 mol% of NbF₅ under solvent‐free conditions. These conditions are extremely mild, simple, and tolerate various functional groups. Copyright © 2007 John Wiley & Sons, Ltd.     

Bacterial Lux-Fluoro test for biological assessment of pollutants in water samples from urban and rural origin

During the 20th century, population growth and urbanization, together with changes in production and consumption, have placed unprecedented demands on the quality of water. The ongoing extraordinary economic growth, industrialization, and urbanization of many developing countries results in widespread water pollution from agricultural, industrial, and domestic sources. In consequence, people consume contaminated drinking water, thereby increasing the risk of exposure not only to infectious and parasitic disease but also to a growing volume of genotoxic and cytotoxic chemicals. In light of these trends, new, rapid and low-cost approaches are urgently needed to assess the quality of water supplies. Because of their simplicity and sensitivity, bacterial tests play an important role in the detection and screening of genotoxins or cytotoxins in water. Thus, the bacterial Lux-Fluoro test, which is a combination of two bioassays that simultaneously measure the genotoxicity (SOS-Lux test) and the cytotoxicity (LAC-Fluoro test), was used to identify polluted water from samples of rural and urban sources, collected from 10 different locations in the Punjab rivers’ basin. We identified at least three samples from rural origin having a high cytotoxic potential. The highest toxicity was found for the sample obtained from a draining canal collecting runoff water from the fields. The two other highly contaminated samples identified were taken from two ponds of different villages. The water samples obtained from the Ravi river and from the water tap in a suburb of the megacity Lahore showed no sign of genotoxicity or cytotoxicity. Seven control samples with differing genotoxic and cytotoxic potency were shown for comparison.     

溶剂效应对聚喹啉铝发光特性的影响

研究了非共轭聚喹啉铝（Palq)在氯仿和乙醇不同极性的溶剂下所获得的薄膜的吸收和发光光谱。由于溶剂性的不同，聚喹啉铝链在氯仿和乙醇溶液中表现出不同的聚集状态。当各种溶液分别旋涂成膜时，溶液中的聚喹啉铝的聚集态仍部分地保存下来，导致不同聚喹啉铝薄膜的电子结构状态的差别。结果，聚喹啉铝的薄膜表现出不同的发光特性。实验表明，在制作聚合物器件中，溶剂的选择对共轭聚合物的发光特性有着重要的影响。     

Structural features responsible for GFPuv and S147P-GFP’s improved fluorescence

Green fluorescent protein (GFP) is used as a biological marker. It is a protein in the jellyfish, Aequorea victorea, which is found in the cold Pacific Northwest. Mature GFP, i.e. fully fluorescent GFP, is most efficiently formed at temperatures well below 37 °C. The GFPuv (F99S/M153T/V163A) and S147P-GFP mutants mature more efficiently at room temperature than wild-type GFP, and therefore result in increased fluorescence at room temperature. Computational methods have been used to examine whether the low-energy precyclized forms of these improved GFP-mutants are preorganized so that they can more efficiently form the chromophore than the wild-type and S65T-GFP. All mutations examined (S147P, F99S, M153T, V163A and F99S/M153T/V163A) more efficiently preorganize the immature precyclized forms of GFP for chromophore formation than immature wild-type GFP. It has been proposed that Arg96 is involved in chromophore formation. Our calculations suggest that the M153T and V163A mutations in GFPuv maybe partially responsible for the increased maturation efficiency observed in GFPuv because they improve the Arg96–Tyr66 interaction. The same is true for the S147P mutation in S147P-GFP.     

Elementary reaction analysis of the radical polymerization of α‐ethyl β‐N‐(α′‐methylbenzyl)itaconamates carrying (RS)‐ and (S)‐α‐methylbenzylaminocarbonyl groups

The polymerizations of α‐ethyl β‐N‐(α′‐methylbenzyl)itaconamates carrying (RS)‐ and (S)‐α‐methylbenzylaminocarbonyl groups (RS‐EMBI and S‐EMBI) with dimethyl 2,2′‐azobisisobutyrate (MAIB) were studied in methanol (MeOH) and in benzene kinetically and with electron spin resonance (ESR) spectroscopy. The initial polymerization rate (R_p) at 60 °C was given by R_p = k[MAIB]^{0.58 ± 0.05}[RS‐EMBI]^{2.4 ± 0.l} and R_p = k[MAIB]^{0.61 ± 0.05}[S‐EMBI]^{2.3 ± 0.l} in MeOH and R_p = k[MAIB]^{0.54 ± 0.05}[RS‐EMBI]^{1.7 ± 0.l} in benzene. The rate constants of initiation (k_df), propagation (k_p), and termination (k_t) as elementary reactions were estimated by ESR, where k_d is the rate constant of MAIB decomposition and f is the initiator efficiency. The k_p values of RS‐EMBI (0.50–1.27 L/mol s) and S‐EMBI (0.42–1.32 L/mol s) in MeOH increased with increasing monomer concentrations, whereas the k_t values (0.20?7.78 × 10⁵ L/mol s for RS‐EMBI and 0.18?6.27 × 10⁵ L/mol s for S‐EMBI) decreased with increasing monomer concentrations. Such relations of R_p with k_p and k_t were responsible for the unusually high dependence of R_p on the monomer concentration. The activation energies of the elementary reactions were also determined from the values of k_df, k_p, and k_t at different temperatures. R_p and k_p of RS‐EMBI and S‐EMBI in benzene were considerably higher than those in MeOH. R_p of RS‐EMBI was somewhat higher than that of S‐EMBI in both MeOH and benzene. Such effects of the kinds of solvents and monomers on R_p were explicable in terms of the different monomer associations, as analyzed by ¹H NMR. The copolymerization of RS‐EMBI with styrene was examined at 60 °C in benzene. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1819–1830, 2003     

Boundary Behavior of Harmonic Functions for Truncated Stable Processes

For any α∈(0,2), a truncated symmetric α-stable process in ℝ ^d is a symmetric Lévy process in ℝ ^d with no diffusion part and with a Lévy density given by c|x|^−d−α 1_{|x|<1} for some constant c. In (Kim and Song in Math. Z. 256(1): 139–173, [2007]) we have studied the potential theory of truncated symmetric stable processes. Among other things, we proved that the boundary Harnack principle is valid for the positive harmonic functions of this process in any bounded convex domain and showed that the Martin boundary of any bounded convex domain with respect to this process is the same as the Euclidean boundary. However, for truncated symmetric stable processes, the boundary Harnack principle is not valid in non-convex domains. In this paper, we show that, for a large class of not necessarily convex bounded open sets in ℝ ^d called bounded roughly connected κ-fat open sets (including bounded non-convex κ-fat domains), the Martin boundary with respect to any truncated symmetric stable process is still the same as the Euclidean boundary. We also show that, for truncated symmetric stable processes a relative Fatou type theorem is true in bounded roughly connected κ-fat open sets. The research of P. Kim is supported by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD, Basic Research Promotion Fund) (KRF-2007-331-C00037). The research of R. Song is supported in part by a joint US-Croatia grant INT 0302167.     

Solvent‐free free‐radical frontal polymerization: A new approach to quickly synthesize poly(N‐vinylpyrrolidone)

The first synthesis of poly(N‐vinylpyrrolidone) without solvent by free‐radical frontal polymerization at ambient pressure is reported. The appropriate amounts of two reactants N‐vinyl‐2‐pyrrolidone (NVP) and initiator 2,2′‐azobis‐isobutyronitrile (AIBN) without solvent were mixed together at ambient temperature. Frontal polymerization was initiated by heating the wall of the tube with a soldering iron, and the resultant hot fronts were allowed to self‐propagate throughout the reaction vessel. Once initiated, no further energy was required for polymerization to occur. To suppress the fingers of molten monomer, a small amount of nanosilica was added. The dependence of the front velocity and front temperature on the AIBN concentration was thoroughly investigated. The as‐prepared polymers were characterized by gel permeation chromatography (GPC) and thermogravimetric analysis (TGA). Results show that without postpolymerization solvent removal, waste production can be reduced. Solvent‐free FP could be exploited as a means for preparation of PVP with the potential advantage of higher throughput than solvent‐based methods. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2177–2185, 2008