Preparation and characterization of crosslinked proton conducting membranes based on chitosan and PSSA-MA copolymer

Proton conducting crosslinked complex membranes were prepared by blending of a cationic polyelectrolyte, i.e. chitosan (CS) and an anionic polyelectrolyte, i.e. poly(4-styrenesulfonic acid-co-maleic acid) (PSSA-MA). In particular, the dual function of PSSA-MA as a crosslinker and a proton conductor is described. The esterification reaction between –OH of CS and –COOH of PSSA-MA and the complex formation of NH₃⁺ of CS and SO₃^? of PSSA-MA were confirmed using FT-IR spectroscopy. The ion exchange capacity (IEC) of membranes continuously increased with PSSA-MA concentrations, resulting from the increase of ionic groups. However, the membranes exhibited the minimum values of proton conductivity and water uptake at 50–67 wt.% of PSSA-MA due to the effect of crosslinking and complex formation. In addition, a maximum of Young's modulus was achieved at 50 wt.% of PSSA-MA, as revealed by universal testing machine (UTM). Thermogravimetric analysis (TGA) showed that the thermal stability of membranes increased with increasing PSSA-MA concentrations and was the highest at 50 wt.% of PSSA-MA.     

Utilization of radiochemical and mass-spectrometric analysis of the spent fuel of the A-1 power plant for non-destructive burn-up determination

During the burning-up fuel in a nuclear reactor, changes in the isotopic composition of the fuel as well as in the reactor power generation take place. To explain these effects, destructive radiochemical analyses of the spent fuel were carried out. The results obtained have been used for the calibration of non-destructive burn-up determination and for the evaluation of simple computer codes. The main results of the codes as well as the methods applied for the separation of radionuclides studied are presented.     

Coordination chemistry of polyoxomolybdates: The versatile behavior of amidoximes

The reactions of 2-thienylamidoxime and 2-thienylmethylamidoxime with [MoO₂(acae)₂] or x-(NBu₄ [Mo₈O₂₆]. in alcohols or acetonitrile, yield a number of compounds with different nuclearities and various molybdenum cores, such as the compact {Mo₄O₁₀(OMe)₂}²⁺ the cyclic {Mo₄O₁₂}, and the open {Mo₁₁On_211-1}²⁺ (n= 2 or 4) cores. Addition of NH₂OH to the reaction mixtures results in the formation of nitrosyl complexes containing either the Mo(NO)³ or the Mo(NO) ₂ ² units. The amidoxime component may be present either as RC(NH₂)NHO. RC(NHi2), RC(NH)NHO or RC(NH)NO²: ligands, or as hydrogen-bonded RC(NH₂)NOH molecules. The crystal structures of [MoO(acac)RIC'(NH₂)NO] {R^JC(NH)NO}](1), [Mo(NO)(acae)₂ {R^IC(NH₂)NO}] (4), (NBu₄)₂[Mo₄O₁₀(OMe)₂{R^IC(NH) NO}₂] (12a),(NBu₄)₂(H₃O)[Mo₅O₁₃(OMe)₄(NO)].2R¹C(NH₂)NOH(13b) and [R¹C(NH₂)₂)]₃[Mo₅O₁₃(OEt)₄(NO)] (14) (R¹=2-thienyl) are reported. The cryslallographic data for these compounds are as follows:1, mono-clinic. P2₁ a.a=24.547(4)A. b=8.188(4)A. c=9.607(3)A, ß=96.18(3)^c, R=0.046. R₁₀=0.050: 4. monoclinic, P2₁c.a=8.265(2)A, b=9.381(2)A,_c=24.770(4)A, c = 24.7701(4) A, ß=93.99(2). R=0.039. R=0.042;12a, monoclinic, C2/c, a= 19.570(5)A. b=16.883(4)A, c = 19.82(l)A. ß= 114.36(5)°, R=0.064,R.=0.074;13b monoclinic;. P2₁ c.a=18.197(5)A, b=15.857(14) A, c = 23.075(17) A, =93.20(3). R=O.050. R_w=0.057;14, trictinic PI, a = 9.871(3),b= 14.138(3).c= 14.781(8)A. =92.67(2)^c =99.36(1)° =90.52(2)°. R = 0.044. R_w = 0.049. Particular attention is focused on the various coordination modes that the different ligand forms adopt: µ- O, ²N,O, ₂N',O, µ-N: ²O. and ₃- N:N:₂O.     

The origin of the dynamic transition in proteins

Despite extensive efforts in experimental and computational studies, the microscopic understanding of dynamics of biological macromolecules remains a great challenge. It is known that hydrated proteins, DNA and RNA, exhibit a so-called "dynamic transition." It appears as a sharp rise of their mean-squared atomic displacements r2 at temperatures above 200-230 K. Even after a long history of studies, this sudden activation of biomolecular dynamics remains a puzzle and many contradicting models have been proposed. By combining neutron and dielectric spectroscopy data, we were able to follow protein dynamics over an extremely broad frequency range. Our results show that there is no sudden change in the dynamics of the protein at temperatures around approximately 200-230 K. The protein's relaxation time exhibits a smooth temperature variation over the temperature range of 180-300 K. Thus the experimentally observed sharp rise in r2 is just a result of the protein's structural relaxation reaching the limit of the experimental frequency window. The microscopic mechanism of the protein's structural relaxation remains unclear.     

An efficient synthesis of dihydrofuranyl spirooxindoles from isatin-derived propargylic alcohols and 1,3-dicarbonyls

Various dihydrofuranyl spirooxindoles have been synthesized via montmorillonite K-10-catalyzed propargylation of 1,3-dicarbonyl compounds with isatin-derived propargylic alcohols and subsequent base-mediated 5-exo-dig cyclization.     

Sol–gel synthesis of porous titania fibers by electro-spinning for water purification

In this study, porous ceramic fibers were prepared by the sol–gel-assisted electro-spinning process using colloidal dispersion of complex fluids for the application of phtotocatalysts. First, polystyrene nanospheres were synthesized by dispersion polymerization as sacrificial templates for porous fibers. Then, the mixture of polyvinylpyrrolidone and the ceramic precursor with the polymeric nanospheres was prepared as the spinning solution and self-organized by electro-spinning, followed by calcination of the electrospun composite fibers. The morphologies of the porous fibers could be controlled according to the size of the templates and the amount of the ceramic precursor. The nano-structure of the pores in the fibrous materials could also be adjusted as open or closed cavities with various potential applications. As a demonstrative application, the macroporous titania fibers could be utilized as photocatalysts for the removal of organic dyes dissolved in water. A better photocatalytic activity of the macroporous fibers with 700-nm pore diameter was observed compared to the result of nonporous titania fibers due to the increased porosity. Collectively, the macroporous ceramic fibers were found to be efficient functional materials to prepare the unique nano-structured materials other than simple nonporous fibers.     

Investigation of sulfhydryl groups in cabbage phospholipase D by combination of derivatization methods and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

All eight cysteine residues in 92 kDa cabbage phospholipase D (PLD), deduced from the cDNA sequence, were shown to have free sulfhydryl groups by analysis using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) of tryptic peptides of PLD derivatized with p-chloromercurybenzoate, iodoacetic acid, and N-ethylmaleimide, as well as of underivatized PLD. Assignment of sulfhydryl groups by any one method was not conclusive. However, complementary information derived from tryptic peptides derivatized with different reagents made full assignment of sulfhydryl groups possible.     

Carbon Dioxide Reforming of Methane over Ni Catalysts Supported on Al2O3 Modified with La2O3, MgO, and CaO

The preparation of synthesis gas from carbon dioxide reforming of methane (CDR) has attracted increasing attention. The present review mainly focuses on CDR to produce synthesis gas over Ni/MO_x/Al₂O₃ (X = La, Mg, Ca) catalysts. From the examination of various supported nickel catalysts, the promotional effects of La₂O₃, MgO, and CaO have been found. The addition of promoters to Al₂O₃-supported nickel catalysts enhances the catalytic activity as well as stability. The catalytic performance is strongly dependent on the loading amount of promoters. For example, the highest CH₄ and CO₂ conversion were obtained when the ratios of metal M to Al were in the range of 0.04–0.06. In the case of Ni/La₂O₃/Al₂O₃ catalyst, the highest CH₄ conversion (96%) and CO₂ conversion (97%) was achieved with the catalyst (La/Al = 0.05 (atom/atom)). For Ni/CaO/Al₂O₃ catalyst, the catalyst with Ca/Al = 0.04 (atom/atom) exhibited the highest CH₄ conversion (91%) and CO₂ conversion (92%) among the catalysts with various CaO content. Also, Ni/MgO/Al₂O₃ catalyst with Mg/Al = 0.06 (atom/atom) showed the highest CH₄ conversion (89%) and CO₂ conversion (90%) among the catalysts with various Mg/Al ratios. Thus it is most likely that the optimal ratios of M to Al for the highest activities of the catalysts are related to the highly dispersed metal species. In addition, the improved catalytic performance of Al₂O₃-supported nickel catalysts promoted with metal oxides is due to the strong interaction between Ni and metal oxide, the stabilization of metal oxide on Al₂O₃ and the basic property of metal oxide to prevent carbon formation.