How does cross-linking affect the stability of block copolymer vesicles in the presence of surfactant?

Block copolymer vesicles are conveniently prepared directly in water at relatively high solids by polymerization-induced self-assembly using an aqueous dispersion polymerization formulation based on 2-hydroxypropyl methacrylate. However, dynamic light scattering studies clearly demonstrate that addition of small molecule surfactants to such linear copolymer vesicles disrupts the vesicular membrane. This causes rapid vesicle dissolution in the case of ionic surfactants, with nonionic surfactants proving somewhat less destructive. To address this problem, glycidyl methacrylate can be copolymerized with 2-hydroxypropyl methacrylate and the resulting epoxy-functional block copolymer vesicles are readily cross-linked in aqueous solution using cheap commercially available polymeric diamines. Such epoxy-amine chemistry confers exceptional surfactant tolerance on the cross-linked vesicles and also leads to a distinctive change in their morphology, as judged by transmission electron microscopy. Moreover, pendent unreacted amine groups confer cationic character on these cross-linked vesicles and offer further opportunities for functionalization.     

Lateral sol–gel cross-linking of polyurethane using the a grafted triethoxysilyl group

3-Triethoxysilylpropyl isocyanate was used to graft a triethoxysilyl group to polyurethane (PU), and the grafted triethoxysilyl groups were used to cross-link PU chains through a sol–gel process. The soft segment melting temperature and enthalpy change were not significantly altered by the sol–gel cross-linking. The sol–gel cross-linked PUs exhibited significantly increased tensile strength and better tensile strain compared to the plain linear PU: the maximum stress and strain increased to 41 MPa and 1,972 %, respectively. Control series containing tetraethyl orthosilicate, a series without cross-linking, was also prepared for comparison with the sol–gel cross-linked PU series. The control series did not exhibit the increased tensile strength shown by the sol–gel cross-linked PU series. The cyclic shape memory tests demonstrated that the shape recovery was as high as 97 %, and both shape recovery and shape retention remained high after the four repeated tests. The sol–gel cross-linked PU series exhibited enhanced low-temperature flexibility compared to the plain linear PU due to the flexible silyl cross-linking group.     

Use of γ-irradiation cross-linking to improve the water vapor permeability and the chemical stability of milk protein films

γ-irradiation was used to produce free-standing cross-linked milk proteins. Film forming solutions were prepared according to a method previously developed in our laboratory using calcium caseinate (cas) with various proportions of whey protein isolate (wpi) or whey protein concentrate (wpc). The following caseinate–whey protein (cas:wp) ratio were prepared: 100:0, 75:25, 50:50, 25:75, and 0:100. The WVP of the films was determined gravimetrically at 23°C using a modified ASTM procedure. Molecular properties characterization was performed by size exclusion chromatography (SEC). Results showed significant (p⩽0.05) reduction of the WVP of protein films for the following formulations: cas:wpi or cas:wpc (100:0); cas:wpi (25:75); cas:wpc (25:75); and cas:wpc (0:100). Mixture of cas and wpi produced a synergistic effect. The strongest combined effect was obtained for cas:wpi (25:75) formulation with permeability values of 2.07 and 1.38 g mm/m² d mm Hg for unirradiated and irradiated samples, respectively. γ-irradiation also induced a substantial increase of high molecular weight protein components in film forming solutions. The predominant fraction was ⩾10×10⁶ Da for irradiated film forming solutions, compared to less than 0.2×10⁶ Da for native unirradiated solutions.     

Remarkable Improvement of Methylglyoxal Synthase Thermostability by His–His Interaction

Lately it has been proposed that interaction between two positively charged side chains can stabilize the folded state of proteins. To further explore this point, we studied the effect of histidine–histidine interactions on thermostability of methylglyoxal synthase from Thermus sp. GH5 (TMGS). The crystal structure of TMGS revealed that His23, Arg22, and Phe19 are in close distance and form a surface loop. Here, two modified enzymes were produced by site-directed mutagenesis (SDM); one of them, one histidine (TMGS-HH^O), and another two histidines (TMGS-HHH^O) were inserted between Arg22 and His23 (H^O). In comparison with the wild type, TMGS-HH^O thermostability increased remarkably, whereas TMGS-HHH^O was very unstable. To explore the role of His23 in the observed phenomenon, the original His23 in TMGS-HHH^O was replaced with Ala (TMGS-HHA). Our data showed that the half-life of TMGS-HHA decreased in relation to the wild type. However, its half-life increased in comparison with TMGS-HHH^O. These results demonstrated that histidine–histidine interactions at position 23 in TMGS-HH^O probably have the main role in TMGS thermostability.     

Cationic polymerization of dienes VIII: Is the elimination of cross-linking by a bulky electron donor a general behavior in the presence of aluminium trichloride?

Previous works on the polymerization of 1,3-pentadiene initiated by aluminium trichloride in non polar solvent at room temperature in the presence of bulky electron donor (ED) as tri-p-tolylamine have highlighted a stabilization of the polymerizing actives centres by ED, which allowed a reduction of some side reactions and the formation of more precisely defined polypentadienes than ever by cationic polymerization in non polar medium. The aim of this research was to investigate the role of bulky EDs such as tri-p-tolylamine and similar compounds in polar medium in order to obtain if possible a complete control of the polymerization of isoprene and 1,3-pentadiene. The beneficial effect of tri-p-tolylamine was shown in the case of isoprene polymerization at room temperature, with an important reduction of the cross-linked fraction for long reaction times and strong reduction of termination reactions. At −30 °C in the presence of tri-p-tolylamine, polypentadienes more controlled than in non polar solvent could be obtained, with a nearly complete elimination of the cross-linked fraction, while keeping the microstructure approximately constant.     

Does chemical cross-linking with NHS esters reflect the chemical equilibrium of protein-protein noncovalent interactions in solution?

Chemical cross-linking in combination with mass spectrometry has emerged as a powerful tool to study noncovalent protein complexes. Nevertheless, there are still many questions to answer. Does the amount of detected cross-linked complex correlate with the amount of protein complex in solution? In which concentration and affinity range is specific cross-linking possible? To answer these questions, we performed systematic cross-linking studies with two complexes, using the N-hydroxysuccinimidyl ester disuccinimidyl suberate (DSS): (1) NCoA-1 and mutants of the interacting peptide STAT6Y, covering a K_D range of 30 nM to >25 μM, and (2) α-thrombin and basic pancreatic trypsin inhibitor (BPTI), a system that shows a buffer-dependent K_D value between 100 and 320 μM. Samples were analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). For NCoA-1· STAT6Y, a good correlation between the amount of cross-linked species and the calculated fraction of complex present in solution was observed. Thus, chemical cross-linking in combination with MALDI-MS can be used to rank binding affinities. For the mid-affinity range up to about K_D ≈ 25 μM, experiments with a nonbinding peptide and studies of the concentration dependence showed that only specific complexes undergo cross-linking with DSS. To study in which affinity range specific cross-linking can be applied, the weak α-thrombin · BPTI complex was investigated. We found that the detected complex is a nonspecifically cross-linked species. Consequently, based on the experimental approach used in this study, chemical cross-linking is not suitable for studying low-affinity complexes with K_D ? 25 μM.     

Friedrich Wöhler (1800–1882), on the Bicentennial of His Birth

The life and contributions to various areas of chemistry of German chemist Friedrich Wöhler (1800–1882) are briefly sketched. His serendipitous synthesis of urea from ammonium cyanate in 1828, which is dealt with in some detail, challenged the vitalistic theory that organic compounds can be produced only by living organisms and led to todays synthetic chemical industry and its host of products that we take for granted.     

Lars Onsager (1903–1976), Chemist-Physicist, on the Silver Anniversary of His Death

The Norwegian-born theoretical chemist-physicist Lars Onsager (1903–1976) received the 1968 Nobel Prize for Chemistry for the discovery of the reciprocal relations bearing his name, which are fundamental for the thermodynamics of irreversible processes. A recipient of numerous awards and honorary degrees, which he did not receive until relatively late in life, he taught at the Johns Hopkins and Brown universities, but spent most of his academic career at Yale University (1933–1972). He spent his post-retirement years (1972–1976) as Distinguished University Professor at the University of Miamis Center for Theoretical Studies, where he continued his work with several postdoctoral research fellows.     

Charles Goodyear (1800–1860), American Inventor, on the Bicentennial of His Birth

Goodyear was neither a chemist nor scientist and, like Thomas Edison, used trial-and-error methods. He recognized rubbers valuable properties—elasticity, plasticity, strength, durability, electrical nonconductance, and resistance to water, and he became preoccupied with this elastomer. His vulcanization process, accidentally discovered in 1839 after five years of countless experiments, transformed rubber from a smelly, virtually useless substance that became sticky in summer, hardened and cracked in winter, and was attacked by various solvents into a stable, versatile commercial product with literally hundreds of uses. He devoted the last quarter-century of his life to experimenting with ways to improve, promote, and exhibit it to the great detriment of his own and his familys finances and health.Series Editor contribution     

Victor Moritz Goldschmidt (1888–1947): A Tribute to the Founder of Modern Geochemistry on the Fiftieth Anniversary of His Death

Goldschmidt combined a number of widely separated sciences to synthesize a new structural crystal chemistry. Although his work on the relative abundances of the elements, atomic and ionic radii, interionic distances, the effect of radius ratio on coordination number in crystals, replacement of ions in minerals, and the lanthanide contraction is found in almost every textbook of general and inorganic chemistry and has provided the basis for modern crystal chemistry and the use of size relationships for interpreting properties of inorganic substances, Goldschmidts name, life, and career remain relatively unknown to most chemical educators and practicing chemists.Goldschmidt used the basic properties of matter to provide simple and elegant explanations for the composition of our environment. Throughout his relatively brief career, filled with sorrow and tragedy, he continued to maintain his intense interest in the elements and their genesis, affinities, and associations despite his changes from one method to another in his attempts to obtain new and more complete data. Thus, although he used petrology, crystallography, and chemistry and enriched all these fields greatly, to him they were only tools for exploring the earth and its history.     

Congratulationsto Professor He Binglin on the Occasion of His 80th Birthday——Biographic Sketch of Professor He Binglin

He Binglin was born on August 24, 1918 in Fanyu County, Guangdong Province.He graduated from the Chemistry Department of Southwest Associated Universityin 1942. After graduation he worked in Chongqing Central Institute of Industry forone year as an assistant engineer and then returned to his Alma Mater University     

C–H bond addition and copolymerization reactions of N-arylmaleimides: Fundamentals of coagent-assisted polymer cross-linking

Solid-state rheometry and model compound reactions are used to investigate free radical reactions of N-arylmaleimide coagents with saturated and unsaturated polymers. N,N′-m-phenylene dimaleimide (BMI) is shown to provide superior cross-link densities over diacrylate and diallyl coagents for all of the polymers studied, including linear low density polyethylene (LLDPE), poly(ethylene oxide) (PEO), cis-poly(butadiene) (PBD) and cis-poly(isoprene) (PIP). Studies of the N-phenylmaleimide (NPM) + cis-cyclooctane system show that C–H bond addition to yield N-aryl-2-alkylsuccimide grafts is the predominant reaction pathway, as opposed to maleimide homopolymerization. In contrast, peroxide-initiated reactions of cis-cyclooctene with small NPM concentrations generate highly alternating poly(cycloctene-alt-N-phenylmaleimide) in high yield, indicating that unsaturated mers in materials such as PBD engage maleimides in an efficient alternating copolymerization between electron-rich and electron-deficient monomer pairs. Factors that affect the reactivity of different polymers in these C–H bond additions and alternating copolymerizations are discussed.     

Congratulation to Professor Renynyuan Qian on the Occasion of His 80th Birthday——Biographic Sketch of Professor Renyuan Qian

Renyuan Qian was born on September 19, 1917 in Changshu, Jiangsu province.He graduated from the Chemistry Department of Zhejiang University in 1939. Inthe year of 1943, he went to the United States to take postgraduate studies mainlyin the University of Wisconsin. In 1948, he returned to China and associated with Xiamen University and Zhe-     

Performances of NaCS–WSC protein drug microcapsules with different degree of substitution of NaCS using sodium polyphosphate as cross-linking agent

Sodium cellulose sulfate–water soluble chitosan (NaCS–WSC) microcapsules loaded with lactoferrin were fabricated with special performances using different degree of substitution (DS) of NaCS and WSC as potential micro-drug-carriers for colon. Effect of using cross-linking agent (sodium polyphosphate) and DS of NaCS on the structures and performances of microcapsules was studied. The results of laser scanning confocal microscope showed that fluorescein isothiocyanate-labeled lactoferrin distributed evenly in the drug-loaded microcapsules with cross-linker. NaCSs (DS: 0.51 and DS: 0.66, respectively) were chosen to prepare lactoferrin loaded microcapsules with WSC and cross-linker for comparison studies. DS of NaCS had some effects on erosion properties in which the erosion ratios of microcapsules with DS of 0.51 were higher than that with DS of 0.66, but showed no effect on swelling behaviors. Drug loading and encapsulation efficiencies of microcapsules (DS: 0.66) were 51.05 ± 0.97 and 75.88 ± 1.44 %, respectively, which were higher than that of microcapsules with DS of 0.51. In vitro release studies showed that the percentage of drug release of microcapsules (DS: 0.51) were higher than that of microcapsules with DS of 0.66 in simulated colonic fluid (pH 6.4) under mechanism of Anomalous (non-Fickian) transport, indicating that they are promising candidates as sustained protein drug delivery carriers with special performances.     

Optimizing functional layer of cation exchange membrane by three-dimensional cross-linking quaternization for enhancing monovalent selectivity

Monovalent cation perm-selective membrane（MCPMs） allow fast and selective transport of monovalent cations, and they are promisingly required for extraction of special ions, such as lithium extraction, acid recovery and sea salt production. Herein, we report a novel strategy to design the critical functional layers of MCPMs with both space charge repulsion and cross-linked dense screenability. The in-situ deposition polymerization of pyrrole was carried out on the surface of sulfonated polyphenyl...     

Catalytic properties of Phe41→His mutant of horseradish peroxidase expressed inE. coli

The recombinant horseradish peroxidase and its single-point F41H mutant have been reactivated fromE. coli inclusion bodies. The influence of the mutation on the heme entrapment, stability and activity of the enzyme was demonstrated. The catalytic rate constants for H₂O₂ cleavage and ammonium 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonate (ABTS) oxidation decrease by two and one orders of magnitude, respectively. Unlike the wild-type recombinant horseradish peroxidase, the elimination of the ABTS oxidation product is not a rate-determining step for the mutant. The F41H replacement results in significant changes of kinetics of iodide ion oxidation. The reaction rate is linear to the concentrations of iodide, H₂O₂, and the enzyme. The results suggest the direct interaction of iodide with the porphyrin ring of the heme. The decrease in ABTS oxidation activity accompanied by retention of activity in iodide oxidation in the course of low-dosage radiolysis of the F41H mutant is additional evidence of the direct electron transfer from iodide to the heme, in contrast to ABTS oxidation, in which the electron transfer chain in the protein molecule is involved.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2034–2038, November, 1994.     

Congratulations to Professor Bao-tong Huang on the Occasion of His 80~(th) Birthday——Biographic Sketch of Professor Bao-tong Huang

Professor Bao-tong Huang (formerly known as Pao-tung Huang, Paul) of the Changchun Institute ofApplied Chemistry, Chinese Academy of Sciences was born in Shanghai on May 1~(st) 1921. He waseducated at the University of Shanghai (1940～1942) and the National Central University (1942-1944)and conferred the degree of B.S. in chemistry. He retried to Shanghai after the end of the war againstJapan. Prof. Huang undertook his graduate studies at the Texas A & M College (M.S. in Chemistry,     

Anionic polymerization of ϵ-caprolactam-lix effect of the ratio of reacting components,of the medium and of the ring size on the initial stage of the anionic polymerization of lactams

Effects of the concentrations and ratio of reacting components and of temperature on the kinetics of reaction of N-propionyllactam (I) with potassium salt of lactam (KL) were studied for derivatives of ϵ-caprolactam, 8-octanelactam and 12-dodecanelactam. For ϵ-caprolactam, the initial rates of propagation, acylation of open-chain amide groups and condensation of growth centres were estimated. At the ratio of the starting components [I]₀/[KL]₀ = 0.5-3, the participation of the polymerization reaction is constant, amounting to ca 45% of the overall consumption of 1. The condensation reaction is 14–36% of the total consumption of I; its initial rate passes through a maximum at [I]₀/[KL]₀ = 2. With increasing permittivity of the medium, the total rate of consumption of I increases; in two media with the same bulk permittivity, however, the rates may differ by as much as one order of magnitude.     

Construction of the Skeleton of Phthalascidin, Mechanism of the Formation of the Key Tricyclic Lactam Intermediate

Phthalascidin is a structurally simplified version of Et-743, which is a potent anti-tumor marine natural product isolated from Ecteinascidia turbinata. Its antiproliferative activity is greater than that of the agents taxol, camptothecin, adriamycin, mitomycin C, cisplatin, bleomycin, and etoposide by 1-3 orders of magnitude. An elegant synthesis of Et-743 and phthalascidin has been reported by E. J. Corey and co-workers1,2. As part of our continuing program, we have also engaged in dev…