Copolymerization of ethylene and 1-butene with highly active Ticl4/THF/Mgcl2, Ticl4/THF/Mgcl2/SiO2, and TiCl3.1/3AlCl3 catalysts

Highly active catalysts for copolymerization have been prepared by the precipitation of MgCl₂/ToCl₄ complex with or without high surface area silica. Copolymerization of ethylene and 1-butene has been tested by using the prepared catalysts at various concentrations of 1-butene. The catalytic activities are 20–80 kg/g Ti h. The rate of copolymerization is strongly affected by the addition of 1-butene. The decay rate of copolymerization is first order with respect to time. Analyses of copolymers with solvent extraction, DSC, IR, XRD, and NMR were performed. Ethylene reactivity ratio (k₁₁) for TiCl₄/MgCl₂/THF catalyst is calculated to be about 26 by NMR spectrum. © 1994 John Wiley & Sons, Inc.     

Efficiency of tributyltin extraction from rhine river sediment

A Rhine river sediment sample was spiked with tributyltin (TBT), equilibrated for ten days and the tributyltin extraction efficiency was optimised using a simplex algorithm. Analysis was effected using hydride generation gas chromatography-atomic absorption spectroscopy (GC-AAS) apparatus. The results show that, in this sediment sample, different molarities of HCl in methanol extract different species with varying extraction efficiencies. The least polar extraction solution extracted TBT more efficiently, whilst DBT and MBT require molar solution of HCl in methanol for efficient extraction.     

A facile approach to architecturally defined nanoparticles via intramolecular chain collapse

A novel approach is presented for the controlled intramolecular collapse of linear polymer chains to give well-defined single-molecule nanoparticles whose structure is directly related to the original linear polymer. By employing a combination of living free radical polymerization and benzocyclobutene (BCB) chemistry, nanoparticles can be routinely prepared in multigram quantities with the size being accurately controlled by either the initial degree of polymerization of the linear chain or the level of incorporation of the BCB coupling groups. The latter also allows the cross-link density of the final nanoparticles to be manipulated. In analogy with dendritic macromolecules, a significant reduction of up to 75% in the hydrodynamic volume is observed on going from the starting random coil linear chains to the corresponding nanoparticles. The facile nature of the living free radical process also permits wide variation in monomer selection and functional group incorporation and allows novel macromolecular architectures to be prepared. Furthermore, the use of block copolymers functionalized with benzocyclobutene groups in only one of the blocks gives, after intramolecular collapse, a hybrid architecture in which a single linear polymer chain is attached to the globular nanoparticle.     

Reductive activation of nitrate reductases

Protein film voltammetry of Paracoccus pantotrophus respiratory nitrate reductase (NarGH) and Synechococcus elongatus assimilatory nitrate reductase (NarB) shows that reductive activation of these enzymes may be required before steady state catalysis is observed. For NarGH complementary spectroscopic studies suggest a structural context for the activation. Catalytic protein film voltammetry at a range of temperatures has allowed quantitation of the activation energies for nitrate reduction. For NarGH with an operating potential of ca. 0.05 V the activation energy of ca. 35 kJ mol-1 is over twice that measured for NarB whose operating potential is ca. -0.35 V.     

Detection of ClSO with time-resolved Fourier-transform infrared absorption spectroscopy

ClSO was produced as an intermediate upon irradiating a flowing mixture of Cl2SO and Ar with a KrF excimer laser at 248 nm. A step-scan Fourier-transform infrared spectrometer coupled with a small multipass absorption cell was employed to detect time-resolved absorption spectrum of ClSO. A transient spectrum in the region 1120-1200 cm(-1), which diminished on prolonged reaction, is assigned to the S-O stretching (nu1) mode of ClSO. A spectrum with a resolution of 0.3 cm(-1) partially reveals rotational structure with the Q-branch at 1162.9 cm(-1). Calculations with density-functional theory (B3LYP/aug-cc-pVTZ) predict the geometry, vibrational, and rotational parameters of ClSO. An IR absorption spectrum of ClSO simulated based on predicted rotational parameters agrees satisfactorily with experimental results. ClSO produced from photolysis of Cl2SO at 248 nm is internally hot.     

Pattern generation of biological ligands on a biodegradable poly(glycolic acid) film

The micropatterns of biological ligands (biotin and RGD peptides) were generated on a flat surface of biodegradable polymer, poly(glycolic acid) (PGA). The immobilization of biological ligands onto the surface of biodegradable polymers (especially aliphatic polyesters) is usually hampered by the absence of functionalizable groups on the polymer backbone. We demonstrate herein that PGA polymer films were modified by surface hydrolysis to introduce carboxylic acid groups on the film surfaces, which were subsequently used for patterning amine-terminated ligands by microcontact printing. Fluorescence microscopy was used to verify the pattern of biotin on the surface of the PGA films after complexation with fluorescein-conjugated streptavidin. In addition, the cellular micropatterns were obtained from micropatterns of RGD peptides on the surface-hydrolyzed PGA films.     

An addition to the oxoacid family: H2B12(OH)12

The acid H(2)B(12)(OH)(12) can be isolated as a crystalline solid by protonation of the hydroxylated borane anion, B(12)(OH)(12)(2)(-). This acidic compound has low solubility in water, conducts protons in the solid state, and has thermal stability to a temperature of 400 degrees C. The conductivity mechanism is a Grotthuss mechanism with a low activation enthalpy (9-13 kcal/mol). This new acid represents an addition to the class of oxoacids, of which sulfuric and phosphoric acid are the most prominent examples.     

Total synthesis of kendomycin: a macro-C-glycosidation approach

Kendomycin, also known as (-)-TAN 2162, is a novel polyketide-derived ansamycin isolated from Streptomyces sp., which exhibits potent antagonist and agonist activities at the endothelin and calcitonin receptors, respectively. This bacterial metabolite also possesses a strong antibiotic activity against a range of gram-positive and -negative bacteria and cytostatic effects on the growth of human cancer cell lines. When a novel macroglycosidation reaction is employed as the key step, the first enantioselective total synthesis of kendomycin has been accomplished. A Friedel-Crafts-type ring closure of the acyclic precursor containing tetrahydropyran and benzofuran moieties produces the macrocycle as a single stereoisomer in good yield, thus establishing the aryl C-glycosidic linkage of the ansa core. This reaction requires a phenolic glycosyl acceptor and appears to proceed through a rapid O-glycosidation followed by a slow rearrangement to an aryl C-glycoside. The requisite secomacrocycle is prepared by the Pd(0)-catalyzed B-alkyl Suzuki-Miyaura cross-coupling of two subunits, which in turn can be expeditiously assembled from readily available building blocks in a modular fashion.     

Elemental analysis of Korean women’s blood serums using instrumental neutron activation analysis

Instrumental neutron activation analysis was used to assess the concentration of the inorganic trace elements in Korean women’s blood serums. It was found that a high concentration of Na and Cl incurs an analytical interference, but the 12 elements such as Br, Ca, Cl, Co, Cr, Cs, Fe, K, Na, Rb, Se and Zn could be determined under the condition of an interference minimization. Serum samples collected from 63 women were analyzed and the concentration level and range of the elements were evaluated. NIST SRMs were analyzed simultaneously for quality control. The average values of the Na and Cl determined in the serum samples were 3,365 and 3,533 mg/l, Ca was 96.4 mg/l and K was 191 mg/l. Besides, Br, Se and Zn have a concentration level of 6.46, 0.13 and 0.98 mg/l, respectively. It was found that there is no significant difference between the present values and the reported values.     

取代1,1'-联-2-萘酚在铜胺络合物催化作用下的氧化反应

用CuCl2?2H2O与小分子的有机胺形成络合物,模拟氧化还原酶对多米诺式反应(Dominoreaction)进行催化反应,在氧气存在条件下,取代1,1'-联-2-萘酚化合物被氧化为二苯并呫吨类化合物,产物的结构经核磁共振、红外光谱及质谱进行确证.