Electroinitiated polymerization of allylphenylether

Electroinitiated polymerization of allylphenylether via constant potential electrolysis was accomplished in acetonitrile at room temperature. Electroinitiated polymerization of the monomer yielded insoluble polymers on the surface of the anode together with soluble polymers in the bulk solution. The structural analyses of the polymers were done by ¹H-NMR and FTIR spectroscopy. ¹H-NMR results showed that monosubstituted aromatic ring of the monomer becomes tri-substituted during the electroinitiated polymerization. The effect of monomer concentration and applied potential on the rate of electroinitiated polymerization were also studied. © 1995 John Wiley & Sons, Inc.     

Effects of counterion valency on the damping of phonons propagating along the axial direction of liquid-crystalline DNA

The phonon propagation and damping along the axial direction of films of aligned 40 wt % calf-thymus DNA rods are studied by inelastic x-ray scattering (IXS). The IXS spectra are analyzed with the generalized three effective eigenmode theory, from which we extract the dynamic structure factor S(Q,E) as a function of transferred energy E=variant Planck's over 2piomega, and the magnitude of the transferred wave vector Q. S(Q,E) of a DNA sample typically consists of three peaks, one central Rayleigh scattering peak, and two symmetric Stokes and anti-Stokes Brillouin side peaks. By analyzing the Brillouin peaks, the phonon excitation energy and damping can be extracted at different Q values from about 4 to 30 nm(-1). A high-frequency sound speed is obtained from the initial slope of the linear portion of the dispersion relation below Q=4 nm(-1). The high-frequency sound speed obtained in this Q range is 3100 ms, which is about twice faster than the ultrasound speed of 1800 ms, measured by Brillouin light scattering at Q approximately 0.01 nm(-1) at the similar hydration level. Our observations provide further evidence of the strong coupling between the internal dynamics of a DNA molecule and the dynamics of the solvent. The effect on damping and propagation of phonons along the axial direction of DNA rods due to divalent and trivalent counterions has been studied. It is found that the added multivalent counterions introduce stronger phonon damping. The phonons at the range between approximately 12.5 and approximately 22.5 nm(-1) are overdamped by the added counterions according to our model analyses. The intermediate scattering function is extracted and it shows a clear two-step relaxation with the fast relaxation time ranging from 0.1 to 4 ps.     

Generation of aryl radicals from arylboronic acids by manganese(III) acetate: synthesis of biaryls and heterobiaryls

The efficient generation of aryl radicals from arylboronic acids by manganese(III) acetate is described. In aromatic solvents, in situ generated aryl radicals afford the corresponding biaryls in very good yields. This method works selectively, and yields are better than those from similar, previously described methods. Arylboronic acids carrying sensitive functional groups also work efficiently.     

Preparation of a potentiometric immobilized urease electrode and urea determination in serum

Polyvinylalcohol was activated with 2-fluoro-1-methylpyridiniumtoluene-4-sulphonate and urease (EC.3.5.1.5) was covalently linked to the activated matrix. PVA-urease was then immobilized on the surface of a pH glass electrode with gelatine gel and it was cross-linked using glutaraldehyde. This potentiometric membrane electrode provides a linearity to urea in the 8.910⁻⁵ to 1.110⁻³ M concentration range, but by changing the buffer concentration can be studied in the range of 10⁻⁴ to 10⁻² M urea concentration. Reproducibility experiments (n:20) were carried out with the urease enzyme electrode and with photometric methods for pooled serum sample. Average values for the two methods were 5.96 and 5.86 mM, variation coefficients were 2.5 and 3.5% respectively.     

Reactions of cage metal siloxanes with functionalized organochlorosilanes

The reactions of [(2-acetoxyetoxy)methyl]dimethylchlorosilane and 1-acetoxy-2-(dimethylchlorosilylmethoxy)benzene with the cage phenylcopper and phenylmanganese siloxanes leads to the cleavage of the M—O—Si bond to give metal chlorides and six-unit cyclosiloxanes with an acetoxy group in the organic substituent at the silicon atom. Methanolysis of these acetoxy derivatives does not affect the ring structure and affords the corresponding polyhydric alcohols.     

Aryl Oxalate Derivatives as Convenient Precursors for Generation of Aryloxyl Radicals

The use of aryloxy oxalyl chlorides (AOCs), aryloxy oxalyl tert-butyl peroxides (AOBs), and diaryl oxalates (DAOs) for unimolecular generation of phenoxyl-based radicals under solution and rigid matrix conditions is described. AOCs are usable for photochemical generation of phenoxyl radicals, but are only conveniently stable as precursors when 2,6-di-tert-butylated derivatives are used. AOBs may be used as thermal precursors to aryloxyl radicals, since they typically decompose within 2-3 h at 60-85 degrees C to give phenols. (1)H-NMR solution kinetic studies find that DeltaH() = 31 kcal/mol, and DeltaS() = +3.4 cal/mol-K for decomposition of phenoxyoxalyl tert-butyl peroxide, consistent with substantial concertedness in peroxide bond cleavage. AOBs and the more stable DAOs are also convenient photochemical phenoxyl radical precursors. AOBs yield phenoxyl radicals more readily by photolysis than do corresponding DAOs, but the DAOs have fewer side reactions that can quench the product phenoxyl radicals.     

Phytochemical compounds and antiradical,antimicrobial, and cytotoxic activities of the extracts from Hypericum scabrum L. Flowers

Abstract

Hypericum scabrum L. has been widely used in traditional medicine for the treatment of many diseases just as the other Hypericum species. In the present study, the antiradical, antimicrobial and cytotoxic activities of water and ethanol extracts of H. scabrum flowers were investigated. Their phytochemical contents and composition were also determined. The water and ethanol extracts are better scavenged ABTS (97.89 and 98.99%) and OH radicals (96.36 and 97.33%); the water extract is better scavenged DPPH radicals (91.66%) than the standard antioxidant BHA (94.33, 85.19, 90.16%, respectively). Flowers of H. scabrum contain flavonoids, phenolic acids, vitamins and phytosterols, dominated by catechin, vanillic acid, vitamin K and ergosterol. The extracts exhibit a strong cytotoxic activity against MCF-7, HCT-116, and LNCaP cancer cell lines. It is found that their antimicrobial activities are higher than the standard antibiotics. These results indicate that H. scabrum flowers have potent antiradical, antimicrobial and cytotoxic activities.     

Influence of surface modification of fillers and polymer on flammability and tensile behaviour of polypropylene-composites

An intumescent system consisting of ammonium polyphosphate (APP) as an acid source and blowing agent, pentaerythritol (PER) as a carbonific agent and natural zeolite (clinoptilolite, Gördes II) as a synergistic agent was used in this study to enhance flame retardancy of polypropylene (FR-PP). Zeolite was incorporated into flame retardant formulation at four different concentrations (1, 2, 5, and 10 wt%) to investigate synergism with the flame retardant materials. Filler content was fixed at 30 wt% of total amounts of flame retardant PP composites. Zeolite and APP were treated with two different coupling agents namely, 3-(trimethoxysilyl)-1-propanethiol and (3-aminopropyl)-triethoxysilane for investigation of the influence of surface treatments on mechanical properties and flame retardant performance of composites. Maleic anhydride grafted polypropylene (MAPP) was used for making polypropylene hydrophilic. Flammability of FR-PP composites was measured by the determination of limiting oxygen index (LOI). The LOI values reached to a maximum value of 41% for mercapto silane treated APP:PER (2:1) PP composite containing 5 wt% zeolite. The tensile strength of composites was increased by the addition of MAPP and elongation at break of composites was increased with silane treatments.     

Enantioselective Synthesis of 2‐(2‐Arylcyclopropyl)glycines: Conformationally Restricted Homophenylalanine Analogs

Starting from simple aromatic aldehydes and acetylfuran, (E)‐1‐(furan‐2‐yl)‐3‐arylprop‐2‐en‐1‐ones ( 2 ) were synthesized in high yields. Cyclopropanation of the C?C bond with trimethylsulfoxonium iodide (Me₃SO⁺I^?) furnished (furan‐2‐yl)(2‐arylcyclopropyl)methanones 3 in 90–97% yields. Selective conversion of cyclopropyl ketones to their (E)‐ and (Z)‐oxime ethers 5 and oxazaborolidine‐catalyzed stereoselective reduction of the C?N bond followed by separation of the formed diastereoisomers, furnished (2‐arylcyclopropyl)(furan‐2‐yl)methanamines 6 in optically pure form and high yield. Oxidation of the furan ring of (S,S,S)‐, (S,R,R)‐, (R,S,S)‐, and (R,R,R)‐ 6a afforded the four stereoisomers of α‐(2‐phenylcyclopropyl) glycine ( 1a ).