C-13 NMR study of ethylene/propylene/octene-1 terpolymers synthesized with TiCl4/MgCl2/i-Bu3Al as the catalyst

The theory of chemical shift effect of substituent was applied to the assignment of the C-13 NMR spectra of the ethylene/propylene and ethylene/octene-1 copolymers. Using the parameters derived above and the DEFT technique, we then entirely assigned the C-13 NMR spectra of the ethylene/propylene/octene(-1) terpolymers synthesized in the presence of the same heterogeneous supported Ziegler-Natta catalyst, TiCl4/MgCl2/i-Bu3Al. The present paper also covers the terpolymer composition and the monomer sequence distributions of a series of ethylene/propylene/octene-1 terpolymers.

Dimerization of hydroxylated species of m-aminophenol by cytochrome c with hydrogen peroxide

The cytochrome c and hydrogen peroxide-dependent oxidation of m-aminophenol was investigated by electrochemistry and spectrophotometry. The results indicated that the hydroxylated species of m-aminophenol have at least two conjugated substituted groups on the ring system (most possibly, its oxidized form 2-hydroxy-4-iminoquinone), and that the degradation of cytochrome c by hydrogen peroxide can also be prevented in the presence of m-aminophenol. The hydroxyl radical scavengers, mannitol and sodium benzoate, almost completely eliminate the hydroxylation of m-aminophenol. But oxo-heme species scavenger, uric acid, does not inhibit the hydroxylation. Combining the results of mass spectrum, nuclear magnetic resonance and element analysis with that of spectrophotometry, electrochemistry and chemical scavengers, it is suggested that cytochrome c may act as a peroxidase, which facilitates the hydroxylation and subsequent dimerization of m-aminophenol. (C) 1998 Elsevier Science B.V. All rights reserved.

Identification of o-phenylenediamine polymerization product catalyzed by cytochrome c

The hydrogen peroxide (H2O2) and cytochrome c-dependent oxidation of o-phenylenediamine (o-PD) was investigated by spectrophotometry and electrochemistry. The results indicated that o-PD underwent facile catalytic oxidation in the presence of cytochrome c, and that the degradation of cytochrome c by hydrogen peroxide can also be partly prevented in the presence of o-PD. The hydroxyl radical scavengers (mannitol and sodium benzoate) and oxo-heme species scavenger (uric acid) do not inhibit the oxidation, which implies that the hydroxylation of o-PD may not be involved in its oxidation. Combining with the results of the mass spectrum, elemental analysis, nuclear magnetic resonance and Fourier transform infrared spectrum of the isolated product, a conceivable structure of the product was suggested. (C) 1998 Elsevier Science B.V.

SEQUENCE STRUCTURE OF ETHYLENE-VINYL SUBSTITUTED COPOLYMER WITH C-13 NMR .4.

The substituent chemical shift (SCS) has been applied to the assignment of the C-13 NMR spectrum of chlorinated polyethylene (CPE). CPE of different chlorine contents has been employed and their sequence structure discussed. The results show that characteristic of CPE with medium chlorine content is the dichloroethane structure in molecular chain. SCS parameters have been obtained from the C-13 NMR spectra. It was found that the effects of chlorine content and temperature on SCS are negligible, but the substituent parameter S1 reduced by 0.39 ppm when C2Cl4 was added to solvent ODCB.

C-13 AND H-1 NMR STUDIES OF SOLUTION STRUCTURE OF LANTHANIDE COMPLEX WITH GLYCYL-GLYCINE

C-13 and H-1 NMR technique was used to study the interaction of Gly-Gly with heavy lanthanide cations Dy3+, Ho3+, Er3+, Tm3+ and Yb3+ in aqueous solution. The stability constants for the 1:1 and 1:2 complexes of Gly-Gly with Ho3+ and Yb3+ were determined from the titration curves of chemical shift versus concentration ratio of lanthanide to Gly-Gly. The solution structure of the Ln-Gly-Gly complex was analyzed based upon the C-13 and H-1 lanthanide induced shifts and the results show that in the complex Gly Gly is coordinated to the lanthanide ion through the carboxyl oxygens with the backbone of the ligand in an extended state.

Frog skins keep redox homeostasis by antioxidant peptides with rapid radical scavenging ability

The question of how amphibians can protect themselves from reactive oxygen species when exposed to the sun in an oxygen-rich atmosphere is important and interesting, not only from an evolutionary viewpoint, but also as a primer for researchers interested in mammalian skin biology, in which such peptide systems for antioxidant defense are not well studied. The identification of an antioxidant peptide named antioxidin-RL from frog (Odorrana livida) skin in this report supports the idea that a peptide antioxidant system may be a widespread antioxidant strategy among amphibian skins. Its ability to eliminate most of the 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) radical tested within 2 s, which is much faster than the commercial antioxidant factor butylated hydroxytoluene, suggests that it has a potentially large impact on redox homeostasis in amphibian skins. Cys10 is proven to be responsible for its rapid radical scavenging function and tyrosines take part in the binding of antioxidin-RL to radicals according to our nuclear magnetic resonance assay. (C) 2010 Elsevier Inc. All rights reserved.

Structural characterization of stable amorphous silicon films

A kind of hydrogenated diphasic, silicon films has been prepared by a new regime of plasma enhanced chemical vapor deposition (PECVD) in the region adjacent to the phase transition from amorphous to crystalline state. The photoelectronic and microstructural properties of the films have been investigated by the constant photocurrent method (CPM), Raman scattering and nuclear magnetic resonance (NMR). Our experimental results and corresponding analyses showed that the diphasic films, incorporated with a subtle boron compensation, could gain both the fine photosensitivity and high stability, provided the crystalline fraction (f) was controlled in the range of 0 < f < 0.3. When compared with the conventional hydrogenated amorphous silicon (a-Si:H), the diphasic films are more ordered and robust in the microstructure, and have a less clustered phase in the Si-H bond configurations. (C) 2002 Elsevier Science Ltd. All rights reserved.

Hydrothermal synthesis and characterization of microporous crystals of trivalent metal-containing zirconium phosphates

Two organically templated trivalent metal-containing crystalline zirconium phosphate materials FeZrPO-8 and AlZrPO-8 have been prepared hydrothermally by using fluoride as a mineralizer, and 1,6-diaminohexane (DAH) as templates. The powder XRD patterns indicate that the as-synthesized products are new materials. Substitutions of Al3+ or Fe3+ into Zr4+ sites were confirmed by a combination of powder X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) studies. The thermal behavior of the title compounds have been investigated using TG-DTA and X-ray thermodiffractometry, which indicated that the inorganic framework of the compounds are thermally stable up to similar to400 degreesC. (C) 2004 Elsevier B.V. All rights reserved.

Synthesis and spectroscopic study of mesoporous aluminum methylphosphonate foam templated by dibutyl methylphosphonate

New types of templates and novel interactive mechanisms between template and framework are very important for creating porous materials. In this work, by using neutral dibutyl methylphosphonate as a template, an inorganic-organic hybrid mesoporous material, aluminum methylphosphonate, was prepared. The as-synthesized material was studied by P-31 magnetic angle spinning nuclear magnetic resonance (MAS NMR), Al-27 MAS NMR, C-13 CP/MAS, FT-IR spectroscopy, thermogravimetry (TG), differential thermal analysis (DTA), and transmission electron microscopy. After thermal treatment at 673 K and 10 mmHg for 2 h, hybrid mesoporous foam was obtained. The transformation process was investigated by FT-IR. TG-DTA results indicate that the methyl group bonded to the framework keeps intact up to 792 K under air and 823 K under nitrogen. The characterization results from nitrogen gas adsorption-desorption measurements show that the BET surface area and the Barrett-Joyner-Halenda desorption cumulative pore volume of the foam are 90 m(2) g(-1) and 0.32 cm(3) g(-1) respectively. (C) 2003 Elsevier Inc. All rights reserved.

Transient state of chiral recognition in a binary mixture of cyclodextrins in capillary electrophoresis

The transient state (as the defined point where no enantioseparation is obtained in a dual chiral selector system) of chiral recognition of aminoglutethimide in a binary mixture of neutral cyclodextrins (CDs) was studied by capillary electrophoresis (CE). The following three dual selector systems were used: alpha-cyclodextrin (alpha-CD) and beta-cyclodextrin (beta-CD); alpha-CD and heptakis(di-O-methyl-beta-cyclodextrin) (DM-beta-CD); alpha-CD and heptakis(tri-O-methyl-beta-cyclodextrin) (TM-beta-CD). The S-(-) enantiomer of the analyte was more strongly retained in the presence of either alpha-CD or TM-beta-CD at pH 2.5, 100 mM phosphate buffer, while the R-(+) enantiomer was more strongly retained in the presence of either P-CD or DM-P-CD. In the more simple case, the elution order is invariably kept if the enantiomers have the same elution order in either one of the two hosts of the binary mixture. In contrast, the elution order may be switched by varying the concentration ratio of two hosts that produce opposite elution order for this particular analyte. In such a dual selector system, the enantioselectivity will disappear at the transient state at a certain ratio of host,:host, Moreover, the migration times of the two enantiomers with host, alone (diluted in buffer) is approximately equal to the migration times at the corresponding concentration of host, alone (diluted in buffer), where the ratio of concentrations of host,:host, is the same as in the binary mixture at the transient state. As found by nuclear magnetic resonance experiments, the analyte is forming a 1:1 complex with either one of the CDs applied. From this finding, a theoretical model based on the mobility difference of the two enantiomers was derived that was used to simulate the transient state. (C) 2000 Elsevier Science B.V. All rights reserved.

Synthesis and evaluation of Gd-DTPA-labeled arabinogalactans as potential MRI contrast agents

Arabinogalactan derivatives conjugated with gad olinium-diethylenetriaminepentaacetic acid (Gd-DTPA) by ethylenediamine (Gd-DTPA-CMAG-A(2)) or hexylamine (Gd-DTPA-CMAG-A(6)) have been synthesized and characterized by means of Fourier transform infrared spectra (FTIR), C-13 nuclear magnetic resonance (C-13 NMR), size exclusion chromatography (SEC), and inductively coupled plasma atomic emission spectrometry (ICP-AES).

Effect of Copolymerization Time on the Microstructure and Properties of Polypropylene/Poly(ethylene-co-propylene) In-Reactor Alloys

Three Polypropylene/Poly(ethylene-co-propylene) (PP/EPR) in-reactor alloys produced by a two-stage slurry/gas polymerization had different ethylene contents and mechanical properties, which were achieved by controlling the copolymerization time. The three alloys were fractionated into five fractions via temperature rising dissolution fractionation (TRDF), respectively. The chain structures of the whole samples and their fractions were analyzed using high-temperature gel permeation chromatography (GPC), Fourier transform infrared (FT-IR), C-13 nuclear magnetic resonance (C-13 NMR), and differential scanning calorimetry (DSC) techniques. These three in-reactor alloys mainly contained four portions: ethylenepropylene random copolymer (EPR), ethylene-propylene (EP) segmented and block copolymers, and propylene homopolymer. The increased copolymerization time caused the increased ethylene content of the sample. The weight percent of EPR, EP segmented and block copolymer also became higher.

Effect of main-chain rigidity on the phase transitional behavior of comblike polymers

The influence of the rigidity of polymer backbones on the side-chain crystallization and phase transition behavior was systematically investigated by a combination of differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), and high-resolution solid-state nuclear magnetic resonance spectroscopy (NMR). DSC investigation indicated that the crystallization number of alkyl carbon atoms of the side chains grafted onto the rigid polymer backbone, poly(p-benzamide) (PBA), is much lower than that of the alkyl carbon atoms of the side chains grafted onto the flexible polymer backbone, poly(ethyleneimine) (PEI), implying that the conformational state of the polymer backbones has a strong effect on the side-chain crystallization behavior in comblike polymers. WAXD and FTIR results proved that these two comblike polymers pack into hexagonal (PBA18C) and orthorhombic (PEI18C) crystals, respectively, depending on the adjusting ability of the polymer backbones for particular conformational states. It was also found that the presence of the crystalline-amorphous interphase (delta = 31.6 ppm) in PBA18C detected by solid-state C-13 NMR spectroscopy can be attributed to the rigid PBA backbone, which restricts the mobility of the alkyl side chains.