Ion/neutral complex-mediated reactions generated from some ionized tetrahydroimidazole-substituted methylene beta-diketones

The dissociation of gaseous metastable ions of m/z 153 and the formation of ions of m/z 139 from the unimolecular fragmentations of ionized tetrahydroimidazole-substituted methylene beta-diketones were examined by tandem mass spectrometry. In addition, some other fragments accompanying the elimination of either an H2O molecule or an CHO. radical were also observed in the collision-induced dissociation spectra of molecular ions of the compounds bearing an aromatic ring. Collision-induced dissociation and isotopic labeling showed that these processes may involve reactions of intermediate ion/neutral complexes and multistep rearrangements. The corresponding mechanisms are discussed. (C) 1997 by John Wiley & Sons, Ltd.

Plasma modification of aromatic polyamide reverse osmosis composite membrane surface

The surface of aromatic polyamide reverse osmosis composite membrane was modified by oxygen and argon plasma. The water permeability of oxygen-plasma-modified membrane increases, and the chlorine resistance of argon-plasma-modified membrane increases. The spectra of the attenuated total reflection-Fourier transform infrared and X-ray photoelectron spectroscopy and the contact angle of the water were analyzed to explain the improvement of the two performances of the composite membrane. The carboxyl groups were introduced when modified by oxygen plasma, and cross-linking occurred when modified by argon plasma. (C) 1997 John Wiley & Sons, Inc.

H-1 nmr study on the ring opening selectivity of aromatic dianhydrides towards methanol

Several isomeric aromatic diester-diacids may appear as a result of the opening selectivity of anhydride groups towards the alcohol. H-1 n.m.r. was thus used to characterize the isomeric structure and to quantify the isomer composition. It was found that the isomer ratios quantitatively correlate with electron affinity of bridged dianhydrides and is independent of the alcohol structure used. Furthermore, the H-1 n.m.r chemical shift of bridged diester-diacids was found to be a very sensitive probe of chemical nature of bridged groups and can be used as indices of the opening selectivity. (C) 1997 Elsevier Science Ltd.

Separation and determination of organogermanium compounds by ion chromatography

For nearly three decades, organogermanium compounds have become increasingly of interest owing to their extensive physiological and pharmaceutical activity. In this paper, two new high performance ion chromatographic methods for separation and determination of three kinds of organogermanium compounds beta-carboxyethylgermanium sesquioxide (I), beta-(alpha-methyl)-carboxyethylgermanium sesquioxide (II) and d-(beta-carboxyethyl)germanium hydroxide (III) were proposed. A Dionex DX-300 ion chromatograph equipped with a Dionex FED-II pulsed electrochemical detector (conductivity mode), and a Dionex AI-450 chromatography workstation was employed. The separation was achieved by using ion-exchange or ion-exclusion mechanism. The detection limits(S/N=3, expressed as germanium) for the three compounds were all below sub- mu g/mL level. The methods have been applied to the analysis of tonic oral drinks, and the average recoveries for the three compounds range from 95 - 108%. The results obtained were in agreement with those of hydride generation atomic fluorescence spectrometry (HG-AFS).

Gas separation properties of aromatic polyetherimides from 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride and 3,5-diaminobenzic acid or its esters

The gas transport properties of a series polyetherimides, which were prepared from 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride (HQDPA) with 1,3-phenylenediamine or 3,5-diaminobenzic acid (DBA) or its esters are reported. The effects of carboxylic group (-COOH) and carboxylic ether groups (-COOR), at five positions of 1,3-phenylenediamine moiety, on H-2, CO2, O-2, and N-2 permeability, diffusivity, and solubility of the polyetherimides were investigated. The gas permeability, diffusion, and solubility coefficients of the polyetherimides containing COOR are bigger than those of HQDPA-PDA, but the ideal separation factors and ideal diffusivity selectivity factors are much smaller than that of HQDPA-PDA because COOR decreases chain segmental packing efficiency and increases chain segmental mobility. The permeability coefficients of HQDPA-DBA to H-2, CO2, and O-2 are bigger than those of HQDPA-PDA; the ideal separation factors for gas pairs H-2/N-2, CO2/N-2, and O-2/N-2 are also much bigger than those of HQDPA-PDA. Both the diffusion coefficients of CO2 and O-2 and the ideal diffusivity selectivity factors for CO2/N-2 and O-2/N-2 are bigger than those of HQDPA-PDA because COOH decreases both chain segmental packing efficiency and chain segmental mobility. The copolyimides, which were prepared from 3,5-diaminobenzic acid and 3,5-diaminobenzic esters, have both high permeability and high permselectivity. (C) 1997 John Wiley & Sons, Inc.

Activation of a ring methyl substituent in pentamethylcyclopentadienyl rhenium(V) compounds: Synthesis and characterization of the 1,2,3,4-tetramethyl-5,6-dihydrofulvene-5,6-dithiolato complex [ReO{(S)(SCH2)C(5)Me(4)}(C(5)Me(5))]

Reaction of the half-sandwich rhenium(v) complexes [Re-Cl-4(C(5)Me(5))] or [Re(O)Cl-2(C(5)Me(5))] with H2S in chloroform in the presence of pyridine leads to the chiral dithiolato complex [ReO((S)(SCH2)C(5)Me(4))(C(5)Me(5))] 1.

Studies on three-dimensional quantitative structure-activity relationships between the structures of N-nitroso compounds and their carcinogenic activities

Comparative molecular fiels analysis (CoMFA) has been applied to the studies of the correlation of the N-nitroso compounds and their carcinogenic activities, The comparison of CoMFA results with different lattice spacing and different atom probes was investigated, CoMFA resulted in a quantitative description of the major steric and electrostatic field effects and gave significant new insights to factors governing potency.

Synthesis and characterization of aromatic liquid crystalline poly(ester-imide)s derived from an imidodicarboxylic acid

A new class of liquid crystalline poly(ester-imide)s was synthesized by melt polycondensation. The basic physical properties of the resulting polymers were investigated by differential scanning calorimetry (d.s.c.), wide-angle X-ray diffraction (WAXD), polarized light microscopy, scanning electron microscopy (SEM), thermogravimetric analysis (t.g.a.), and rheological and mechanical testing. All of these poly(ester-imide)s were amorphous, as reflected by the results obtained from the WAXD and d.s.c. studies. Characterization and comparison of these poly(ester-imide)s with the corresponding polyesters suggested that the introduction of imide groups into the polyester chain is favourable for the formation of liquid crystalline phases. These results, together with the rheological studies, suggested that there existed a form of strong inter- or intramolecular electron donor-acceptor interaction which played a significant role in the liquid crystalline properties of the poly(ester-imide)s. The polymer products thus obtained exhibited good mechanical properties, with flexural strengths and moduli as high as 174 MPa and 6.9 GPa, respectively. The morphology of the fracture surfaces of extruded rod samples showed a sheet-like structure which consisted of ribbons and fibres oriented along the flow direction. The glass transition temperatures and thermal stabilities of the polymers were improved by the incorporation of imide groups. Copyright (C) 1996 Elsevier Science Ltd.

Chlorination and oxidation of aromatic polyamides .2. Chlorination of some aromatic polyamides

The effects of chlorine on three kinds of aromatic polyamides: those not containing a substituent, those containing substituents, and those containing heterocyclic aromatic rings, were studied. The correlations between the chemical structures of polyamides and the reactivity to hypochlorous acid were examined by IR and C-13 solid-state NMR spectra before and after chlorination. It was found that the chlorination of polyamides depends not only on their chemical structures but also on chlorination conditions such as pH value and reaction time. Their response to chlorination corresponds to four types: ring-chlorination, no reaction, N-chlorination, and chain cleavage. (C) 1996 John Wiley & Sons, Inc.

Effects of molecular structure on the permeability and permselectivity of aromatic polyimides

Permeability coefficients of H-2, O-2, and N2 were measured under 10 atm at the temperature from ambient temperature up to 150 degrees C in a series of structurally different aromatic homo- and copolyimides, which were prepared from 4,4'-oxydianiline (ODA) or 4,4'-methylene dianiline (MDA) with various aromatic dianhydrides. The study shows that the molecular structure of the polyimides strongly influences gas permeability and permselectivity. As a result, the permeability coefficients of the polyimide membranes for each gas vary by over two orders of magnitude. In general, among the polyimide membranes studied, the increase in permeability of polymers is accompanied by the decrease in permselectivity, and the MDA-based polyimide membranes have higher permeability than ODA-based ones. Among the polyimides prepared from bridged dianhydrides, the permeability coefficients to H-2, O-2, and N-2 are progressively increased in the order BPDA < BTDA < ODPA similar to TDPA < DSDA ( SiDA < 6FDA, while H-2/N-2 and O-2/N-2 permselectivity coefficients are progressively decreased in the same order. The copolyimide membranes, which were prepared from 3,3',4,4' biphenyltetracarboxylic dianhydride (BPDA), bis(3,4-dicarboxyphenyl)dimethylsilane dianhydride (SiDA), and ODA, have favorable gas separation properties and are useful for H-2/N-2 separation applications. (C) 1996 John Wiley & Sons, Inc.

Chlorination and oxidation of aromatic polyamides .1. Synthesis and characterization of some aromatic polyamides

The synthesis is described of some aromatic polyamides based on unsubstituted, and methyl-, carboxy-, and sulfo-substituted diamines by interfacial polycondensation. Some of them are crosslinked and some of them contain heterocyclic aromatic rings. Their chemical structures are characterized by IR and C-13 solid-state NMR spectra and the spectra are interpreted. (C) 1996 John Wiley & Sons, Inc.

Influence of intraperitoneal injection of rare earth compounds on the activities of antioxidant enzymes and the level of lipid peroxidation in mice livers

Following intraperitoneal injection of lanthanum and terbium chloride and their complexes of diethyltriaminopentagacetic acid (DTPA) to adult mice with a dose of 0.28 mmol/kg body weight/day for three days. The activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) and the content of lipid end product, malonaldehyde (MDA) in the mice livers have been assayed respectively. The results show that the activity of SOD was increased and the content of MDA was reduced for LaCl3 treated mice and the two targets were not changed for TbCl3, but the activity of GSH-Px was reduced markedly for both LaCl3 and TbCl3 while the above three targets were not changed for La-DTPA and Tb-DTPA complexes.

The reactivity of lanthanide alkyl compounds with phenylacetylene: Synthesis and structure of [(Bu(t)Cp)(2)LnC CPh](2) (Ln=Nd, Gd)

[(Bu(t)Cp)(2)LnCH(3)](2) (Ln = Nd, Gd) react with PhC=CH to form the dimeric alkynide-bridged complexes [(Bu(t)Cp)(2)LnC=CPh](2) [Ln = Nd (I), Gd (II)]. Both compounds crystallized from toluene in the monoclinic space group C2/c. The two complexes are homologous, composed of asymmetric metal-alkynide bridges with Nd-C, Gd-C (alkynide) bond lengths of 2.602(4), 2.641(5) (I) and 2.532(6), 2.601(7) Angstrom (II), respectively. The average Nd-C (ring) and Gd-C (ring) distances are 2.746(13) and 2.703(19)Angstrom.

Chromatographic separation and C-13 NMR characterization of aromatic diester-diacids isomers

Reverse phase high performance liquid chromatography (HPLC) was used to separate and quantify aromatic diester-diacids isomers which arise from the opening selectivity of anhydride rings towards methanol. C-13 NMR spectroscopy was a supplementary tool to characterize the isomer structure. It was found that a meta-position attack is slightly preferred in pyromellitic dianhydride (PMDA), while the preferred position of an attack in bridged dianhydrides is determined by the chemical nature (donors or accepters) of the bridged group. The stronger its electron-withdrawing abilities, the lower the probability of a meta-position attack.