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At least 991 records · Page 55Linked to original sources
PubMed2006

Poly(dimethylamino)ethyl methacrylate for use as a surfactant in the miniemulsion polymerization of styrene.

A novel Y-shaped macromonomer based on poly[(dimethylamino)ethyl methacrylate] (PDMAEMA) with a narrow molecular weight distribution was synthesized via oxyanion-initiated polymerization in which a potassium alcoholate of trimethylol propane allyl ether (2K-TMPAE) was used as a difunctional initiator. For the miniemulsion polymerization of styrene, this macromonomer acted well both as a comonomer carrying a reactive C=C double bond in its central section and as a pH-responsive polycationic surfactant in media with different pH values. The resulting microspheres composed of a hydrophobic polystyrene core and a hydrophilic PDMAEMA-protonated corona have shown spherical morphology and are quite stable. The nature of the reactive group, the amount of polymeric surfactant, and pH values in the aqueous medium have been systematically investigated during the miniemulsion polymerization by analyzing the evolution of the monomer conversions. The results of FTIR and (1)H NMR spectra demonstrated the generation of the functional particles. The analyses of TEM micrographs and dynamic light scattering (DLS) confirmed that the latices had a relatively narrow particle size distribution. The measurement of the zeta potential gave further evidence of the "hairy" particle structure. Because the reactive group is located in the central section of the macromonomer, the stabilization mechanism of the polymeric surfactant can be ascribed to (1) the absorption of two polycationic and hydrophilic tails that have electrostatic and steric stabilization to decrease the interface tension and (2) the copolymerization with the styrene monomer.

Journal Article↗
PubMed2001

Stereoselective synthesis of styrene oxides via a Mitsunobu cyclodehydration.

[reaction: see text] The Mitsunobu cyclodehydration of chiral phenethane-1,2-diols (4), readily accessed from the styrene derivative (5), has been demonstrated to provide the corresponding styrene oxides (2) with high levels of stereoretention (up to 99%). Optimized reaction conditions are described, from which the combination of tricyclohexylphosphine (Chx(3)P) and diisopropylazodicarboxylate (DIAD) in THF and R = EWG provides the best results.

Cyclization↗
PubMed2002

Catalytic hydrophosphination of styrenes.

[reaction: see text] The first example of intermolecular hydrophosphination of styrenes catalyzed by Ni and Pd complexes is described. The reaction of Ph2PH with styrene, 4-vinylpyridine, 2-vinylpyridine, 4-methoxystyrene, 2-methoxystyrene, and 5-vinyl-2-methylpyridine in benzene under Ni[P(OEt)3]4 catalysis proceeds with high yield and selectivity to give only anti-Markovnikov product.

Journal Article↗
PubMed2002

Oxiranyl anion-mediated synthesis of highly enantiomerically enriched styrene oxide derivatives.

[reaction: see text] The stereospecific alpha-lithiation of optically active styrene oxides and the trapping reaction of the corresponding highly reactive intermediates with electrophiles to produce optically active styrene oxide derivatives are described. This methodology has been applied to the synthesis of an optically active oral antifungal agent of industrial interest.

Aluminum Compounds↗
PubMedDate not supplied

Bis(hydroxyphenylethyl)deoxyguanosine adducts identified by [32P]-postlabeling and four-sector tandem mass spectrometry: unanticipated adducts formed upon treatment of DNA with styrene 7,8-oxide.

Calf thymus DNA was incubated with [8-14C]styrene oxide in vitro, and six covalent xenobiotic-DNA adducts were detected using the [32P]-postlabeling procedure. Adducts 1-3 were purified by HPLC and identified as bis-substituted-2'-deoxyguanosine 3'-phosphate derivatives using four-sector tandem mass spectrometry. These adducts represented less than 2% of the total adducts detected by [14C]-radioactivity. Adducts 1-3 were also detected when styrene oxide was allowed to react with the mononucleotide, 2'-deoxyguanosine 3'-phosphate only. The elemental compositions of these adducts (C26H30N5O9P) were determined by measurement of their accurate masses by high-resolution mass spectrometry and revealed the unusual incorporation of 2 mol of hydroxyphenylethyl moieties. The structures of these bis(phenylethyl) adducts were established by interpretation of high-energy collision-induced dissociation (CID) mass spectra, together with UV/visible and fluorescence spectrophotometry as N2-(2-hydroxy-1-phenylethyl)-O6-(2-hydroxy-2-phenylethyl)-2'-deoxygua nos ine 3'-phosphate (adduct 1), N2-(2-hydroxy-1-phenylethyl)-O6-(2-hydroxy-1-phenylethyl)-2'-deoxygua nos ine 3'-phosphate (adduct 2), and N1,N2-bis(2-hydroxy-1-phenylethyl)-2'-deoxyguanosine 3'-phosphate (adduct 3). The other most abundant adducts were detected only by [14C]-radioactivity and represented approximately 65% of the total covalent binding. These were identified as depurinated N7-substituted guanines by tandem mass spectrometry and UV/visible spectroscopy. The combination of advanced techniques of mass spectrometry with the [32P]-postlabeling assay and spectroscopic techniques is a comprehensive strategy to assure complete structural identification of all xenobiotic-DNA adducts.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Application of Raney nickel to measure adducts of styrene oxide with hemoglobin and albumin.

Adducts of styrene 7,8-oxide (SO) with the blood proteins, Hb and albumin (Alb), were measured following treatment of the proteins with Raney nickel (Ra-Ni) to cleave 2-phenylethanol, which was subsequently assayed. Internal standards were prepared by modifying Hb and Alb with 4-methyl-SO to produce similar adducts. In a preliminary experiment with human blood, which had been modified with [14C]SO in vitro, it was determined that Ra-Ni released 6% of the total binding to globin and 76% of the total binding to Alb. Since Ra-Ni primarily cleaves covalently-bound sulfur species, this suggests that much more binding to human serum Alb occurred at a free cysteine residue than to human Hb. The overall rate of reaction of SO at 37 degrees C in vitro had a half-time of 0.70 h in human blood and of 0.36 h in blood from Sprague-Dawley rats. Adducts of SO with Hb and Alb were measured following SO modification of blood from humans and rats in vitro at 37 degrees C. Slopes of the linear relationships between adduct level and SO concentration allowed the following second-order rate constants [(L/mol of protein)/h] to be estimated: rat Hb, 72; human Hb, 2.4; rat Alb, 63; human Alb, 32. These rate constants show that intrinsic reactivity of SO toward the cysteine residue of human Hb is much lower than that of rat Hb or of Alb from either species. Adducts of Hb and Alb were also measured following administration of both SO and styrene to rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2004

A novel approach based on solid phase microextraction gas chromatography and mass spectrometry to the determination of highly reactive organic compounds in cells cultures: styrene oxide.

A solid phase microextraction (SPME) gas chromatography/mass spectrometry (GC/MS) method was developed to assess actual doses of highly reactive organic compounds like styrene oxide (SO) in exposed cell cultures. Using SPME, we set up a method to measure accurately extracellular SO concentrations as well as to obtain an approximate assessment of intracellular levels. The SPME-GC/MS method was developed and validated using two different coating materials, carboxen-PDMS and polyacrylate. In cell-free systems, linearity was established over 3 orders of magnitude for both fibers, but carboxen-PDMS showed higher extraction efficiency and a lower limit of detection (0.5 x 10(-7) vs 10(-6) M for polyacrylate). Precision calculated as % RSD was within 4-16% for all intra- and interday determinations. Experiments performed to study SO stability in cell-free medium showed a time-dependent decrease in SO concentration (11% of initial the concentration after 24 h), mostly due to the spontaneous hydrolysis of SO into styrene glycol, which was measured by liquid chromatography/tandem mass spectrometry (LC/MS/MS). When the neuronal cell line (SK-N-MC) was exposed to a nominal concentration of 0.3 x 10(-4) M SO, the actual concentration measured in the supernatant was considerably lower and was found to decrease during incubation. Intracellular SO was estimated indirectly, by difference between the amount measured in the medium without cells and in the supernatant of the cell-containing medium.

Acrylates↗
PubMed1999

32P-Postlabeling analysis of DNA adducts of styrene 7,8-oxide at the O6-position of guanine.

A 32P-postlabeling method was established for the quantitative characterization of 2'-deoxyguanosyl O6-adducts of styrene 7,8-oxide in DNA. The two regioisomeric adducts, O6-(2-hydroxyl-1-phenylethyl)-2'-deoxyguanosine 3'-phosphate (alpha-isomer) and O6-(2-hydroxyl-2-phenylethyl)-2'-deoxyguanosine 3'-phosphate (beta-isomer), were synthesized and used for optimizing and quantifying the various analytical steps. The adducts were stable at pH 7 and 10, but not at pH 4. The adducts were sensitive to dephosphorylation during the standard nuclease P1 (NP1) treatment. Within 30 min, 73 and 94% of the alpha- and beta-isomers were digested. Adducts could not be extracted into butanol, and micropreparative chromatography on reversed-phase thin layers resulted in a loss of adducts at low levels. Therefore, further methods of enrichment had to be investigated. Micropreparative reversed-phase HPLC chromatography on a C18 column resulted in a many thousand-fold purification from the normal nucleotides. Further enrichment was achieved with a mild NP1 treatment. The phosphorylation efficiency with polynucleotide kinase was 5 and 15% for the alpha- and beta-isomers, respectively. Adduct analysis was performed with reversed-phase TLC followed by contact transfer of the origin to a polyethyleneimine-cellulose sheet and two-dimensional development. Addition of various amounts of adduct standard to the hydrolysate of 30 microg of DNA isolated from a control rat liver showed limits of detection of three and two adducts per 10(7) nucleotides for the alpha- and beta-isomers, respectively. The applicability of the newly developed method was demonstrated by the DNA analysis of styrene-exposed rats.

Adenosine Triphosphate↗
PubMed1999

Formation of deaminated products in styrene oxide reactions with deoxycytidine.

The reaction of racemic styrene oxide with deoxycytidine under aqueous conditions was studied. The four principal products isolated were a pair of diastereomeric N(4)-(2-hydroxy-1-phenylethyl)deoxycytidines ( approximately 20% of the products) and a pair of diastereomeric 3-(2-hydroxy-2-phenylethyl)deoxyuridines ( approximately 80% of the products). Reactions with optically active styrene oxides allowed the configurations of the 3-(2-hydroxy-2-phenylethyl)deoxyuridines to be assigned, and these structures were confirmed by an independent synthesis from deoxyuridine. Also, it was possible to tentatively assign the configurations of the N(4)-(2-hydroxy-1-phenylethyl)deoxycytidines that had undergone some racemization during the reaction (the ratio of the retained to inverted configuration of the products was approximately 1:7).

Amides↗
PubMed2006

Spatial distribution of stabilizer-derived nitroxide radicals during thermal degradation of poly(acrylonitrile-butadiene-styrene) copolymers: a unified picture from pulsed ELDOR and ESR imaging.

Double Electron-Electron Resonance (DEER) provides information on the spatial distribution of radicals on the length scale of a few nanometres, while Electron Spin Resonance Imaging (ESRI) provides information on a length scale of millimetres with a resolution of about 100 micrometres. Despite the gap between these length scales, results from the two techniques are found to complement and support each other in the characterization of the identity and distribution of nitroxide radicals derived from the Hindered Amine Stabilizer (HAS) Tinuvin 770 in poly(acrylonitrile-butadiene-styrene) (ABS) copolymers. DEER measurements demonstrate that there is no significant formation of biradicals from the bifunctional HAS, and provide the distributions of local radical concentrations. These distributions are poorly resolved for model-free analysis of the DEER data by the Tikhonov regularization; the resolution was significantly improved by utilizing information obtained by ESRI. DEER data can be fitted with only one adjustable parameter, namely the average radical concentration, if 1D and 2D spectral--spatial ESRI results on both the spatial distribution of nitroxides and their distribution between the acrylonitrile--styrene-rich (SAN) and butadiene-rich (B) microphases are considered.

Journal Article↗
PubMed2005

Ethylene-styrene copolymerization with constrained geometry catalysts: a density functional study.

A density functional theory (DFT) study of the ethylene-styrene copolymerization process with titanium-based constrained geometry catalyst (CGC) is presented. To establish the difference between simplified CGC or real CGC models, i.e., considering all ligands of the catalyst, we have performed calculations for ethylene and styrene insertions in both models. Thus, we have used two different DFT functional, BP86 and B3L YP along with two basis set, LANL 2DZ (without polarization functions) and DZVP (including polarization functions). We have noted certain differences between theoretical results published by other authors and our theoretical and experimental data.

Journal Article↗
PubMed1997

Probing structure/function relationships of HIV-1 reverse transcriptase with styrene oxide N2-guanine adducts.

Details of the interactions between the human immunodeficiency virus (HIV-1) reverse transcriptase and substrate DNA were probed both by introducing site-specific and stereospecific modifications into DNA and by altering the structure of potential critical residues in the polymerase. Unadducted 11-mer DNAs and 11-mer DNAs containing R and S enantiomers of styrene oxide at N2-guanine were ligated with two additional oligonucleotides to create 63-mers that served as templates for HIV-1 reverse transcriptase replication. Oligonucleotides that primed synthesis 5 bases 3' to the adducts could be extended up to 1 base 3' and opposite the lesion. However, when the positions of the 3'-OH of the priming oligonucleotides were placed 1, 2, 3, 4, 5, and 6 bases downstream of the styrene oxide guanine adducts, replication was initiated, only to be blocked after incorporating 4, 5, 6, and 7 bases beyond the lesion. The sites of this adduct-induced termination corresponded to the position of the DNA where alpha-helix H makes contact with the DNA minor groove, 3-5 bases upstream of the growing 3' end. In addition, mutants of the polymerase in alpha-helix H (W266A and G262A) alter the termination probabilities caused by these DNA adducts, suggesting that alpha-helix H is a sensitive monitor of modifications in the minor groove of newly synthesized template-primer DNA several bases distal to the 3'-OH.

Base Sequence↗
PubMedDate not supplied

Metabolism and acute hepatotoxicity of styrene oxide in rats.

The metabolism and acute hepatotoxicity of styrene oxide were studied after ip administration of a high dose of 375 mg/kg to adult male rats. Liver glutathione was significantly depleted at 2 h, but became normal at 6 h. The activity of serum glutamic-oxaloacetic transaminase was increased during the entire period (24 h) of study, while the activities of alkaline phosphatase and serum glutamic-pyruvic transaminase were elevated at 2 and 24 h, respectively, after administration of the dose. Decreased body weights and increased liver weights were observed at 24 h. Both prothrombin time and urinary urobilinogen concentration were temporarily increased. While urinary mandelic and phenylglyoxylic acids were increased during the entire time period, urinary (but no fecal) nonprotein sulfhydryl contents were increased at 2 and 6 h. The results of biochemical tests of liver function suggest a mild liver pattern in rats treated acutely with styrene oxide.

Alanine Transaminase↗
PubMed1992

Investigation of the covalent binding of styrene-7,8-oxide to DNA in rat and mouse.

Styrene-7,8-oxide (SO), the main intermediate metabolite of styrene, induces hyperkeratosis and tumors in the forestomach of rats and mice upon chronic administration by gavage. The aim of this study was to investigate whether DNA binding could be responsible for the carcinogenic effect observed. [7-3H]SO was administered by oral gavage in corn oil to male CD rats at two dose levels (1.65 or 240 mg/kg). After 4 or 24 h, forestomach, glandular stomach and liver were excised, DNA was isolated and its radioactivity determined. At the 4 h time point, the DNA radioactivity was below the limit of detection in the forestomach and the liver. Expressed in the units of the covalent binding index, CBI = (mumol adduct/mol DNA nucleotide)/(mmol chemical administered/kg body wt), the DNA-binding potency was below 2.6 and 2.0 respectively. In the glandular stomach at 4 h, and in most 24 h samples, DNA was slightly radiolabeled. Enzymatic degradation of the DNA and separation by HPLC of the normal nucleotides showed that the DNA radioactivity represented biosynthetic incorporation of radiolabel into newly synthesized DNA. The limit of detection of DNA adducts in the glandular stomach was 1.0. In a second experiment, [7-3H]SO was administered by i.p. injection to male B6C3F1 mice. Liver DNA was analyzed after 2 h. No radioactivity was detectable at a limit of detection of CBI less than 0.6. In agreement with the relatively long half-life of SO in animals, the chemical reactivity of SO appears to be too low to result in a detectable production of DNA adducts in an in vivo situation. Upon comparison with the DNA-binding of other carcinogens, a purely genotoxic mechanism of tumorigenic action of SO is unlikely. The observed tumorigenic potency in the forestomach could be the result of strong tumor promotion by high-dose cytotoxicity followed by regenerative hyperplasia.

Animals↗
PubMed1992

Study of interaction of styrene oxide with angiotensin by mass spectrometry.

The present study describes how mass spectrometry was extensively applied to the characterization and quantification of modified amino acids within the polypeptide chain of Angiotensin I, chosen as model substrate, combining the use of fast atom bombardment mass spectrometry with gas chromatography--mass spectrometry. The reaction products after in vitro incubation of Angiotensin I with styrene oxide, a well known carcinogen, under different conditions, have been characterized: a prominent reactivity of several potential nucleophilic sites of Angiotensin I was shown, including two histidine residues and a tyrosine residue; it is worth noting that it has never been stated that tyrosine is highly reactive with styrene oxide. The results obtained demonstrate the usefulness of mass spectrometry for the structural determination of chemically modified amino acids in peptides and proteins, and the presence of a reliable relationship between reaction conditions and the production of alkylated amino acids. This characterization procedure offers the possibility of identifying reactive sites following exposure to unknown alkylating agents.

Angiotensin I↗