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PubMed2000

Effects of Gas-Phase Basicity on the Proton Transfer between Organic Bases and Trifluoroacetic Acid in the Gas Phase: Energetics of Charge Solvation and Salt Bridges.

The unimolecular dissociation pathways and kinetics of a series of protonated trimer ions consisting of two organic bases and trifluoroacetic acid were investigated using blackbody infrared radiative dissociation. Five bases with gas-phase basicities (GB) ranging from 238.4 to 246.2 kcal/mol were used. Both the dissociation pathways and the threshold dissociation energies depend on the GB of the base. Trimers consisting of the two most basic molecules dissociate to form protonated base monomers with an E(0) ~ 1.4 eV. Trimers consisting of the two least basic molecules dissociate to form protonated base dimers with an E(0) ~ 1.1-1.2 eV. These results indicate that the structures of the trimers change as a function of the GB of the basic molecule. The predominant structure of the protonated trimers consisting of the two most basic molecules is consistent with a salt bridge in which both of the basic molecules are protonated, and the trifluoroacetic acid molecule is deprotonated, whereas the predominant structure of the protonated trimers consisting of the two least basic molecules are consistent with charge-solvated complexes in which the proton is shared. The structure of the trimer consisting of the base of intermediate basicity is less clear; it dissociates to form primarily protonated base dimer, but has an E(0) ~ 1.2 eV. These results are consistent with the structure of this trimer as a salt bridge, but the resulting dissociation A(-). BH(+) product does not appear to be stable as an ion pair in the dissociative transition state.

Journal Article↗
PubMed2005

Comprehensive density functional theory study on serine and related ions in gas phase: conformations, gas phase basicities, and acidities.

Density functional theory (DFT) calculations have been performed to investigate the gas-phase conformations of serine and its three related ions (serineH(+), serine(-), and serine(2-)). The full ensemble of possible conformations, 324 conformations for serine, 108 for serineH(+), 162 for serine(-) and 54 for serine(2-), were first surveyed at B3LYP/6-31G level, and then the obtained unique conformations were further refined at B3LYP/6-311+G level. From full optimizations, 74 unique conformations for seine, 14 for serineH(+), 11 for serine(-), and 4 for serine(2-) were located, and their relative energies were also determined at B3LYP/6-311+G level. Atoms in molecules (AIM) analysis was carried out to establish rigorous definition of hydrogen bonds. Six types of intramolecular H-bonds in conformers of serine, six types in serineH(+), three types in serine(-), and two types in serine(2-) were identified within the framework of AIM theory and their relative strengths were determined based on topological properties at bond critical points (BCPs) of H-bonds. The intramolecular H-bonds were demonstrated to play an important role in deciding the relative stability of conformations of amino acids and the related ions. The enthalpies and Gibbs free energies of protonation and deprotonation reactions of serine and its related ions were calculated at B3LYP/6-311+G//B3LYP/6-31G, and B3LYP/6-311+G//B3LYP/6-311+G level. The calculated results are both in excellent agreement with the experimental data. We demonstrate in this study that B3LYP is an efficient and accurate method to predict the thermochemical and structural parameters of amino acids and the related ions.

Journal Article↗
PubMed2004

Effect of varying the oil phase on the behavior of pH-responsive latex-based emulsifiers: demulsification versus transitional phase inversion.

Sterically stabilized polystyrene latexes (previously described by Amalvy, J. I.; et al. Chem. Commun. 2003, 1826) were evaluated as pH-responsive particulate emulsifiers for the preparation of both oil-in-water and water-in-oil emulsions. The steric stabilizer was a well-defined AB diblock copolymer where A is poly(2-(dimethylamino)ethyl methacrylate) and B is poly(methyl methacrylate). Several parameters were varied during the emulsion preparation, including the polarity of the oil phase, the latex concentration, surface concentration of copolymer stabilizer, and solution pH. Nonpolar oils such as n-dodecane gave oil-in-water emulsions, and polar oils such as 1-undecanol produced water-in-oil emulsions. In both cases, these emulsions proved to be stimulus-responsive: demulsification occurred rapidly on adjusting the solution pH. Oils of intermediate polarity such as methyl myristate or cineole led to emulsions that underwent transitional inversion on adjusting the solution pH. All emulsions were polydisperse and typically ranged from 40 to 400 microm diameter, as judged by optical microscopy and Malvern Mastersizer measurements. Critical point drying of the emulsion droplets, followed by scanning electron microscopy studies, confirmed that the latex particles were adsorbed as a single monolayer at the oil/water interface, as anticipated.

Journal Article↗
PubMed1990

Phase I/II study of the anti-oestrogen zindoxifene (D16726) in the treatment of advanced breast cancer. A Cancer Research Campaign Phase I/II Clinical Trials Committee study.

We report a phase I/II study of the indole derivative, zindoxifene, an anti-oestrogen with intrinsic oestrogenic activity. We have treated 28 women with advanced breast cancer of whom 26 had received prior endocrine therapy. Oral zindoxifene doses ranged from 10 to 100 mg daily; doses were escalated in some patients. Twenty-five patients were assessed for response; the remaining three patients completed less than 3 weeks of treatment. There were no objective responses; disease stabilised in seven patients for up to 5 months and progressed in the remaining 18. Five patients (including three treated with tamoxifen) responded to subsequent endocrine therapy. Nausea, which was dose-limiting, affected half of the patients treated with 80 mg daily. Metabolites of zindoxifene were detectable in serum at all doses used, and sex hormone binding globulin (SHBG) levels showed a strong tendency to rise at the higher doses, indicating that zindoxifene is absorbed and has biological activity. We conclude that zindoxifene in the doses used in this study has only marginal therapeutic activity in the treatment of advanced breast cancer.

Aged↗
PubMed1992

Phase II trials of fosquidone, (GR63178A), in colorectal, renal and non-small cell lung cancer. CRC Phase II Clinical Trials Committee.

A total of 61 eligible patients with metastatic cancer have been treated in a series of Phase II trials of the novel pentacyclic pyrroloquinone, fosquidone. Tumour types were colorectal (23), renal (21), and non small cell lung (17). No patient had received prior chemotherapy. The drug was given intravenously as a 20 min infusion at the dose of 120 mg-2 on days 1 to 5 every 3 weeks. Treatment was well tolerated; the only significant side effects being mild nausea and generalised musculo-skeletal pains. Response was assessed after two cycles of therapy. No patient achieved an objective partial response. A total of nine patients demonstrated stable disease for a median duration of 11 weeks. Using this schedule of administration, fosquidone has no significant antitumour activity in this group of tumours.

Adult↗
PubMed2000

Screening, identification and quantitation of benzodiazepines in serum by solid phase extraction on a cyanopropyl phase using high performance liquid chromatography and photodiode array detection.

A screening procedure for benzodiazepines in serum is presented. The compounds are extracted over a cyanopropyl phase followed by identification and determination via high performance liquid chromatography and photodiode array detection. Diazepam (CAS 439-14-5), flunitrazepam (CAS 1622-62-4), nordazepam (CAS 1088-11-5), oxazepam (CAS 604-75-1) and temazepam (CAS 846-50-4) are quantified. Retention data of 42 benzodiazepines and their metabolites as well as hydrolysis products are listed. This assay leads to an expansion of a known systematic toxicological analysis system to identify pharmaceuticals, drugs of abuse and pesticides.

Anti-Anxiety Agents↗
PubMed1986

Fluid phase endocytosis by cultured rat hepatocytes and perfused rat liver: implications for plasma membrane turnover and vesicular trafficking of fluid phase markers.

Hepatocytes take up a variety of ligands via receptor-mediated endocytosis, yet little is known regarding either the volume of fluid or the amount of membrane internalized via endocytosis in liver cells. In these studies, we have utilized radiolabeled inulin to characterize fluid phase endocytosis by rat hepatocytes in primary culture and perfused rat liver. Uptake of inulin by cultured hepatocytes was nonlinear with time, occurring most rapidly during the first 2 min. Inulin uptake and efflux in cultured hepatocytes and inulin uptake by perfused rat liver were kinetically compatible with the entry of inulin into a rapidly (t1/2, 1-2 min) turning-over (presumably endosomal) compartment that exchanged contents with the extracellular space and comprised approximately 3% of hepatocyte volume, as well as entry into and concentration of inulin within slowly (t1/2, greater than 1 hr) turning-over storage compartments. Based on inulin uptake, it is estimated that cultured hepatocytes endocytosed the equivalent of 20% or more of their volume and 5 or more times their plasma membrane surface area each hour. Neither chloroquine (1 mM) nor taurocholate (200 microM) affected inulin handling by cultured cells, whereas colchicine (10 microM) inhibited transfer to storage compartments by greater than 50%. In conjunction with our previous observations, the present findings suggest that inulin endocytosed across the basolateral membrane is largely (congruent to 80%) regurgitated back into plasma, with smaller amounts transported to intracellular storage compartments (congruent to 18%) or to bile (congruent to 2%). Transport of inulin via these pathways is unaffected by taurocholate and does not require vesicle acidification, whereas intact microtubular function is required for transfer to storage compartments or biliary secretion.

Animals↗
PubMed2004

Solid-phase microextraction (SPME) of permethrin residues from cucumber using a silica-bonded phase-coated stainless steel fibre.

Solid-phase microextraction (SPME) is a rapid, economic and solvent-free sample preparation method for the isolation of an analyte from its matrix. The technique uses a few centimetres of some adsorptive materials such as activated charcoal, polydimethylsiloxane or octadecyl silane coated onto fused silica optical fibres or, more recently, stainless steel fibres mounted into a microsyringe. The proposed method allows the extraction of permethrin from cucumber matrix into the coating, avoiding sample handling and saving evaporation of solvents and concentration steps. Adsorbed permethrin was desorbed in the split/splitless injection port of the gas chromatograph. The time required for each run was about 1.5 h, which gave a preconcentration of several orders of magnitude. The method could separate and quantify cis- and trans-isomers of permethrin. The calibration curve showed linearity in the range 1-9 micrograms ml-1, with detection limits of 0.03 and 0.05 microgram ml-1 for the cis- and trans-isomers of permethrin, respectively. The method had a recovery rate of about 70% and a relative standard deviation of less than 13%. Results suggest that this procedure provides a rapid and sensitive alternative method to those currently available.

Adsorption↗
PubMed2002

Hg reactions in the presence of chlorine species: homogeneous gas phase and heterogeneous gas-solid phase.

The kinetics of Hg chlorination (with HCl) was studied using a flow reactor system with an online Hg analyzer, and speciation sampling using a set of impingers. Kinetic parameters, such as reaction order (alpha), overall rate constant (k'), and activation energy (Ea), were estimated based on the simple overall reaction pathway. The reaction order with respect to C(Hg), k', and Ea were found to be 1.55, 5.07 x 10(-2) exp(-1939.68/T) [(microg/m3)(-055)(s)(-1)]. and 16.13 [kJ/ mol], respectively. The effect of chlorine species (HCl, CH2Cl2) on the in situ Hg capture method previously developed (28) was also investigated. The efficiency of capture of Hg by this in situ method was higher than 98% in the presence of chlorine species. Furthermore, under certain conditions, the presence of chlorine enhanced the removal of elemental Hg by additional gas-phase oxidation.

Environmental Pollutants↗
PubMed2002

An integrated "4-phase" approach for setting endocrine disruption screening priorities--phase I and II predictions of estrogen receptor binding affinity.

Recent legislation mandates the US Environmental Protection Agency (EPA) to develop a screening and testing program for potential endocrine disrupting chemicals (EDCs), of which xenoestrogens figure prominently. Under the legislation, a large number of chemicals will undergo various in vitro and in vivo assays for their potential estrogenicity, as well as other hormonal activities. There is a crucial need for priority setting before this strategy can be effectively implemented. Here we report an integrated computational approach to priority setting using estrogen receptor (ER) binding as an example. This approach rationally integrates different predictive computational models into a "Four-Phase" scheme so that it can effectively identify potential estrogenic EDCs based on their predicted ER relative binding affinity (RBA). The system has been validated using an in-house ER binding assay dataset for 232 chemicals that was designed to have both broad structural diversity and a wide range of binding affinities. When applied to 58,000 chemicals identified by Walker et al. as candidates for endocrine disruption screening, some 9100 chemicals were predicted to bind to ER. Of these, only 3600 were expected to bind to ER at RBA values up to 100,000-fold less than that of 17beta-estradiol. The method ruled out 83% of the chemicals as non-binders with a very low rate of false negatives. We believe that the same integrated scheme will be equally applicable to endpoints of other endocrine disrupting mechanisms, e.g. androgen receptor binding.

Biological Assay↗
PubMed1987

A modified, solid phase radioimmunoassay for the differential diagnosis of acute and convalescent phases of hepatitis A infection.

The commercial assays for diagnosing the presence of hepatitis A antibodies (HAVAB; Abbott Laboratories, North Chicago, IL) or the presence of IgM class anti-hepatitis A virus antibodies (HAVAB-M; Abbott) do not provide precise information as to the timing of the acute infection. IgM class antibodies are detected as late as six months after the acute infection. In this study the authors describe a modified HAVAB test that inactivates the IgM class antibodies. It thus measures the proportion of IgG antibodies out of the total anti-hepatitis A virus antibodies. In a study of 139 patients with impaired liver function, the available and modified tests showed good agreement except for the convalescent phase of hepatitis A. During serial testing for three months after the acute infection, the commercial tests continuously detected IgM class antibodies. The modified test detected predominantly IgG class antibodies from four weeks on. By six weeks, 85% of the patients had predominantly IgG class antibodies. The modified test thus provides information on the timing of recent hepatitis A infection.

Acute Disease↗
PubMed1984

Direct separation of enantiomer of ephedrine and some analogues by reversed-phase liquid chromatography using (+)-di-n-butyltartrate as the liquid stationary phase.

A new chromatographic technique for the separation of enantiomers of beta-aminoalcohols is presented. A chiral complexing agent, (+)-di-n-butyltartrate (DBT), is used as liquid stationary phase, adsorbed on Phenyl Hypersil. The solutes are eluted with phosphate buffer solutions containing hexafluorophosphate as the counter ion. The resolution of the enantiomers is based on a stereoselective complex formation between DBT and the ion pairs. Separation factors of 1.1 to 1.2 are obtained for ephedrine and norephedrine. The influence of sample structure of some analogues on stereoselectivity is demonstrated.

Chemical Phenomena↗
PubMed2000

Solid-phase microextraction and headspace solid-phase microextraction for the determination of high molecular-weight polycyclic aromatic hydrocarbons in water and soil samples.

The feasibility of direct-immersion (DI) solid-phase microextraction (SPME) and headspace (HS) SPME for the determination of high-ring polycyclic aromatic hydrocarbons (PAHs) (4- to 6-ring PAHs) in water and soil samples is studied. Three SPME fibers--100- and 30-microm polydimethylsiloxane (PDMS) and 85-microm polyacrylate (PA) fibers-are compared for the effective extraction of PAHs. Parameters affecting the sorption of PAHs into the fiber such as sampling time, sampling volume, and temperature are also evaluated. The extracted amounts of high-ring PAHs decrease with the decreasing of film thickness, and the 100-microm PDMS has the highest extraction efficiency than 85-microm PA and 30-microm PDMS fibers. Also, the extraction efficiency decreases with the increasing molecular weights of PAHs. Of the 10 high-ring PAHs, only fluoranthene and pyrene can reach equilibrium within 120 min at 25 degrees C for DI-SPME in a water sample. Increasing the temperature to 60 degrees C can increase the sensitivity of PAHs and shorten the equilibrium time. A 0.7- to 25-fold increase in peak area is obtained for DI-SPME when the working temperature is increased to 60 degrees C. For HS-SPME, the extraction efficiency of PAHs decrease when the headspace volume of the sampling system increases. All high-ring PAHs can be detected in a water sample by increasing the temperature to 80 degrees C. However, only 4- and 5-ring PAHs can be quantitated in a CRM soil sample when HS-SPME is used. The addition of a surfactant with high hydrophilic property can effectively enhance the sensitivity of high-ring PAHs. HS-SPME as well as DI-SPME with 100-microm PDMS or 85-microm PA fibers are shown to be suitable methods for analyzing high-ring PAHs in a water sample; however, this technique can only apply in a soil sample for PAHs having up to 5 rings.

Chromatography, Gas↗
PubMedDate not supplied

Application of HPLC with silica-phase and reversed-phase eluents for the determination of clomipramine and demethylated and 8-hydroxylated metabolites.

A rapid and efficient high-performance liquid chromatographic method using a reversed-phase eluent of methanol-water with butylamine on a silica column was developed for the separation and quantitation of clomipramine (CMI), its demethylated metabolites (desmethyl-clomipramine and didesmethyl-clomipramine [DDCMI]), and its hydroxylated metabolites (8-hydroxy-clomipramine and 8-hydroxy-desmethylclomipramine). A liquid-liquid extraction procedure, which involved an alkaline extraction with heptane-isoamyl alcohol, first from a 1-mL serum sample and then from the acidic back extract, was used. The chromatographic separation was rapid (20 min), and the ultraviolet detection (at 254 nm) was sufficiently sensitive (limit of detection, 5-10 ng/mL). Except for DDCMI, the calibration was linear (r > 0.99, n = 5), and within-day and day-to-day coefficients of variation remained less than 11%. The method was used to analyze CMI and its metabolites in the serum of depressive patients and to determine their hydroxylation and demethylation capacities.

Adult↗
PubMed1983

Solid phase synthesis of polynucleotides. VIII. Synthesis of mixed oligodeoxyribonucleotides by the phosphotriester solid phase method.

A solid phase method for the simultaneous synthesis of mixed oligonucleotides using a phosphotriester approach has been developed. For this synthesis, a mixture of mono or dimeric coupling units is used, and a slight difference in the reactivity of those units is found. However, this difference does not hamper the simultaneous, mixed oligonucleotide synthesis, and the sequence analysis of a product demonstrates the existence of all desired sequences in the final mixture.

Base Sequence↗
PubMed2000

Efficacy of phase-feeding in supporting growth performance of broiler chicks during the starter and finisher phases.

A feeding regimen has been developed that uses regression equations to predict amino acid requirements over time. Phase-feeding (PF) of broilers was tested to evaluate its efficacy compared with feeding broilers NRC or Illinois ideal chick protein (IICP) recommendations. In Experiment 1, NRC or IICP requirements for lysine, sulfur amino acids, and threonine were fed from 0 to 21 d, whereas PF was tested using a series of three diets (0 to 7, 7 to 14, and 14 to 21 d). No differences (P > 0.05) in weight gain, feed intake, feed efficiency, digestible amino acid intake, or gain per unit digestible amino acid intake were noted among chicks fed NRC, IICP, or PF diets. In Experiment 2, NRC or IICP requirements were fed from 40 to 61 d, whereas PF was tested using a series of three diets (40 to 47, 47 to 54, and 54 to 61 d). No differences (P > 0.05) in weight gain or feed intake were observed, but the feed efficiency of birds fed the IICP diet was decreased (P < 0.05). The IICP and PF diets resulted in decreased (P < 0.05) digestible lysine and threonine intake; gain per unit digestible lysine and threonine intake was increased (P < 0.05) by PF. No differences (P < 0.05) in breast meat, wing, or leg yield were noted among treatments. Economic analysis indicated that PF may facilitate reduced dietary costs without sacrificing growth performance or carcass yield.

Amino Acids, Sulfur↗