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PubMed1994

Microbial predation in coupled chemostats: a global study of two coupled nonlinear oscillators.

Predator-prey systems in continuously operated chemostats exhibit sustained oscillations over a wide range of operating conditions. When two such chemostats interact through flow exchange, the interplay of the oscillation frequencies gives rise to a wealth of dynamic behavior patterns. Using numerical bifurcation techniques, we perform a detailed computational study of these patterns and the transitions between them as the coupling strength and relative frequencies of the two chemostats vary. We concentrate on certain strong resonance phenomena between the two frequencies as well as their mutual extinction and provide a representative sampling of possible phase portraits for our model system. Our observations corroborate recent mathematical results and case studies of coupled nonlinear chemical oscillators in which regions of mutual extinction as well as the Arnol'd structure for two-parameter families of maps of the plane have been observed. We highlight certain unexpected features of the operating diagram discovered through our computational study and discuss their implication for the dynamic response of the chemostat system.

Animals↗
PubMed1996

Coupled Markov chain model: characterization of membrane channel currents with multiple conductance sublevels as partially coupled elementary pores.

A parameterized Markov chain model is developed to represent the characteristics of channel currents that either are the superposition of many single channels or show multiple conductance sublevels. The simplified model takes the form of a set of binary chains that are interdependent according to a simple lumped coupling parameter. When varied, this parameter realizes a range of behaviors from tight coupling to complete independence. Other model parameters describe the intrinsic characteristics of the binary chains. An identification procedure for the model parameters is developed based on hidden Markov modeling ideas but incorporating a novel parameter estimation. The usefulness of the model in analyzing certain types of data is demonstrated with examples of real channel currents.

Animals↗
PubMed1993

Antioxidants impair the coupling of cell-surface ligand receptors to the inositol lipid signalling pathway in human T lymphocytes but not in Jurkat T lymphoblastic leukemia cells. Evidence that leukotrienes are not involved in the coupling mechanism.

Ligands including phytohaemagglutinin (PHA) and anti-CD3 monoclonal antibodies trigger the generation of inositol lipid-derived second messengers following their binding to cell-surface structures of human T lymphoid cells. Previous evidence has suggested that the generation of leukotrienes may play an intermediary role in coupling the ligation of T lymphoid cell-surface structures to the inositol lipid signalling system in these cells (A.R. Mire-Sluis et al. (1989) FEBS Lett. 258, 84-88). Here we have studied the actions of two novel selective leukotriene biosynthesis inhibitors, MK 886 and BW A4C and of two general lipid soluble antioxidants, butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) on this pathway. Neither MK 886 nor BW A4C abrogated stimulation of inositol lipid breakdown following PHA or anti CD3 treatment of T lymphocytes. By contrast, this pathway was inhibited by BHT and BHA. These observations, together with our failure to demonstrate the generation of lipoxygenase products following PHA stimulation of T lymphocytes, suggests that an antioxidant-sensitive step other than the generation of leukotrienes plays a critical role in coupling cell-surface receptors to the inositol lipid signalling system in these cells. By contrast none of these inhibitors abrogated ligand-stimulated inositol lipid signalling in Jurkat T acute lymphoblastic leukaemia cells. These results suggest a heterogeneity in the organization of the signal transduction machinery in lymphoid cells at different stages of differentiation.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1992

Determination of nalbuphine using high-performance liquid chromatography coupled to photodiode-array detection and gas chromatography coupled to mass spectrometry.

A procedure involving capillary column gas chromatography coupled to mass spectrometry and a method involving liquid chromatography coupled to a diode-array detector have been developed for the analysis of nalbuphine. The extraction step is the same for both techniques and involves extraction under alkaline conditions in chloroform-2-propanol-n-heptane (50:17:33, v/v/v) with levallorphan as the internal standard. After purification by acidic extraction and back alkaline extraction, drugs are derivatized with N,O-bis-(trimethylsilyl)trifluoroacetamide with 1% trimethylchlorosilane for gas chromatography-mass spectrometry and directly injected for high-performance liquid chromatography-diode-array detection. The limits of detection are 2.0 and 25.0 ng/mg, respectively.

Chromatography, High Pressure Liquid↗
PubMed2005

Determination of phosphoric acid triesters in human plasma using solid-phase microextraction and gas chromatography coupled to inductively coupled plasma mass spectrometry.

A simple and sensitive method for determination of phosphoric acid triesters at trace levels in human plasma sample is described. In this work, solid-phase microextraction (SPME) is employed as a sample preparation procedure for extraction and pre-concentration of alkyl and aryl phosphates followed by gas chromatography coupled to inductively coupled plasma mass spectrometry (GC-ICP-MS) for phosphorus-specific and very sensitive determination of these compounds in human plasma. The detection limits from blood plasma were 50 ngL(-1) (tripropyl phosphate), 17 ngL(-1) (tributyl phosphate), 240 ngL(-1) (tris(2-chloroethyl) phosphate) and 24 ngL(-1) (triphenyl phosphate). Sample preparation involves plasma deproteinization followed by direct immersion SPME with 65 microm poly(dimethylsiloxane/divinylbenzene) fiber. Extraction was performed at 40 degrees C for 30 min and at pH 7.0 in 10 mM sodium carbonate buffer. The reported method, to our knowledge, describes the first application of SPME with element-specific detection for analysis of phosphoric acid esters. Application of the method to the plasma samples, previously stored in poly(vinyl chloride) plasma bags revealed the presence of triphenyl phosphate, which was further confirmed by SPME GC time-of-flight high-resolution mass spectrometry.

Chemical Fractionation↗
PubMed2006

On-fibre solid-phase microextraction coupled to conventional liquid chromatography versus in-tube solid-phase microextraction coupled to capillary liquid chromatography for the screening analysis of triazines in water samples.

This paper compares the advantages and disadvantages of two different configurations for the extraction of triazines from water samples: (1) on-fibre solid-phase microextraction (SPME) coupled to conventional liquid chromatography (LC); and (2) in-tube SPME coupled to capillary LC. In-tube SPME has been effected either with a packed column or with an open capillary column. A critical evaluation of the main parameters affecting the performance of each method has been carried out in order to select the most suitable approach according to the requirements of the analysis. In the on-fibre SPME configuration the fibre coating was polydimethylsiloxane (PDMS)-divinylbenzene (DVB). The limits of detection (LODs) obtained with this approach under the optimized extraction and desorption conditions were between 25 and 125 microg/L. The in-tube SPME approach with a C18 packed column (35 mm x 0.5 mm I.D., 5 microm particle size) connected to a switching micro-valve provided the best sensitivity; under such configuration the LODs were between 0.025 and 0.5 microg/L. The in-tube SPME approach with an open capillary column coated with PDMS (30 cm x 0.25 mm I.D., 0.25 microm of thickness coating) connected to the injection valve provided LODs between 0.1 and 0.5 microg/L. In all configurations UV detection at 230 nm was used. Atrazine, simazine, propazine, ametryn, prometryn and terbutryn were selected as model compounds.

Chromatography, Liquid↗
PubMed2006

Flow injection on-line solid phase extraction coupled with inductively coupled plasma mass spectrometry for determination of (ultra)trace rare earth elements in environmental materials using maleic acid grafted polytetrafluoroethylene fibers as sorbent.

A new sorbent, maleic acid grafted polytetrafluoroethylene fiber (MA-PTFE), was prepared and evaluated for on-line solid-phase extraction coupled with inductively coupled plasma mass spectrometry (ICP-MS) for fast, selective, and sensitive determination of (ultra)trace rare earth elements (REEs) in environmental samples. The REEs in aqueous samples at pH = 3.0 were selectively extracted onto a microcolumn packed with the MA-PTFE fiber, and the adsorbed REEs were subsequently eluted on-line with 0.9 mol l(-1) HNO3 for ICP-MS determination. The new sorbent extraction system allows effective preconcentration and separation of the REEs from the major matrix constituents of alkali and alkali earth elements, particularly their separation from barium that produces considerable isobaric interferences of 134Ba16O1H+, 135Ba16O+, 136Ba16O1H+, and 137Ba16O+ on 151Eu+ and 153Eu+. With the use of a sample loading flow rate of 7.4 ml min(-1) for 120 s preconcentration, enhancement factors of 69-97 and detection limits (3s) of 1-20 pg l(-1) were achieved at a sample throughput of 22 samples h(-1). The precision (RSD) for 16 replicate determinations of 50 ng l(-1) of REEs was 0.5-1.1%. The developed method was successfully applied to the determination of (ultra)trace REEs in sediment, soil, and seawater samples.

Journal Article↗
PubMed2005

Distribution of elements binding to molecules with different molecular weights in aqueous extract of Antarctic krill by size-exclusion chromatography coupled with inductively coupled plasma mass spectrometry.

The distribution of silver, arsenic, cadmium, cobalt, chromium, copper, iron, manganese, nickel, lead, selenium and zinc binding to species with different molecular weight in aqueous extract of krill was studied by on-line size-exclusion chromatography (SEC)/inductively coupled plasma mass spectrometry (ICP-MS). The extract was fractionated in three fractions with different molecular weight (MW) ranges (>20,000 relative molecular mass (rel. mol. mass), 2000-20,000 rel. mol. mass and <2000 rel. mol. mass), which were further analyzed by SEC with columns having different optimum fractionation ranges in order to obtain more detailed information about the MW distribution of the elements. Various distribution profiles for the target elements among different MW ranges were observed. The results obtained indicated that manganese, zinc, silver, cadmium and lead species were mostly distributed in the higher MW range (>20,000 rel. mol. mass). In the case of chromium, iron, cobalt, arsenic and selenium, most of them bind to species with lower MW (<2000 rel. mol. mass). Only copper and nickel species was predominantly present in middle MW range (2000-20,000 rel. mol. mass). Further speciation of arsenic compounds in the small MW fraction was carried out with anion exchange chromatography (AEC) coupled with ICP-MS. The results showed that the dominant arsenic species in this fraction is As(III) (63% of extractable arsenic), while As(V) (13%) and two unknown arsenic species (19% and 5%, respectively) are present in lower amounts.

Animals↗
PubMed2005

Relating coupled map lattices to integro-difference equations: dispersal-driven instabilities in coupled map lattices.

Recently there has been a great deal of interest within the ecological community about the interactions of local populations that are coupled only by dispersal. Models have been developed to consider such scenarios but the theory needed to validate model outcomes has been somewhat lacking. In this paper, we present theory which can be used to understand these types of interaction when population exhibit discrete time dynamics. In particular, we consider a spatial extension to discrete-time models, known as coupled map lattices (CMLs) which are discrete in space. We introduce a general form of the CML and link this to integro-difference equations via a special redistribution kernel. General conditions are then derived for dispersal-driven instabilities. We then apply this theory to two discrete-time models; a predator-prey model and a host-pathogen model.

Animals↗
PubMed1989

Dynamics of a tightly coupled mechanism for flagellar rotation. Bacterial motility, chemiosmotic coupling, protonmotive force.

The bacterial flagellar motor is a molecular engine that couples the flow of protons across the cytoplasmic membrane to rotation of the flagellar filament. We analyze the steady-state behavior of an explicit mechanical model in which a fixed number of protons carries the filament through one revolution. Predictions of this model are compared with experimentally determined relationships between protonmotive force, proton flux, torque, and speed. All such tightly coupled mechanisms produce the same torque when the motor is stalled but vary greatly in their behavior at high speed. The speed at zero load predicted by our model is limited by the rates of association and dissociation of protons at binding sites on the rotor and by the mobility of force generators containing transmembrane channels that interact with these sites. Our analysis suggests that more could be learned about the motor if it were driven by an externally applied torque backwards (at negative speed) or forwards at speeds greater than the zero-load speed.

Bacterial Physiological Phenomena↗
PubMed1977

The preparation of carbohydrate-protein conjugates: cyanuric trichloride coupling of 2-aminoethyl glycosides, and mixed-anhydride coupling of 8-carboxyoctyl glycosides to bovine serum albumin.

Preparation of the following glycosides is described: 2-aminoethyl beta-D-glycosides of (A) 2-acetamido-3,4,6-trio-O-acetyl-2-deoxy-D-glucopyranose, (B) 2-acetamido-4-O-(2-acetamido-3,4,6-trio-O-acetyl-2-deoxy-beta-D-glucopyranosyl)-3,6-di-O-acetyl-2-deoxy-beta-D-glucopyranose (N,N'-diacetylchitobiose pentaacetate), (C) 4-O-(2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl)-2,3,6-trio-O-acetyl-beta-D-glucopyranose (cellobiose heptaacetate); 8-carboxyoctyl glycosides of (D) cellobiose, and (E) N,N'-diacetylchitobiose. Conjugates were prepared from (A), (B), and (C) by coupling to bovine serum albumin by cyanuric trichloride and subsequent deacetylation; (D) and (E) were coupled to bovine serum albumin by the mixed-anhydride reaction. Conjugates (A) and (B) were insoluble; conjugates (C), (D), and (E) functioned as artificial antigens and gave rise to precipitating antibodies in rabbits. Specificities of the antisera were determined by inhibition studies.

Antibodies↗
PubMed2000

Determination of inorganic and organic anionic arsenic species in water by ion chromatography coupled to hydride generation-inductively coupled plasma atomic emission spectrometry.

The development of an analytical methodology for the specific determination of arsenite, arsenate and the organic species monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), is described. The method is based on an ion chromatographic separation, coupled on-line to post-column generation of the gaseous hydrides by reaction with sodium tetrahydroborate in acidic medium. Detection and measurement were performed by inductively coupled plasma spectrometry operated in the atomic emission mode. Arsenic emission was monitored at 193.7 nm. Different types and sizes of anion-exchange columns, silica and polymeric, were tested using EDTA as eluent. Composition, acidity and flow-rate of the mobile phase were optimized in order to obtain the required resolution. Complete elution and resolution of the four species was achieved in about 6 min. Linear calibration curves were obtained in the 0.05-2 microg ml(-1) range for As(III), As(V) and MMA, and between 0.1 and 2.0 microg ml(-1) for DMA. The absolute limits of detection for 200-microl sample injections were in the ng range, with DMA the compound measured with less sensitivity. Results of the analyses of natural samples, such as river and ground waters spiked with the studied species, suggested that analyte recoveries might be dependent on the sample composition.

Arsenicals↗
PubMed2001

Determination of actinides in environmental and biological samples using high-performance chelation ion chromatography coupled to sector-field inductively coupled plasma mass spectrometry.

High-performance chelation ion chromatography, using a neutral polystyrene substrate dynamically loaded with 0.1 mM dipicolinic acid, coupled with sector-field inductively coupled plasma mass spectrometry has been successfully used for the separation of the actinides thorium, uranium, americium, neptunium and plutonium. Using this column it was possible to separate the various actinides from each other and from a complex sample matrix. In particular, it was possible to separate plutonium and uranium to facilitate the detection of the former free of spectral interference. The column also exhibited some selectivity for different oxidation states of Np, Pu and U. Two oxidation states each for plutonium and neptunium were found, tentatively identified as Np(V) and Pu(III) eluting at the solvent front, and Np(IV) and Pu(IV) eluting much later. Detection limits were 12, 8, and 4 fg for 237Np, 239Pu, and 241Am, respectively, for a 0.5 ml injection. The system was successfully used for the determination of 239Pu in NIST 4251 Human Lung and 4353 Rocky Flats Soil, with results of 570+/-29 and 2939+/-226 fg g(-1), respectively, compared with a certified range of 227-951 fg g(-1) for the former and a value of 3307+/-248 fg g(-1) for the latter.

Actinoid Series Elements↗
PubMed1999

Interface for capillary electrophoresis coupled with inductively coupled plasma atomic emission spectrometry.

A modified concentric nebulizer was used as the interface to couple capillary electrophoresis (CE) to inductively coupled plasma atomic emission spectrometry (ICP-AES). The CE capillary replaces the central tube of the concentric nebulizer. The tip of the nebulizer tapers slowly to allow uncertainty in the position of the capillary. A platinum wire was inserted into the CE capillary to provide electrical connection to the CE power supply. pH changes inside the capillary due to electrolysis of the background buffer electrolyte was small and has minimal effects on the CE separation. The peak broadening effects due to the nebulizing gas flow, however, were significant. Resolution decreases quickly when the flow-rate of the carrier gas increases. Sample stacking technique was used to improve the resolution of species of opposite charge, e.g., Cr(VI) vs. Cr(III) ions. Detection limit of Cr based on peak area is approximately 10 ppb for the CE-ICP-AES system.

Chromium↗
PubMed1997

63Cu-31P coupling constants and 63Cu quadrupole couplings from 31P CP/MAS spectra of copper (I)--phosphine complexes with aryldithiocarboxylates or benzoate.

Magic-angle spinning 31P NMR spectra of solid [CuS2C-Ph(PPh3)2] 1, [{CuS2C-pT}4(PPh3)2] 2, [{CuS2C-Ph}4(PPh3)2] 3. [CuS2C-Ph(dppm)]2 4 and [CuO2C-Ph(dppm)]2 5, (T = tolyl, dppm = bis(diphenylphosphino)methane) were obtained at 109.6 MH2. They consist of distorted quartets from non-equivalent phosphorus atoms and provide approximate values of the indirect spin-spin coupling constant J[63Cu,31P], that are indicative of the covalency of the dithiocarboxylate-copper bonding. The spacing distortions are related to a number of molecular and structural parameters and thereby allow an estimation of the copper quadrupole coupling constant e2qQ/h which, as expected, is smaller for tetra-coordinated (1, 2, 3 and 4) than for tri-coordinated (5) copper sites. The spectrum of 2 has been successfully simulated (including the isotope effects from the less abundant 65Cu isotope) using the full theory for calculation of the spin eigenfunctions of the quadrupolar nucleus.

Benzoates↗
PubMed1993

Determination of arsenic(III) and selenium(IV) using an on-line anodic stripping voltammetry flow cell with detection by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry.

An on-line anodic stripping voltammetry (ASV) flow system, interfaced with inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICPMS) detectors, has been used for determination of arsenic(III) and selenium(IV) and for elimination of polyatomic interferences which arise from chloride in sample matrices. Details of the working electrode preparation are discussed. Arsenic signals in ICP-AES were enhanced by as much as 10 times through preconcentration of sample volumes up to 5 mL. Using ICP-AES detection, recoveries for analyte spikes in 1:10 diluted urine were 102% for As(III) (matrix-matched standards) and 91% for Se(IV) (standards in electrolyte). Using ICPMS detection, determination of certified Se(IV) and Se(IV) spikes in diluted NIST SRM 2670 elevated urine gave recoveries of 92-103%, while recoveries of As(III) spikes in diluted NIST SRM 2670 urine ranged from 94 to 113%. High levels of chloride matrix exhibited little effect on the arsenic signal with ICP-AES or ICPMS detection. Elimination of the polyatomic interference ArCl+ in ICPMS was very efficient for diluted NIST SRM 2670 urine and for a synthetic matrix of 1000 micrograms/mL chloride.

Arsenic↗
PubMed2001

Sulfur-specific detection of impurities in cimetidine drug substance using liquid chromatography coupled to high resolution inductively coupled plasma mass spectrometry and electrospray mass spectrometry.

The use of liquid chromatography coupled to sector field inductively coupled plasma mass spectrometry (SF-ICP-MS) for the specific detection of sulfur-containing compounds is described. In the sulfur-containing drug substance cimetidine, structurally related impurities well below the 0.1% mass fraction level relative to the main drug substance could easily be detected. The structure of most of the impurities was confirmed by electrospray mass spectrometry (ESI-MS), and thus, the complementarity of the two techniques for drug analysis is shown. The limit of detection by SF-ICP-MS for cimetidine in solution was approximately 4-20 ng x g(-1), but it was blank-limited.

Chromatography, Liquid↗