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PubMed2002

Quantitation in gradient high performance liquid chromatography/inductively coupled mass spectrometry investigated using diclofenac and chlorpromazine.

The use of directly coupled high performance liquid chromatography/inductively coupled plasma mass spectroscopy (HPLC/ICPMS) employing chlorine ((35)Cl/(37)Cl) detection has been investigated with respect to the detection and quantitation of the drugs diclofenac and chlorpromazine. By integration of peak areas in the 'chloratogram' (the chlorine specific HPLC chromatogram), a calibration curve was constructed, from which the concentrations could be determined. Chlorine detected HPLC/ICPMS is quantitative over a wide range of concentrations of pharmaceutical relevance for metabolite detection and the results reproducible (standard deviation +/- 0.43%) over multiple injections. Application of gradient chromatography and variation in the bulk mobile phase physicochemical properties has little effect on the ICPMS detection response for these compounds. This work indicates that the use of HPLC/ICPMS is likely to be quantitatively reliable for metabolism studies for a range of chlorinated xenobiotics.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1997

Solution structure by site directed tryptophan fluorescence in tear lipocalin.

The solution structure of the G strand of human tear lipocalin was deduced by site directed tryptophan fluorescence (SDTF). The fluorescent amino acid, tryptophan, was sequentially substituted for each native amino acid in the sequence of the G strand. The fluorescent properties resolved alternating periodicity as predicted for beta sheet structure, twists in the beta sheet, strand orientation in the lipocalin cavity, and the relative depth of residues in the cavity. A distribution of microstates with various orientations of dipoles in the side chain environments of the G strand revealed mobility on the nanosecond time scale. SDTF is broadly applicable to most proteins and will complement x-ray crystallography, site directed spin labeling by electron paramagnetic resonance (EPR), and nuclear magnetic resonance (NMR) in the determination of solution structure.

Carrier Proteins↗

PubMed1988

Computer simulation of biological interactions and reactivity.

Computer simulations of molecular motion provide a useful tool for analyzing dynamic aspects of macromolecular structure and function. In many cases, simulations can be compared to experimental results that provide an average estimate of molecular flexibility. For example, variations in computed molecular motions in different regions of a protein structure can be compared to refined B-values obtained from X-ray crystallographic refinement. Such comparisons both provide a detailed view of the motions responsible for crystalline disorder, and allow an evaluation of how crystal packing affects mobility of groups on the protein surface. In these applications, dynamics simulations provide a means of regenerating the temporal dimension of a structure whose average behavior is experimentally well defined in the crystal lattice. An additional benefit of the detailed and instantaneous view of molecular flexibility offered by simulation methods lies in its potential for exploring infrequent structural fluctuations or dynamic states of molecular association that cannot be examined in detail by X-ray methods, but are suggested on the basis of alternative structural information. For example, studies of the effects of surface chemical modification on interacting proteins can produce information concerning the sites, if not the exact details, of the intermolecular interactions. The present work describes some applications of molecular dynamics methods to the study of large molecular aggregates whose dynamic properties thus far have precluded detailed structural descriptions. These include simulations of an electrostatically associated electron transfer complex between cytochromes c and b5, some model systems for trans-membrane ion channels, and a phospholipid micelle.

Computer Simulation↗

PubMed2006

Minimally invasive total hip replacement with the patient in the supine position and the contralateral leg elevated.

OBJECTIVE: Supine positioning of the patient taking into account - the demands of anesthesia in an emergency requiring intubation, - minimal time for sterile draping, - patient position can be adjusted by the assistants, - easier implant positioning due to the supine position. Reduction of operative trauma with earlier mobilization and shorter rehabilitation time compared with conventional technique. Application of standard instruments and implants. INDICATIONS: Coxarthroses, necroses of the femoral head. CONTRAINDICATIONS: For the "gynecologic position": - hip joint arthrodesis of the contralateral side. - flexion of the contralateral side < 20 degrees . For minimally invasive total hip replacement: - severe anatomic deformities. - revision operations. POSITIONING AND SURGICAL TECHNIQUE: Supine position of the patient with the contralateral leg held at approximately 30 degrees flexion in a gynecologic footrest attached to the operating table. Leg support that can be lowered for the leg being operated on. Minimally invasive anterolateral approach without dissection of muscles or tendons. Resection of the femoral neck and removal of the femoral head. Preparation of the acetabulum and implantation of the cup. Hyperextension of the leg by lowering the leg support with subsequent adduction and external rotation beneath the elevated contralateral leg. Preparation of the femur and implantation of the stem with subsequent repositioning and wound closure. RESULTS: 185 total hip replacements were performed with this positioning and surgical technique from September 2004 to June 2005. The first 108 minimally invasive procedures were compared with 117 conventional procedures. The patients operated in minimally invasive technique generally did better in terms of operating time, blood loss, use of analgesics, rehabilitation time, and functional outcomes. In seven patients, shaft fissures occurred within the first 3 months due to too abrupt intraoperative dislocation of the leg (learning curve!), but were all treated by application of cerclage and healed uneventfully.

Adult↗

PubMed1998

Use of electron spectroscopic imaging to determine element composition of the melanin granules in the stria vascularis of the guinea pig.

Electron spectroscopic imaging (ESI) was used to analyze the element content of melanin granules in the stria vascularis seen in ultrathin sections of Spurr-embedded cochleae of the guinea pig. To determine element composition, ESI images were taken at different ionization edges, and non-specific background signals were subtracted digitally by an image processing system. The presence of calcium and nitrogen in the melanin granules could be demonstrated clearly. The calcium identified in the melanin granules was then compared with the spatial distributions of calcium binding sites after the application of an antimonate precipitation method, which was used to localize loosely bound calcium. Despite a high calcium concentration within the granules, only very small single scattered calcium precipitates could be detected between these structures as compared with the amount of calcium precipitates attached to the plasma membrane or located within the cell nuclei. The nearly complete absence of precipitates within the melanin granules after the application of antimonate suggests differences in calcium binding and mobility involved in various physiological processes of ion balance regulation within the stria vascularis.

Animals↗

PubMed1980

Testing carrier models of cotransport using the binding kinetics of non-transported competitive inhibitors.

The kinetic equations representing the binding of a non-transported competitive inhibitor are derived from three variations of the carrier model of cotransport. These are (a) the model in which the binding sequence of activator and substrate is random (random bi-bi); (b) the model in which activator must bind before substrate (ordered bi-bi, activator essential), and (c) the model in which substrate must bind before activator (ordered bi-bi, activator non-essential). In general it is found that the kinetic equations for inhibitor binding are considerably simpler and easier to test than the corresponding transport equations. The effect of trans-inhibitor, transported substrate, activator concentration and membrane potential on inhibitor binding are examined in some detail. The use of these results to test and characterize the three transport models is emphasized. Applications to transport mechanisms which are not of the mobile carrier type are also discussed. A summary of relevant experimental data interpreted in terms of the theoretical models concludes the paper.

Biological Transport↗

PubMed2006

Examination of a long-term clozapine administration by high resolution segmental hair analysis.

The long-term administration of clozapine could be verified by fine segmentation and analysis of single hairs of one person to examine the history of a multiple poisoning case. Segments of 1-2.5mm length were extracted by ultrasonification in 30 microl of the mobile phase (mixture of methanol+water, 50+50). By application of isocratic liquid chromatography and using narrow bore columns (Synergy Polar-RP, Phenomenex), an acceleration and miniaturization of the HPLC-MS-MS assay could be achieved. Total amounts of clozapine down to 30 fg (on column) and its desmethyl metabolite could be analysed in multiple reaction monitoring mode. According to typical sample amounts of approximately 16 microg, relevant hair concentrations higher than 1 pg/mg were detected. Significant and reproducible concentration profiles along the hair fibres revealed characteristic administration cycles. The administration time course - in particular the time of its termination - could be verified with a precision of a few days. The accuracy and reproducibility of the concentration profile was proven based on multiple investigations of single hairs. An individual hair growth rate of 0.55 mm/day was determined with a relative standard deviation of 8% by comparison of concentration profiles in hairs collected after a time span of 165 days.

Adult↗

PubMed2005

High-performance liquid chromatographic determination of lamivudine in human serum using liquid-liquid extraction; application to pharmacokinetic studies.

A simple, fast, and sensitive high performance liquid chromatographic (HPLC) assay was developed for quantitation of lamivudine in human serum. Lamivudine is polar compound and its extraction from the human serum in previously published HPLC methods involved either protein precipitation or solid phase extraction techniques. However, existence of endogenous peaks which interfere with the drug or appeared as late eluting peaks and lead to long run time of analysis has been reported. Application of either an ion pairing agent in the mobile phase or time consuming column purge has been used in the published methods. Present paper describes liquid - liquid extraction of lamivudine and internal standard (famotidine) using dichloromethane-isopropyl alcohol (1:1, v/v) as an extracting solvent and salting out approach. The mobile phase was a mixture of phosphate buffer (0.05 M) containing triethylamine (1 mL/L, v/v; pH 3.5) and methanol (91:9, v/v) at a flow rate of 2.2 mL/min. The analysis was performed on a column (150 mm x 6 mm i.d.) which was packed with 5 microm particles of ODS packing material. Under these conditions no interference in the assay from any endogenous substance was observed. The limit of quantification was evaluated to be 5 ng/mL. Accuracy and precision of the method were also studied and the technique was shown to be selective and linear into the concentration range of 5-2500 ng/mL. This method has been used in two randomized crossover bioequivalence studies of 100 and 150 mg lamivudine preparations in 12 and 24 healthy volunteers, respectively.

Administration, Oral↗

PubMed2004

The containment of oil spills in unconsolidated granular porous media using xanthan/Cr(III) and xanthan/Al(III) gels.

The gelation in situ of aqueous solutions of the biopolymer xanthan gum may be a method for temporarily containing oil spills in soil whilst the remediation procedure is planned and accomplished. The gelling reaction has been carried out using as crosslinking agents either Cr(III) or Al(III) cations. By using Cr(III) the gelation time, which has been measured for a range of xanthan and/or Cr(III) concentrations, is of the order of the hour. On the contrary, the gelation by means of Al(III) cations takes place at quite low pH and is instantaneous. Therefore, depending on the crosslinker adopted, rather different techniques must be used for generating the gel structure in situ. The gels have proven to be suitable for the containment of water and of many hydrocarbons without loosing their strength even for a long period of time. The rheological properties of xanthan aqueous solutions evidence a shear-thinning behaviour that is most favourable for the application. Theoretical considerations have permitted the establishment of the mobility conditions of xanthan solutions in porous media before the gelation, and the estimation of a suitable injection pressure. The experiments for investigating the mobility of xanthan solutions in porous media, and for simulating the containment of an oil spill, have been done using packed beds of uniformly sized spherical glass beads, in glass columns. The glass assembly made it possible to visualize the evolution of the phenomena of interest.

Aluminum↗

PubMed1998

Antihelminthic drugs in diffuse unilateral subacute neuroretinitis.

PURPOSE: To evaluate the efficacy of ivermectin and thiabendazole in confirmed cases of diffuse unilateral subacute neuroretinitis. METHODS: Two patients with diffuse unilateral subacute neuroretinitis were treated with anthelminthic drugs. The first patient was treated with ivermectin and the second, with thiabendazole. RESULTS: The worms were still mobile after treatment with ivermectin or thiabendazole. With the application of photocoagulation, the organisms were destroyed, and the patients' vision improved. CONCLUSION: In these two patients, ivermectin and thiabendazole were not effective in treating confirmed diffuse unilateral subacute neuroretinitis.

Acute Disease↗

PubMed1999

Treatment of metal-contaminated wastes: why select a biological process?

Nature has demonstrated some subtle and intricate mechanisms for selectively controlling the mobility of metal pollutants in the environment. However, the application of this science to technology has been disappointing. A small number of pilot-plant studies have been carried out to investigate the potential of microorganisms (primarily bacteria) to remove metals from liquid wastes but only one system in the past 15 years has been commercialized. In order to explain this lack of application, it is important to understand the effectiveness, robustness and reliability of biological processes involving metals and their ability to compete with proven physicochemical technologies.

Adsorption↗

PubMed2003

Phosphate-induced metal immobilization in a contaminated site.

To assess the efficiency of P-induced metal immobilization in soils, a pilot-scale field experiment was conducted at a metal contaminated site located in central Florida. Phosphate was applied at a P/Pb molar ratio of 4.0 with three treatments: 100% of P from H3PO4, 50% of P from H3PO4+ 50% of P from Ca(H2PO4)2, and 50% of P from H3PO4+5% phosphate rock in the soil. Approximately 1 year after P application, soil and plant samples were collected to determine mobility and bioavailability of selected metals (Pb, Zn, and Cu) using sequential extraction procedure and mineralogical characterization using X-ray diffraction (XRD) and scanning electron microscope-energy dispersive X-ray (SEM-EDX) analysis. Phosphorus distribution and soil pH effects were also evaluated. Phosphate was more effective in transforming soil Pb (to 53%) from the non-residual to the residual phase than soil Zn (to 15%) and soil Cu (to 13%). This was because Pb was immobilized by P via formation of an insoluble pyromorphite-like mineral in the surface and subsurface of the soil, whereas no phosphate mineral Zn or Cu was identified. While P amendment enhanced metal uptake in the roots of St. Augustine grass (Stenotaphrum secundatum), it significantly reduced metal translocation from root to shoot, especially Pb via formation of a pyromorphite-like mineral on the membrane surface of the root. A mixture of H3PO4 and phosphate rock was effective in metal immobilization, with less soil pH reduction and less soluble P. Although H3PO4 was effective in immobilizing Pb, its use should be limited to minimize soil pH reduction and potential eutrophication risk.

Biological Availability↗

PubMedDate not supplied

A new probe of pore geometry: diffusive MASS NMR.

NMR methods are widely used to probe the structure and fluid dynamics of porous materials, as they are uniquely suited to these studies since NMR records the correlation of changing local magnetic fields over a time scale of ns to seconds. The local magnetic fields are established by local variations in the bulk magnetic susceptibility of the sample (and so are directly tied to the sample's local structure). The fluctuation in field that a spin sees is due to molecular transport (including molecular diffusion) through these local fields, and so reports on the length scales of structures and impediments to transport. We have developed a new set of methods DIFFUSIVE-MASS to provide a means of systematically varying the effective time scale of the measurement and thus the effective length scale. This new handle permits a detailed, microscopic picture of the structure and dynamics. Diffusive MASS NMR methods will permit a systematic set of methods and analysis for characterizing the chemistry, structure and fluid dynamics of the mobile phase in porous materials. The approach will be applicable to any diamagnetic material. In particular, the industry of oil discovery depends on understanding heterogeneous porous media.

Diffusion↗

PubMedDate not supplied

Separation of a breast cancer cell line from human blood using a quadrupole magnetic flow sorter.

We have developed a quadrupole magnetic flow sorter (QMS) to facilitate high-throughput binary cell separation. Optimized QMS operation requires the adjustment of three flow parameters based on the immunomagnetic characteristics of the target cell sample. To overcome the inefficiency of semiempirical operation/optimization of QMS flow parameters, a theoretical model of the QMS sorting process was developed. Application of this model requires measurement of the magnetophoretic mobility distribution of the cell sample by the cell tracking velocimetry (CTV) technique developed in our laboratory. In this work, the theoretical model was experimentally tested using breast carcinoma cells (HCC1954) overexpressing the HER-2/neu gene, and peripheral blood leukocytes (PBLs). The magnetophoretic mobility distribution of immunomagnetically labeled HCC1954 cells was measured using the CTV technique, and then theoretical predictions of sorting recoveries were calculated. Mean magnetophoretic mobilities of (1-3) x 10(-4) mm(3)/(T A s) were obtained depending on the labeling conditions. Labeled HCC1954 cells were mixed with unlabeled PBLs to form a "spiked" sample to be separated by the QMS. Fractional recoveries of cells for different flow parameters were examined and compared with theoretical predictions. Experimental results showed that the theoretical model accurately predicted fractional recoveries of HCC1954 cells. High-throughput (3.29 x 10(5) cells/s) separations with high recovery (0.89) of HCC1954 cells were achieved.

Algorithms↗

PubMed2004

Geochemical modulation of pesticide sorption on smectite clay.

Pesticide adsorption by soil clays can be dramatically influenced by the exchangeable cations present. Among the common exchangeable base cations in soils (Ca2+, Mg2+, K+, and Na+), K+-saturated clays frequently demonstrate the strongest affinity for pesticides. In the presence of multiple exchangeable cations in the system, we hypothesize that the magnitude of pesticide sorption to soil minerals is proportional to the fraction of clay interlayers saturated with K+ ions. To test this hypothesis, we measured sorption of three pesticides with different polarities (dichlobenil, monuron, and biphenyl) by homoionic K- and Ca-smectite (SWy-2) in KCl/CaCl2 aqueous solutions. The presence of different amounts of KCl and CaCl2 resulted in varying populations of K+ and Ca2+ on the clay exchange sites. The sorption of dichlobenil and, to a lesser extent monuron, increased with the fraction of K+ on clay mineral exchange sites. Ca- and K-SWy-2 displayed the same sorption capacities for nonpolar biphenyl. X-ray diffraction patterns indicated that at lower fractions of K+-saturation, exchangeable K+ ions were randomly distributed in clay interlayers and did not enhance pesticide sorption. At higher populations of K+ (vs Ca2+), demixing occurred causing some clay interlayers, regions, or tactoids to become fully saturated by K+, manifesting greatly enhanced pesticide sorption. The forward and reverse cation exchange reactions influenced not only K+ and Ca2+ populations on clays but also the nanostructures of clay quasicrystals in aqueous solution which plays an important, if not dominant, role in controlling the extent of pesticide sorption. Modulating the cation type and composition on clay mineral surfaces through cation exchange processes provides an environmental-safe protocol to manipulate the mobility and availability of polar pesticides, which could have applications for pesticide formulation and in environmental remediation.

Adsorption↗

PubMed2001

Ionic conductivity in crystalline polymer electrolytes.

Polymer electrolytes are the subject of intensive study, in part because of their potential use as the electrolyte in all-solid-state rechargeable lithium batteries. These materials are formed by dissolving a salt (for example LiI) in a solid host polymer such as poly(ethylene oxide) (refs 2, 3, 4, 5, 6), and may be prepared as both crystalline and amorphous phases. Conductivity in polymer electrolytes has long been viewed as confined to the amorphous phase above the glass transition temperature, Tg, where polymer chain motion creates a dynamic, disordered environment that plays a critical role in facilitating ion transport. Here we show that, in contrast to this prevailing view, ionic conductivity in the static, ordered environment of the crystalline phase can be greater than that in the equivalent amorphous material above Tg. Moreover, we demonstrate that ion transport in crystalline polymer electrolytes can be dominated by the cations, whereas both ions are generally mobile in the amorphous phase. Restriction of mobility to the lithium cation is advantageous for battery applications. The realization that order can promote ion transport in polymers is interesting in the context of electronically conducting polymers, where crystallinity favours electron transport.

Journal Article↗

PubMed1996

Lysophosphatidic acid-induced neurite retraction in PC12 cells: control by phosphoinositide-Ca2+ signaling and Rho.

The endogenous phospholipid mediator lysophosphatidic acid (LPA) caused growth cone collapse, neurite retraction, and cell flattening in differentiated PC12 cells. Neurite retraction was blocked by cytochalasin B and ADP-ribosylation of the small-molecular-weight G protein Rho by the Clostridium botulinum C-3 toxin. LPA induced a transient rise in the level of inositol 1,4,5-trisphosphate, and retraction was blocked by inhibitors of phospholipase beta. Repeated application of LPA elicited homologous desensitization of the Ca2+ mobilization response. The activation of the phosphoinositide (PIP)-Ca2+ second messenger system played a permissive role in the morphoregulatory response. Blockers of protein kinase C--chelerythrine, a myristoylated pseudosubstrate peptide, staurosporine, and depletion of protein kinase C from the cells by long-term phorbol ester treatment--all diminished neurite retraction by interfering with LPA-induced Ca2+ mobilization, which was required for the withdrawal of neurites. A brief 15-min treatment with 4 beta-phorbol 12-myristate 13-acetate also blocked retraction and Ca2+ mobilization, by inactivating the LPA receptor. Inhibition of protein tyrosine phosphorylation by herbimycin diminished retraction. Although activation of the PIP-Ca2+ second messenger system appears necessary for the Rho-mediated rearrangements of the actin cytoskeleton, bradykinin, which activates similar signaling events, failed to cause retraction, indicating that a yet unidentified novel mechanism is also involved in the LPA-induced morphoregulatory response.

Actins↗

PubMedDate not supplied

Arthroscopic "interval slide" in the repair of large rotator cuff tears.

An arthroscopic technique for coracohumeral ligament release from a retracted supraspinatus tendon is presented. The procedure is technically simple and can greatly improve the mobility of retracted rotator cuff tears, thus expanding the application of arthroscopic repair to larger tears.

Aged↗