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Phosphate Buffer Solution (phosphate + buffer_solution)
Selected AbstractsA colorimetric study of oenin copigmented by procyanidinsJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 2 2007Bénédicte Berké Abstract A colorimetric method was used to analyse the influence of procyanidin structure on colour changes of malvidin 3- O -glucoside (oenin) solution resulting from copigmentation. The study was performed in hydroalcoholic citrate/phosphate buffer solution (120 g L,1) at pH 3.6 and ionic strength 0.2 mol L,1. Chromatic L*, a* and b* coordinates (CIELAB, D65/10° illuminant/observer condition) obtained from spectral curves recorded between 360 and 830 nm allowed the calculation of lightness L*, chroma C* and hue angle hab. In general, addition of copigment induced colour enhancement (loss of lightness and increased chroma). The prevailing parameters affecting colour changes were lightness and chroma for monomers and lightness and hue for procyanidins B5 and B8 (C4,C6 dimers). A small blueing effect was observed only for catechin monomer-copigmented solutions. For procyanidin copigments, as the structural complexity of the copigment increased, the hue angle moved to yellower values. The ester gallate of dimer B2 produced the strongest modification of colour attributes of oenin solution. Copyright © 2006 Society of Chemical Industry [source] Poly(pyridine-3-boronic acid)/Multiwalled Carbon Nanotubes Modified Glassy Carbon Electrodes for Simultaneous Determination of Ascorbic Acid, 3,4-Dihydroxyphenylacetic Acid and Uric AcidELECTROANALYSIS, Issue 19 2010Zhijiao Wu Abstract Poly(pyridine-3-boronic acid) (PPBA)/multiwalled carbon nanotubes (MWCNTs) composite modified glassy carbon electrode (GCE) was used for the simultaneous determination of ascorbic acid (AA), 3,4-dihydroxyphenylacetic acid (DOPAC) and uric acid (UA). The anodic peaks for AA, DOPAC and UA at the PPBA/MWCNTs/GCE were well resolved in phosphate buffer solution (pH,7.4). The electrooxidation of AA, DOPAC and UA in the mixture solution was investigated. The peak currents increase with their concentrations increasing. The detection limits (S/N=3) of AA, DOPAC and UA are 5,µM, 3,µM and 0.6,µM, respectively. [source] Green Synthesis of Silver Nanoparticles Using Ionic Liquid and Application for the Detection of Dissolved OxygenELECTROANALYSIS, Issue 6 2010Tsung-Hsuan Tsai Abstract The electrochemical synthesis of silver nanoparticles (nano-Ag) has been successfully carried out on glassy carbon electrode (GCE) and indium tin oxide electrode (ITO) using 1-butyl-3-methylimidazolium tetrafluoroborate (BMT) as green electrolytes. Further the electrodeposited nano-Ag modified ITO electrode has been examined using atomic force microscopy (AFM), and X-ray diffraction studies (XRD). The electrodeposited Ag nanoparticles on ITO were found in the size range of 5 to 35,nm. The nano-Ag film modified GCE was further coated with nafion (Nf) and BMT (1,:,1 ratio) mixture and found to be stable in BMT and in pH,7 phosphate buffer solution (PBS). The nano-Ag/BMT-Nf film modified GCE successfully applied for the oxygen reduction reaction in neutral pH (pH,7.0 PBS). The proposed film modified GCE successfully reduces the over potential and show well defined reduction peaks for the detection of dissolved oxygen using cyclic voltammetry (CV) and rotating disc voltammetry (RDE). The film also applied for the detection of dissolved oxygen using electrochemical impedance spectroscopic studies (EIS). [source] Direct Electrochemistry and Electrocatalysis of Myoglobin Immobilized on Gold Nanoparticles/Carbon Nanotubes Nanohybrid FilmELECTROANALYSIS, Issue 17 2008Wei Cao Abstract A novel nanohybrid material, constructed by gold nanoparticles (GNPs) and multiwalled carbon nanotubes (MWNTs), was designed for immobilization and biosensing of myoglobin (Mb). Morphology of the nanohybrid film was characterized by SEM. UV-vis spectroscopy demonstrated that Mb on the composite film could retain its native structure. Direct electrochemistry of Mb immobilized on the GNPs/MWNTs film was investigated. The immobilized Mb showed a couple of quasireversible and well-defined cyclic voltammetry peaks with a formal potential of about ,0.35,V (vs. Ag/AgCl) in pH,6.0 phosphate buffer solution (PBS) solution. Furthermore, the modified electrode also displayed good sensitivity, wide linear range and long-term stability to the detection of hydrogen peroxide. The experiment results demonstrated that the hybrid matrix provided a biocompatible microenvironment for protein and supplied a necessary pathway for its direct electron transfer. [source] Study on Glucose Biofuel Cells Using an Electrochemical Noise DeviceELECTROANALYSIS, Issue 14 2008Yueming Tan Abstract An electrochemical noise (ECN) device was utilized for the first time to study and characterize a glucose/O2 membraneless biofuel cell (BFC) and a monopolar glucose BFC. In the glucose/O2 membraneless BFC, ferrocene (Fc) and glucose oxidase (GOD) were immobilized on a multiwalled carbon nanotubes (MWCNTs)/Au electrode with a gelatin film at the anode; and laccase (Lac) and an electron mediator, 2,2,-azinobis (3-ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS), were immobilized on a MWCNTs/Au electrode with polypyrrole at the cathode. This BFC was performed in a stirred acetate buffer solution (pH,5.0) containing 40,mmol/L glucose in air, with a maximum power density of 8,,W/cm2, an open-circuit cell voltage of 0.29,V, and a short-circuit current density of 85,,A/cm2, respectively. The cell current at the load of 100,k, retained 78.9% of the initial value after continuous discharging for 15,h in a stirred acetate buffer solution (pH,5.0) containing 40,mmol/L glucose in air. The performance decrease of the BFC resulted mainly from the leakage of the ABTS mediator immobilized at the cathode, as revealed by the two-channel quartz crystal microbalance technique. In addition, a monopolar glucose BFC was performed with the same anode as that in the glucose/O2 membraneless BFC in a stirred phosphate buffer solution (pH,7.0) containing 40,mmol/L glucose, and a carbon cathode in Nafion-membrane-isolated acidic KMnO4, with a maximum power density of 115,,W/cm2, an open-circuit cell voltage of 1.24,V, and a short-circuit current density of 202,,A/cm2, respectively, which are superior to those of the glucose/O2 membraneless BFC. A modification of the anode with MWCNTs for the monopolar glucose BFC increased the maximum power density by a factor of 1.8. The ECN device is highly recommended as a convenient, real-time and sensitive technique for BFC studies. [source] Chitosan Incorporating Cetyltrimethylammonium Bromide Modified Glassy Carbon Electrode for Simultaneous Determination of Ascorbic Acid and DopamineELECTROANALYSIS, Issue 17 2007Xuelian Zou Abstract Simultaneous determination of a neurotransmitter, dopamine (DA), and ascorbic acid (AA) is achieved at neutral pH on a chitosan incorporating cetyltrimethylammonium bromide (CTAB) modified glassy carbon (GC) electrode. Differential pulse voltammetry (DPV) technique was used to investigate the electrochemical response of DA and AA at a glassy carbon electrode modified with chitosan incorporating CTAB. An optimum 6.0,mmol L,1 of CTAB together with 0.5 wt% of chitosan was used to improve the resolution and the determination sensitivity. In 0.1,mol L,1 aqueous phosphate buffer solution of pH,6.8, the chitosan-CTAB modified electrode showed a good electrocatalytic response towards DA and AA. The anodic peak potential of DA shifted positively, while that of AA shifted negatively. Thus, the difference of the anodic peaks of DA and AA reached 0.23,V, which was enough to separate the two anodic peaks very well. The presented method herein could be applied to the direct simultaneous determination of DA and AA without prior treatment. The anodic peak currents (Ipa) of DPV are proportional to DA in the concentration range of 8,,M to 1000,,M, to that of AA 10,,M to 2000,,M, with correlation coefficients of 0.9930 and 0.9945, respectively. The linear range is much wider than previously reported. [source] Photoelectrocatalytic Oxidation of NADH with Electropolymerized Toluidine Blue OELECTROANALYSIS, Issue 2-3 2007Yusuf Dilgin Abstract A poly(Toluidine Blue O) (poly-TBO) modified electrode was successfully prepared by repeated sweeping the applied potential from ,0.6 to +0.8,V (vs. SCE) on a glassy carbon electrode (GCE) in borate buffer solution at pH,9.1,containing 0.1,M NaNO3 and 0.4,mM Toluidine Blue O (TBO). The poly-TBO modified GCE shows electrocatalytic activity toward NADH oxidation in phosphate buffer solution at pH,7.0, with an overpotential of ca. 350,mV lower than that at the bare electrode. The photoelectrocatalytic oxidation of NADH at this electrode was also successfully investigated by using cyclic voltammetry and amperometry at constant potential. When the modified electrode surface was irradiated with a 250,W halogen lamp, a photoelectrocatalytic effect was observed for NADH oxidation and the current was increased about 2.2 times. The applied potential was selected at +100,mV for amperometric and photoamperometric detection of NADH. A linear calibration graph for NADH was obtained in the range between 1.0×10,5 and 1.0×10,3 M and between 5.0×10,6 and 1.0×10,3 M for amperometric and photoamperometric studies, respectively. The effect of some interfering compounds, such as ascorbic acid and dopamine on the electrocatalytic and photoelectrocatalytic oxidation of NADH was tested. [source] Direct and Rapid Detection of Diphtherotoxin via Potentiometric Immunosensor Based on Nanoparticles Mixture and Polyvinyl Butyral as MatrixesELECTROANALYSIS, Issue 24 2005Dianping Tang Abstract In this paper a novel potentiometric immunosensor for direct and rapid detection of diphtherotoxin (D-Ag) has been developed by means of self-assembly of monoclonal diphtheria antibody (D-Ab) onto a platinum electrode based on nanoparticles mixture (containing gold nanoparticles and silica nanoparticles) and polyvinyl butyral (PVB) as matrixes. At first, D-Ab was absorbed onto the surface of nanoparticles mixture, and then they were entrapped into polyvinyl butyral sol-gel network on a platinum electrode. The detection is based on the change in the potentiometric response before and after the antigen-antibody reaction in a phosphate buffer solution (pH,7.0). The immobilized D-Ab exhibited direct potentiometric response toward D-Ag. In comparison to the conventional applied methods, this strategy could allow antibodies immobilized with higher loading amount and better retained immunoactivity, as demonstrated by potentiometric response, cyclic voltammetry and electrochemical impedance spectroscopy of the immunosensor. The immunosensor with nanoparticles mixture exhibited much higher sensitivity, better reproducibility, and long-term stability than that with gold nanoparticles or silica nanoparticles alone. The linear range was from 5.0×10,3 to 1.2,,g,mL,1 with a detection limit of 1.1×10,3,,g,mL,1. Up to 16 successive assay cycles with retentive sensitivity were achieved for the probes regenerated with in 0.2,mol,L,1 glycine-hydrochloric acid (Gly-HCl) buffer solution and 0.25,mol,L,1 NaCl. Moreover, the immunosensor with nanoparticles mixture was applied to evaluate a number of practical specimens with potentiometric results in acceptable agreement with those given by the ELISA method, implying a promising alternative approach for detecting diphtherotoxin in the clinical diagnosis. [source] Barrel Plating Rhodium Electrode: Application to Flow Injection Analysis of HydrazineELECTROANALYSIS, Issue 14 2005Jun-Wei Sue Abstract We introduce here the application of barrel plating technology for mass production of disposable-type electrodes. Easy for mass production, barrel plating rhodium electrode (Rh-BPE) is for the first time demonstrated for analytical application. Hydrazine was chosen as a model analyte to elucidate the electrocatalytic and analytical ability of the Rh-BPE system in pH,7 phosphate buffer solution. Flow injection analysis (FIA) of hydrazine showed a linear calibration range of 25,1000,ppb with a slope and a regression coefficient of 5,nA/ppb and 0.9946, respectively. Twenty-two replicate injections of 25,ppb hydrazine showed a relative standard deviation of 3.17% indicating a detection limit (S/N=3) of 2.5,ppb. The system can be continuously operated for 1 day without any alteration in the FIA signals and is tolerable to the interference of oxalic acid, gelatine, Triton X-100, and albumin for even up to 100 times excess in concentration with respect to 400,ppb hydrazine. Since the fabrication cost of the electrode is cheap, it is thus disposable in nature. Furthermore, barrel plating technique can be extendable to other transition metals for application in many fields of research interest. [source] Poly(,-caprolactone)-Functionalized Carbon Nanotubes and Their Biodegradation Properties,ADVANCED FUNCTIONAL MATERIALS, Issue 6 2006H.-L. Zeng Abstract Biodegradable poly(,-caprolactone) (PCL) has been covalently grafted onto the surfaces of multiwalled carbon nanotubes (MWNTs) by the "grafting from" approach based on in-situ ring-opening polymerization of ,-caprolactone. The grafted PCL content can be controlled easily by adjusting the feed ratio of monomer to MWNT-supported macroinitiators (MWNT-OH). The resulting products have been characterized with Fourier-transform IR (FTIR), NMR, and Raman spectroscopies, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). After PCL was coated onto MWNT surfaces, core/shell structures with nanotubes as the "hard" core and the hairy polymer layer as the "soft" shell are formed, especially for MWNTs coated with a high density of polymer chains. Such a polymer shell promises good solubility/dispersibility of the MWNT,PCL nanohybrids in low-boiling-point organic solvents such as chloroform and tetrahydrofuran. Biodegradation experiments have shown that the PCL grafted onto MWNTs can be completely enzymatically degraded within 4,days in a phosphate buffer solution in the presence of pseudomonas (PS) lipase, and the carbon nanotubes retain their tubelike morphologies, as observed by SEM and TEM. The results present possible applications for these biocompatible PCL-functionalized CNTs in bionanomaterials, biomedicine, and artificial bones. [source] Expression and characterization of ,-glucosidase III in the dwarf honeybee, Apis florea (Hymenoptera: Apoidea: Apidae)INSECT SCIENCE, Issue 4 2007CHANPEN CHANCHAO Abstract Alpha-glucosidase is synthesized in the hypopharyngeal glands located in the head of worker bees including Apis florea. To analyze the developmental stage-specific expression of the ,-glucosidase gene in A. florea, total RNA was isolated from eggs, and the heads of nurse and forager bees. By reverse transcription polymerase chain reaction (RT-PCR), it was shown that the highest expression levels of the ,-glucosidase III gene, in the three examined developmental stadia, were found in forager bees, with much lower expression levels in nurse bees and no detectable expression in eggs. A complete ,-glucosidase III cDNA was obtained by RT-PCR and sequenced. The 1 701 bp cDNA nucleotide sequence and the predicted 567 amino acids it encodes were assayed by BLASTn, BLASTp and BLASTx programs and revealed a 95% and 94% similarity to the A. mellifera,-glucosidase III gene at the DNA and amino acid sequence levels, respectively. For purification of the active encoded enzyme, forager bee heads were homogenized in sodium phosphate buffer solution and the crude extract (0.30 U/mg) sequentially precipitated with 95% saturated ammonium sulfate (0.18 U/mg), and purified by DEAE cellulose ion exchange chromatography (0.17 U/mg), and gel filtration on Superdex 200 (0.52 U/mg). After resolution through sodium dodecyl sulfate-polyacrylamide gel electrophoresis, a single enzymically active band (73 kDa) was identified from renatured substrate gels. Excision of this band, elution of the protein and tryptic peptide digestives identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) revealed six matching masses to the A. mellifera (Q17958) and predicted A. florea,-glucosidase III protein with 12% coverage, supporting the probable purification of the same ,-glucosidase III protein as that encoded by the cloned cDNA. [source] Nalidixic Acid Resistance Increases Sensitivity of Escherichia coli O157:H7 to Ionizing Radiation in Solution and on Green Leaf LettuceJOURNAL OF FOOD SCIENCE, Issue 2 2005Brendan A. Niemira ABSTRACT: Nalidixic acid resistance has been used as a selective marker for studies of pathogen-inoculated fruits and vegetables. Three nalidixic acid-sensitive outbreak strains of Escherichia coli O157:H7 were used to generate mutants resistant to nalidixic acid (NalR, 50 ,g/mL) by successive culturing and selection in nalidixic acid-amended broth. The resistance to ionizing radiation of the parent and NalR strains was determined (a) in a phosphate buffer solution and (b) on green leaf lettuce. The NalR strains of each of the 3 isolates were significantly (P < 0.05) more sensitive to ionizing radiation than the nalidixic acid-sensitive (NalS) parent strains in both systems. D10 values (the amount of ionizing radiation required to achieve 1 log10 reduction) determined in buffer for the parent strains ranged from 0.18 to 0.33 kGy, whereas for the NalR strains, D10 were approximately 0.10 kGy, a reduction of up to 69%. When evaluated on green leaf lettuce, the D10 for the NalS strains was approximately 0.18 kGy as opposed to 0.10 to 0.12 kGy for the NalR strains, a reduction of up to 45%. The D10 values obtained on lettuce were significantly different than those obtained in buffer for 4 of the 6 isolates examined. The magnitude of the increase in radiation sensitivity resulting from resistance to nalidixic acid varied among the strains tested and also varied depending on the suspending medium. These results suggest that the use of nalidixic acid resistance as a selective marker may result in significant overestimates of the antimicrobial efficacy of ionizing radiation against E. coli O157:H7. [source] Thyroid hormone enhances transected axonal regeneration and muscle reinnervation following rat sciatic nerve injuryJOURNAL OF NEUROSCIENCE RESEARCH, Issue 8 2010Petrica-Adrian Panaite Abstract Improvement of nerve regeneration and functional recovery following nerve injury is a challenging problem in clinical research. We have already shown that following rat sciatic nerve transection, the local administration of triiodothyronine (T3) significantly increased the number and the myelination of regenerated axons. Functional recovery is a sum of the number of regenerated axons and reinnervation of denervated peripheral targets. In the present study, we investigated whether the increased number of regenerated axons by T3-treatment is linked to improved reinnervation of hind limb muscles. After transection of rat sciatic nerves, silicone or biodegradable nerve guides were implanted and filled with either T3 or phosphate buffer solution (PBS). Neuromuscular junctions (NMJs) were analyzed on gastrocnemius and plantar muscle sections stained with rhodamine ,-bungarotoxin and neurofilament antibody. Four weeks after surgery, most end-plates (EPs) of operated limbs were still denervated and no effect of T3 on muscle reinnervation was detected at this stage of nerve repair. In contrast, after 14 weeks of nerve regeneration, T3 clearly enhanced the reinnervation of gastrocnemius and plantar EPs, demonstrated by significantly higher recovery of size and shape complexity of reinnervated EPs and also by increased acetylcholine receptor (AChRs) density on post synaptic membranes compared to PBS-treated EPs. The stimulating effect of T3 on EP reinnervation is confirmed by a higher index of compound muscle action potentials recorded in gastrocnemius muscles. In conclusion, our results provide for the first time strong evidence that T3 enhances the restoration of NMJ structure and improves synaptic transmission. © 2010 Wiley-Liss, Inc. [source] Oligopeptide-mediated helix stabilization of model peptides in aqueous solutionJOURNAL OF PEPTIDE SCIENCE, Issue 2 2003Yoshitaka Maeda Abstract Oligopeptide-mediated helix stabilization of peptides in hydrophobic solutions was previously found by NMR and CD spectroscopic studies. The oligopeptide included the hydrophobic amino acids found in its parent peptide and were interposed by relevant basic or acidic amino acids. The strength of the interactions depended on the amino acid sequences. However, no helix-stabilizing effect was seen for the peptides in phosphate buffer solution, because the peptides assumed a random-coil structure. In order to ascertain whether the helix-stabilizing effect of an oligopeptide on its parent peptide could operate in aqueous solution, model peptides EK17 (Ac-AEAAAAEAAAKAAAAKA-NH2) and IFM17 (Ac-AEAAAAEIFMKAAAAKA-NH2) that may assume an ,-helix in aqueous solutions were synthesized. Interactions were examined between various oligopeptides (EAAAK, KAAAE, EIFMK, KIFME, KIFMK and EYYEE) and EK17 or IFM17 in phosphate buffer and in 80% trifluoroethanol (TFE),20% H2O solutions by CD spectra. EAAAK had little effect on the secondary structures of EK17 in both buffer and TFE solutions, while KAAAE, which has the reverse amino acid sequence of EAAAK, had a marked helix-destabilizing effect on EK17 in TFE. EIFMK and KIFME were found to stabilize the ,-helical structure of EK17 in phosphate buffer solutions, whereas KIFMK and EYYEE destabilized the ,-helical structure of EK17. EIFMK and KIFME had no effect on IFM17, because unexpectedly, IFM17 had appreciable amounts of ,-sheet structure in buffer solution. It was concluded that in order for the helix-stabilizing effects to operate effectively, the following factors should be satisfied: (1) the model peptide, the ,-helical conformation of which is to be stabilized, should essentially assume an ,-helical structure by nature, and (2) the hydrophobicity of the side-chains of the oligopeptide should be high enough for the oligopeptide to perform stable specific side chain,side chain intermolecular hydrophobic interactions with the model peptide. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd. [source] Biodegradable polymers based on renewable resources.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2005Abstract Novel polycarbonates, with pendant functional groups, based on 1,4:3,6-dianhydrohexitols and L -tartaric acid derivatives were synthesized. Solution polycondensations of 1,4:3,6-dianhydro-bis- O -(p -nitrophenoxycarbonyl)hexitols and 2,3-di- O -methyl- L -threitol or 2,3- O -isopropylidene- L -threitol afforded polycarbonates having pendant methoxy or isopropylidene groups, respectively, with number average molecular weight (Mn) values up to 3.61 × 104. Subsequent acid-catalyzed deprotection of isopropylidene groups gave well-defined polycarbonates having pendant hydroxyl groups regularly distributed along the polymer chain. Differential scanning calorimetry (DSC) demonstrated that all the polycarbonates were amorphous with glass transition temperatures ranging from 57 to 98 °C. Degradability of the polycarbonates was assessed by hydrolysis test in phosphate buffer solution at 37 °C and by biochemical oxygen demand (BOD) measurements in an activated sludge at 25 °C. In both tests, the polycarbonates with pendant hydroxyl groups were degraded much faster than the polycarbonates with pendant methoxy and isopropylidene groups. It is noteworthy that degradation of the polycarbonates with pendant hydroxyl groups was remarkably fast. They were completely degraded within only 150 min in a phosphate buffer solution and their BOD-biodegradability reached nearly 70% in an activated sludge after 28 days. The degradation behavior of the polycarbonates is discussed in terms of their chemical and physical properties. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3909,3919, 2005 [source] Preparation and characterization of biodegradable poly(trimethylenecarbonate-,-caprolactone)-block-poly(p -dioxanone) copolymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2005J.-T. Hong Abstract A series of poly(trimethylenecarbonate-,-caprolactone)-block-poly(p- dioxanone) copolymers were prepared with varying feed rations by using two step polymerization reactions. Poly(trimethylenecarbonate)(,-caprolactone) random copolymer was synthesized with stannous-2-ethylhexanoate and followed by adding p- dioxanone monomer as the other block. The ring opening polymerization was carried out at high temperature and long reaction time to get high molecular weight polymers. The monofilament fibers were obtained using conventional melting spun methods. The copolymers were identified by 1H and 13C NMR spectroscopy and gel permeation chromatography (GPC). The physicochemical properties, such as viscosity, molecular weight, melting point, glass transition temperature, and crystallinity, were studied. The hydrolytic degradation of copolymers was studied in a phosphate buffer solution, pH = 7.2, 37 °C, and a biological absorbable test was performed in rats. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2790,2799, 2005 [source] Enantioselective analysis of mirtazapine, demethylmirtazapine and 8-hydroxy mirtazapine in human urine after solid-phase microextractionJOURNAL OF SEPARATION SCIENCE, JSS, Issue 2 2010Fernando José Malagueńo de Santana Abstract A selective and reproducible off-line solid-phase microextraction procedure was developed for the simultaneous enantioselective determination of mirtazapine (MRT), demethylmirtazapine and 8-hydroxymirtazapine in human urine. CE was used for optimization of the extraction procedure whereas LC-MS was used for method validation and application. The influence of important factors in the solid-phase microextraction efficiency is discussed, such as the fiber coatings, extraction time, pH, ionic strength, temperature and desorption time. Before extraction, human urine samples were submitted to enzymatic hydrolysis at 37°C for 16,h. Then, the enzyme was precipitated with trichloroacetic acid and the pH was adjusted to 8 with 1,mol/L pH 11 phosphate buffer solution. In the extraction, the analytes were transferred from the aqueous solution to the polydimethylsiloxane-divinylbenzene fiber coating and then desorbed in methanol. The mean recoveries were 5.4, 1.7 and 1.0% for MRT, demethylmirtazapine and 8-hydroxymirtazapine enantiomers, respectively. The method was linear over the concentration range of 62,1250,ng/mL. The within-day and between-day assay precision and accuracy were lower than 15%. The method was successfully employed in a preliminary cumulative urinary excretion study after administration of racemic MRT to a healthy volunteer. [source] Number of Spermatozoa in the Crypts of the Sperm Reservoir at About 24 h After a Low-Dose Intrauterine and Deep Intrauterine Insemination in SowsREPRODUCTION IN DOMESTIC ANIMALS, Issue 2 2010P Tummaruk Contents The aim of this study was to investigate the number of spermatozoa in the crypts of the utero-tubal junction (UTJ) and the oviduct of sows approximately 24 h after intrauterine insemination (IUI) and deep intrauterine insemination (DIUI) and compared with that of conventional artificial insemination (AI). Fifteen crossbred Landrace × Yorkshire (LY) multiparous sows were used in the experiment. Transrectal ultrasonography was performed every 4 h to examine the time of ovulation in relation to oestrous behaviour. The sows were inseminated with a single dose of diluted fresh semen by the AI (n = 5), IUI (n = 5) and DIUI (n = 5) at approximately 6,8 h prior to the expected time of ovulation, during the second oestrus after weaning. The sperm dose contained 3000 × 106 spermatozoa in 100 ml for AI, 1,000 × 106 spermatozoa in 50 ml for IUI and 150 × 106 spermatozoa in 5 ml for DIUI. The sows were anaesthetized and ovario-hysterectomized approximately 24 h after insemination. The oviducts and the proximal part of the uterine horns (1 cm) on each side of the reproductive tracts were collected. The section was divided into four parts, i.e. UTJ, caudal isthmus, cranial isthmus and ampulla. The spermatozoa in the lumen in each part were flushed several times with phosphate buffer solution. After flushing, the UTJ and all parts of the oviducts were immersed in a 10% neutral buffered formalin solution. The UTJ and each part of the oviducts were cut into four equal parts and embedded in a paraffin block. The tissue sections were transversely sectioned to a thickness of 5 ,m. Every fifth serial section was mounted and stained with haematoxylin and eosin. The total number of spermatozoa from 32 sections in each parts of the tissue (16 sections from the left side and 16 sections from the right side) was determined under light microscope. The results reveal that most of the spermatozoa in the histological section were located in groups in the epithelial crypts. The means of the total number of spermatozoa in the sperm reservoir (UTJ and caudal isthmus) were 2296, 729 and 22 cells in AI, IUI and DIUI groups, respectively (p < 0.01). The spermatozoa were found on both sides of the sperm reservoir in all sows in the AI and the IUI groups. For the DIUI group, spermatozoa were not found on any side of the sperm reservoir in three out of five sows, found in unilateral side of the sperm reservoir in one sow and found in both sides of the sperm reservoir in one sow. No spermatozoa were found in the cranial isthmus, while only one spermatozoon was found in the ampulla part of a sow in the IUI group. In conclusion, DIUI resulted in a significantly lower number of spermatozoa in the sperm reservoir approximately 24 h after insemination compared with AI and IUI. Spermatozoa could be obtained from both sides of the sperm reservoir after AI and IUI but in one out of five sows inseminated by DIUI. [source] Influence of cigarette smoking on spermatozoa via seminal plasmaANDROLOGIA, Issue 4 2005M. Arabi Summary Numerous investigations have been conducted on the relationship between cigarette smoking and male infertility, however, the exact molecular mechanisms are not well understood in most of the cases. Few studies have indicated the direct effect of seminal plasma (SP) [in different dilutions with phosphate buffer solution (PBS)] from smokers (SM) on the sperm functional parameters from nonsmokers (non-SM). The aim of this study was to provide evidence that cigarette smoking affects male fertility via altering the sperm quality. Our results indicated that exposure of spermatozoa from the non-SM to the SP from the SM yielded a significant reduction in the sperm motility and acrosome reaction and an elevation in the amount of malondialdehyde (MDA), in a certain time course. Exposure of spermatozoa from the SM to the SP from the non-SM or with PBS resulted in the nonsignificant improvement in the altered sperm functional parameters indicating removal of SM's SP and then subsequent reconstitution with physiological media could be of clinical significance in the various assisted reproductive technologies applied for SM. However, the detrimental effect of SM's SP on non-SM's spermatozoa was prominent. In addition, as spermatozoa in SM's SP are susceptible to peroxidative damages, men with such cells who wish to have children should especially benefit from quitting smoking. [source] Penicillin G splitting in a flow-through electro-membrane reactor with the membrane-bound enzymeASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2009Pavel Hasal Abstract Penicillin G (PenG) (0.05 mol dm,3 in phosphate buffer, pH = 8) was hydrolyzed in a continuous flow-through electro-membrane reactor (EMR) with the penicillin G acylase (PGA) (EC 3.5.1.11) immobilized in 10% (w/v) polyacrylamide membrane with an area of 900 mm2, thickness of 1 mm and enzyme activity of 100 U cm,3 and 160 U cm,3, respectively. The PenG was continuously fed to the substrate compartment adjacent to one membrane surface. Reaction products were washed from the membrane by a phosphate buffer solution fed to the product compartment adjacent to the other membrane surface. The mean residence time of both streams was varied from 11.3 min to 45 min. An electric field perpendicular to the membrane surface was imposed on the reactor and the electric current density was varied from 0 to 822 A m,2. Substrate conversion was determined as a function of the mean residence time, of the applied electric current density and of the enzyme activity of the membrane. The conversion increased with increasing residence time. The applied electric current increased substrate conversion by 200% at short residence times and at low enzyme activity of the membrane. Oscillatory reaction regime was evoked by step change of the mean residence time of reactant streams in the reactor. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Development of a novel HPLC-MS/MS method for the determination of aconitine and its application to in vitro and rat microdialysis samplesBIOMEDICAL CHROMATOGRAPHY, Issue 7 2009Quan-long Zhang Abstract A sensitive and selective LC-MS/MS method was developed and validated for the determination of aconitine in microdialysate and rat plasma. Extraction of plasma sample was conducted by use of 1% trichloracetic acid and acetonitrile solution with 10 ng/mL internal standard (propafenone) spiked. Microdialysates were analyzed without sample purification. After sample preparation, 2 µL were injected and separated with an isocratic mobile phase consisting of acetonitrile:0.1% formic acid (60:40, v/v) at a flow rate of 0.3 mL/min. The Agilent G6410A triple quadrupole LC/MS system was operated under the multiple-reaction monitoring mode (MRM) using the electrospray ionization technique in positive mode. Overall, the assay exhibited good precision and accuracy. The diffusion properties of aconitine investigated in in vitro microdialysis experiments revealed unfavourable concentration dependence avertable by keeping a constant pH 5.77 using isotonic phosphate buffer solution as perfusate. The mean relative recoveries were 48.23% [coefficient of variation (CV 4.47%)] and 55.38% (CV 2.89%) for retrodialysis and recovery experiments, respectively. The in vivo recovery of aconitine was 34.48% (CV 3.05%) and was stable over the 6 h study period. Following characterization of aconitine both in vitro and in vivo microdialysis, the developed setting is suitable for application in pharmacokinetics and pharmacodynamics studies. Copyright © 2009 John Wiley & Sons, Ltd. [source] Study on the Interaction of Ketoconazole with Human and Bovine Serum Albumins by Fluorescence SpectroscopyCHINESE JOURNAL OF CHEMISTRY, Issue 12 2008Qing-Lian GUO Abstract The binding of ketoconazole to human serum albumin and bovine serum albumin was studied by using fluorescence and ultraviolet spectroscopy. The measurements were performed in 0.1 mol·L,1 phosphate buffer solution at pH=7.40±0.1. Decreasing of quenching constant was observed in association with temperature increase. Our findings show that the quenching mechanism of fluorescence of serum albumins by ketoconazole was static quenching because of compound formation. The thermodynamic parameters ,G, ,H, and ,S at different temperatures were calculated, showing that the electrostatic interactions and hydrophobic interaction are the main forces for the binding of ketoconazole to serum albumins. The distance r between the donor (Trp-214) and acceptor (ketoconazole) was obtained according to fluorescence resonance energy transfer theory. [source] Amperometric Determination of Glucose at Conventional vs.ELECTROANALYSIS, Issue 12 2010Nanostructured Gold Electrodes in Neutral Solutions Abstract The conventional gold electrodes were compared with recently published electrodes based on gold nanoparticles and gold nanostructured films as amperometric sensors for glucose in pH,7.40 phosphate buffer solutions. The conventional electrodes provided similar electroanalytical benefits while required much simpler and shorter preparation. It is recommended that the future reports on the development of electrochemical sensors based on metal nanoparticles/nanostructures include also the analytical figures of merit obtained at relevant conventional metal electrodes. The voltammetric studies indicated that, in contrast to phosphate buffers, the Tris buffers were not suitable for activation of gold surface toward the direct oxidation of glucose. [source] Voltammetric Determination of L -Dopa on Poly(3,4-ethylenedioxythiophene)-Single-Walled Carbon Nanotube Composite Modified MicroelectrodesELECTROANALYSIS, Issue 4 2010Jayaraman Mathiyarasu Abstract In the present communication, it is shown that platinum microelectrodes electrochemically coated with a composite of poly(3,4-)ethylenedioxythiophene and single-walled carbon nanotubes (PEDOT/SWNT) enable determinations of 3,4-dihydroxy- L -phenylalaines (L -dopa) in neutral phosphate buffer solutions containing an excess of ascorbic acid. The interpenetrated networked nanostructure of the composite was characterized by scanning electron microscope (SEM) and Raman spectroscopy. It is shown that the presence of the composite gives rise to an increase in the electroactive area of an order of magnitude in compared to the area for the bare microelectrodes. The composite film-coated microelectrode, which yielded reversible cyclic voltammograms for the ferro/ferricyanide redox couple for scan rates between 0.01 and 0.10,V s,1, also gave rise to two well-resolved oxidation peaks for L -dopa and ascorbic acid (AA). The latter effect, which was not seen in the absence of the composite, enabled differential pulse voltammetric determinations of L -dopa in the concentration range between 0.1 to 20,,M with a detection limit of 100,nM. [source] New Anthraquinone Derivatives as Electrochemical Redox Indicators for the Visualization of the DNA Hybridization ProcessELECTROANALYSIS, Issue 1 2010Agata Kowalczyk Abstract Interactions of dsDNA and ssDNA, at the surface of gold and silver electrodes, with three novel anthraquinone derivatives: 3-(9,,10,-dioxo-9,,10,-dihydro-anthracen-1-yl)-7,11-di(carboxymethyl)-3,7,11-triazatridecanedioic acid, (AQ-1); 1-(9,,10,-dioxo-9,,10,-dihydro-anthracen-1yl)-9-carboxymethyl-5-methyl-1,5,9-triazaundecanoicacid, (AQ-2); and N -(2-(9,10-dioxo-9,10-dihydro-anthracen-1-ylamino)ethyl)-2-(1,4,10,13-tetraoxa-7,16-diazacyclooctadecan-7-yl)acetamide, (AQ-3) are studied. These derivatives are well soluble in water and phosphate buffer solutions. The square wave voltammetric behavior of these redox indicators is described and the parameters of interactions with DNA are reported. It is also pointed out that these compounds can be employed as the hybridization indicators. The difference in the binding ability of the particular redox indicator to single and double stranded DNA can be used for the detection of the complementary nucleic acids. [source] Reagentless Glucose Biosensor Based on the Direct Electrochemistry of Glucose Oxidase on Carbon Nanotube-Modified ElectrodesELECTROANALYSIS, Issue 11 2006Xiliang Luo Abstract The direct electrochemistry of glucose oxidase (GOD) was revealed at a carbon nanotube (CNT)-modified glassy carbon electrode, where the enzyme was immobilized with a chitosan film containing gold nanoparticles. The immobilized GOD displays a pair of redox peaks in pH,7.4 phosphate buffer solutions (PBS) with the formal potential of about ,455,mV (vs. Ag/AgCl) and shows a surface-controlled electrode process. Bioactivity remains good, along with effective catalysis of the reduction of oxygen. In the presence of dissolved oxygen, the reduction peak current decreased gradually with the addition of glucose, which could be used for reagentless detection of glucose with a linear range from 0.04 to 1.0,mM. The proposed glucose biosensor exhibited high sensitivity, good stability and reproducibility, and was also insensitive to common interferences such as ascorbic and uric acid. The excellent performance of the reagentless biosensor is attributed to the effective enhancement of electron transfer between enzyme and electrode surface by CNTs, and the biocompatible environment that the chitosan film containing gold nanoparticles provides for immobilized GOD. [source] Synthesis of pH dependent chitosan-EPI hydrogel films and their application for in vitro release of promethazine hydrochlorideJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Yolda Abstract Chitosan-epichlorohydrin hydrogel films (ChitEPI) were synthesized by using chitosan in the presence of epichlorohydrin (EPI) as a crosslinking agent at various amounts. SEM, FTIR, TGA, and DSC analysis were conducted for the characterization of the hydrogels. The DSC measurements indicate that ChitEPI hydrogels did not exhibit better thermal stability when compared to chitosan. Swelling behavior of Chitosan-EPI hydrogel film is pH dependent and showed a reversible swelling behavior with a fast response. The hydrogels were used for in vitro release of promethazine hydrochloride (PHCl) in pH = 1.2 and pH = 7.4 phosphate buffer solutions (PBS). The release of PHCl synthesized from hydrogels at pH = 7.4 is quite low while at pH = 1.2, the highest value was observed as 49% for ChitEPI600. It has been also found that PHCl release from ChitEPI thin films is mainly controlled by diffusion control mechanism. ChitEPI hydrogels may be used for the delivery of drug in stomach and gastrointestinal tract. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Swelling characteristics and drug delivery properties of nifedipine-loaded pH sensitive alginate,chitosan hydrogel beadsJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2008Ya-Ni Dai Abstract The aim of the present work was to investigate the swelling behavior and in vitro release of nifedipine from alginate,chitosan hydrogel beads. Structure and surface morphology of the hydrogel were characterized by FTIR and SEM, respectively. Alginate,chitosan mixed beads and alginate,chitosan coated beads were prepared by ionic gelation method. The swelling ability of the beads and in vitro release of nifedipine in simulated gastric fluid (pH 1.5) and different phosphate buffer solutions (pH 2.5, 5.0, 6.8, 7.4, and 8.0) were found to be dependent on the presence of the polyelectrolyte complex between chitosan and alginate. The amount of nifedipine released from the mixed beads at pH 1.5 was relatively low (42%), whereas this value approached to 99% at pH 6.8. In comparison with the mixed beads, the released nifedipine from the coated beads was minimal at pH 1.5 (18%), whereas ,99% nifedipine was released at pH 6.8. The results suggested that the coated beads can hold drug better at low pH than the mixed beads and show excellent pH sensitivity. Therefore, the alginate,chitosan coated beads could be a suitable polymeric carrier for drug delivery in the intestinal tract. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008 [source] Oligopeptide-mediated acceleration of amyloid fibril formation of amyloid ,(A,) and ,-synuclein fragment peptide (NAC)JOURNAL OF PEPTIDE SCIENCE, Issue 1 2004Dr Yoshihiro Kuroda Abstract The effects of oligopeptides on the secondary structures of A, and NAC, a fragment of ,-synuclein protein, were studied by circular dichroism (CD) spectra. The effects of oligopeptides on the amyloid fibril formation were also studied by fluorescence spectra due to thioflavine-T. The oligopeptides were composed of a fragment of A, or NAC and were interposed by acidic or basic amino acid residues. The peptide, Ac-ELVFFAKK-NH2, which involved a fragment Leu-Val-Phe-Phe-Ala at A,(17,21), had no effect on the secondary structures of A,(1,28) in 60% or 90% trifluoroethanol (TFE) solutions at both pH 3.2 and pH 7.2. However, it showed pronounced effects on the secondary structure of A,(1,28) at pH 5.4. The Ac-ELVFFAKK-NH2 reduced the ,-helical content, while it increased the ,-sheet content of A,(1,28). In phosphate buffer solutions at pH 7.0, Ac-ELVFFAKK-NH2 had little effect on the secondary structures of A,(1,28). However, it accelerated amyloid fibril formation when monitored by fluorescence spectra due to thioflavine-T. On the other hand, LPFFD, a peptide known as a ,-sheet breaker, caused neither an appreciable extent of change in the secondary structure nor amyloid fibril formation in the same buffer solution. The peptide, Ac-ETVK-NH2, which involved a fragment Thr-Val at NAC(21,22), had no effect on the secondary structure of NAC in 90% TFE and in isotonic phosphate buffer. However, Ac-ETVK-NH2 in water with small amounts of NaN3 and hexafluoroisopropanol greatly increased the ,-sheet content of NAC after standing the solution for more than 1 week. Interestingly, in this solution, Ac-ETVK-NH2, accelerated the fibril formation of NAC. It was concluded that an oligopeptide that involves a fragment of amyloidogenic proteins could be a trigger for the formation of amyloid plaques of the proteins even when it had little effect on the secondary structures of the proteins as monitored by CD spectra for a short incubation time. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd. [source] Oligopeptide-mediated helix stabilization of model peptides in aqueous solutionJOURNAL OF PEPTIDE SCIENCE, Issue 2 2003Yoshitaka Maeda Abstract Oligopeptide-mediated helix stabilization of peptides in hydrophobic solutions was previously found by NMR and CD spectroscopic studies. The oligopeptide included the hydrophobic amino acids found in its parent peptide and were interposed by relevant basic or acidic amino acids. The strength of the interactions depended on the amino acid sequences. However, no helix-stabilizing effect was seen for the peptides in phosphate buffer solution, because the peptides assumed a random-coil structure. In order to ascertain whether the helix-stabilizing effect of an oligopeptide on its parent peptide could operate in aqueous solution, model peptides EK17 (Ac-AEAAAAEAAAKAAAAKA-NH2) and IFM17 (Ac-AEAAAAEIFMKAAAAKA-NH2) that may assume an ,-helix in aqueous solutions were synthesized. Interactions were examined between various oligopeptides (EAAAK, KAAAE, EIFMK, KIFME, KIFMK and EYYEE) and EK17 or IFM17 in phosphate buffer and in 80% trifluoroethanol (TFE),20% H2O solutions by CD spectra. EAAAK had little effect on the secondary structures of EK17 in both buffer and TFE solutions, while KAAAE, which has the reverse amino acid sequence of EAAAK, had a marked helix-destabilizing effect on EK17 in TFE. EIFMK and KIFME were found to stabilize the ,-helical structure of EK17 in phosphate buffer solutions, whereas KIFMK and EYYEE destabilized the ,-helical structure of EK17. EIFMK and KIFME had no effect on IFM17, because unexpectedly, IFM17 had appreciable amounts of ,-sheet structure in buffer solution. It was concluded that in order for the helix-stabilizing effects to operate effectively, the following factors should be satisfied: (1) the model peptide, the ,-helical conformation of which is to be stabilized, should essentially assume an ,-helical structure by nature, and (2) the hydrophobicity of the side-chains of the oligopeptide should be high enough for the oligopeptide to perform stable specific side chain,side chain intermolecular hydrophobic interactions with the model peptide. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd. [source] | |||||||||||||||||||