Electrochemical cell design for the impedance studies of chlorine evolution at DSA(®) anodes.

A new electrochemical cell design suitable for the electrochemical impedance spectroscopy (EIS) studies of chlorine evolution on Dimensionally Stable Anodes (DSA(®)) has been developed. Despite being considered a powerful tool, EIS has rarely been used to study the kinetics of chlorine evolution at DSA anodes. Cell designs in the open literature are unsuitable for the EIS analysis at high DSA anode current densities for chlorine evolution because they allow gas accumulation at the electrode surface. Using the new cell, the impedance spectra of the DSA anode during chlorine evolution at high sodium chloride concentration (5 mol dm(-3) NaCl) and high current densities (up to 140 mA cm(-2)) were recorded. Additionally, polarization curves and voltammograms were obtained showing little or no noise. EIS and polarization curves evidence the role of the adsorption step in the chlorine evolution reaction, compatible with the Volmer-Heyrovsky and Volmer-Tafel mechanisms.

Which psychotic experiences are associated with a need for clinical care?

BACKGROUND: The aims of this study were to identify (1) the factor structure of anomalous experiences across the psychosis continuum; (2) qualitative and quantitative differences in psychotic experiences (PEs) between "non need-for-care" and two clinical groups: psychosis patients and individuals at ultra high risk (UHR) of psychosis. We aimed to distinguish which types of experiences would be related to malign (need-for-care and/or help-seeking) versus benign outcomes. METHODS: Component scores obtained from a Principal Components Analysis of PEs from lifetime scores on the Appraisals of Anomalous Experience Inventory (Brett et al., 2007) were compared across 96 participants: patients diagnosed with a psychotic disorder (n=37), help-seeking UHR people (n=21), and non-clinical individuals presenting with enduring PEs (n=38). RESULTS: A five-component structure provided the best solution, comprising dissociative-type experiences, subjective cognitive deficits, and three separate components relating to "positive" symptoms. All groups reported "positive" experiences, such as ideas of reference and hallucinations, with the non-clinical group displaying more PEs in the Paranormal/Hallucinatory component than both clinical groups. "Cognitive/Attentional anomalies" was the only component where the clinical groups reported significantly more anomalies than the non-clinical group. However psychosis patients reported more frequent first-rank type symptoms and "hypomanic" type PEs than the other groups. DISCUSSION: "Positive" PEs were common across the psychosis spectrum, although first-rank type symptoms were particularly marked in participants diagnosed with a psychotic disorder. Help-seeking and need-for-care were associated with the presence of subjective cognitive disturbances. These findings suggest that anomalies of cognition and attention may be more relevant to poorer outcomes than the presence of anomalous experiences.

Electrochemical sensor for simultaneous determination of herbicide MCPA and its metabolite 4-chloro-2-methylphenol. Application to photodegradation environmental monitoring.

The development and application of a polyaniline/carbon nanotube (CNT) cyclodextrin matrix (PANI-ß-CD/MWCNT)-based electrochemical sensor for the quantitative determination of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) and its main transformation product 4-chloro-2-methylphenol in natural waters are described. A simple cyclic voltammetry-based electrochemical methodology, in phosphate buffer solution at pH 6.0, was used to develop a method to determine both MCPA and 4-chloro-2-methylphenol, without any previous extraction or derivatization steps. A linear concentration range (10 to 50 µmol L(-1)) and detection limits of 1.1 and 1.9 µmol L(-1), respectively, were achieved using optimized cyclic voltammetric parameters. The proposed method was successfully applied to the determination of MCPA and 4-chloro-2-methylphenol in natural water samples with satisfactory recoveries (94 to 107%) and in good agreement with the results obtained by an established high-performance liquid chromatography technique, no significant differences being found between the methods. Interferences from ionic species and other herbicides used for broad-leaf weed control were shown to be small. The newly developed methodology was also successfully applied to MCPA photodegradation environmental studies.

The effect of novel promoter variants in MATE1 and MATE2 on the pharmacokinetics and pharmacodynamics of metformin.

Interindividual variation in response to metformin, first-line therapy for type 2 diabetes, is substantial. Given that transporters are determinants of metformin pharmacokinetics, we examined the effects of promoter variants in both multidrug and toxin extrusion protein 1 (MATE1) (g.-66T → C, rs2252281) and MATE2 (g.-130G → A, rs12943590) on variation in metformin disposition and response. The pharmacokinetics and glucose-lowering effects of metformin were assessed in healthy volunteers (n = 57) receiving metformin. The renal and secretory clearances of metformin were higher (22% and 26%, respectively) in carriers of variant MATE2 who were also MATE1 reference (P < 0.05). Both MATE genotypes were associated with altered post-metformin glucose tolerance, with variant carriers of MATE1 and MATE2 having an enhanced (P < 0.01) and reduced (P < 0.05) response, respectively. Consistent with these results, patients with diabetes (n = 145) carrying the MATE1 variant showed enhanced metformin response. These findings suggest that promoter variants of MATE1 and MATE2 are important determinants of metformin disposition and response in healthy volunteers and diabetic patients.

Enhanced host-guest electrochemical recognition of herbicide MCPA using a ß-cyclodextrin carbon nanotube sensor.

An electrochemical sensor for the determination of the chlorophenoxy herbicide MCPA has been developed, based on a combination of multi-walled carbon nanotubes with incorporated ß-cyclodextrin and a polyaniline film modified glassy carbon electrode. The proposed molecular host-guest recognition based sensor has a high electrochemical sensitivity for the determination of MCPA. The electrochemical behaviour of MCPA at the chemically modified electrode was investigated in detail by cyclic voltammetry. The results indicate that the ß-CD/MWCNT modified glassy carbon electrode exhibits efficient electrocatalytic oxidation of MCPA with high sensitivity, stability and lifetime. The analytical characteristics of this film were used for the quantitative determination of MCPA in natural waters. Cyclic voltammetry in phosphate buffer solution at pH 6.0, allowed the development of a method to determine MCPA, without any previous steps of extraction, clean-up, or derivatization, in the range of 10-100 µmol L(-1), with a detection limit of 0.99 µmol L(-1) in water. The results were statistically compared with those obtained through an established high-performance liquid chromatography technique, no significant differences having been found between the two methods.

Mechanism of formation and construction of self-assembled myoglobin/hyaluronic acid multilayer films: an electrochemical QCM, impedance, and AFM study.

Self-assembled multilayer films of hyaluronic acid (HA) and the protein myoglobin (Mb) were built up layer by layer on Au covered quartz crystal microbalance (AuQCM) electrode substrates. Film formation and growth were monitored by an electrochemical quartz crystal microbalance (EQCM), and the step-by-step construction was investigated through quantification of the mass variation corresponding to adsorption of each monolayer together with cyclic voltammetry. A decrease of friction at the liquid/electrode interface was observed, indicating that the electrode surface becomes less rough after deposition of several monolayers. The properties of the {HA/Mb}(n) films were evaluated by electrochemical impedance spectroscopy (EIS). Modeling of the impedance spectra shows smoothing of the modified electrode surface with reorganization of the film structure after few monolayers, and the contribution of each layer to the electron transfer process was analyzed. The smoothing of the surfaces and the structural differences between successive bilayers was confirmed by morphological observations by using atomic force microscopy.

The role of metacognitive beliefs in determining the impact of anomalous experiences: a comparison of help-seeking and non-help-seeking groups of people experiencing psychotic-like anomalies.

BACKGROUND: Current psychological models of psychotic symptoms suggest that metacognitive beliefs impact on an individual's appraisal of anomalous experiences, and thereby influence whether these lead to distress and become clinical symptoms. This study examined the relationship between maladaptive metacognitive beliefs, anomalous experiences, anomaly-related distress, anxiety and depression and diagnostic status. METHOD: The Metacognitions Questionnaire (MCQ), Symptom Checklist 90 - Revised, and Appraisals of Anomalous Experiences interview were administered to 27 people diagnosed with a psychotic disorder, 32 people meeting At Risk Mental State (ARMS) criteria, 24 people with psychotic-like experiences but no need for care, and 32 healthy volunteers. RESULTS: The two clinical groups scored higher than non-patient controls and individuals experiencing psychotic-like anomalies with no need for care on most subscales of the MCQ, particularly the 'general negative beliefs about thoughts' (NEG) subscale. However, most group differences became non-significant when anxiety and depression were controlled for. Few relationships were found between the MCQ subscales and psychotic-like anomalies and anomaly-related distress. Cognitive/attentional difficulty was the only type of anomaly to be significantly associated with maladaptive metacognitive beliefs. Anomaly-related distress was associated with only the NEG subscale of the MCQ. CONCLUSIONS: Maladaptive metacognitive beliefs, as measured by the MCQ, appear to be related more to elevated levels of general psychopathology in psychotic and at-risk groups than to the presence of, and distress associated with, psychotic experiences. Processes by which metacognitions may impact upon the need for care are discussed.

Effect of genetic variation in the organic cation transporter 1, OCT1, on metformin pharmacokinetics.

The goal of this study was to determine the effects of genetic variation in the organic cation transporter 1, OCT1, on the pharmacokinetics of the antidiabetic drug, metformin. Twenty healthy volunteers with known OCT1 genotype agreed to participate in the study. Each subject received two oral doses of metformin followed by collection of blood and urine samples. OCT1 genotypes had a significant (P<0.05) effect on metformin pharmacokinetics, with a higher area under the plasma concentration-time curve (AUC), higher maximal plasma concentration (Cmax), and lower oral volume of distribution (V/F) in the individuals carrying a reduced function OCT1 allele (R61C, G401S, 420del, or G465R). The effect of OCT1 on metformin pharmacokinetics in mice was less than in humans possibly reflecting species differences in hepatic expression level of the transporter. Our studies suggest that OCT1 genotype is a determinant of metformin pharmacokinetics.

Effects of genetic variation in the novel organic cation transporter, OCTN1, on the renal clearance of gabapentin.

Gabapentin is an anticonvulsant that is widely prescribed for epilepsy and other neuropathic disorders. The pharmacokinetics, particularly the absorption and renal elimination, of gabapentin appear to involve membrane transporters. In this study, we tested the hypothesis that organic cation transporter 1 (OCTN1), a multispecific transporter expressed at the apical membrane in intestine and kidney, plays a role in gabapentin pharmacokinetics and that the common variant of OCTN1, OCTN1-L503F, contributes to variation in the pharmacokinetics of the drug. We observed that OCTN1 facilitates the Na+-independent transport of gabapentin, and that the OCTN1-L503F variant is deficient in gabapentin transport activity in stably transfected HEK-293 cells (fourfold enhanced uptake of gabapentin by OCTN1-503L vs twofold enhanced uptake by OCTN1-L503F, compared to mock-transfected cells). In clinical studies, we found that in subjects homozygous for the L503F variant, gabapentin renal clearance (CL(R)) approximates the glomerular filtration rate (mean+/-SE: 110+/-12 ml/min, n=9), whereas in subjects homozygous for the reference allele, gabapentin undergoes net secretion in the kidney (141+/-7.8 ml/min, n=11, P<0.05). Creatinine clearance and OCTN1 genotype accounted for 56% of the variation in CL(R) and were the only significant predictors of CL(R) (P<0.05). Importantly, OCTN1 genotype was the only significant predictor of net secretion of gabapentin (P<0.008). Oral bioavailability of gabapentin was not affected by OCTN1 genotype. We conclude that OCTN1 contributes to active tubular secretion of gabapentin, and that this effect may be diminished or absent in individuals carrying the OCTN1-L503F polymorphism. These results provide clinical evidence of the role of genetic variation in renal drug transporters in active drug secretion in vivo.

The pharmacogenetics research network: from SNP discovery to clinical drug response.

The NIH Pharmacogenetics Research Network (PGRN) is a collaborative group of investigators with a wide range of research interests, but all attempting to correlate drug response with genetic variation. Several research groups concentrate on drugs used to treat specific medical disorders (asthma, depression, cardiovascular disease, addiction of nicotine, and cancer), whereas others are focused on specific groups of proteins that interact with drugs (membrane transporters and phase II drug-metabolizing enzymes). The diverse scientific information is stored and annotated in a publicly accessible knowledge base, the Pharmacogenetics and Pharmacogenomics Knowledge base (PharmGKB). This report highlights selected achievements and scientific approaches as well as hypotheses about future directions of each of the groups within the PGRN. Seven major topics are included: informatics (PharmGKB), cardiovascular, pulmonary, addiction, cancer, transport, and metabolism.

Appraisals of Anomalous Experiences Interview (AANEX): a multidimensional measure of psychological responses to anomalies associated with psychosis.

BACKGROUND: Cognitive models of psychosis suggest that whether anomalous experiences lead to clinically relevant psychotic symptoms depends on how they are appraised, the context in which they occur and the individual's emotional response. AIMS: To develop and validate a semi-structured interview (the Appraisals of Anomalous Experiences Interview; AANEX) to assess (a) anomalous experiences and (b) appraisal, contextual and response variables. METHOD: Following initial piloting, construct validity was tested via cross-sectional comparison of data from clinical and non-clinical samples with anomalous experiences. Interrater reliability was also assessed. RESULTS: Scores from AANEX measuring appraisals, responses and social support differentiated the clinical and nonclinical groups. Interrater reliability was satisfactory for 65 of the 71 items. Six items were subsequently amended. CONCLUSIONS: The AANEX is a valid multidimensional instrument that provides a detailed assessment of psychotic-like experiences and subjective variables relevant to the development of a need for clinical care.

Functional analysis of genetic variants in the human concentrative nucleoside transporter 3 (CNT3; SLC28A3).

The human concentrative nucleoside transporter, CNT3 (SLC28A3), plays an important role in mediating the cellular entry of a broad array of physiological nucleosides and synthetic anticancer nucleoside analog drugs. As a first step toward understanding the genetic basis for interindividual differences in the disposition and response to antileukemic nucleoside analogs, we examined the genetic and functional diversity of CNT3. In all, 56 variable sites in the exons and flanking intronic region of SLC28A3 were identified in a collection of 270 DNA samples from US populations (80 African-Americans, 80 European-Americans, 60 Asian-Americans, and 50 Mexican-Americans). Of the 16 coding region variants, 12 had not been previously reported. Also, 10 resulted in amino-acid changes and three of these had total allele frequencies of >/=1%. Nucleotide diversity (pi) at nonsynonymous and synonymous sites was estimated to be 1.81 x 10(4) and 18.13 x 10(4), respectively, suggesting that SLC28A3 is under negative selection. All nonsynonymous variants, constructed by site-directed mutagenesis and expressed in Xenopus laevis oocytes, transported purine and pyrimidine model substrates, except for c. 1099G>A (p. Gly367Arg). This rare variant alters an evolutionarily conserved site in the putative substrate recognition domain of CNT3. The presence of three additional evolutionarily conserved glycine residues in the vicinity of p. Gly367Arg that are also conserved in human paralogs suggest that these glycine residues are critical in the function of the concentrative nucleoside transporter family. The genetic analysis and functional characterization of CNT3 variants suggest that this transporter does not tolerate nonsynonymous changes and is important for human fitness.

Carbon film electrodes for oxidase-based enzyme sensors in food analysis.

Carbon film resistor electrodes have been evaluated as transducers for the development of multiple oxidase-based enzyme electrode biosensors. The resistor electrodes were first modified with Prussian Blue (PB) and then covered by a layer of covalently immobilized enzyme. Electrochemical impedance spectroscopy was used to characterize the interfacial behaviour of the Prussian Blue modified and enzyme electrodes; the spectra demonstrated that the access of the substrates is essentially unaltered by application of the enzyme layer. These enzyme electrodes were used to detect the substrate of the oxidase (glucose, ethanol, lactate, glutamate) via reduction of hydrogen peroxide at +50mV versus Ag/AgCl in the low micromolar range. Response times were 1-2min. Finally, the glucose, ethanol and lactate electrochemical biosensors were used to analyse complex food matrices-must, wine and yoghurt. Data obtained by the single standard addition method were compared with a spectrophotometric reference method and showed good correlation, indicating that the electrodes are suitable for food analysis.

Copper-modified gold electrode specific for monosaccharide detection Use in amperometric determination of phenylmercury based on invertase enzyme inhibition.

The electrochemical oxidation of mono- and disaccharides at various copper-modified electrodes is reported: glassy carbon modified at open circuit or by electrochemical deposition of copper, gold modified by electrochemical deposition, and at bulk copper electrodes. A comparative study of these four electrodes was made by linear sweep voltammetry and amperometry. The maximum oxidation peak separation between disaccharides and monosaccharides is about 200mV. After optimization, amperometric determination of monosaccharides was done at +0.30 versus Ag/AgCl in 0.15M NaOH at the copper-modified gold electrode. Using the developed method, the enzymatic activities of invertase and beta-galactosidase were determined through their reaction with sucrose and lactose, respectively. Validation was carried out by a spectrophotometric method based on 3,5-dinitrosalicylic acid, and it was shown that the proposed electrochemical method is more sensitive. The analytical utility of the copper-modified gold electrode was tested for the determination of organic mercury. Addition of phenylmercury standards to the invertase solution caused a decrease in the enzyme activity, and allowed the determination of phenylmercury in pharmaceutical samples. The concentration has been determined in the 10-55ngml(-1) range.

An impedance study of the adsorption of nucleic acid bases at glassy carbon electrodes.

Electrochemical impedance has been used to study the adsorption at glassy carbon electrodes of guanine, its corresponding nucleoside, guanosine, and adenine. Impedance studies at different concentrations and applied potentials show clearly that all three bases are adsorbed on the electrode, blocking the surface. Irradiating the electrode with low-frequency (20 kHz) ultrasound whilst recording the impedance spectra increased transport of molecules to the electrode surface with cavitation cleaning the surface and removing strongly adsorbed molecules of bases. In this way, sonoelectrochemical experiments enabled the electrode processes to be studied in the absence of adsorption.

Poly(ester sulphonic acid) coated mercury thin film electrodes: characterization and application in batch injection analysis stripping voltammetry of heavy metal ions.

Mercury-thin film electrodes coated with a thin film of poly(ester sulphonic acid) (PESA) have been investigated for application in the analysis of trace heavy metals by square wave anodic stripping voltammetry using the batch injection analysis (BIA) technique. Different polymer dispersion concentrations in water/acetone mixed solvent are investigated and are characterised by electrochemical impedance measurements on glassy carbon and on mercury film electrodes. The influence of electrolyte anion, acetate or nitrate, on polymer film properties is demonstrated, acetate buffer being shown to be preferable for stripping voltammetry applications. Although stripping currents are between 30 and 70% less at the coated than at bare mercury thin film electrodes, the influence of model surfactants on stripping response is shown to be very small. The effect of the composition of the modifier film dispersion on calibration plots is shown; however, detection limits of around 5 nM are found for all modified electrodes tested. This coated electrode is an alternative to Nafion-coated mercury thin film electrodes for the analysis of trace metals in complex matrices, particularly useful when there is a high concentration of non-ionic detergents.

Development of batch injection analysis for electrochemical measurements of trace metal ions in ecotoxicological test media.

Batch injection analysis with square-wave anodic stripping voltammetry has been developed as a powerful and rapid technique for obtaining data on the concentration of the fraction of labile metal ions present in media used in ecotoxicological tests. Microlitre samples of solution, without pretreatment, are injected directly over a detector electrode, the surface of which is protected by a thin Nafion polymer coating against irreversible adsorption by organic components. Examples are given showing the effect of adding vitamins and organic extract, singly and together, to the ASTM medium employed for tests using Daphnia magna and with lead and cadmium test ions. Such a methodology can be extended to other electroactive species present in these and similar media.

Electrochemical behaviour of cytochrome c at electrically heated microelectrodes.

The structural changes in cytochrome c with temperature have been been followed using a recently developed electrically-heated microelectrode sensor. Differential pulse voltammetry was used to perform electrochemical measurements of cytochrome c oxidation at different temperatures at heated bare gold electrodes contained in phosphate-buffered cytochrome c solution at room temperature. The voltammetric response shows the onset of unfolding and a marked dependence of the signal on electrode temperature. This augurs well for applications of heated electrodes as local probes in the study of the temperature dependence of electron transfer processes of other redox proteins, avoiding problems of bulk deterioration.