Characterization of the enhanced peroxidatic activity of amyloid β peptide–hemin complexes towards neurotransmitters

Binding of heme to the amyloid peptides Aβ40/42 is thought to be an initial step in the development of symptoms in the early stages of Alzheimer’s disease by enhancing the intrinsic peroxidatic activity of heme. We found considerably higher acceleration of the reaction for the physiologically relevant neurotransmitters dopamine and serotonin than reported earlier for the artificial substrate 3,3′,5,5′-tetramethylbenzidine (TMB). Thus, the binding of hemin to Aβ peptides might play an even more crucial role in the early stages of Alzheimer’s disease than deduced from these earlier results. To mimic complex formation, a new surface architecture has been developed: The interaction between the truncated amyloid peptide Aβ1-16 and hemin immobilized on an aminohexanethiol spacer on a gold electrode has been analyzed by cyclic voltammetry. The resulting complex has a redox pair with a 25 mV more cathodic formal potential than hemin alone.     

An original ultrasonic reaction with dual coaxial frequencies for biomass processing

An advanced dual frequency ultrasonic coaxial reactor enabling simultaneously low and high frequencies irradiating in the same direction was developed to focus both mechanical and chemical effects on a concentrated area. The prototype was straightforward employed for the conversion of a starch-based industrial waste into sugars.     

Fractionation of polyphenols in hawthorn into polymeric procyanidins, phenolic acids and flavonoids prior to high-performance liquid chromatographic analysis

Polymeric procyanidins, phenolic carboxylic acids and flavonoids of hawthorn (Crataegus laevigata) were fractionated prior to HPLC analysis using column chromatography and solid-phase extraction (SPE). The flavonoid fraction also contained (-)-epicatechin. The three groups of phenolics, each with clearly different UV spectra, were examined by means of high-performance liquid chromatography-diode array detection (HPLC-DAD) analysis. The average repeatability of the method (RSD) was in the range of 8-13% for chlorogenic acid, (-)-epicatechin and hyperoside. The polymeric procyanidins of hawthorn flowers consisted mainly of (-)-epicatechin subunits, and their mean degree of polymerization (DP) was 22.2. The HPLC methods developed can be used for the qualitative and quantitative analysis of different phenolic compounds in hawthorn plant material and their extracts.     

Multivariate data analysis of dynamic amperometric biosensor responses from binary analyte mixtures-application of sensitivity correction algorithms

In this paper, it is demonstrated that a single-receptor biosensor can be used to quantitatively determine each analyte in binary mixtures using multivariate data analysis tools based on the dynamic responses received from flow injection peaks. Mixtures with different concentrations of two phenolic compounds, catechol and 4-chlorophenol, were measured with a graphite electrode modified with tyrosinase enzyme at an applied potential of −50 mV versus Ag/AgCl. A correction algorithm based on measurements of references in-between samples was applied to compensate for biosensor ageing as well as differences caused by deviations between biosensor preparations. After correction, the relative prediction errors with partial least squares regression (PLS-R) for catechol and 4-chlorophenol were 7.4 and 5.5%, respectively, using an analysis sequence measured on one biosensor. Additional validation mixtures of the two phenols were measured with a new biosensor, prepared with the same procedure but with a different batch of tyrosinase enzyme. Using the mixture responses for the first sensor as a calibration set in PLS-R, the relative prediction errors of the validation mixtures, after applying correction procedures, were 7.0% for catechol and 16.0% for 4-chlorophenol. These preliminary results indicate that by applying correction algorithms it could be possible to use less stable biosensors in continuous on-line measurements together with multivariate data analysis without time-consuming calibration procedures.     

Electropolymerization of Preadsorbed Layers of Some Azine Redox Dyes on Graphite

The redox-active azine dyes Nile blue A (NB) and Toluidine blue O (TB) were electropolymerized after preadsorption onto the surface of graphite electrodes by potential cycling, using an anodic scan limit of 0.9 or 1.0 V vs SCE, where irreversible electrooxidation of the dye proceeds, yielding polymerizable species. Electropolymerization of both dyes is followed by the progressive disappearance of the characteristic current peaks in the cyclic voltammograms, and formation of new ones, shifted by ca. 0.21 V to the positive direction. Also, a decrease and gradual disappearance of the characteristic luminescence at a maximum of 671 nm was observed during the electropolymerization of NB. The resulting electrodes, modified by electropolymerized derivatives of NB and TB, were shown to be able to catalyze the electrooxidation of the coenzyme NADH. Thus, the modified electrodes prepared can be used for amperometric detection of the reduced form of the coenzyme. Copyright 2000 Academic Press.     

Electrocatalytic Oxidation of Coenzyme NADH at Carbon Paste Electrodes, Modified with Zirconium Phosphate and Some Redox Mediators

Carbon paste electrodes (CPE), modified with zirconium phosphate (ZrP) along with some redox mediators, were prepared and shown to be active in electrocatalytic oxidation of coenzyme NADH. Nile blue (NB), methylviologen (MV), and benzylviologen (BV) were added to ZrP-containing CPE, showing a shift of their redox potentials toward the positive direction, ranging from ca. 0.20 to 0.35 V. This shift was interpreted in terms of different complexation abilities of oxidized and reduced forms of mediators with the host matrix. The modified electrodes prepared showed electrocatalytic activity for electrooxidation of NADH. The i,c-dependencies for the modified electrodes were shown to follow Michaelis-Menten kinetics. For C:ZrP:NB and C:ZrP:MV electrodes, Michaelis constants of 0.870 +/- 0.012 and 0.153 +/- 0.015 mM, respectively, were obtained. The sensitivity of C:ZrP:NB and C:ZrP:MV electrodes to NADH varied from 19.2 to 60.8 and from 18.4 to 50.9 μA/mM c cm(2), respectively, by changing the working potential from -0.2 to 0.2 V vs. SCE. Copyright 2000 Academic Press.     

Graph properties for splitting with grounded Laplacian matrices

With any undirected, connected graphG containing no self-loops one can associate the Laplacian matrixL(G). It is also the (singular) admittance matrix of a resistive network with all conductances taken to be unity. While solving the linear system involved, one of the vertices is grounded, so the coefficient matrix is a principal submatrix ofL which we will call the grounded Laplacian matrixL ₁. In this paper we consider iterative solutions of such linear systems using certain regular splittings ofL ₁ and derive an upper bound for the spectral radius of the iteration matrix in terms of the properties of the graphG.This work was supported by the Academy of Finland