Voltammetric determination of DNA hybridization using methylene blue and self-assembled alkanethiol monolayer on gold electrodes

An electrochemical DNA biosensor based on the recognition of single stranded DNA (ssDNA) by hybridization detection with immobilized complementary DNA oligonucleotides is presented. DNA and oligonucleotides were covalently attached through free amines on the DNA bases using N-hydroxysulfosuccinimide (NHS) and N-(3-dimethylamino)propyl-N′-ethylcarbodiimide hydrochloride (EDC) onto a carboxylate terminated alkanethiol self-assembled monolayers (SAM) preformed on a gold electrode (AuE). Differential pulse voltammetry (DPV) was used to investigate the surface coverage and molecular orientation of the immobilized DNA molecules. The covalently immobilized probe could selectively hybridize with the target DNA to form a hybrid on the surface despite the bases being attached to the SAM. The changes in the peak currents of methylene blue (MB), an electroactive label, were observed upon hybridization of probe with the target. Peak currents were found to increase in the following order: hybrid-modified AuE, mismatched hybrid-modified AuE, and the probe-modified AuE which indicates the MB signal is determined by the extent of exposed bases. Control experiments were performed using a non-complementary DNA sequence. The effect of the DNA target concentration on the hybridization signal was also studied. The interaction of MB with inosine substituted probes was investigated. Performance characteristics of the sensor are described.     

Dye-sensitized photooxygenation of the C=N bond. 5. substituent effects on the cleavage of the C=N bond of C-aryl-N-aryl-N-methylhydrazones

The title compounds are cleaved cleanly at the C=N bond by singlet oxygen ((1)O(2), (1)Delta(g)) yielding arylaldehydes and N-aryl-N-methylnitrosamines. These reactions take place more rapidly at -78 degrees C than at room temperature. The effects of substituent variation at both the C-aryl and N-aryl groups were studied using a competitive method. Good correlations of the resulting rate ratios with substituent constants (sigma(-) or sigma(+)) were obtained yielding small to very small rho values indicative of small to very small changes in charge distribution between the reactant and the rate determining transition state. Electron withdrawing groups on the C-aryl moiety retard reaction somewhat by preferential stabilization of the hydrazone. Electron donors on the other hand slightly stabilize the rate determining transition state. Substituents on the N-aryl group have almost no effect. Inhibition by 3,5-di-tert-butylphenol was not observed showing that free (uncaged) radical intermediates are not involved in the mechanism. We postulate a mechanism in which the initial event is exothermic electron transfer from the hydrazone to (1)O(2) leading to an ion-radical caged pair. Subsequent covalent bond formation between the hydrazone carbon and an oxygen atom is rate controlling. The transition state for this step also has a lower enthalpy than the starting reactants, but the free energy of activation is dominated by a large negative TDeltaS++term leading to the negative temperature dependence. Direct formation of a C-O bond in the initial step is not unambiguously ruled out. Subsequent steps lead to C-N cleavage.     

Finding minimum height elimination trees for interval graphs in polynomial time

The elimination tree plays an important role in many aspects of sparse matrix factorization. The height of the elimination tree presents a rough, but usually effective, measure of the time needed to perform parallel elimination. Finding orderings that produce low elimination is therefore important. As the problem of finding minimum height elimination tree orderings is NP-hard, it is interesting to concentrate on limited classes of graphs and find minimum height elimination trees for these efficiently. In this paper, we use clique trees to find an efficient algorithm for interval graphs which make an important subclass of chordal graphs. We first illustrate this method through an algorithm that finds minimum height elimination for chordal graphs. This algorithm, although of exponential time complexity, is conceptionally simple and leads to a polynomial-time algorithm for finding minimum height elimination trees for interval graphs.This work was supported by grants from the Norwegian Research Council.     

Novel antifoam for fermentation processes: fluorocarbon-hydrocarbon hybrid unsymmetrical bolaform surfactant

As foaming appears as a problem in chemical and fermentation processes that inhibits reactor performance, the eminence of a novel fluorocarbon-hydrocarbon unsymmetrical bolaform (FHUB: OH(CH2)11N+(C2H4)2(CH2)2(CF2)5CF3 I-) surfactant as an antifoaming agent as well as a foam-reducing agent was investigated and compared with other surfactants and a commercial antifoaming agent. The surface elasticity of FHUB was determined as 4 mN/m, indicating its high potential on thinning of the foam film. The interactions between FHUB and the microoganism were investigated in a model fermentation process related with an enzyme production by recombinant Escherichia coli, in V = 3.0 dm3 bioreactor systems with V(R) = 1.65 dm3 working volume at air inlet rate of Q(o)/V(R) = 0.5 dm3 dm(-3) min(-1) and agitation rate of N = 500 min(-1) oxygen transfer conditions, at T = 37 degrees C, pH(o) = 7.2, and C(FHUB) = 0 and 0.1 mM, in a glucose-based defined medium. As FHUB did not influence the metabolism, specific enzyme activity values obtained with and without FHUB were close to each other; however, because of the slight decrease in oxygen transfer coefficient, slightly lower volumetric enzyme activity and cell concentrations were obtained. However, when FHUB is compared with widely used silicon oil based Antifoam A, with the use of the FHUB, higher physical oxygen transfer coefficient (K(L)a) values are obtained. Moreover, as the amount required for the foam control is very low, minute changes in the working volume of the bioreactor were obtained indicating the high potential of the use of FHUB as an antifoaming agent as well as a foam-reducing agent.     

Synthesis and Structural Studies of 2,2′-[(2E,5E)-hexane-2,5-diylidenedi-nitrilo]-dibenzenethiol and 2-Hydroxybenzaldehyde (2E,5E)-hexane-2,5-diylidenehydrazone ligands and their Mononuclear Cu(II) and Ni(II) Complexes

Monomeric copper(II) and nickel(II) complexes with tetradentate two new ligands, 2,2′-[(2E,5E)-hexane-2,5-diylidenedi- nitrilo]dibenzenethiol(H₂L) and 2-hydroxybenzaldehyde (2E,5E)-hexane-2,5-diylidenehydrazone(H₂L¹) have been synthesized and characterized by elemental analyses, magnetic moments, molar conductance, ¹H-NMR and ¹³C-NMR, IR, mass spectral studies, theoretical calculations (MM2 and AM1) molecular methods. The mononuclear metal complexes of H₂L and (H₂L¹) were found to have a 1:1 metal:ligand ratio. Elemental analyses, stoichiometric and spectroscopic data of metal complexes indicated that the metal ions were coordinated to the sulphur (-SH) and/or (-OH) oxygen and imine nitrogen atoms (C = N). All of the data obtained from spectral, and molecular mechanics (MM2) or semi empirical calculations (AM1) studies support the structural properties of ligands and its Cu(II) and Ni(II) metal complexes.     

An Electrochemical Biosensor Platform for Testing of Dehydroepiandrosterone 3‐Sulfate (DHEA−S) as a Model for Doping Materials

Endogenous steroids such as dehydroepiandrosterone (DHEA) and dehydroepiandrosterone 3‐sulfate (DHEA?S) have commonly used as doping materials by athletes and to date novel techniques are needed for detection of these molecules. In this study, antibody‐based electrochemical biosensor has developed for testing level of the DHEA?S. For this aim, gold surfaces were initially modified with cysteamine (Cys) and then, DHEA?S antibody was immobilized on the surface via glutaraldehyde (GA) as a crosslinking agent. The stepwise modification of electrode surface was monitored by using various electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Linear range was determined as 2.5–100 ng/mL DHEA?S using differential pulse voltammetry (DPV) technique, as well. Moreover, repeatability (±S.D.), coefficient of variation (%) and limit of detection (LOD) values were calculated as 0.033, 1.030 and 3.971, respectively. Also, DHEA?S in synthetic serum and urine samples were successfully determined with standard addition method and confirmation analysis were performed with liquid chromatography quadrupole‐time of flight mass spectrometry (LC‐QTOF/MS) system. The selectivity was studied with the addition of some interfering molecules (testosterone, bovine serum albumin (BSA), cholesterol, uric acid, lactic acid, codein (COD), ascorbic acid, DHEA). Consequently, this work is proposed as practical, innovative and cost‐effective technique that can be easily adapted for the miniaturized form for the analysis of other doping substances as well as DHEA?S for the future works.     

in vitro Selection of Aptamer for Imidacloprid Recognition as Model Analyte and Construction of a Water Analysis Platform

Pesticide use in agriculture is one of the threats to water safety. Therefore, detection of pesticide residues is crucial for human health. Compared to conventional chromatographic methods, aptasensors are promising tools for fast, cheap and sensitive detection of environmental contaminants. To the best of our knowledge, such an aptasensor has not been reported for imidacloprid (Imi) which is one of the most widely used pesticides. In order to meet this demand, we initially selected two novel aptamers designated as ‘Apta‐1’ and ‘Apta‐2’ by graphene oxide‐SELEX (GO‐SELEX) method. Then, these aptamers were used to fabricate the gold electrode‐based aptasensor platforms and characterized by using electrochemical methods such as cyclic voltammetry, and electrochemical impedance spectroscopy as well as X‐Ray photoelectron spectroscopy. It was found that the limit of detection value of Apta‐1 based sensor for the Imi was found better than Apta‐2 based system, although linear ranges were similar. Based on that finding, Apta‐1 based system was further tested against possible interference molecules. The proposed platform was successfully used for detection of very low concentrations of Imi in the range of ng/mL. Thus, it eliminates the need for sample pre‐treatment and enables a practical analysis in real wastewater samples.     

Artificial Iono‐ and Photosensitive Membranes Based on an Amphiphilic Aza‐Crown‐Substituted Hemicyanine

Artificial iono‐ and photosensitive membranes based on an amphiphilic aza‐crown‐substituted hemicyanine are assembled on liquid and solid supports and their aggregation behaviour, which is influenced by the binding of metal cations and surface density, is studied. The photoinduced charge‐transfer properties of an analogous non‐amphiphilic hemicyanine in solution are also demonstrated. An asymmetric sandwich dimer model is proposed and existence of such dimers in solution is evidenced by transient absorption and fluorescence anisotropy experiments. Changes in absorption and emission spectra, as well as compression isotherms of the amphiphile observed in the presence of cations, are discussed in terms of 2D molecular reorganisation. Surface‐pressure‐controlled reversible excimer formation at the air–water interphase and excimer‐type emission of Langmuir–Blodgett films in the presence of cations are demonstrated and are discussed on the basis of fibre‐optic fluorimetry and fluorescence microscopy results.     

Surface characterization of biocidal polyurethane modifiers having poly(3,3-substituted)oxetane soft blocks with alkylammonium side chains

This paper focuses on surface characterization of P[ AB] copolyoxetane soft block polyurethanes having either fluorous (3FOx, -CH2OCH 2CF3) or PEG-like (ME2Ox, -CH2(OCH2CH2) 2OCH3), A side chains and alkylammonium, B side chains. Physical surface characterization data were analyzed in light of the previously observed order of antimicrobial effectiveness for a set of four surface modifiers. Ample physical evidence for surface concentration of fluorous 2 wt % P[ AB]-polyurethane modifiers was obtained from XPS, contact angles, ATR-IR spectroscopy, and TM-AFM. In TM-AFM phase imaging, the most effective biocidal surface modifier, 2 wt % HMDI-BD(30)/P[(3FOx)(C12)-0.89:0.11]-PU, showed a nanoscale phase-separated structure consisting of 200 nm domains with background features about 10 times smaller. Despite similar surface characterization data, the 2 wt % fluorous C6 analog ranked third in contact biocidal effectiveness. Physical evidence for surface concentration of 2 wt % P[(ME2Ox)(C12)-0.86:0.14]-PU was modest, considering that antimicrobial effectiveness was second only to 2 wt % HMDI-BD(30)/P[(3FOx)(C12)-0.89:0.11]-PU. In this set of surface modifiers, nanoscale morphology is largely driven by the fluorous component, whereas antimicrobial effectiveness is more strongly influenced by alkylammonium chain length. The effect of alkylammonium side chain length on surface concentration and antimicrobial behavior is more pronounced for ME2Ox polyurethanes compared to the 3FOx analogs.     

Tri-nuclear phthalocyanine complexes carrying N/O donor ligands as hydrogen peroxide catalysts,and their bleaching activity measurements by an online spectrophotometric method

A phthalocyanine (4) with four salicylhydrazone ligating groups that are directly linked through oxygen bridges to the macrocyclic core has been synthesized by condensation of tetrakis(4-formylphenoxy)phthalocyaninato zinc(II) (3) with salicylhydrazine. Salicylhydrazine was crystallized in methanol during the synthetic procedure. The crystal structure has triclinic space group P-1 with a = 5.8292(6) Å, b = 7.3039(7) Å, c = 17.9798(18) Å, α = 84.272(8)°, β = 89.184(8)°, γ = 81.469(8)°, and Z = 4. Intramolecular O–H?O and intermolecular O–H?O, N–H?N, N–H?O hydrogen bonds were determined in the crystal structure. In addition, there is a weak C–H?π interaction. Complexation on the periphery to yield tri-nuclear Zn(II)Pcs (5–7) was performed through the reaction of a Schiff base-substituted phthalocyanine (4) with MnCl₂·4H₂O, CoCl₂·6H₂O, or Ni(OAc)₂ salts. Fourier transform infrared, ¹H NMR, ¹³C NMR, UV–Vis, ICP-OES (inductively coupled plasma optical emission spectroscopy), mass spectroscopies, and elemental analyses were applied to characterize the prepared compounds. Bleach catalyst activity of the prepared phthalocyanine complexes (5–7) was examined by the degradation of morin and curcumin, respectively. The catalysts had better activity for color removing in solutions at ambient temperature than to that of tetraacetylethylenediamine (TAED).