Damir Iveković

Glucose determination in blood samples using flow injection analysis and an amperometric biosensor based on glucose oxidase immobilized on hexacyanoferrate modified nickel electrode

Abstract A very simple amperometric enzyme-based glucose sensor is applied as detector in flow injection analysis (FIA) of diabetic patients blood glucose. The enzyme glucose oxidase (GOD) is immobilized by a glutaraldehyde/bovine serum albumin crosslinking procedure on the surface of an alkali nickel hexacyanoferrate thin film electrocrystallized on the nickel electrode. An alkali nickel hexacyanoferrate modified nickel electrode catalyzes the reduction of the hydrogen peroxide, formed by selective biocatalytic GOD action on glucose oxidation by oxygen present in sample solutions. The developed glucose sensor has shown good sensitivity at low negative operating potentials ( −300 to −100 mV vs. Ag AgCl ), sufficiently wide linear glucose concentration range (5 μM–2.9 mM), relatively long operating time (during three months of operation the initial sensitivity decreased only 30%) and no influence of the most common interferences present in human blood like proteins, ascorbic and uric acids.

Study of thermal stability of (3-aminopropyl) trimethoxy silane-grafted titanate nanotubes for application as nanofillers in polymers

Protonated titanate nanotubes (TiNT-H) were surface-modified with (3-aminopropyl)trimethoxy silane (APTMS) by a novel method suitable for the syntheses of large amounts of materials at a low cost. The usage of prepared nanotubes for polymer reinforcement was studied. Since the thermal stability of the nanofiller was important to preserve its functional properties, its stability was studied by in situ high-temperature measurements. The most thermally stable nanotubes were silanized for 20 min and used for the preparation of epoxy-based nanocomposites. The nanofiller formed smaller (a few hundred nm) and larger (a few μm) aggregates in the polymer matrix, and the amount of aggregates increased as the nanofiller content increased. The APTMS-modified titanate nanotubes bonded well with the epoxy matrix since amine groups on the TiNTs surface can react with an epoxy group to form covalent bonds between the matrix and the nanofiller. A very small addition (0.19-1.52 wt%) of the nanotubes significantly increased the glass transition temperature and the modulus in the rubbery state of the epoxy-based polymer. Smaller nanofiller content leads to a larger increase in these parameters and therefore better dynamic mechanical properties due to the smaller amount of large aggregates. APTMS-modified titanate nanotubes have proven to be a promising nanofiller in epoxy-based nanocomposites.

Structure elucidation of the photoproducts obtained by the photolysis of N-acetyl-2-styrylpyrroles

Abstract From the irradiation mixture of N -acetyl-2-styrylpyrroles ( 5a , b ) the deacylated ( 6a , b ), phototransposition ( 7a , b – 10a , b ), electrocyclisation ( 12 ), addition and reduction ( 11 , 13 and 14 ) and dimerisation products ( 15 ) have been detected. No intramolecular cycloaddition products have been observed.

The fate of carbapenem-resistant bacteria in a wastewater treatment plant

Wastewater treatment plants have been considered potential sources of antibiotic resistance gene exchange and release into the environment. The aim of our study was to quantify environmental and human-associated carbapenem-resistant bacterial populations (CRBPs) across wastewater treatment stages and correlate bacterial counts to physicochemical and other bacteriological parameters in order to see their behaviour in wastewater and sludge and their potential dissemination in the environment. Samples were taken from five sites (treatment stages) of the largest Croatian wastewater treatment plant (20 per site) over 10 months of monitoring. CRBPs were found at all wastewater treatment stages save for the lime-treated, stabilised sludge, which underlines the importance of effluent and digested sludge disinfection. Secondary sludge settling removed 99% of CRBP from the effluent, but the relative proportion of CRBP in the total bacterial count significantly increased in the effluent (0.0020%) and digested sludge (0.0019%) compared to the influent (0.0006%), indicating selection for resistant bacteria in these settings. CRBP counts did not correlate with measured carbapenem concentrations in wastewater, which suggests that antibiotic concentrations were not the reason for CRBP selection. Negative correlation between activated sludge retention time and CRBP indicated that their number could be reduced by increasing the retention time during secondary treatment. Despite the indications that WWTPs select for antibiotic-resistant bacteria, wastewater treatment is very efficient in reducing their absolute numbers, and proper effluent and sludge disinfection can significantly reduce dissemination of antibiotic-resistant bacteria into the environment.

Electrochemical reduction of desmycosin, structure investigation and antibacterial evaluation of the resulting products

Electrochemical reduction of desmycosin at the mercury electrode in aqueous medium was investigated by cyclic voltammetry and preparative scale electrolysis was carried out for the isolation and identification of products. Structure analyses of the resulting products were accomplished by MS, 1D and 2D NMR spectroscopy. The results obtained show that dimerization and two electron reduction of desmycosin occur in parallel yielding a symmetric dimer at position C13 and 10,11-dihydrodesmycosin as the end products. 10,11-dihydrodesmycosin shows decreased antibacterial activity in vitro in comparison with desmycosin, while the dimer is inactive.