Vol 71, No 1 (2016)

Lytic enzymes of bacteriophages K, phi11, and phi80α can lyse (destroy) cells of antibiotic-resistant strains of Staphylococcus aureus, which makes these enzymes promising antimicrobial agents. The stability of recombinant lysins of phages K, phi11, and phi80α was investigated under the conditions of storage and functioning, and the correlation between the stability and the secondary structure of the enzymes was found. It has been shown that the lower the content of disordered structures in the enzyme molecules, the greater the stability (half-inactivation time) of the lysins. At the storage temperature, the beta-structural lysin of phage phi11 shows the highest stability, while the phage K lysin with an alpha-helical structure and the phi80α lysin with a disordered secondary structure are less stable.

A new type of chiral matrix based on silver–thiocholesterol hybrid nanosystems adsorbed on silica gel has been proposed. The molar ratio of stabilized thiocholesterol (L) ligand and silver (Ag) was found to have little effect on the size of the resulting silver nanoparticles (SNPs). The average diameter of SNPs was 2.7 ± 0.4, 2.2 ± 0.4, and 2.1 ± 0.6 nm upon the ratios Ag: L = 1: 5, Ag: L = 1: 2, and Ag: L = 1: 0.5, respectively. The resulting chiral matrices possess enantioselectivity relative to the 1,1’-binaphthyl-2,2’-diamine (BNDA) and trifluoroanthranyl ethanol (TFAE) optical isomers. The TFAE optical isomers were successfully separated using thin layer chromatography (α = 1.56).

The development of the receptor layer of the biosensor for detecting explosive compounds is described. The covalent modification has been chosen for immobilizing E. coli nitroreductase on the gate oxide of the ion-sensitive field effect transistor (ISFET) that is comprised of silicon dioxide. The self-assembled monolayer technique has been used for immobilization. This method assumes the usage of different silanes and spacer molecules for activating the surface of SiO₂. Two different immobilization strategies have been compared, one using asymmetric spacers (3-maleimidobenzoic acid N-hydroxysuccinimide ester (MBS) and 4-(4-maleimidophenyl)butyric acid N-hydroxysuccinimide ester (SMPB)) and another using a symmetric glutaric dialdehyde linker both accompanied by appropriate silanes. For the first method, the dependence of functionalization efficiency on silane concentration has been studied. The sufficient density of enzyme molecules on the surface of SiO₂ has been achieved at a concentration of silane of 0.0015%. The type of asymmetric linker has no influence on immobilization efficiency. The method implying glutaric dialdehyde results in higher activity of the immobilized enzyme. For this method, the immobilization procedure has been optimized. The method has been adapted for immobilization of E. coli nitroreductase inside the channel of a microfluidic system on the surface of ISFET. For this purpose, (3-aminopropyl)triethoxysilane (APTES) has been changed to the corresponding silatrane, and the concentration of the enzyme has been increased to 30 μg/mL. The optimized procedure has been successfully used to develop a biosensor for detecting explosives.

The behavior of Pt-containing catalysts based on mesoporous amorphous aluminosilicate in the process of hydroconversion of C₁₉–C₃₈n-paraffins with the goal to produce diesel and kerosene fractions with improved cold flow properties was investigated. These systems were characterized by high efficiency and selectivity in the process of producing diesel and kerosene fractions. A 91% degree of conversion was achieved with a yield of liquid hydrocarbons of 76% (320°C, volume feed rate 0.5 h^–1, molar ratio hydrogen: feed = 600: 1, pressure 50 atm). The initial freezing point of the isolated kerosene fraction was below minus 50°C, and the cold filter plugging point of the diesel fraction was minus 34°C.

Pseudo-homogeneous enzyme immunoassay (EIA) of aflatoxin B1 (AFB1) was accomplished using anti-AFM1 monoclonal antibodies conjugated with magnetic particles (MPs). The assay includes the concentration of AFB1 from the test sample on the surface of the MP-antibody conjugate, the binding of the AFB1-peroxidase conjugate to free sites of the antibodies, the separation of the complexes that formed from unreacted components by means of magnetic field, and the evaluation of the enzymatic activity of MP-bound peroxidase. A comparative study of antibody conjugates, which were prepared by three different methods, namely, by physical adsorption on native MP and covalent binding to oleic acidor polystyrene-coated MPs, was performed. For these conjugates, the detection limits of EIA for AFB1 are 2.6, 0.4, and 0.6 ng/mL, respectively. The advantages of the pseudo-homogeneous EIA format as a tool for the highly sensitive control of toxic contaminants in food are the shorter time of incubation of immunoassay reagents (5 min; the total assay time is 20 min) and the possibility of concentrating the analyte from the test samples.

The modification of hydrophilic fiberglass and cellulose membrane materials with zinc oxide has been investigated. The surfaces of zinc oxide nanoparticles was hydrophilized by modification with 3-amino-propyltriethoxysilane. It was shown using methods of Fourier transform IR-spectroscopy and scanning electron microscopy that coating with hydrophilized zinc oxide nanoparticles did not change the structure of glass fibers and membrane material, while the treatment of cellulose-based membrane materials caused irreversible changes in the structure of fibers and the material as a whole.

Sensitive coatings for piezoelectric sensors used to assess the presence of anthropogenic volatile organic substances in the equilibrium gas phase over natural water have been selected using an array of measuring elements, and the data have been processed using principal component analysis. Groups of piezoelectric sensors with similar characteristics for substance identification have been determined based on the correlation between piezoelectric sensor responses when vapors of organic substances were detected. The stepby-step optimization of the piezoelectric sensor array has been carried out in order to identify the greatest number of organic compounds (vapors) in the sample. Volatile organic compounds can be identified in their aqueous solutions and natural water using the optimized piezoelectric sensor array.

Extraction of cadmium(II), lead(II), cobalt(II), copper(II), and zinc(II) into ionic liquids tetraoctylammonium N-lauroyl sarcosinate and trioctylmethylammonium salicylate is studied. Cadmium(II), lead(II), copper(II) in tetraoctylammonium N-lauroyl sarcosinate and copper(II) in trioctylmethylammonium salicylate are quantitatively extracted from neutral and weakly alkaline solutions in the absence of additional reagents. The effect of the composition of aqueous and organic phases, as well as the contact time, on metal extraction is investigated.