Physicochemical Analysis of the System Zr(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>–Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>–H<Subscript>2</Subscript>SO<Subscript>4</Subscript>–H<Subscript>2</Subscript>O at 25°С

The solubility in the quaternary water–salt system Zr(SO₄)₂ · 4Н₂О–Na₂SO₄–H₂SO₄–H₂O at 25°C was studied. It was found that, in the system, there is crystallization of not only Na₂SO₄ and Zr(SO₄)₄ · 4H₂O, but also sodium sulfate zirconates Na₂Zr(SO₄)₂(OH)₂ · 0.3H₂O, Na₄Zr(SO₄)₄ · 3H₂O, and Na₂Zr(SO₄)₂ · 3H₂O and two new compounds, S₁ and S₂, which are presumably Na₂ZrO(SO₄)₂ · 2H₂O and Na₂Zr₂O₂(SO₄)₃ · 6H₂O.     

Optimization of silicon dioxide surface functionalization protocol for designing the receptor layer of a biosensor for detecting explosives

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.     

On peculiarities of heat and mass transfer in a hot metal particle-liquid fuel condensed substance-air system

Results of numerical modeling are used for validating the governing role of the ratio of areas of contact between the heater with the combustible liquid and the formed vapor-gas mixture in a complex of interrelated processes of heat and mass transfer at gas-phase ignition of a liquid condensed substance film by small-size hot metal particle. Critical values of the ratio at which the ignition conditions cannot be realized are marked out. Ranges of varying the main igniter parameters for which the influence of the parameter on the ignition parameters may be neglected are determined.     

Domain dynamics in a Gunn diode inserted in a resistive circuit

Temporal parameters of the current pulses generated by a Gunn diode operating in domain mode in relation to the supply voltage and load resistance are numerically simulated. The results of the numerical and analytical studies are compared. The validity range of the analytical formulas is ascertained in detail. In the context of the considered model, the minimum pulse duration and the time of domain formation are obtained at zero load and for a supply voltage exceeding the critical value by a factor of 1.25.     

Formation of Nickel-Tantalum Compounds in NaCl-K2TaF7 Melts

The formation of nickel-tantalum compounds in halide fluorotantalate melts was studied at 750°C. The mechanism of electroless tantalum plating onto nickel is considered and it is suggested that disproportionation underlies the spontaneous transfer.     

Conformational Composition of 5-Alkyl-1,3-Oxathianes

Conformational equilibrium of 5-isopropyl-1,3-oxathiane occurs mainly between the forms of chair with equatorial and axial orientation of the substituent at the C⁵ atom, and in the case of 2,2,5-trimethyl- and, apparently, in the case of 5-tert-butyl-1,3-oxathianes is characterized by a more noticeable contribution of flexible forms.     

Energetics of Long-Range Coordination Interactions of Gold Atoms in Inorganic Complexes

The energy of the Au(I)···Au(I) interaction was estimated within the framework of the structural thermodynamic model for 40 various complexes in which the interaction of gold atoms occurred in the d ¹⁰configuration. The estimation was compared to the results of quantum-chemical calculations using the Herchbach–Laurie formula. A conclusion was made that the Au···Au coordination interactions exhibit no specific features.