Kinetics of Complexation in the Monolayers of Amphiphilic Dicetylcyclene on the Surface of Aqueous Copper(II) Chloride Solutions

The kinetics of complexation in monolayers of dicetycyclene at the surface of aqueous copper(II) chloride solutions was studied. It was shown that the changes in the phase state of monolayer related to the conformational transitions of macrocycle are responsible for the differences in the rate and binding mechanism of copper ions. It was concluded that the sterically more advantageous (for the coordination with the metal ion) conformation of macrocyclic polyamine is ensured in a monolayer. In addition, it was established that the rate and mechanism of complexation in such monolayers greatly depend on the degree of protonation of ligands, the latter being dependent on the subphase pH. It was also demonstrated that an increase in subphase pH to 7 and higher results in an almost total suppression of metal ion binding due to strong conformational distortion of dicetylcyclene macrocycles in a monolayer and the hydrogen bonding between macrocycles.     

Pressure and temperature dependences in p-ZnAs2 at high pressures

Kinetic effects in p-ZnAs₂ were measured at hydrostatic (P ≤ 9 GPa) and quasi-hydrostatic (to P ≤ 50 GPa) pressures on pressure buildup and depressurization. A conclusion on the occurrence of two phase transitions was made: I–II at P = 9–15 GPa and II-III at P = 30–35 GPa. Based on the temperature dependences of electrical resistance, it was shown that the conductivity is determined by activation mechanisms in a temperature range of 250–400 K; in this case, the activation energy changed with temperature and pressure. The pressure dependences of the activation energy and the coefficient R ₀, which characterizes the mobility, concentration, and effective mass of carriers, were calculated.     

Two-dimensional arrays of amphiphilic Zn2+-cyclens for guided molecular recognition at interfaces

The sterically guided molecular recognition of nucleobases, phosphates, adenosine, and uridine nucleotides on Langmuir monolayers and Langmuir-Blodgett monolayers of amphiphilic mono- or bis(Zn2+-cyclen)s assembled on thiolated surfaces was investigated. The stepwise selective binding of metal ions, uracil, or phosphate by dicetyl cyclen monolayers with variously tuned structures at the air/water interface was corroborated by the measurements of the corresponding LB films deposited onto quartz crystals. Two types of recognition surfaces were fabricated from Zn2+-dicetyl cyclen. The surface covered with a complex preformed in the Langmuir monolayer was capable both of imide and of phosphate binding. The similar complex formed directly in an LB film on thiolated gold was inactive with respect to imide. The surface plasmon resonance measurements evidenced the stepwise assembly of complementary nucleotides on SAM/LB templates through consecutive phosphate-Zn2+-cyclen coordination. Base pairing between nucleotides resulted in a formation of A-U bilayers comprising two complementary monolayers. Finally, we report on SAM/LB patterns designed for divalent molecular recognition of uridine phosphate by amphiphilic bis(Zn2+-cyclen).     

Stabilization of Ferromagnetism in BiFeO<Subscript>3</Subscript>:Ho at Hydrostatic Pressure

The isothermal magnetization of the Bi_{1 – x}Ho _x FeO₃ (x = 0?0.2) multiferroic has been studied at a hydrostatic pressure up to 9 GPa in the range of room temperatures. A new anomaly at P_C ≈ 3.81 GPa related to intermediate phases between the structural transition R3c → Pnma has been found against the background of the pressure-induced antiferromagnetic ordering in BiFeO₃ (BFO) at P ≈ 2.59 GPa. It is established that the ferromagnetic behavior under pressure depends on the Ho impurity concentration: P_C decreases at 0.05 ≤ x ≤ 0.1 because of the decrease in R3c bond lengths in the structure, and the stabilization of ferromagnetism is implemented at 0.1 ≤ x ≤ 0.2 probably because of the coexistence of the R3c and Pnma phases. The results of studies indicate that, in Bi_{1 – x}Ho _x FeO₃ with x = 0.2, the transition pressure P_C = 3.7 GPa exceeds the values for BFO doped with other 4f elements (Eu, Y, Sm) in the region R3c → Pnma of the transition.     

Synthesis of Polyacrylamide Gels for Restricting the Water Inflow in Development of Oil Fields

Thermally stable hydrogels resistant to highly mineralized stratal water were synthesized from the nonionogenic polyacrylamide, paraform, resorcinol, sulfosalycilic acid, and Atren Fibre structuring additive. It was shown that the hydrogels are promising for development of gel screens in the borehole zone of oil-producing wells to restrict the water inflow and raise the oil recovery factor.     

Analytical micelles containing amphiphilic aminoanthraquinone solvatochromic reporter receptor

The feasibility of using an amphiphilic photoactive derivative of aminoanthraquinone (C18) as both a local solvatochromic probe reporting its position in a micelle and a component of an analytical supramolecular unit in mixed micelles based on a nonionic surfactant, Triton X100, has been considered. The solvatochromism of the 1,8-anthraquinone derivative (C18) has, for the first time, been investigated. Dipole moments of C18 molecules have been determined within the frameworks of the Lippert–Mataga, Kawski, and Reichardt approaches. It has been found that the Δμ values, as calculated with the help of the first two approaches and the Onsager radius, which is, for C18, equal to 5.8 Å, are markedly higher than the value obtained in terms of the Reichardt model. Possible reasons for discrepancies, which arise between experimental data and theoretical predictions when analyzing the solvatochromic properties of dyes, have been briefly discussed. C18 has been employed as an example to show that, for chromophores capable of donor–acceptor interactions, the use of protic solvents is more reasonable, because they ensure realization of a wider spectrum of interactions with a probe, among which the van der Waals interactions play an important role. Therewith, polarization effects, rather than charge separation, make a substantial contribution. In the case of amphiphilic chromophores, “enveloping” of polar groups with hydrocarbon chains decreases the local dielectric permittivity and the probability of intermolecular donor–acceptor interactions (hydrogen bonding). The character of the microenvironment of C18 reporter in micelles has been determined with the use of the “relative polarity parameter” proposed in this work. This parameter makes it possible to compare results obtained for different models of solvatochromism. It has been shown that the characteristics of C18 microenvironment in micelles correspond to those of water–alcohol solutions, with the chromophoric moieties of dye molecules located in the polar region of a micelle, this region being formed by hydrated ethylene-oxide chains of Triton X100. Polar receptor groups of C18, which face the aqueous phase, complete the hydrophilic shell of a micelle, while hydrocarbon chains of both components compose its hydrophobic core. This structure of the normal micelle and the markedly higher intensity of fluorescence of the micellar system than that of an aqueous C18 solution make possible the analytical determination of metal ions in aqueous media.     

Thermooxidative degradation of watersoluble acetylcellulose and its carboxycontaining derivatives

The thermooxidative degradation of water-soluble acetylcellulose and some of its carboxy-containing derivatives has been studied by the methods of thermal analysis. A relationship has been established between the thermostability of the aceto-mixed derivatives and the nature of the substituting group. Tashkent Institute of Chemical Technology. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 703–705, September–October, 1998.     

Polynomial algorithms for guillotine cutting of a rectangle into small rectangles of two kinds

In this paper the problem of optimally guillotine cutting a rectangle (A, B  ) into small rectangles of two kinds is considered. Rectangles of the first kind (c,_ai),i∈I$(c\text{,}{a}_i)\text{,}i\in I$ have the same width, and their heights can be various. Rectangles of the second kind (_bj,d),j∈J$(b_j\text{,}d)\text{,}j\in J$ have the same height, and their widths can be various. The number of occurrences of each small rectangle in a cutting pattern is not restricted. Similar problems often appear in the furniture industry. This cutting problem is reduced to the shortest path problem in a special rectangular grid, for which a linear time algorithm is suggested. This approach generalizes the approach of [E. Girlich, A.G. Tarnowski, On polynomial solvability of two multiprocessor scheduling problems, Mathematical Methods of Operations Research 50 (1999) 27–51; A.G. Tarnowski, Advanced polynomial time algorithm for guillotine generalized pallet loading problem, in: The International Scientific Collection: Decision Making Under Conditions of Uncertainty (Cutting-Packing Problems), Ufa State Aviation Technical University, 1997, pp. 93–124] and allows us to construct polynomial algorithms for the guillotine cutting problem considered with a fixed number of small rectangles of two kinds.