The system of self-consistent QSPR-models for refractive index of polymers

Structural Chemistry - Quantitative structure–property/activity relationships (QSPRs/QSARs) are a component of modern natural science. The system of self-consistent models is a specific...     

Oscillation and nonoscillation of nonlinear second order difference equations

In this paper, we study oscillation and nonoscillation behaviour of the second order nonlinear difference equations of the form $$\Delta (r_n \psi (x_n )\Delta x_n ) + q_{n + 1} f(x_{n + 1} ) = 0, n \in N(n_o ),$$ and $$\Delta (r_n \psi (x_n )\Delta x_n ) + q_n f(n,x_n ) = 0, n \in N(n_o ),$$ whereN(n _o ) =n _o ,n _o + 1, …, (n _o is a fixed nonnegative integer number), Δx_n =x _n +1?x _n is the forward difference operator,x :N(n _o ) → ?,r :N(n _o ) → (0, ∞), Ψ : ? → (0, ∞),f is a real valued continuous function, andq _n is a sequence of real valued.     

The definition of the molecular structure for potential anti-malaria agents by the Monte Carlo method

A series of 53 endochin analogs (4(1-H)-quinolone derivatives) with anti-malarial activity against the clinically relevant multidrug resistant malarial strain TM-90-C2B has been studied. The CORAL (http://www.insilico.eu/coral) software has been used as a tool to build up the quantitative structure–activity relationships (QSAR) for the anti-malaria activity. The QSAR models were calculated with the representation of the molecular structure by simplified molecular input-line entry system and by the molecular graph of atomic orbitals. The method for splitting data into the sub-training set, the calibration set, the test set, and the validation set is suggested. Three various splits were examined. Statistical quality of models for the validation sets (which are not involved in the building up models) is good. Structural indicators (alerts) for increase and decrease of the anti-malaria activity are defined.     

Simple and effective method for the synthesis of 3′,5′-substituted 1-β-D-arabinofuranosyluracil

3,5-Substituted arabinofuranosyluracil is a starting compound in 2-modifications. A convenient and effective method is proposed for the synthesis of 1-(3,5-di-o-trityl--D-arabinofuranosyl)uracil by successive reactions of 2,2-cyclization of uridine, 3,5-tritylation of the 2,2-anhydrouridine, and hydrolytic cleavage of the 2,2-anhydro bond.Institute of Organic Synthesis, Riga LV-1006. Odense Universitet, Kemisk Institut, Odense, Denmark. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 975–977, July, 1996. Original article submitted April 25, 1996.     

Liquid-liquid phase transitions in supercooled water studied by computer simulations of various water models

Liquid-liquid and liquid-vapor coexistence regions of various water models were determined by Monte Carlo (MC) simulations of isotherms of density fluctuation-restricted systems and by Gibbs ensemble MC simulations. All studied water models show multiple liquid-liquid phase transitions in the supercooled region: we observe two transitions of the TIP4P, TIP5P, and SPCE models and three transitions of the ST2 model. The location of these phase transitions with respect to the liquid-vapor coexistence curve and the glass temperature is highly sensitive to the water model and its implementation. We suggest that the apparent thermodynamic singularity of real liquid water in the supercooled region at about 228 K is caused by an approach to the spinodal of the first (lowest density) liquid-liquid phase transition. The well-known density maximum of liquid water at 277 K is related to the second liquid-liquid phase transition, which is located at positive pressures with a critical point close to the maximum. A possible order parameter and the universality class of liquid-liquid phase transitions in one-component fluids are discussed.     

Ratios of substrates and inhibitors of prostaglandin synthesis in blood plasma of atients with heart ischemia

To check the proposed hypothesis that the relative content of individual polyunsaturated fatty acids (PUFAs)—substrates and inhibi tors of prostanoid synthesis—in plasma can be regarded as a quantita tive risk factor of blood clotting, a test was conducted on free fatty acids content in blood plasma of healthy people (group 0) and patients with heart ischemia before (group 1) and after (group 2) they were treated for a month with a food additive called “Eiconol,” enriched with PUFA ω3. Different proportions of PUF As have been calculated in all cases, accounting for the contribution of each acid to the process of primary clotting. Comparison of PUFA rations among the three groups showed significant differences of means between groups 0 and 1 and also group 1 and 2 for 6 out of 7 proposed coefficients, which disappeared after “Eiconol” treatment (comparison of groups 0 and 2). The results led to the conclusion that out of the proposed PUFA proportions, the coefficients describing the relative content of arachidonic acid in blood plasma may be the most informative for diagnosis and treatment efficiency in evaluation of heart and vascular diseases.     

Structure and swelling-release behaviour of poly(vinyl pyrrolidone) (PVP) and acrylic acid (AAc) copolymer hydrogels prepared by gamma irradiation

Copolymer network hydrogels were prepared by gamma irradiation of aqueous solutions of poly(vinyl pyrrolidone) (PVP) and acrylic acid monomer (AAc). The composition of the final hydrogels compared to the composition of the initial preparation solutions of hydrogels was determined. The chemical structure and nature of bonding was characterized by IR spectroscopy analysis, while the thermal durability of the prepared hydrogels was assessed by thermogravimetric analysis (TGA). The kinetic swelling in water and the pH-sensitivity of PVP/AAc copolymer hydrogels was studied. The drug release properties of PVP/AAc hydrogels taking methyl orange indicator as a drug model was investigated. The IR spectra indicate the formation of copolymer networks, whereas the TGA study showed that the PVP/AAc hydrogels possess higher thermal stability than pure PAAc and lower than PVP hydrogels. The kinetic swelling in water showed that all the hydrogels reached equilibrium after 24 h and that the degree of swelling increases with increasing the ratio of AAc in the initial feeding solutions. It was found that the degree of swelling of PVP/AAc hydrogels increases greatly within the pH range 4-7 depending on composition.     

Synthesis and characterization of polyamides obtained from tartaric acid and L-lysine

Two sets of AA · BB-type polyamides (PLyTA) were synthesized from natural compounds L-lysine and D- or L-tartaric acid via the active ester polycondensation method. The carboxyl and hydroxyl side groups were orthogonally protected as methyl ester and methyl ether, respectively. Direct reaction of methyl L-lysinate dihydrochloride with bis(pentachlorophenyl) di-O-methyl tartaric acid led to the aregic polyamide ar-PLyTA, whereas isoregic (ir-PLyTA) and syndioregic (sr-PLyTA) polyamides were obtained by polycondensation of specifically designed amide–aminoacid and amide–diamine monomeric precursors, respectively. These polyamides have intrinsic viscosities in the 0.50–0.76 dl g⁻¹ range, display optical activity, and are readily soluble in chloroform. They start to decompose well above 200 °C and display glass-transition temperatures at 100–105 °C. DSC and X-ray diffraction results indicated that these polyamides are not crystalline but they seem to adopt a partially ordered phase. No differences in properties other than optical rotation were observed between PLyTA made of D- and L-tartaric acid.