Volumetric properties of {PEG 200 (or 300) (1) + water (2)} mixtures at several temperatures and correlation with the Jouyban–Acree model

Molar volumes and excess molar volumes were investigated from density values for {PEG 200 (1) + water (2)} and {PEG 300 (1) + water (2)} binary mixtures at temperatures from 278.15 to 313.15 K. Both systems exhibit negative excess volumes probably due to increased interactions such as hydrogen bonding and/or large differences in molar volumes of components. Volume thermal expansion coefficients were also calculated for both binary mixtures and pure solvents. The Jouyban–Acree model was used for density and molar volume correlations of the studied mixtures at different temperatures. The mean relative deviations between experimental and calculated density data were 0.02% and 0.04%, for aqueous mixtures of PEG 200 and PEG 300, respectively; whereas the corresponding values for molar volume data were 1.76% and 2.72%.     

Preferential solvation of some antiepileptic drugs in {cosolvent (1) + water (2)} mixtures at 298.15 K

The solubility of lamotrigine (LTG), clonazepam (CZP) and diazepam (DZP) in some {cosolvent (1) + water (2)} mixtures expressed in mole fraction at 298.15 K was calculated from reported solubility values expressed in molarity by using the densities of the saturated solutions. Aqueous binary mixtures of ethanol, propylene glycol and N-methyl-2-pyrrolidone were considered. From mole fraction solubilities and some thermodynamic properties of the solvent mixtures, the preferential solvation of these drugs by both solvents in the mixtures was analysed by using the inverse Kirkwood–Buff integrals. It is observed that LTG, CZP and DZP are preferentially solvated by water in water-rich mixtures in all the three binary systems analysed. In {ethanol (1) + water (2)} mixtures, preferential solvation by water is also observed in ethanol-rich mixtures. Nevertheless, in {propylene glycol (1) + water (2)} and {N-methyl-2-pyrrolidone (1) + water (2)} mixtures preferential solvation by the cosolvent was observed in cosolvent-rich mixtures.     

Efficient one-pot synthesis of some new pyrimido[5′,4′:5,6]pyrido[2,3-d]pyrimidines catalyzed by magnetically recyclable Fe3O4 nanoparticles

The study is devoted to one-pot reaction of 1,3-dimethylbarbituric acid with aromatic aldehydes and ammonium acetate using Fe₃O₄ nanoparticles as efficient and magnetically recyclable catalysts. Aromatic aldehydes substituted with electron-withdrawing groups or none, reacted successfully with 1,3-dimethylbarbituric acid and ammonium acetate to give new pyrimido[5′,4′:5,6]pyrido[2,3-d]pyrimidine derivatives (can be also named as pyrido[2,3-d:6,5-d′]dipyrimidines) in high yields over relatively short reaction time. The Knoevenagel condensation products were isolated using aromatic aldehydes bearing electron-donating substituents. The catalyst could be efficiently used for four times without substantial reduction in its activity. The new products were characterized on the basis of FT-IR, ¹H NMR and ¹³C NMR spectral data.

     

Preferential solvation of nifedipine in some aqueous co-solvent mixtures

Preferential solvation parameters of nifedipine (NIF) in ethanol (EtOH) + water and propylene glycol (PG) + water mixtures were obtained from their thermodynamic properties in solution using the inverse Kirkwood–Buff integrals. Preferential solvation parameter (δx_1,3) by both co-solvents is negative in the water-rich mixtures but positive in almost all the other compositions at 293.2, 303.2 and 313.2 K. Nevertheless, in EtOH-rich mixtures the values of δx_1,3 are also negative. It can be assumed that in water-rich mixtures the hydrophobic hydration around the non-polar groups of NIF plays a relevant role in the solvation. The higher drug solvation by co-solvent in mixtures of similar solvent proportions and in co-solvent-rich mixtures could be due mainly to polarity effects. Moreover, in these mixtures the drug could be acting as a Lewis acid with the co-solvents molecules. Finally, in EtOH-rich mixtures the drug could be acting as a Lewis base with water molecules.     

Ultratrace determination of lead,cadmium and copper in environmental and biological samples by atomic absorption spectrometry after their separation and preconcentration using octadecyl silica membrane disks modified with a new n–s schiff base

Pb(II), Cd(II) and Cu(II) ions were separated and preconcentrated by solid-phase extraction on octadecyl-bonded silica membrane disks modified with a new S–N-containing Schiff base (bis-2-thiophenal propandiamine) (BTPD) followed by elution and atomic absorption spectrometric detection. The method was applied as a separation and detection method for lead(II), cadmium(II) and copper(II) in environmental and biological samples. Extraction efficiency and the influence of sample matrix, flow rate, pH, and type and minimum amount of stripping acid were investigated. The maximum capacity of the membrane disks modified by 4?mg of BTPD was found to be 668 ± 10, 480 ± 8 and 454 ± 7?µg of lead, cadmium and copper, respectively. The limit of detection of the proposed method is 0.25, 0.01 and 0.02?ng/mL for lead, cadmium and copper, respectively.     

Synthesis of Novel [1,2,4]triazolo[3,2-b][2,4,6]benzothiadiazocin-11(5H,10H)-One Derivatives

Several [1,2,4]triazolobenzothiadiazocin-11-ones 3 were prepared via ring expansion of [1,2,4]triazolo[3,2-b][2,4]benzothiazepin-10(5H)-ones 1 in presence of sodium azide. The reaction intermediate was isolated and characterized as an aryl isocyanate 2b . A possible pathway for formation of novel triazolobenzothiadiazocin-11-one 3 is described.     

Crystal structure of a binuclear polymeric self-assembled lead(II) complex.

A polymeric self-assembled complex [[Pb(pydc)(pydc-H2)(H2O)2]2]n is prepared from the complexation of a novel pyridine containing self-assembling system, LH2, [pyda-H2]2+[pydc]2- (pyda = 2,6-pyridindiamine and pydc-H2 = 2,6-pyridinedicarboxilic acid) and lead(II) nitrate in 84% yield. The characterization was performed using X-ray crystallography. The crystal system is triclinic with space group P1 and two molecules per unit cell. The unit cell dimensions are a = 6.913(2) A, b = 10.687(4) A and c = 11.182(4) A with alpha = 92.805(6) degrees, beta = 101.821(6) degrees and gamma = 95.688(6) degrees. The final R value is 0.0373 for 4633 reflections measured. This compound is a nine-coordinate binuclear complex with two metal fragments linked via the central four-membered Pb2O2 ring. The crystal also contains a neutral [pydc-H2] molecule, that form hydrogen and coordination bonds that dominate the crystal packing, by forming layers of molecules.     

A unified cosolvency model for calculating solute solubility in mixed solvents

Organic solvents are amongst the most powerful solubilization agents for a large number of water-insoluble drugs. A number of equations has been reported for mathematical representation of solute solubility in mixed solvents. The question is then posed--is there a mathematical difference between these models? To address this point, it has been demonstrated that all cosolvency models could be made equivalent by using algebraic manipulations. In order to familiarize the readers with the available cosolvency models, they are briefly reviewed. The models can be divided into two mathematical categories, i.e. linear and non-linear models. The linear models include: the log-linear, extended Hildebrand solubility approach, excess free energy equations, combined nearly ideal binary solvent/Redlich-Kister equation and Margule equations which can be converted to a general single model which expresses the logarithm of mole fraction solubility of a solute as a power series of volume fraction of the cosolvent. The non-linear models include the mixture response surface methods, two step solvation model and modified Wilson model which can be converted to a non-linear general form. Also, it has been shown that both the general single model and a non-linear general model are mathematically identical. To show the applicability of the models on real experimental data, 35 data sets have been collected from the literature. Both linear and nonlinear models produced comparable accuracies when an equal number of constant terms was employed in numerical analyses.