Thermodynamic and structural study of tolfenamic acid polymorphs.

The article deals with the study of two polymorphic modifications in the space groups P2(1)/c (white form) and P2(1)/n (yellow form) of the tolfenamic acid. It also describes how the white form vapor pressure temperature dependence was determined by using the transpiration method and how thermodynamic parameters of the sublimation process were calculated. We have estimated the difference between the crystal lattice energies of the two polymorphic forms by solution calorimetry and found that the crystal lattice energy of the yellow form is 6.7+/-1.2 kJ mol(-1) higher than that of the white form, whereas Gibbs free energies of the forms obtained from the vapor pressure temperature dependence are practically the same. The modifications under consideration are monotropically related. From the practical point of view, the white form is more preferable due to its lower crystal lattice energy and better performing procedure. We have also studied the solubility, solvation and transfer processes of the tolfenamic acid white form in buffers (with various values of pH and ionic strengths), n-hexane and n-octanol. The thermodynamic parameters of the investigated processes have been discussed and compared with those determined for others fenamates. In the study we estimated specific and non-specific contributions of the solvation enthalpic term of the fenamate molecules with the solvents as well. The driving forces of the transfer processes from the buffers with pH 7.4 and different ionic strengths to n-octanol were analyzed. It was found that the relationship between the enthalpic and entropic terms depends essentially on the ionic strength. For the considered fenamates the transfer processes of the neutral molecules and the ionic forms are enthalpy-determined, whereas for the niflumic acid this process is entropy-determined.

HEW lysozyme salting by high-concentration NaCl solutions followed by titration calorimetry.

Concentration dependence of NaCl salting of 0-1.5 mM lysozyme solution in 0.1 M sodium acetate buffer, pH 4.25, was investigated for NaCl concentration varying up to 0.9 M. Calorimetric experiments demonstrated that depending on the salt concentration the estimated number of the binding sites on the lysozyme surface varied in the range of 5 up to 13, and the increase of salt concentration caused the decrease of the number of accessible sites. The small, but significant, local maximum centered at 0.63 M NaCl concentration indicated the specific salting-out of the lysozyme accompanied by binding of approximately 2-3 chloride anions. Generalized McMillan and Mayer's approach reduced to the third-order virial coefficients demonstrates the domination of lysozyme aggregation upon salt addition (a(21)-h(xxy)) and salt organization on the lysozyme surface (a(12)-h(xyy)) processes.

Partial molar volumes of mRNA 5' cap analogues.

Partial molar volumes in aqueous solution of eleven selected 7-methylguanine cap-analogues and their guanine counterparts were determined by means of density measurements. Hydrophobicity of the investigated compounds regarding their structural features was analysed within the framework of the solute-solvent interaction model, based on the relative density of the molecular solvation shell.

Interaction between yeast eukaryotic initiation factor eIF4E and mRNA 5' cap analogues differs from that for murine eIF4E.

Measurements of interaction of 7-methyl-GTP eIF4E from S. cerevisiae were performed by means of two methods: Isothermal Titration Calorimetry (ITC) and fluorescence titration. The equilibrium association constants (Kas) derived from the two methods show significantly different affinity of yeast eIF4E for the mRNA 5' cap than those of the murine and human proteins. The observed differences in the Kas values and the enthalpy changes of the association (deltaH(o)) suggest some dissimilarity in the mode of binding and stabilization of cap in the complexes with eIF4E from various sources.