A new equation for calculating partial cohesion parameters of solid substances from solubilities

Abstract

to that of PS is observed when A is added to Py aqueous solutions containing CDx. Therefore, it is concluded that the equilibria corresponding to those for PS exist in the Py solutions containing both CDx and A. In fact, at low concentrations of A, the Py fluorescence is quenched without a change in the fluorescence spectrum, indicating the existence of a ternary inclusion compound PyAC which is formed from PyC and A. On the other hand, at high A concentrations a broad structureless emission appears with a maximum at 480 nm. The broad emission can be assigned to the CT fluorescence from an inclusion compound PyAC-AC which is formed by the association of two different kinds of inclusion compounds PyAC and AC.28 The peak position of the fluorescence from an exciplex between Py and A has been found to locate at 484 nm in 1,4-dioxane. This maximum wavelength is very close to that of the CT fluorescence from PyAC-AC. This finding exhibits that the polarity around an emissive species in PyAC-AC is nearly identical with that in neat 1,4-dioxane. With respect to the polarity around a species responsible for a CT fluorescence, the same result has already been pointed out for the system of CDx-2-methoxynaphthalene-l ,2-dicyanobenzene.1 (28) The Py excimer fluoresces with almost the same peak maximum. As mentioned below in the text, however, a short lifetime, 29 ns, of the broad emission suggests that the broad emission band is not due to the Py excimer.The CT fluorescence from PyAC-AC decays monoexponentially like that from PAC-AC: A lifetime of 29 ns has been obtained for the CT fluorescence from PyAC-AC. As in the case of PAC-AC, the species that emits the CT fluorescence in PyAC-AC is attributed to a binary excited complex between Py and A.By use of the same methods as those employed for the case of PS, equilibrium constants for Py, K3(Py), K4(Py), and K5(Py), which respectively correspond to K3, KA, and Ks for PS, were determined to be 66000, 54000, and 20000 mol"1 dm3, respectively. These values are about 30-50 times larger than those for PS. Such large differences in the equilibrium constants between Py and PS are due mainly to the steric hindrance of a sulfonato group of PS to the formation of each inclusion compound. In addition, the hydrophilic sulfonato group of PS appears to diminish the relevant equilibrium constants. Although there are significant differences in the relevant equilibrium constants between Py and PS, it should be emphasized that the same type of association occurs for parent Py and PS which posesses the bulky sulfonato group.Acknowledgment. I thank Professor Fumio Hirayama for his valuable discussion.

Prediction of Solubility Parameters and Miscibility of Pharmaceutical Compounds by Molecular Dynamics Simulations

“…Experimentally, the solubility parameter can be estimated by direct and indirect methods, as reported in the literature. The direct methods include measuring the heat of vaporization by calorimetry or measuring the solubility/miscibility of compounds of interest in solvents of a known solubility parameter. , The former method cannot be used for pharmaceutical compounds with thermal instabilities and low vapor pressures. The latter method, though widely used in the field of polymer science, is very subjective and time-consuming.…”

A Molecular Dynamics Approach for Predicting the Glass Transition Temperature and Plasticization Effect in Amorphous Pharmaceuticals

“…The role of temperature and moisture in influencing molecular mobility and crystallization in amorphous matrices, especially in the presence of specific molecular interactions, is not fully understood and cannot be predicted a priori based on existing methodologies. Further, during development of amorphous dispersions, the drug-carrier screening is conducted empirically or based on thermal properties. − The long-term stability is assessed based on storage of the formulation prototypes under stressed conditions (high temperature and humidity) for a period ranging from days to several months. Such studies, though useful for crystalline systems, have limitations when evaluating the physical stability of amorphous dispersions due to inherent challenge in extrapolating temperature/RH effects spanning varied molecular mobility regimes.…”

A New Model for Evaluating Interactions in Liquids

“…The Asoiv.E may be considered as the sum of two components:23 Asoiv^~Ac-Eb Aint£ (5) AqEb is the energy of cavity formation (kJ mol-1) in the Lewis base, B, for 1 mol of the Lewis acid, A. Aint£ is the interaction energy (kJ mol-1) between the Lewis acid, A, and the Lewis base, B.…”