Entrapment efficiency in protein microencapsulation into biodegradable polymer microspheres depends on the nature of the solvents used for dissolving the polymer. In such a system, three main interactions are present, i.e., polymer-water (aqueous protein solution), polymer-solvent, and solvent-water (aqueous protein solution). These interactions are quantified by the three interaction energies, AintEp, AintE,, and AintE2, respectively. For a given polymer, Ai&, is constant, but AintEl and AintEZ vary as a function of the nature of the solvent used. In this contribution, the model protein bovine serum albumin was microencapsulated into poly(D,L-lactic acid) by spray-drying. It was demonstrated that increasing absolute values of the sum AintEl -t AintE2 leads to decreasing encapsulation efficiencies. AintE1 was estimated from the heat of dissolution of the polymer in the selected solvents and the energy of cavity formation, and Ai& from 6 d and 6, and Drago's parameters E and C. A linear fit between the sum of interaction energies, equivalent to AintEl iAintE2, and the actual microencapsulation efficiency gave a reasonable correlation with a correlation coefficient r = 0.954. This represents an acceptable correlation considering enthalpies were used to predict interaction energies. Moreover, if microencapsulation efficiency is correlated directly with AintEl (expressed by its equivalent calculated value), and the parameters a d , 6,, E, and C, instead of Aint&, an even better correlation with a multiple r = 0.9995 is observed. This rational approach in microencapsulation is of high importance as it is based on thermodynamic parameters.
In this paper, a new interpretative model for evaluating the interaction energy in Lewis acid-base systems is proposed. The interaction energy in such a model has only four molecular interaction capacity parameters as variables, Le. two Hansen partial cohesion parameters (MPa1/2), 6d (dispersive) and 6, (polar), and two Drago parameters (kJ1/Z E (electrostatic) and C (covalent). The developed model includes a cavity energy term which is mainly dispersive. Experimental calorimetric data taking tert-butyl alcohol as a Lewis acid mixed in nine Lewis bases were used to verify the interaction energy balance sheet and the predicting quality of the proposed model.
Dispersive and specific adsorption energies resulting from adsorption of alkanes and basic probes on silica gel (Fischer, lot 712393 60/200 mesh) were determined respectively by gas-solid chromatography and titration calorimetry. These adsorption energies are related to the inkraction capacity of silica gel. Fitting the adsorption energies to Snyder-Karger and modified Drago interaction models, the interaction capacity can be quantified by four interaction capacity parameters, i.e., the two Hansen partial cohesion parameters (MPa'") Bd,s (dispersive) = 18.60 f 0.42 and B,,s (polar) = 5.01 f 6.16, and the two Drago parameters (H'" mol-') ES (electrostatic) = 7.73 f 2.63, and CS (covalent) = 2.53 f 0.18, with CIE = 0.33. These values are in very good agreement with the currently used scale. The adsorption energies, calculated in return, compare well with the experimentally determined values and give at the same time different components (dispersive, polar, and hydrogen bonding) of the total interaction energies.
This study aims at providing a model for the internal mixing energy of two liquids. The concerned variables are the solute molar volume V (cm 3 /mol.), the cohesion parameters and the Drago's parameters. The model is based on the following fundamental novelties: The fragmentation of molar cohesive energy Ecoh (kJ/mol) into two distinct categories. Indeed, the dispersive and polar cohesion energies are magnetic and electrical in nature, and the cohesive energy of the chemical bonds (Hydrogen Bond) is due to charge transfer and orbital overlap. The origins of these two categories of energy are different, requiring two different treatments in use. For the first time, a relationship has been established between the cohesive energy from chemical bonds Eh (kJ/mol) and Drago's parameters Ea, Eb, Ca, and Cb (KJ 1/ 2 mol-1/2). A simple equation has been proposed for the salvation energy of a gaseous solute in a liquid solvent. This equation contains a term for the perturbation energy of the solvent in the presence of the solute, namely the cavity formation energy, and different types of interaction energies between the solvent and the solute at infinite dilution. Based on calorimetric data published, the proposed model is compared with the classic model in terms of the mixing energy. The result shows a clear advantage of the new model over the old or conventional one. Clearly, this new model should provide a new method to determine the interaction parameters or interaction capacities of complex pharmaceutical molecules using a series of simple and well-chosen solvents.
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