Partial solubility parameters molecule

The simplest criterion for a theoretical calculation of the miscibility of the hydrophobic portions of small molecules with the hydrophobic microphase of a membrane polymer appears to be a partial solubility parameter that is, calculation of the solubility parameter of only the hydrophobic portions of the molecules. This can be done using a group contribution approach in which each group (for example, a CHg-group) in the molecule contributes a certain attractive force and a certain volume to the molecule. In this way, a solubility parameter may be estimated for either a portion of a molecule or for a whole molecule. 

The interactions of small solvent molecules are short range. However, the polymer molecules are much larger and they do not have sharply defined solubility parameters. The region of solubility can be drawn as a rough sphere in the three-dimensional space of partial solubility parameters. The description of a polymer s solubility characteristics by Hansen has four components - three partial... 

As already mentioned molecules cohere because of the presence of one or more of four types of forces, namely dispersion, dipole, induction and hydrogen bonding forces. In the case of aliphatic hydrocarbons the dispersion forces predominate. Many polymers and solvents, however, are said to be polar because they contain dipoles and these can enhance the total intermolecular attraction. It is generally considered that for solubility in such cases both the solubility parameter and the degree of polarity should match. This latter quality is usually expressed in terms of partial polarity which expresses the fraction of total forces due to the dipole bonds. Some figures for partial polarities of solvents are given in Table 5.5 but there is a serious lack of quantitative data on polymer partial polarities. At the present time a comparison of polarities has to be made on a commonsense rather than a quantitative approach. 

Equation 2.41 would be useful if we could estimate the values of the solubility parameters and the partial molal volume of the supercooled liquid solute. Additive procedures, based on functional groups found in the molecule, have been developed to estimate partial molal volumes and solubility parameters (Small, 1951 Hoy, 1970 Konstam and Feairheller, 1970 Fedors, 1974). Another... 

Here V" is the partial molar volume of the solute gas, and 8 and 8b are the solubility parameter values of the solute and the bulk liquid. The solubility parameter is also cohesive-energy density, a measure of the forces between the molecules given by... 

There have been numerous attempts to determine HLB numbers from other fundamental properties of surfactants, e.g., from cloud points of nonionics (Schott, 1969), from CMCs (Lin, 1973), from gas chromatography retention times (Becher, 1964 Petrowski, 1973), from NMR spectra of nonionics (Ben-et, 1972), from partial molal volumes (Marszall, 1973), and from solubility parameters (Hayashi, 1967 McDonald, 1970 Beerbower, 1971). Although relations have been developed between many of these quantities and HLB values calculated from structural groups in the molecule, particularly in the case of nonionic surfactants, there are few or no data showing that the HLB values calculated in these fashions are indicative of actual emulsion behavior. 

Arguably the most important parameter for any surfactant is the CMC value. This is because below this concentration the monomer level increases as more is dissolved, and hence the surfactant chemical potential (activity) also increases. Above the CMC, the monomer concentration and surfactant chemical potential are approximately constant, so surfactant absorption at interfaces and interfacial tensions show only small changes with composition under most conditions. For liquid crystal researchers, the CMC is the concentration at which the building blocks (micelles) of soluble surfactant mesophases appear. Moreover, with partially soluble surfactants it is the lowest concentration at which a liquid crystal dispersion in water appears. Fortunately there are well-established simple rules which describe how CMC values vary with chain length for linear, monoalkyl surfactants. From these, and a library of measured CMC values (35-38), it is possible to estimate the approximate CMC for branched alkyl chain and di- (or multi-) alkyl surfactants. Thus, most materials are covered. This includes the gemini surfactants, a new fashionable group where two conventional surfactant molecules are linked by a hydrophobic spacer of variable length (38). 

Solubility parameter can be expressed by Equation (39), where [F] is molar attraction constant and V molar volume. Small [45] has shown that [F] is an additive and constitutive property and has derived partial molar attraction constants for a range of substituent groups, from which molar attraction constants and solubility parameters of the parent molecules can be calculated. Small quotes partial molar attraction constants of 250 for Cl and 28 for CH, which yield a molar attraction constant of 778 for chloroform. In comparison, 745 is obtained from the product of molar volume and solubility parameter. 

Deviations of from K can be of three sorts. Deviations at low and moderate concentrations from the zero-concentration limiting value are most important where ionic solutes are dissolved in nonionic solvents. Where all the solutes are molecular, even at extreme dilution, departures from Raoult s law on the part of each solute can arise in two distinct ways, with opposite effects. Deviations that are due to specific chemical or quasi-chemical attractive interactions between unlike molecules and that lead to enhanced mutual solubilities, lower partial vapor pressures, and activity coefficients less than unity are called negative deviations. Those that arise from mere differences between the molecules of the two kinds, such as differences of size or shape or of the intensity of intermolecular forces (reflected in differences in the solubility parameter, defined later), and that lead to diminished solubility, higher partial vapor pressures, and activity coefficients greater than unity are called positive deviations (see Fig. 1.2). 

There have been many attempts to describe the process of mixing and solubility of polymer molecules in thermodynamic terms. By assuming that the sizes of polymer segments are similar to those of solvent molecules, Flory and Huggins derived an expression for the partial molar Gibbs free energy of dilution that included the dimensionless Flory Higgins interaction parameter X = ZAH/RT, where Z is the lattice coordination number. It is now... 

Complexation is one of several ways to favorably enhance the physicochemical properties of pharmaceutical compounds. It may loosely be defined as the reversible association of a substrate and ligand to form a new species. Although the classification of complexes is somewhat arbitrary, the differentiation is usually based on the types of interactions and species involved, e.g., metal complexes, molecular complexes, inclusion complexes, and ion-exchange compounds. Cyclodextrins (CDs) are classic examples of compounds that form inclusion complexes. These complexes are formed when a guest molecule is partially or fully included inside a host molecule e.g., CD with no covalent bonding. When inclusion complexes are formed, the physicochemical parameters of the guest molecule are disguised or altered and improvements in the molecule s solubility, stability, taste, safety, bioavailability, etc., are commonly seen. 

Mukhopadhyay proposed the relative partial volume reduction of the solvent as the key parameter for the selection of the solvent and of the optimum GAS process conditions. The solute solubility is proportional to the partial molar volume of the solvent due to CO2 molecules clustering around solvent molecules, which lead to the loss of solvent power. 

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