Some micellar properties of long-chain acylcarnitines

The acid dissociation constants of long-chain esters of carnitine ([beta]-hydroxy-[gamma]-trimethylammonium-butyrate) above the critical micelle concentration were determined potentiometrically at several concentrations of added KCl. As the degree of protonation [beta] increases the apparent pK values decrease owing to the increased positive charge on the micelle. The difference in pK between the neutral (zwitterionic) micelle and the value at any given [beta] was used to determine the surface potential of the micelle [Psi] at that degree of protonation. At each degree of protonation the measured surface potential was related to the surface charge density [sigma] with the aid of the calculations of Loeb, Wiersema, and Overbeek for a spherical impenetrable particle. The surface potentials and surface charge densities of lauryl-, myristyl-, and palmitylcarnitine are nearly identical at a given degree of protonation and ionic strength, and, as expected, increasing the ionic strength produces a decrease in the surface potential. From the partial molal volume of each surfactant in the micelle and the calculated surface charge density it was possible to calculate the aggregation number n of the micelle. Good agreement was found between the calculated values of n and values obtained from light-scattering experiments at several ionic strengths and degrees of protonation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32652/1/0000016.pd

2-[N-(2,4-Difluoro­phen­yl)carbamo­yl]-3,4,5,6-tetra­fluoro­benzoic acid

The title compound, C14H5F6NO3, was synthesized by condensation of tetra­fluoro­phthalic anhydride and 2,4-difluoro­aniline. It was then recrystallized from hexane to give a nonmerohedral twin with two crystallographically unique mol­ecules in the asymmetric unit. The refined twin fraction is 0.460 (3). Torsional differences between the aryl rings and the central amide group account for the presence of two unique mol­ecules. The compound packs as double tapes formed by O—H⋯O and N—H⋯O hydrogen-bonding inter­actions between each unique mol­ecule and its symmetry equivalents

The influence of heat capacity assumptions on the estimation of solubility parameters from solubility data

Regular solution theory indicates that solubility parameters of crystalline organic compounds can be estimated from solubilities in London solvents. The equation for this purpose is: where X2 is the mole fraction solubility of a compound in a solvent with a solubility parameter of [delta]1. With the exception of [Delta]Cp, all parameters in the equation necessary to estimate the solute parameter, [delta]2, can either be suitably approximated or readily determined experimentally. In order to use the equation, simplifying assumptions have been made concerning [Delta]Cp, namely: [Delta]Cp = 0 or [Delta]Cp = [Delta]Sf, the entropy of fusion. In the present work, we have considered the extent to which these assumptions influence the magnitude of solubility parameters estimated from solubilities in n-hexane, n-heptane, n-dodecane, cyclohexane, carbon tetrachloride, toluene and benzene. Using n-alkyl p-aminobenzoates as test compounds, it is shown that solubility-based solubility parameters are relatively insensitive to the form of the equation used to calculate [delta]2. Specifically, solubility parameter estimations based on the two simplifying assumptions differ by no more than 0.2 (cal/ml)1/2, an increment of the order of the presumed inherent error of estimation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28068/1/0000511.pd

physical chemical properties of drugs

xvi,ill,361hal,;28c

physical chemical properties of drugs

xvi,ill,361hal,;28c