Molecular recognition of phenobarbital in plasticizers equilibrium investigations on the solubility of the barbiturate artificial receptor and its binding to phenobarbital in plasticizers

Artificial Receptor-Facilitated Solid-Phase Microextraction of Barbiturates

“…Thus, the small slopes of mephobarbital and thiopental shown in Figures and are the direct result of small binding constants of those solutes to the receptor. The slopes for the other drugs are in the range 10 2 −10 3 , which is lower than one would expect, , even taking into account the factor of 3 due to the lack of achieving equilibrium. Furthermore, in contradiction to the prediction of eq 2, the extraction efficiency no longer increases beyond about 0.1 M. It is likely that both the low estimate of the binding constant and the shapes of Figures and are explained by self-association of the receptor.…”

“…Replacing the butyryl groups in 1a with 2-ethylhexanoyl groups, 1b, is effective in increasing the solubility of the receptor. The solubility of receptor 1a in CHCl 3 is about 4 mM, in dioctylphthalate it is 1.2 mM, and in chloroparaffin it is about 300 μM …”

“…Table shows values of pf and maximum npf values for the barbiturate solutes. The data show that chloroparaffin- and dioctylphthalate-plasticized PVC matrixes are poor solvents, reflecting the behavior of the pure plasticizers. , However, the barbiturates can all be extracted to some degree into the receptor-free solvents. There is modest selectivity displayed by such a system based on hydrophobicity.…”

“…Thus, the general problem exists to develop receptors that can function in, or for that matter even dissolve in, very poor solvents. Receptor 1a N , N ‘-bis-[6-(butyrylamino)-pyridin-2-yl]-isophthalamide (Figure ) is effective in chloroform but fails in plasticized PVC because it is not very soluble . In the current work, we use solid-phase microextraction (SPME) , using plasticized poly(vinyl chloride) (PVC) as the nonvolatile, reuseable extraction medium.…”

Prediction of molecular recognition-enhanced phenobarbital extraction based on solvatochromic analysis

“…This is because solvent not only determines the partitioning of solute and interferences between two phases, but the solubility of the receptor and its affinity for the substrate as well. In an effort to understand better the role of non-volatile solvents in synthetic receptor-enhanced extractions, Valenta et al (1996Valenta et al ( , 1998 have recently determined Kamlet-Taft solvatochromic parameters (Kamlet et al, 1986), H-bond acidity a, H-bond basicity b, dipolarity p*, polarizability d, as well as solvent cohesive energy density 2 H , and solute molar volume parameter m for several plasticizers and their mixtures. The free energy of the processes relevant to extraction, namely the partitioning of phenobarbital, the solubility of barbiturate receptor and the formation of complex, correlated well with solvent solvatochromic parameters.…”