Solvatochromic Study of Poly(vinyl chloride) Plasticizers and Their Solutions in Chloroform: Application to Phenobarbital Partitioning and Molecular Recognition of Phenobarbital.

The possibility now exists, with the availability of several families of artificial molecular receptors, to create selective extraction media. More selective extractions will lead to cleaner chromatograms, with lower detection limits and perhaps higher accuracy for trace organic analysis by chromatography. Furthermore, laboratories will be expected to minimize the use of volatile organic solvents. Consequently, nonvolatile, reusable solvents will be the basis for extractions. In addition, as artificial molecular receptors become more widely available, these solvents will be used to support molecular recognition. We have focused on plasticizers of poly(vinyl chloride) as examples of these solvents. We have determined solvatochromic parameters of several plasticizers and their solutions in chloroform. These parameters, along with cohesive energy density and solvent molar volume, were used to derive linear free energy relationships for the free energies of phenobarbital partitioning between solvent and aqueous solution, receptor solubility, formation of a complex with a barbiturate receptor [1,3-bis[[[6-(1-butyrylamino)pyrid-2-yl]amino]carbonyl]benzene (2)], and the transfer of the complex (artificial receptor and phenobarbital) from chloroform to other solvents. Solvent dipolarity/polarizability and hydrogen bond basicity, but not acidity, support complex dissociation. Solvents with large molar volumes dissolve the polar solutes, phenobarbital, receptor, and complex more poorly than solvents with lower molar volume, but there is no influence of molar volume on complex formation.

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

Environmental concern is renewing interest in selective, waste-free extractions. A recent report demonstrated an improved extraction of phenobarbital by means of a specifically designed molecular receptor. In that work, the solvent was CHCl3. The current work is the first step in extending extractions based on molecular recognition to reusable solvents, namely plasticizers. Phenobarbital aqueous/organic partition coefficients, receptor solubility, and phenobarbital-receptor-formation constants in several plasticizers and in their CHCl3 solutions are reported. In addition, by a thermodynamic cycle, the free energy for transfer of the barbiturate-receptor complex from CHCl3 to plasticizers has been calculated. Finally, the data have been displayed in coordinate systems representing extraction efficiency and selectivity. The most selective extraction medium yielding useful extraction efficiency is dioctyl phthalate.

Enhanced extraction of phenobarbital from serum with a designed artificial receptor.

The primary goal of this work was to determine whether artificial receptors that function on the basis of molecular recognition have analytical capabilities. As an example of such a receptor, we have chosen one directed toward barbiturates. Chloroform enriched with this artificial receptor (1 mM) can extract more than 90% of the phenobarbital from a 20 microM phenobarbital solution in human control serum using a volume ratio (organic/serum) as small as 0.5. In the absence of this receptor, the volume ratio must be greater than 10 to achieve similar extraction efficiencies. In addition to volume ratio, the role of pH, receptor concentration, and solvent type are discussed. The experimental results are found to be in good agreement with predictions based on chemical equilibria. Through the use of this and other similar receptors, the amount of organic solvent used in extractions can be minimized.

Chemical control of reaction time in an enzyme assay and feasibility of enzyme spot tests.

There are many circumstances in which the understanding of a patient's status would be improved by knowing one or more enzyme activities. Such data are routinely produced in clinical laboratories, but simple, noninstrumental tests for enzymes are a rarity, so their extralaboratory determination is also rare. The essential problem is that effective clinical determinations of enzyme activities are typically carried out by measuring reaction rates, so the reaction time needs to be controlled. The reaction time of a sample can be controlled by using a passive, ion exchange-based titration. In this work, OH-, H+, and quinidine have been used to stop the enzymes LDH (EC 1.1.1.27) (with H+ and OH-) and cholinesterase (EC 3.1.1.8) (with quinidine). The ion exchange material containing the enzyme-stopping ion is separated from the sample by a filter. The sample contains ions that can exchange with the enzyme-stopping ion in the ion exchange material, and it may contain species that buffer the enzyme-stopping ion. The reaction time is governed by the exchanging ion's concentration in the sample, the quantity of buffer in the sample, the thickness of the filter between the ion exchange material and the sample, and the temperature. A test for LDH requiring 50 microL of serum and no instrumentation can be made so that results from sera with elevated levels appear different than those with normal levels.