Ion pairing as a strategy for extraction by modified supercritical carbon dioxide: extraction of radioactive metal ions.

Supercritical fluid carbon dioxide was investigated for its potential to extract perrhenate ion pairs. This has implications for radioactive waste processing because Tc-99, the second row congener of Re, is produced in approximately 6% fission yield from nuclear fuel and pertechnetate is its most common chemical form in aqueous environments. The variables examined to maximize extraction of the perrhenate ion pair were temperature, pressure, solvent modification, and ion-pairing agents. The tetrabutyl-ammonium cation was found to form the most efficient ion pair for extracting perrhenate using methanol-modified (approximately 10%) SFCO2 at 70 degrees C and 477 atm, with 0.083 mg of Re/g of SFCO2 extracted.

Interconversion of the CD and EF sites in oncomodulin. Influence on the Eu3+ 7F0-->5D0 excitation spectrum.

The appearance of the parvalbumin Eu3+ 7F0-->5D0 spectrum is markedly pH dependent, the result of a hitherto unidentified deprotonation event in the CD ion-binding domain [Treviño, C.L., et al. (1991) J. Biol. Chem. 265, 9694-9700]. We are studying this phenomenon in the mammalian placental parvalbumin called oncomodulin. As in other parvalbumins, the liganding residues in the CD and EF sites of oncomodulin differ at the +z and -x coordination positions: serine and aspartate, respectively, in the CD site; aspartate and glycine in the EF site. We have prepared a series of oncomodulin variants in which the +z and/or -x residue(s) from one site have been replaced by the corresponding residue(s) from the other. We herein characterize the resulting proteins by Eu3+ luminescence spectroscopy. Simultaneous replacement of serine-55 by aspartate and aspartate-59 by glycine affords the CD site with a coordination sphere superficially equivalent to that of the EF site. As observed previously for the S55D mutation [Henzl, M. T., et al. (1992) FEBS Lett. 314, 130-134], the Eu3+ 7F0-->5D0 spectrum of the 55/59 variant is pH independent. Interestingly, replacement of aspartate-94 by serine at the +z position of the EF site of 55/59 imparts pH dependent behavior to the EF site. The identical mutation in the wild-type background likewise imparts pH dependence to the EF site, affording a protein in which both sites display broad signals near 578.2 nm at pH 8. Significantly, a variant in which threonine replaces serine-55 retains the pH dependent spectroscopic signature. These results indicate that the presence of a hydroxyl group at the +z position is sufficient to confer pH dependence on the 7F0-->5D0 spectrum of a parvalbumin EF-hand domain. Importantly, the data also suggest that the component peaks of the low-pH doublet are not site-specific signals, as previously believed. Rather, they probably represent differences in coordination environment arising from differential hydration or conformational heterogeneity. In wild-type oncomodulin, the CD site signal dominates the low-pH spectrum. Since this dominance persists even when serine-55 and aspartate-59 are replaced by the corresponding EF site residues, it appears that the context of the CD binding site, as dictated by the global polypeptide fold, exerts a major influence on the metal ion-binding properties of the site.

A strategy for the biological assessment of addiction.

Substances and drugs with powerful psychotropic effects have come into common use during the past decade. Involvement with these substances can range from benign to tragic experiences. Such use may include: experimental, social or recreational use, long-term habituation, toxic reactions, medical-psychologic complications, overdose, and death. Although clinicians tend to analyze and explain many patterns of drug use in terms of various psychodynamic, sociologic and behavioral theories, all of these perspectives begin with the biological and pharmacological effects produced by the various drugs. During the assessment process, the clinician can avoid much confusion by learning to differentiate between the direct pharmacological effects and the diverse psychological and behavioral effects of the drug(s) or substances(s) in question. In order to make these distinctions, a foundation in the "biological basics" is essential. This paper presents a strategy for learning the direct tropic effects produced by various drugs. This approach organizes commonly used drugs into six basic categories reflecting the primary action of each: narcotics and related analgesics; sedative-hypnotics (including barbiturates, non-barbiturate sedatives, minor tranquilizers and alcohol); stimulants (including amphetamines, cocaine, and others); hallucinogens; and others like phencyclidine, cannabis and inhalants, which do not readily fit the other categories.

Lens Antennas that Provide Both Amplitude and Phase Transformation.

The equations for the relationships between the input and output power and phase distribution of a general lens with two refracting surfaces have been derived. The equations are specialized to the case of transforming a spherical wave with constant power per unit solid angle into a uniform power and phase distribution over the lens aperture. These equations are obtained for the purpose of solving for the coordinates of the two surfaces of a lens which will perform the indicated transformation. Existence of solutions and bounds on solutions are examined in terms of the lens parameters. Solutions for the lens contours are obtained numerically for different values of index of refraction and thickness. Changes in the contours as a function of these parameters are discussed.