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Chiral separations employing four diastereomers of poly sodium N-undecanoyl leucylvalinate (p-SULV) as chiral selectors are probed by use of MEKC, steady-state fluorescence anisotropy, and NMR. By employing diastereomers and thus altering the stereochemistry of a single amino acid in a systematic way, one may control the enantiorecognition ability of the chiral selector. As a result, one can gain a better understanding of the mechanisms of chiral recognition for the two classes of neutral or anionic chiral analytes studied. Evaluation of the chiral interactions leading to chiral separations confirmed our earlier observation of a strong relationship between the selectivity () observed using a chromatographic separation technique (MEKC) and that determined from the spectroscopic parameter, . A linear versus relationship was observed for the molecular micelle p-(l)-SULV with all eight analytes included in this study. However, as we earlier predicted, different groups of analytes had different slopes, i.e., values of m, suggesting different chiral separation mechanisms. Evaluation of the data allowed a grouping of the analytes according to the primary site of chiral interaction with the leucine or valine moiety of molecular micelle chiral headgroup. [ABSTRACT FROM AUTHOR]

Ground state absorption, first excited-singlet state, and properties of reactive intermediates of mononitropyrene isomers encountered in the atmospheric aerosol have been studied under different conditions that could mimic the environment. The nitro group can present different orientations relative to the pyrene ring depending on its geometric location and could induce differences in the photochemistry of the isomers. The 2-NO(2)Py isomer has the largest red shift and lowest oscillator strength in the UV-visible band associated with the nitro group. The isomers show very low fluorescence yields (10(-3)-10(-4)). Only 1-NO(2)Py and 4-NO(2)Py have phosphorescence emission (Φ(p) ≈ 10(-4)), indicating that the lowest triplet state decays mainly through effective radiationless channels. Laser photolysis produces a low-lying triplet state (τ(T) = 10(-5)-10(-6) s), a long-lived pyrenoxy radical, and a PyNO(2)H radical in solvents in which the triplet can abstract a hydrogen atom. Similar triplet yields were calculated (0.1-0.6) for the isomers, while significant differences in the relative yield of the long-lived species were determined. Differences in the quenching rate constants of the triplet by water and phenols suggest a strong hydrogen-bond interaction with the nitro group in the C-2 position, which provides for radiationless deactivation routes.

1-Nitropyrene (1NPy) is the most abundant nitropolycyclic aromatic contaminant encountered in diesel exhausts. Understanding its photochemistry is important because of its carcinogenic and mutagenic properties, and potential phototransformations into biologically active products. We have studied the photophysics and photochemistry of 1NPy in solvents that could mimic the microenvironments in which it can be found in the atmospheric aerosol, using nanosecond laser flash photolysis, and conventional absorption and fluorescence techniques. Significant interactions between 1NPy and solvent molecules are demonstrated from the changes in the magnitude of the molar absorption coefficient, bandwidth at half-peak, oscillator strengths, absorption maxima, Stokes shifts, and fluorescence yield. The latter are very low (10 (-4)), increasing slightly with solvent polarity. Low temperature phosphorescence and room temperature transient absorption spectra demonstrate the presence of a low energy (3)(pi,pi*) triplet state, which decays with rate constants on the order of 10 (4)-10 (5) s (-1). This state is effectively quenched by known triplet quenchers at diffusion control rates. Intersystem crossing yields of 0.40-0.60 were determined. A long-lived absorption, which grows within the laser pulse, and simultaneously with the triplet state, presents a maximum absorption in the wavelength region of 420-440 nm. Its initial yield and lifetime depend on the solvent polarity. This species is assigned to the pyrenoxy radical that decays following a pseudo-first-order process by abstracting a hydrogen atom from the solvent to form one the major photoproducts, 1-hydroxypyrene. The (3)(pi,pi*) state reacts readily ( k approximately 10 (7)-10 (9) M (-1) s (-1)) with substances with hydrogen donor abilities encountered in the aerosol, forming a protonated radical that presents an absorption band with maximum at 420 nm.

Schistosoma mansoni fatty acid binding protein (Sm14) was crystallized with bound oleic acid (OLA) and arachidonic acid (ACD), and their structures were solved at 1.85 and 2.4 A resolution, respectively. Sm14 is a vaccine target for schistosomiasis, the second most prevalent parasitic disease in humans. The parasite is unable to synthesize fatty acids depending on the host for these nutrients. Moreover, arachidonic acid (ACD) is required to synthesize prostaglandins employed by schistosomes to evade the host's immune defenses. In the complex, the hydrocarbon tail of bound OLA assumes two conformations, whereas ACD adopts a unique hairpin-looped structure. ACD establishes more specific interactions with the protein, among which the most important is a pi-cation bond between Arg78 and the double bond at C8. Comparison with homologous fatty acid binding proteins suggests that the binding site of Sm14 is optimized to fit ACD. To test the functional implications of our structural data, the affinity of Sm14 for 1,8-anilinonaphthalenesulfonic acid (ANS) has been measured; moreover the binding constants of six different fatty acids were determined from their ability to displace ANS. OLA and ACD exhibited the highest affinities. To determine the rates of fatty acid binding and dissociation we carried out stopped flow kinetic experiments monitoring displacement by (and of) ANS. The binding rate constant of ligands is controlled by a slow pH dependent conformational change, which we propose to have physiological relevance.