A recently constructed high-resolution He atom scattering (HAS) instrument has been used to carry out experiments on several ionic insulating surfaces--namely RbI (001), MgO (001), and NiO (001). The HAS technique is nearly an ideal probe for measuring the low-energy surface vibrational modes or dispersion curves (2-50 meV) of a crystalline surface with extremely high resolution ($<$0.5 meV). Each mode consists of a quantized wave vibration called a surface phonon which has a characteristic frequency, $\omega$, and wavevector, Q. Experimentally, the surface dispersion curves can be mapped over the entire irreducible Brillouin zone by measuring $\omega$(Q) versus Q. The shapes of these curves are directly affected by the atomic force constants. Therefore, the measured surface lattice dynamics leads to an evaluation of the surface forces of crystals. Recently, there has been an increased interest in the heavier, more polarizable alkali halides, RbI (001) for example, since theoretical calculations predict relaxation-induced modes that are surface localized and well-separated from the bulk bands. The results for RbI (001) experimentally confirm the predicted relaxation-induced modes. MgO (001) and NiO (001) represent the first HAS results performed on ionic insulating crystals in our laboratory that are not alkali halide crystals. MgO (001) is an interesting surface since it is a well-known catalyst and a common substrate material used for making thin films. NiO (001) is also interesting since it is an antiferromagnet, and the possibility of coupling between the intrinsic crystalline magnetic field and the surface phonon modes exists. The lattice dynamical results for these two surfaces are also given. The results from earlier HAS studies on MgO (001) were extended and later corroborated by independent HAS observations. The results for the NiO (001) represent / the first experimental surface dynamical measurements for this crystal, and they are compared with bulk theoretical and experimental results as well as HAS dynamical measurements from the Ni(001) + c-(2 x 2)O surface, where oxygen is chemisorbed on the Ni (001) surface. / Source: Dissertation Abstracts International, Volume: 52-03, Section: B, page: 1520. / Major Professor: Sanford A. Safron. / Thesis (Ph.D.)--The Florida State University, 1991.

The first two sections of this work discuss the development of a sensor system for metal ions. The same receptor, 2,2'-bipyridine, was used in all of the systems explored, and the overall specificity of the sensing system was achieved through binding equilibria and relative quenching rates. The first system discussed is a tetra-bipyridylphenyl-porphyrin. In all cases quenching results following formation of a ground state complex between a bipyridyl moiety of the porphyrin and the metal ion. For the Zn(II) tetra-bipyridylphenyl-porphyrin, luminescence quenching is only observed with Co(Il), Ni(II), and Cu(II). For luminescent species having multiple, independent, metal ion binding sites, detailed examination of the luminescence quenching clearly shows that association equilibria for binding metal ions at least two of the available sites must be taken into account In the second section, the results of varying the chromophore (from metalloporphyrin to Ru(bpy)3), the spacer (from a phenyl group to an ethyl-phenyl-ethyl group), and the number of binding sites (one vs. three) on the sensitivity and the selectivity of the sensor system are examined. Surprisingly, the Ru(bpy) 3 chromophore systems were also strongly selective for Cu(Il), Co(II), and Ni(II). The sensitivity of the sensor was increased by an increase in the number of binding sites, and decreased by the decrease in electronic coupling that was a result of adding the ethyl groups to the spacer portion of the molecule The photochemical and photophysical behavior of dodecafluorosubphthalocyanaoto boron (III) chloride is examined in the last section. The absorption maximum of the complex is 570 nm, and the luminescence mirrors the absorption with a maximum at 586 nm (Stokes shift 480 cm-1). The emission is strong, with a quantum yield in deaerated acetonitrile of 0.66 and a lifetime of 2.6 ns. The complex exhibits a reversible one electron reduction (E o = -0.53 V vs. SCE) and this, combined with the high singlet energy, indicates that the emissive excited state is a strong oxidant. Evaluation of the free energy dependence of the emission quenching with a series of donors yields a value of 1.7 V vs. SCE for the excited state reduction potential / acase@tulane.edu

Part I. Epidemiological and experimental studies support the hypothesis that dietary estrogens from plant sources (phytoestrogens) may play a role in the prevention of breast and prostate cancer. The molecular mechanisms for such chemopreventive effect are still unclear. We have investigated the possibility that phytoestrogens may bind differentially to estrogen receptor proteins (ERalpha and ERbeta) and affect the interactions of the ligand-ER complexes with different ERE sequences. Fluorescence polarization was used to measure the binding affinities of genistein, coumestrol, daidzein, glyceollin and zearalenone for human ERalpha and ERbeta. Competition binding experiments revealed higher affinity of the phytoestrogens; for ERbeta than ERalpha. Genistein (IC50 12nM) is the most potent and has the same relative binding affinity for ERbeta as E2. We have also studied the effect of these phytoestrogens on the ability of ERalpha and ERbeta to associate with specific DNA sequences (EREs). Direct binding of human recombinant estrogen receptors to fluorescein-labeled estrogen response elements (EREs) indicate that phytoestrogens can cause conformational changes in both human estrogen receptors which result in altered affinities of the complexes for the ERE from the Xenopus vit A2 gene and an ERE from the human pS2 gene Synthetic estrogens have diverse chemical structures and may either positively or negatively affect the estrogenic signaling pathways through interactions with the estrogen receptors. Modeling studies suggest that 4-(1-adamantyl)phenol and 4,4'(1,3-adamantanediyl)diphenol can bind in the ligand binding site of ERalpha. We used fluorescence polarization to compare the binding affinities of 4-(1-adamantyl)phenol (AdP), 4,4'-(1,3-adamantanediyl)diphenol (AdDP), and 2-(1-Adamantyl)-4-methylphenol (AdMP) for human ERalpha and ERbeta with the binding affinities of the known ER ligands, diethylstilbestrol and 4-hydroxytamoxifen. Competition binding experiments show that AdDP has greater affinity for both ERs than AdP, while AdMP does not bind the receptor proteins. We also found that AdDP and AdP can cause conformational changes in ERalpha and ERbeta, which result in altered affinities of the ERs for fluorescein-labeled EREs Part II. Cytochrome P450 monooxygenases are one of the most catalytically versatile enzyme system in nature and have been detected m essentially all animals, plants, fungi, and bacteria studied. Physiological functions are broad and diverse, including, detoxification of foreign chemicals (drugs, carcinogens, etc) and biosynthesis of prostaglandins, leukotreins, and steroids This part of the thesis is focused on the design and synthesis of specific acetylenic mechanism-based inhibitors for the hepatic cytochrome P450 2D6 and the plant P450 73A1. Ethynyl phenethylamines and propynyloxyphenylamines have been synthesized as putative mechanism-based inhibitors of P450 2D6. Several propynyloxybenzoic and propynyoxycinnamic; acids mechanism-based inhibitors of the plant P450 73A1 have been also prepared. Enzyme inhibition studies show that 4-propynyloxybenzoic acid is the most potent mechanism-based inhibitor of P450 73A1 among the compounds synthesized / acase@tulane.edu

Results are presented for a novel approach to the measurement of product-state populations arising out of the photodissociation of small gas phase molecules. Photoionization at the endpoint of a time-of-flight (TOF) apparatus using two, alternative probe beam geometries allows for the interrogation of reaction photofragments in either Doppler space or TOF space. The probe beam orientation, colinear with the photofragment flight path, provides a high-resolution variation of velocity-aligned Doppler spectroscopy (VADS). The second orientation, orthogonal to the TOF axis, is a variation of the well established photofragment translational energy spectroscopy The variation on velocity-aligned Doppler spectroscopy uses 1+1$\sp\prime$ resonance-enhanced ionization through the Lyman-$\alpha$ transition to interrogate hydrogen atom photofragments having their velocity vector aligned anti-parallel to the probe beam's axis. The VADS experiment provides baseline-resolved spectra of the nuclear hyperfine states in the $\sp2$S$\sb{1/2}$ ground state of atomic hydrogen from the 193nm, 248nm and 266nm photodissociation of jet-cooled hydrogen halide parent molecules. In addition, the onset of Stark effects in the n = 2 resonance state of atomic hydrogen has been observed in the modest electric fields of the ion extraction region of the detector The probe beam can be set orthogonal to the average velocity vector of the photofragments. In this manner, the wavelength of the probe is set to the zero-Doppler resonance frequency for 1+1$\sp\prime$ ionization, and the time-of-flight is measured for the photofragment of interest. The TOF spectra for the 193nm, 248nm and 266nm photodissociation of H$\sb2$Se, transformed to center-of-mass translational energy distributions, show photolysis wavelength dependent vibrational distributions and 'cold' rotational distributions for the HSe fragment. Both one-and two-photon dissociation channels are observed, with all eight possible exit channels present for the 266nm dissociation. The current resolution, when using the 266nm YAG line as the photolysis source, is $\rm\Delta E/E\sim 0.7\%$, or $\sim$65cm$\sp{-1}$. For 266nm dissociation, the rotational structure in the v$\sb0$ (HSe) vibrational level is well resolved. An analysis of the energy disposal distributions for H$\sb2$Se photodissociation will allow assignment of bond dissociation energies and provide data for characterization of the potential energy surfaces involved in the reaction / acase@tulane.edu

Nuclear magnetic resonance spectroscopy and computational methods were applied to the elucidation of solution structure of some fructans. A rigid compound, gibberellic acid, was studied by both NMR and a variety of computational methods to find suitable computational methods for the molecular modeling. MMX in PCMODEL gave the best correlation in torsion angles with those from X-ray diffraction data among the tested methods (MMX in PCMODEL, AM1, MNDO, MINDO/3 in MOPAC). $\sp3J\sb{\rm C-H}$ information from NMR experiment showed good correlation with torsion angles from MMX optimized structure. This indicated that data obtained from NMR spectroscopy could be used together with molecular modeling results to give a good picture of a molecule NMR spectral assignments of 6-kestose and neokestose were carried out by various two dimensional techniques. $\sp3J\sb{\rm C-H}$ coupling NOESY data were used to differentiate the two fructose units in neokestose and 6-kestose, respectively. Levanbiose and $\beta$- scD-fructofuranosyl-(2$\to$6)-$\beta$- scD-glucopyranoside were studied by molecular mechanics (MM2-87) with the flexible modeling method. The N-H study of extended oligomers from dimers indicated that the lowest energy dimers were not suitable for polymer structures although some of the dimers with moderate energies were To study larger carbohydrates, flexible method used here is impractical considering the computing time requirements. Standard rigid-residue methods will not properly model fructans. A new method was proposed and tested on a fructan tetramer. Starting from flexible modeling of the constituent trimers, a library of conformer files was created. Each file contains information on one constituent ring with specific adjacent residues of the target tetramer. By combining the different rings together from this library, a series of oligomer structures with different linkage angle combinations were constructed. The initial steric energies of these structures were calculated to screen for low energy structures. These would then be used for searching energy minima. The results were compared with the standard rigid rotation method and flexible modeling. Two FORTRAN programs, DBCREATE and OLIGOGEN, were written to extract monomers from flexible study for the library files, and to build the structure of the oligomer under analysis / acase@tulane.edu

Large amounts of neutral hydrogen atoms are easily produced by photolysis of various haloalkanes. The natural propensity for a species to produce H atoms from chemically distinct sites within a molecule is investigated. The primary targets are alkyl radical intermediates, and a variety of haloalkane systems are used as precursors. Deuterium atoms are selectively substituted for H atoms to mark a specific site in the parent molecule. This labelling allows one to determine with relative certainty the site from which the H atoms are being produced. The experiments are conducted using different photolysis wavelengths, specifically 193, 222, and 248 nm. Combinations of photolysis wavelengths, in conjunction with a 1 + 1 (121.6 + 364.7 nm) resonance-enhanced multiphoton ionization probe through the Lyman-$\alpha$ transition in atomic hydrogen, allow positive identification of the reactive site. Once the H atoms are ionized they are accelerated into a time-of-flight mass spectrometer, detected by a microchannel plate detector, and converted into an intensity signal. Doppler spectroscopy is used to analyze and quantify the data. Normal and branched propyl systems of three common halogens (Cl, Br, and I) are used as precursors. Previous experiments have shown that photolysis of these systems at 248 nm yields definite site-specific production of H atoms whereas similar photolysis at 193 nm gives probabilistic results. This investigation takes an important step by adding a second photolysis laser to the system to show conclusively that the H atoms are being produced from alkyl radical intermediates / acase@tulane.edu

Interactions between proteins and interfaces are widespread. The role of protein adsorption in tissue culture, biocompatibility, serological tests, emulsification and stability of dispersions is well documented. The proposed role of protein adsorption as a conditioning film required for microbial colonization has far-reaching implications for the design of dental implants and prosthetic devices and for marine engineering. Yet, a comprehensive theory of protein adsorption has remained elusive This work presents the results of the first attempt to chemically characterize adsorbable dissolved organic material from naturally-occurring water and to define the role of surface charge on the chemical composition and quantity of the adsorbed material. Pyrolysis - chemical ionization, mass spectrometry and fluorescence spectroscopy were used to characterize adsorbed dissolved organic material (ADOM) from the estuarine waters of Bay St. Louis, MS, as proteinaceous in nature. Microelectrophoretic mobilities and corrosion potential measurements substantiate this conclusion. Adsorbed organic material results in a net negative change and a negative shift in the surface potential similar to that induced by other proteinaceous materials. Surface properties such as potential, charge, and critical surface tension influence the composition of the adsorbed film during the first hour of exposure. However, after four hours it appears that a uniformity is reached and that the composition of the adsorbed material is substratum independent. Voltage clamping experiments were conducted on titanium surfaces exposed in an estuarine (3('o)/oo) and a marine (35('o)/oo) environment. The estuarine environment contained slightly higher concentrations of total organic carbon and amine-containing compounds. The quantity and chemical composition of the ADOM was independent of imposed charge over a wide range of potentials for both locations, but there was a great deal of variation between the sites. A three-fold increase in the amount of adsorbed material was observed from the marine environment, indicating that adsorption increases as ionic strength increases. Furthermore, an enhanced adsorption at the anodic potential, +1.16 V/SCE was observed at the marine site, due to an electrostatic attraction between the adsorbing protein and the titanium surface. The mass pyrograms of ADOM from four locations demonstrate that the chemical composition is site specific / acase@tulane.edu

No description available.

No description available.

No description available.