PFI-ZEKE SPECTROSCOPY AND THEORETICAL CALCULATIONS OF TRANSITION METAL-AROMATIC HYDROCARBON COMPLEXES

Transition metal-aromatic hydrocarbon complexes were generated in a supersonic jet and studied by zero electron kinetic energy (ZEKE) photoelectron spectroscopy and theoretical calculations. The target metal complexes were identified using time-of-flight mass spectrometry, and their ionization thresholds were located via photoionization efficiency spectroscopy. ZEKE spectroscopy was used to measure the ionization energies and vibrational frequencies of the metal complexes. Their electronic states and corresponding molecular structures were determined by comparing the experimental spectra to quantum chemical calculations and Franck-Condon simulations. In this dissertation, the metal complexes of four different aromatic hydrocarbon ligands were studied: benzene (bz), naphthalene (np), biphenyl (bp) and 1-phenyl naphthalene (phnp). In these complexes, the metal atom or ion was determined to bind to either one or two -rings. Three different bonding schemes were observed in these complexes. A twofold bonding scheme was observed in M+/M-np (M = Sc, Y, Ti, Zr, Hf), while a sixfold bonding scheme was observed in Sc+/Sc-bz and M+/M-bz2 (M = Sc, Ti, V, Cr, Mo, W). In the metal-polyphenyl complexes (i.e. Sc-, La-, and Ti-bp and Sc-phnp), twelve-fold metal-ligand bonding occurred, sixfold to two -rings of the ligand. This twelve-fold bonding mechanism requires rotation of the -rings by ~ 42 o and bending of the -rings by 40 to 57 o to clamp the metal atom or ion between the two -surfaces. Although the ground state spin multiplicities of the bare metal atoms and ions varied quite extensively, the multiplicities of the metal complexes were determined to be either singlet or doublet, except for Sc+/Sc-bz, V+-bz2, Ti-np, and Zr-np, where the triplet or quartet spin multiplicities were favored. The low spin and relatively narrower range of electron-spin multiplicities in the complexes were the result of d orbital splitting, where the degeneracy of the d orbitals was broken. Thus, the valence electrons were paired in each metal d-based molecular orbital of the complex to form low-spin singlet or doublet spin states. Some complexes favored triplet and quartet multiplicities, because the energy difference between the two highest occupied molecular orbitals was smaller than the electron pairing energy

Detection of autoantibodies against reactive oxygen species modified glutamic acid decarboxylase-65 in type 1 diabetes associated complications

<p>Abstract</p> <p>Background</p> <p>Autoantibodies against glutamate decarboxylase-65 (GAD₆₅Abs) are thought to be a major immunological tool involved in pathogenic autoimmunity development in various diseases. GAD₆₅Abs are a sensitive and specific marker for type 1 diabetes (T1D). These autoantibodies can also be found in 6-10% of patients classified with type 2 diabetes (T2D), as well as in 1-2% of the healthy population. The latter individuals are at low risk of developing T1D because the prevalence rate of GAD₆₅Abs is only about 0.3%. It has, therefore, been suggested that the antibody binding to GAD₆₅in these three different GAD₆₅Ab-positive phenotypes differ with respect to epitope specificity. The specificity of reactive oxygen species modified GAD₆₅(ROS-GAD₆₅) is already well established in the T1D. However, its association in secondary complications of T1D has not yet been ascertained. Hence this study focuses on identification of autoantibodies against ROS-GAD₆₅(ROS-GAD₆₅Abs) and quantitative assays in T1D associated complications.</p> <p>Results</p> <p>From the cohort of samples, serum autoantibodies from T1D retinopathic and nephropathic patients showed high recognition of ROS-GAD₆₅as compared to native GAD₆₅(N-GAD₆₅). Uncomplicated T1D subjects also exhibited reactivity towards ROS-GAD₆₅. However, this was found to be less as compared to the binding recorded from complicated subjects. These results were further proven by competitive ELISA estimations. The apparent association constants (AAC) indicate greater affinity of IgG from retinopathic T1D patients (1.90 × 10^-6M) followed by nephropathic (1.81 × 10^-6M) and uncomplicated (3.11 × 10^-7M) T1D patients for ROS-GAD₆₅compared to N-GAD₆₅.</p> <p>Conclusion</p> <p>Increased oxidative stress and blood glucose levels with extended duration of disease in complicated T1D could be responsible for the gradual formation and/or exposing cryptic epitopes on GAD₆₅that induce increased production of ROS-GAD₆₅Abs. Hence regulation of ROS-GAD₆₅Abs could offer novel tools for analysing and possibly treating T1D complications.</p

External cueing influences drop jump performance in trained young soccer players

Drop jump (DJ) characteristics provide insight on power production and injury risk. The purpose of this study was to investigate the effect of external cueing on drop jump characteristics in young male soccer players. Fourteen academy soccer players performed DJs with four different conditions, control (CONT), contact cue (CC), height cue (HC), and quiet cue (QC). Performance measures were reactive strength index (RSI), jump height, ground contact time (GCT), and take-off impulse, with injury risk reflected by impact peak, impact timing and landing impulse. CC showed a very large significant reduction in GCT (ES > 2.0, p0.05) to CONT. The data showed that all cues provided a specific response; CC reduced GCT and increased RSI, HC increased jump height and QC reduced outcomes associated with injury risk. HC may be advantageous for young soccer players with a low training age as it shows a small to moderate increase in jump height without increasing injury risk. Young players may need to be safely progressed to be able to use a CC to facilitate high reactive strength without being exposed to undue injury risk

Conformation-dependent GAD65 autoantibodies in diabetes

Aims/hypothesis. Conformation-dependent autoantibodies directed against GAD65 are markers of Type 1 diabetes. In this study we aimed to determine whether the substitution of GAD65 with GAD67 amino acids would affect the binding of conformation-dependent GAD65 autoantibodies. Methods. We used PCR-based site-directed mutagenesis to generate a series of mutated GAD65 cDNA constructs in which specific GAD65 coding sequences for regions of the protein critical for autoantibody binding were replaced with GAD67 coding sequences. Results. The introduction of a point mutation at position 517, substituting glutamic acid with proline, markedly reduced the binding of disease-associated GAD65 antibodies. The binding of GAD65 antibodies to the E517P mutant was reduced in the sera of all newly diagnosed Type 1 diabetes patients (n=85) by a mean of 72% (p<0.0001) compared with binding to wild-type GAD65. Patients with latent autoimmune diabetes in adults (n=24) showed a similar reduction in binding (79% reduction, p<0.0001). First-degree relatives who subsequently progressed to Type 1 diabetes (n=12) showed a reduction in binding of 80% compared with a reduction of only 65% among relatives who had not progressed to disease (n=38; p=0.025). In healthy GAD65Ab-positive individuals who did not progress to diabetes during a 9-year follow-up period (n=51), binding to GAD65-E517P was reduced by only 28% compared with binding to wild-type GAD65. Conclusions/interpretation. Differences in autoantibody binding to wild-type GAD65 versus GAD65-E517P may provide predictive information about Type 1 diabetes risk beyond that provided by the presence or absence of GAD65 autoantibodies. Lack of binding to mutant GAD65-E517P defines GAD65-positive individuals who are at higher risk of developing diabetes

PFI-ZEKE SPECTROSCOPY AND THEORETICAL CALCULATIONS OF TRANSITION METAL-AROMATIC HYDROCARBON COMPLEXES

Transition metal-aromatic hydrocarbon complexes were generated in a supersonic jet and studied by zero electron kinetic energy (ZEKE) photoelectron spectroscopy and theoretical calculations. The target metal complexes were identified using time-of-flight mass spectrometry, and their ionization thresholds were located via photoionization efficiency spectroscopy. ZEKE spectroscopy was used to measure the ionization energies and vibrational frequencies of the metal complexes. Their electronic states and corresponding molecular structures were determined by comparing the experimental spectra to quantum chemical calculations and Franck-Condon simulations. In this dissertation, the metal complexes of four different aromatic hydrocarbon ligands were studied: benzene (bz), naphthalene (np), biphenyl (bp) and 1-phenyl naphthalene (phnp). In these complexes, the metal atom or ion was determined to bind to either one or two π-rings. Three different bonding schemes were observed in these complexes. A twofold bonding scheme was observed in M + /M-np (M = Sc, Y, Ti, Zr, Hf), while a sixfold bonding scheme was observed in Sc + /Sc-bz and M + /M-bz2 (M = Sc, Ti, V, Cr, Mo, W). In the metal-polyphenyl complexes (i.e. Sc-, La-, and Ti-bp and Scphnp)

ZEKE SPECTROSCOPY OF GROUP VIB M(C6_6H6_6)2_2 (M = Cr, Mo, W) SANDWICH COMPLEXES

Author Institution: Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055Dibenzene complexes of chromium, molybdenum, and tungsten, M(C$_6$H$_6$)$_2$ (M = Cr, Mo, W), were produced by laser ablation in a supersonic jet and probed by pulsed field ionization-zero electron kinetic energy (PFI-ZEKE) electron spectroscopy. The adiabatic ionization potentials were measured to be 44081(6), 44581(11), and 43635(6) cm$^{-1}$ for Cr(C$_6$H$_6$)$_2$, Mo(C$_6$H$_6$)$_2$, and W(C$_6$H$_6$)$_2$, respectively. The chromium-dibenzene spectrum displays three quanta excitations of the 265 cm$^{-1}$ metal-benzene symmetric stretch mode in the cation, whereas the molybdenum and tungsten complexes show only one excitation of the metal-ligand stretch of 277 and 370 cm$^{-1}$, respectively. The shift in the ionization energy from the bare metal atom to the complex (10494, 12623 and 19792 cm$^{-1}$) and metal-ligand stretch frequencies increase, as the group is descended. These observations indicate a stronger metal-benzene interaction for the heavier atoms, especially tungsten. The ground states of the neutral and ionic complexes appear to be in D$_{6h}$ symmetry with the hydrogen atoms slightly bent towards the metal center, as suggested by the good agreement between experiment and theory

CLAMCLAM STRUCTURES OF METAL-BIPHENYL COMPLEXES: M-C12_{12}H10_{10} (M = Sc, La, Ti)

Author Institution: Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055In the gas phase, the two phenyl rings of biphenyl (C$_{12}$H$_{10}$) are twisted with respect to each other by about 45$^0$. This rotation of the phenyl rings about the bridging C-C bond is driven by $\pi$-conjugation of the phenyl rings and steric repulsions between the ortho hydrogen atoms. We have discovered that metal coordination induces phenyl ring rotation and bending to form a $clam$ structure, where a metal atom is clamped by the two phenyl rings. In this talk, we will present examples of how this clam-type structure was identified using pulsed field ionization zero electron kinetic energy photoelectron spectroscopy and density functional theory calculations. The examples include the biphenyl complexes of scandium (Sc), lanthanum (La), and titanium (Ti), which are synthesized by laser vaporization molecular beam techniques. All these complexes are determined to have $C_{2v}$ symmetry. The ground electronic states are $^2$B$_1$ for the neutral Sc- and La-C$_{12}$H$_{10}$ complexes and $^1$A$_1$ for the corresponding ions. The ground electronic states of Ti- and Ti$^+$-C$_{12}$H$_{10}$ are $^1$A$_1$ and $^2$B$_1$, respectively. In addition, we will discuss the binding effects of metal atomic size and electron configuration in these molecular systems

ZEKE SPECTROSCOPY AND ELECTRONIC STATES OF BIS(BENZENE) TITANIUM AND VANADIUM SANDWICH COMPLEXES

Author Institution: Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055Ti- and V-(C$_{6}$H$_{6}$)$_2$ sandwich complexes seeded in helium supersonic beams have been studied by pulsed field ionization zero electron kinetic energy photoelectron spectroscopy and theoretical calculations. The electronic states of the neutral and ionic complexes have been determined by comparison of experimental and simulated spectra. The ground electronic states of the neutral Ti- and V-(C$_{6}$H$_{6}$)$_2$ complexes are determined to be $^1$A$_{1g}$ and $^2$A$_{1g}$, respectively. In these states, the sandwich complexes have $\eta^{6}$-binding between the metal and each benzene ring and are in an eclipsed $D_{6h}$ configuration. Ionization of these neutral states causes the benzene rings to pucker slightly and leads to Jahn-Teller distorted $D_{2h}$ sandwich ions. The Ti$^+$- and V$^+$-(C$_{6}$H$_{6}$)$_2$ ions are in the $^2$B$_{3g}$ and $^3$B$_{3g}$ electronic states. The ionization energies of Ti- and V-(C$_{6}$H$_{6}$)$_2$ are measured to be 5.731(3) and 5.784(5) eV, and the symmetric metal-benzene stretching frequencies in these corresponding ions are 228 and 231 cm$^{-1}$