Selectivity and enantioselectivity in the palladium catalysed hydrogenation of pyrazine and some substituted pyrazines

The palladium catalysed hydrogenation of pyrazine and some substituted pyrazines has been investigated over a range of reaction conditions.This thesis reports and discusses work in three areas. The first being the hydrogenation of pyrazine over Pd/C, second the hydrogenation of some monosubstituted pyrazines also over Pd/C and finally, the enantioselective hydrogenation of methyl pyrazine-2- carboxylate over different chirally modified catalysts.The hydrogenation of pyrazine over Pd/C and some other platinum group metal (PGM) catalysts has given an insight into its reactivity and selectivity. The interaction of pyrazine with the catalyst surface has been examined by use of deuterium-exchange which indicates pyrazine adsorbs in a co-planar manner to the surface. This has been verified experimentally by interpreting results obtained from the rates of hydrogenation for a range of aromatic N-heterocycles.The hydrogenation of methyl pyrazine-2-carboxylate and 2-pyrazinecarbonitrile (2- PCN) over Pd/C has given an insight into the effects of substituents on the reactivity of the aromatic heterocyclic ring. In the case of methyl pyrazine-2-carboxylate, hydrogenation occurs in two distinct stages. The first stage is the rapid uptake of two moles hydrogen, followed by no further hydrogenation. Investigation of the compound formed after this two-mole uptake has shown 1, 4, 5, 6-tetrahydro methyl pyrazine-2- carboxylate as the product. On an electronic level, this compound is very stable and resists further reaction due to its conjugation and is in fact an a, p-unsaturated ester having a carbamate-like structure.The unmodified hydrogenation of 2-PCN gave different results. It became evident that this compound, like methyl pyrazine-2-carboxylate before, is only partially hydrogenated because reaction stops after a two-mole hydrogen uptake. Further investigation showed the cyano substituent is being partially hydrogenated as well as the ring. However, the degree of ring/substituent hydrogenation is affected by the pH ot the reaction solvent, and the mechanism of hydrogenation is not complying with traditional observations.The major aim of this project i.e. achieving the enantioselective hydrogenation of methyl pyrazine-2-carboxylate, has been fulfilled. An enantioselective outcome has been achieved over several differently modified catalysts. This is of particular importance to the industrial collaborator in this project, Zeneca Specialities.The action of an adsorbed chiral modifier onto Pd/C is to induce the preferential formation of methyl piperazine-2-carboxylate in a typical enantiomeric excess of 2- 25%; the highest value being obtained using a cinchonidine-modified catalyst.The presented results indicate the first ever example of direct enantioselective hydrogenation of an aromatic N-heterocycle.Mechanisms for the reaction predicting the experimental observations are given

Electrical Properties of SrBi₂Ta₂O₉ Ferroelectric Thin Films at Low Temperature

The temperature dependence of electrical properties for SrBi2Ta2O9 thin film capacitors with platinum electrodes (Pt/SBT/Pt) on silicon wafers was studied from 10 to 300 K. with a decrease in temperature from 300 to 200 K, the remanent polarization of the thin films shows about an 11% reduction from its 300 K value; however, it is reduced by about 87% reduction from its 200 K value when the temperature drops from 200 to 100 K. with a decrease to 200 K, the polarization fatigue was significant, and the capacitor shows an approximate 29% reduction in polarization from its initial value following 10^10 cycles. The dielectric response and leakage current of the thin films were also studied over the same lower temperature region. These results are helpful in the understanding of the fatigue-free behavior observed in SrBi2Ta2O9 thin films at room temperature and provide additional insight into their use for ferroelectric memory applications

Growth and Optical Properties of SrBi₂Nb₂O₉ Ferroelectric Thin Films Using Pulsed Laser Deposition

High quality SrBi2Nb2O9 ferroelectric thin films were fabricated on platinized silicon using pulsed laser deposition assisted with dc glow discharge plasma. Microstructure and ferroelectric properties of the films were characterized. Optical properties of the thin films were studied by spectroscopic ellipsometry and photoluminescence from the ultraviolet to the infrared region. Optical constants, n~0.56 in the infrared region and n~2.24 in the visible spectral region, were determined through multilayer analyses on their respective pseudodielectric functions. The band-gap energy is estimated to be 3.60 eV. A photoluminescence peak at 0.78 µm, whose intensity decreases with decreasing temperature, was observed when excited with subband-gap energy (2.41 eV). This emission process may involve intermediate defect states at the crystallite boundaries. A possible mechanism for the observed photoluminescence, a Nb4+-O- exciton in the NbO6 octahedron, is discussed

Avian taxonomic and functional diversity in early stage of longleaf pine (Pinus palustris) stands restored at agricultural lands: Variations in scale dependency

In agricultural landscapes, the Longleaf Pine Initiative (LLPI) and the Bobwhite Quail Initiative (BQI) aim to restore longleaf pine forests and early successional habitats, respectively. The early stage of longleaf pine stands and grass and forb vegetation produced by a combination of both restoration programs (LLPI-BQI) may form habitat conditions favorable to early successional bird species and other birds, increasing avian diversity. We investigated how the LLPI and BQI programs affected taxonomic and functional diversity of birds and abundance of early successional birds (grassland and scrub/shrub species), and what environmental characteristics were associated with the diversity and abundance of birds. Our study was performed at 41 fields in Georgia, USA, during 2001-2002 by considering environmental characteristics at two spatial scales: local-scale vegetation features and restoration program type (LLPI or LLPI-BQI) and landscape-scale vegetation features and landscape heterogeneity. Functional evenness, species richness, and abundance of grassland and scrub/shrub species did not show a clear association with local- or landscape-scale variables. Shannon-Wiener diversity was slightly influenced by restoration program type (local-scale variable) with higher value at LLPI-BQI stands than at LLPI stands despite no significant differences in local vegetation features between those stands. Functional divergence was strongly positively associated with landscape-scale variables. That is, niche differentiation increased with increasing shrub coverage within a landscape, reducing competition between abundant bird species and others. Our results suggest that although a combination of BQI and LLPI program may have a positive effect on avian taxonomic diversity, it is important to consider shrub vegetation cover within a landscape to improve functional diversity

Optical Limiting in SrBi₂Ta₂O₉ and PbZrxTi₁₋ₓO₃ Thin Films

Optical limiting effects in SrBi2Ta2O9 (SBT) and PbZrxTi1-xO3 (PZT) ferroelectric thin films have been observed with nanosecond laser pulses at 1.064 µm. Limiting thresholds were found to be 5.84 J/cm2 for SBT and between 4.53 and 5.93 J/cm2 for PZT, depending on composition, whereas saturation thresholds for the films were about 2.92 J/cm2 and between 2.27 J/cm2 to 2.97 J/cm2, respectively. Damage thresholds around 10.0 J/cm2 and between 10.37 J/cm2 to 10.54 J/cm2, respectively for SBT and PZT, were also determined. A possible mechanism for the observed limiting, nonlinear optical scattering from the ferroelectric domains, is discussed. These results elucidate the origin of the nonlinear optical properties in perovskite-type ferroelectric thin films and show the potential role such materials can play in photonic devices based on nonlinear optical effects

Avian taxonomic and functional diversity in early stage of longleaf pine (Pinus palustris) stands restored at agricultural lands: Variations in scale dependency

In agricultural landscapes, the Longleaf Pine Initiative (LLPI) and the Bobwhite Quail Initiative (BQI) aim to restore longleaf pine forests and early successional habitats, respectively. The early stage of longleaf pine stands and grass and forb vegetation produced by a combination of both restoration programs (LLPI-BQI) may form habitat conditions favorable to early successional bird species and other birds, increasing avian diversity. We investigated how the LLPI and BQI programs affected taxonomic and functional diversity of birds and abundance of early successional birds (grassland and scrub/shrub species), and what environmental characteristics were associated with the diversity and abundance of birds. Our study was performed at 41 fields in Georgia, USA, during 2001-2002 by considering environmental characteristics at two spatial scales: local-scale vegetation features and restoration program type (LLPI or LLPI-BQI) and landscape-scale vegetation features and landscape heterogeneity. Functional evenness, species richness, and abundance of grassland and scrub/shrub species did not show a clear association with local- or landscape-scale variables. Shannon-Wiener diversity was slightly influenced by restoration program type (local-scale variable) with higher value at LLPI-BQI stands than at LLPI stands despite no significant differences in local vegetation features between those stands. Functional divergence was strongly positively associated with landscape-scale variables. That is, niche differentiation increased with increasing shrub coverage within a landscape, reducing competition between abundant bird species and others. Our results suggest that although a combination of BQI and LLPI program may have a positive effect on avian taxonomic diversity, it is important to consider shrub vegetation cover within a landscape to improve functional diversity

Database management and analysis of fisheries in Illinois: Final report, 1 March 1999-28 February 2002

Issued May 2002; F-69-RReport issued on: May 200

Activated lymphocyte recruitment into the tumor microenvironment following preoperative sipuleucel-T for localized prostate cancer.

BackgroundSipuleucel-T is a US Food and Drug Administration-approved immunotherapy for asymptomatic or minimally symptomatic metastatic castration-resistant prostate cancer (mCRPC). Its mechanism of action is not fully understood. This prospective trial evaluated the direct immune effects of systemically administered sipuleucel-T on prostatic cancer tissue in the preoperative setting.MethodsPatients with untreated localized prostate cancer were treated on an open-label Phase II study of sipuleucel-T prior to planned radical prostatectomy (RP). Immune infiltrates in RP specimens (posttreatment) and in paired pretreatment biopsies were evaluated by immunohistochemistry (IHC). Correlations between circulating immune response and IHC were assessed using Spearman rank order.ResultsOf the 42 enrolled patients, 37 were evaluable. Adverse events were primarily transient, mild-to-moderate and infusion related. Patients developed T cell proliferation and interferon-γ responses detectable in the blood following treatment. Furthermore, a greater-than-three-fold increase in infiltrating CD3(+), CD4(+) FOXP3(-), and CD8(+) T cells was observed in the RP tissues compared with the pretreatment biopsy (binomial proportions: all P < .001). This level of T cell infiltration was observed at the tumor interface, and was not seen in a control group consisting of 12 concurrent patients who did not receive any neoadjuvant treatment prior to RP. The majority of infiltrating T cells were PD-1(+) and Ki-67(+), consistent with activated T cells. Importantly, the magnitude of the circulating immune response did not directly correlate with T cell infiltration within the prostate based upon Spearman's rank order correlation.ConclusionsThis study is the first to demonstrate a local immune effect from the administration of sipuleucel-T. Neoadjuvant sipuleucel-T elicits both a systemic antigen-specific T cell response and the recruitment of activated effector T cells into the prostate tumor microenvironment

Self-efficacy and academic achievement in Australian high school students: The mediating effects of academic aspirations and delinquency

Studies have shown that self-efficacy, aspirational, and other psychosocial influences account for considerable variance in academic achievement through a range of mediational pathways, although no research to date has tested the mediational relationships identified. The present research investigated the structural relations among self-efficacy, academic aspirations, and delinquency, on the academic achievement of 935 students aged 11-18 years from ten schools in two Australian cities. The Children's Self-Efficacy, Scale, Adapted Self-Report. Delinquency Scale (Revised), and Children's Academic Aspirations Scale were administered to participants prior to academic achievement being assessed using mid-year school grades. Structural equation modeling was employed to test three alternative models for the relationships from academic, social, and self-regulatory efficacy on academic achievement. A partial mediation model showed the best overall fit to the data. Academic and self-regulatory efficacy had an indirect negative effect through delinquency and a direct positive effect on academic achievement. Academic and social self-efficacy had positive and negative relationships, respectively, with academic aspiration and academic achievement; however, the relationship between academic aspiration and academic achievement was not significant in the final model. (C) 2008 The Association for Professionals in Services for Adolescents. Published by Elsevier Ltd. All rights reserved

Assessing Photoreceptor Structure Associated with Ellipsoid Zone Disruptions Visualized with Optical Coherence Tomography

Purpose: To compare images of photoreceptor layer disruptions obtained with optical coherence tomography (OCT) and adaptive optics scanning light ophthalmoscopy (AOSLO) in a variety of pathologic states.Methods: Five subjects with photoreceptor ellipsoid zone disruption as per OCT and clinical diagnoses of closed-globe blunt ocular trauma (n = 2), macular telangiectasia type 2 (n = 1), blue-cone monochromacy (n = 1), or cone-rod dystrophy (n = 1) were included. Images were acquired within and around photoreceptor lesions using spectral domain OCT, confocal AOSLO, and split-detector AOSLO.Results: There were substantial differences in the extent and appearance of the photoreceptor mosaic as revealed by confocal AOSLO, split-detector AOSLO, and spectral domain OCT en face view of the ellipsoid zone.Conclusion: Clinically available spectral domain OCT, viewed en face or as B-scan, may lead to misinterpretation of photoreceptor anatomy in a variety of diseases and injuries. This was demonstrated using split-detector AOSLO to reveal substantial populations of photoreceptors in areas of no, low, or ambiguous ellipsoid zone reflectivity with en face OCT and confocal AOSLO. Although it is unclear if these photoreceptors are functional, their presence offers hope for therapeutic strategies aimed at preserving or restoring photoreceptor function