A new cyanoscorpionate - tris(4-cyano-3,5-diphenylpyrazolyl)borate (TpPh2,4CN) has been synthesized and characterized. The thallium complex of this ligand TlTpPh2,4CN has also been prepared and characterized by FT-IR, 1H NMR, and single-crystal X-ray-diffraction. The complex TlTpPh2,4CN crystalized in the monoclinic space group C2/c with unit cell a = 14.6697(10) Å, b = 13.9493(10) Å, c = 19.3347(12) Å, and b= 91.761(2)°. Structural comparison of TlTpPh2,4CN with analogous complexes demonstrated the effects of both steric and electron-withdrawing substituents on coordination geometry and the electronic properties of the metal ion. There were short contacts between the cyano groups and neighboring thallium ions that also indicated the ligand’s potential to form coordination polymers.

Charge transfer salts of Tetracyanoquinodimethane (TCNQ) were synthesised and their electrical and magnetic properties were investigated. These salts show unusual electrical and magnetic behaviour in contrast to conventional organic compounds. These salts have crystal structures which in general consist of TCNQ radical ions stacked in chains, isolated from each other by the diamagnetic cations. They are thus regarded as "one-dimensional" electrical and magnetic systems. The ESR spectra of these salts are attributed to triplet excitons showing that the spin-spin and electronelectron correlation effects are important. In the ESR spectra (Chapter III) of some TCNQ salts dipolar splitting is observed confirming the spin-spin interaction. These triplet excitons are regarded as bound electron-hole pairs. The experimentally determined dipolar splitting tensors are presented in Chapter III and the intensity data in Chapter IV. A large number of fine structure lines are observed in the ESR spectra of Pyridinium-TCNQ and 4-Aminopyridinium-TCNQ apart from regular triplet exciton lines (Chapter III). These lines are attributed to the trapping of excitons on an extended formula finit (TCNQ2 )n. In Chapter IV the temperature dependent magnetic susceptibilities are discussed in terms of Heisenberg antiferromagnetism and Pauli paramagnetism. In Chapter V temperature dependent behaviour of electrical conductivity is discussed in terms of an exciton band model, the lattice structure of the salts and one-dimensional lattice consisting of defects giving rise to high and low conducting segments. Low temperature electrical and magnetic phases are discussed (Chapters IV and VII) in terms of a band and hopping mechanisms.In Chapter VI self consistent field calculations are made with reference to the tight binding one electron band theory using simplified Roothaan equations considering CNDO approximations. Theoretical results are related to experimental band gaps, spinspin interactions and charge alteration.

The knowledge of the packing behaviour of small organic compounds in crystal lattices is of great importance for industries dealing with solid state materials. The properties of materials depend on how the molecules arrange themselves in a crystalline environment. Crystal structure prediction provides a theoretical approach through the application of computational strategies to seek possible crystal packing arrangements (or polymorphs) a compound may adopt. Based on the chemical diagrams, this thesis investigates polymorphism of several small organic compounds. Plausible crystal packings of those compounds are generated, and their lattice energies are minimised using molecular mechanics and/or quantum mechanics methods. Most of the work presented here is conducted using two software packages commercially available in this field, Polymorph Predictor of Materials Studio 4.0 and GRACE 1.0. In general, the computational techniques implemented in GRACE are very good at reproducing the geometries of the crystal structures corresponding to the experimental observations of the compounds, in addition to describing their solid state energetics correctly. Complementing the CSP results obtained using GRACE with isostructurality offers a route by which new potential polymorphs of the targeted compounds might be crystallised using the existing experimental data. Based on all calculations in this thesis, four new potential polymorphs for four different compounds, which have not yet been determined experimentally, are predicted to exist and may be obtained under the right crystallisation conditions. One polymorph is expected to crystallise under pressure. The remaining three polymorphs might be obtained by using a seeding technique or the utilisation of suitable tailor made additives. / University of Bradford

Compound semiconductors are the foundation of many electronic and optoelectronic devices. As a result semiconductor epitaxy can be viewed as the first significant step in device engineering. Accurate and reliable characterization methods are needed to measure semiconductor properties including optical, electrical, vibrational and crystal structure. In this thesis, the epitaxy of ZnTe thin films on sapphire substrate by Pulsed Laser Deposition system at different growth temperatures is studied. The texture analysis is inspected by Two Dimensional X-Ray Diffraction. The lattice constant of the films and strain studies are investigated by High Resolution X-Ray Diffraction. UV-Vis spectroscopy is applied to find absorption edge in ZnTe thin film in order to estimate optical bandgap. These common characterization methods reveal the great effect of growth temperature on crystalline and optical properties of ZnTe thin films. In addition, Raman spectroscopy is used for the first time in the Preston's group to examine vibrational modes in ZnTe thin films. This new characterization method, which is the main focus of this thesis, uncovers some new features of ZnTe thin films not accessible through other techniques. In this thesis, optimum experimental conditions, instrumentation and data analysis of Raman observations in thin films are studied in detail. The final results are in good agreement with other characterization methods and they can justify crystalline and optical observations. These results demonstrate that Raman spectroscopy is a non-destructive characterization method applicable to thin film analysis. / Thesis / Master of Applied Science (MASc)

The crystal structures of Co₃(AsO₄)₂, Co₂₄ٜ₂As₉O₄₈, Co₂As₂O₇ and Co₇As₃ٜ₆O₁₆ have been determined by x-ray diffraction methods. The crystal structure of Mg₃(VO₄)₂ have been refined using single crystal x-ray diffraction data. General structural relations between M₃(XO₄)₂ type compounds where M refers to a divalent cation with radius comparable to that of cobalt, and x = As or V, are discussed. The deviations from ideality in cation polyhedral groups in crystal structures are analysed. / Thesis / Doctor of Philosophy (PhD)

No description available.

Blockering av NKG2A receptorn på NK - och CD8+ T celler med en anti-NKG2A antikropp, medför en aktivering av cytolytisk aktivitet, och är en lovande immunkontrollpunkt i immunterapi mot cancer. Nyligen har en TCR-liknande antikropp, EXX1, som binder till liganden för NKG2A receptorn, Qa-1b - en icke-klassisk MHC klass Ib molekyl i möss -studerats i tumör modeller in vitro. Resultat påvisar att den TCR-liknande antikroppen endast binder till Qa-1b om denna presenterar Qdm peptiden på sin yta, som erhålls från ledarsekvensen hos klassika MHC klass Ia H-2D. Detta väcker frågor kring strukturella faktorer som möjliggör antigenpresentation på Qa-1b och de exakta molekylära parametrarna som ger upphov till antikroppens specificitet. Syftet med denna studie var att bestämma och jämföra kristallstrukturerna för Qa-1b med Qdm (AMAPRTLLL) samt peptid 001 (AQAERTPEL). Den tunga peptidkedjan hos Qa-1b och beta-2-mikroglobulin producerades rekombinant i E.coli, återveckades med respektive peptid, renades med kromatografimetoder och slutligen kristalliserades genom ångdiffusionsmetoden med hängande droppar. Värmestabilitet hos MHC/peptid undersöktes med nano differential scanning fluorimetry, där Qa-1b /001 uppvisade bättre stabilitet. Kristaller för Qa-1b /Qdm och Qa-1b /001 kunde erhållas med 8% PEG4000, 10mM NiCl2, 0.1M natriumacetat vid pH 5.7, respektive 10% PEG4000, 10 mM NiCl2 och 0.1 M natriumacetat vid pH 6.0. Strukturen för Qa-1b /001 kunde bestämmas vid 2.43 Å med molekylär ersättning. Med anledning av negativt laddade sidogrupper i peptid 001 som har en ytlig konformation i bindningsfickan, kan avsaknaden av bindning till EXX1 förklaras av en skillnad i elektrostatiska interaktioner mellan Qdm och peptid 001. Ytterligare strukturella karakteriseringar av Qa-1b komplexen med antikroppen är av fortsatt stort intresse. / Blocking of the NKG2A receptor expressed on NK cells and CD8+ T cells with an anti-NKG2A antibody for elicitation of cytolytic activity, is a promising immune checkpoint in cancer immunotherapy. EXX1, a novel TCR-like antibody with specificity for the NKG2A ligand, Qa-1b - a murine non-classical MHC class Ib ortholog of HLA-E - has been assessed in tumor models in vitro. The antibody only engages with Qa-1b when it presents the dominant peptide Qdm, derived from the leader sequence of the classical MHC class Ia H-2D. This raises questions about the structural features of antigen presentation by Qa-1b, and the molecular parameters driving the specificity of the TCR-like antibody. The purpose of this study is to determine and compare the crystal structures of Qa-1b in complex with Qdm (AMAPRTLLL) and peptide 001 (AQAERTPEL). The Qa-1b heavy chain and mouse beta-2 microglobulin were recombinantly expressed in E.coli, refolded in the presence of respective peptide, purified using size exclusion chromatography and crystallized with the hanging drop vapor diffusion method. Thermal stability of the MHC/peptide complexes was assessed with nano differential scanning fluorimetry, implying a higher stability of Qa-1b/001. Crystals of the Qa-1b/Qdm and Qa-1b/001 were obtained with 8% PEG4000, 10 mM NiCl2, 0.1 M sodium acetate at pH 5.7, and 10% PEG4000, 10mM NiCl2 and 0.1 M sodium acetate at pH 6.0, respectively. The structure of Qa-1b/001 was resolved by molecular replacement at 2.43 Å, and the presence of negatively charged side chains that protrude from the binding groove, may imply that differences in electrostatic interactions between Qdm and 001 will determine antibody-binding. Further structural characterizations, of Qa-1b complexes with bound EXX1 are of great interest.

No description available.

No description available.

No description available.