75 research outputs found

    The Halogen Bond

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    The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design

    Dielectrophoresis of single-walled carbon nanotubes

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    STRUCTURE-PROPERTY RELATIONSHIPS IN TWO-COMPONENT LIQUIDS

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    This thesis tackles several two-component liquids where we currently have a poor understanding of their fundamental structures and influence on properties. A novel approach was taken to investigate hydrophobic interactions.1 Rather than studying the aqueous liquid, for which only very low hydrophobe concentrations are possible, the metastable glassy state formed by thermally annealing a H2O/C60 fullerene vapour deposit was examined. These ‘trapped solutions’ of fullerene in an amorphous solid water (ASW) matrix were prepared in newly built apparatus (Chapter 3) using deposition rates of about 5 H2O monolayers per second to give a total mass > 1 g without crystalline ice contamination. H2O desorption rate analysis indicated that the limits of ASW growth are associated with the influence of deposition rate on porosity and consequent decreases in deposit to cooling plate heat transfer with increasing deposit thickness. Characterisations by FT-IR, Raman, optical absorbance and photoluminescence spectroscopies, as well as by X-ray and neutron diffraction showed unexpected continual structural relaxation until their crystallisation to ice I at 150–160 K (Chapter 4).2 Contrary to Frank and Evans’s description of ‘iceberg’ hydration structures,3 for C60 in ASW there is a weakening of the average hydrogen bonding interaction and increases in dynamics of the first hydration layer. The present work tentatively supports theories of hydrophobic hydration forces involving a disconnection of water in the hydration shell from the extended hydrogen bonding network (Chapter 5).4-5 The intermolecular interactions in the chloroform–acetone (negative) and benzene–methanol (positive) azeotropes were investigated by Raman spectroscopy and neutron diffraction. Structural models of pure liquid chloroform and the chloroform-acetone azeotrope were prepared by Empirical Potential Structural Refinement6 of experimental data and described using radial distribution functions, spatial density functions, orientation correlation functions and Kirkwood correlation factors. These analyses revealed that ‘super dipole’ Cl3H - Cl3H - Cl3H self-associations in pure liquid chloroform (29 % molecules) may contribute to its good solvent quality and anaesthetic properties (Chapter 6),7 and that C2H6O - HCCl3 hydrogen bonding interactions are present in the chloroform-acetone azeotrope (Chapter 7). Through comparisons of radial distribution functions between ‘like’ and ‘unlike’ species in the azeotropes it is revealed that the azeotropic vapour pressure condition is not only characterised by the non-ideality of intermolecular interaction but also by significant deviations in mixing character from that of a regular mixture; the benzene-methanol azeotrope exhibit microscopic statistical demixing and the chloroform-acetone azeotrope exhibits transient complexation

    Spectroscopic Investigations in Chiral Crystalline and Solution Phases

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    Chirality is an interesting phenomenon that is not completely understood, and the present work broadens the present body of knowledge using various methods. Crystallization experiments of glycine have confirmed the previously reported phenomenon of nonphotochemical laser induced nucleation (NPLIN), and experiments utilizing a geometry with focused lasers may also display NPLIN, though the results indicate that new factors such as pH of the irradiated solution may affect the crystallizing process. Sodium bromate, NaBrO3, may also crystallize via NPLIN, though the results are not as conclusive as the glycine experiments. For both glycine and sodium bromate, sound waves produced micron sized crystals of high quality. The optical rotatory dispersion (ORD) curve of sodium chlorate and sodium bromate was recorded, and good agreement was found with previous literature. Laser light with a sufficient intensity gave rise to non-linear effects (NL-ORD) in the optical rotation. The NL-ORD was composed of a main contribution from n1, but multi-photon contributions, nn1, affected the optical rotation. The compressibility of racemic and enantiomerically pure a-methylbenzylamine was measured using a novel apparatus, and low frequency intermolecular vibrations measured via Raman spectroscopy gave good agreement with the magnitude of the compressibility. The compressibility of the enantiomerically pure a-methylbenzylamine was slightly higher than the racemic solution. The ORD of (S)-(a)-methylbenzylamine was recorded in a series of 39 solvents with widely ranging solvent properties. Calculations of the optical rotation via Gaussian03 were insufficient in describing the solvent effect upon the optical rotation. A good correlation of the optical rotation and the Kamlet-Taft parameters (a, b, p*) was established, and good agreement was found between the predicted model and the experimental results. Spectroscopic characterization of a-methylbenzylamine over the entire mole fraction concentration range in five distinct solvents (cyclohexane, toluene, nitrobenzene, DMSO, and methanol) via FTIR and NMR helped illuminate mitigating factors affecting the optical rotation. The nitrogen site was the only contributor that dominantly affected the optical rotation in the selected solvents
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