Application of optically pure chiral anionic complexes in the construction of molecular conductors

Chapter 1 introduces the phenomenon of Magnetic Chiral Anisotropy in chiral conductors and reviews the current literature on chiral charge transfer molecular conductors and synthetic routes towards them. The second part of the chapter focuses on examples of chiral anionic species reported in the literature. Chapter 2 describes the synthesis and improvements to the literature procedures for organic donor molecules: tetrathiafulvalene, tetraselenafulvalene and bis(ethylenedithio)tetraselenafulvalene. The synthesis and characterisation of new chiral TTF imine systems are also reported. A stable TTF imine derivative of chiral biphenyl amine was used in the synthesis of a homochiral bimetallic helicate with copper(I). Unusual structural and magnetic properties of this compound are reported. Chapter 3 focuses on the synthesis and properties of optically pure anionic complexes, [MIII(Ln)2]-(M = Co, Fe), of chiral pyridinecarboxamide ligands (Ln). The complexes show interesting extended structures ranging from 0D discrete units through 1D zigzag chains to 2D honeycomb layers. The complex anions were used in the synthesis of radical cation salts with tetrathiafulvalene (TTF). The salts (TTF)[CoIII(R,R-L1)2] and (TTF)[CoIII(S,S-L2)2]·EtOAc were characterised by single crystal X-ray diffraction and conductivity measurements. Solution spectroscopic and cyclic voltammetric evidence points to the formation of soluble assemblies between TTF+ and the counterion which correspond to the stoichiometry observed by crystallography and other methods in the solid state. Chapter 4 describes the synthesis of the first diastereomerically pure, organicsoluble salts of cobalt, iron and chromium complexes of optically pure chelate: H4EDDS. A number of synthetic approaches were attempted, but finally the PPh4[MIII(EDDS)]·2H2O series emerged providing readily accessible compounds in reasonable yields via the silver salts. The species are very soluble in methanol, acetonitrile and even THF and isolation of highly crystalline solids is possible upon addition of water. The structures of the three compounds are isomorphous and comprise of H2O-bridged extended hydrogen bonded structures with large channels occupied by the counterion molecules. The magnetic properties and circular dichroism spectra are reported. The diastereomeric purity in the paramagnetic systems is assessed through powder XRD. Chapter 5 focuses on the use of organic-soluble EDDS complexes in the resolution of optically active cations and as a chiral NMR shift agent. The initial results of the resolution of (±)-[RuII(bpy)3]2+ are reported along with the crystal structure of the {Λ-[RuII(bpy)3]}{Λ-[FeIII(S,S-EDDS)]}Cl·H2O adduct. The result of testing of the diamagnetic PPh4[CoIII(S,S-EDDS)] salt as·a 1H NMR shift agent for chiral complex cations: [ML3]2+, (M = Co, Ru, Fe; L = bpy, phen, en) and small organic molecules are also reported. Chapter 6 describes the electrochemical synthesis of a new family of conductive optically pure tetrathiafulvalenium and tetraselenafulvalenium salts D3[MIII(S,S-EDDS)]2·nH2O (where D = TTF, TSF; M = Co, Fe, Cr). The compounds are characterised by single crystal X-ray diffraction, conductivity measurements and elemental microanalysis and exhibit well-behaved semiconductor behaviour with conductivities up to 2.8·10-4 S·cm-1 (Ea ca 0.1 eV). Computational work indicates that it is feasible to generate metallic conductors with similar structures. Initial results for an ET analogue showing metallic conductivity are also reported. Chapter 7 details the experimental procedures used to carry out the work in this thesis.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Hepatic VLDL secretion : DGAT1 determines particle size but not particle number, which can be supported entirely by DGAT2

We investigated whether, in view of its activity being expressed on both aspects of the endoplasmic reticulum (ER; dual membrane topology), diacylglycerol acyltransferase 1 (DGAT1) plays a distinctive role in determining the triglyceride (TAG) content of VLDL particles secreted by the liver. Mice in which the DGAT1 gene was specifically ablated in hepatocytes (DGAT1-LKO mice) had the same number of VLDL particles (apoB concentration) in the plasma 1 h after Triton 1339 treatment, but these particles were approximately half the size of VLDL particles secreted by control mice and had a proportionately decreased content of TAG, with normal cholesterol and cholesteryl ester contents. Analyses of purified microsomal fractions prepared from 16 h fasted control and DAGT1-LKO mice showed that the TAG/protein ratio in the ER was significantly lower in the latter. Electron micrographs of these livers showed that those from DGAT1-LKO mice did not show the increased lipid content of the smooth ER shown by control livers. The effects of DGAT1- and DGAT2-specific inhibitors on apoB secretion by HepG2 cells showed that DGAT1 is not indispensable for apoB secretion and demonstrated redundancy in the ability of the two enzymes to support apoB secretion. Therefore, our findings show that DGAT1 is essential for the complete lipidation and maturation of VLDL particles within the lumen of the ER, consistent with its dual topology within the ER membrane. In the mouse, DGAT2 can support apoB secretion (particle number) even when TAG availability for full VLDL lipidation is restricted in the absence of DGAT1

Spatial positioning of EB family proteins at microtubule tips involves distinct nucleotide-dependent binding properties

EB proteins track the ends of growing microtubules and regulate microtubule dynamics both directly and by acting as the hub of the tip-tracking network. Mammalian cells express cell type-specific combinations of three EB proteins with different cellular roles. Here we reconstitute EB1, EB2 and EB3 tip tracking in vitro. We find that all three EBs show rapid exchange at the microtubule tip and that their signal correlates to the microtubule assembly rate. However, the three signals differ in their maxima and the position from the microtubule tip. Using microtubules built with nucleotide analogues and site-directed mutagenesis, we show that EB2 prefers binding to microtubule lattices containing a 1:1 mixture of different nucleotides and its distinct binding specificity is conferred by amino acid substitutions at the right-hand side interface of the EB microtubule-binding domain with tubulin. Our data are consistent with the model that all three EB paralogs sense the nucleotide state of both β-tubulins flanking their binding site. Their different profile of preferred binding sites contributes to occupying spatially distinct domains at the temporally evolving microtubule tip structure

A strained alkyne-containing bipyridine reagent ; synthesis, reactivity and fluorescence properties

We report the synthesis of a bipyridyl reagent containing a strained alkyne, which significantly restricts its flexibility. Upon strain-promoted alkyne-azide cycloaddition (SPAAC) with an azide, which does not require a Cu catalyst, the structure becomes significantly more flexible and an increase in fluorescence is observed. Upon addition of Zn(II), the fluorescence is enhanced further. The reagent has the potential to act as a fluorescent labelling agent with azide-containing substrates, including biological molecules

Light scattering corrections to linear dichroism spectroscopy for liposomes in shear flow using calcein fluorescence and modified Rayleigh-Gans-Debye-Mie scattering

The interpretation of data from absorbance spectroscopy experiments of liposomes in flow systems is often complicated by the fact that there is currently no easy way to account for scattering artefacts. This has proved particularly problematic for linear dichroism (LD) spectroscopy, which may be used to determine binding modes of small molecules, peptides and proteins to liposomes if we can extract the absorbance signal from the combined absorbance/scattering experiment. Equations for a modified Rayleigh-Gans-Debye (RGD) approximation to the turbidity (scattering) LD spectrum are available in the literature though have not been implemented. This review summarises the literature and shows how it can be implemented. The implementation proceeds by first determining volume loss that occurs when a spherical liposome is subjected to flow. Calcein fluorescence can be used for this purpose since at high concentrations (> 60 mM) it has low intensity fluorescence with maxima at 525 and 563 nm whereas at low concentrations (<1 mM) the fluorescence intensity is enhanced and the band shifts to 536 nm. The scattering calculation process yields the average axis ratios of the distorted liposome ellipsoids and extent of orientation of the liposomes in flow. The scattering calculations require methods to estimate liposome integrity, volume loss, and orientation when subjected to shear stresses under flow

Influence of the tetraalkoxysilane crosslinker on the properties of polysiloxane-based elastomers prepared by the Lewis acid-catalysed Piers-Rubinsztajn reaction

This is an accepted manuscript of an article published by Royal Society of Chemistry in Polymer Chemistry, available online: https://doi.org/10.1039/D1PY00872B The accepted version of the publication may differ from the final published version.We investigate the preparation of polysiloxane-based networks under solvent-free, ambient conditions using the Lewis acid catalysed Piers-Rubinsztajn (PR) reaction of hydride-terminated siloxanes with various tetrafunctional alkoxysilanes (tetraethoxysilane, tetrapropoxysilane, tetra-n-buxoxysilane, tetra-s-butoxysilane, tetra-s-butoxysilane, and tetrakis(2- ethylbutoxy)silane) as crosslinkers. We explore the effects of polysiloxane chain length and crosslinker alkyl group on the rheological performance of the elastomers. By analysing the reaction progress by grazing angle Fourier-transform infrared spectroscopy (FTIR) and determining the rheological properties of the resulting materials, we show that the use of linear or branched alkoxysilanes strongly influences the morphology and properties of these network polymers. We have shown the PR process is can be tailored to reliably produce homogeneous, polysiloxane network materials. This work provides information on the relative rates of network formation under ambient conditions with an emphasis on the impact of crosslinker alkyl chain length. Our results show that electronics and s terics both play critical roles in influencing the the rate of the curing reaction. Crucially, we newly demonstrate the benefit of a having tertiary carbon α to the SiO reaction centre, as is the case for the tetra-s-butoxysilane crosslinker, for delivering exceptionally rapid network cure and a concomitant enhancement in storage modulus of the resultant materials

Infrared absorbance spectroscopy of aqueous proteins : comparison of transmission and ATR data collection and analysis for secondary structure fitting

Attenuated total reflectance (ATR) infrared absorbance spectroscopy of proteins in aqueous solution is much easier to perform than transmission spectroscopy, where short path‐length cells need to be assembled reproducibly. However, the shape of the resulting ATR infrared spectrum varies with the refractive index of the sample and the instrument configuration. Refractive index in turn depends on the absorbance of the sample. In this work, it is shown that a room temperature triglycine sulfate detector and a ZnSe ATR unit can be used to collect reproducible spectra of proteins. A simple method for transforming the protein ATR spectrum into the shape of the transmission spectrum is also given, which proceeds by approximating a Kramers‐Krönig–determined refractive index of water as a sum of four linear components across the amide I and II regions. The light intensity at the crystal surface (with 45° incidence) and its rate of decay away from the surface is determined as a function of the wave number–dependent refractive index as well as the decay of the evanescent wave from the surface. The result is a single correction factor at each wave number. The spectra were normalized to a maximum of 1 between 1600 cm−1 and 1700 cm−1 and a self‐organizing map secondary structure fitting algorithm, SOMSpec, applied using the BioTools reference set. The resulting secondary structure estimates are encouraging for the future of ATR spectroscopy for biopharmaceutical characterization and quality control applications

SOMSpec as a general purpose validated self-organising map tool for rapid protein secondary structure prediction from infrared absorbance data

A protein’s structure is the key to its function. As protein structure can vary with environment, it is important to be able to determine it over a wide range of concentrations, temperatures, formulation vehicles, and states. Robust reproducible validated methods are required for applications including batch-batch comparisons of biopharmaceutical products. Circular dichroism is widely used for this purpose, but an alternative is required for concentrations above 10 mg/mL or for solutions with chiral buffer components that absorb far UV light. Infrared (IR) protein absorbance spectra of the Amide I region (1,600–1700 cm−1) contain information about secondary structure and require higher concentrations than circular dichroism often with complementary spectral windows. In this paper, we consider a number of approaches to extract structural information from a protein infrared spectrum and determine their reliability for regulatory and research purpose. In particular, we compare direct and second derivative band-fitting with a self-organising map (SOM) approach applied to a number of different reference sets. The self-organising map (SOM) approach proved significantly more accurate than the band-fitting approaches for solution spectra. As there is no validated benchmark method available for infrared structure fitting, SOMSpec was implemented in a leave-one-out validation (LOOV) approach for solid-state transmission and thin-film attenuated total reflectance (ATR) reference sets. We then tested SOMSpec and the thin-film ATR reference set against 68 solution spectra and found the average prediction error for helix (α + 310) and β-sheet was less than 6% for proteins with less than 40% helix. This is quantitatively better than other available approaches. The visual output format of SOMSpec aids identification of poor predictions. We also demonstrated how to convert aqueous ATR spectra to and from transmission spectra for structure fitting. Fourier self-deconvolution did not improve the average structure predictions

Oxidized polyethylene films for orienting polar molecules for linear dichroism spectroscopy

Stretched polyethylene (PE) films have been used to orient small molecules for decades by depositing solutions on their surface and allowing the solvent to evaporate leaving the analyte absorbed on the polymer film. However, the non-polar hydrophobic nature of PE is an obstacle to aligning polar molecules and biological samples. In this work PE film was treated with oxygen plasma in order to increase surface hydrophilicity. Different treatment conditions were evaluated using contact angle measurement and X-ray photoelectron spectroscopy. Treated PE (PEOX) films are shown to be able to align molecules of different polarities including progesterone, 1-pyrenecarboxaldehyde, 4′,6-diamidino-2-phenylindole (DAPI) and anthracene. The degree of alignment of each molecule was studied by running series of linear dichroism (LD) experiments and the polarizations of electronic transition moments were determined. For the first time optimal conditions (such as stretching factor and concentration of the sample) for stretched film LD were determined. PEOX aligning ability was compared to that of normal PE films. Progesterone showed a slightly better alignment on PEOX than PE. 1-Pyrenecarboxaldehyde oriented differently on the two different films which enabled transition moment assignment for this low symmetry molecule. DAPI (which does not align on PE) aligned well on PEOX and enabled us to obtain better LD data than had previously been collected with polyvinyl alcohol. Anthracene alignment and formation of dimers and higher order structures were studied in much more detail than previously possible, showing a variety of assemblies on PE and PEOX films

Redox-active and DNA-binding coordination complexes of clotrimazole

DNA interactions of anticancer mononuclear Cu2+, Co2+, Zn2+, and Ni2+ complexes with the biologically active ligand clotrimazole (clotri) are reported. To fully characterize DNA binding modes for these complexes of the formulae [M(clotri)2Cl2]·nH2O (1–4), [M(clotri)2Br2]·nH2O (5,6), [M(clotri)3NO3]NO3·nH2O (9), and [M(clotri)3(NO3)2] (10), circular dichroism (CD) and linear dichroism (LD) spectroscopy, UV melting experiments, atomic force microscopy (AFM) and ethidium bromide (EtBr) displacement methods were used. Results indicate mixed electrostatic interactions, possibly through groove binding, that result in accretion and coiling of DNA. Electrochemical studies indicate that the Cu2+ complex 9 readily reduces to the reactive-oxygen-species-generating Cu+, which oxidatively damages DNA. There is a subtle correlation between log P values, calculated electrostatic potentials, and cytotoxicity of the complexes. The extent of cell-nucleus DNA-metal adduct formation in the HeLa cervix-uterine carcinoma cell line does not necessarily correlate with cytotoxicity, indicating that the nature of DNA lesions may be crucial to activity