http://hdl.handle.net/1842/3013 2013-05-24T05:50:01Z 2013-05-24T05:50:01Z Sanchez Perucha, Alejandro Perucha, Alejandro Sanchez http://hdl.handle.net/1842/6575 2013-02-27T12:28:39Z 2007-06-25T00:00:00Z

Title: Novel synthesis of tripodal borate ligands Authors: Sanchez Perucha, Alejandro; Perucha, Alejandro Sanchez Abstract: Poly(azolyl)borate ligands have proven to be extremely popular ligands since their introduction by Trofimenko in the late 60´s. The basic skeleton of these ligands involves usually three heterocycle units linked to a central boron apex via the azole nitrogen atoms. These ligands have been applied in diverse research areas such as homogeneous catalysis, materials science and bio-inorganic chemistry. More than 2000 papers, including books and reviews regarding the properties of these compounds, have been published. However, only a few synthetic methods for the preparation of such ligands have been reported and only a few examples of chiral borate-centred ligands are known. This thesis deals with the development of a novel synthetic route to tripodal borate ligands using B(NMe2)3 as the boron source. The mechanism of the reaction of this borane with azole heterocycles has been established by exploring the reactivity of a range of azoles. One of the major features of this new synthetic protocol is that it allows the formation of chiral tripodal ligands where the chiral groups are located either at the forth position at the boron atom or at the azole heterocycles. Coordination studies of the ligands have been undertaken and the metal complexes have been studied by a combination of spectroscopic and X- ray diffraction techniques. Preliminary application of the most representative ligands in the Asymmetric Transfer Hydrogenation (ATH) of prochiral ketones has been undertaken in collaboration with Prof. Dieter Vogt at the Technical University of Eindhoven.

2007-06-25T00:00:00Z Lynch, Jennifer Ann http://hdl.handle.net/1842/6572 2013-02-27T12:08:13Z 2007-06-25T00:00:00Z

Title: Structural role of linker histone H5 tails in the formation of the 30nm fiber of chromatin Authors: Lynch, Jennifer Ann Abstract: Eukaryotic DNA associates with histones to form nucleosomes, the fundamental component of chromatin. There are two functionally distinct classes of histones, core histones and linker histones. The core histones form an octamer around which DNA winds and a molecule of linker histone associates with this complex completing the nucleosome. The binding of linker histones to chromatin appears to be directed by the interaction of two sites in the folded globular domain with a site or sites close to the dyad axis of the core particle at the point where the DNA enters and exits after making two turns around the core histone octamer. This interaction must determine the location and orientation of the ‘tails’ of the linker histones allowing them to neutralize the linker DNA and permit the nucleosomal chain to adopt higher-order folding. However, there is little evidence of how the tails are organized or how they affect this folding process. It is toward this problem that this project is directed. The tails of the linker histones are rich in basic amino acids with the majority of the lysines and arginines found in the C-terminal and N-terminal tails. The tails also remain unstructured in contrast to the globular domain, which is folded even in low ionic strength buffers. Taking advantage of the structured and unstructured nature of the linker histone the proteolytic enzyme trypsin will be used as a probe to assess the structure of the tails. The aim is to mildly cleave the molecule and identify the sites of the cutting under a variety of relevant conditions using mass spectrometry to measure the mass of the digest products. The organization of the tails was probed under the following conditions; by first digesting the H5 alone, then digesting the H5 in the presence of DNA and finally by digesting the H5 in the presence of chromatin, previously stripped of linker histones, in varying ionic strength buffers. The digest products were run on SDS/PAGE gel and by direct mass spectrometric analysis. The aim of investigating the linker histone tails is to build upon the body of evidence regarding the higher-order organization of chromatin.

2007-06-25T00:00:00Z Melchionna, Michele http://hdl.handle.net/1842/6571 2013-02-27T12:06:40Z 2007-06-25T00:00:00Z

Title: Synthesis and study of novel zwitterionic transition metal complexes and their application as olefin polymerisation catalysts Authors: Melchionna, Michele Abstract: The synthesis, characterization and coordination chemistry of novel zwitterionic late transition metal complexes has been carried out, and an investigation of their ability to act as olefin polymerisation catalysts has been conducted. These systems are based on 6- aminofulvene-2-aldiminate ligands (R2AFA¯) which are capable of binding metal centres via two nitrogen donors, delocalising the negative charge into their cyclopentadienyl moiety, thus resulting in the formation of neutral zwitterionic complexes. Preparation and characterisation of mono- and di-substituted complexes such as Ph2AFACuPPh3, (Ph2AFA)2Zn, (Ph2AFA)2Co, (Ph2AFA)2Ni and (Ph2AFA)2Pd have revealed that this type of ligand has enough flexibility to distort upon coordination to the metal depending on geometrical or steric restrictions. As a result, when the ligand coordination involves narrow binding angle of the metal chelate, as it happens in the square-planar species, a severe loss of planarity of the ligand framework is observed, in contrast with the tetrahedral structures where such binding angles are wider. Although the coordination of the ligand primarily occurs through the nitrogen donors, once they have been occupied by the metal centre, it is possible to exploit the aromatic Cp ring for coordination to a Cp*Ru+ unit. In this way, the synthesis and characterisation of two- and tri-metallic complexes [(Cp*Ru)(Ph’2AFA)Pd(η3-C3H5)][BF4] (where Ph’= 2,4,6-trimethylphenyl) and [(Cp*Ru)2(Ph2AFA)2Pd][BF4]2 has been achieved, featuring the R2AFA¯ molecule acting as an ambidentate ligand, binding the palladium atom in a diimine fashion and the ruthenium centres by means of the C5 ring. The synthesis of the complex Cp*RuPh2AFA where the two N atoms are vacant was also achieved and it was found that this compound acts as a proton sponge in the presence of protic solvents. In an effort to prepare AFA-metal complexes which could be of potential use in olefin polymerisation catalysis, two novel species, [(Ph2AFA)Pd(Me)PPh3] and [(Ph’2AFA)Pd(C3H5)] (where Ph’= 2,4,6-trimethylphenyl) have been synthesised and characterised, and polymerisation tests with ethylene have been carried out. Some preliminary screening of other molecules as monomers for polymerisation catalysis has also been conducted.

2007-06-25T00:00:00Z Hill, John M. http://hdl.handle.net/1842/6532 2012-12-06T13:53:18Z 1931-01-01T00:00:00Z

Title: Rotatory Power of optically active Benzoic Esters containing Ionisable ortho-substituents. Authors: Hill, John M. Abstract: Among the many and varied fields of present day chemistry, that of optical activity occupies a not unimportant position. The rotatory powers of the alkali and ammonium salts of d-sec-βoctyl hydrogen phthalate have been studied in alcoholic and aqueous solution. The rotations of the salts were found to be in the order H > Li > NH4 > Na > K > Rb. It has been concluded that the variation of the molecular rotation of the salts with concentration may be explained by assuming changes in the degree of dissociation of the electrolytes and a deforming influence of the cations on the optically active anions. The effect of the addition of inorganic salts of various valence types to 0.2 M aqueous solutions of d-sec-β-octyl sodium phthalate has been investigated. The series for the depressive influence of the alkali and ammonium chlorides on the rotatory power of the optically active electrolyte is Cs+> Rb+> K+> Na+> NH4+> Li+. The corresponding series for the divalent chlorides is Ba++> Sr++> Ca++> Mg++. It is concluded that the observed effects may be attributed mainly to a deforming influence of the positive ion on the optically active negative ion, the explanation involving a consideration of the ionic radii. It is worthy of comment that the above results have been obtained by use of a carboxylic acid containing no hydroxyl group.

1931-01-01T00:00:00Z