1,721,145 research outputs found
Preparation, characterisation and structural analysis of salts and co-crystals of organic compounds
No full textIn this thesis the factors influencing the formation of a binary compound and the proton transfer within the binary compound have been investigated. The formation of a binary compound, or heteromeric system, over a homomeric system requires the heteromeric system to be more energetically favourable than the homomeric system. In some circumstances, however, no solid crystallises at all. Proton transfer within the binary compound can lead to the formation of a salt, whereas a binary compound containing neutral components is called a co-crystal. The ‘rule of three’ which predicts that proton transfer requires a difference of at least three units between the pKa of the acid and the pKa of the conjugate acid has also been investigated. In particular the relevance of this rule to diprotic acids and bases, and amide groups has been examined. The expression of starting material properties in the binary compounds was also explored.To achieve this an array of diacids and bases have been chosen that consist of ?,?-alkanedicarboxylic acids, ?,?-alkenedicarboxylic acids and tartaric acids with a selection of aliphatic amines, nitrogen-containing heterocycles and imidazole derivatives. The nitrogen-containing heterocycles include some amide functionalities. These compounds have been systematically crystallised together using a liquid-handling robot in a high-throughput manner commonly used in the pharmaceutical industry.The novel structures of 42 salts, 11 co-crystals and 6 mixed co-crystal/salt systems have been prepared and characterised using single crystal X-ray diffraction. Together with the binary compounds already present on the CSD, this has provided the opportunity to assess the impact of various factors on the crystal structures and properties of a total of 61 salts, 11 co-crystals and 8 mixed salt/co-crystal systems. Across the series of ?,?-alkanedicarboxylic acids it has been found that members with an even number of carbons in their alkyl chain (even diacids) form binary compounds more often than those with an odd number of carbons (odd diacids). The diacids with four carbons in their alkyl chains are most likely to form binary compounds. The melting point alternation seen in the ?,?-alkanedicarboxylic acids is also expressed in the binary products. This is particularly prominent with the 2-imidazoldinone-alkanedicarboxylic acid co-crystals, where the supramolecular structure formed by the even diacids is different to that formed by the odd diacids. This has been attributed to the different orientation of the carboxyl groups in the odd diacids.Although the ‘rule of three’ has been found to be applicable to the first ionisation of the diacids, it does not account for the ubiquitous formation of diprotonated bases where the pKa difference is often less than 2 units. Indeed the stoichiometry of the binary compounds was found to often be unpredictable and difficult to rationalise simply. The deprotonation of the diacids appeared to be determined by the optimal hydrogen bonding motifs rather than the pKa. There were also found to be similarities in supramolecular structures within the groups of compounds which could be used to predict the structures of other similar compounds
A systematic study of the crystallisation products of a series of dicarboxylic acids with imidazole derivatives
No full textNineteen new crystal structures are reported containing alpha,omega-alkanedicarboxylic acids (HOOC-(CH(2))(n-2)-COOH, n = 0-6), maleic acid and fumaric acid with imidazole, 1-methylimidazole, 2-methylimidazole, 4-methylimidazole and 1,2-dimethylimidazole. These were characterised by single crystal X-ray diffraction at 120 K and their crystal structures are discussed together with five published structures. In all of the characterised acid-base combinations at least one of the acidic hydrogens has been transferred to the base and most have a 1 : 1 stoichiometry. Nearly two thirds of the crystal structures adopt a basic sheet topology containing hydrogen bonded anion chains linked by cations. The sheet topologies have been classified based upon the principles of a scheme proposed by MacDonald et al. (J. C. MacDonald, P. C. Dorrestein and M. M. Pilley, Cryst. Growth Des., 2001, 1, 29-38)
Neutron diffraction data for 5M aqueous imidazole solution
No full textThe zipped file has the raw neutron diffraction data and processed (Gudrun) data for 5M aqueous imidazole solutions as well as the data files generated from the emperical potential structure refinement (EPSR) simulation</p
Synthesis and solid state study of pyridine- and pyrimidine-based fragment libraries
No full textA library of pyridines and pyrimidines has been synthesised in excellent yields employing microwave and flow chemistry methodologies. Work-up bottlenecks have been facilitated substantially by the use of supported reagents and many of the final compounds have been studied in the solid state by single crystal X-ray diffraction
Crystal structures of two palladacycles from the C-H activation of 2-(Thiophen-2-yl)pyridine
No full textA C,N-bound palladacycle dimer has been synthesised by reaction of 2-(thiophen-2-yl)pyridine, LH, with palladium acetate in acetic acid. Characterisation by single crystal X-ray diffraction showed the palladacycle dimer, [(L)Pd(OAc)]2, to crystallise in the monoclinic space group P21/n with cell parameters a = 9.5853(1) Å, b = 19.1332(3) Å, c = 12.3889(2) Å, β = 103.732(1)°. Reaction of [(L)Pd(OAc)]2 with triphenylphosphine afforded a trans-substituted monomeric complex, [(L)PdPPh3(OAc)] which was also analysed using single crystal X-ray diffraction. [(L)PdPPh3(OAc)] crystallises in the monoclinic space group P21/c with cell parameters a = 9.4839(1) Å, b = 11.0427(2) Å, c = 26.0770(4) Å, β = 95.022(1)°
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
On the structure of an aqueous propylene glycol solution
Get PDFUsing a combination of neutron diffraction and empirical potential structure refinement computational modelling, the interactions in a 30 mol. % aqueous solution of propylene glycol (PG), which govern both the hydration and association of this molecule in solution, have been assessed. From this work it appears that PG is readily hydrated, where the most prevalent hydration interactions were found to be through both the PG hydroxyl groups but also alkyl groups typically considered hydrophobic. Hydration interactions of PG dominate the solution over PG self-self interactions and there is no evidence of more extensive association. This hydration behavior for PG in solutions suggests that the preference of PG to be hydrated rather than to be self-associated may translate into a preference for PG to bind to lipids rather than itself, providing a potential explanation for how PG is able to enhance the apparent solubility of drug molecules in vivo.<br/
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Microwave-mediated synthesis and manipulation of a 2-substituted-5-aminooxazole-4-carbonitrile library
No full textA 2-substituted-5-aminooxazole-4-carbonitrile library has been synthesised and modified via microwave-mediated and flow chemistries. One synthesised compound, 5-(1H-pyrrol-1-yl)-4-(1H-tetrazol-5-yl)-2-(thien-2-yl)oxazole, contains three distinct heterocycles attached to the central oxazole core, highlighting the structural diversity of this approach. Three oxazoles had micromolar ki values against cannabinoid (CB1/CB2) receptors
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