Biomedical subjects
Publications and source records attributed to Mark E Light.
The first evidence for thallium(I) complexes involving selenoether ligands is presented, together with the structure determinations for the 1D chain species [T1[MeSe(CH2)3SeMe]]PF6 and the 3D network species [T1[MeSe(CH2)2SeMe]]PF6.
Two molecules containing two 2,5-diamido,3,4-dichloropyrrole units linked via 1,3- or 1,4-substituted benzene rings have been synthesized. The pyrrole groups in these compounds deprotonate in the presence of tetrabutylammonium fluoride and form pyrrole anion dimers via NH...N- hydrogen bonds. This dimerization process results in the formation of polyanionic chains linked via an unusual "orthogonal" hydrogen-bonding array.
The propensity of amine, ammonium and amide pendant arm 2,5-diamidopyrrole derivatives to act as anion receptors has been investigated; the anion-coordination ability of these species has been determined by 1H NMR titration techniques revealing a marked selectivity of the amine functionalised receptor for hydrogen sulfate anions.
Aza-crown ethers 2 and 3 with anthracene-containing pendant arms have been synthesised and characterised. Both compounds bind Group 1 metal cations in solution, forming complexes of 1:1 stoichiometry. The properties of compound 2 and its complexes have been studied by a range of techniques, including NMR, UV and fluorescence spectroscopy and X-ray crystallography. The pendant arms can adopt either a cis or a trans geometry, the cis geometry favoured with larger cations. The geometry of the complex affects the fluorescence properties of the system, with larger cations giving higher excimer/monomer ratios. Upon irradiation at lambda>300 nm, coronand 2 forms the cryptand 5 through a reversible intramolecular [4pi+4pi] cycloaddition reaction. The rates of the forward and reverse reactions of this photochromic process are cation dependent; in particular the rate of the thermal reverse reaction is decreased by smaller cations and increased by larger cations, especially Rb(+). The metal binding constants in methanol for 2 and 5 have been determined, revealing that the cryptand 5 binds Na(+) and Rb(+) more weakly than crown ether 2 by over two orders of magnitude.
A new "super-extended cavity" tetraacetylcalix[4]pyrrole derivative was synthesized and characterized, and X-ray crystal structures of complexes bound to fluoride and acetonitrile were obtained. The binding behavior of this receptor was investigated by NMR titration, and the complex was found to exclusively bind fluoride ions in DMSO-d(6). This unusual binding behavior was investigated by Monte Carlo free energy perturbation simulations and Poisson calculations, and the ion specificity was seen to result from the favorable electrostatic interactions that the fluoride gains by sitting lower in the phenolic cavity of the receptor. The effect of water present in the DMSO on the calculated free energies of binding was also investigated. Owing to the use of a saturated ion solution, the effect of contaminating water is small in this case; however, it has the potential to be very significant at lower ion concentrations. Finally, the adaptive umbrella WHAM protocol was investigated and optimized for use in binding free energy calculations, and its efficiency was compared to that of the free energy perturbation calculations; adaptive umbrella WHAM was found to be approximately two times more efficient. In addition, structural evidence demonstrates that the protocol explores a wider conformational range than free energy perturbation and should therefore be the method of choice. This paper represents the first complete application of this methodology to "alchemical" changes.
Some N-substituted-3-azabicyclo[3.3.0]octen-7-one derivatives have been synthesized in an enantiomerically pure form starting from tri-O-acetyl-D-glucal via intramolecular Pauson-Khand (IPK) cycloaddition.
3,4-Dichoro-1H-pyrrole-2,5-dicarboxylic acid bis-phenylamide 3 and 3,4-dichoro-1H-pyrrole-2,5-dicarboxylic acid bis-butylamide 4 have been prepared and shown to deprotonate in the presence of basic anions: the X-ray crystal structure of the tetrabutylammonium salt of 3-H+ reveals the formation of a dimer in the solid state.
The present contribution discloses a simple and unexpected acid-catalyzed cleavage of tetrahydrotetrazines leading to 1,2-bis(hydrazones). Incorporation of a chiral fragment derived from carbohydrates enables the rapid preparation of glycosazones, a family of compounds employed by Emil Fischer to elucidate the configuration of sugars. In addition, a mechanistic proposal accounts for experimental observations.
The U.K. National Crystallography Service (NCS) has developed a prototype e-science infrastructure for the provision of a small molecule crystallography service from sample receipt to results dissemination. This paper outlines the two strands of this service, which (a) enable a user to contribute in the conduction of an experiment and (b) provide an effective route for the archival and dissemination of the arising results. Access to use the NCS facilities and expertise and a mechanism to submit samples is granted through a secure Grid infrastructure, which seamlessly provides instantaneous feedback and the ability to remotely monitor and guide diffraction experiments and stage the diffraction data to a securely accessible location. Publication of all the data and results generated during the course of the experiment, from processed data to analyzed structures, is then enabled by means of an open access data repository. The repository publishes its content through established digital libraries' protocols, which enable harvester and aggregator services to make the data searchable and accessible.