Multivalent binding in platinum metal complexes

In this doctoral thesis, iodotrimethylplatinum(IV) complexes of different pyridine and 2,2´ bipyridine ligands are investigated. The crystal structures of both the mononuclear and dinuclear pyridine complexes reveal an octahedral coordination around the platinum(IV) and a facial arrangement of the methyl groups. The crystal structure of the dinuclear complexes confirms that the iodide ligand acts as a bridging ligand that holds the two platinum metal ions together. The reaction of the mononuclear pyridine complexes with iodotrimethylplatinum(IV) in chloroform results in the formation of the corresponding dinuclear complexes (both cis and trans isomers) of pyridines. Although the pyridine substituents have no significant influence on the crystal structures of either the mononuclear or the dinuclear complexes, the equilibrium population of these complexes in solution depends largely on the electronic effect of the pyridine substituent as well as on the steric bulk of the pyridine substituent. Iodotrimethylplatinum(IV) on treatment with 2,2´-bipyridine and its derivatives gives mono-nuclear 2,2´-bipyridine complexes. The crystal structure of the bipyridine complexes confirms the fac-octahedral coordination of the trimethylplatinum moiety and the bidentate coordination of the 2,2´-bipyridines. Bond length comparison shows that Pt-N bond distances in bipyridine complexes are slightly shorter than in the corresponding pyridine complexes, reflecting the better pi-acceptor character of the 2,2´-bipyridines. In addition, the N-Pt-N bite angle in the bipyridine complexes is much lower than in the pyridine complexes. It was also observed that in the crystal packing of 4,4´-Dichloro-2,2´-bipyridine complex of iodotrimethylplatinum(IV), intermolecular non-covalent interaction between methyl hydrogen and chlorine atom leads to the formation of zig-zag chain structures, which are linked through weak pi-pi interactions to form two-dimensional layer structure. The reaction of iodotrimethylplatinum(IV) complexes of pyridines with the corresponding 2,2´-bipyridines lead to the substitution of ligands resulting in the formation of chelate bipyridine complexes. The equilibrium for these substitution reactions strongly favours the formation of chelate products. The formation of chelate complexes in solution at equilibrium depends largely on the electronic effect of the substituent as well as on the nature of the solvent.In dieser Arbeit wurden Iodidotrimethylplatin(IV)-Komplexe mit verschiedenen Pyridin- und 2,2´-Bipyridin-Liganden untersucht. Die Kristallstrukturen von sowohl mononuklearen und dinuklearen Pyridin-Komplexen zeigen eine oktaedrische Koordination des Platin(IV) und eine faciale Anordnung der Methylgruppen. Die Kristallstrukturen von dinuklearen Komplexen bestätigen, dass der Iodid-Ligand als verbrückender Ligand, der zwei Platin-Ionen zusammenhält, dient. Die Reaktion von mononuklearen Pyridin Komplexen mit Iodidotrimethylplatin(IV) in Chloroform resultiert in der Bildung des entsprechenden dinuklearen Pyridinkomplexes (sowohl cis- als auch trans-Isomer). Obwohl die Pyridinsubstituenten keinen signifikanten Einfluss auf die Kristallstruktur sowohl von mononuklearen als auch von dinuklearen Komplexen haben, hängt das Gleichgewichtsverhältnis beider Spezies in Lösung zu einem großen Teil von den elektronischen Einflüssen der Substituenten, sowie deren sterischem Anspruch ab. Die Reaktion von Iodidotrimethylplatin(IV) mit 2,2´-Bipyridin und dessen Derivaten erzeugt mononukleare 2,2´-Bipyridin-Komplexe. Die Kristallstrukturen der Bipyridin-Komplexe bestätigen die fac-oktaedrische Koordination des Trimethylplatin-Rests und die bidentale Koordination der 2,2´-Bipyridine. Ein Vergleich der Bindungslängen zeigt, dass der Pt-N Bindungsabstand in Bipyridin-Komplexen leicht kürzer ist als in den entsprechenden Pyridin-Komplexen, was die besseren pi-Akzeptor Eigenschaften von 2,2´-Bipyridinen zeigt. Des Weiteren ist der N-Pt-N Winkel in Bipyridin-Komplexen wesentlich kleiner als in Pyridin-Komplexen. Zudem wurden in der Kristallpackung des 4,4´-Dichlorido-2,2´-bipyridin-Komplexes von Iodidotrimethylplatin(IV) intermolekulare, nicht kovalente Wechselwirkungen zwischen den Methyl-Wasserstoffatomen und den Chloratomen festgestellt, die zu der Ausbildung von kettenartigen Zick-Zack-Strukturen führen, die über schwache pi-pi-Wechselwirkungen verbunden sind und eine zweidimensionale Schichtstruktur erzeugen. Die Reaktion von Iodidotrimethylplatin(IV)-Pyridinkomplexen mit den entsprechenden 2,2´-Bipyridinen führt zu einer Substitution der Liganden, die in der Bildung von Chelat-Bipyridin-Komplexen resultiert. Im Gleichgewicht ist die Bildung des Chelatprodukts bei dieser Substitutionsreaktion stark bevorzugt. Die Bildung von Chelat-Komplexen in Lösung hängt im Gleichgewicht zu einem großen Teil von den elektronischen Effekten der Substituenten sowie von der Natur des Lösungsmittels ab

A simple copper(II) dppy-based receptor for sensing of L-Cysteine and L-Histidine in aqueous acetonitrile medium

The development of simple yet efficient receptors that rapidly detect and monitor amino acids with high sensitivity and reliability is crucial for the early-stage identification of various diseases. In this work, we report the synthesis and characterisation of a copper(II) complex, CuCl2L, by employing a 2,6-dipyrazinylpyridine (dppy)-based ligand (L = 2,2'-(4-(3,4,5-trimethoxyphenyl)pyridine-2,6-diyl)dipyrazine). The in-situ prepared CuCl2L receptor exhibits an instantaneous response to the presence of L-Cysteine (Cys) and L-Histidine (His) in aqueous acetonitrile (4:1 v/v, 10 mM HEPES buffer, pH 7.4). Furthermore, competitive experiments demonstrate the selectivity of CuCl2L towards Cys (1 equiv.) in the vicinity of other L-amino acids in the aforementioned solvent conditions. The lowest detection limits for Cys and His are calculated as 0.33 µM and 1.40 µM, respectively. DFT calculations offer a plausible explanation for the observed selectivity of the CuCl2L receptor towards Cys and His. They reveal that the most stable conformer of Cu:Cys complex (1:1) is a five-membered ring formed through N,S-coordination mode (ΔG = –26.7 kcal mol–1) over various other possible coordination modes, while comparable ΔG values are only obtained for Cu:His complexes featuring two His moieties

Mutual exclusivity of hyaluronan and hyaluronidase in invasive group A Streptococcus

A recent analysis of group A Streptococcus (GAS) invasive infections in Australia has shown a predominance of M4 GAS, a serotype recently reported to lack the antiphagocytic hyaluronic acid (HA) capsule. Here, we use molecular genetics and bioinformatics techniques to characterize 17 clinical M4 isolates associated with invasive disease in children during this recent epidemiology. All M4 isolates lacked HA capsule, and whole genome sequence analysis of two isolates revealed the complete absence of the hasABC capsule biosynthesis operon. Conversely, M4 isolates possess a functional HA-degrading hyaluronate lyase (HylA) enzyme that is rendered nonfunctional in other GAS through a point mutation. Transformation with a plasmid expressing hasABC restored partial encapsulation in wild-type (WT) M4 GAS, and full encapsulation in an isogenic M4 mutant lacking HylA. However, partial encapsulation reduced binding to human complement regulatory protein C4BP, did not enhance survival in whole human blood, and did not increase virulence of WT M4 GAS in a mouse model of systemic infection. Bioinformatics analysis found no hasABC homologs in closely related species, suggesting that this operon was a recent acquisition. These data showcase a mutually exclusive interaction of HA capsule and active HylA among strains of this leading human pathogen

Radio Astronomy

Contains reports on eleven research projects.National Science Foundation (Grant AST79-25075)National Science Foundation (Grant AST79-20984)National Science Foundation (Grant AST79-19553)U.S. Navy - Office of Naval Research (Contract N00014-80-C-0348)National Aeronautics and Space Administration (Grant NAG2-50)MIT Sloan Fund for Basic ResearchJoint Services Electronics Program(Contract DAAG80-C-0104)Lockheed Aircraft Corporation (Contract LS90B4860F)National Aeronautics and Space Administration (Grant NAG5-10)National Aeronautics and Space Administration (Contract NAS5-22929)U.S. Department of Commerce, National Oceanic and Atmospheric Administration (Grant 04-8-MO1-1)California Institute of Technology Jet Propulsion Laboratory (Contract LZ-727891)California Institute of Technology Jet Propulsion Laboratory Subcontract 956059California Institute of Technology Jet Propulsion Laboratory Task Order RD-15

Radio Astronomy

Contains reports on sixteen research projects.National Science Foundation (Grant AST81-21416)National Science Foundation (Grant AST80-22864)National Aeronautics and Space Administration (Contract S-10665-C)National Aeronautics and Space Administration (Contract NAGW373)National Science Foundation (Grant AST79-19553)National Oceanic and Atmospheric Administration (Grant 04-8-M01-1)National Aeronautics and Space Administration (Grant NAG5-10)National Aeronautics and Space Administration (Contract NAS5-22929)Defense Advanced Research Projects Agency (Contract MDA 903-82-K-0521)Intelsat (Contract Intel-188)Joint Services Electronics Program (Contract DAAG29-80-C-0104)Lockheed Missiles and Space Company (Contract LS90B4860F

Radio Astronomy

Contains summary of research and reports on nine research projects.National Science Foundation (Grant AST81-21416)National Science Foundation (Grant AST82-14296)National Aeronautics and Space Administration (Grant S-10781-C)National Aeronautics and Space Administration (Grant NAGW-373)National Science Foundation (Grant AST79-19553)M.I.T. Sloan Fund for Basic ResearchNational Oceanic and Atmospheric Administration (Grant 04-8-M01-1)National Aeronautics and Space Administration (Grant NAG5-10)National Aeronautics and Space Administration (Contract NAS5-22929)Defense Advanced Research Projects Agency (Contract MDA 903-82-K-0521)Center for Advanced Television Studie

Synthesis and structural characterization of new transition metal complexes of a highly luminescent amino-terpyridine ligand

The synthesis, NMR and UV-Vis spectroscopy measurements and X-ray diffraction analysis of four new metal complexes of the amino terpyridine ligand 4́-[4-(4-aminophenyl)phenyl]-2,2́:6́,2́́-terpyridine L, namely [FeL2](ClO4)2 (1), [ZnL2](ClO4)2 (2), [CdL2](ClO4)2 (3) and [PtMe3IL] (4), are reported. The X-ray crystal structures of complexes 1-3 are 1:2 metal:ligand structures with tridentate ligands decorated around the octahedral metal centers. In complex 4, with L in a bidentate coordination mode, the Pt(IV) coordinated methyl and iodine groups form a fac-arrangement. The 1H NMR spectrum of 4 shows three 195Pt-1H resonances for the methyl groups incorporating the fac-arrangement, which confirms the bidentate coordination mode of L in solution. The X-ray crystal structure of L shows a transoid conformation of the pyridine ring nitrogen atoms along the interannular bond in the terpyridine core. Ligand L exhibits a bright blue emission in dichloromethane [fluorescence quantum yield (ΦF) = 68%] and its emission maxima shows significant solvatochromism (461 nm in dichloromethane to 533 nm in N,N-dimethylformamide), while its complexes 2 and 3 are only very weakly emissive and 1 and 4 are found to be non-emissive.peerReviewe

Transition metal ion induced hydrogelation by amino-terpyridine ligands

Hydrogelation behavior of two amino-terpyridine ligands in the presence of divalent metal ions in water was studied in detail. The effect of ligand structure and different counter anions on the gel morphologies was also explored.peerReviewe

Synthesis, characterization and self-assembly of three dicyanamide bridged polynuclear copper(II) complexes with N2O donor tridentate Schiff bases as blocking ligands

Three copper(II) complexes [Cu(L1)(μ1,5-dca)]n (1), [Cu(L2)(μ1,5-dca)]n (2) and [Cu(L3)(μ1,5-dca)]n (3) [where HL1 = (1-(2-(dimethylamino)ethylimino)ethyl) naphthalene-1-ol, HL2 = (1-(2-(methylamino)ethylimino)ethyl) naphthalene-1-ol and HL3 = (1-(2-(ethylamino)ethylimino)ethyl)naphthalene-1-ol] have been synthesized and characterized by elemental analysis, IR and UV–Vis spectroscopy. The structure of each complex has been confirmed by single-crystal X-ray diffraction studies. In all three complexes, copper(II) centres are bridged by dicyanamide in end to end fashion. Complexes 1 and 2 are zigzag polymers, whereas complex 3 is a helical one. The weak forces like C–H⋯π and π⋯π interactions influence the self-assembly process in all three complexes. Such types of interactions lead to the formation of interesting supra molecular networks in three complexes.peerReviewe