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Binding Units (binding + unit)
Selected AbstractsA Theoretical ab initio Study of the Capacity of Several Binding Units for the Molecular Recognition of AnionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2005Carolina Garau Abstract Noncovalent bonding between anions and the ,-cloud of electron-deficient aromatic rings has recently attracted considerable attention. Complexes of bromide with different electron-deficient aromatic rings and with other binding units based on hydrogen bonding (urea, thiourea and squaramide) have been studied and compared using high level B3LYP/6-31++G** ab initio and Molecular Interaction Potential with polarization (MIPp) calculations. Our findings reveal that electron-deficient aromatic rings are excellent candidates for constructing anion receptors and that the interaction strength can be modulated by the nature of the ring. Supporting experimental evidence has been obtained from X-ray structures retrieved from the Cambridge Structural Database. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Synthesis and Photophysical Properties of LnIII,DOTA,Bipy Complexes and LnIII,DOTA,Bipy,RuII Coordination ConjugatesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 28 2010Miguel Vázquez López Abstract The synthesis and the systematic and comparative photophysical study of a series of visible (EuIII, TbIII) and NIR-emitting (NdIII, YbIII) lanthanide complexes (Ln2L) and ruthenium,lanthanide coordination conjugates (Ln2LRu) are reported. The GdIII complex, the GdIII,RuII coordination conjugate, as well as the RuII complex of the ligand H6L have also been synthesized and photophysically studied as control systems. The ligand H6L, composed of a central bipyridine binding unit and functionalized on each 5,-position with a DOTA macrocycle, has been successfully synthesized from cyclen, 5,5,-dimethyl-2,2,-bipyridine and 1,2-ethylendiamine in a nine-step process. Detailed luminescence studies of all complexes, including the determination of the quantum yield and lifetime, were carried out on finely powdered microcrystalline samples as well as in water, deuterated water and [D6]DMSO at ambient (295 K) and low temperature (77 K). The photophysical data corroborate the existence of energy transfer in the Ln2L complexes and in the Nd2LRu coordination conjugate. However, no (or at most, very little) energy transfer is takes place from the Ru(bipy)3 chromophore to the LnIII ion in the other Ln2LRu heteropolymetallic complexes. Moreover, the photophysical studies reveal that all the complexes and coordination conjugates adopt different conformations and hydration states in solution and in the solid state, which influences the efficiency of the energy transfer between the bipy and/or Ru(bipy)3 antennae and the LnIII ions. [source] Mixed-Valence, Mixed-Spin-State, and Heterometallic [2×2] Grid-type Arrays Based on Heteroditopic Hydrazone Ligands: Synthesis and Electrochemical FeaturesCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2005Lindsay H. Uppadine Dr. Abstract An extended family of heterometallic [M12M22(L,)4]n+ [2×2] grid-type arrays 1,9 has been prepared. The three-tiered synthetic route encompasses regioselective, redox and enantioselective features and is based on the stepwise construction of heteroditopic hydrazone ligands A,C. These ligands contain ionisable NH and nonionisable NMe hydrazone units, which allows the metal redox properties to be controlled according to the charge on the ligand binding pocket. The 2-pyrimidine (R) and 6-pyridine (R,) substituents have a significant effect on complex geometry and influence both the electrochemical and magnetic behaviour of the system. 1H NMR spectroscopic studies show that the FeII ions in the grid can be low spin, high spin or spin crossover depending on the steric effect of substituents R and R,. This steric effect has been manipulated to construct an unusual array possessing two low-spin and two spin-crossover FeII centres (grid 8). Electrochemical studies were performed for the grid-type arrays 1,9 and their respective mononuclear precursor complexes 10,13. The grids function as electron reservoirs and display up to eight monoelectronic, reversible reduction steps. These processes generally occur in pairs and are assigned to ligand-based reductions and to the CoIII/CoII redox couple. Individual metal ions in the heterometallic grid motif can be selectively addressed electrochemically (e.g., either the CoIII or FeII ions can be targeted in grids 2 and 5). The FeII oxidation potential is governed by the charge on the ligand binding unit, rather than the spin state, thus permitting facile electrochemical discrimination between the two types of FeII centre in 7 or in 8. Such multistable heterometallic [2×2] gridlike arrays are of great interest for future supramolecular devices incorporating multilevel redox activity. Une famille de complexes hétérométalliques [M12M22(L,)4]n+du type grille [2×2] 1,9 a été préparée. Les trois approches synthétiques multiétapes des ligands hydrazone hétéroditopiques A,C possèdent chacune des caractéristiques régio-, rédox-, énantio-sélectives. Ces ligands possèdent un groupement NH ionisable et un groupement hydrazone non-ionisable NMe, qui permettent un contrôle des propriétés rédox du métal complexé en fonction de la charge de la cavité coordinante. Les substituants 2-pyrimidine (R) et 6-pyridine (R,) influencent de manière significative la géométrie des complexes formés ainsi que leurs propriétés électrochimiques et magnétiques. Les études par spectroscopie RMN1H montrent que les ions FeII, dans ces complexes, possèdent une configuration électronique soit de bas spin, soit de haut spin ou encore de transition de spin en fonction de l'encombrement stérique du substituant. Cet effet stérique a été utilisé pour construire des grilles originales possédant deux cations FeIIde bas spin et deux cations FeIIà transition de spin (grille 8). Des études électrochimiques détaillées ont été réalisées pour les assemblages du type grille 1,9 et leurs précurseurs mononucléaires 10,13. Ces grilles fonctionnent comme réservoir à électrons. Jusqu'à huit étapes de réduction monoélectronique réversibles peuvent être observées. Ces transferts d'électrons se font généralement par paire et interviennent sur le ligand à l'exception des deux premières réductions correspondant aux couples CoIII/CoII. Chaque cation métallique d'une grille peut être sollicité sélectivement par voie électrochimique (les ions CoIIIou FeIIpeuvent être ciblés dans les grilles 2 et 5). Le potentiel d'oxydation du FeIIest tributaire de la charge des ligands et non de l'état de spin, permettant une discrimination électrochimique parmi les deux types de FeIIdans 7 ou 8. De telles grilles [2×2] hétérométalliques ont des niveaux de stabilité multiples et présentent un grand intérêt pour des systèmes supramoléculaires possédant une multiplicité de niveaux d'oxydo-réduction. [source] Synthesis and Luminescence Properties of New Dinuclear Complexes of Lanthanide(III) IonsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2004Violetta Patroniak Abstract As a result of coordination of the ligand L, containing two tridentate binding units, to samarium(III), europium(III), terbium(III), and dysprosium(III) ions, new dinuclear architectures containing two ions with coordination number 9 were formed. The structures of the complexes have been assigned on the basis of their solution spectroscopic and microanalytical data, and confirmed by X-ray crystallography in the case of the europium(III) complex 2. The structural analysis of the dinuclear complex 2 showed the presence of two europium centers [Eu(1) and Eu(2)] and four ligands L. Each europium ion is coordinated by 9 donor atoms with typical Eu,N and Eu,O distances. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] A Theoretical ab initio Study of the Capacity of Several Binding Units for the Molecular Recognition of AnionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2005Carolina Garau Abstract Noncovalent bonding between anions and the ,-cloud of electron-deficient aromatic rings has recently attracted considerable attention. Complexes of bromide with different electron-deficient aromatic rings and with other binding units based on hydrogen bonding (urea, thiourea and squaramide) have been studied and compared using high level B3LYP/6-31++G** ab initio and Molecular Interaction Potential with polarization (MIPp) calculations. Our findings reveal that electron-deficient aromatic rings are excellent candidates for constructing anion receptors and that the interaction strength can be modulated by the nature of the ring. Supporting experimental evidence has been obtained from X-ray structures retrieved from the Cambridge Structural Database. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Salivary mucin as related to oral Streptococcus mutans in elderly peopleMOLECULAR ORAL MICROBIOLOGY, Issue 1 2000L. W. Baughan MG1 (MUC5b and MUC4 ) and MG2 (MUC7), predominant mucins in human whole saliva, provide lubrication and antimicrobial protection for oral tissues. This study examines potential relationships between Streptococcus mutans titers in the oral cavity and the following: mucin concentrations; unstimulated and stimulated whole saliva flow rates; decayed, missing, and filled tooth surfaces; and age of 24 elderly patients. S. mutans titers were determined using Denticult SM. Mucin concentrations were determined using Stains-all, sodium dodecyl sulfate,polyacrylamide gel electrophoresis. Logistic regression was used to identify potential relationships between the above variables. S. mutans classification served as the dependent variable. The remaining variables were possible predictor variables. The best model for predicting S. mutans category contained log MG2 as a predictor variable for all of its parameter estimates. No other set of parameter estimates were statistically significant. These results suggest that elevated S. mutans titers are significantly associated with diminished concentrations of MG2 in unstimulated whole saliva, as quantified in mucin-dye binding units. [source] | ||||||||||