Tetraoxotetraamide macrocyclic complexes

A new class of 16- and 17-membered tetraamide macrocyclic complexes, [ML¹X₂] and [ML²X₂] [M = Mn^II, Co^II, Ni^II, Cu^II or Zn^II; X = NO₃ or Cl], have been prepared by the template reaction of anthranilic acid, 1,2-diaminoethane or 1,3-diaminopropane and succinic acid in 2:1:1 molar ratio. The stoichiometries and coordination modes of the complexes have been deduced from physicochemical and spectroscopic measurements. This revised version was published online in June 2006 with corrections to the Cover Date.     

An electrochemical study of the incorporation of cobalt macrocyclic complexes into nafion films

Cobalt complexes of the macrocyclic ligand, 2,3,9,10-tetramethyl-1,4, 8,11-tetraazacyclotetradeca-1,3,8,10-tetraene (TIM) and its hydroxy derivatives, were incorporated in Nafion films by electrochemical cycling and by ion exchange in aqueous solution. Cyclic voltammetric studies show that the redox potentials of the Co(TIM) complexes undergo a significant anodic shift when incorporated in the films. Electrochemical studies also indicate that, while the Co(TIM) complexes reside in hydrophilic regions of the Nafion film, the metallated porphine complex, cobalt tetrakis(pentafluorophenyl)porphine, is probably immobilized in hydrophobic regions. The incorporation of the complexes was also followed by electronic absorption spectrophotometry.     

Novel dithiolene complexes incorporating conjugated electroactive ligands

A series of new metal (M) dithiolene complexes bearing terthiophene (3, 12, M = Ni; 4, M = Pd; 5, 6, M = Au) and 2,5-bis(para-methoxyphenyl)thiophene units (14, M = Ni; 15, 16, M = Au; 17, M = Pd) have been synthesised in 38-99% yield. The electrochemical properties of the materials have been characterised by cyclic voltammetry and UV-vis spectroelectrochemistry. The nickel complexes possess low oxidation potentials (-0.12 to -0.25 V vs Ag/AgCl) due to the electron-rich dithiolene centres and all complexes display ligand-based redox activity. The terthiophene derivatives have been polymerised by electrochemical oxidation to give stable films with, in the case of poly(3), broad absorption characteristics. Charge transfer materials have been isolated from 14 and 16 with conductivities in the range 9 x 10(-6) to 7 x 10(-8) S cm(-1).     

Biomedical applications of macrocyclic ligand complexes

Macrocyclic chelators can form highly stable complexes with transition metals and lanthanides. In this review, the recent advances towards biomedical applications of macrocyclic complexes are outlined. The use of such complexes in imaging as MRI contrast agents, radiopharmaceuticals and luminescent probes is discussed. The considerable scope for future development of novel metal based therapeutics based on protein binding, targeting of radioisotopes or dual function agents is also highlighted.     

Instabilities during the formation of electroactive polymer thin films

The solvent-induced film structure of poly(n-vinyl carbazole) (PVK) thin films on indium tin oxide (ITO)-coated glass was examined. PVK thin films were prepared via spin-coating using five different solvents. We investigated the relationship between the solvent characteristics and film properties, including surface roughness and structure, film thickness, and density. The spin-coated polymer thin films are not in thermodynamic equilibrium; rather, the film properties are affected by the dynamics of the spin-coating process. We found that water present in tetrahydrofuran (THF) induces dewetting of PVK films during the spin-coating process. Solvents with a high evaporation rate lead to high surface roughness due to Marangoni convection. The results show that the surface roughness and structure of the films are dominated by the dynamics of the film formation process, rather than thermodynamic interactions between the polymer and solvents.     

The structures of macrocyclic heterocyclophane inclusion complexes

Crystal and molecular structures of (1:1) molecular complexes of N,N,N,N-tetramethyl-2, 11, 20, 29-tetraaza [3.3.3.3] paracyclophane (1) with CHCl₃, CH₂Cl₂, CH₃CN and CO₂ are reported. The macrocycle has square-box structure, giving hydrophobic cavity surrounded by four benzene rings. The guest molecules are included in the cavity. The uncomplexed1 was found to have a rectangular form, indicating large conformational flexibility of1. In solution,1 is achiral because rapid RS interconversion, but in solid, the macrocyclic conformation is frozen as R-conformer or S-conformer. The macrocycles with the same chirality are stacked alongb-axis to form chiral molecular columns, R-colums or S-columns. Complexes of1 crystallize differently depending on the guest molecules. R-columns (S-columns) packed alonga-axis produce R-layers (S-layers), which are further packed alongc-axis using R-layer to R-layer contact (RR) or SS and RS or SR. The crystals of1·CHCl₃ are formulated as--RRR--=[R]_n (Type I, chiral) and those of1·CH₃CN or1·CO₂ and1·CH₂Cl₂ are represented by [RS]_n (Type IIA, racemic) and [RRSS]_n (Type IIB, racemic), respectively.     

五氮齿大环金属配合物的光褪色动力学研究

五氮齿大环金属配合物是一类具有潜在应用价值的非线性光学材料。在不同溶液中研究了六种五氮齿金属配合物对不同波长及不同光强下的光褪色动力学过程,实验证明,褪色过程对反应物的初始浓度呈零级反应,是一个受光强控制的光化学过程。光褪色速率常数,对于≥500nm的可见光在1.2×10^-7(苯)～2.0×10^-5h^-1(甲醇)范围内,短波长的可见光使光褪色速率增大一个数量级。吸电子取代基和大半径的金属离子以及强极性溶剂均使该类配合物的光褪色速率增大,但仍然显示出较高的光稳定性。     

Nanoparticle routes to mesoporous titania thin films

Controlled aging of TiO2 nanoparticles blended with diblock copolymers and processed into dip-coated thin films led to ordered mesostructures with cubic and hexagonal symmetries that can be transformed into mesoporous TiO2 by calcination.     

Oscillatory Briggs-Rauscher reactions involving macrocyclic transition-metal complexes

New forms have been observed for oscillatory Briggs-Rauscher reactions catalyzed by macrocyclic nickel complexes. The number of oscillations in the reaction increases in the presence of cobalt complexes. Suggestions are made on how the catalysts act in these systems.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 3, pp. 167–171, May–June, 1994.     

Transition metal ion directed bimetallic macrocyclic complexes

Template condensation of 1,4-phenylenediamine, formaldehyde, 1,3-diaminopropane and benzil in a 1:4:4:2, molar ratio results in the formation of a new series of binuclear decaazamacrocyclic complexes: dichloro/nitrato [1-phenyl bis(8,9-diphenyl-1,3,7,10,14 pentaazacyclo-pentadeca-7,9-diene) metal (II)], [M₂LX₄](M = MnII, Co^II, Ni^II, CuII and Zn^II, X = Cl or NO₃), which were characterised by i.r., ¹H-n.m.r., e.p.r., u.v–vis. spectral studies, conductivity and magnetic susceptibility measurements. All the complexes show octahedral geometry.     

Optical properties of hybrid dendritic-mesoporous titania nanocomposite films

New hybrid optical sensors have been prepared by grafting specifically designed fluorescent, functionalised, phosphorus-containing dendrimers onto a nanocrystalline mesoporous titania thin film formed by evaporation-induced self-assembly. The structural characterisation and optical behaviour of these new fluorescent probes have been studied both in solution and after being grafted onto an inorganic network, which resulted in the discovery of improved probing selectivity in the solid state. This new hybrid sensor exhibits high sensitivity to phenolic OH moieties (especially those from resorcinol and 2-nitroresorcinol), which induce the quenching of fluorescence more efficiently in the solid state than in solution. This effect is a result of the increased spatial proximity of the fluorescent molecules, which is induced by pore confinement that makes the formation of hydrogen bonds between the hydroxyl moieties of the quenchers and the carbonyl groups of the dendrimer easier.     

Temperature programmed desorption analysis of sol-gel-derived titania films

Sol-gel-derived titania films were analyzed by temperature programmed desorption (TPD) and X-ray diffraction (XRD) techniques. The relationship between the TPD curves measured for two types of titania gel films and their crystal structures was investigated. On the basis of the analyses, a preparation process for a titania sol solution containing anatase nanocrystals was designed and developed. Using this process, a colloidal anatase titania sol solution was prepared by heating aqueous titanium hydroxide containing HCl at 60°C for 2 h. The nanocrystal structure of the titania films obtained by coating the sol on glass substrates was confirmed by TPD and XRD measurements.     

Quasi-reversible voltammetric response of electrodes coated with electroactive monolayer films

Quasi-reversible voltammetric response of the surface-confined redox species is treated, including both ion pairing and double-layer effects. The Smith–White model and the Butler–Volmer formulation are chosen as the electrode|solution interface model and the electrode kinetics, respectively. An algorithm to simulate the voltammogram is derived.     

Cathodically deposited polypyridine films: A novel electroactive polyconjugated polymer

Poly-2,5- and poly-2,6-pyridine coatings have been produced on glassy-carbon electrodes by nickelcatalysed reduction of the corresponding dibromopyridine in acetonitrile. Poly-2,5-pyridine films display two reversible cathodic cycles, one of which is due to nickel ions coordinated to pyridine moieties and the other to the polymeric backbone. Both reductions lead to the polymer changing from the insulating to the conductive state. Conversely, Poly-2,6-pyridine films are not reversibly electroactive and the differences are discussed in terms of conjugation along the polymeric chain.     

Assembly of layer-by-layer films of electroactive hemoglobin and surfactant didodecyldimethylammonium bromide

When a solid substrate with negative surface charges was placed in an aqueous didodecyldimethylammonium bromide (DDAB) vesicle dispersion, the cationic surfactant DDAB with two hydrocarbon chains could be assembled into the biomembrane-like tail-to-tail double-layer structure on the solid surface with the positively charged head groups toward outside, making the surface charge reverse from negative to positive. After the solid substrate with DDAB was immersed in a hemoglobin (Hb) solution at pH 9.0, the negatively charged Hb was adsorbed on the surface of DDAB layer by electrostatic attraction, forming a DDAB/Hb film. By repeating this adsorption cycle, the {DDAB/Hb}(n) layer-by-layer films were assembled on solid surfaces, which was confirmed by UV-vis spectroscopy, quartz crystal microbalance (QCM), and cyclic voltammetry (CV). The stable {DDAB/Hb}(n) films assembled on pyrolytic graphite (PG) electrodes showed two pairs of nearly reversible redox peaks at about -0.22 and -1.14 V vs SCE in pH 7.0 buffers, characteristic of the Hb heme Fe(III)/Fe(II) and Fe(II)/Fe(I) redox couples, respectively. The direct electrochemistry of Hb in the films could be used to electrocatalyze reduction of various substrates. UV-vis and IR spectroscopic results and comparison experiments with {DDAB/hemin}(n) films indicate that Hb in the {DDAB/Hb}(n) films essentially retains its native structure. Atomic force microscopy (AFM) was used to characterize the morphology of the films with different outermost layers.     

Covalent association of polyaza macrocyclic units to the electroactive tetrathiafulvalene moiety: synthesis and structural analysis

The synthesis of new macrocyclic receptors associating the electroactive tetrathiafulvalene unit (TTF) to different polyaza ligands is described. The structure of these receptors varies by the size of the coordinating unit (polyaza chains of various lengths), and by the nature of the latter, since a macrocyclic cyclam or a diazatetraoxa macrocycle derivative has been also introduced. The X-ray diffraction study on a single crystal of one of these receptors, demonstrates the electroactive TTF framework to be planar enough to present the expected reversible electrochemical behaviour. A preliminary study of the coordination ability of these polyazaTTF receptors is also given. To cite this article: G. Trippé et al., C. R. Chimie 6 (2003).