Fine tuning of MLCT states in new mononuclear complexes of ruthenium(II) containing tris(1-pyrazolyl)methane, 2,2′-bipyridine and aromatic nitrogen heterocycles

The syntheses of new mononuclear ruthenium(II) complexes of the type: [Ru(bpy)(L)(tpm)](PF6)2 {tpm = tris(1-pyrazolyl)-methane; bpy = 2,2′-bipyridine; L = pz (pyrazine; 1), 4,4′-bpy (4,4′-bipyridine; 2), and bpe [trans-1,2-bis(4-pyridyl)ethylene; 3]} are described, together with their spectroscopic, electrochemical, and photophysical properties. A complete assignment of the NMR resonances of the three species could be made in CD3CN by bidimensional techniques. A fine tuning of the energies of MLCT (metal-to-ligand charge transfer) states in these complexes is disclosed when comparing, in CH3CN, the values of their maximum absorption wave-lengths for the most intense visible bands (λ max) and their redox potentials for the RuIII/Ru II couples; this effect, relevant to the design of efficient photocatalysts, can be attributed to a decreasing order of dπ(Ru) →*(2,2′-bpy) backbonding when decreasing the distance between both N atoms in the aromatic nitrogen heterocycle L that acts in a monodentate manner. Only the species with L = bpe emits at room temperature, pointing to the conclusion that MLCT excited states in this series become higher in energy than dd excited states when the value of λmax is lower than 400 nm. These species are also useful building blocks for new dinuclear mixed-valent complexes. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.Fil: Katz, Néstor Eduardo. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; ArgentinaFil: Romero, Isabel. Universidad de Girona; EspañaFil: Llobet, Antoni. Universidad de Girona; EspañaFil: Parella, Teodor. Universitat Autònoma de Barcelona; EspañaFil: Benet Buchholz, Jordi. Bayer Industry Services; Alemani

Hydrogen-bond landscapes, geometry and energetics of squaric acid and its mono- and dianions: a Cambridge Structural Database, IsoStar and computational study

As part of a programme of work to extend central-group coverage in the Cambridge Crystallographic Data Centre's (CCDC) IsoStar knowledge base of intermolecular interactions, we have studied the hydrogen-bonding abilities of squaric acid (H(2)SQ) and its mono-and dianions (HSQ(-) and SQ(2-)) using the Cambridge Structural Database (CSD) along with dispersion-corrected density functional theory (DFT-D) calculations for a range of hydrogen-bonded dimers. The -OH and -C=O groups of H(2)SQ, HSQ(-) and SQ(2-) are potent donors and acceptors, as indicated by their hydrogenbond geometries in available crystal structures in the CSD, and by the attractive energies calculated for their dimers with acetone and methanol, which were used as model acceptors and donors. The two anions have sufficient examples in the CSD for their addition as new central groups in IsoStar. It is also shown that charge-and resonance-assisted hydrogen bonds involving H(2)SQ and HSQ(-) are similar in strength to those made by carboxylate COO- acceptors, while hydrogen bonds made by the dianion SQ(2-) are somewhat stronger. The study reinforces the value of squaric acid and its anions as cocrystal formers and their actual and potential importance as isosteric replacements for carboxylic acid and carboxylate functions

Biotin–specific synthetic receptors prepared using molecular imprinti

The composition of new molecularly imprinted polymers (MIPs) specific for biotin was optimised using molecular modelling software. Three functional monomers: methacrylic acid (MAA), 2-(trifluoromethyl)acrylic acid (TFAA) and 2-acrylamido- 2-methyl-propanesulfonic acid (AMPSA), which demonstrated the highest binding scores with biotin, were tested on their ability to generate specific binding sites. The imprinted polymers were photografted to the surface of polystyrene microspheres in water. The affinity of the synthetic "receptor" sites was evaluated in binding experiments using horseradish peroxidase-labelled biotin. A good correlation was found between the modelling results and the performance of the materials in the template rebinding study. The dissociation constants for all MIPs were 1.4-16.8 nM, which is sufficient for most analytical applications where biotin is used as a label

Optical sensing of pH using thin films of substituted polyanilines

Polyanilines (PANIs) are viable materials for use in optical sensing of pH. Thin films of substituted PANI readily deposit on the inner walls of polystyrene cuvettes when a substituted aniline is chemically polymerized in hydrochloric acid solution. The films have been characterized by absorption spectra which have maxima between 600 and 810 nm, except for halogenated or p-substituted anilines. They undergo pH-dependent changes in their absorption spectra in the physiological pH range, and substituents exhibit a strong effect on pKa values. PANI films are advantageous over indicator-based pH sensor films in that they are not based on the use of indicator dyes, are compatible with LED and diode laser light sources, and can easily be prepared. Copolymers of aniline and anthranilic acid are shown to be useful supports for immobilization of the enzyme urease, and the resulting films can be used to detect urea. Films of substituted PANIs are redox-active and also respond to reductants such as ascorbic acid and hydrogen sulfide