Study of the Nature of the Surface of Mixed Titanosilicas by Flash Photolysis of Adsorbed Pyrenemethanol

We have used nanosecond laser flash photolyis in diffuse reflectance mode to study processes of photoinduced charge transfer between an adsorbed acene (pyrenemethanol) and the surface of titanosilicas containing 1% TiO₂, and we have determined the role of titanium in the processes of adsorption and formation of radical cations. We have shown that the nature of the reactivity of mixed TiO₂/SiO₂ materials is determined by synthesis method (sol–gel or impregnation).     

Ruthenium,osmium and rhodium-2,3-bis(2′-pyridyl)quinoxaline complexes

Ru₃(CO)₁₂ reacts with 2,3-bis (2-pyridyl)quinoxaline (dpq) in benzene in the presence of either 2,2(dipyridine (dpy) or pyridine (py) to give the mononuclear complexes Ru(CO)₃(dpq) (1) and Ru(CO)₂(dpq)(py) (2), respectively. On the other hand, reactions of Os₃(CO)₁₂ with dpq alone, or in the presence of dipyridine, yield only Os(CO)₃(dpq) (3). Spectroscopic studies of the three complexes were consistent with the proposed structures. Reactions of RuCl₃ with dpq, under reduced pressure in PhH/EtOH gave bis-[Ru(dpq)₂Cl₂]Cl (4). Magnetic measurements showed Ru^III, d⁵, to be in a low-spin electronic configuration. Three complexes, Rh₂(dpq)₂Cl₆ (5), [Rh(dpq)₂Cl₂]Cl (6) and Rh(dpq)(py)Cl₃ (7), were isolated from reactions of RhCl₃ with dpq. The type of product was dependent on the reactants and conditions. The complexes exhibit either irreversible or quasi-reversible ligand-based reductions. In addition, the zerovalent complexes (1)–(3) displayed one metal(based oxidation in their cyclic voltammograms, due to the formation of M⁺ species.     

Inclusion of Paracetamol into β-cyclodextrin nanocavities in solution and in the solid state

We report on steady-state UV-visible absorption and emission characteristics of Paracetamol, drug used as antipyretic agent, in water and within cyclodextrins (CDs): β-CD, 2-hydroxypropyl-β-CD (HP-β-CD) and 2,6-dimethyl-β-CD (Me-β-CD). The results reveal that Paracetamol forms a 1:1 inclusion complex with CD. Upon encapsulation, the emission intensity enhances, indicating a confinement effect of the nanocages on the photophysical behavior of the drug. Due to its methyl groups, the Me-β-CD shows the largest effect for the drug. The observed binding constant showing the following trend: Me-β-CD>HP-β-CD>β-CD. The less complexing effectiveness of HP-β-CD is due to the steric effect of the hydroxypropyl-substituents, which can hamper the inclusion of the guest molecules. The solid state inclusion complex was prepared by co-precipitation method and its characterization was investigated by Fourier transform infrared spectroscopy, 1H NMR and X-ray diffractometry. These approaches indicated that Paracetamol was able to form an inclusion complex with CDs, and the inclusion compounds exhibited different spectroscopic features and properties from Paracetamol.     

Flow injection fluorimetric determination of chromium(VI) in electroplating baths by luminescence quenching of tris(2,2'-bipyridyl) ruthenium(II)

A sensitive and selective luminescence quenching method is developed and used for manual and flow injection analysis (FIA) of chromium(VI) by reaction with [Ru(bpy)₃]²⁺. The emission peak of ruthenium(II) at 595 nm is linearly decreased as a function of Cr(VI) concentration. This permits determination of chromium(VI) ion over the concentration range 0.1-20 μg ml⁻¹ with a detection limit of 33 ng ml⁻¹. The quenching process is due to an electron transfer from the luminescent [Ru(bpy)₃]²⁺ complex ion to Cr(VI) resulting in the formation of the non-luminescent [Ru(bpy)₃]³⁺ complex ion. Selectivity for Cr(VI) over many anions and transition, alkali and alkaline earth metal cations is demonstrated. High concentration levels of sulphate, chloride, borate, acetate, phosphate, nitrate, cyanide, Pb²⁺, Zn²⁺, Hg²⁺, Cu²⁺, Cd²⁺, Ni²⁺ and Mn²⁺ ions are tolerated. The effects of solution pH and [Ru(bpy)₃]²⁺ reagent concentration are examined and the reaction conditions are optimized. Validation of the method according to the quality assurance standards show suitability of the proposed method for use in the quality control assessment of Cr(VI) in complex matrices without prior treatment. The method is successfully applied to determine chromium(VI) in electroplating baths using flow injection analysis. Results with a mean standard deviation of ±0.6% are obtained which compare fairly well with data obtained using atomic absorption spectrometry.