A mixed MgF 2 -MgO system has been tested as a potential support of iridium catalysts in the hydrodesulfurization of thiophene. Samples of MgF 2 -MgO with different contents of MgO (0-100%) have been prepared by one-step sol-gel method in the reaction of magnesium methoxide dissolved in methanol with hydrofluoric acid. They have been used as supports for the synthesis of iridium (1 wt% Ir) catalysts. The supports have been characterized by XRD, low temperature nitrogen adsorption and thermogravimetric measurements. The one-step method of MgF 2 -MgO synthesis has been shown to permit the control of MgO content in the mixed system. The MgF 2 -MgO samples are classified as mesoporous, of large surface area (100-450 m 2 g -1 ) depending on the amount of MgO introduced, with the maximum for 71 mol% MgO. The presence of two phases in the mixture delays the process of both MgF 2 and MgO crystallization and increases the resistance of the MgF 2 -MgO texture to treatment at temperatures up to 800°C. The catalysts obtained by deposition of the iridium phase on MgF 2 , MgO and MgF 2 -MgO (62 mol% MgO) calcined at 400-700°C, have been tested in the reaction of hydrodesulfurization of thiophene. The most active has been the iridium catalyst supported on MgF 2 -MgO.

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Dedicated to Professor Andre¬ M. Braun on the occasion of his 60th birthday A simple and efficient transformation of the zwitterionic luminarosine into a brightly fluorescent cationic analogue, namely 1-amino-9-methoxy-2,4,10-triaza-4b-azoniaphenanthrene (3), is reported. The fluorescence quenching of 3 by common nucleotides, calf-thymus (CT) DNA, and halide ions was investigated by means of spectrophotometric and spectrofluorometric methods. Intermolecular static and dynamic fluorescencequenching constants for quenching of 3 by nucleotides and halide ions were determined in aqueous solution. Evidence for formation of nonfluorescent ground-state complexes of 3 with nucleotides and CT-DNA is presented. Scatchard analysis of the CT-DNA quenching data resulted in a binding constant of 2.8 Â 10 4 m À1 and a number of binding sites per base pair of 0.049., which has excitation and emission maxima at 430 and 530 nm in aqueous solution, belongs to a rather limited number of modified nucleosides that absorb and emit light in the visible region. The attractive photophysical properties of this compound [2], as well as its chemical stability under oligonucleotide-synthesis conditions, make it an excellent candidate for a fluorescent probe of nucleic acids and other biological systems. Sequence-specific introduction of this fluorophore into oligodeoxynucleotides has already been achieved [3]. Recent studies on fluorescence quenching of the parent de-O-acetylated nucleoside (luminarosine) and the aglycone (luminarine) by I À ions in living cells revealed the great potential of the former as a long-wavelength iodidesensitive fluorescent indicator for measurements of the cystic fibrosis transmembraneconductance regulator (CFTR) gene expression in cells [4]. The high intracellular fluorescence of the luminarosine, combined with its red-shifted emission and I À selectivity, make it superior to quinolinium-based halide indicators and indicates its possible application in the high-throughput screening of compounds for correction of the cystic fibrosis phenotype. Encouraged by these findings, we have undertaken the synthesis and detailed photophysical studies of some analogues of the luminarosine modified within the chromophoric part in the hope of obtaining fluorophores of different and possibly improved photophysical properties. In this communication, we present the simple and efficient transformation of the zwitterionic luminarosine into another very bright fluorophore, namely its cationic analog, 1-amino-9-methoxy-2,4,10-triaza-4b-azoniaphenanthrene (3). The spectral properties as well as the results of a fluorescence-quenching study of 3 by common nucleotides and halide ions is discussed.