Fluorescence of certain metal 8-quinolinolates as a function of solvent and substituents

Synthesis, structural characterization, experimental, and computational spectrophotometric studies of 8-quinolinyloxymethyphosphonate compounds

The synthesis of diethyl-8-quinolinyloxymethylphosphonate 1 and 8-quinolinyloxymethylphosphonic acid hemihydroiodide 2 is reported along with their spectroscopic and analytical characteristics (NMR, infrared, mass spectra, and elemental analysis). The single-crystal X-ray structure of 2 is described. Solutions of the disodium phosphonate 3, from 2 and sodium hydroxide, were prepared and used in situ. The coordination complex between 1 and zinc chloride 4 is described according to its single-crystal X-ray structure. The spectrophotometric features (absorption and emission) of 1, 2, 3, and 4 are reported along with the fluorescence response and affinity of 3 to some metal cations. The origin of the fluorescence from compounds 1 and 4 is investigated using density functional theory and the oscillator strength for each transition is computed. Two deactivation pathways, one of which is only weakly emissive, are identified in 4. In contrast to 4, which is only moderately more emissive than 1 a strong zinc-activated fluorescence response is observed from aqueous solutions of 3.

7-Trifluoromethylquinoline-Functionalized Luminescent Photochromic Spiropyran with the Stable Merocyanine Species Both in Solution and in the Solid State

A new spiropyran (SP2) with the stable merocyanine form (MC2) both in solution and in the solid state at room temperature was designed and synthesized. The stability of MC2 is believed to be due to the electron-withdrawing effect of both the quinoline and the trifluoromethyl groups. (1)H NMR spectra indicate that the ratio of the open form vs the closed form of SP2 is dependent on the polarity of solvents. Single crystals composed of only the open form (MC2) were successfully obtained. X-ray structural analysis indicates that except trifluoromethyl and two methyl groups MC2 is completely planar with an s-trans,s-cis conformation. It should be noted that this is the first report of the X-ray crystal structure of the pure open form of spiropyran. MC2 can be slowly transformed into SP2 at -30 degrees C or lower temperature, and the process is accelerated by visible light irradiation. This special photochromic behavior can be explained by the calculated thermodynamic data. The spectral properties of SP2/MC2 in the presence of different metal ions are also studied, and the results show the potential application of SP2/MC2 in sensing metal ions.

Mutagenesis Studies of Protein Farnesyltransferase Implicate Aspartate β352 as a Magnesium Ligand

Protein farnesyltransferase (FTase) catalyzes the addition of a farnesyl chain onto the sulfur of a C-terminal cysteine of a protein substrate. Magnesium ions enhance farnesylation catalyzed by FTase by several hundred-fold, with a KMg value of 4 mM. The magnesium ion is proposed to coordinate the diphosphate leaving group of farnesyldiphosphate (FPP) to stabilize the developing charge in the farnesylation transition state. Here we further investigate the magnesium binding site using mutagenesis and biochemical studies. Free FPP binds Mg2+ with a Kd of 120 microM. The 10-fold weaker affinity for Mg2+ observed for the FTase.FPP.peptide ternary complex is probably caused by the positive charges in the diphosphate binding pocket of FTase. Furthermore, mutation of aspartate beta 352 to alanine (D beta 352A) or lysine (D beta 352K) in FTase drastically alters the Mg2+ dependence of FTase catalysis without dramatically affecting the rate constant of farnesylation minus magnesium or the binding affinity of either substrate. In D beta 352A FTase, the KMg increases 28-fold to 110 +/- 30 mM, and the farnesylation rate constant at saturating Mg2+ decreases 27-fold to 0.30 +/- 0.05 s-1. Substitution of a lysine for Asp-beta 352 removes the magnesium activation of farnesylation catalyzed by FTase but does not significantly enhance the rate constant for farnesylation in the absence of Mg2+. In wild type FTase, Mg2+ can be replaced by Mn2+ with a 2-fold lower KMn (2 mM). These results suggest both that Mg2+ coordinates the side chain carboxylate of Asp-beta 352 and that the role of magnesium in the reaction includes positioning the FPP prior to catalysis.

Electrochemiluminescence of tris(8-hydroxyquinoline-5-sulfonic acid)aluminum(III) in aqueous solution

The electrochemiluminescence (ECL) of tris(8-hydroxyquinoline-5-sulfonic acid)aluminum(III) in aqueous solution is reported. ECL is generated by complexing aluminum ions with the chelating agent 8-hydroxyquinoline-5-sulfonic acid (HQS) to form Al(HQS)3, followed by oxidation in the presence of tri-n-propylamine (TPrA). The ECL intensity peaks a potential corresponding to oxidation of both TPrA and Al(HQS)3, and the ECL emission spectrum (lambda(max) = 499 nm) matches the photoluminescence emission spectrum, indicating that the emission is from a Al(HQS)3* excited state. ECL efficiencies (phi(ecl), photons generated per redox event) of 0.002 using Ru(bpy)3(2+) (phi(ecl) = 1) as relative standard. Conditions for ECL emission were optimized and used to generate a calibration curve that was linear over the 7 x 10(-6)-4 x 10(-4) M (5-281 mg/L (ppm)) range with a theoretical limit of detection of 1 ppm. The ECL of several metal ions other than aluminum with HQS and effects on Al(HQS)3 ECL were also examined.