Voltage-Controlled Fluorometry of the Transfer of Nonfluorescent Ions across the 1,2-Dichloroethane/Water Interface Using Fluorescent Ionophores.

The voltage-driven transfer of alkali and alkaline-earth metal ions across the polarized 1,2-dichloroethane (DCE)/water interface has been measured fluorometrically by using two fluorescent ionophores, coumarin 153-linked monoaza-15-crown-5 (C153-crown(O(4))) and two-coumarin 153-linked diaza-18-crown-6 ((C153)(2)-K(22)). The 1:1 complex formation prevails for both monovalent and divalent ion transfer, when the concentration of C153-crown(O(4)) in DCE is at the micromolar level. In the Mg(2+) ion transfer, the formation of the 1:2 (metal-ligand) complex becomes significant at the millimolar level of C153-crown(O(4)). C153-crown(O(4)) seems to adsorb at the interface. The complexation of Ba(2+) with (C153)(2)-K(22) is significantly slower than the complexation with C153-crown(O(4)).

Fluorescence energy transfer as a probe for nucleic acid structures and sequences.

The primary or secondary structure of single-stranded nucleic acids has been investigated with fluorescent oligonucleotides, i.e., oligonucleotides covalently linked to a fluorescent dye. Five different chromophores were used: 2-methoxy-6-chloro-9-amino-acridine, coumarin 500, fluorescein, rhodamine and ethidium. The chemical synthesis of derivatized oligonucleotides is described. Hybridization of two fluorescent oligonucleotides to adjacent nucleic acid sequences led to fluorescence excitation energy transfer between the donor and the acceptor dyes. This phenomenon was used to probe primary and secondary structures of DNA fragments and the orientation of oligodeoxynucleotides synthesized with the alpha-anomers of nucleoside units. Fluorescence energy transfer can be used to reveal the formation of hairpin structures and the translocation of genes between two chromosomes.

A new concept of photogeneration of cations: Evidence for photoejection of Ca(2+) and Li (+) from complexes with a crown-ether-linked merocyanine by picosecond spectroscopy.

Time-resolved transient absorption and gain spectra of DCM-crown and its complexes with Li(+) and Ca(2+) in acetonitrile are measured in the wavelength range 370-670 nm after subpicosecond excitation at 425 nm. The results give evidence for the fast formation of free DCM-crown from both excited complexes, with a faster rate for the Li(+) complex. A two-step mechanism is found for the initial decay (within 30 ps) of the free DCM-crown.

Coumarinic fluorescent chemosensors for the detection of transition metal ions.

Fluoroionophores consisting of coumarin-153 linked to mono- and diaza-crown ethers are able to complex transition metal cations (Ni(2+), Zn(2+), Cd(2+)) and Pb(2+), with concomitant large changes in photophysical properties. The stability constants in acetonitrile are higher than 3×10(6) M (-1) except for Ni(2+).