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A GAAA tetraloop domain and receptor domain are connected by a single-strander A7 linker to investigate the metal ion dependence, kinetics and thermodynamics for the isolated tertiary interaction in RNA of the GAAA-tetraloop motif. Studies of docking induced using a variety of metal ions show that the single-stranded region functions primarily as a flexible tether and inhibition of docking by oligonucleotides complementary to the linker is investigated.

Docking kinetics and equilibrium of fluorescently labeled RNA molecules are studied with single-molecule FRET methods. Time-resolved FRET is used to monitor docking/undocking transitions for RNAs containing a single GAAA tetraloop-receptor tertiary inter-action connected by a flexible single-stranded linker. The rate constants for docking and undocking are measured as a function of [Mg.sup.2+], revealing a complex dependence on metal ion concentration. Despite the simplicity of this model system, conformational heterogeneity similar to that noted in more complex RNA systems is observed; relatively rapid docking/undocking transitions are detected for approximately two-thirds of the RNA molecules, with significant subpopulations exhibiting few or no transitions on the 10- to 30-s time scale for photobleaching. The rate constants are determined from analysis of probability densities, which allows a much wider range of time scales to be analyzed than standard histogram procedures. The data for the GAAA tetraloop receptor are compared with kinetic and equilibrium data for other RNA tertiary interactions. RNA | tertiary interactions | heterogeneity | time-correlated single photon counting

A transient absorption spectroscopic study of the photosensitization of differently sized TiO2 nanoparticles by anthracenecarboxylic acid dye molecules is reported.

The development of dye-sensitized semiconductor systems spawned scientific interest on factors affecting back electron transfer dynamics. Experiments were conducted to characterize the Marcus inverted region. The effects of water on the forward and back electron transfers in 9-anthracenecarboxylic acid (9AC) bound to titanium dioxide particles were also examined. The findings indicated a slight increase in back electron transfer reactions upon the addition of water and confirmed the Marcus inverted region as the site where high rates of this reaction occur.

An attempt is made to investigate the laser-induced melting and alloy formation in AucoreAgshell nanoparticles and the associated spectral changes. The thresholds for laser-induced transformations are lower for picosecond laser pulses compared to nanosecond laser pulses.

The photophysics of metal nanoparticles, that include Au particles with sizes ranging from 2nm diameter to 120nm diameter, and bimetallic core-shell particles composed of Au, Ag, Pt and/or Pb are investigated. The findings indicate that for Au the time scale for electron-phonon coupling does not depend on size, in contrast to metals such as Ga and Ag.

A study was conducted to analyze the influence of structure on the electron transfer reactions between anthracene dyes and TiO2 nanoparticles. Controlled hydrolysis was carried in water of titanium(IV) isopropoxide to prepare anatase TiO2 nanoparticles. The Perkin-Elmer Lambda 6UV-vis spectrometer was then utilized to obtain steady-state absorption spectra. Results indicated that the preparation of the particles influenced the time constants for electron transfer for semiconductor particles-bound dye molecules.

Femtosecond transient absorption spectroscopic studies were conducted to investigate the electron-phonon relaxation dynamics in nanometer-sized gold and silver (Ag) particles. Simple spectral calculations were combined with two-temperature model for electron-phonon equilibration. The findings showed that strong transient bleach at the peak of the plasmon band are caused by pump-laser-induced heating and that the transient bleach signal for Ag increased after a high pump laser power. Moreover, electron-phonon coupling in small metal particles can only be obtained at low excitation levels.