Time-Resolved Fluorescence Anisotropy Study of the Interaction Between DNA and a Peptide Truncated from the p53 Protein Core Domain.

Time-resolved fluorescence anisotropy spectroscopy was applied to study the interaction between a peptide truncated from the binding site of tumor suppressor p53 protein and the DNAs covalently labeled with 6-carboxyfluorescein (FAM) dye. Fluorescence intensity quenching and changes of anisotropy decay lifetime were monitored when FAM labeled DNA formed complex with the peptide. The results demonstrated that the sequence of DNA could not define the binding specificity between the peptide and DNA. But the anisotropy decay of FAM can be used to examine the binding affinity of the peptide to DNA. The fluorescent dynamics of FAM can also be used to represent the rigidity of the complex formed between the peptide and DNA.

Laser-induced fluorescence of isobutoxy in competition with ground state decomposition.

Spectroscopic detection is an important method to monitor alkoxy radicals in atmospheric photochemistry studies. In this work, we report the first observation of the laser-induced fluorescence (LIF) spectra of isobutoxy, 2-methyl-1-butoxy, and 3-methyl-1-butoxy in supersonic jet-cooled condition. Ground state unimolecular decomposition and isomerization as well as excited state relaxation dynamics of isobutoxy were discussed in combination with the theoretical calculations. Analysis of the experimental and theoretical results showed that methyl substitution on the ß carbon of the alkoxy radicals changed the LIF spectra of alkoxy radicals significantly. The competition between the ground state reactions and the photoexcitation process depended strongly on the radical structure and hence affected the involvement of alkoxy radicals in the photochemical reactions in the upper troposphere. This study will help to understand the dynamic role of alkoxy radicals in the atmosphere.

Vibrationally resolved LIF spectrum of tertiary methylcyclohexoxy radical.

Cyclohexoxy radical and its substitutes are intermediates of the combustion reaction in automobile engines, and hence play an important role in the atmospheric chemistry. Spectroscopic and conformational studies can provide convenient methods to monitor these species. In this work, we report the observation of the laser induced fluorescence (LIF) excitation spectrum of 1-methylcyclohexoxy, a tertiary ring alkoxy radical, in supersonic jet condition. The spectrum was assigned preliminarily to the chair-axial and chair-equatorial conformers of 1-methylcyclohexoxy. No C-O stretch progression was observed in 1-methylcyclohexoxy spectrum, which was different from t-butoxy. The short lifetime of excited state 1-methylcyclohexoxy and increased C-O bond length suggested a less stable excited state induced by the increased steric repulsion via methyl substitution on the alkoxy carbon. Dissociation rather than H transfer was suggested as the major nonradiative relaxation process, which competed with the fluorescence path.