Guan-Sheng Jiao

Syntheses and spectroscopic properties of energy transfer systems based on squaraines

The purpose of this project was to prepare fluorescent dyes that could absorb energy at relatively short wavelengths, and fluoresce in the near-IR region. To achieve this, copper- and palladium-mediated C–N couplings were used to prepare the ‘cassettes’, i.e the carbazole derivative 3b and the carbazole-, phenothiazine-, and phenoazine-squaraines 4b–d. These compounds have carbazole, phenothiazine, and phenoazine donor-components that absorb around about 300–320 nm, and squaraine acceptor-parts that fluoresce in the range 650–700 nm. The efficiencies of energy transfer from the donor to the acceptor, and the overall quantum yields of the cassettes were determined.

Oligonucleotides with strongly fluorescent groups π-Conjugated to a nucleobase: syntheses, melting temperatures, and conformation

Phosphoramidite 1 was prepared, incorporated into oligonucleotides, and these were studied via thermal denaturation and circular dichroism.

On the stability of furanopyrimidin-2-one bases in oligonucleotidesElectronic supplementary information (ESI) available: experimental procedures for the preparation of the new compounds, protocols for the thermal denaturation and enzyme digestion experiments. See http://www.rsc.org/suppdata/cc/b4/b402559h/

The fluoresceinated furanopyrimidin-2-one nucleobase incorporated into an oligonucleotide undergoes unexpectedly facile hydrolytic ring-opening in aqueous buffer at slightly elevated temperatures.

Femtosecond-Domain Dynamical Studies of Energy-Transfer Cassettes

Energy-transfer labeling cassettes, having two different chromophores in the visible region, are widely used in the fluorescence-aided sequencing of DNA. After chemically selective binding of the labeling cassettes to different fragments of DNA followed by gel separation, the mixture is irradiated at a single laser wavelength. The resulting fluorescence in four different wavelength bands provides a means to color-code the fragments, which in turn can identify the terminal bases and provide a method for sequencing. Commercial labeling agents employ a fluorescein derivative as an energy absorber near 500 nm and four different chemically attached rhodamine derivatives to provide fluorescent signals in four resolvable bands. The dominant energy-transfer mechanism in such cassettes, where the chromophores are linked by partially saturated chains, is usually modeled according to a Forster energy transfer mechanism. New applications of fluorescent labels generate the need for alternative probe molecules, having greater chemical stability and rigid structure.