Introduction: Microdosimetry is a fundamental method that studies the nature of energy transfer in micron volumes in the particular biological cells. In a biological target, the amount of ionization does not indicate the magnitude of biological radiation-induced damage. However, the severity of biological harm depends strongly on the amount of the linear energy transfer along t...

The ultrafast excited state dynamics of the fluorescent protein Kaede has been investigated by employing time resolved fluorescence and transient absorption. Upon irradiation of its neutral state, the protein undergoes an efficient conversion to a state that fluoresces at longer wavelengths. The molecular basis of the photoconversion involves an expansion of the chromophore π-conjugation by for...

Förster resonance energy transfer (FRET) is a widely used single-molecule technique for measuring nanoscale distances from changes in the non-radiative transfer of energy between donor and acceptor fluorophores. For macromolecules and complexes this observed transfer efficiency is used to infer changes in molecular conformation under differing experimental conditions. However, sometimes shifts ...

Fluorescence resonance energy transfer (FRET) refers to the nonradiative transfer of energy from one fluorescent molecule (the donor) to another fluorescent molecule (the acceptor). Measurement of FRET between two fluorophore-labeled proteins can be used to infer the subnanometer spatial and temporal characteristics of protein interactions in their native cellular environment. Multiple experime...

Fluorescence resonance energy transfer provides valuable long-range distance information about macromolecules in solution. Fluorescein and Cy3 are an important donor-acceptor pair of fluorophores; the characteristic Förster length for this pair on DNA is 56 A, so the pair can be used to study relatively long distances. Measurement of FRET efficiency for a series of DNA duplexes terminally label...

Coumarin analogues were synthezised and evaluated as acceptors for the intrinsic fluorescence resonance energy transfer (iFRET) of tryptophan residues in target proteins. The fluorescence properties such as quantum yields, iFRET efficiencies, and Förster distances of the prepared coumarin analogs were determined in a model system, by their conjugation to biotin, utilizing streptavidin (SAV) as ...

Single molecule Förster resonance energy transfer (FRET) experiments are used to infer the properties of the denatured state ensemble (DSE) of proteins. From the measured average FRET efficiency, , the distance distribution P(R) is inferred by assuming that the DSE can be described as a polymer. The single parameter in the appropriate polymer model (Gaussian chain, wormlike chain, or self-av...

Single-molecule Förster resonance energy transfer (FRET) experiments are an important method for probing biomolecular structure and dynamics. The results from such experiments appear to be surprisingly independent of the excitation power used, in contradiction to the simple photophysical mechanism usually invoked for FRET. Here we show that excited-state annihilation processes are an essential ...

Forster resonance energy transfer (FRET) is a nonradiative transfer of energy between two fluorescent molecules (a donor and an acceptor) in nanometer range proximity. FRET imaging methods have been applied to proteomic studies and drug discovery applications based on intermolecular FRET efficiency measurements and stoichiometric measurements of FRET interaction as quantitative parameters of in...

Protein machines often exhibit long-range interplay between different sites in order to achieve their biological tasks. We investigate and characterize the nonlinear energy localization and the basic mechanisms of energy transfer in protein devices. By studying two different model protein machines, with different biological functions, we show that genuinely nonlinear phenomena are responsible f...