Distributions of distances in donor-acceptor pairs

The donor-acceptor distance may not be unique, especially when the donor and acceptor are linked by a flexible chain (e.g. end-labeled oligomers of polymethylene or polyethylene oxide, oligopeptides, oligonucleotides, polymer chains). 

The most commonly used method for the evaluation of a distribution of distances is based on the measurement of the donor fluorescence decay3. If the 5-response of the donor fluorescence is a single exponential in the absence of acceptor, it becomes multi-exponential in the presence of acceptor  

In the case of fluorophores linked by a flexible chain, the distance distribution is 

Interestingly, one of the conformers obtained from data analysis corresponds to the bound conformation of the same chain in a biantennary oligosaccharide-lectin complex from X-ray diffraction. 

The flexibility of the sugar linkages in glycoproteins results in multiple conformations that can be detected by time-resolved fluorescence experiments. 

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