Barbiturates, dansylation

Consistent with the principles outlined in Chapter 1, strong hydrogen-bonded association may be achieved by multiple complementary interactions, as in the barbiturate-appended porphyrin system shown in 11.21 (cf. molecular rosettes, Section 10.6.4). This receptor binds a complementary dansyl (dimethylaminonapthalene-sulfonyl) group with an association constant in excess of 106 M-1. In this case, electron transfer is from the photoabsorbing dansyl group to the porphyrin acceptor quenching is almost total, suggesting very fast electron transfer relative to the rate of fluorescence.12... 

Unfortunately, the hydrolysis product, dansylic acid is strongly fluorescent and can cause interferences with water-soluble derivatives. These derivatives, however, are often removed by the subsequent chromatographic process. The detection limits of the dansyl derivatives are often in the low nanogram range (ca. 1 x 10" g/ml) and the excitation and emission maxima can vary between 350-370 nm excitation and 490-540 nra emission. Some examples of the application of this reagent are in the analysis of amino acids (13), alkaloids (14), barbiturates (15) and pesticides (16). 

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