Enantiomer-selective ultraviolet photolysis of temperature-controlled protonated tryptophan on a chiral crown ether in the gas phase

Enantiomer-selective ultraviolet photolysis of temperature-controlled protonated tryptophan (TrpH+) on the chiral crown ether, (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (18C6TA), was examined using a tandem mass spectrometer containing a temperature-variable 22-pole ion trap. The spectra of d-TrpH+-(+)-18C6TA at 9–320 K showed that the loss of NH2CH2COOH due to CαCβ bond cleavage decreased gradually with increasing temperature. The spectrum at room temperature was similar to that of l-TrpH+-(+)-18C6TA, which showed no temperature dependence on photolysis. The chiral-specific photolysis of cold d-TrpH+-(+)-18C6TA was attributed to the structures involving the chiral-dependent interactions of the CαH group of TrpH+ with the oxygen atoms of (+)-18C6TA.