PHOTORESPONSIVE SYNTHETIC RECEPTORS - BINDING-PROPERTIES AND PHOTOCONTROL OF CATALYTIC ACTIVITY

The photoresponsive ditopic receptors 1a,b bearing two adenine binding sites linked by an azobenzene moiety were prepared. Photochromism, bi nding of mono- and bis-adenine derivatives and template effects on the coupling reaction of aminoadenosine 2 and the adenosine-derived activ e ester-3 were studied. Photoswitching of the azobenzene linker from t he extended E to the folded Z isomer enhances the catalytic activity o f the template 1a by a factor of 50. The binding studies provide evide nce for the formation of termolecular complexes 1 . 2 . 3 and allow fo r mechanistic considerations. The influence of various adenine derivat ives on the rate of the thermal Z --> E isomerization of (Z)-1a,b was evaluated and a significant stabilization of the Z isomers by the bis- adenine guest 4 was observed.