Abstract
The effects of the physical environment on the molecular recognition of some aromatic amino esters (A = 3-(3,4)dihydroxyphenyl)alanine methyl ester ( DOPA OMe ), 3-(3,4)dihydroxyphenyl)alanine ethyl ester ( DOPA OEt ) and tryptophan ethyl ester ( trp OEt )) by the flattened-cone 2,8,14,20-tetrakis( L-valinamido)[4]resorcinarene ( 1 L ) have been investigated in both the gas-phase by ESI-MS spectrometry and in CDCl 3 solutions by 1H and 13C NMR spectroscopy. It is found that the non-covalent [ 1 L ·H· DOPA OMe ] + and [ 1 L ·H· DOPA OEt ] + complexes are stable in the gas-phase. The last one is stable in CDCl 3 solutions as well, while [ 1 L ·H· trp OEt ] + is not. The formation of the stable [ 1 L ·H· DOPA OEt ] + complex in CDCl 3 is not affected by the presence of traces of additives, like D 2O, DCl or ethyl acetate, or by absorption on silica. APT- 13C NMR analysis of [ 1 L ·H· DOPA OEt ] + suggests that the amino ester is mainly located inside the resorcinarene cavity, in conformity with the most stable structure arising from MC/MD simulations.
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