SEARCHING FOR MINIMUM INCREMENTS OF HYDROPHOBIC COLLAPSE - FLEXIBLE DINAPHTHYL CARBOXYLATES

In an effort to identify minimal units of hydrophobically induced fold ing, we have examined flexible molecules containing two naphthyl moiet ies connected by a four-atom linker that also bears a carboxyl group. Crystallographic data show that the linkers allow intramolecular edge- to-face association of the naphthyl groups without excessive strain in the backbone. For the carboxylate forms of the dinaphthyl compounds, the occurrence of intramolecular naphthyl-naphthyl proximity in aqueou s solution (24 degrees C) was detected via upfield shifts in the aroma tic region H-1 NMR signals, relative to mononaphthyl control compounds . The naphthyl-naphthyl proximity does not appear to be strongly ''hyd rophobically driven'', however, because similar upfield shifts (dinaph thyl vs mononaphthyl carboxylates) were observed in 8 M aqueous urea, and for the corresponding carboxylic acids in CDCl3 and C6D6. We concl ude that these upfield shifts largely reflect chance encounters betwee n the naphthyl groups resulting from random conformational motion.