SEARCHING FOR MINIMUM INCREMENTS OF HYDROPHOBIC COLLAPSE - FLEXIBLE DINAPHTHYL CARBOXYLATES

In an effort to identify minimal units of hydrophobically induced folding, we have examined flexible molecules containing two naphthyl moieties 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 aqueous solution (24 degrees C) was detected via upfield shifts in the aromatic region H-1 NMR signals, relative to mononaphthyl control compounds. The naphthyl-naphthyl proximity does not appear to be strongly ''hydrophobically driven'', however, because similar upfield shifts (dinaphthyl vs mononaphthyl carboxylates) were observed in 8 M aqueous urea, and for the corresponding carboxylic acids in CDCl3 and C6D6. We conclude that these upfield shifts largely reflect chance encounters between the naphthyl groups resulting from random conformational motion.