SOLVENT CONTROLS SYNTHESIS AND PROPERTIES OF SUPRAMOLECULAR STRUCTURES

A template effect by solvent was found in the synthesis of self-assemb led capsules. Use of aromatic solvents such as benzene, toluene, and p -xylene leads predominantly to the formation of the C-shaped molecules 3 and 6, which form hydrogen-bonded dimeric capsules. This is the med ium in which the solvent-occupied dimeric capsule enjoys the greatest stability, and the best solvated surfaces with properly filled niches are formed preferentially. The dimerization constant (K-D) value and a Delta G(0) value of >14.0 kcal mol(-1) for the capsules 16 (3.3) were estimated for the first time in guest-exchange experiments. When solv ents not suitable for dimerization (CHCl3 and CH2Cl2) or those solvent s that compete for hydrogen bonds (DMSO and THF) were employed, only s tatistical yields of the stereoisomers (C-, S-, and W-shaped) were obs erved. Experimental evidence is presented that the solvent molecules c ontrol the covalent bond formation through molecular recognition withi n the monomeric tetrahedral intermediate. It is proposed that solvatio n effects can be treated as a subset of molecular recognition events.