Insight into the mechanisms of cooperative self-assembly: the "sergeants-and-soldiers" principle of chiral and achiral C3-symmetrical discotic triamides

J Am Chem Soc. 2008 Jan 16;130(2):606-11. doi: 10.1021/ja075987k.

Abstract

On the basis of temperature-dependent UV-vis and circular dichroism (CD) spectroscopy measurements, we observed that C3-symmetrical discotic molecules, chiral (R)-1 and achiral 2, both self-assemble in a highly cooperative fashion. Chiral (R)-1 shows a higher degree of cooperativity, meaning it requires a larger nucleus before elongation sets in, as compared to achiral 2. Next to that, we investigated the mechanism of the "sergeants-and-soldiers" principle, where we found that the chiral sergeant (R)-1 strongly amplifies the preference in handedness of the mixed stacks of (R)-1 and 2. However, the elongation temperature and the degree of cooperativity are linearly dependent on both, at least in the regime above 4% of sergeant in the mixed system. Remarkably, we observed that at room temperature a fast exchange on the second time scale exists between molecules and stacks of sergeant (R)-1 and soldier 2, and that interconversion between M and P helices is fast at this temperature.