Investigating the Spontaneous Resolution of an Abiotic Metallofoldamer Using Solid‐State Circular Dichroism Spectroscopy

Benavidez, Ann
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University of Delaware
Crystals of an abiotic metallofoldamer were used to investigate the viability of solid‐state circular dichroism spectroscopy (solid‐state CD) as an alternative to X‐ray diffraction studies in spontaneous resolution analysis. The metallofoldamer is devoid of chiral centers and the molecules assemble into secondary structures with helical chirality. Although the metallofoldamer complexes racemize in solution, they produce a single enantiomerically pure crystal when subjected to vapor diffusion in a crystallization experiment. CD spectra of microcrystalline samples were obtained by scanning pellets of each crushed crystal mixed with KBr. The reliability, efficiency, and effectiveness of solid‐state CD in spontaneous resolution analysis were established. Thus, it was demonstrated that an enantiomerically pure helical molecule can be produced from a dynamic macromolecule without any element of central chirality. A hypothesis for the evolutionary origin of chirality is discussed. Interestingly, all seven crystals characterized thus far have been left‐handed. The probability of such an occurrence is 1 in 64. It is plausible that a chiral contaminant serves as a nucleation site for crystallization.