(636f) Evidence for Self-Assembly-Driven Trans-to-Cis Amide Bond Isomerization in Peptoid Nanosheets | AIChE

(636f) Evidence for Self-Assembly-Driven Trans-to-Cis Amide Bond Isomerization in Peptoid Nanosheets


Hudson, B. C. - Presenter, Florida A & M University and Florida State University
Zuckermann, R. N., Lawrence Berkeley National Laboratory
Paravastu, A., Georgia Institute of Technology
Battigelli, A., Lawrence Berkeley National Laboratory
Spencer, R., Lawrence Berkeley National Laboratory
Connolly, M., Lawrence Berkeley National Laboratory
Whitelam, S., Lawrence Berkeley National Laboratory
Edison, J., Lawrence Berkeley National Laboratory
Peptoids are synthetic polymers developed with the goal of mimicking the folding and functions of peptides. Peptoids have the same backbone structure as peptides, but with side chains that branch from the amide nitrogen instead of the α-carbon. For biomaterials applications, peptoids benefit from the ability to adopt peptide-mimetic 3-dimensional structures but with decreased susceptibility to enzymatic degradation. Here we focus on peptoid B28 which adopts a Σ-strand conformation, analogous to β-strands in peptides, and self-assembles into nanosheets. Potential nanosheet applications have been proposed in the areas of catalysis, membranes, sensing, and molecular recognition. However, structural studies have proven difficult. To fill this knowledge gap, we have applied 13C-13C dipolar recoupling solid-state NMR measurements to reveal the configuration of backbone amide bonds selected by 13C isotopic labeling of adjacent α-carbons. Measurements on the same molecules in the amorphous and assembled states revealed that amide bonds in the center of the amino block of peptoid B28 favor the trans configuration in the amorphous state and the cis configuration in the nanosheet. This unexpected result contrasts with previous NMR and theoretical studies of short solvated peptoids. Furthermore, examination of the amide bond at the junction of the two charged blocks within B28 revealed a mixture of both cis and trans configurational states, consistent with a previously-predicted brickwork-like intermolecular organization. The data we show here indicate a self-assembly driven isomerization process. This is a previously unreported phenomenon in peptoid biology and should be a point of consideration for peptoid self-assembly studies moving forward.