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PPII is stabilized in part by\n                    <jats:italic>n<\/jats:italic>\n                    \u2192\u03c0* interactions between consecutive carbonyls, via electron delocalization between an electron\u2010donor carbonyl lone pair (\n                    <jats:italic>n<\/jats:italic>\n                    ) and an electron\u2010acceptor carbonyl (\u03c0*) on the subsequent residue. We previously demonstrated that changes to the electronic properties of the acyl donor can predictably modulate the strength of\n                    <jats:italic>n<\/jats:italic>\n                    \u2192\u03c0* interactions, with data from model compounds, in solution in chloroform, in the solid state, and computationally. Herein, we examined whether the electronic properties of acyl capping groups could modulate the stability of PPII in peptides in water. In\n                    <jats:bold>X<\/jats:bold>\n                    \u2212PPGY\u2010NH\n                    <jats:sub>2<\/jats:sub>\n                    peptides (\n                    <jats:bold>X<\/jats:bold>\n                    =10 acyl capping groups), the effect of acyl group identity on PPII was quantified by circular dichroism and NMR spectroscopy. Electron\u2010rich acyl groups promoted PPII relative to the standard acetyl (Ac\u2212) group, with the pivaloyl and\n                    <jats:italic>iso<\/jats:italic>\n                    \u2010butyryl groups most significantly increasing PPII. In contrast, acyl derivatives with electron\u2010withdrawing substituents and the formyl group relatively disfavored PPII. Similar results, though lesser in magnitude, were also observed in\n                    <jats:bold>X<\/jats:bold>\n                    \u2212APPGY\u2010NH\n                    <jats:sub>2<\/jats:sub>\n                    peptides, indicating that the capping group can impact PPII conformation at both proline and non\u2010proline residues. The pivaloyl group was particularly favorable in promoting PPII. The effects of acyl capping groups were further analyzed in\n                    <jats:bold>X\u2013<\/jats:bold>\n                    DfpPGY\u2010NH\n                    <jats:sub>2<\/jats:sub>\n                    and\n                    <jats:bold>X<\/jats:bold>\n                    \u2212ADfpPGY\u2010NH\n                    <jats:sub>2<\/jats:sub>\n                    peptides, Dfp=4,4\u2010difluoroproline. Data on these peptides indicated that acyl groups induced order Piv\u2010 &gt; Ac\u2010 &gt; For\u2010. These results suggest that greater consideration should be given to the identity of acyl capping groups in inducing structure in peptides.\n                  <\/jats:p>","DOI":"10.1002\/chem.202401454","type":"journal-article","created":{"date-parts":[[2024,4,25]],"date-time":"2024-04-25T06:34:50Z","timestamp":1714026890000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Electronic Control of Polyproline II Helix Stability via the Identity of Acyl Capping Groups: the Pivaloyl Group Particularly Promotes PPII"],"prefix":"10.1002","volume":"30","author":[{"given":"Megh R.","family":"Bhatt","sequence":"first","affiliation":[{"name":"Department of Chemistry and Biochemistry University of Delaware  Newark, DE 19716 United States"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7417-8085","authenticated-orcid":false,"given":"Neal 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