Hydrogen-bonded double strands: Crystal structure and spectroscopic properties of a 2,2′-dipyrryl ketone

Michael T. Huggins, Adrianne K. Tipton, Qingqi Chen, David A. Lightner

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

The synthesis, crystal structure determination, conformational analysis, and spectroscopic properties of 3,3′-diethyl-4,4′-dimethyl-2,2′-dipyrryl ketone (1) are reported. The dipyrryl ketone is a model for the dipyrrole core of 10-oxobilirubin, a presumed metabolite in alternate pathways of excretion of the yellow pigment of jaundice, bilirubin. In the crystal, 1 adopts a helical conformation, with a molecule of one helicity being hydrogen-bonded to two molecules of the opposite helicity. Thus, 1 self-assembles via hydrogen bonding into supramolecular double-stranded arrays, where molecules of the same helicity comprise one strand and are paired through hydrogen bonding to molecules of opposite helicity in the second strand. In the observed molecular conformation each pyrrole ring and adjacent carbonyl group are rotated into an sc conformation (torsion angle ∼ 29°), with each N-H pointing in the same direction as the C=O. Molecular mechanics/dynamics calculations predict the sc,sc conformation, absent hydrogen bonding, to be the most stable, but only by a few tenths of a kj/mol. In CHCl3, 1 is monomeric according to vapor pressure osmometry studies (MWobs = 251 ± 10 vs. MWcalc = 244). 1H NMR NH chemical shifts in CDCl3 suggest a predominantly anti orientation of the C = O and pyrrole NHs, which is opposite to the orientation observed in the crystal.

Original languageEnglish
Pages (from-to)825-838
Number of pages14
JournalMonatshefte fur Chemie
Volume131
Issue number8
DOIs
StatePublished - 2000
Externally publishedYes

Scopus Subject Areas

  • General Chemistry

Keywords

  • Conformation
  • Hydrogen bonding
  • Pyrrole

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