TY - JOUR
T1 - Hydrogen-bonded double strands
T2 - Crystal structure and spectroscopic properties of a 2,2′-dipyrryl ketone
AU - Huggins, Michael T.
AU - Tipton, Adrianne K.
AU - Chen, Qingqi
AU - Lightner, David A.
PY - 2000
Y1 - 2000
N2 - 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.
AB - 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.
KW - Conformation
KW - Hydrogen bonding
KW - Pyrrole
UR - http://www.scopus.com/inward/record.url?scp=0034388911&partnerID=8YFLogxK
U2 - 10.1007/s007060070060
DO - 10.1007/s007060070060
M3 - Article
AN - SCOPUS:0034388911
SN - 0026-9247
VL - 131
SP - 825
EP - 838
JO - Monatshefte fur Chemie
JF - Monatshefte fur Chemie
IS - 8
ER -