ISSN:
1600-5740
Quelle:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Thema:
Chemie und Pharmazie
,
Geologie und Paläontologie
,
Physik
Notizen:
The hydrogen-bond networks and crystal packing of 81 unique secondary di- and polyamides in the Cambridge Structural Database are investigated. Graph-set analysis, as implemented in the RPluto program, is used to classify network motifs. These have been rationalized in terms of the relative dispositions of the amide groups. Peptide and retropeptides exhibit significant conformational flexibility, which permits alternative hydrogen-bonding patterns. In peptides, dihedral angles of −ψ ∼ φ ∼ 105° allow an antiparallel ladder arrangement, containing rings of either the same or alternating sizes. For retropeptides, and diamides with an odd number of CH2 spacers, this conformation leads to a parallel ladder with rings of equal size. If φ approaches −60° and ψ 180°, ladders adopt a helical twist, and if the conformation is distorted further, a three-dimensional network is usually adopted. Diamides with aromatic or an even number of CH2 spacers generally form either antiparallel ladders or sheets, although some exhibit both polymorphs. Symmetry relationships within and between hydrogen-bonded chains, ladders and sheets in the crystal packing have also been analysed. Polyamides form considerably more complex networks, although many of the structural motifs present in the diamides occur as components of these networks.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1107/S0108768100007230
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