Chain extension hydrogen bonding

Open chain polyamine ligands have been widely studied. Often the coordination of zinc is compared with other first row transition metals and factors, such as behavior across a pH range, studied. The protonation patterns and stability constants are of particular interest. Octahedral zinc tris(ethylenediamine) structures have been characterized by X-ray diffraction with a number of different counter anions.94 The X-ray structure of zinc tris(ethylenediamine) with fluoride counter ions reveals extensive hydrogen bonding.95... 

The extended chains, that is, the backbones, may further organize into assemblies that have characteristic properties. The two most important of these are the a- helix and the /3-sheet. The latter is illustrated in Figure 1.23. Panel (a) shows the extensive hydrogen bond organization of peptide chains that are oriented in opposite directions. The arrows indicate the nitrogen to carbonyl (arrowhead) direction. The lower panel (b) shows an alternate FI-bond organization when the two peptide chains are parallel rather than antiparallel. 

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