It has been repeatedly postulated that the high heat resistance of bacterial spores is due to stabilization of biopolymers in the spore interior by a solid deposit of protective cement consisting of coordination complexes of ligands with divalent metal ions. This report presents data on metal-binding characteristics of some of the ligands related to spores as determined by means of potentiometric equilibrium measurements under conditions of temperature and ionic strength (t = 25.0 degrees C; mu = 1.0 KNO(3)) identical with those reported earlier by the authors in order to facilitate correlation by using comparable data. The spore ligands investigated in this study included 2,6-pyridinedicarboxylic acid (DPA), alpha,epsilon-diaminopimelic acid, D-glutamic acid, and D-alanine in a ratio of 1:1 with metal ions which are known to play a role in heat resistance of spores. Stability constants of the chelates of these spore ligands with metal ions such as Ca(II), Mg(II), Cu(II), Ni(II), Zn(II), Co(II), and Mn(II) have been determined. In general the metal chelates of DPA exhibited the greatest stability. On the basis of a consideration of the stability data together with the known configurations of the ligand and the coordination requirements of the metal ions, possible structures indicating the coordinate binding of the spore ligands with the metal ions are presented. All the metal chelates except those of Ca(II) were found to undergo hydrolysis and separation of solid phase in the pH range 7-8.5. The relatively greater hydrolytic stability of Ca(II) chelates and the high affinity of DPA for metal ions appear to be of biological significance insofar as these two spore components are more widely associated with the heat resistance of bacterial spores.

The template condensation of 6,6'-bis( hydrazino)-2,2'-bipyridines or 2,9-bis(hydrazino)-l ,I 0-phenanthrolines with 2,6-pyridine dicarbonyls in the presence of chromium(iii) chloride leads to the formation of free macrocycles rather than the expected metal complexes; the origin of this 'transient-template' effect is discussed and the crystal structural analysis of a chromium(iii) macrocyclic complex is described.

A range of metal-free quinquedentate macrocyclic ligands incorporating 2,2'-bipyridine or 1 ,I 0phenanthroline donor groups has been prepared by the use of a chromium(iti) transient template.The transient template effect is shown to be due to pH effects resulting from the presence of chromium(iii) complexes in aqueous solution, rather than a process in which the open-chain ligands become co-ordinated to the metal centre. The crystal and molecular structure of a free macrocyclic ligand is reported, as is the preparation of some chromium(iit) complexes of open-chain and macrocyclic complexes.

The metal‐free quinquedentate macrocyclic ligands (IV) and (V) are prepared by the use of a Cr(III) transient template as demonstrated for the example (IVa)·HCl·4 H2O (space group P21/n, Z=4).