Photoregulated Ion-binding to Azobenzene-linked Ethylenediamines and Iminodiacetic Acids

Article abstract of DOI:10.1246/bcsj.58.2340

New photoresponsive complexones bearing two iminodiacetic acid units or ethylenediamine units at the two sides of an azobenzene through CH2 or (CH2)2 (AzoIDA(n=1,2) and AzoED(n=1,2), respectively) have been synthesized.The CH2 and (CH2)2 spcers were selected in order to examine the influence of the spacer length on the intramolecular cooperativity for the two ligands in the cis-isomers to coordinate to one metal ion.The thermal cis-to-trans isomerization of AzoIDA was efficiently suppressed by Zn(II) and Cu(II) while that of AzoED was suppressed only by Cu(II).The rate suppression supports the formation of the intramolecular chelate complexes with the metal ion.The measurements of ESR spectra of the cis-isomer Cu(II) complexes indicated that the square-planar structure of the complexes is somewhat distorted and probably close to a lozenge.The stability constants (K_s) were determined by a displacement method.The K_s values for the cis-isomers were generally greater than those for the trans-isomers, and the K_s for n=2 series increased more clearly.In particular, the K_s for cis-AzoED(n=2)+Cu(II) was improved by 43.8 fold.The photoresponsive change in the stability constants suggests a possible application of the present system as light-driven ion pumps for heavy metal ions.