A new class of azobenzene chelators for Mg2+ and Ca2+ in buffer at physiological pH

A new class of azobenzene-based chelators, trans-3a and trans-3b (3a and 3b), were designed and synthesized in two steps. Both 3a and 3b were readily dissolved in a buffer solution at physiological pH. The values of the dissociation constant of 3a and 3b for Mg2+ and Ca2+ were determined by the Hills plot; KdMg=1.12 mM and KdCa=660 μM for 3a and KdMg=158 μM and KdCa=200 μM for 3b, respectively. On irradiation at 489 nm light, 3a isomerized to give cis-form, which underwent cis-to-trans thermal isomerization in darkness at room temperature. The change in the absorption spectrum of the irradiated solution of 3a in the presence of Mg2+, showing the cis-to-trans thermal isomerization, indicates that the affinity of cis-3a for Mg2+ is lower than that of 3a.