Figure 4.

Spectral changes that accompany Zn²⁺ binding to HPhen1 as monitored by UV-vis spectroscopy. Spectra show a typical ferric heme spectrum with a Soret band at 415 nm (ε = 0.148 μM⁻¹ cm⁻¹) along with a transition between metal-free (λ_max= 272 nm) and metal-bound (λ_max= 282 nm) Phen species. Inset: Close-up view of the UV region showing a clean isobestic point at 274 nm consistent with a 1:1 Zn²⁺:Phen binding model.