Light-Induced Copper(II) Coordination by a Bicyclic Tetraaza Chelator through a Ligand-to-Metal Charge-Transfer Reaction

Jacob Rørdam Holm-Jørgensen, Mikael Jensen, Morten Bjerrum

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    To enable utilization of the broad potential of copper isotopes in nuclear medicine, rapid and robust chelation of the copper is required. Bowl adamanzanes (bicyclic tetraaza ligands) can form kinetically stable copper complexes, but they are usually formed at low rates unless high pH values and high temperatures are applied. We have investigated the effects of the variation in the pH, different anions, and UV irradiation on the chelation rate. UV spectra of mixtures of Cu2+ and [24.31]adz in water show the existence of a longlived two-coordinated copper(II) intermediate (only counting coordinated amine groups) at pH above 6. These findings are supported by pH titrations of mixtures of Cu and [24.31]adz in water. Irradiation of this complex in the ligand-to-metal charge-transfer (LMCT) band by a diode-array spectrophotometer leads to photodeprotonation and subsequently to formation of the four-coordinated copper(II) complex at a rate up to 7800fold igher at 25 °C than in the dark. Anions in the solution were found to have three major effects: competitive inhibition due to Cu2+ binding anions, inhibition of the
    photoinduced transchelation from UV-absorbing anions, and photoredox inhibition from acido ligands capable of acting as electron donors in LMCT reactions. Dissolved O2 was also found to result in photoredox inhibition.
    TidsskriftInorganic Chemistry
    Udgave nummer24
    Sider (fra-til)12705–12713
    Antal sider9
    StatusUdgivet - nov. 2011