Light-induced copper(II) coordination by a bicyclic tetraaza chelator through a ligand-to-metal charge-transfer reaction

TY - JOUR

T1 - Light-induced copper(II) coordination by a bicyclic tetraaza chelator through a ligand-to-metal charge-transfer reaction

AU - Holm-Jørgensen, Jacob Rørdam

AU - Jensen, Mikael

AU - Bjerrum, Morten Jannik

N1 - PT: J; UT: WOS:000297782200050 M1 - Journal Article

PY - 2011/12/19

Y1 - 2011/12/19

N2 - 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 Cu 2+ and [2 4.3 1]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 2+ and [2 4.3 1]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 7800 fold higher at 25 °C than in the dark. Anions in the solution were found to have three major effects: competitive inhibition due to Cu II 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 O 2 was also found to result in photoredox inhibition

AB - 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 Cu 2+ and [2 4.3 1]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 2+ and [2 4.3 1]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 7800 fold higher at 25 °C than in the dark. Anions in the solution were found to have three major effects: competitive inhibition due to Cu II 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 O 2 was also found to result in photoredox inhibition

U2 - 10.1021/ic201839w

DO - 10.1021/ic201839w

M3 - Journal article

C2 - 22074363

SN - 0020-1669

VL - 50

SP - 12705

EP - 12713

JO - Inorganic Chemistry

JF - Inorganic Chemistry

IS - 24

ER -