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Paramagnetic Properties of the Halide‐Bound Derivatives of Oxidised Tyrosinase Investigated by 1 H NMR Spectroscopy
Author(s) -
Tepper Armand W. J. W.,
Bubacco Luigi,
Canters Gerard W.
Publication year - 2006
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200501494
Subject(s) - chemistry , paramagnetism , halide , crystallography , hyperfine structure , copper , ion , excited state , relaxation (psychology) , chemical shift , analytical chemistry (journal) , inorganic chemistry , atomic physics , social psychology , psychology , physics , chromatography , organic chemistry , quantum mechanics
The 1 H NMR relaxation characteristics of the histidines in the oxidised type‐3 copper site of tyrosinase (Ty met ) from the bacterium Streptomyces antibioticus in the halide‐bound forms (Ty met X with X = F − , Cl − , Br − ) have been determined and analysed. The 1 H NMR spectra of the Ty met X species display remarkably sharp, well‐resolved, paramagnetically shifted 1 H signals, which originate from the protons of the six His residues coordinated to the two Cu II ions in the type‐3 centre. From the temperature‐dependence of the 1 H paramagnetic shifts the following values for the exchange‐coupling parameter −2 J were determined: 260 (Ty met F), 200 (Ty met Cl) and 162 cm −1 (Ty met Br). The 1 H T 1 relaxation is dipolar in origin and correlates with the CuH distances. Electronic relaxation times τ S derived from the 1 H T 1 data amount to about 10 −11 s and follow the order Ty met F>Ty met Cl>Ty met Br. They are two orders of magnitude shorter than the τ S values reported for mononuclear copper systems, in accordance with the sharpness of the 1 H signals. The results corroborate the Cu 2 bridging mode of the halide ions. On the basis of the measured hyperfine interaction constants for the ligand histidine nuclei, it is concluded that 70–80 % of the spin density in the excited triplet state resides on the two copper ions and the bridging atoms.