TY - JOUR
T1 - Temperature-independent electron transfer in mixed-metal hemoglobin hybrids
AU - Kuila, Debasish
AU - Baxter, Wade W.
AU - Natan, Michael J.
AU - Hoffman, Brian M.
PY - 1991
Y1 - 1991
N2 - Long-range electron transfer (ET) in mixed-metal hemoglobin hybrids [(MP),Fe(CN-)P] (M = Mg, Zn) is measured as a function of temperature from ambient to 100 K. Triplet-state quenching of 3(MP) is found to be inadequate to determine ET rate constants when the quenching rate is low, as it is in these hybrids at low temperature. Direct observation of the ET intermediate, [(MP)+,Fe2+(CN-)P], has allowed us to determine the temperature response of the ET rate constants kt and kb for the 3(MP) → Fe3+(CN-)P and Fe2+(CN-)P → (MP)+ electron-transfer steps, respectively. The ET process is not affected by the freezing of the cryosolvent, which may indicate that coupling of ET to low-frequency solvent modes may be minimal. For both M, but especially for M = Mg, kb is nearly temperature independent. Calculation of the electron coupling matrix element gives HAB ≈ 10-3 cm-1. Comparison with results for ruthenated myoglobin indicates that the Hb interface exhibits efficient electronic coupling even across the noncovalent interface between the subunits.
AB - Long-range electron transfer (ET) in mixed-metal hemoglobin hybrids [(MP),Fe(CN-)P] (M = Mg, Zn) is measured as a function of temperature from ambient to 100 K. Triplet-state quenching of 3(MP) is found to be inadequate to determine ET rate constants when the quenching rate is low, as it is in these hybrids at low temperature. Direct observation of the ET intermediate, [(MP)+,Fe2+(CN-)P], has allowed us to determine the temperature response of the ET rate constants kt and kb for the 3(MP) → Fe3+(CN-)P and Fe2+(CN-)P → (MP)+ electron-transfer steps, respectively. The ET process is not affected by the freezing of the cryosolvent, which may indicate that coupling of ET to low-frequency solvent modes may be minimal. For both M, but especially for M = Mg, kb is nearly temperature independent. Calculation of the electron coupling matrix element gives HAB ≈ 10-3 cm-1. Comparison with results for ruthenated myoglobin indicates that the Hb interface exhibits efficient electronic coupling even across the noncovalent interface between the subunits.
UR - http://www.scopus.com/inward/record.url?scp=0009003549&partnerID=8YFLogxK
U2 - 10.1021/j100154a001
DO - 10.1021/j100154a001
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AN - SCOPUS:0009003549
SN - 0022-3654
VL - 95
SP - 1
EP - 3
JO - Journal of Physical Chemistry
JF - Journal of Physical Chemistry
IS - 1
ER -