Azurin is a small electron-transfer protein belonging to the cupredoxin family. The Cu atom is located within a trigonal plane coordinated by two histidines (His46 and His117) and a cysteine (Cys112) with two more distant ligands (Gly45 and Met121) providing axial interactions. A Cys112SeCys derivative has been prepared by expressed protein ligation, and detailed UV/vis, EPR and EXAFS studies at the Cu and Se K-edges have been carried out. Marked changes are observed between the EPR parameters of the Cys112SeCys and WT azurin derivatives, which include a 2-fold increase in A(||), a decrease in g-values, and a large increase in rhombicity of the g-tensor. The Cu-Se and Se-Cu bond lengths obtained from analysis of the Cu and Se K-EXAFS of the oxidized protein were found to be 2.30 and 2.31 A, respectively, 0.14 A longer than the Cu-S distance of the WT protein. Unexpectedly, the Cu-Se bond lengths were found to undergo only minor changes during reduction, suggesting a very similar structure in both redox states and extending the "rack" hypothesis to the Se-substituted protein.
The preparation of radicals with intense and redox-switchable absorption beyond 1000 nm is a long-standing challenge in the chemistry of functional dyes. Here we report the preparation of a series of unprecedented stable neutral nickel(II) and copper(II) complexes of "Manitoba dipyrromethenes" (MB-DIPYs) in which the organic chromophore is present in the radical-anion state. The new stable radicals have an intense absorption at λmax ∼1300 nm and can be either oxidized to regular [MII (MB-DIPY)]+ (M=Cu or Ni) or reduced to [MII (MB-DIPY)]- compounds. The radical nature of the stable [MII (MB-DIPY)] complexes was confirmed by EPR spectroscopy with additional insight into their electronic structure obtained by UV-Vis spectroscopy, electro- and spectroelectrochemistry, magnetic measurements, and X-ray crystallography. The electronic structures and spectroscopic properties of the radical-based chromophores were also probed by density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. These nickel(II) and copper(II) complexes represent the first stable radical compounds with a MB-DIPY ligand.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
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The binuclear CuA site engineered into Pseudomonas aeruginosa azurin has provided a CuA-azurin with a well-defined crystal structure and a CuSSCu core having two equatorial histidine ligands, His120 and His46. The mutations His120Asn and His120Gly were made at the equatorial His120 ligand to understand the histidine-related modulation to CuA, notably to the valence delocalization over the CuSSCu core. For these His120 mutants Q-band electron nuclear double resonance (ENDOR) and multifrequency electron paramagnetic resonance (EPR) (X, C, and S-band), all carried out under comparable cryogenic conditions, have provided markedly different electronic measures of the mutation-induced change. Q-band ENDOR of cysteine Cβ protons, of weakly dipolar-coupled protons, and of the remaining His46 nitrogen ligand provided hyperfine couplings that were like those of other binuclear mixed-valence CuA systems and were essentially unperturbed by the mutation at His120. The ENDOR findings imply that the CuA core electronic structure remains unchanged by the His120 mutation. On the other hand, multifrequency EPR indicated that the H120N and H120G mutations had changed the EPR hyperfine signature from a 7-line to a 4-line pattern, consistent with trapped-valence, Type 1 mononuclear copper. The multifrequency EPR data imply that the electron spin had become localized on one copper by the His120 mutation. To reconcile the EPR and ENDOR findings for the His120 mutants requires that either: if valence localization to one copper has occurred, the spin density on the cysteine sulfurs and the remaining histidine (His46) must remain as it was for a delocalized binuclear CuA center, or if valence delocalization persists, the hyperfine coupling for one copper must markedly diminish while the overall spin distribution on the CuSSCu core is preserved.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
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