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Normal coordinate calculations are carried out for all the in-plane modes of octaethylporphyrinato-Ni (II) and its meso-deuterated and 15N substituted derivatives. With 37 constants of a modified Urey–Bradley force field and a structural model with D4h symmetry, 59 resonance Raman lines (A1g+B1g +A2g+B2g) and 38 infrared bands (Eu) of these three molecules are assigned. The vibrational modes of the Raman active species are represented in terms of the Cartesian atomic displacement vectors. Based on the present results, some important resonance Raman lines of hemoproteins are interpreted. The so-called ’’oxidation state maker’’ (Band IV) is due to an in-phase breathing-like mode of four pyrrole rings although being somewhat deformed by the large contribution of the Cα–N symmetric stretching term. The spin state sensitive Raman lines, namely, Band I and III, are associated mainly with methine bridge (Cα–Cm) stretching modes. Two prominent anomalously-polarized Raman lines of hemoproteins around 1580 and 1300 cm−1 are primarily due to the Cα–Cm stretching and Cm–H bending modes, respectively.

Histidine-93(F8) in human myoglobin (Mb), which is the proximal ligand of the heme iron, has been replaced with cysteine or tyrosine by site-directed mutagenesis. The resultant proximal cysteine and tyrosine mutant Mbs (H93C and H93Y Mbs, respectively) exhibit the altered axial ligation analogous to P-450, chloroperoxidase, and catalase. Coordination of cysteine or tyrosine to the ferric heme iron is confirmed by spectroscopic measurements including electronic absorption, hyperfine-shifted 1H-NMR, EPR, resonance Raman spectroscopies, and redox potential measurements of ferric/ferrous couple. H93C Mb is five-coordinate ferric high-spin with the proximal cysteine. H93Y Mb bearing the proximal tyrosine ligated to the iron is also in a ferric high-spin, five-coordinate state. The reactions of the mutants with cumene hydroperoxide show that the thiolate ligand enhances heterolytic O-O bond cleavage of the oxidant, while the phenolate ligand hardly affects the heterolysis/homolysis ratio for O-O bond scission in comparison with wild-type Mb. Monooxygenase activities such as epoxidation of styrene and N-demethylation of N,N-dimethylaniline, and catalase activity (dismutation of hydrogen peroxide) by wild-type Mb and the mutants, are examined by using H2O2. The increase of the catalytic activities by the mutation was, at most, 5-fold in the epoxidation reaction.

The formation of vibrationally excited heme upon photodissociation of carbonmonoxy myoglobin and its subsequent vibrational energy relaxation was monitored by picosecond anti-Stokes resonance Raman spectroscopy. The anti-Stokes intensity of the nu4 band showed immediate generation of vibrationally excited hemes and biphasic decay of the excited populations. The best fit to double exponentials gave time constants of 1.9 +/- 0.6 and 16 +/- 9 picoseconds for vibrational population decay and 3.0 +/- 1.0 and 25 +/- 14 picoseconds for temperature relaxation of the photolyzed heme when a Boltzmann distribution was assumed. The decay of the nu4 anti-Stokes intensity was accompanied by narrowing and frequency upshift of the Stokes counterpart. This direct monitoring of the cooling dynamics of the heme cofactor within the globin matrix allows the characterization of the vibrational energy flow through the protein moiety and to the water bath.

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Tyrosinase is a copper monooxygenase that catalyzes oxygenation of phenols to catechols (phenolase activity) and the subsequent two-electron oxidation of catechols to the corresponding o-quinones (catecholase activity). 1 Chemical and spectroscopic studies have indicated that the enzyme has a dinuclear copper active site nearly identical to that found in hemocyanin, 1,2 where a side-on type (µ-η 2 :η 2 ) peroxo species 3 is generated by the reaction of the reduced dicopper(I) form and O 2 . 1 As a pioneering work by Karlin and co-workers in Cu/O 2 chemistry, aromatic ligand hydroxylation in a dinuclear Cu(I) complex by O 2 was first reported in early 1980s. 4 The mechanistic studies have indicated that the aromatic ligand hydroxylation reaction involves an electrophilic attack on the arene ring by a (µ-η 2 :η 2 -peroxo)-dicopper(II) intermediate. 5 After their finding, several examples of the aromatic ligand hydroxylation have been reported using similar type of m-xylyl dinucleating ligands. 6 With respect to the intermolecular reactions between phenols and the peroxo intermediate, however, most of the reactions so far reported afford a C-C coupling dimer as a major product. 7 Casella and co-workers have recently reported the first synthetic (µ-η 2 :η 2 -peroxo)dicopper-(II) complex which can react with an exogenous phenolate to yield the corresponding catechol. 8,9 Unfortunately, the low yield of the product (20% based on the dicopper complex) has precluded the kinetic and mechanistic investigation on the reaction between the peroxo intermediate and the phenolate. 8 As such, the mechanism for the catechol formation via intermolecular reactions between the peroxo intermediate and phenol derivatives has yet to be clarified. 10 We report herein that efficient conversion of phenol derivatives to the corresponding catechols is achieved for the first time by intermolecular reactions of a (µ-η 2 :η 2 -peroxo)dicopper(II) complex, supported by tridentate ligand L Py2Bz (N,N-bis[2-(2-pyridyl)-ethyl]-R,R-dideuteriobenzylamine), 11 with lithium salts of phenols. The mechanistic studies on the catechol formation have been performed to provide valuable mechanistic insight into the phenolase activity of the enzyme.Treatment of the copper(I) complex, [Cu I (L Py2Bz )](PF 6 ), with dioxygen in anhydrous acetone at -94°C afforded a brown color solution which exhibited a strong absorption band at 364 nm ( ) 26400 M -1 cm -1 ) together with a small one at 530 nm (1500 M -1 cm -1 ) and a resonance Raman band at 737 cm -1 that shifted to 697 cm -1 upon 18 O-substitution. 12,13 The frozen acetone solution of the intermediate was ESR silent at 77 K, and a Cu:O 2 ) 2:1 stoichiometry was obtained for formation of the intermediate by manometry. These results unambiguously indicate that the oxygenated intermediate is a (µ-η 2 :η 2 -peroxo)dicopper(II) complex as suggested previously by Karlin et al. 11 This compound is quite stable (no self-decomposition) at the low-temperature enabling us to examine the reaction with external subst...

Electronic absorption, Fe K-edge X-ray absorption, resonance Raman, and Mössbauer data collected for these complexes conclusively demonstrate that the characteristic spectroscopic features of the S = 1 Fe IV =O unit, namely i) the near-IR absorption properties, ii) X-ray absorption pre-edge intensities, and iii) quadrupole splitting parameters, are strongly dependent on the identity of the trans ligand. However, on the basis of EXAFS data, most [Fe IV (O)(TMC)(X)] + species have Fe=O bond lengths similar to that of [Fe IV (O)(TMC)(NCMe)] 2+ (1.66 ± 0.02 Å). The mechanisms by which the trans ligands perturb the Fe IV =O unit were probed using density functional theory (DFT) computations, yielding geometric and electronic structures in good agreement with our experimental data. These calculations revealed that the trans ligands modulate the energies of the Fe=O σ-and π-antibonding molecular orbitals, causing the observed spectroscopic changes. Time-dependent DFT methods were used to aid in the assignment of the intense near-UV absorption bands found for the oxoiron(IV) complexes with trans N 3 − , NCS − , and NCO − ligands as X − -to-Fe IV =O charge transfer transitions, thereby rationalizing the resonance enhancement of the ν(Fe=O) mode upon excitation of these chromophores.

Axial ligand substitution of a mononuclear nonheme oxoiron(IV) complex, [FeIV(O)(TMC)(NCCH3)]2+ (1) (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), leads to the formation of new FeIV=O species with relatively intense electronic absorption features in the near-UV region. The presence of these near-UV features allowed us to make the first observation of Fe=O vibrations of S = 1 mononuclear nonheme oxoiron(IV) complexes by resonance Raman spectroscopy. We have also demonstrated that the reactivity of nonheme oxoiron(IV) intermediates is markedly influenced by the axial ligands.