We report picosecond time-resolved x-ray diffraction from the myoglobin (Mb) mutant in which Leu 29 is replaced by Phe (L29Fmutant). The frame-by-frame structural evolution, resolved to 1.8 angstroms, allows one literally “watch” protein as it executes its function. Time-resolved mid-infrared spectroscopy of flash-photolyzed L29F MbCO revealed a short-lived CO intermediate whose 140-ps lifetime shorter than that found wild-type factor 1000. electron density maps unveil transient...

The reactivities of mononuclear nonheme iron(IV)-oxo complexes bearing different axial ligands, [Fe(IV)(O)(TMC)(X)](n+) [where TMC is 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane and X NCCH(3) (1-NCCH(3)), CF(3)COO(-) (1-OOCCF(3)), or N(3)(-) (1-N(3))], [Fe(IV)(O)(TMCS)](+) (1'-SR) (where TMCS 1-mercaptoethyl-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane), have been investigated with respect to oxo-transfer PPh(3) hydrogen atom abstraction from phenol O H alkylaromatic C...

The relative orientations of carbon monoxide (CO) bound to and photodissociated from myoglobin in solution have been determined with time-resolved infrared polarization spectroscopy. CO is oriented < or = 7 degrees the heme normal, corresponding nearly linear FE-C-O. Upon dissociation Fe, becomes trapped a docking site that orientationally constrains it lie approximately plane heme. Because "docked" are orthogonal directions binding suppressed. These solutions results help establish how...

A series of complexes [Fe(IV)(O)(TMC)(X)](+) (where X = OH(-), CF3CO2(-), N3(-), NCS(-), NCO(-), and CN(-)) were obtained by treatment the well-characterized nonheme oxoiron(IV) complex [Fe(IV)(O)(TMC)(NCMe)](2+) (TMC tetramethylcyclam) with appropriate NR4X salts. Because topology TMC macrocycle, represents an extensive collection S 1 that only differ respect to ligand trans oxo unit. Electronic absorption, Fe K-edge X-ray resonance Raman, Mossbauer data collected for these conclusively...

Oxoiron(IV) species have been found to act as the oxidants in catalytic cycles of several mononuclear nonheme iron enzymes that activate dioxygen. To gain insight into factors govern oxidative reactivity such complexes, a series five synthetic S = 1 [Fe(IV)(O)(L(N5))](2+) complexes has characterized with respect their spectroscopic and electrochemical properties well relative abilities carry out oxo transfer hydrogen atom abstraction. The Fe=O units these are supported by neutral...

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 new FeIV=O species with relatively intense electronic absorption features in near-UV region. The presence these allowed us make first observation Fe=O vibrations S 1 complexes by resonance Raman spectroscopy. We have also demonstrated that reactivity intermediates is markedly influenced axial ligands.

Time-resolved mid-ir absorption spectra of CO at 283 K have been measured 100 ps after photodissociation from human hemoglobin A, horse myoglobin, and sperm whale myoglobin. The reveal two vibrational features that are narrower than any reported for in the condensed phase near room temperature, indicating becomes localized a rotationally constrained environment. integrated absorbance under these narrow is 0.53±0.05 times found myoglobin low temperature glasses. A model developed relates this...

High-valent versatility: N4Py is a versatile pentadentate ligand demonstrated to stabilize both high-valent oxo and imido compounds. The [FeIV(NTs)(N4Py)]2+ complex (see DFT-optimized structure) has been characterized spectroscopically formulated as having an S=1 iron(IV) center with FeN bond (1.73 Å) that longer than the FeO of its analogue (1.65 Å). Supporting information for this article available on WWW under http://www.wiley-vch.de/contents/jc_2002/2006/z602799_s.pdf or from author....

The mononuclear hydroxomanganese(III) complex, [MnIII(OH)(dpaq)]+, which is supported by the amide-containing N5 ligand dpaq (dpaq = 2-[bis(pyridin-2-ylmethyl)]amino-N-quinolin-8-yl-acetamidate) was generated treatment of manganese(II) species, [MnII(dpaq)](OTf), with dioxygen in acetonitrile solution at 25 °C. This oxygenation reaction proceeds essentially quantitative yield (greater than 98% isolated yield) and represents a rare example an O2-mediated oxidation complex to generate single...

A non-porphyrinic, mononuclear oxomanganese(IV) complex was generated at room temperature and characterized by spectroscopic methods. The MnIVO adduct is capable of activating C–H bonds a H-atom transfer mechanism more reactive in this regard than most species.

The molecular bis-(tris(carbene)borate) manganese(IV) complex [{PhB(MeIm) 3 } 2 Mn](OTf) shows E g → 4 A 2g luminescence at 828 nm in the solid state 85 K; this wavelength is longer by approximately 100 than wavelengths typically observed for and chromium(III) doped solids complexes. Weak also from a LMCT excited with an absorption maximum 500 nm. This represents first compound which has been reported.

Superoxide dismutases (SODs) are metalloenzymes that protect aerobic organisms from oxidative damage mediated by the superoxide radical. While Fe- and Mn-dependent SODs E. coli possess virtually identical protein folds active-site geometries, they strictly metal specific. To explore origin of this extraordinary metal-ion specificity to elucidate mechanisms which these enzymes tune geometric electronic properties, thus reactivity, their ions, we utilized a combination spectroscopic...

Mn K-edge X-ray absorption spectroscopy (XAS) was used to gain insights into the geometric and electronic structures of [MnII(Cl)2(Me2EBC)], [MnIV(OH)2(Me2EBC)]2+, [MnIV(O)(OH)(Me2EBC)]+, which are all supported by tetradentate, macrocyclic Me2EBC ligand (Me2EBC = 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane). Analysis extended fine structure (EXAFS) data for [MnIV(O)(OH)(Me2EBC)]+ revealed Mn–O scatterers at 1.71 1.84 Å Mn–N 2.11 Å, providing first unambiguous support formulation...

The Mn+OH moiety in a manganese(IV) complex has more powerful electron-transfer capability than its corresponding Mn+O moiety. An can abstract hydrogen from substrate, then rebind the OH group reduced M(n−1)+OH form to substrate radical. In contrast, active center with an cannot perform similar rebound M(n−1)+OH2 (see scheme; HAT=hydrogen abstraction). Detailed facts of importance specialist readers are published as "Supporting Information". Such documents peer-reviewed, but not...

Three complexes of Mn(III) with “scorpionate” type ligands have been investigated by a variety physical techniques. The are [Tp2Mn]SbF6 (1), [Tp2*Mn]SbF6 (2), and [{PhB(MeIm)3}2Mn](CF3SO3) (3a), where Tp– = hydrotris(pyrazolyl)borate anion, Tp*– hydrotris(3,5-dimethylpyrazolyl)borate PhB(MeIm)3– phenyltris(3-methylimidazol-2-yl)borate anion. crystal structure 3a is reported; the structures 1 2 previously reported, but were reconfirmed in this work. synthesis characterization...

Abstract Manganese(IV)‐oxo complexes are often invoked as intermediates in Mn‐catalyzed C−H bond activation reactions. While many synthetic Mn IV ‐oxo species mild oxidants, other members of this class can attack strong bonds. The basis for these reactivity differences is not well understood. Here we describe a series with N5 pentadentate ligands that modulate the equatorial ligand field center, assessed by electronic absorption, electron paramagnetic resonance, and K‐edge X‐ray absorption...

Density functional theory calculations have been performed to gain insight into the origin of ligand effects in rhodium (Rh)-catalyzed hydroformylation olefins. In particular, olefin insertion step Wilkinson catalytic cycle, which is commonly invoked as regioselectivity-determining step, has examined by considering a large variety density functionals (e.g., B3LYP, M06-L); range substrates, including simple terminal hexene, octene), heteroatom-containing vinyl acetate), and...

The mononuclear Mn(IV)-oxo complex [MnIV(O)(N4py)]2+, where N4py is the pentadentate ligand N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine, has been proposed to attack C–H bonds by an excited-state reactivity pattern [Cho, K.-B.; Shaik, S.; Nam, W. J. Phys. Chem. Lett. 2012, 3, 2851−2856 (DOI: 10.1021/jz301241z)]. In this model, a 4E excited state utilized provide lower-energy barrier for hydrogen-atom transfer. This proposal intriguing, as it offers both rationale relatively high...

The vibrational energy relaxation of carbon monoxide in the heme pocket sperm whale myoglobin was studied by using molecular dynamics simulation and normal mode analysis methods. Molecular trajectories solvated were run at 300 K for both δ- ɛ-tautomers distal His-64. Vibrational population times 335 ± 115 ps δ-tautomer 640 185 ɛ-tautomer estimated Landau–Teller model. Normal used to identify those protein residues that act as primary “doorway” modes oscillator. Although CO rates ɛ-...

The dynamics of electronic and thermal relaxation the heme in myoglobin (Mb) have been determined from subpicosecond time-resolved near-IR absorbance spectra photoexcited Mb. A broad, short-lived feature near 12 000 cm-1 (833 nm) was observed assigned to an excited state heme. relaxes its ground with a time constant 3.4 ± 0.4 ps, leading spectrum that is indicative "hot" ensuing characterized by probing spectral evolution band III, porphyrin−iron charge-transfer transition 13 110 (763...

X-ray absorption spectroscopy has been used to characterize the novel nitridoiron(IV) units in two [PhBPR3]Fe(N) complexes (R = iPr and CyCH2) obtain direct spectroscopic evidence for a very short Fe−N distance. The distance of 1.51−1.55 Å reflects presence an Fe⋮N triple bond accord with observed vibration one these species (νFeN 1034 cm-1). This highly covalent bonding interaction results appearance unusually intense pre-edge peak, whose estimated area 100(20) is much larger than those...