Zwei Trikupfer‐Komplexe wurden entwickelt, die die effiziente Oxidation von Methan zu Methanol unter Umgebungsbedingungen vermitteln: ein biomimetischer Trikupfer‐Komplex (siehe Bild) und eine von ...der Methan‐Monooxygenase (pMMO) abgeleitete Trikupferpeptid‐Spezies.
Charge density studies of chemical bonds for two iron complexes, (NO)Fe(S,S-C
6H
4)
2 PPN (
1), where PPN
=
N(Pph
3)
2 and Fe
3(NO)
3(S,S-C
6H
4)
3 (
2) are investigated in terms of the topological ...properties at bond critical points based on the ‘atoms in molecule’ theory. The one electron reduction form (
1R) of complex
1 and the one electron oxidation form (
2O) of complex
2 are also included for comparison. The X-ray absorption spectroscopy of Fe K- and L
III,II-edges, as well as the N/S K-edge are applied to verify the illustration in the variation of the electronic structures. Based on the
ρ
c, ▿
2
ρ
c, and
H
b values among the compound studied, Fe-S/N can be regarded as polarized covalent bond, and Fe-N bonds show stronger covalent character than that of the Fe–S bond, which is believed to be a highly polarized covalent bond.
Seventy percent of the ferrocene moieties in double-stranded polybisnorbornenes containing linearly aligned ferrocene linkers are oxidised and each of the neighbouring monomeric units in these ...polymers may strongly interact with each other; the oxidised form of has been shown to be antiferromagnetic.
With Cd and Zn metal ions removed from the native rabbit-liver metallothionein upon unfolding, Cu-modified metallothioneins (Cu-MTs) were obtained during refolding in solutions containing CuI or CuII ...ions. X-ray absorption near-edge spectroscopic results confirm the respectively assigned oxidation states of the copper ions in CuI-MT and CuII-MT. Global and local structures of the Cu-MTs were subsequently characterized by anomalous small-angle x-ray scattering (ASAXS) and extended x-ray absorption fine structure. Energy-dependent ASAXS results indicate that the morphology of CuII-MT resembles that of the native MT, whereas CuI-MT forms oligomers with a higher copper content. Both dummy-residue simulation and model-shape fitting of the ASAXS data reveal consistently rodlike morphology for CuII-MT. Clearly identified Cu-S, Cu-O, and Cu-Cu contributions in the extended x-ray absorption fine structure analysis indicate that both CuI and CuII ions are bonded with O and S atoms of nearby amino acids in a four-coordination environment, forming metal clusters smaller than metal thiolate clusters in the native MT. It is demonstrated that a combination of resonant x-ray scattering and x-ray absorption can be particularly useful in revealing complementary global and local structures of metalloproteins due to the atom specific characteristics of the two techniques.
Equilibrium unfolding behaviors of cytochrome c and lysozyme induced by the presence of urea (0–10M) as well as changes in temperature (295–363K) or pH (1.8–7) are examined via small-angle x-ray ...scattering and spectroscopic techniques, including circular dichroism and optical absorption. Denaturant and temperature effects are incorporated into the free energy expression for a general multigroup unfolding process. Results indicate that there are at least four unfolding groups in the temperature-, urea-, or pH-induced unfolding of cytochrome c: two of these are related to the prosthetic heme group, and the other two correspond, respectively, to the unfolding of α-helices and global changes in protein morphology that are largely unaccounted for by the first two groups. In contrast, the unfolding of lysozyme approximately follows a simple one-group process. A modified mean-field Ising model is adopted for a coherent description of the unfolding behaviors observed. Thermodynamic parameters extracted from simple denaturing processes, on the basis of the Ising model, can closely predict unfolding behaviors of the proteins in compounded denaturing environments.
The neutral trinuclear iron−thiolate−nitrosyl, (ON)Fe(μ-S,S-C6H4)3 (1), and its oxidation product, (ON)Fe(μ-S,S-C6H4)3PF6 (2), were synthesized and characterized by IR, X-ray diffraction, X-ray ...absorption, electron paramagnetic resonance (EPR), and magnetic measurement. The five-coordinated, square pyramidal geometry around each iron atom in complex 1 remains intact when complex 1 is oxidized to yield complex 2. Magnetic measurements and EPR results show that there is only one unpaired electron in complex 1 (S total = 1/2) and no unpaired electron (S total = 0) in 2. The detailed geometric comparisons between complexes 1 and 2 provide understanding of the role that the unpaired electron plays in the chemical bonding of this trinuclear complex. Significant shortening of the Fe−Fe, Fe−N, and Fe−S distances around Fe(1) is observed when complex 1 is oxidized to 2. This result implicates that the removal of the unpaired electron does induce the strengthening of the Fe−Fe, Fe−N, and Fe−S bonds in the Fe(1) fragment. A significant shift of the νNO stretching frequency from 1751 cm-1 (1) to 1821, 1857 cm-1 (2) (KBr) also indicates the strengthening of the N−O bonds in complex 2. The EPR, X-ray absorption, magnetic measurements, and molecular orbital calculations lead to the conclusion that the unpaired electron in complex 1 is mainly allocated in the Fe(1) fragment and is best described as {Fe(1)NO}7, so that the unpaired electron is delocalized between Fe and NO via d−π* orbital interaction; some contributions from Fe(2)NO and Fe(3)NO as well as the thiolates associated with Fe (1) are also realized. According to MO calculations, the spin density of complex 1 is predominately located at the Fe atoms with 0.60, −0.15, and 0.25 at Fe(1), Fe(2), and Fe(3), respectively.
Powder, and seldom single crystal diffraction, provides the first structural information about zeolites. However, because it is unable to take account of local defects or disorder, diffraction has to ...be supplemented ancillary information e.g. from local spectroscopies. The resulting structure may be used subsequently as a starting point for molecular dynamics/Monte Carlo studies of (guest-host) systems that gives in their turn new insight on the structural hypotheses assumed during diffraction data refinement.
The local and global structural changes of cytochrome c induced by urea in aqueous solution have been studied using X-ray absorption spectroscopy (XAS) and small-angle X-ray scattering (SAXS). ...According to the XAS result, both the native (folded) protein and the unfolded protein exhibit the same preedge features taken at Fe K-edge, indicating that the Fe(III) in the heme group of the protein maintains a six-coordinated local structure in both the folded and unfolded states. Furthermore, the discernible differences in the X-ray absorption near-edge structure (XANES) of these two states are attributed to a possible spin transition of the Fe(III) from a low-spin state to a high-spin state during the unfolding process. The perseverance of six-coordination and the spin transition of the iron are reconciled by a proposed ligand exchange, with urea and water molecules replacing the methionine-80 and histidine-18 axial ligands, respectively. The SAXS result reveals a significant morphology change of cytochrome c from a globular shape of a radius of gyration R g = 12.8 Å of the native protein to an elongated ellipsoid shape of R g = 29.7 Å for the unfolded protein in the presence of concentrated urea. The extended X-ray absorption fine structure (EXAFS) data unveil the coordination geometries of Fe(III) in both the folded and unfolded state of cytochrome c. An initial spin transition of Fe(III) followed by an axial ligand exchange, accompanied by the change in the global envelope, is proposed for what happened in the protein unfolding process of cytochrome c.
博士
國立臺灣大學
化學研究所
91
This work is focused on the characterization of chemical bonding of Ni/Fe complexes and electronic configuration of Ni/Fe by using X-ray diffraction ( XRD ), X-ray absorption ...spectroscopy ( XAS ), electron paramagnetic resonance ( EPR ), magnetic measurement and density functional theory ( DFT ) calculation.
In the Ni(C4N4H2)(C4S2F6) compound, the local charge concentrations of electron density of Ni atom are at the bisection angles of ∠S/N-Ni-S/N (the dp direction), and the charge depletions are along the Ni-N and Ni-S directions (the ds direction). Based on the rc, Ñ2rc, Hb values at the bond critical points, and Fermi-hole functions, the Ni-S/N bonds can be regarded as polarized covalent bonds. The dipole moment of molecule in crystal is obtained from both AIM charge and monopole of multipole model, which is close to the experimental result.
In the Ni(XC6H4-o-Y) PPN (X = S, Se, Te, Y = NH) compounds, the covalent character is in the order Ni-N > Ni-S ~ Ni-Se > Ni-Te. A mixed valence
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