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CO Ligand (co + ligand)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

CO migration pathways in cytochrome P450cam studied by molecular dynamics simulations

PROTEIN SCIENCE, Issue 5 2007
Liliane Mouawad
Abstract Previous laser flash photolysis investigations between 100 and 300 K have shown that the kinetics of CO rebinding with cytochrome P450cam(camphor) consist of up to four different processes revealing a complex internal dynamics after ligand dissociation. In the present work, molecular dynamics simulations were undertaken on the ternary complex P450cam(cam)(CO) to explore the CO migration pathways, monitor the internal cavities of the protein, and localize the CO docking sites. One trajectory of 1 nsec with the protein in a water box and 36 trajectories of 1 nsec in the vacuum were calculated. In each trajectory, the protein contained only one CO ligand on which no constraints were applied. The simulations were performed at 200, 300, and 320 K. The results indicate the presence of seven CO docking sites, mainly hydrophobic, located in the same moiety of the protein. Two of them coincide with xenon binding sites identified by crystallography. The protein matrix exhibits eight persistent internal cavities, four of which corresponding to the ligand docking sites. In addition, it was observed that water molecules entering the protein were mainly attracted into the polar pockets, far away from the CO docking sites. Finally, the identified CO migration pathways provide a consistent interpretation of the experimental rebinding kinetics. [source]

The X-ray structure determination of bovine carbonmonoxy hemoglobin at 2.1 Å resoultion and its relationship to the quaternary structures of other hemoglobin crystal forms

PROTEIN SCIENCE, Issue 6 2001
Martin K. Safo
Abstract Crystallographic studies of the intermediate states between unliganded and fully liganded hemoglobin (Hb) have revealed a large range of subtle but functionally important structural differences. Only one T state has been reported, whereas three other quaternary states (the R state, B state, and R2 or Y state) for liganded Hb have been characterized; other studies have defined liganded Hbs that are intermediate between the T and R states. The high-salt crystal structure of bovine carbonmonoxy (CO bovine) Hb has been determined at a resolution of 2.1 Å and is described here. A detailed comparison with other crystallographically solved Hb forms (T, R, R2 or Y) shows that the quaternary structure of CO bovine Hb closely resembles R state Hb. However, our analysis of these structures has identified several important differences between CO bovine Hb and R state Hb. Compared with the R state structures, the ,-subunit N-terminal region has shifted closer to the central water cavity in CO bovine Hb. In addition, both the ,- and ,-subunits in CO bovine Hb have more constrained heme environments that appear to be intermediate between the T and R states. Moreover, the distal pocket of the ,-subunit heme in CO bovine Hb shows significantly closer interaction between the bound CO ligand and the Hb distal residues Val 63(E11) and His 63(E7). The constrained heme groups and the increased steric contact involving the CO ligand and the distal heme residues relative to human Hb may explain in part the low intrinsic oxygen affinity of bovine Hb. [source]

Reactions of 7,8-Dithiabicyclo[4.2.1]nona-2,4-diene 7- exo -Oxide with Dodecacarbonyl Triiron Fe3(CO)12: A Novel Type of Sulfenato Thiolato Diiron Hexacarbonyl Complexes

CHEMISTRY - AN ASIAN JOURNAL, Issue 7 2010
Jochen Windhager Dr.
Abstract The reaction of Fe3(CO)12 (13) with 7,8-dithiabicyclo[4.2.1]nona-2,4-diene 7- exo -oxide (12) yields the sulfenato-thiolato complex 14, which is used as starting material for further reactions. The disulfenato complex 17 is obtained by using one equivalent of dimethyldioxirane (DMD), and the monoepoxide 18 is prepared by the oxidation of 14 with an excess of DMD. Complex 14 can be converted to the monophosphine complexes 19,a and 19,b by subsequent substitution of one CO ligand using trimethylaminoxide Me3NO and triphenylphosphine PPh3. Additional substitution reactions are done with 17 by using acetonitrile as a ligand to form 20,a and 20,b. In the electrochemical part of the paper, the reactions of the reduced iron species 14, 15, 17, and 19,a are studied. [source]

Structural Identification of Spectroscopic Substates in Neuroglobin

CHEMPHYSCHEM, Issue 1 2010
Karin Nienhaus Dr.
Abstract The structural origins of infrared absorptions of photodissociated CO in murine neuroglobin (Ngb) are determined by combining Fourier transform infrared (FTIR) spectroscopy and molecular dynamics (MD) simulations. Such an approach allows to identify and characterize both the different conformations of the Ngb active site and the transient ligand docking sites. To capture the influence of the protein environment on the spectroscopy and dynamics, experiments and simulations are carried out for the wild type protein and its F28L and F28W mutants. It is found that a voluminous side chain at position 28 divides site B into two subsites, B' and B". At low temperatures, CO in wt Ngb only migrates to site B' from where it can rebind, and B" is not populated. The spectra of CO in site B' for wt Ngb from simulations and experiments are very similar in spectral shift and shape. They both show doublets, red-shifted with respect to gas-phase CO and split by,8 cm,1. The FTIR spectra of the F28L mutant show additional bands which are also found in the simulations and can be attributed to CO located in substate B". The different bands are mainly related to different orientations of the His64 side chain with respect to the CO ligand. Large red-shifts arise from strong interactions between the HistidineNH and the CO oxygen. After dissociation from the heme iron, the CO ligand visits multiple docking sites. The locations of the primary docking site B and a secondary site C, which corresponds to the Mb Xe4 cavity, could be identified unambiguously. Finally, by comparing experiment and simulations it is also possible to identify protonation of its , position (His,64 NgbCO) as the preferred heme-bound conformation in the wild type protein with a signal at 1935 cm,1. [source]

Highly Efficient Redox Isomerization of Allylic Alcohols at Ambient Temperature Catalyzed by Novel Ruthenium,Cyclopentadienyl Complexes,New Insight into the Mechanism

CHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2005
Belén Martín-Matute Dr.
Abstract A range of ruthenium cyclopentadienyl (Cp) complexes have been prepared and used for isomerization of allylic alcohols to the corresponding saturated carbonyl compounds. Complexes bearing CO ligands show higher activity than those with PPh3 ligands. The isomerization rate is highly affected by the substituents on the Cp ring. Tetra(phenyl)methyl-substituted catalysts rapidly isomerize allylic alcohols under very mild reaction conditions (ambient temperature) with short reaction times. Substituted allylic alcohols have been isomerized by employing Ru,Cp complexes. A study of the isomerization catalyzed by [Ru(Ph5Cp)(CO)2H] (14) indicates that the isomerization catalyzed by ruthenium hydrides partly follows a different mechanism than that of ruthenium halides activated by KOtBu. Furthermore, the lack of ketone exchange when the isomerization was performed in the presence of an unsaturated ketone (1 equiv), different from that obtained by dehydrogenation of the starting allylic alcohol, supports a mechanism in which the isomerization takes place within the coordination sphere of the ruthenium catalyst. [source]

An Iron(II) Carbonyl Thiolato Complex Bearing 2-Methoxy-Pyridine: A Structural Model of the Active Site of [Fe] Hydrogenase

CHEMISTRY - AN ASIAN JOURNAL, Issue 9 2010
Soichiro Tanino Dr.
Model complex: An FeII complex bearing a thiolate, 2-methoxy-pyridine, and three facially arranged CO ligands was synthesized as a structural analogue of the active site of a CO-inhibited form of [Fe] hydrogenase, from the reaction of [FeBr2(CO)4] with NaS{2,6-(mesityl)2C6H3} and the successive treatment with 2-methoxy-pyridine. [source]

Dithiolate-Bridged Fe-Ni-Fe Trinuclear Complexes Consisting of Fe(CO)3,n(CN)n (n=0, 1) Components Relevant to the Active Site of [NiFe] Hydrogenase

CHEMISTRY - AN ASIAN JOURNAL, Issue 6 2009
Satyanarayan Pal Dr.
Abstract Step-by-step: A trinuclear Fe-Ni-Fe complex 1 was synthesized from the reaction of [Fe(CO)4I2] with Li2[Ni(norbornane- exo -2,3-dithiolate)2]. The CO ligands in 1 were transformed into CN, upon treatment with ,N(SiMe3)2, and the monocyanide complex 3 and the dicyanide complex 4 were obtained. Complexes 3 and 4 were found to react with protonic acids, whereas 1 is robust. A dithiolate-bridged Fe-Ni-Fe trinuclear carbonyl complex [(CO)3Fe(,-ndt)Ni(,-ndt)Fe(CO)3] (1, ndt=norbornane- exo -2,3-dithiolate) has been synthesized from the reaction of [Fe(CO)4I2] and Li2[Ni(ndt)2]. This reaction was found to occur with concomitant formation of a tetranuclear cluster [Ni3(,-ndt)4FeI] (2). Treatment of 1 with Na[N(SiMe3)2] transforms some of the CO ligands into CN,, and the monocyanide complex (PPh4)[(CO)2(CN)Fe(,-ndt)Ni(,-ndt)Fe(CO)3] (3) and the dicyanide complex (PPh4)2[(CO)2(CN)Fe(,-ndt)Ni(,-ndt)Fe(CO)2(CN)] (4) were isolated. X-ray structural analyses of the trinuclear complexes revealed a Fe-Ni-Fe array in which the metal centers are connected by the ndt sulfur bridges and direct FeNi bonds. Hydrogen bonding between the CN ligand in 3 and cocrystallized ethanol was found in the solid-state structure. The monocyanide complex 3 and dicyanide complex 4 reacted with acids such as HOTf or HCl generating insoluble materials, whereas complex 1 did not react. [source]