Carbon Monoxide Complex Research Articles

1H and 15N resonance assignments and secondary structure of the carbon monoxide complex of sperm whale myoglobin.

Sequence-specific backbone 1H and 15N resonance assignments have been made for 95% of the amino acids in sperm whale myoglobin, complexed with carbon monoxide (MbCO). Many assignments for side-chain resonances have also been obtained. Assignments were made by analysis of an extensive series of homonuclear 2D spectra, measured with unlabeled protein, and both 2D and 3D 1H-15N-correlated spectra obtained from uniformly 15N-labeled myoglobin. Patterns of medium-range NOE connectivities indicate the presence of eight helices in positions that are very similar to those found in the crystal structures of sperm whale myoglobin. The resonance assignments of MbCO form the basis for determination of the solution structure and for hydrogen-exchange measurements to probe the stability and folding pathways of myoglobin. They will also form a basis for assignment of the spectra of single-site mutants with altered ligand-binding properties.

Photoselection in polarized photolysis experiments on heme proteins

Polarized photolysis experiments have been performed on the carbon monoxide complex of myoglobin to assess the effects of photoselection on the kinetics of ligand rebinding and to investigate the reorientational dynamics of the heme plane. The results are analyzed in terms of the optical theory developed in the preceding paper by Ansari and Szabo. Changes in optical density arising from rotational diffusion of the photoselected population produce large deviations from the true geminate ligand rebinding curves if measurements are made with only a single polarization. The apparent ligand rebinding curves are significantly distorted even at photolysis levels greater than 90%. These deviations are eliminated by obtaining isotropically-averaged optical densities from measurements using both parallel and perpendicular polarizations of the probe pulse. These experiments also yield the optical anisotropy, which gives a novel method for accurately determining the degree of photolysis, as well as important information on the reorientational dynamics of the heme plane. The correlation time for the overall rotational diffusion of the molecule is obtained from the decay of the anisotropy. The anisotropy prior to rotational diffusion is lower than that predicted for a rigidly attached, perfectly circular absorber, corresponding to an apparent order parameter of S = 0.95 +/- 0.02. Polarized absorption data on single crystals suggest that the decreased anisotropy results more from internal motions of the heme plane which take place on time scales shorter than the duration of the laser pulse (10 ns) than from out-of-plane polarized transitions.

Characterization of nickel species at Ni/γ-Al 20 3 and Ni/faujasite catalysts by carbon monoxide adsorption

The catalysts Ni/γ-Al 2O 3, Ni/HY deal and Ni/NaX are studied by carbon monoxide adsorption and desorption at 30° C and a broad range of pressures. Novel bands of carbon monoxide stretching vibrations and assignments to carbon monoxide complexes are considered for (i) Ni/γ-Al 2O 3 at 2082 cm t¯1 related to Ni δ+ sites at metallic Ni clusters-NiAl 2O 4 boundaries, (ii) Ni/HY deal at 2100+2140 cm t¯1 (adsorption) and 2118 cm t¯1 (desorption), referred to bicarbonyls and monocarbonyls, respectively, on Ni δ+ sites stabilized by nonskeletal Al species, and (iii) Ni/NaX at 1812–2068 cm t¯1 formed after the decomposition of Ni(CO) 4 and attributed to polynuclear nickel carbonyls. The reducibility of the Ni species characterized by the maxima of TPR peaks in starting materials increases in the sequence: cationic Ni 2+ in Ni(II)NaY and Ni(II)NaX<NiO clusters on Al 20 3<NiO in Ni(II)HY deal- The degrees of reduction of the individual catalysts are reflected by their methanation activities.

Speed of intersubunit communication in proteins.

To determine the speed of communication between protein subunits, time-resolved absorption spectra were measured following partial photodissociation of the carbon monoxide complex of hemoglobin. The experiments were carried out using linearly polarized, 10-ns laser pulses, with the polarization of the excitation pulse both parallel and perpendicular to the polarization of the probe pulse. The substantial contribution to the observed spectra from photoselection effects was eliminated by isotropically averaging the polarized spectra, allowing a detailed comparison of the kinetics as a function of the degree of photolysis. These results show that prior to 1 microsecond both geminate ligand rebinding and conformational relaxation are independent of the number of ligands dissociated from the hemoglobin tetramer, as expected for a two-state allosteric model. After this time the kinetics depend on the ligation state of the tetramer. The conformational relaxation at 10 microseconds can be interpreted in terms of the two-state allosteric model as arising from the R to T quaternary conformational change of both unliganded and singly liganded molecules. These results suggest that communication between subunits requires about 1 microsecond and that the mechanism of the communication which occurs after this time is via the R to T conformational change. The optical anisotropy provides a novel means of accurately determining the extinction coefficients of the transient photoproduct. The decay in the optical anisotropy, moreover, provides an accurate determination of the rotational correlation time of 36 +/- 3 ns.

Weakly bound complexes of carbon monoxide

The authors have carried out a wide-ranging theoretical investigation of weakly bound complexes containing carbon monoxide that reveals at least one general feature of CO weak bonding, its electrical polarization. Included in this study are high-level ab initio calculations of two dimer complexes and of the electrical response properties of CO. The electrical properties were used in model calculations of weakly bound complexes of CO and, in particular, to achieve a representation of CO for the electrical interaction scheme of the molecular mechanics for clusters (MMC) model. MMC calculations were carried out to explore the difference between oxygen-end and carbon-end bonding, and in the course of these calculations predictions of multiple minima have come about for several complexes. The calculational results also provide information about how the properties of CO change upon weak bonding and how electrical polarization influences structure. 65 refs., 7 figs., 16 tabs.

Geminate recombination of carbon monoxide complexes of hemes and heme proteins

Geminate recombination of carbon monoxide complexes of hemes and heme proteins

Electrochemical Quantification of Carbon Monoxide Complexation to Copper(I) in a Chloroaluminate Molten Salt

The reversible complexation of carbon monoxide to Cu(I) in the 1.5:1.0 (BuPyCl = 1‐butylpyridinium chloride) molten salt at ambient temperature was investigated using voltammetric and potentiometric techniques. The infrared spectrum of the carbon monoxide complex exhibits a strong band at 2142 cm−1. Staircase cyclic and normal pulse voltammetries reveal that the Cu(II)/Cu(I) couple is reversible under nitrogen but becomes quasi‐reversible or hampered by homogeneous kinetics under carbon monoxide. From the potentiometric data, the equilibrium constant for the reaction was determined to be with equal to one.

Carbonmonoxy dopamine beta-hydroxylase. Structural characterization by Fourier transform infrared, fluorescence, and x-ray absorption spectroscopy.

The carbon monoxide complex of ascorbate-reduced dopamine beta-hydroxylase has been prepared and characterized by Fourier transform infrared, fluorescence, and x-ray absorption spectroscopies. CO has previously been shown to be a competitive inhibitor with respect to O2, and binds to only one of the two copper atoms/active site (Blackburn, N. J., Pettingill, T. M., Seagraves, K. S., and Shigeta, R. T. (1990) J. Biol. Chem. 265, 15383-15386). Thus, it acts as an excellent probe of the O2-binding site. A single C-O infrared absorption band is observed at 2089 cm-1, shifting by 46 cm-1 to lower energy on substitution with either 13C16O or 12C18O. The 13C isotope shift is reversed to the position expected for 12CO upon vacuum flushing with 12CO gas, indicating that formation of the CO adduct is a fully reversible process. Binding of the substrate tyramine does not eliminate the infrared peak but causes a 3-cm-1 shift to lower energy. On the other hand, binding of a bifunctional inhibitor which cross-links the substrate and O2-binding site does eliminate the CO peak. These data, in conjunction with the competitive nature of CO binding with respect to O2, identify the CO-binding site as the O2-binding site, and place it in close proximity to the substrate-binding site. CO-dopamine beta-hydroxylase exhibits no luminescence in the visible region, suggesting a structure different from carbonmonoxy hemocyanin, and in all probability mononuclear. Analysis of extended x-ray absorption spectroscopy data is most consistent with an average coordination per Cu of 2-3 histidines, 0.5 CO, and 0.5 S atoms as ligands, and absorption edge comparisons indicates pseudo-4 coordination as the most likely geometry at each Cu(I) center. The results can be interpreted by a model involving inequivalent 4-coordination at each Cu(I) center in the CO adduct with CuAHis3S...CuBHis2CO-X as the coordination most consistent with all of the data.

Dynamics of the quaternary conformational change in trout hemoglobin

The kinetics of conformational changes in trout hemoglobin I have been characterized over the temperature range 2-65 degrees C from time-resolved absorption spectra measured following photodissociation of the carbon monoxide complex. Changes in the spectra of the deoxyheme photoproduct were used to monitor changes in the protein conformation. Although the deoxyheme spectral changes are only about 8% of the total spectral change due to ligand rebinding, a combination of high-precision measurements and singular value decomposition of the data permits a detailed analysis of both their amplitudes and relaxation rates. Systematic variation of the degree of photolysis was used to alter the distribution of liganded tetramers, permitting the assignment of the spectral relaxation at 20 microseconds to the R----T quaternary conformational change of the zero-liganded and singly liganded molecules and spectral relaxations at about 50 ns and 2 microseconds to tertiary conformational changes within the R structure. Analysis of the effect of photoselection by the linearly polarized excitation pulse indicates that a major contribution to the apparent geminate rebinding in the 50-ns relaxation arises from rotational diffusion of molecules containing unphotolyzed heme-CO complexes. The activation enthalpy and activation entropy for the R0----T0 transition are +7.4 kcal/mol and -12 cal mol-1 K-1. Using the equilibrium data, delta H = +29.4 kcal/mol and delta S = +84.4 cal mol-1 K-1 [Barisas, B. G., & Gill, S. J. (1979) Biophys. Chem. 9, 235-244], the activation parameters for the T0----R0 transition are calculated to be delta H = +37 kcal/mol and delta S = +73 cal mol-1 K-1. The similarity of the equilibrium and activation parameters for the T0----R0 transition indicates that the transition state is much more R-like than T-like. This result suggests that in the path from T0 to R0 the subunits have already almost completely rearranged into the R configuration when the transition state is reached, while in the path from R0 to T0 the subunits remain in a configuration close to R in the transition state. The finding of an R-like transition state explains why the binding of ligands causes much smaller changes in the R----T rates than in the T----R rates.

Resonance Raman study of cytochrome aa3 from Sulfolobus acidocaldarius

The single subunit terminal oxidase of Sulfolobus acidocaldarius, cytochrome aa 3, was studied by resonance Raman spectroscopy. Results on the fully oxidized, the fully reduced, and the reduced carbon monoxide complex are reported and compared with those of sucaryotic cytochrome oxidase. It is shown that in both redox states the hemex a and a 3 are in the six-coordinated low-spin and six-coordinated high-spin configuration, respectively. The resonance Raman spectra reveal far-reaching similarities of this archaebacterial with mammalian or plant enzymes except for the reduced form of heme a. The formyl substituent of this heme appears above 1 640 cm −1, ruling out significant hydrogen bonding interactions which is in sharp contrast to beef heart cytochrome oxidase. In addition, frequency upshifts of the marker bands ν 4 and ν 2 are noted indicating differences in the electron density distribution within the molecular orbitals of the porphyrin.

Synthesis of cycloprop[c]indol-5-ones from 4-diazo-3-[n-(2-propenyl)amido]cyclohexadien-1-ones. Exploration of copper(I) and copper(II) complexes as catalysts

The cyclization of 4-diazo-3-[N-(2-propenyl)amido]cyclohexadienones to cycloprop[c]indol-5-ones under the influence of copper(I) and copper(II) compounds has been investigated. Catalysis is observed with copper(I) triflate, the carbon monoxide complexe of copper(I) triflate, and the carbon monoxide complexes of trifluoropentanedionato- and hexafluoropentanedionatocopper(I). The best results, essentially quantitative conversion, are achieved with a catalyst solution containing trifluoropentanedionatocopper(I) carbonyl and 1 equiv of n-butalymine. No significant enantioselectivity is observed with a chiral salicyliminatocopper(II), [(trifluoroacetyl)camphorato]copper(I) carbonyl, or a trifluoropentanedionatocopper(I) carbonyl solution containing (S)-α-naphthylethylamine. A mechanistic interpretation involving reductive dediazonization, exo-trig radical cyclization, and cyclopropane formation by the resulting intermediate is proposed

Complexes of Carbon Monoxide and Its Relatives: An Organometallic Family Celebrates Its Birthday

AbstractNickel tetracarbonyl was discovered one hundred years ago. Its hundredth birthday deserves to be celebrated not only by metal carbonyl chemists. The pioneering work of Mond, Langer, and Quincke has led to developments which, particularly in the last 30 years, have had consequences in many areas outside that of metal carbonyl chemistry. The parent ligand of the family, CO, has been joined by a series of relatives which are isoelectronic with it and which in some cases are even more effective as π acceptors. These are in the main extremely reactive molecules such as CS, CNH, and C= CH2, which, though very short‐lived in the free state, form very stable complexes with transition metals. This article documents the family relationships by structure and reactivity comparisons; attention is also drawn to the synthetic potential of the metal carbonyl analogues, which is still virtually untapped. The final section ventures a look towards the next 100 years, which promise to be just as exciting as the past century.

Studies of the solution structure of the bleomycin A2-iron(II)-carbon monoxide complex by means of two-dimensional NMR spectroscopy and distance geometry calculations

Studies of the solution structure of the bleomycin A2-iron(II)-carbon monoxide complex by means of two-dimensional NMR spectroscopy and distance geometry calculations

Characterization of a carbon monoxide complex of reduced dopamine beta-hydroxylase. Evidence for inequivalence of the Cu(I) centers.

Ascorbate-reduced dopamine beta-hydroxylase (DBH) is inhibited by CO in a competitive manner with respect to molecular O2. Measurement of the stoichiometry of CO binding indicates 0.50 CO bound per Cu(I), which provides the first evidence that the Cu(I) centers in the reduced enzyme are structurally inequivalent. FTIR spectroscopy has been used to detect an infrared absorption band characteristic of coordinated CO, with v(CO) = 2089 cm-1. Comparison of this frequency with those of other Cu(I)-carbonyls in both inorganic and protein systems suggests a coordination site with fewer or less basic ligands than the 3-histidine site of carbon-monoxy hemocyanin.

Water hydrogen bonding: The structure of the water–carbon monoxide complex

Rotational transitions between J≤3 levels within the K=0 manifold have been observed for H2O–CO, HDO–CO, D2O–CO, H2O–13CO, HDO–13CO, and H217O–CO using the molecular beam electric resonance and Fourier transform microwave absorption techniques. ΔMJ=0→1 transitions within the J=1 level were also measured at high electric fields. A tunneling motion which exchanges the equivalent hydrogens gives rise to two states in the H2O and D2O complexes. The spectroscopic parameters for H2O–CO in the spatially symmetric tunneling state are [∼(B0) =2749.130(2)MHz, D0=20.9(2)kHz, and μa=1.055 32(2)D] and in the spatially antisymmetric state are [∼(B0) =2750.508(1)MHz, D0=20.5(1)kHz, and μa=1.033 07(1)D]. Hyperfine structure is resolved for all isotopes. The equilibrium structure of the complex has the heavy atoms approximately collinear. The water is hydrogen bonded to the carbon of CO; however the bond is nonlinear. At equilibrium, the O–H bond of water makes an angle of 11.5° with the a axis of the complex; the C2v axis of water is 64° from the a axis of the complex. The hydrogen bond length is about 2.41 Å. The barrier to exchange of the bound and free hydrogens is determined as 210(20) cm−1 (600 cal/mol) from the dipole moment differences between the symmetric and antisymmetric states. The tunneling proceeds through a saddle point, with C2v structure, with the hydrogen directed towards the CO subunit. The equilibrium tilt away from a linear hydrogen bond is in the direction opposite to the tunneling path.

Characterization of two low Em forms of cytochrome a3 and their carbon monoxide complexes in mammalian cytochrome c oxidase

Evidence is presented for the existence of two forms of low-potential cytochrome a3. One appears to be similar to the low-spin form reported by Nicholls, P., and V. Hildebrandt (1978 Biochem. J. 173:65-72) and Wrigglesworth, J. M., J. Elsden, A. Chapman, N. Van der Water, and M. F. Grahn (1988. Biochim. Biophys. Acta. 936:452-464). It has a reduced Soret peak near 428 nm and a prominent alpha peak near 602 nm. This form is seen when the enzyme is either supplemented with lipoprotein or incorporated into a liposomal membrane, preexposed to a voltage greater than 400 mV for at least 30 min, and titrated in the presence of approximately 1 mM K3Fe(CN)6. The other form has a reduced Soret peak near 446 nm, and no prominent alpha peak. The 428-nm form has an Em near 175 mV and forms a CO complex with an Em near 225 mV. The 446-nm form has an Em near 200 mV and forms a CO complex with an Em near 335 mV.

Ligand binding and structural perturbations in cytochrome c peroxidase. A crystallographic study.

Crystal structures of the complexes formed between cytochrome c peroxidase and cyanide, nitric oxide, carbon monoxide, and fluoride have been determined and refined to 1.85 A. In all four complexes significant changes occur in the distal heme pocket due to movement of Arg-48, His-52, and a rearrangement of active site water molecules. In the cyanide, nitric oxide, and carbon monoxide complexes, Arg-48 moves away from the ligand while in the fluoride complex Arg-48 moves in toward the ligand to form a hydrogen bond or ion pair with the fluoride. More subtle changes occur on the proximal side of the heme. In an earlier study at lower resolution (Edwards, S. L., Kraut, J., and Poulos, T. L. (1988) Biochemistry 27, 8074-8081), we found that nitric oxide binding causes perturbations in the proximal domain involving Trp-191 which has been confirmed by the present study. Trp-191 is stacked parallel to and in contact with the proximal ligand, His-175. Nitric oxide binding results in a slight movement of Trp-191 away from His-175 and a large increase in crystallographic temperature factors indicating increased mobility of these residues on the proximal side of the heme. These proximal-side changes are unique to nitric oxide and are not related strictly to spin-state or oxidation state of the iron atom since similar changes were not observed in the cyanide (low-spin ferric), carbon monoxide (low-spin ferrous), or fluoride (high-spin ferric) complexes.

Substitution chemistry of carbonyl and sulphur dioxide triangulo-platinum clusters. Crystal structure of [Pt3(µ-CO)(µ-SO2)2{P(C6H11)3}3

The simple substitution chemistry of the triangulo-platinum clusters [Pt3(µ-CO)3 –n(µ-SO2)n{P(C6H11)3}3](n= 0–3) with carbon monoxide and sulphur dioxide ligands is described and some mechanistic implications discussed. Different products were isolated depending on the concentration of the gaseous reactants. For example, when 1 molar equivalent of carbon monoxide was added to [Pt3(µ-SO2)3{P(C6H11)3}3](1) the monosubstituted carbon monoxide complex [Pt3(µ-CO)(µ-SO2)2{P(C6H11)3}3](2) was formed. However, with excess of carbon monoxide, using dichloromethane as the solvent, a relatively unstable dimer, [Pt2(µ-SO2)(CO)2{P(C6H11)3}2](3) was isolated. This dimer was also prepared by the reaction of SO2 with [Pt3(µ-CO)3{P(C6H11)3}3](5). With benzene as the solvent, compound (1) reacts with excess of CO to give the disubstituted cluster [Pt3(µ-CO)2(µ-SO2){P(C6H11)3}3](4). The molecular structure of (2) has been determined by a single-crystal X-ray diffraction study. It crystallises in monoclinic space group C2/m, with four units of formula [Pt3(µ-CO)(µ-SO2)2{P(C6H11)3}3]·0.5C6H6 in a cell of dimensions of a= 24.909(9), b= 21.694(4), c= 15.559(4)A, and β= 125.41(3)°. The structure consists of an isosceles triangle of Pt atoms with Pt–Pt distances of 2.678(1) and 2.710(1)A. The Pt–Pt edges bridged by the sulphur dioxide ligands are appreciably longer than that bridged by carbon monoxide. The substitution chemistry of the mixed substituted clusters, (2) and (4) with xylyl isocyanide has been studied. The reactivities of both clusters resemble that of (1).

A carbon-monoxide complex of reduced dopamine-β-hydroxylase (DBH)

A carbon-monoxide complex of reduced dopamine-β-hydroxylase (DBH)

Vibration–rotation spectrum of the acetylene–carbon monoxide van der Waals molecule in the 3 μ region

The infrared absorption spectrum of the acetylene–carbon monoxide van der Waals molecule has been obtained in the 3 μ region. A color center laser was used to excite the vibration of the complex which corresponds to the antisymmetric hydrogen stretching mode in the monomer in a pulsed molecular jet. The form of the spectrum indicates that the molecule is a linear, hydrogen bonded complex, although excited state perturbations are present. The vibrational origin is at 3279.898(2) cm−1 and the ground state B value is 1397.4(6) MHz, corresponding to a separation of 5.011 Å for the monomer centers of mass. The spectrum cannot directly distinguish between the HCCH–CO and the HCCH–OC configurations, but the combined evidence of other hydrogen bonded complexes of carbon monoxide, the expectation that the observed hydrogen bond should be slightly shorter than the sum of van der Waals radii, and a distributed multipole analysis strongly favors the HCCH–CO configuration.