Resonance Raman Spectroscopic Studies of Hydroperoxo Derivatives of Cobalt-substituted Myoglobin

Recent progress in generating and stabilizing reactive heme protein enzymatic intermediates by cryoradiolytic reduction has prompted application of a range of spectroscopic approaches to effectively interrogate these species. The impressive potential of resonance Raman spectroscopy for characterizing such samples has been recently demonstrated in a number of studies of peroxo- and hydroperoxo-intermediates. While it is anticipated that this approach can be productively applied to the wide range of heme proteins whose reaction cycles naturally involve these peroxo- and hydroperoxo-intermediates, one limitation that sometimes arises is the lack of enhancement of the key intraligand ν(O–O) stretching mode in the native systems. The present work was undertaken to explore the utility of cobalt substitution to enhance both the ν(Co–O) and ν(O–O) modes of the CoOOH fragments of hydroperoxo forms of heme proteins bearing a trans–axial histidine linkage. Thus, having recently completed RR studies of hydroperoxo myoglobin, attention is now turned to its cobalt-substituted analogue. Spectra are acquired for samples prepared with 16O2 and 18O2 to reveal the ν(M–O) and ν(O–O) modes, the latter indeed being observed only for the cobalt-substituted proteins. In addition, spectra of samples prepared in deuterated solvents were also acquired, providing definitive evidence for the presence of the hydroperoxo-species

A Comment on "Brans-Dicke Cosmology with a scalar field potential"

We show that a recent letter claiming to present exact cosmological solutions in Brans-Dicke theory actually uses a flawed set of equations as the starting point for their analysis. The results presented in the letter are therefore not valid.Comment: 2 pages, no figures. To appear in Europhysics Letter

Resonance Raman Interrogation of the Consequences of Heme Rotational Disorder in Myoglobin and its Ligated Derivatives

Resonance Raman spectroscopy is employed to characterize heme site structural changes arising from conformational heterogeneity in deoxyMb and ligated derivatives, i.e., the ferrous CO (MbCO) and ferric cyanide (MbCN) complexes. The spectra for the reversed forms of these derivatives have been extracted from the spectra of reconstituted samples. Dramatic changes in the low-frequency spectra are observed, where newly observed RR modes of the reversed forms are assigned using protohemes that are selectively deuterated at the four methyl groups or at the four methine carbons. Interestingly, while substantial changes in the disposition of the peripheral vinyl and propionate groups can be inferred from the dramatic spectral shifts, the bonds to the internal histidyl imidazole ligand and those of the Fe−CO and Fe−CN fragments are not significantly affected by the heme rotation, as judged by lack of significant shifts in the ν(Fe−NHis), ν(Fe−C), and ν(C−O) modes. In fact, the apparent lack of an effect on these key vibrational parameters of the Fe−NHis, Fe−CO, and Fe−CN fragments is entirely consistent with previously reported equilibrium and kinetic studies that document virtually identical functional properties for the native and reversed forms

What can 14 CO measurements tell us about OH?

The possible use of 14CO measurements to constrain hydroxyl radical (OH) concentrations in the atmosphere is investigated. 14CO is mainly produced in the upper atmosphere from cosmic radiation. Measurements of 14CO at the surface show lower concentrations compared to the upper atmospheric source region, which is the result of oxidation by OH. In this paper, the sensitivity of 14CO mixing ratio surface measurements to the 3-D OH distribution is assessed with the TM5 model. Simulated 14CO mixing ratios agree within a few molecules 14CO cm¿3 (STP) with existing measurements at five locations worldwide. The simulated cosmogenic 14CO distribution appears mainly sensitive to the assumed upper atmospheric 14C source function, and to a lesser extend to model resolution. As a next step, the sensitivity of 14CO measurements to OH is calculated with the adjoint TM5 model. The results indicate that 14CO measurements taken in the tropics are sensitive to OH in a spatially confined region that varies strongly over time due to meteorological variability. Given measurements with an accuracy of 0.5 molecules 14CO cm¿3 STP, a good characterization of the cosmogenic 14CO fraction, and assuming perfect transport modeling, a single 14CO measurement may constrain OH to 0.2¿0.3×106 molecules OH cm¿3 on time scales of 6 months and spatial scales of 70×70 degrees (latitude×longitude) between the surface and 500 hPa. The sensitivity of 14CO measurements to high latitude OH is about a factor of five higher. This is in contrast with methyl chloroform (MCF) measurements, which show the highest sensitivity to tropical OH, mainly due to the temperature dependent rate constant of the MCF¿OH reaction. A logical next step will be the analysis of existing 14CO measurements in an inverse modeling framework. This paper presents the required mathematical framework for such an analysis