It is of great importance to understand the origin of high oxygen-evolving activity of state-of-the-art multimetal oxides/(oxy)hydroxides at atomic level. Herein we report an evident improvement of oxygen evolution reaction activity via incorporating iron and vanadium into nickel hydroxide lattices. X-ray photoelectron/absorption spectroscopies reveal the synergistic interaction between iron/vanadium dopants and nickel in the host matrix, which subtly modulates local coordination environments and electronic structures of the iron/vanadium/nickel cations. Further, in-situ X-ray absorption spectroscopic analyses manifest contraction of metal-oxygen bond lengths in the activated catalyst, with a short vanadium-oxygen bond distance. Density functional theory calculations indicate that the vanadium site of the iron/vanadium co-doped nickel (oxy)hydroxide gives near-optimal binding energies of oxygen evolution reaction intermediates and has lower overpotential compared with nickel and iron sites. These findings suggest that the doped vanadium with distorted geometric and disturbed electronic structures makes crucial contribution to high activity of the trimetallic catalyst.

/pdf/atomic-level-insight-into-super-efficient-electrocatalytic-clkoqde6yj.pdf

Atomic-level insight into super-efficient electrocatalytic oxygen evolution on iron and vanadium co-doped nickel (oxy)hydroxide.

https://www.cell.com/biophysj/pdf/S0006-3495(99)77056-6.pdf

Crystal structures of myoglobin-ligand complexes at near-atomic resolution.

A review. Ultrafast x-ray techniques using diffraction and absorption are discussed with an emphasis on the absorption techniques. Ultrafast x-ray sources and detectors for use in x-ray absorption spectroscopy are also reviewed. [on SciFinder (R)]

Ultrafast X-ray absorption spectroscopy

The seminal discovery of light-induced changes in transition-metal nitrosyl complexes in the late 1970s and their identification as metastable linkage isomers almost 20 years after the initial discoveries have in recent years motivated a plethora of experimental and theoretical studies. They have raised the question of whether the linkage isomers play a role in the many crucial biological processes involving nitric oxide, which though likely, is still a subject of investigation. The linkage isomers have potential technological importance, as the change in refractive index on a molecular scale, associated with the photoinduced change in the crystals, in principle allows the design of very high capacity storage devices. This review summarizes the current knowledge in the still-developing field and includes a discussion of photoinduced metastable linkage isomers of related substances.

/pdf/photoinduced-linkage-isomers-of-transition-metal-nitrosyl-4qufu4r1tv.pdf

Photoinduced linkage isomers of transition-metal nitrosyl compounds and related complexes.

Chemical imaging of biological tissue with synchrotron infrared light

Hemeproteins play an important role in the signaling processes mediated by nitric oxide (NO). For example, the production of NO by nitric oxide synthase, the activation of guanylate cyclase by binding NO, and the scavenging of NO by hemoglobin, myoglobin, and cytochrome c oxidase all occur through unique mechanisms of interaction between NO and hemeproteins. Unlike carbon monoxide (CO) and oxygen (O2), which have been studied extensively, the reactions of NO with ferric and ferrous hemeproteins are not as well characterized. In this work, NO binding to myoglobin is studied using cryogenic optical spectroscopy and Fourier transform infrared spectroscopy (FTIR) in order to characterize the ligand-bound and photoproduct states involved in the interaction of NO with the heme iron and the distal pocket of the protein. For ferrous nitrosyl myoglobin (MbIINO), optical spectroscopy is used to show that the ligand-bound state can be converted to >95% stable photoproduct below 10 K. The Soret peak of the photoproduct is red-shifted by 4 nm relative to deoxy-myoglobin (Mb), similar to previous results for carbonmonoxy- (MbCO) and oxy-myoglobin (MbO2) (Miller et al., 1996). MbIINO completely rebinds by 35 K, indicating that the rebinding barrier for NO is lower than MbCO, consistent with room temperature picosecond kinetic measurements. For ferric nitrosyl myoglobin (MbIIINO), we find that the photoproduct yield at cryogenic temperatures is less than unity and dependent on the distal pocket residue. Native MbIIINO has a lower photoproduct yield than the mutant, MbIII(H64L)NO, where the distal histidine is replaced by leucine. The rebinding rates for the native and mutant species are similar to each other and to MbIINO. By using FTIR difference spectroscopy (photolyzed/unphotolyzed) of isotopically labeled ferrous nitrosyl myoglobin (MbIINO), the NO stretching frequencies in both the ligand-bound states and photoproduct states are determined. Two ligand-bound conformational states (1607 and 1613 cm-1) and two photoproduct conformational states (1852 and 1857 cm-1) are observed for MbIINO. This is the first direct observation of photolyzed NO in the distal pocket of myoglobin. The ligand-bound frequencies are consistent with a bent MbIINO moiety, where the unpaired pi*(NO) electron remains localized on NO, causing nu(N-O) to be approximately 300 cm-1 lower than MbIIINO. Similar to MbO2, we suggest that Nepsilon of the distal histidine is protonated, forming a hydrogen bond to the NO ligand. For native MbIIINO, a single ligand-bound conformational state with respect to nu(N-O) is observed at 1927 cm-1. This frequency decreases to 1904 cm-1 for the mutant, MbIII(H64L)NO, contrary to the increase of the carbon monoxide (CO) stretching frequency in the isoelectronic MbII(H64L)CO mutant versus native MbCO. For linear MbIIINO, we suggest that backbonding from the unpaired pi*(NO) electron to iron results in an increased positive charge on the NO ligand, Fe(delta-)-NO(delta+). This can be facilitated by tautomerism of the distal histidine, leaving Nepsilon of the imidazole ring unprotonated and able to accept positive charge from the Fe(delta-)-NO(delta+) moiety, resulting in a higher bond order (and a 23 cm-1 shift to higher frequency) for native MbIIINO versus MbIII(H64L)NO, where this interaction is absent. These different interactions between the distal histidine and the ferrous versus ferric species illustrate potential ways the protein can stabilize the bound ligand and demonstrate the versatile nature by which NO can bind to hemeproteins.

Identification of conformational substates involved in nitric oxide binding to ferric and ferrous myoglobin through difference Fourier transform infrared spectroscopy (FTIR).

Infrared microspectroscopy combines microscopy and spectroscopy for the purpose of chemical microanalysis Light microscopy provides a way to generate and record magnified images and visibly resolve microstructural detail Infrared spectroscopy provides a means for analyzing the chemical makeup of materials Combining light microscopy and infrared spectroscopy permits the correlation of microstructure with chemical composition Inherently, the long wavelengths of infrared radiation limit the spatial resolution of the technique However, synchrotron infrared radiation significantly improves both the spectral and spatial resolution of an infrared microspectrometer, such that data can be obtained with high signal-to-noise at the diffraction limit, which is 3-5 microm in the mid-infrared region In this study, we use infrared microspectroscopy to study the chemical composition of bone using two mapping methods In the osteon method, linear maps are collected from the center of an osteon (newer bone) to the periphery (older bone) and their chemical compositions are compared In the transverse method, applied specifically to subchondral bone, line maps are collected from the edge of the articular cartilage (older bone) to the marrow space (newer bone) A significant advantage of infrared microspectroscopy over other chemical methods is that the bone does not need to be homogenized for testing; we are able to study cross-sectional samples of bone in situ at a resolution better than 5 microm and compare the results with morphological findings on stained serial sections immediately adjacent to those examined by infrared microspectroscopy The infrared absorption bands of bone proteins and mineral are sensitive to mineral content (ie carbonate, phosphate, acid phosphate), mineral crystallinity and the content/nature of the organic matrix In this study, they are analyzed as a function of (1) age, ie distance with respect to the center of an osteon, and (2) morphology, ie cortical versus cancellous (notably subchondral) bone Results show that the protein/mineral ratio is higher in younger bone As bone matures, mineralization increases, as does carbonate substitution into the hydroxyapatite lattice Finally, most of the changes in chemical composition of bone occur within 20 microm of the site of new bone growth, eg the center of an osteon, demonstrating the need for the high spatial resolution achieved only with the use of a synchrotron infrared source

A method for examining the chemical basis for bone disease: synchrotron infrared microspectroscopy.

We demonstrate the first application of L-edge X-ray absorption spectroscopy (XAS) to the electronic characterization of biological photolysis products. The experimental L-edge XAS spectra of deoxymyoglobin (deoxy Mb), oxymyoglobin (MbO2), carbonmonoxymyoglobin (MbCO), and the low-temperature photoproducts (Mb*CO and Mb*O2) are presented and compared to simulated spectra using a ligand field multiplet calculation. This analysis indicates that MbCO and MbO2 are both low spin and does not support some previous studies which suggest that MbO2 has an intermediate spin. Both photoproducts, Mb*CO and Mb*O2, are different from deoxy Mb in the FeII electronic structure. In addition, different low-temperature photolysis intermediates are suggested for MbCO and MbO2. The L-edge XAS spectra for FeIII in aquometmyoglobin (met Mb) and azidomet myoglobin (MbN3) provide a comparison of the ferrous versus ferric myoglobin species. Finally, the special advantages of using soft X-ray absorption spectroscopy for understandi...

/pdf/iron-l-edge-x-ray-absorption-spectroscopy-of-myoglobin-2e6f5p92te.pdf

Iron L-Edge X-ray Absorption Spectroscopy of Myoglobin Complexes and Photolysis Products

Low frequency vibrations of amino acid homopolymers observed by synchrotron far-IR absorption spectroscopy: Excited state effects dominate the temperature dependence of the spectra

X-ray methods based on synchrotron technology have the promise of providing time-resolved structural data based on the high flux and brightness of the X-ray beams. One of the most closely examined problems in this area of time-resolved structure determination has been the examination of intermediates in ligand binding to myoglobin. Recent crystallographic experiments using synchrotron radiation have identified the protein tertiary and heme structural changes that occur upon photolysis of the myoglobin--carbon monoxide complex at cryogenic temperatures [Schlichting, I., Berendzen, J., Phillips, G., & Sweet, R. (1994) Nature 371, 808--812]. However, the precision of protein crystallographic data (approximately 0.2 A) is insufficient to provide precise metrical details of the iron--ligand bond lengths. Since bond length changes on this scale can trigger reactivity changes of several orders of magnitude, such detail is critical to a full understanding of metalloprotein structure--function relationships. Extended X-ray absorption fine structure (EXAFS) spectroscopy has the potential for analyzing bond distances to a precision of 0.02 A but is hampered by its relative insensitivity to the geometry of the backscattering atoms. Thus, it is often unable to provide a unique solution to the structure without ancillary structural information. We have developed a suite of computer programs that incorporate this ancillary structural information and compute the expected experimental spectra for a wide ranging series of Cartesian coordinate sets (global mapping). The programs systematically increment the distance of the metal to various coordinating ligands (along with their associated higher shells). Then, utilizing the ab initio EXAFS code FEFF 6.01, simulated spectra are generated and compared to the actual experimental spectra, and the differences are computed. Finally, the results for hundreds of simulations can be displayed (and compared) in a single plot. The power of this approach is demonstrated in the examination of high signal to noise EXAFS data from a photolyzed solution sample of the myoglobin--carbon monoxide complex at 10 K. Evaluation of these data using our global mapping procedures placed the iron to pyrrole nitrogen average distances close to the value for deoxymyoglobin (2.05 +/- 0.01 A), while the distance from iron to the proximal histidine nitrogen is seen to be 2.20 +/- 0.04 A. It is also shown that one cannot uniquely position the CO ligand on the basis of the EXAFS data alone, as a number of reasonable minima (from the perspective of the EXAFS) are observed. This provides a reasonable explanation for the multiplicity of solutions that have been previously reported. The results presented here are seen to be in complete agreement with the crystallographic results of Schlichting et al. (1994) within the respective errors of the two techniques; however, the extended X-ray absorption fine structure data allow the iron--ligand bond lengths to be precisely defined. An examination of the available spectroscopic data, including EXAFS, shows that the crystallographic results of Schlichting et al. (1994) are highly relevant to the physiological solution state and must be taken into account in any attempt to understand the incomplete relaxation process of the heme iron for the Mb*CO photoproduct at low temperature.

Global mapping of structural solutions provided by the extended X-ray absorption fine structure ab initio code FEFF 6.01: structure of the cryogenic photoproduct of the myoglobin-carbon monoxide complex.

Lisa M. Miller

Papers

Identification of conformational substates involved in nitric oxide binding to ferric and ferrous myoglobin through difference Fourier transform infrared spectroscopy (FTIR).

A method for examining the chemical basis for bone disease: synchrotron infrared microspectroscopy.

Iron L-Edge X-ray Absorption Spectroscopy of Myoglobin Complexes and Photolysis Products

Low frequency vibrations of amino acid homopolymers observed by synchrotron far-IR absorption spectroscopy: Excited state effects dominate the temperature dependence of the spectra

Global mapping of structural solutions provided by the extended X-ray absorption fine structure ab initio code FEFF 6.01: structure of the cryogenic photoproduct of the myoglobin-carbon monoxide complex.