A continuous-wave electron–nuclear double resonance (X-band) study of the Cu2+ sites of particulate methane mono-oxygenase of Methylococcus capsulatus (strain M) in membrane and pure dopamine β-mono-oxygenase of the adrenal medulla

2002 ◽  
Vol 363 (3) ◽  
pp. 677-686
Author(s):  
Bettina KATTERLE ◽  
Rudolf I. GVOZDEV ◽  
Ntei ABUDU ◽  
Torbjørn LJONES ◽  
K. Kristoffer ANDERSSON
Keyword(s):  
Continuous Wave ◽  
Dipolar Coupling ◽  
Double Resonance ◽  
Coupling Constants ◽  
Methylococcus Capsulatus ◽  
Electron Nuclear Double Resonance ◽  
Strongly Coupled ◽  
Copper Site ◽  
Typical Type

All methanotrophic bacteria express a membrane-bound (particulate) methane mono-oxygenase (pMMO). In the present study, we have investigated pMMO in membrane fragments from Methylococcus capsulatus (strain M). pMMO contains a typical type-2 Cu2+ centre with the following EPR parameters: gz 2.24, gx,y 2.06, ACuz 19.0mT and ACux,y 1.0mT. Simulation of the Cu2+ spectrum yielded a best match by using four equivalent nitrogens (AN = 1.5mT, 42MHz). Incubation with ferricyanide neither changed nor increased the amount of EPR-active Cu2+, in contrast with other reports. The EPR visible copper seems not to be part of any cluster, as judged from the microwave power saturation behaviour. Continuous-wave electron—nuclear double resonance (CW ENDOR; 9.4GHz, 5–20K) experiments at g⊥ of the Cu(II) spectrum show a weak coupling to protons with an AH of 2.9MHz that corresponds to a distance of 3.8Å (1Å≡0.1nm), assuming that it is a purely dipolar coupling. Incubation in 2H2O leads to a significant decrease in these 1H-ENDOR intensities, showing that these protons are exchangeable. This result strongly suggests that the EPR visible copper site of pMMO is accessible to solvent, which was confirmed by the chelation of the Cu2+ by diethyldithiocarbamic acid. The 1H and 14N hyperfine coupling constants confirm a histidine ligation of the EPR visible copper site in pMMO. The hyperfine structure in the ENDOR or EPR spectra of pMMO is not influenced by the inhibitors azide, cyanide or ammonia, indicating that they do not bind to the EPR visible copper. We compared pMMO with the type-2 Cu2+ enzyme, dopamine β-mono-oxygenase (DβM). For DβM, it is assumed that the copper site is solvent-accessible. CW ENDOR shows similar weakly coupled and 2H2O-exchangeable protons (2.9MHz), as observed in pMMO, as well as the strongly coupled nitrogens (40MHz) from the co-ordinating N of the histidines in DβM. In conclusion, the resting EPR visible Cu in pMMO is not part of a trinuclear cluster, as has been suggested previously.

Using Hyperfine Interaction for the Structural Characterization of Amorphous Silicon

1986 ◽  
Vol 69 ◽  
Author(s):  
Martin Stutzmann ◽  
David K. Biegelsen
Keyword(s):  
Hyperfine Interaction ◽  
Amorphous Silicon ◽  
Dipolar Coupling ◽  
Double Resonance ◽  
Nuclear Spins ◽  
Electron Nuclear Double Resonance ◽  
Resonance Frequencies ◽  
Spin Resonance ◽  
Nuclear Spin System

AbstractThe hyperfine interaction between electronic and nuclear spins in hydrogenated amorphous silicon has been observed for the various paramagnetic defects in this material by electron spin resonance (ESR) and electron nuclear double resonance (ENDOR). The large hyperfine interaction between dangling bonds and 29Si as well as between donor electrons and 31p or 75 As nuclei can be resolved in ESR and provides direct information about the structure of the underlying electronic states. The smaller dipolar coupling of all paramagnetic states to more distant nuclei leads to an ENDOR response near the free nuclear resonance frequencies, which can be used to study the coupling of the electronic and nuclear spin system to the lattice phonons and to each other.

Mo(V) co-ordination in the periplasmic nitrate reductase from Paracoccus pantotrophus probed by electron nuclear double resonance (ENDOR) spectroscopy

2002 ◽  
Vol 363 (3) ◽  
pp. 817-823 ◽  
Author(s):  
Clive S. BUTLER ◽  
Shirley A. FAIRHURST ◽  
Stuart J. FERGUSON ◽  
Andrew J. THOMSON ◽  
Ben C. BERKS ◽  
...  
Keyword(s):  
Nitrate Reductase ◽  
Double Resonance ◽  
Electron Nuclear Double Resonance ◽  
Time Resolved ◽  
Strongly Coupled ◽  
Periplasmic Nitrate Reductase ◽  
Weakly Coupled ◽  
Endor Spectroscopy ◽  
X Band ◽  
Paracoccus Pantotrophus

The first electron nuclear double resonance (ENDOR) study of a member of the Mo-bis-molybdopterin guanine dinucleotide family of molybdoenzymes is presented, using the periplasmic nitrate reductase from Paracoccus pantotrophus. Rapid freeze-quenched time-resolved EPR revealed that during turnover the intensity of a Mo(V) EPR signal known as High-g [resting] increases. This signal is split by two interacting protons that are not solvent-exchangeable. X-band proton-ENDOR analysis resolved broad symmetrical resonance features that arose from four classes of protons weakly coupled to the Mo(V). Signals from two of these were lost upon exchange into deuterated buffer, suggesting that they may originate from OH− or H2O groups. One of these signals was also lost when the enzyme was redox-cycled in the presence of azide. Since these protons are very weakly coupled OH/H2O groups, they are not likely to be ligated directly to the Mo(V). This suggests that protonation of a Mo(VI)=O group does not occur on reduction to Mo(V), but most probably accompanies reduction of Mo(V) to Mo(IV). A resonance feature from a more strongly coupled proton, that was not lost following exchange into deuterated buffer, could also be resolved at 22–24MHz. The anisotropy of this feature, determined from ENDOR spectra collected at a range of field positions, indicated a Mo—proton distance of approx. 3.2Å, consistent with this being one of the β-methylene protons of a Mo—Cys ligand.

Solvent effects of cobalt(II) phthalocyanine in sulfuric acid: a continuous wave and pulse EPR study

2003 ◽  
Vol 07 (02) ◽  
pp. 89-96 ◽  
Author(s):  
Cinzia Finazzo ◽  
Sabine Van Doorslaer ◽  
Arthur Schweiger
Keyword(s):  
Sulfuric Acid ◽  
Continuous Wave ◽  
Hyperfine Interactions ◽  
Double Resonance ◽  
Resonance Spectroscopy ◽  
Electron Nuclear Double Resonance ◽  
Paramagnetic Resonance ◽  
Metal Phthalocyanines ◽  
The Matrix ◽  
Detailed Assessment

Products based on metal phthalocyanines are widely used in industry. In the processing of these materials it is essential to control the conditions of the matrix the metal phthalocyanines are embedded in. Using the example of cobalt(II) phthalocyanine in sulfuric acid we show that continuous wave and pulse electron paramagnetic resonance and electron nuclear double resonance spectroscopy provide excellent tools to monitor the influence of the matrix on paramagnetic phthalocyanines. The g values, the cobalt hyperfine values, and the hyperfine and nuclear quadrupole couplings of the isoindole nitrogens, as well as the hyperfine interactions of the surrounding protons allow for a detailed assessment of the electronic structure of cobalt(II) phthalocyanine in sulfuric acid. Subtle differences between the system under study and related Co ( II ) porphyrin and corrin systems could be traced.

First-Principles Study of Soliton Hyperfine Interactions in Polyacetylene

1990 ◽  
Vol 209 ◽  
Author(s):  
C. T. White ◽  
F. W. Kutzler ◽  
J. W. Mintmire ◽  
M. R. Cook
Keyword(s):  
Density Functional ◽  
Local Density ◽  
Hyperfine Interactions ◽  
Double Resonance ◽  
Broad Band ◽  
Coupling Constants ◽  
Electron Nuclear Double Resonance ◽  
Neutral Radical ◽  
Fermi Contact ◽  
Spin Densities

ABSTRACTAll-trans-polyacetylene is considered the prototypical broad band gap quasi onedimensional organic semiconductor. Intrinsicsoliton defects have long been known to be important to the understanding of the observed properties of this system at low doping levels. Magnetic resonance techniques provide powerful experimental probes into the nature and environment of these neutral-radical defects. In an earlier work we showed that firstprinciples spin-polarized local density functional (LDF) methods reliably predict proton Fermi-contact coupling constants for planar, neutral, organic π-radicals. We have also used these methods to calculate the Fermi-contact proton coupling constants associated with the soliton defect in polyacetylene.Herein we compare the results of these earlier soliton calculations to results from recent electron-nuclear double-resonance (ENDOR) experiments. Our predicted ratio of the negative to positive spin densities is in good agreement with these ENDORstudies. The negative spin densities arise from spin-polarization effects which are found to cause the soliton level at midgap to be split by several tenths of an eV.

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