scholarly journals Spectroscopic studies on the interaction of hypocrellin A with myoglobin

2007 ◽  
Vol 21 (4) ◽  
pp. 235-243 ◽  
Author(s):  
J. H. Zhou ◽  
X. H. Wu ◽  
C. Yang ◽  
X. T. Gu ◽  
L. Zhou ◽  
...  
Keyword(s):  
Binding Sites ◽  
Spectroscopic Analysis ◽  
Spectroscopic Studies ◽  
Interaction Process ◽  
Quenching Mechanism ◽  
Visible Absorption ◽  
Paramagnetic Resonance ◽  
Hypocrellin A ◽  
Uv Visible ◽  
Electron Paramagnetic

Experimental results of UV-visible absorption spectroscopy and fluorescence spectroscopy indicate that hypocrellin A, which has been studied in photodynamic therapy, can interact with the surface of myoglobin through hydrophobic forces, and form a complex. Based on the Stern–Volmer equation, the quenching constants of the process can be calculated to be 4.81×1012L mol−1s−1(t=25°C) and 4.54×1012L mol−1s−1(t=42°C) respectively, and the binding constant is 5.53×104M−1(t=25°C), while the binding sites is 0.94 (t=25°C). In addition, Electron paramagnetic resonance and fluorescence spectroscopic analysis suggests that that the quenching mechanism of the interaction process occurs through the electron transfer between hypocrellin A and myoglobin.

scholarly journals Nitrosomonas europaeacytochrome P460 is a direct link between nitrification and nitrous oxide emission

2016 ◽  
Vol 113 (51) ◽  
pp. 14704-14709 ◽  
Author(s):  
Jonathan D. Caranto ◽  
Avery C. Vilbert ◽  
Kyle M. Lancaster
Keyword(s):  
Nitrous Oxide ◽  
Nucleophilic Attack ◽  
Ammonia Oxidizing Bacteria ◽  
Anaerobic Conditions ◽  
Visible Absorption ◽  
Paramagnetic Resonance ◽  
Aerobic Conditions ◽  
Rate Determining Step ◽  
Uv Visible ◽  
Electron Paramagnetic

Ammonia oxidizing bacteria (AOB) are major contributors to the emission of nitrous oxide (N2O). It has been proposed that N2O is produced by reduction of NO. Here, we report that the enzyme cytochrome (cyt) P460 from the AOBNitrosomonas europaeaconverts hydroxylamine (NH2OH) quantitatively to N2O under anaerobic conditions. Previous literature reported that this enzyme oxidizes NH2OH to nitrite (NO2−) under aerobic conditions. Although we observeNO2−formation under aerobic conditions, its concentration is not stoichiometric with the NH2OH concentration. By contrast, under anaerobic conditions, the enzyme uses 4 oxidizing equivalents (eq) to convert 2 eq of NH2OH to N2O. Enzyme kinetics coupled to UV/visible absorption and electron paramagnetic resonance (EPR) spectroscopies support a mechanism in which an FeIII–NH2OH adduct of cyt P460 is oxidized to an {FeNO}6unit. This species subsequently undergoes nucleophilic attack by a second equivalent of NH2OH, forming the N–N bond of N2O during a bimolecular, rate-determining step. We propose thatNO2−results when nitric oxide (NO) dissociates from the {FeNO}6intermediate and reacts with dioxygen. Thus,NO2−is not a direct product of cyt P460 activity. We hypothesize that the cyt P460 oxidation of NH2OH contributes to NO and N2O emissions from nitrifying microorganisms.

scholarly journals DFT Protocol for EPR Prediction of Paramagnetic Cu(II) Complexes and Application to Protein Binding Sites

2018 ◽  
Vol 4 (4) ◽  
pp. 55 ◽  
Author(s):  
Giuseppe Sciortino ◽  
Giuseppe Lubinu ◽  
Jean-Didier Maréchal ◽  
Eugenio Garribba
Keyword(s):  
Binding Sites ◽  
Density Functional ◽  
Computational Procedure ◽  
Paramagnetic Resonance ◽  
Functional Theory ◽  
Protein Binding Sites ◽  
The Mean ◽  
Hamiltonian Parameters ◽  
Electron Paramagnetic

With the aim to provide a general protocol to interpret electron paramagnetic resonance (EPR) spectra of paramagnetic copper(II) coordination compounds, density functional theory (DFT) calculations of spin Hamiltonian parameters g and A for fourteen Cu(II) complexes with different charges, donor sets, and geometry were carried out using ORCA software. The performance of eleven functionals was tested, and on the basis of the mean absolute percent deviation (MAPD) and standard deviation (SD), the ranking of the functionals for Az is: B3LYP > B3PW91 ~ B3P86 > PBE0 > CAM-B3LYP > TPSSh > BH and HLYP > B2PLYP > MPW1PW91 > ω-B97x-D >> M06; and for gz is: PBE0 > BH and HLYP > B2PLYP > ω-B97x-D > B3PW91~B3LYP~B3P86 > CAM-B3LYP > TPSSh~MPW1PW91 >> M06. With B3LYP the MAPD with respect to A z exp t l is 8.6% with a SD of 4.2%, while with PBE0 the MAPD with respect to g z exp t l is 2.9% with a SD of 1.1%. The results of the validation confirm the fundamental role of the second order spin-orbit contribution to Az. The computational procedure was applied to predict the values of gz and Az of the adducts formed by Cu(II) with albumin and two fragments of prion protein, 106–126 and 180–193.

A spectroscopic study of the reaction of gold atoms with CO in a rotating cryostat: formation of a variety of gold carbonyls

1989 ◽  
Vol 67 (4) ◽  
pp. 655-661 ◽  
Author(s):  
J. H. B. Chenier ◽  
J. A. Howard ◽  
H. A. Joly ◽  
B. Mile ◽  
M. Tomietto
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Optical Spectrum ◽  
Narrow Band ◽  
Visible Spectroscopy ◽  
Broad Absorption ◽  
Paramagnetic Resonance ◽  
Magnetic Parameters ◽  
Uv Visible ◽  
Electron Paramagnetic ◽  
Rotating Cryostat

Reaction of 197Au atoms with CO has been studied in inert hydrocarbon matrices in a rotating cryostat at 77 K by EPR, FTIR, and UV/visible spectroscopy. Au(CO)2 has been positively identified by FTIR spectroscopy and there is evidence for the formation of AuCO, a gold microcrystallite – CO complex and, upon annealing, Au2(CO)4. Electron paramagnetic resonance spectra are consistent with the formation of Au(CO) (OC) with the magnetic parameters: a13 = 325 MHz, a17 = 44 MHz, and g = 2.0014 and a gold microcrystallite – CO complex with g = 2.014. An intense broad absorption in the optical spectrum at 525 nm is assigned to Au(CO)2 and a less intense narrow band at 320 nm is assigned to AunCO. There is no spectroscopic evidence for the formation of Au(CO)3 in hydrocarbon matrices. Keywords: gold carbonyls, EPR, FTIR, UV/visible, matrix isolation.

Structural and spectropscopic studies of a three-dimensional hydrogen-bonded copper(II) complex: aqua[bis(pyridin-2-ylcarbonyl)amidato]cyanidocopper(II)

2015 ◽  
Vol 71 (2) ◽  
pp. 165-168 ◽  
Author(s):  
Jiang-Yun Wang
Keyword(s):  
Three Dimensional ◽  
Spectroscopic Studies ◽  
Epr Spectrum ◽  
Cyclic Voltammetric ◽  
Paramagnetic Resonance ◽  
Irreversible Oxidation ◽  
Square Planar ◽  
Voltammetric Studies ◽  
Cyclic Voltammetric Studies ◽  
Electron Paramagnetic

The preparation and X-ray and spectroscopic studies of the title copper(II) complex, [Cu(C12H8N3O2)(CN)(H2O)], are reported. The CuIIcation is five-coordinated, forming a distorted square-planar pyramid with an Addison τ parameter of 0.14. The UV–vis spectrum shows ad–dtransition of the CuIIcentre at 638 nm, and the electron paramagnetic resonance (EPR) spectrum confirms that the CuIIcation has an axial symmetry coordination and that the unpaired electrons occupy thedx2–y2orbital. Cyclic voltammetric studies show two irreversible oxidation and reduction peaks.

scholarly journals The cytochromes of anaerobically grown Escherichia coli. An electron-paramagnetic-resonance study of the cytochrome bd complex in situ

1989 ◽  
Vol 261 (2) ◽  
pp. 437-443 ◽  
Author(s):  
R A Rothery ◽  
W J Ingledew
Keyword(s):  
Escherichia Coli ◽  
High Spin ◽  
Binding Sites ◽  
Electron Paramagnetic Resonance Study ◽  
Paramagnetic Resonance ◽  
Cytochrome Bd ◽  
Ligand Binding Sites ◽  
Electron Paramagnetic ◽  
Spin Species

The e.p.r. signals attributable to a cytochrome bd-type ubiquinol: O2 oxidoreductase (cytochrome b-558-b-595-d) were studied in a cytoplasmic membrane preparation of Escherichia coli that had been grown on glycerol with fumarate as respiratory-chain oxidant. Two major high-spin ferric haem signals were resolved on the basis of their potentiometric behaviour: a rhombic high-spin species (gx = 6.25, gy = 5.54) was assigned to haem b-595, and an axial high-spin (gx = 5.97, gy = 5.96) species was assigned to the haem d. These signals titrated with Em.7 values of 154 and 261 mV respectively, corresponding closely to optically determined values for haem b-595 and haem d. At high potentials (greater than 300 mV) the rhombic species attributable to haem b-595 underwent a partial transition to a second rhombic species with g-values of 6.24 (gx) and 5.67 (gy). The high-spin ferric haem spectra were affected by O2, CO, cyanide and pH. A low-spin ferric haem signal was observed at g = 3.3 (gz), which titrated with an Em.7 of 226 mV, and this was assigned to haem b-558. The data support a model for cytochrome bd with two ligand-binding sites, a single haem d and a single haem b-595.

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