Role of axial ligand in the electronic structure of model compound I complexes

1992 ◽  
Vol 44 (2) ◽  
pp. 251-261 ◽  
Author(s):  
Ping Du ◽  
Gilda H. Loew
Keyword(s):  
Electronic Structure ◽  
Model Compound ◽  
Axial Ligand ◽  
Compound I

Proximal ligand effects on electronic structure and spectra of compound I of peroxidases

2001 ◽  
Vol 05 (03) ◽  
pp. 334-344 ◽  
Author(s):  
DANNI L. HARRIS ◽  
GILDA H. LOEW
Keyword(s):  
Electronic Structure ◽  
Density Functional ◽  
Axial Ligand ◽  
Compound I ◽  
Imidazole Ligand ◽  
Axial Ligands ◽  
Transient Spectra ◽  
Main Determinants ◽  
And Function ◽  
Optimized Geometries

Computational studies exploring the extent to which differences in proximal axial ligands modulate structure, spectra, and function of peroxidases have been performed. To this end, three heme models of compound I were characterized differing only in the axial ligand. The axial ligands considered were L = ImH , Im -, that are alternative protonation models for a typical peroxidase with an imidazole ligand such as horseradish peroxidase (HRP-I), and L = SCH - that is a model for an unsual peroxidase, chloroperoxidase (CPO-I). Density functional calculations (DFTs) were performed to determine the optimized geometries and electronic structure of each of these three species. Their electronic spectra were also calculated at the DFT optimized geometries, using the INDO/S/CI method. The results of these studies led to the following conclusions: (1) the presence of the nearby Asp in a typical peroxidase does indeed decrease the energy required to deprotonate the imidazole making the two forms essentially degenerate, (2) neither the state of protonation of the imidazole ligand nor the change in axial ligand from an imidazole in typical peroxidases such as HRP to a mercaptide in CPO significantly alters the characteristics of the lowest energy spin state or the electronic structure of compound I in a way that can obviously affect function, (3) both the Im - and ImH forms of the peroxidase compound I (HRP-I) lead to the same dramatic reduction in intensity relative to the ferric resting form observed experimentally. However, only in the ImH form of HRP-I does the calculated relative shift of one component of the Soret bands relative to CPO-I agree with that observed in the transient spectra of HRP-I compared to CPO-I. These results taken together strongly indicate that factors other than the nature of the proximal axial ligand are the main determinants of function.

Spectroscopic Studies of the Met182Thr Mutant of Nitrite Reductase:  Role of the Axial Ligand in the Geometric and Electronic Structure of Blue and Green Copper Sites

2003 ◽  
Vol 125 (48) ◽  
pp. 14784-14792 ◽  
Author(s):  
Lipika Basumallick ◽  
Robert K. Szilagyi ◽  
Yiwei Zhao ◽  
James P. Shapleigh ◽  
Charles P. Scholes ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Nitrite Reductase ◽  
Spectroscopic Studies ◽  
Axial Ligand ◽  
Copper Sites

Activation of cytochrome c to a peroxidase compound I-type intermediate by H2O2: relevance to redox signalling in apoptosis

2004 ◽  
Vol 71 ◽  
pp. 97-106 ◽  
Author(s):  
Mark Burkitt ◽  
Clare Jones ◽  
Andrew Lawrence ◽  
Peter Wardman
Keyword(s):  
Cytochrome C ◽  
Hydroxyl Radical ◽  
Redox Regulation ◽  
Chemotherapeutic Agents ◽  
Tyrosyl Radical ◽  
Compound I ◽  
Definitive Evidence ◽  
Enhanced Production ◽  
Physico Chemical

The release of cytochrome c from mitochondria during apoptosis results in the enhanced production of superoxide radicals, which are converted to H2O2 by Mn-superoxide dismutase. We have been concerned with the role of cytochrome c/H2O2 in the induction of oxidative stress during apoptosis. Our initial studies showed that cytochrome c is a potent catalyst of 2′,7′-dichlorofluorescin oxidation, thereby explaining the increased rate of production of the fluorophore 2′,7′-dichlorofluorescein in apoptotic cells. Although it has been speculated that the oxidizing species may be a ferryl-haem intermediate, no definitive evidence for the formation of such a species has been reported. Alternatively, it is possible that the hydroxyl radical may be generated, as seen in the reaction of certain iron chelates with H2O2. By examining the effects of radical scavengers on 2′,7′-dichlorofluorescin oxidation by cytochrome c/H2O2, together with complementary EPR studies, we have demonstrated that the hydroxyl radical is not generated. Our findings point, instead, to the formation of a peroxidase compound I species, with one oxidizing equivalent present as an oxo-ferryl haem intermediate and the other as the tyrosyl radical identified by Barr and colleagues [Barr, Gunther, Deterding, Tomer and Mason (1996) J. Biol. Chem. 271, 15498-15503]. Studies with spin traps indicated that the oxo-ferryl haem is the active oxidant. These findings provide a physico-chemical basis for the redox changes that occur during apoptosis. Excessive changes (possibly catalysed by cytochrome c) may have implications for the redox regulation of cell death, including the sensitivity of tumour cells to chemotherapeutic agents.

scholarly journals Band alignment of monolayer CaP3, CaAs3, BaAs3 and the role of p–d orbital interactions in the formation of conduction band minima

2021 ◽  
Vol 23 (12) ◽  
pp. 7418-7425
Author(s):  
Magdalena Laurien ◽  
Himanshu Saini ◽  
Oleg Rubel
Keyword(s):  
Electronic Structure ◽  
Conduction Band ◽  
Electron Affinity ◽  
Band Alignment ◽  
Orbital Interactions

We calculate the band alignment of the newly predicted phosphorene-like puckered monolayers with G0W0 according to the electron affinity rule and examine trends in the electronic structure. Our results give guidance for heterojunction design.

Activators in Accelerated Sulfur Vulcanization

2004 ◽  
Vol 77 (3) ◽  
pp. 512-541 ◽  
Author(s):  
Geert Heideman ◽  
Rabin N. Datta ◽  
Jacques W. M. Noordermeer ◽  
Ben van Baarle
Keyword(s):  
Reaction Mechanisms ◽  
Model Compound ◽  
Background Information ◽  
Zinc Compounds ◽  
Chemical Mechanisms ◽  
Sulfur Vulcanization ◽  
Multifunctional Additives ◽  
Vulcanization Process

Abstract This review provides relevant background information about the vulcanization process, as well as the chemistry of thiuram- and sulfenamide-accelerated sulfur vulcanization with emphasis on the role of activators, to lay a base for further research. It commences with an introduction of sulfur vulcanization and a summary of the reaction mechanisms as described in literature, followed by the role of activators, particularly ZnO. The various possibilities to reduce ZnO levels in rubber compounding, that have been proposed in literature, are reviewed. A totally different approach to reduce ZnO is described in the paragraphs about the various possible roles of multifunctional additives (MFA) in rubber vulcanization. Another paragraph is dedicated to the role of amines in rubber vulcanization, in order to provide some insight in the underlying chemical mechanisms of MFA systems. Furthermore, an overview of Model Compound Vulcanization (MCV) with respect to different models and activator/accelerator systems is given. In the last part of this review, the various functions of ZnO in rubber are summarized. It clearly reveals that the role of ZnO and zinc compounds is very complex and still deserves further clarification.

Site-projected electronic structure of two-dimensional Ti3C2MXene: the role of the surface functionalization groups

2016 ◽  
Vol 18 (45) ◽  
pp. 30946-30953 ◽  
Author(s):  
Damien Magne ◽  
Vincent Mauchamp ◽  
Stéphane Célérier ◽  
Patrick Chartier ◽  
Thierry Cabioc'h
Keyword(s):  
Electronic Structure ◽  
Surface Functionalization ◽  
Chemical Bonding ◽  
Surface Groups ◽  
Two Dimensional ◽  
Object Level

The role of the surface groups in chemical bonding in two dimensional Ti3C2is evidenced at the nano-object level.

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