Base-Free Iron Hydrosilylene Complexes via an α-Hydride Migration that Induces Spin Pairing

2018 ◽  
Vol 140 (11) ◽  
pp. 3880-3883 ◽  
Author(s):  
Patrick W. Smith ◽  
T. Don Tilley
Keyword(s):  
Free Iron ◽  
Spin Pairing

The valence-bond theory of molecular structure II. Reformulation of the theory

1954 ◽  
Vol 223 (1154) ◽  
pp. 306-323 ◽  
Keyword(s):  
Valence Bond ◽  
Closed Shell ◽  
Numerical Illustration ◽  
Atomic Orbitals ◽  
Spin Eigenfunctions ◽  
Spin Pairing ◽  
Vb Structures ◽  
Bond Theory ◽  
Strong Repulsion ◽  
A Charge

The construction of spin eigenfunctions and the evaluation of matrix elements between ,them are discussed generally in preparation for a development of the valence bond (VB) theory along the lines indicated in I. The customary approximation of considering explicitly only the electrons outside a ‘closed shell’ is shown to be defensible. The reformulation of the VB theory is now straightforward, but its final description of bonding is quite new. Atomic orbitals (AO’s) are replaced, whenever they appear, by orthogonalized atomic orbitals (AO’s); but when the assumptions of the conventional theory are rigorously validated in this way the ‘covalent’ structures (now ‘VB’ structures) are found, quite generally, to indicate only strong repulsion between the ‘bonded’ atoms, and formal descriptions of bonding and of bond orders, in terms of ‘spin-pairing’, become nonsensical. Bonding can be described only by admitting into the wave functions polar VB structures; a bond between two atoms demands the appearance (with considerable weight) of pairs of structures differing by a ‘charge hop’ between the atoms concerned. The conventional VB structures are found to be equivalent to certain groupings of VB structures (non-polar and polar) and do, indeed, predict bonds between spin-paired atoms and repulsion between the atoms of different pairs. It is then possible to make full use of chemical intuition, using a plausible combination of conventional structures as a starting approximation in the more rigorous theory. A numerical illustration is provided by a discussion of the Kekulé structures of benzene. Some important characteristics of energy calculations in the VB theory are pointed out. Quantities of intra - and inter -atomic origin are well separated, and the method is apparently well suited to development along either ab initio or empirical lines.

ENDOTOXIN MEDIATED EXPRESSION OF HEMOXYGENASE IN RATS IS LIKELY A SOURCE OF FREE IRON, IMPAIRING MITOCHONDRIAL FUNCTION

Shock ◽  
2006 ◽  
Vol 26 (Supplement 1) ◽  
pp. 5
Author(s):  
J. Catharina Duvigneau ◽  
Christina Piskernik ◽  
Romana T. Hartl ◽  
Susanne Haindl ◽  
Ingeborg Kehrer ◽  
...  
Keyword(s):  
Mitochondrial Function ◽  
Free Iron

Free Iron Oxide Determination in Mediterranean Soils using Diffuse Reflectance Spectroscopy

2009 ◽  
Vol 73 (1) ◽  
pp. 72-81 ◽  
Author(s):  
N. Richter ◽  
T. Jarmer ◽  
S. Chabrillat ◽  
C. Oyonarte ◽  
P. Hostert ◽  
...  
Keyword(s):  
Iron Oxide ◽  
Diffuse Reflectance ◽  
Diffuse Reflectance Spectroscopy ◽  
Reflectance Spectroscopy ◽  
Free Iron ◽  
Mediterranean Soils

CLAY ILLUVIATION IN SOME ORTHIC PODZOLS OF EASTERN CANADA

1965 ◽  
Vol 45 (2) ◽  
pp. 127-138 ◽  
Author(s):  
J. E. Brydon
Keyword(s):  
Organic Matter ◽  
New Brunswick ◽  
Iron Oxides ◽  
Clay Content ◽  
Granular Structure ◽  
Charge Component ◽  
Eastern Canada ◽  
Free Iron ◽  
Fine Clay ◽  
Ph Dependent

The Arago, Barney, and Holmesville soils, Podzols from Quebec, Nova Scotia, and New Brunswick, respectively, each had friable Bfh horizons with moderate granular structure, and with organic matter and free Fe2O3 contents greater than the Ae and C horizons. The Arago and Holmesville had thin Bhft horizons containing over 10% organic matter and 5% free iron oxides. The C horizons of these two soils had some features characteristic of fragipans.The B horizons of the three soils had a high "pH-dependent charge component" in the C.E.C. values. The "permanent charge component" was similar throughout the Arago profile except for the Bhft horizon where clay accumulation had occurred.Translocation of clay from the Ae to the upper B horizons was indicated by the twofold increase in clay content and the relative enrichment of fine clay in the B horizons. Removal of free iron affected the clay contents differently in the different: horizons but the maximum clay content in the upper B horizons remained. The definitions of Orthic Podzols, Textural Podzols, and t horizons should be re-examined.

scholarly journals Influence of Microbial Metabolites on the Nonspecific Permeability of Mitochondrial Membranes under Conditions of Acidosis and Loading with Calcium and Iron Ions

Biomedicines ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 558
Author(s):  
Nadezhda Fedotcheva ◽  
Andrei Olenin ◽  
Natalia Beloborodova
Keyword(s):  
Calcium Ions ◽  
Mitochondrial Permeability Transition ◽  
Rat Liver Mitochondria ◽  
Radical Scavenger ◽  
Pathological State ◽  
Microbial Metabolites ◽  
Mitochondrial Membranes ◽  
Active Metabolites ◽  
Free Iron ◽  
Mptp Opening

Mitochondrial dysfunction is currently considered one of the main causes of multiple organ failure in chronic inflammation and sepsis. The participation of microbial metabolites in disorders of bioenergetic processes in mitochondria has been revealed, but their influence on the mitochondrial membrane permeability has not yet been studied. We tested the influence of various groups of microbial metabolites, including indolic and phenolic acids, trimethylamine-N-oxide (TMAO) and acetyl phosphate (AcP), on the nonspecific permeability of mitochondrial membranes under conditions of acidosis, imbalance of calcium ions and excess free iron, which are inherent in sepsis. Changes in the parameters of the calcium-induced opening of the mitochondrial permeability transition pore (MPTP) and iron-activated swelling of rat liver mitochondria were evaluated. The most active metabolites were indole-3-carboxylic acid (ICA) and benzoic acid (BA), which activated MPTP opening and swelling under all conditions. AcP showed the opposite effect on the induction of MPTP opening, increasing the threshold concentration of calcium by 1.5 times, while TMAO activated swelling only under acidification. All the redox-dependent effects of metabolites were suppressed by the lipid radical scavenger butyl-hydroxytoluene (BHT), which indicates the participation of these microbial metabolites in the activation of membrane lipid peroxidation. Thus, microbial metabolites can directly affect the nonspecific permeability of mitochondrial membranes, if conditions of acidosis, an imbalance of calcium ions and an excess of free iron are created in the pathological state.

scholarly journals Ferric uptake regulator (Fur) reversibly binds a [2Fe-2S] cluster to sense intracellular iron homeostasis in Escherichia coli

2020 ◽  
Vol 295 (46) ◽  
pp. 15454-15463 ◽  
Author(s):  
Chelsey R. Fontenot ◽  
Homyra Tasnim ◽  
Kathryn A. Valdes ◽  
Codrina V. Popescu ◽  
Huangen Ding
Keyword(s):  
Escherichia Coli ◽  
Iron Content ◽  
Iron Homeostasis ◽  
Ferric Uptake Regulator ◽  
Intracellular Iron ◽  
Free Iron ◽  
E Coli ◽  
Genes Encoding ◽  
Fur Protein ◽  
Mutant Cells

The ferric uptake regulator (Fur) is a global transcription factor that regulates intracellular iron homeostasis in bacteria. The current hypothesis states that when the intracellular “free” iron concentration is elevated, Fur binds ferrous iron, and the iron-bound Fur represses the genes encoding for iron uptake systems and stimulates the genes encoding for iron storage proteins. However, the “iron-bound” Fur has never been isolated from any bacteria. Here we report that the Escherichia coli Fur has a bright red color when expressed in E. coli mutant cells containing an elevated intracellular free iron content because of deletion of the iron–sulfur cluster assembly proteins IscA and SufA. The acid-labile iron and sulfide content analyses in conjunction with the EPR and Mössbauer spectroscopy measurements and the site-directed mutagenesis studies show that the red Fur protein binds a [2Fe-2S] cluster via conserved cysteine residues. The occupancy of the [2Fe-2S] cluster in Fur protein is ∼31% in the E. coli iscA/sufA mutant cells and is decreased to ∼4% in WT E. coli cells. Depletion of the intracellular free iron content using the membrane-permeable iron chelator 2,2´-dipyridyl effectively removes the [2Fe-2S] cluster from Fur in E. coli cells, suggesting that Fur senses the intracellular free iron content via reversible binding of a [2Fe-2S] cluster. The binding of the [2Fe-2S] cluster in Fur appears to be highly conserved, because the Fur homolog from Hemophilus influenzae expressed in E. coli cells also reversibly binds a [2Fe-2S] cluster to sense intracellular iron homeostasis.

Combination of Iron Overload Plus Ethanol and Ischemia Alone Give Rise to the Same Endogenous Free Iron Pool

BioMetals ◽  
2005 ◽  
Vol 18 (6) ◽  
pp. 567-575 ◽  
Author(s):  
Odile Sergent ◽  
Aldo Tomasi ◽  
Daniela Ceccarelli ◽  
Alberto Masini ◽  
Hans Nohl ◽  
...  
Keyword(s):  
Iron Overload ◽  
Free Iron ◽  
Iron Pool
Sign in / Sign up

Export Citation Format

Share Document