Was HO generated before oxygenic photosynthesis?

We obviously agree with Wu et al. that HO might accumulate in the Archean land waters devoid of Fe. We do disagree on the topic of the half-life of HO, as the work cited in support for a longer half-live is not relevant to the conditions in the Archean ocean.

Was hydrogen peroxide present before the arrival of oxygenic photosynthesis? The important role of iron(II) in the Archean ocean.

We address the chemical/biological history of HO back at the times of the Archean eon (2.5-3.9 billion years ago (Gya)).

Ferryl for real. The Fenton reaction near neutral pH.

According to the literature, the Fenton reaction yields HO˙ and proceeds with 53 M s at 25 °C and low pH. Above pH 5, the reaction becomes first-order in HO, and oxygen atom transfer has been detected, which indicates formation of oxidoiron(2+), FeO. These observations, and the assumption that the intermediate [FeHOO] decays approximately iso-energetically to FeO, allow one to estimate an Gibbs energy of formation FeO of +15 ± 10 kJ mol, from which follows the one-electron °'(FeO, HO/[Fe(HO)]) = +2.

Comment on "Theoretical investigations on hydrogen peroxide decomposition in aquo" by T. Tsuneda and T. Taketsugu, , 2018, , 24992.

In an study, Tsuneda and Taketsugu (, 2018, , 24992-24999) discuss the Fenton reaction, the reaction of Fe with HO. They claim that reaction is endergonic and therefore introduce a new intermediate, a monovalent iron complex. I show here that kinetically and thermodynamically such a monovalent iron complex cannot be formed.

Thinking Outside the Cage: A New Hypothesis That Accounts for Variable Yields of Radicals from the Reaction of CO with ONOO.

In biology, the reaction of ONOO with CO is the main sink for ONOO. This reaction yields CO, NO, NO, and CO. There is a long-standing debate with respect to the yield of the radicals relative to ONOO.

Reaction of CO with ONOO: One Molecule of CO Is Not Enough.

With CO present in excess, ONOO reacts to form an adduct in solution and in the solid state, most likely ONOOCO. In solution, the adduct appears within 2 ms and absorbs at 300 with an extinction coefficient, which is either 50% or 100% (preferred) of that of ONOO, 1.70 × 10 M cm, and at 685 nm with an extinction coefficient of 85 M cm.

Rust never sleeps: The continuing story of the Iron Bolt.

Since 1981, Gordon Research Conferences have been held on the topic of Oxygen Radicals on a biennial basis, to highlight and discuss the latest cutting edge research in this area. Since the first meeting, one special feature of this conference has been the awarding of the so-called Iron Bolt, an award that started in jest but has gained increasing reputation over the years. Since no written documentation exists for this Iron Bolt award, this perspective serves to overview the history of this unusual award, and highlights various experiences of previous winners of this "prestigious" award and other interesting anecdotes.

Jumpstarting the cytochrome P450 catalytic cycle with a hydrated electron.

Cytochrome P450cam (CYP101Fe) regioselectively hydroxylates camphor. Possible hydroxylating intermediates in the catalytic cycle of this well-characterized enzyme have been proposed on the basis of experiments carried out at very low temperatures and shunt reactions, but their presence has not yet been validated at temperatures above 0 °C during a normal catalytic cycle. Here, we demonstrate that it is possible to mimic the natural catalytic cycle of CYP101Fe by using pulse radiolysis to rapidly supply the second electron of the catalytic cycle to camphor-bound CYP101[FeO] Judging by the appearance of an absorbance maximum at 440 nm, we conclude that CYP101[FeOOH] (compound 0) accumulates within 5 μs and decays rapidly to CYP101Fe, with a of 9.

Low-Temperature Trapping of Intermediates in the Reaction of NO with O.

The autoxidation of NO was studied in glass-like matrices of 2-methylbutane at 110 K and in a 8:3 v/v mixture of 2,2-dimethylbutane and n-pentane (rigisolve) at 80-90 K, by letting gaseous NO diffuse into these solvents that were saturated with O. In 2-methyllbutane, we observed a red compound. However, in rigisolve at 85-90 K, a bright yellow color appears that turns red when the sample is warmed by 10-20 K.

Signaling by sulfur-containing molecules. Quantitative aspects.

There is currently interest in sulfur-containing molecules that may or may not play a role in signaling. We have collected relevant thermodynamic data, namely standard Gibbs energies of formation and electrode potentials at pH 7, and used these to construct a Frost diagram. Thermodynamic data not available in the literature could be estimated with reasonable confidence.

Electrode Potentials of l-Tryptophan, l-Tyrosine, 3-Nitro-l-tyrosine, 2,3-Difluoro-l-tyrosine, and 2,3,5-Trifluoro-l-tyrosine.

Electrode potentials for aromatic amino acid radical/amino acid couples were deduced from cyclic voltammograms and pulse radiolysis experiments. The amino acids investigated were l-tryptophan, l-tyrosine, N-acetyl-l-tyrosine methyl ester, N-acetyl-3-nitro-l-tyrosine ethyl ester, N-acetyl-2,3-difluoro-l-tyrosine methyl ester, and N-acetyl-2,3,5-trifluoro-l-tyrosine methyl ester. Conditional potentials were determined at pH 7.

Hydrogen peroxide, from Wieland to Sies.

A history of the formation of hydrogen peroxide in vivo is presented, starting with the discovery of catalase. The first hypothesis was formulated by Heinrich Wieland, who assumed that dioxygen reacted directly with organic molecules. This view was strongly criticised by Otto Warburg, Helmut Sies' academic grandfather.

Redox properties and activity of iron-citrate complexes: evidence for redox cycling.

Iron in iron overload disease is present as non-transferrin-bound iron, consisting of iron, citrate, and albumin. We investigated the redox properties of iron citrate by electrochemistry, by the kinetics of its reaction with ascorbate, by ESR, and by analyzing the products of reactions of ascorbate with iron citrate complexes in the presence of H2O2 with 4-hydroxybenzoic acid as a reporter molecule for hydroxylation. We report -0.

Concurrent cooperativity and substrate inhibition in the epoxidation of carbamazepine by cytochrome P450 3A4 active site mutants inspired by molecular dynamics simulations.

Cytochrome P450 3A4 (CYP3A4) is the major human P450 responsible for the metabolism of carbamazepine (CBZ). To explore the mechanisms of interactions of CYP3A4 with this anticonvulsive drug, we carried out multiple molecular dynamics (MD) simulations, starting with the complex of CYP3A4 manually docked with CBZ. On the basis of these simulations, we engineered CYP3A4 mutants I369F, I369L, A370V, and A370L, in which the productive binding orientation was expected to be stabilized, thus leading to increased turnover of CBZ to the 10,11-epoxide product.

Protein thiyl radical reactions and product formation: a kinetic simulation.

Protein thiyl radicals are important intermediates generated in redox processes of thiols and disulfides. Thiyl radicals efficiently react with glutathione and ascorbate, and the common notion is that these reactions serve to eliminate thiyl radicals before they can enter potentially hazardous processes. However, over the past years increasing evidence has been provided for rather efficient intramolecular hydrogen transfer processes of thiyl radicals in proteins and peptides.

Iron(II) binding by cereal beta-glucan.

Beta-glucan is a dietary fiber, which possesses several health benefits, such as cholesterol lowering, however this fiber is easily degraded in the presence of Fenton reagents. In the present study, the iron binding capacity of oat beta-glucan and barley beta-glucan was evaluated by investigating the kinetics of the Fenton reaction at pH 2.7 and 4.

ONOOH does not react with H2: Potential beneficial effects of H2 as an antioxidant by selective reaction with hydroxyl radicals and peroxynitrite.

H2 has been suggested to act as an antioxidant when administered just before the reperfusion phase of induced oxidative stress. These effects have been reported, for example, for the heart, brain, and liver. It is hypothesized that this beneficial effect may be due to selective scavenging of HO(⋅) and ONOOH by H2.