Redox Activity as a Powerful Strategy to Tune Magnetic and/or Conducting Properties in Benzoquinone-Based Metal-Organic Frameworks

Multifunctional molecular materials have attracted material scientists for several years as they are promising materials for the future generation of electronic devices. Careful selection of their molecular building blocks allows for the combination and/or even interplay of different physical properties in the same crystal lattice. Incorporation of redox activity in these networks is one of the most appealing and recent synthetic strategies used to enhance magnetic and/or conducting and/or optical properties. Quinone derivatives are excellent redox-active linkers, widely used for various applications such as electrode materials, flow batteries, pseudo-capacitors, etc. Quinones undergo a reversible two-electron redox reaction to form hydroquinone dianions via intermediate semiquinone radical formation. Moreover, the possibility to functionalize the six-membered ring of the quinone by various substituents/functional groups make them excellent molecular building blocks for the construction of multifunctional tunable metal-organic frameworks (MOFs). An overview of the recent advances on benzoquinone-based MOFs, with a particular focus on key examples where magnetic and/or conducting properties are tuned/switched, even simultaneously, by playing with redox activity, is herein envisioned.

Humic fractions as indicators of soil organic matter responses to clear-cutting in the mountain and lowland conditions of south-western Poland

Clear-cutting means forest removing (stem only) and is the most common type of forest harvesting but undoubtedly has a negative impact on the C budget in soils. This work aimed to describe responses of soil organic matter in the forest soils to forest removing under temperate climate conditions of lowland and mountain regions in south-western Poland. Using advanced instrumental analysis, like EPR, 1H NMR and FT-IR spectroscopy it has been found that clear-cutting, alters C cycling and accelerates decomposition in the forest floor leading to loss of humic fractions in the investigated soils. In the mountain forests the more labile, low-molecular fulvic fraction decreased as the effect of harvesting practice. The transformation of organic matter after clear-cutting resulted in the loss of less humified organic matter containing humic substances of less polymerised molecules. Analysis of the semiquinone radical structures and concentrations showed a decrease in radical concentration observed for HA from mountain clear-cut areas compare to the undisturbed forest. Results presented in this paper have proved less aliphatic character of humic acid molecules from the lowlands, compared to the mountain forest as the effect of clear-cutting. Harvesting practices in mountain regions should be approached with particular care due to the risk of erosion of exposed surfaces and soils containing less humified and less stable organic matter than in the lowlands. Humic fractions of higher solubility, less stability and tendency to migrate through the soil profile may favour the leaching of nutrients and consequently cause the eutrophication of waters.

Humic fractions as indicators of soil organic matter responses to clear-cutting in the mountain and lowland conditions of south-western Poland

Clear-cutting means forest removing (stem only) and is the most common type of forest harvesting but undoubtedly has a negative impact on the C budget in soils. This work aimed to describe responses of soil organic matter in the forest soils to forest removing under temperate climate conditions of lowland and mountain regions in south-western Poland. Using advanced instrumental analysis, like EPR, 1H NMR and FT-IR spectroscopy it has been found that clear-cutting, alters C cycling and accelerates decomposition in the forest floor leading to loss of humic fractions in the investigated soils. In the mountain forests the more labile, low-molecular fulvic fraction decreased as the effect of harvesting practice. The transformation of organic matter after clear-cutting resulted in the loss of less humified organic matter containing humic substances of less polymerised molecules. Analysis of the semiquinone radical structures and concentrations showed a decrease in radical concentration observed for HA from mountain clear-cut areas compare to the undisturbed forest. Results presented in this paper have proved less aliphatic character of humic acid molecules from the lowlands, compared to the mountain forest as the effect of clear-cutting. Harvesting practices in mountain regions should be approached with particular care due to the risk of erosion of exposed surfaces and soils containing less humified and less stable organic matter than in the lowlands. Humic fractions of higher solubility, less stability and tendency to migrate through the soil profile may favour the leaching of nutrients and consequently cause the eutrophication of wate

Oxidation of Hydrogen Sulfide by Quinones: How Polyphenols Initiate Their Cytoprotective Effects

We have shown that autoxidized polyphenolic nutraceuticals oxidize H2S to polysulfides and thiosulfate and this may convey their cytoprotective effects. Polyphenol reactivity is largely attributed to the B ring, which is usually a form of hydroxyquinone (HQ). Here, we examine the effects of HQs on sulfur metabolism using H2S- and polysulfide-specific fluorophores (AzMC and SSP4, respectively) and thiosulfate sensitive silver nanoparticles (AgNP). In buffer, 1,4-dihydroxybenzene (1,4-DB), 1,4-benzoquinone (1,4-BQ), pyrogallol (PG) and gallic acid (GA) oxidized H2S to polysulfides and thiosulfate, whereas 1,2-DB, 1,3-DB, 1,2-dihydroxy,3,4-benzoquinone and shikimic acid did not. In addition, 1,4-DB, 1,4-BQ, PG and GA also increased polysulfide production in HEK293 cells. In buffer, H2S oxidation by 1,4-DB was oxygen-dependent, partially inhibited by tempol and trolox, and absorbance spectra were consistent with redox cycling between HQ autoxidation and H2S-mediated reduction. Neither 1,2-DB, 1,3-DB, 1,4-DB nor 1,4-BQ reduced polysulfides to H2S in either 21% or 0% oxygen. Epinephrine and norepinephrine also oxidized H2S to polysulfides and thiosulfate; dopamine and tyrosine were ineffective. Polyphenones were also examined, but only 2,5-dihydroxy- and 2,3,4-trihydroxybenzophenones oxidized H2S. These results show that H2S is readily oxidized by specific hydroxyquinones and quinones, most likely through the formation of a semiquinone radical intermediate derived from either reaction of oxygen with the reduced quinones, or from direct reaction between H2S and quinones. We propose that polysulfide production by these reactions contributes to the health-promoting benefits of polyphenolic nutraceuticals.

o-Semiquinone radical anion isolated as an amorphous porous solid

The use of metal cations is a commonly applied strategy to create S > ½ stable molecular systems containing semiquinone radicals. Persistent mono-semiquinonato complexes of diamagnetic metal ions (S =...

Intramolecular Annulation of Gossypol by Laccase to Produce Safe Cottonseed Protein

The presence of the phenol gossypol has severely limited the utilization of cottonseed meal and oil in the food and animal feed industries. Highly efficient means of biodegradation of gossypol and an understanding of the cytotoxicity of its degradation products remain outside current knowledge and are of universal interest. In this work, we showed for the first time that laccase can catalyze the intramolecular annulation of the aldehyde and hydroxyl groups of gossypol for the o-semiquinone radical and originate the released ·OH radical. It was further found that the oxidation of aldehyde groups significantly decreases reproductive toxicity and hepatotoxicity. These results indicate a novel detoxification pathway for gossypol and reveal the crucial role played by radical species in cyclization. This discovery could facilitate the development of safe, convenient, and low-cost industrial methods for the detoxification of cotton protein and oil resources.