Solution Tetrahydrobiopterin Radical vs. the Enzyme-Bound Radical: A Paramagnetic Reconciliation

Background: Nitric oxide synthase (NOS) catalyzes the formation of nitric oxide (NO) and citrulline from L-arginine, dioxygen (O2), and nicotinamide adenine dinucleotide phosphate (NADPH) in a two-step reaction, with the enzyme-bound intermediate Nω-hydroxy-L-arginine (NHA). Previous electron paramagnetic resonance (EPR) studies of NOS reaction have shown that (6R, 1'R, 2'S)-6-(l',2'-dihydroxypropyl)-5,6,7,8-tetrahydropterin (H4B) acts as a single electron donor in both steps of the reaction, resulting in the transient generation of a tetrahydropterin cation radical (H4B•+). Results: H4B•+ can also be chemically generated in strongly acidic solutions. EPR studies of chemically generated H4B•+ and similar pterin radicals date back to the 1960s. However, the reported paramagnetic parameters of H4B•+ in NOS do not seem to match the corresponding reported parameters for either H4B•+ or other pterin centered radicals chemically generated in solution. In particular, the rather isotropic hyperfine coupling of ca. 45 MHz for 1H6 of H4B•+ in NOS is at least 15 MHz larger than that of H4B•+ or any other previously studies pterin solution radical. In the work reported here, a combination of 9.5 - 9.8 GHz contentious wave (cw-) EPR, 34GHz 1H electron nuclear double resonance (ENDOR), spectral simulation and Density Functional Theory (DFT) calculations were used to investigate this seeming discrepancy. Conclusion: We demonstrated that the differences in the paramagnetic parameters of the chemically generated H4B radicals in solutions and those of the H4B radicals in NOS are consistent with the presence of two different conformers of the same cation radical in the two media.

Donor-Type Nickel–Dithiolene Complexes Fused with Bulky Cycloalkane Substituents and Their Application in Molecular Conductors

The effects of substituents on the arrangement of metal–dithiolene complexes based on π-conjugated systems, which are extensively used to synthesize various functional materials, have not been studied adequately. New donor-type nickel–dithiolene complexes fused with bulky cycloalkane substituents [Ni(Cn-dddt)2] (C5-dddt = 4a,5,6,6a-pentahydro-1,4-benzodithiin-2,3-dithiolate; C6-dddt = 4a,5,6,7,8,8a-hexahydro-1,4-benzodithiin-2,3-dithiolate; C7-dddt = 4a,5,6,7,8,9,9a-heptahydro-1,4-benzodithiin-2,3-dithiolate; and C8-dddt = 4a,5,6,7,8,9,10,10a-octahydro-1,4-benzodithiin-2,3-dithiolate) were synthesized in this study. All the complexes were crystallized in cis-[Ni(cis-Cn-dddt)2] conformations with cis-oriented (R,S) conformations around the cycloalkylene groups in the neutral state. Unique molecular arrangements with a three-dimensional network, a one-dimensional column, and a helical molecular arrangement were formed in the crystals owing to the flexible cycloalkane moieties. New 2:1 cation radical crystals of [Ni(C5-dddt)2]2(X) (X = ClO4− or PF6−), obtained by electrochemical crystallization, exhibited semiconducting behaviors (ρrt = 0.8 Ω cm, Ea = 0.09 eV for the ClO4− crystal; 4.0 Ω cm, 0.13 eV for the PF6− crystal) under ambient pressure due to spin-singlet states between the dimers of the donor, which were in accordance with the conducting behaviors under hydrostatic pressure (ρrt = 0.2 Ω cm, Ea = 0.07 eV for the ClO4− crystal; 1.0 Ω cm, 0.12 eV for the PF6− crystal at 2.0 GPa).

Hydroquinone redox mediator enhances the photovoltaic performances of chlorophyll-based bio-inspired solar cells

Chlorophyll (Chl) derivatives have recently been proposed as photoactive materials in next-generation bio-inspired solar cells, because of their natural abundance, environmental friendliness, excellent photoelectric performance, and biodegradability. However, the intrinsic excitation dynamics of Chl derivatives remain unclear. Here, we show sub-nanosecond pump–probe time-resolved absorption spectroscopy of Chl derivatives both in solution and solid film states. We observe the formation of triplet-excited states of Chl derivatives both in deoxygenated solutions and in film samples by adding all-trans-β-carotene as a triplet scavenger. In addition, radical species of the Chl derivatives in solution were identified by adding hydroquinone as a cation radical scavenger and/or anion radical donor. These radical species (either cations or anions) can become carriers in Chl-derivative-based solar cells. Remarkably, the introduction of hydroquinone to the film samples enhanced the carrier lifetimes and the power conversion efficiency of Chl-based solar cells by 20% (from pristine 1.29% to 1.55%). This enhancement is due to a charge recombination process of Chl-A+/Chl-D–, which is based on the natural Z-scheme process of photosynthesis.

Antioxidant activity of enzyme-assisted extract derived from round kumquat peel (Fortunella japonica)

This study intends to apply enzyme-assisted extraction method to determine the antioxidant activity of round kumquat peel extract. Firstly, chemical composition of the kumquat peel was determined. Then, single factor test was employed to evaluate the effects of enzyme treatment conditions (enzyme amount and extraction time, ethanol concentration, material:ethanol ratio, extraction time and extraction temperature) on total phenolic content (TPC) and antioxidant activity of the kumquat peel extract. The result showed that the content of phenolic compounds in the kumquat peel achieved 1.3%. The peel extract exhibited the maximum TPC of 335.96±16.79 milligrams of gallic acid equivalents (mg GAE)/g dry matter, 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) cation radical (ABTS●+) scavenging activity of 1993.26±99.66 μmol Trolox Equivalent (TE)/g dry matter and ferric reducing antioxidant power (FRAP) value of 3202.86±160.14 μmol TE/g dry matter. This extract was obtained under enzyme treatment condition including enzyme content of 9 U/g dry matter, enzyme-treating time of 90 min and the extraction condition comprising of kumquat peel: 96% ethanol ratio of 1:40 (w/v), extraction time of 150 min and temperature of 50°C. The results revealed that the kumquat peel extract could be used as a potential natural antioxidant in food and/or pharmaceutical products.

Oxidative Intramolecular C-C Bond Formation Reactions of 1,2-Diarylbenzenes: Syntheses of Highly Conjugated Double-Bridged Polycyclic Aromatic Hydrocarbons

Oxidation reactions of 1,2-diarylbenzenes induce intramolecular C-C bond formation. The substrates studied here were prepared by the stepwise Suzuki-Miyaura coupling reaction that introduced 2-naphthyl, 2-anthranyl, and 2-pyrenyl groups on the ortho positions of benzene. The subsequent oxidation reaction with FeCl3 induced an oxidative C-C bond formation reaction in the interior regions of the molecules. In marked contrast to our previous observations, two C-C bonds were formed. Theoretical calculations indicated that large spin densities at the reaction positions of the bis(cation radical) and/or cation radical species are needed for the C-C bond formation. The π-expanded molecules obtained here showed bathochromic shifts in the absorption spectra and amphoteric multi-redox behavior in electrochemistry.

The Versatility of the Aryne–Imine–Aryne Coupling for the ­Synthesis of Acridinium Photocatalysts

The increasing use of acridinium photocatalysts as sustainable alternative to precious metal-based counterparts encourages the design and efficient synthesis of distinct catalyst structures. Herein, we report our exploration of the scope of the aryne–imine–aryne coupling reaction combined with a subsequent acridane oxidation for a short two-step approach towards various acridinium salts. The photophysical properties of the novel photocatalysts were investigated and the practical value was demonstrated by a cation-radical accelerated nucleophilic aromatic substitution reaction.

Effects of Juglone on Neutrophil Degranulation and Myeloperoxidase Activity Related to Equine Laminitis

Experimental laminitis, characterized by a failure of the dermal–epidermal interface of the foot, can be induced in horses by the oral administration of a black walnut extract (BWE). In the early phase of this severe and painful disease, an activation of neutrophil occurs, with the release of myeloperoxidase (MPO), a pro-oxidant enzyme of neutrophils, in plasma, skin, and laminar tissue. Juglone, a naphthoquinone derivative endowed with redox properties, is found in walnuts and has been incriminated in this neutrophil activation. We report for the first time the inhibitory activity of juglone on the degranulation of neutrophils induced by cytochalasin B and formyl-methionyl-leucyl-phenylalanine as monitored by the MPO release (>90% inhibition for 25 and 50 μM). Moreover, it also acts on the peroxidase activity of MPO by interacting with the intermediate “π cation radical,” as evidenced by the classical and specific immunological extraction followed by enzymatic detection (SIEFED) assays. These results are confirmed by a docking study showing the perfect positioning of juglone in the MPO enzyme active site and its interaction with one of the amino acids (Arg-239) of MPO apoprotein. By chemiluminescence and electron paramagnetic resonance techniques, we demonstrated that juglone inhibited reactive oxygen species (ROS) and superoxide anion free radical produced from phorbol myristate acetate (PMA)-activated polymorphonuclear neutrophils (PMNs). These results indicate that juglone is not the trigger for equine laminitis, at least if we focus on the modulation of neutrophil activation.

Evaluation of The Antioxidant, Antidiabetic and Immunomodulatory Activity of Cydonia oblonga Fruit Extract

Dietary natural antioxidant consumption can protect the human body from several diseases induced by free radicals. The aim of this study was to evaluate the antioxidant, antidiabetic and immunomodulatory properties of Cydonia oblonga fruit. For this; hydroethanolic extract of Cydonia oblonga fruit (HECO) was examined for antioxidant activity using DPPH free radical sc avenging, ABTS cation radical decolorization, Cupric reducing antioxidant capacity (CUPRAC), and Metal Chelating on ferrous ions activities. The inhibitory activity of the extract against α-glucosidase enzyme was also investigated. HECO was tested in vivo for the immunomodulatory activity on non-specific immunity by the carbon clearance test. The content of the nonenzymatic antioxidant reduced glutathione (GSH) in liver tissue of used mice was estimated. in vitro studies revealed that the HECO has an inhibitory concentration (IC50) value of 249.26 ± 3.75μg/mL, 117.34 ± 1.41 μg/ml for DPPH and ABTS scavenging activity respectively. As well as the ability to reduce cupric (167.17 ± 1.15μg/mL) and iron (Fe) (417.98 ± 48.82μg/mL). The extract showed antidiabetic activity as evidenced by its capacity to inhibit the α-glucosidase enzyme (IC50: 326.48 ± 18.56 µg/mL) near the acarbose (IC50: 275.98 ± 1.57 µg/mL) used as a positive control. In addition, our results showed that HECO at the concentration of 50 and 100 mg/kg significantly increased the clearance rate of carbon from the bloodstream concomitant with increased liberation of GSH from liver cells. This study demonstrates that HECO is effective in scavenging free radicals and can serve as potent antioxidants that provide potential treatment and prevention for diabetes with benefits on the innate defense system. Keywords: Antidiabetic, Antioxidant, Cydonia oblonga, Hydroethanolic extract, Phagocytic activity