p-Phenylenediamines and p-phenylenediamine quinone derivatives in rubber consumer products and typical urban dust: Sources, transformation profiles, and health risks.

N,N'-Substituted p-phenylenediamines (PPDs) are widely used as antioxidants in the rubber industry and are released into the environment in large quantities during the production and use of rubber products. We quantified PPDs and PPD quinone derivatives (PPD-Qs) in rubber consumer products, including car tires, rubber belts, rubber gloves, rubber cables, and rubber hoses, to obtain information on the degree of weathering over time during their use. Additionally, we investigated the occurrences and sources of PPDs and PPD-Qs in dust samples collected from four typical urban environments (roads, parking lots, automotive repair shops, and residences). The detected compounds included the highly toxic N-(1,3-dimethylbutyl)-N'-phenyl-1,4-phenylenediamine quinone, which can cause acute mortality of coho salmon (Oncorhynchus kisutch). Concentrations of PPDs in the automotive repair shops reached 56.0 µg/g, and were much higher than in the other environments, while the residential samples had the lowest contaminant concentrations. In road and residential samples, N,N'-di-2-naphthyl-p-phenylenediamine accounted for 17 %-30 % of the PPDs, and may have originated from different sources. We preliminarily identified 32 transformation products, and 11 of these were N,N'-di-2-naphthyl-p-phenylenediamine transformation products. The average daily intakes of PPDs and PPD-Qs were calculated to assess the health risks of dust exposure in each environment. Workers had high total intakes of PPD [60.3 ng/(kg day)] and PPD-Qs [20.1 ng/(kg day)], and were at some risk of occupational exposure. These results improve our understanding of the environmental occurrences, sources, transformation, and health risks of PPDs and PPD-Qs.

Crystal structures of the (η2:η2-cyclo-octa-1,5-diene)(η6-toluene)-iridium(I) cation and µ-chlorido-iridium(III) complexes of 2-(phosphinito)- and 2-(phosphinometh-yl)anthra-quinone ligands.

When reacted in dry, degassed toluene, [Ir(COD)Cl]2 (COD = cyclo-octa-1,5-diene) and 2 equivalents of 2-(di-tert-butyl-phosphinito)anthra-quinone (tBuPOAQH) were found to form a unique tri-iridium compound consisting of one monoanionic dinuclear tri-µ-chlorido complex bearing one bidentate tBuPOAQ ligand per iridium, which was charge-balanced by an outer sphere [Ir(toluene)(COD)]+ ion, the structure of which has not previously been reported. This product, which is a toluene solvate, namely, (η2:η2-cyclo-octa-1,5-diene)(η6-toluene)-iridium(I) tri-µ-chlorido-bis-({3-[(di-tert-butyl-phosphan-yl)-oxy]-9,10-dioxoanthracen-2-yl}hydridoiridium(III)) toluene monosolvate, [Ir(C7H8)(C8H12)][Ir2H2(C22H24O3P)2Cl3]·C7H8 or [Ir(toluene)(COD)][Ir(κ-P,C-tBuPOAQ)(H)]2(µ-Cl)3]·toluene, formed as small orange platelets at room temperature, crystallizing in the triclinic space group P. The cation and anion are linked via weak C-H⋯O inter-actions. The stronger inter-molecular attractions are likely the offset parallel π-π inter-actions, which occur between the toluene ligands of pairs of inverted cations and between pairs of inverted anthra-quinone moieties, the latter of which are capped by toluene solvate mol-ecules, making for π-stacks of four mol-ecules each. The related ligand, 2-(di-tert-butyl-phosphinometh-yl)-anthra-quinone (tBuPCAQH), did not form crystals suitable for X-ray diffraction under analogous reaction conditions. However, when the reaction was conducted in chloro-form, yellow needles readily formed following addition of 1 atm of carbon monoxide. Diffraction studies revealed a neutral, dinuclear, di-µ-chlorido complex, di-µ-chlorido-bis-(carbon-yl{3-[(di-tert-butyl-phosphan-yl)-oxy]-9,10-dioxoanthracen-2-yl}hydridoiridium(I)), [Ir2H2(C23H26O2P)2Cl2(CO)2] or [Ir(κ-P,C-tBuPCAQ)(H)(CO)(µ-Cl)]2, Ir2C48H54Cl2O6P2, again crystallizing in space group P. Offset parallel π-π inter-actions between anthra-quinone groups of adjacent mol-ecules link the mol-ecules in one dimension.

Unveiling spatiotemporal distribution, partitioning, and transport mechanisms of tire additives and their transformation products in a highly urbanized estuarine region.

Numerous tire additives are high-production volume chemicals that are used extensively worldwide. However, their presence and partitioning behavior remain largely unknown, particularly in marine environments. This study is the first to reveal the spatiotemporal distribution, multimedia partitioning, and transport processing of 22 tire additives and their transformation products (TATPs) in a highly urbanized estuary (n = 166). Nineteen, 18, and 20 TATPs were detectable in water, suspended particulate matter (SPM), and sediments, respectively, with total levels of 59.7-2021 ng/L, 164-6935 ng/g, and 4.66-58.4 ng/g, respectively. The multimedia partitioning mechanisms of TATPs are governed by their molecular weight, hydrophobicity, and biodegradation rate. Mass inventories coupled with model simulations have revealed that substantial quantities of TATPs accumulate within estuarine environments, and these compounds can be continuously transported into the ocean, particularly during the wet season. According to the multi-criteria evaluation approach, four and three TATPs were identified as high-priority pollutants during the dry and wet seasons, respectively. Unexpectedly, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone was only listed as a medium-priority pollutant. This study underscores the importance of marine surveillance and advocates for particular attention to these ubiquitous but underexplored TATPs in future studies.

A High-capacity Benzoquinone Derivative Anode for All-organic Long-cycle Aqueous Proton Batteries.

Quinone compounds, with the ability to uptake protons, are promising electrodes for aqueous batteries. However, their application is limited by the mediocre working potential range and inferior rate performance. Herein, we examined quinones bearing different substituents, and for the first time introduce tetraamino-1,4-benzoquinone (TABQ) as anode material for proton batteries. The strong electron-donating amino groups can effectively narrow the band gap and negatively shift the redox potentials of quinone material. The protonation of amino groups and the amorphization of structure result in the formation of an intermolecular hydrogen-bond network, supporting Grotthuss-type proton conduction in the electrode with a low activation energy of 192.7 meV. The energy storage mechanism revealed by operando FT-IR and ex-situ XPS features a reversible quinone-hydroquinone conversion during cycling. TABQ demonstrates a remarkable specific capacity of 307 mAh g-1 at 1 A g-1, which is the highest among organic proton electrodes. An all-organic proton battery of TABQ//TCBQ has also been developed, achieving exceptional stability of 3500 cycles at room temperature and excellent performance at sub-zero temperatures.

Hemilabile and Redox-Active Quinone Ligands Unlock sp3-Rich Couplings in Nickel-Catalyzed Olefin Carbosulfenylation.

A three-component coupling approach toward structurally complex dialkylsulfides is described via the nickel-catalyzed 1,2-carbosulfenylation of unactivated alkenes with organoboron nucleophiles and alkylsulfenamide (N-S) electrophiles. Efficient catalytic turnover is facilitated using a tailored N-S electrophile containing an N-methyl methanesulfonamide leaving group, allowing catalyst loadings as low as 1 mol%. Regioselectivity is controlled by a collection of monodentate, weakly coordinating native directing groups, including sulfonamides, amides, sulfinamides, phosphoramides, and carbamates. Key to the development of this transformation is the identification of quinones as a family of hemilabile and redox-active ligands that tune the steric and electron properties of the metal throughout the catalytic cycle. DFT calculations show that the duroquinone (DQ) ligand adopts different coordination modes in different stages of the Ni-catalyzed 1,2-carbosulfenylation-binding as an η6 capping ligand to stabilize the precatalyst/resting state and prevent catalyst decomposition, binding as an X-type redox-active durosemiquinone radical anion to promote alkene migratory insertion with a less distorted square planar Ni(II) center, while binding as an η1 L-type ligand to promote N-S oxidative addition at a relatively more electron-rich and sterically less crowded Ni(I) center.

Oxygen-Stable Electrochemical CO2 Capture using Redox-Active Heterocyclic Benzodithiophene Quinone.

Electrochemical carbon capture offers a promising alternative to thermal amine technology, which serves as the traditional benchmark method for CO2 capture. Despite its technological maturity, the widespread deployment of thermal amine technologies is hindered by high energy consumption and sorbent degradation. In contrast, electrochemical methods, with their inherently isothermal operation, address these challenges, offering enhanced energy efficiency and robustness. Among emerging strategies, electrochemical carbon capture systems using redox-active materials such as quinones stand out for their potential to capture CO2.However, their practical application is currently limited by their low stability in the presence of oxygen. We demonstrate that benzodithiophene quinone (BDT-Q), a heterocyclic quinone, exhibits high stability in electrochemical carbon capture processes with oxygen-containing feed gas. Conducted in a cyclic flow system with a simulated flue gas mixture containing 13% CO2 and 3.5% O2 for over 100 hours, the process demonstrates high oxygen stability with an electron utilization of 0.83 without significant degradation, indicating a promising approach for real world applications. Our study explores the potential of new heterocyclic quinone compounds in the context of carbon capture technologies.

Leveraging Natural Product-inspired Antifungals to Investigate the Mechanism of Action of Peniciaculin A.

Ubiquinone mimics known as quinone outside inhibitors (QoIs) are one of the most prominent fungicides used to protect crops in the agricultural industry. Due to chemotype similarities with known QoIs, peniciaculin A, a triaryl natural product, was proposed to exhibit similar broad spectrum antifungal activity against phytopathogens. Instability of the tertiary alcohol and phenol motif, however, prompted exploration of the antifungal properties of simplified analogues to probe possible overlap in mechanism of action between the natural product and QoIs. Peniciaculin A inspired analogues mimicking known QoI scaffolds displayed broad spectrum antifungal activity while those containing scaffolds dissimilar to QoIs possessed negligible bioactivity. These activity profiles suggest peniciaculin A is likely acting as a QoI.

Bridge-dependent donor-metal-acceptor-metal-donor (D-M-A-M-D) systems: from charge transfer to electron transfer in dioxolene-Ge-diimine complexes.

Synthesis and structural characterization of a family of germanium-dioxolene complexes with ditopic N-donor ligands (L1-L5) (L1 = 1,2-bis(pyridin-2-ylmethylene)hydrazine L2 = 1,6-bis-(pyridin-2-yl)-2,5-diaza-1,5-heхаdiene, L3 = N,N-bis(pyridin-2-ylmethylene)-1,4-benzenediamine, L4 = N,N-bis(pyridin-2-ylmethylene)-(biphenyl)-4,4-diamine, L5 = 2,2'-azopyridine) is reported. The reaction of germanium bis-catecholate with bridging ligands L1 - L4, differing by the nature of the linker between pyridine sites gives rise to dinuclear digermanium complexes (36Cat2Ge)2L1-4 (36Cat = dianion of 3,6-di-tert-butylcatechol) 1-4 of DMAMD type (donor-metal-acceptor-metal-donor) with a charge transfer in the UV-Vis region. In opposite, the interaction of the 36Cat2Ge with 2,2'-azopyridine (L5) results in the two-electron transfer from the donor 36Cat2- ligands to the azopyridine bridge forming stable open-shell complex 5 [(36SQ)(36CatGe)]2(L5)2- (36SQ = radical-anionic semiquinonate ligand). Molecular structures of compounds 3 and 5 were determined by single crystal X-ray diffraction analysis. Electronic structures of complexes 1-5 were studied by means of DFT calculations.

The occurrence and mechanism of field resistance to boscalid and pyraclostrobin in Stemphylium solani, the causal agent of tomato gray leaf spot in China.

The destructive disease gray leaf spot, caused by Stemphylium solani, is prevalent in tomato plants in China. A variety of fungicides have been extensively used for controlling the disease, with a particular focus on succinate dehydrogenase inhibitors (SDHIs) and quinone outside inhibitors (QoIs). However, there was a lack of information regarding the resistance of S. solani to boscalid (SDHI) and pyraclostrobin (QoI) in China. In this study, the sensitivity of S. solani to boscalid and pyraclostrobin was monitored. The EC50 values for boscalid ranged from 0.02 to 3.0 µg∙mL-1, with an average value of 0.62 µg∙mL-1, while the EC50 values for pyraclostrobin ranged from 0.21 to 14.71 µg∙mL-1, with an average value of 6.03 µg∙mL-1. Based on these findings, the frequencies of observed resistance were as follows: 36.7% for boscalid and 50% for pyraclostrobin; while the resistance frequency to both boscalid and pyraclostrobin in S. solani was 19.4%. The mutation associated with boscalid resistance in S. solani within tomato fields was identified as SdhB-H277Y, while the mutation related to pyraclostrobin resistance was found in cytochrome b, specifically Cytb-G143A. The resistant mutants displayed diminished fitness in terms of mycelial growth, yet their pathogenicity exhibited no significant disparities. To delay the development of resistance, it is advisable to employ a rotation strategy using alternative fungicides with different modes of action or mix with fungicides with multi-site-contact activity for disease management.

Pyrroloquinoline Quinone Alleviates Intestinal Inflammation and Cell Apoptosis via the MKK3/6-P38 Pathway in a Piglet Model.

This study investigates the underlying mechanism through which dietary supplementation of pyrroloquinoline quinone disodium (PQQ) alleviates intestinal inflammation and cell apoptosis in piglets challenged with lipopolysaccharide (LPS). Seventy-two barrows were divided into three groups: control (CTRL), LPS challenged (LPS), and LPS challenged with PQQ supplementation (PQQ + LPS). On d 7, 11, and 14, piglets received intraperitoneal injections of LPS or 0.9% of NaCl (80 µg/kg). After a 4 h interval following the final LPS injection on d 14, blood samples were obtained, and all piglets were euthanized for harvesting jejunal samples. The results showed that dietary supplementation of PQQ improved the damage of intestinal morphology, increased the down-regulated tight junction proteins, and reduced the increase of serum diamine oxidase activity, the intestinal fatty acid binding protein, and TNF-α levels in piglets challenged with LPS (p < 0.05). The proteomics analysis revealed a total of 141 differentially expressed proteins (DEPs), consisting of 64 up-regulated DEPs and 77 down-regulated DEPs in the PQQ + LPS group compared to the LPS group. The KEGG pathway analysis indicated enrichment of the tight junction pathway and the apoptosis pathway (p < 0.05). Compared to the LPS group, the piglets in the PQQ + LPS group had increased levels of Bcl-2 protein, reduced positive apoptosis signals, and a decrease in the abundance of MKK 3/6 and p-p38 proteins (p < 0.05). In conclusion, dietary supplementation of PQQ could alleviate jejunal inflammatory damage and cell apoptosis in piglets challenged with LPS through the MKK3/6-p38 signaling pathway.

Quinone chemistry in respiratory complex I involves protonation of a conserved aspartic acid residue.

Respiratory complex I is a central metabolic enzyme coupling NADH oxidation and quinone reduction with proton translocation. Despite the knowledge of the structure of the complex, the coupling of both processes is not entirely understood. Here, we use a combination of site-directed mutagenesis, biochemical assays, and redox-induced FTIR spectroscopy to demonstrate that the quinone chemistry includes the protonation and deprotonation of a specific, conserved aspartic acid residue in the quinone binding site (D325 on subunit NuoCD in Escherichia coli). Our experimental data support a proposal derived from theoretical considerations that deprotonation of this residue is involved in triggering proton translocation in respiratory complex I.

Identifying Quinones in Complex Aqueous Environmental Media (Biochar Extracts) through Tagging with Cysteine and Cysteine-Contained Peptides and High Resolution Mass Spectrometry Analysis.

Quinones are among the most important components in natural organic matter (NOM) for redox reactions; however, no quinones in complex environmental media have been identified. To aid the identification of quinone-containing molecules in ultracomplex environmental samples, we developed a chemical tagging method that makes use of a Michael addition reaction between quinones and thiols (-SH) in cysteine (Cys) and cysteine-contained peptides (CCP). After the tagging, candidates of quinones in representative aqueous environmental samples (water extractions of biochar) were identified through high-resolution mass spectrometry (HRMS) analysis. The MS and UV spectra analysis showed rapid reactions between Cys/CCP and model quinones with ß-carbon from the same benzene ring available for Michael addition. The tagging efficiency was not influenced by other co-occurring nonquinone representative compounds, including caffeic acid, cinnamic acid, and coumaric acid. Cys and CCP were used to tag quinones in water extractions of biochars, and possible candidates of quinones (20 and 53 based on tagging with Cys and CCP, respectively) were identified based on the HRMS features for products of reactions with Cys/CCP. This study has successfully demonstrated that such a Michael addition reaction can be used to tag quinones in complex environmental media and potentially determine their identities. The method will enable an in-depth understanding of the redox chemistry of NOM and its critical chemical compositions and structures.

In vitro modelling of Parkinson's disease using 6-OHDA is associated with increased NQO2 activity.

The pathogenesis of Parkinson's disease (PD) involves abnormalities in the metabolism of catecholamines. The enzyme quinone reductase 2 (NQO2) reduces quinone derivatives of catecholamines, which promotes the formation of reactive oxygen species (ROS), suggesting a role for NQO2 in the development of cellular damage typical of PD. In the present study, we investigated the relationship between 6-hydroxydophamine (6-OHDA) induced cellular damage and NQO2 activity and its levels in SH-SY5Y cell culture to establish an experimental model to evaluate the pharmacological properties of NQO2 inhibitors. Cellular damage was evaluated using the MTT and comet assays. It was shown that oxidative damage of SH-SY5Y cells upon incubation with 6-OHDA for 6, 12 and 24 h was accompanied by an increase in NQO2 activity. The increase in NQO2 protein level in SH-SY5Y cells was observed 24 h after incubation with 6-OHDA at concentrations of 50 and 100 µM. Oxidative damage of SH-SY5Y cells upon 1 h incubation with 6-OHDA is increased in the presence of the selective enzyme co-substrate 1-benzyl-1,4-dihydronicotinamide (BNAH), but is not accompanied by changes in NQO2 activity and protein levels. The data obtained demonstrate the contribution of NQO2 to the cytotoxic mechanism of 6-OHDA action.

Facile Synthesis of Fe-Based Metal-Quinone Networks for Mutually Enhanced Mild Photothermal Therapy and Ferroptosis.

Mild photothermal therapy (MPTT) has emerged as a promising therapeutic modality for attenuating thermal damage to the normal tissues surrounding tumors, while the heat-induced upregulation of heat shock proteins (HSPs) greatly compromises the curative efficacy of MPTT by increasing cellular thermo-tolerance. Ferroptosis has been identified to suppress the overexpression of HSPs by the accumulation of lipid peroxides and reactive oxygen species (ROS), but is greatly restricted by overexpressed glutathione (GSH) in tumor microenvironment and undesirable ROS generation efficiency. Herein, a synergistic strategy based on the mutual enhancement of MPTT and ferroptosis is proposed for cleaving HSPs to recover tumor cell sensitivity. A facile method for fabricating a series of Fe-based metal-quinone networks (MQNs) by coordinated assembly is proposed and the representative FTP MQNs possess high photothermal conversion efficiency (69.3%). Upon 808 nm laser irradiation, FTP MQNs not only trigger effective MPTT to induce apoptosis but more significantly, potentiate Fenton reaction and marked GSH consumption to boost ferroptosis, and the reinforced ferroptosis effect in turn can alleviate the thermal resistance by declining the HSP70 defense and reducing ATP levels. This study provides a valuable rationale for constructing a large library of MQNs for achieving mutual enhancement of MPTT and ferroptosis.

Metabolic and Biochemical Effects of Pyrroloquinoline Quinone (PQQ) on Inflammation and Mitochondrial Dysfunction: Potential Health Benefits in Obesity and Future Perspectives.

Obesity is defined as a complex, systemic disease characterized by excessive and dysfunctional adipose tissue, leading to adverse health effects. This condition is marked by low-grade inflammation, oxidative stress, and metabolic abnormalities, including mitochondrial dysfunction. These factors promote energy dysregulation and impact body composition not only by increasing body fat but also by promoting skeletal muscle mass atrophy. The decline in muscle mass is associated with an increased risk of all-cause mortality in individuals with this disease. The European Food Safety Authority approved pyrroloquinoline quinone (PQQ), a natural compound, as a dietary supplement in 2018. This narrative review aims to provide a comprehensive overview of the potential role of PQQ, based on its anti-inflammatory and antioxidant properties, in addressing dysfunctional adipose tissue metabolism and related disorders.

Protective role of ghrelin against 6PPD-quinone-induced neurotoxicity in zebrafish larvae (Danio rerio) via the GHSR pathway.

The toxicity mechanisms of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-Q), an antioxidant derivative of 6PPD via ozone reaction commonly used in rubber and tire industries, were investigated in zebrafish larvae with concentrations ranging from 0 to 50 µg/L. Despite normal hatchability, 6PPD-Q exposure led to reduced body length and swimming distance in 120 hours post-fertilization (hpf) larvae. At the highest concentration (50 µg/L), 6PPD-Q significantly impaired dopaminergic neuron development and neurotransmitter levels, including dopamine, 5-hydroxytryptamine, and glutamate. Transcriptome profiling unveiled perturbations in growth and developmental gene expression, such as upregulation of runx2a, runx2b, and ghrl (ghrelin and obestatin prepropeptide), and downregulation of stat1b, auto1, and cidea. Notably, anamorelin, a growth hormone secretagogue receptor (GHSR) agonist, recovered the behavioral deficits induced by 6PPD-Q, implying a neuroprotective role of ghrelin possibly mediated via the ghrelin/GHSR pathway. Collectively, our findings indicate that ghrelin upregulation may counteract 6PPD-Q toxicity in zebrafish larvae, shedding light on potential therapeutic avenues for mitigating the adverse effects of this antioxidant byproduct.

Improving the alcohol respiratory chain and energy metabolism by enhancing PQQ synthesis in Acetobacter pasteurianus.

Pyrroquinoline quinone (PQQ) is one of the important coenzymes in living organisms. In acetic acid bacteria (AAB) it plays a crucial role in alcohol respiratory chain, as a coenzyme of alcohol dehydrogenase. In this work, the PQQ biosynthetic genes were overexpressed in Acetobacter pasteurianus CGMCC 3089 to improve the fermentation performance. The result shows that the intracellular and extracellular PQQ contents in the recombinant strain A. pasteurianus (pBBR1-p264-pqq) were 152.53% and 141.08% higher than those of the control A. pasteurianus (pBBR1-p264), respectively. The catalytic activity of alcohol dehydrogenase and aldehyde dehydrogenase increased by 52.92% and 67.04%, respectively. The results indicated that the energy charge and intracellular ATP were also improved in the recombinant strain. The acetic acid fermentation was carried out using a 5 L self-aspirating fermenter, and the acetic acid production rate of the recombinant strain was 23.20% higher compared with the control. Furthermore, the relationship between the PQQ and acetic acid tolerance of cells was analyzed. The biomass of recombinant strain was 180.2%, 44.3%, and 38.6% higher than those of control under 2%, 3%, and 4% acetic acid stress, respectively. After treated with 6% acetic acid for 40 min, the survival rate of the recombinant strain was increased by 76.20% compared with the control. Those result demonstrated that overexpression of PQQ biosynthetic genes increased the content of PQQ, therefore improving the acetic acid fermentation and the cell tolerance against acetic acid by improving the alcohol respiratory chain and energy metabolism.

Pterostilbene, a Dimethyl Derivative of Resveratrol, Exerts Cytotoxic Effects on Melanin-Producing Cells through Metabolic Activation by Tyrosinase.

Pterostilbene (PTS), which is abundant in blueberries, is a dimethyl derivative of the natural polyphenol resveratrol (RES). Several plant species, including peanuts and grapes, also produce PTS. Although RES has a wide range of health benefits, including anti-cancer properties, PTS has a robust pharmacological profile that includes a better intestinal absorption and an increased hepatic stability compared to RES. Indeed, PTS has a higher bioavailability and a lower toxicity compared to other stilbenes, making it an attractive drug candidate for the treatment of various diseases, including diabetes, cancer, cardiovascular disease, neurodegenerative disorders, and aging. We previously reported that RES serves as a substrate for tyrosinase, producing an o-quinone metabolite that is highly cytotoxic to melanocytes. The present study investigated whether PTS may also be metabolized by tyrosinase, similarly to RES. PTS was oxidized as a substrate by tyrosinase to form an o-quinone, which reacted with thiols, such as N-acetyl-L-cysteine, to form di- and tri-adducts. We also confirmed that PTS was taken up and metabolized by human tyrosinase-expressing 293T cells in amounts several times greater than RES. In addition, PTS showed a tyrosinase-dependent cytotoxicity against B16BL6 melanoma cells that was stronger than RES and also inhibited the formation of melanin in B16BL6 melanoma cells and in the culture medium. These results suggest that the two methyl groups of PTS, which are lipophilic, increase its membrane permeability, making it easier to bind to intracellular proteins, and may therefore be more cytotoxic to melanin-producing cells.

Thermodynamic Factors Controlling Electron Transfer among the Terminal Electron Acceptors of Photosystem I: Insights from Kinetic Modelling.

Photosystem I is a key component of primary energy conversion in oxygenic photosynthesis. Electron transfer reactions in Photosystem I take place across two parallel electron transfer chains that converge after a few electron transfer steps, sharing both the terminal electron acceptors, which are a series of three iron-sulphur (Fe-S) clusters known as FX, FA, and FB, and the terminal donor, P700. The two electron transfer chains show kinetic differences which are, due to their close geometrical symmetry, mainly attributable to the tuning of the physicochemical reactivity of the bound cofactors, exerted by the protein surroundings. The factors controlling the rate of electron transfer between the terminal Fe-S clusters are still not fully understood due to the difficulties of monitoring these events directly. Here we present a discussion concerning the driving forces associated with electron transfer between FX and FA as well as between FA and FB, employing a tunnelling-based description of the reaction rates coupled with the kinetic modelling of forward and recombination reactions. It is concluded that the reorganisation energy for FX- oxidation shall be lower than 1 eV. Moreover, it is suggested that the analysis of mutants with altered FA redox properties can also provide useful information concerning the upstream phylloquinone cofactor energetics.

Heterologous expression of sulfur: quinone oxidoreductase (Sqr) to improve Thioalkalivibrio versutus D301 desulfurization performance.

AIMS: Heterologous expression of sulfur: quinone oxidoreductase (Sqr) from Halomonas mongoliensis JS01, which is responsible for oxidizing sulfide to elemental sulfur, in Thioalkalivibrio versutus (T. versutus) D301 improves desulfurization. METHODS AND RESULTS: We expressed sqr in T. versutus D301 by conjugative transfer and then assayed its desulfurization capacity in an airlift reactor and analyzed its transcriptome at -380 mV ORP. Our findings demonstrate that the D301-sqr+ strain, utilizing sodium sulfide as a sulfur source under optimal ORP conditions (-380 mV), achieved an elemental sulfur yield of 95%. This represents an 8% increase over the T. versutus D301. Moreover, the sodium sulfide utilization rate for D301-sqr+ showed a marked improvement [0.741 vs. 0.651 mmol∙(l·h)-1], with a concurrent increase in the rate of elemental sulfur production when compared to the T. versutus D301 (0.716 vs. 0.518 mmol ∙(l·h)-1). Transcriptome analysis revealed that the flavocytochrome c (fcc) and the sox system were differentially transcriptionally down-regulated in D301-sqr+ compared with the T. versutus D301. CONCLUSIONS: Heterologous expression of the gene sqr altered the transcription of related genes in T. versutus D301 sulfur oxidation pathway, increasing the yield of elemental sulfur and the rate of sulfur oxidation, and making D301-sqr+ more potential for industrial applications.