Molecular mechanism of the metal-independent production of hydroxyl radicals by thiourea dioxide and H2O2.

It is well-known that highly reactive hydroxyl radicals (HO•) can be produced by the classic Fenton system and our recently discovered haloquinone/H2O2 system, but rarely from thiol-derivatives. Here, we found, unexpectedly, that HO• can be generated from H2O2 and thiourea dioxide (TUO2), a widely used and environmentally friendly bleaching agent. A carbon-centered radical and sulfite were detected and identified as the transient intermediates, and urea and sulfate as the final products, with the complementary application of electron spin-trapping, oxygen-18 isotope labeling coupled with HPLC/MS analysis. Density functional theory calculations were conducted to further elucidate the detailed pathways for HO• production. Taken together, we proposed that the molecular mechanism for HO• generation by TUO2/H2O2: TUO2 tautomerizes from sulfinic acid into ketone isomer (TUO2-K) through proton transfer, then a nucleophilic addition of H2O2 on the S atom of TUO2-K, forming a S-hydroperoxide intermediate TUO2-OOH, which dissociates homolytically to produce HO•. Our findings represent the first experimental and computational study on an unprecedented new molecular mechanism of HO• production from simple thiol-derived sulfinic acids, which may have broad chemical, environmental, and biomedical significance for future research on the application of the well-known bleaching agent and its analogs.

Molecular mechanism for the unusual enhancement of the second-step chemiluminescence production from the carcinogenic tetrabromohydroquinone and H2O2.

We have found recently that two-step intrinsic hydroxyl radical (·OH)-dependent chemiluminescence (CL) could be produced by carcinogenic tetrahaloquinone and H2O2. However, the first-step CL was too fast to clearly detect the stepwise generation of ·OH and CL, and to distinguish the exact dividing point between the first-step and second-step CL. Here we found that, extremely clear two-step intrinsic CL could be produced by the relative slow reaction of tetrabromohydroquinone (TBHQ) with H2O2, which was directly dependent on the two-step ·OH generation. Interestingly, the second-step, but not the first-step CL production of TBHQ/H2O2 (CRET donor) was markedly enhanced by fluorescein (a typical xanthene dye, CRET acceptor) through a unique chemiluminescence resonance energy transfer (CRET) process. The novel CRET system of TBHQ/H2O2/fluorescein was successfully applied for the sensitive detection of TBHQ with the detection limit as low as 2.5 µmol/L. These findings will help to develop more sensitive and highly efficient CL or CRET systems and specific CL sensor to detect the carcinogenic haloquinones, which may have broad environmental applications.

Unprecedented enantio-selective live-cell mitochondrial DNA super-resolution imaging and photo-sensitizing by the chiral ruthenium polypyridyl DNA "light-switch".

Mitochondrial DNA (mtDNA) is known to play a critical role in cellular functions. However, the fluorescent probe enantio-selectively targeting live-cell mtDNA is rare. We recently found that the well-known DNA 'light-switch' [Ru(phen)2dppz]Cl2 can image nuclear DNA in live-cells with chlorophenolic counter-anions via forming lipophilic ion-pairing complex. Interestingly, after washing with fresh-medium, [Ru(phen)2dppz]Cl2 was found to re-localize from nucleus to mitochondria via ABC transporter proteins. Intriguingly, the two enantiomers of [Ru(phen)2dppz]Cl2 were found to bind enantio-selectively with mtDNA in live-cells not only by super-resolution optical microscopy techniques (SIM, STED), but also by biochemical methods (mitochondrial membrane staining with Tomo20-dronpa). Using [Ru(phen)2dppz]Cl2 as the new mtDNA probe, we further found that each mitochondrion containing 1-8 mtDNA molecules are distributed throughout the entire mitochondrial matrix, and there are more nucleoids near nucleus. More interestingly, we found enantio-selective apoptotic cell death was induced by the two enantiomers by prolonged visible light irradiation, and in-situ self-monitoring apoptosis process can be achieved by using the unique 'photo-triggered nuclear translocation' property of the Ru complex. This is the first report on enantio-selective targeting and super-resolution imaging of live-cell mtDNA by a chiral Ru complex via formation and dissociation of ion-pairing complex with suitable counter-anions.

Rotational isomerization: spontaneous structural transformation of a thermally activated delayed fluorescence binuclear copper(I) complex.

A novel binuclear Cu(I) halide complex, Cu2I2(DPPCz)2, which emits efficient thermally activated delayed fluorescence (TADF), is reported. The crystal of this complex spontaneously undergoes ligand rotation and coordination-configuration transformation, converting to its isomer without any external stimulation.

An unprecedented free radical mechanism for the formation of DNA adducts by the carcinogenic N-sulfonated metabolite of aristolochic acids.

The carcinogenicity of aristolochic acids (AAs) has been attributed mainly to the formation of stable DNA-aristolactam (DNA-AL) adducts by its reactive N-sulfonated metabolite N-sulfonatooxyaristolactam (N-OSO3--AL). The most accepted mechanism for such DNA-AL adduct formation is via the postulated but never unequivocally-confirmed aristolactam nitrenium ion. Here we found that both sulfate radical and two ALI-derived radicals (N-centered and C-centered spin isomers) were produced by N-OSO3--ALI, which were detected and unequivocally identified by complementary applications of ESR spin-trapping, HPLC-MS coupled with deuterium-exchange methods. Both the formation of the three radical species and DNA-ALI adducts can be significantly inhibited (up to 90%) by several well-known antioxidants, typical radical scavengers, and spin-trapping agents. Taken together, we propose that N-OSO3--ALI decomposes mainly via a new N-O bond homolysis rather than the previously proposed heterolysis pathway, yielding reactive sulfate and ALI-derived radicals, which are together and in concert responsible for forming DNA-ALI adducts. This study presents strong and direct evidence for the production of free radical intermediates during N-OSO3--ALI decomposition, providing an unprecedented free radical perspective and conceptual breakthrough, which can better explain and understand the molecular mechanism for the formation of DNA-AA adducts, the carcinogenicity of AAs and their potential prevention.

Molecular mechanism for the activation of the potent hepatotoxin acetylhydrazine: Identification of the initial N-centered radical and the secondary C-centered radical intermediates.

Acetylhydrazine (AcHZ), a major human metabolite of the widely-used anti-tuberculosis drug isoniazid (INH), was considered to be responsible for its serious hepatotoxicity and potentially fatal liver injury. It has been proposed that reactive radical species produced from further metabolic activation of AcHZ might be responsible for its hepatotoxicity. However, the exact nature of such radical species remains not clear. Through complementary applications of ESR spin-trapping and HPLC/MS methods, here we show that the initial N-centered radical intermediate can be detected and identified from AcHZ activated by transition metal ions (Mn(III)Acetate and Mn(III) pyrophosphate) and myeloperoxidase. The exact location of the radical was found to be at the distal-nitrogen of the hydrazine group by 15N-isotope-labeling techniques via using 15N-labeled AcHZ we synthesized. Additionally, the secondary C-centered radical was identified unequivocally as the reactive acetyl radical by complementary applications of ESR spin-trapping and persistent radical TEMPO trapping coupled with HPLC/MS analysis. This study represents the first detection and unequivocal identification of the initial N-centered radical and its exact location, as well as the reactive secondary acetyl radical. These findings should provide new perspectives on the molecular mechanism of AcHZ activation, which may have potential biomedical and toxicological significance for future research on the mechanism of INH-induced hepatotoxicity.

Mechanistic investigation of the differential synergistic neurotoxicity between pesticide metam sodium and copper or zinc.

Epidemiological studies suggest neurological disorders have been associated with the co-exposure to certain pesticides and transition metals. The present study aims to investigate whether co-exposure to the widely-used pesticide metam sodium and copper (Cu2+) or zinc ion (Zn2+) is able to cause synergistic neurotoxicity in neural PC12 cells and its possible mechanism(s). We found that both metam/Cu2+ and metam/Zn2+ synergistically induced apoptosis, intracellular Cu2+/Zn2+ uptake, reactive oxygen species (ROS) accumulation, double-strand DNA breakage, mitochondrial membrane potential decrease, and nerve function disorder. In addition, metam/Cu2+ was shown to release cytochrome c and apoptosis-inducing factor (AIF) from mitochondria to cytoplasm and nucleus, respectively, and activate the caspase 9, 8, 3, 7. However, metam/Zn2+ induced caspase 7 activation and AIF translocation and mildly activated cytochrome c/caspase 9/caspase 3 pathway. Furthermore, metam/Cu2+ activated caspase 3/7 by the p38 pathway, whereas metam/Zn2+ did so via both the p38 and JNK pathways. These results demonstrated that metam/Cu2+ or metam/Zn2+ co-exposure cause synergistic neurotoxicity via different mechanisms, indicating a potential risk to human health when they environmentally co-exist.

Unusual enantioselective cytoplasm-to-nucleus translocation and photosensitization of the chiral Ru(II) cationic complex via simple ion-pairing with lipophilic weak acid counter-anions.

Targeted and enantioselective delivery of chiral diagnostic-probes and therapeutics into specific compartments inside cells is of utmost importance in the improvement of disease detection and treatment. The classical DNA 'light-switch' ruthenium(II)-polypyridyl complex, [Ru(DIP)2(dppz)]Cl2 (DIP = 4,7-diphenyl-1,10-phenanthroline, dppz = dipyridophenazine) has been shown to be accumulated only in the cytoplasm and membrane, but excluded from its intended nuclear DNA target. In this study, the cationic [Ru(DIP)2(dppz)]2+ is found to be redirected into live-cell nucleus in the presence of lipophilic 3,5-dichlorophenolate or flufenamate counter-anions via ion-pairing mechanism, while maintaining its original DNA recognition characteristics. Interestingly and unexpectedly, further studies show that only the Δ-enantiomer is selectively translocated into nucleus while the Λ-enantiomer remains trapped in cytoplasm, which is found to be mainly due to their differential enantioselective binding affinities with cytoplasmic proteins and nuclear DNA. More importantly, only the nucleus-relocalized Δ-enantiomer can induce obvious DNA damage and cell apoptosis upon prolonged visible-light irradiation. Thus, the use of Δ-enantiomer can significantly reduce the dosage needed for maximal treatment effect. This represents the first report of enantioselective targeting and photosensitization of classical Ru(II) complex via simple ion-pairing with suitable weak acid counter-anions, which opens new opportunities for more effective enantioselective cancer treatment.

Generation mechanism of singlet oxygen from the interaction of peroxymonosulfate and chloride in aqueous systems.

Peroxymonosulfate (PMS, HSO5-) is a widely-used disinfectant and oxidant in environmental remediation. It was deemed that PMS reacted with chloride (Cl-) to form free chlorine during water purification. Here, we demonstrated that singlet oxygen (1O2) was efficiently generated from PMS and Cl- interaction. Mechanism of 1O2 formation was uniquely verified by the reaction of HSO5- and chlorine molecule (Cl2) and the oxygen atoms in 1O2 deriving from the peroxide group of HSO5- were revealed. Density functional theory calculations determined that the reaction of HSO5- and Cl2 was thermodynamically favorable and exergonic at 37.8 kcal/mol. Quite intriguingly, 1O2 was generated at a higher yield (1.5 × 105 M - 1 s - 1) than in the well-known reaction of H2O2 with Cl2 (35 M - 1 s - 1). Besides chlorine, 1O2 formed in PMS-Cl- interaction dominated the degradation of micropollutants, also it substantially enhanced the damage of deoxynucleoside in DNA, which were beneficial to micropollutant oxidation and pathogen disinfection. The contribution of 1O2 for carbamazepine degradation was enhanced at higher Cl- level and lower pH, and reached 96.3% at pH 4.1 and 5 min. Natural organic matter (NOM) was a sink for chlorine, thereby impeding 1O2 formation to retard carbamazepine degradation. 1O2 also played important roles (48.3 - 63.5%) on the abatement of deoxyguanosine and deoxythymidine at pH 4.1 and 10 min in PMS/Cl-. On the other hand, this discovery also alerted the harm of 1O2 for human health as it can be formed during the interaction of residual PMS in drinking water/swimming pools and the high-level Cl- in human bodies.

Value of drug resistance and homology of Acinetobacter baumannii in tracing the source of nosocomial infection in Jianyang, Sichuan / 中国热带医学

@#Abstract: Objective　To analyze the drug sensitivity and the carrying of carbapenem resistant gene of Acinetobacter baumannii isolated from clinical patients and clinical objects, and analyze the homology of strains to provide support for the control of nosocomial infection. Methods　A total of 38 strains of Acinetobacter baumannii isolated from patients and clinical objects surface were collected from January 2019 to August 2020. The antimicrobial susceptibility was tested by the minimum inhibitory concentration method. In addition, the resistance related genes were detected by polymerase chain reaction method, and homology analysis was performed by enterobacterial repetitive Enterobacterial Repetitive Intergenic Consensus Polymerase Chain Reaction (ERIC-PCR). Results All 34 strains of Acinetobacter baumannii isolated from Clinical patients and 4 strains isolated from clinical objects carried blaOXA-51 and imp resistance genes, neither of them carried blaVIM gene. 32 Acinetobacter baumannii carrying blaOXA-23 gene, 28 strains carrying blaTEM gene, 7 strains carrying blaOXA-58 gene. After cluster analysis, 38 Acinetobacter baumannii isolates were classified into 7 genotypes (expressed A, B, C, D, E, F, G), and cluster E and cluster G were the main clusters, containing 12 strains (12/38, 31.6%) and 18 strains (18/38, 47.4%), respectively, as the main prevalent clonal strains. Conclusions　Acinetobacter baumannii isolated from different sources have the significant differences in drug resistance and carry different resistance genes. There is no direct correlation between patients and environmental isolates of Acinetobacter baumannii belonging to different clonal strains. Also, there aren’t significant correlation between clinical patients infected with Acinetobacter baumannii.

The critical role of unique azido-substituted chloro-O-semiquinone radical intermediates in the synergistic toxicity between sodium azide and chlorocatecholic carcinogens.

We have shown previously that exposing bacteria to tetrachlorocatechol (TCC) and sodium azide (NaN3) together causes synergistic cytotoxicity in a biphasic mode. However, the underlying chemical mechanism remains unclear. In this study, an unexpected ring-contraction 3(2H)-furanone and two quinoid-compounds were identified as the major and minor reaction products, respectively; and two unusual azido-substituted chloro-O-semiquinone radicals were detected and characterized as the major radical intermediates by complementary applications of direct ESR, HPLC/ESI-Q-TOF and high-resolution MS studies with nitrogen-15 isotope-labeled NaN3. Taken together, we proposed a novel molecular mechanism for the reaction of TCC/NaN3: N3- may attack on tetrachloro-O-semiquinone radical, forming two transient 4-azido-3,5,6-trichloro- and 4,5-diazido-3,6-dichloro-O-semiquinone radicals, consecutively. The second-radical intermediate may either undergo an unusual zwitt-azido cleavage to form the less-toxic ring-contraction 3(2H)-furanone product, or further oxidize to form the more toxic quinoid-product 4-amino-5-azido-3,6-dichloro-O-benzoquinone. A good correlation was observed between the biphasic formation of this toxic quinone due to the two competing decomposition pathways of the radical intermediate and the biphasic synergism between TCC and NaN3, which are dependent on their molar-ratios. This is the first report of detection and identification of two unique azido-substituted chloro-O-semiquinone radicals, and an unprecedented ring-contraction mechanism via an unusually mild and facile zwitt-azido rearrangement.

Detecting and Quantifying Polyhaloaromatic Environmental Pollutants by Chemiluminescence-Based Analytical Method.

Polyhaloaromatic compounds (XAr) are ubiquitous and recalcitrant in the environment. They are potentially carcinogenic to organisms and may induce serious risks to the ecosystem, raising increasing public concern. Therefore, it is important to detect and quantify these ubiquitous XAr in the environment, and to monitor their degradation kinetics during the treatment of these recalcitrant pollutants. We have previously found that unprecedented intrinsic chemiluminescence (CL) can be produced by a haloquinones/H2O2 system, a newly-found ●OH-generating system different from the classic Fenton system. Recently, we found that the degradation of priority pollutant pentachlorophenol by the classic Fe(II)-Fenton system could produce intrinsic CL, which was mainly dependent on the generation of chloroquinone intermediates. Analogous effects were observed for all nineteen chlorophenols, other halophenols and several classes of XAr, and a novel, rapid and sensitive CL-based analytical method was developed to detect these XAr and monitor their degradation kinetics. Interestingly, for those XAr with halohydroxyl quinoid structure, a Co(II)-mediated Fenton-like system could induce a stronger CL emission and higher degradation, probably due to site-specific generation of highly-effective ●OH. These findings may have broad chemical and environmental implications for future studies, which would be helpful for developing new analytical methods and technologies to investigate those ubiquitous XAr.

Mechanistic Study on Oxidative DNA Damage and Modifications by Haloquinoid Carcinogenic Intermediates and Disinfection Byproducts.

Haloquinones (XQs) are a group of carcinogenic intermediates of the haloaromatic environmental pollutants and newly identified chlorination disinfection byproducts (DBPs) in drinking water. The highly reactive hydroxyl radicals/alkoxyl radicals and quinone enoxy/ketoxy radicals were found to arise in XQs and H2O2 or organic hydroperoxides system, independent of transition-metal ions. However, it was not clear whether these haloquinoid carcinogens and hydroperoxides can cause oxidative DNA damage and modifications, and if so, what are the underlying molecular mechanisms. We found that 8-oxodeoxyguanosine (8-oxodG), DNA strand breaks, and three methyl oxidation products could arise when DNA was treated with tetrachloro-1,4-benzoquinone and H2O2 via a metal-independent and intercalation-enhanced oxidation mechanism. Similar effects were observed with other XQs, which are generally more efficient than the typical Fenton system. We further extended our studies from isolated DNA to genomic DNA in living cells. We also found that potent oxidation of DNA to the more mutagenic imidazolone dIz could be induced by XQs and organic hydroperoxides such as t-butylhydroperoxide or the physiologically relevant hydroperoxide 13S-hydroperoxy-9Z,11E-octadecadienoic acid via an unprecedented quinone-enoxy radical-mediated mechanism. These findings should provide new perspectives to explain the potential genotoxicity, mutagenesis, and carcinogenicity for the ubiquitous haloquinoid carcinogenic intermediates and DBPs.

Caffeic Acid Phenyl Ester (CAPE) Protects against Iron-Mediated Cellular DNA Damage through Its Strong Iron-Binding Ability and High Lipophilicity.

Caffeic acid phenethyl ester (CAPE) and its structurally-related caffeic acid (CA), ferulic acid (FA) and ethyl ferulate (EF) are constituents of honeybee propolis that have important pharmacological activities. This study found that CAPE-but not CA, FA, and EF-could effectively prevent cellular DNA damage induced by overloaded iron through decreasing the labile iron pool (LIP) levels in HeLa cells. Interestingly, CAPE was found to be more effective than CA in protecting against plasmid DNA damage induced by Fe(II)-H2O2 or Fe(III)-citrate-ascorbate-H2O2 via the inhibition of hydroxyl radical (•OH) production. We further provided more direct and unequivocal experimental evidences for the formation of inactive CAPE/CA-iron complexes. CAPE was found to have a stronger iron-binding ability and a much higher lipophilicity than CA. Taken together, we propose that the esterification of the carboxylic moiety with phenethyl significantly enhanced the iron-binding ability and lipophilicity of CAPE, which is also responsible for its potent protection against iron-mediated cellular DNA damage. A study on the iron coordination mechanism of such natural polyphenol antioxidants will help to design more effective antioxidants for the treatment and prevention of diseases caused by metal-induced oxidative stress, as well as help to understand the structure-activity relationships of these compounds.

[Network Meta-analysis of 4 acupuncture therapies for shoulder hand syndrome after stroke].

OBJECTIVE: A network Meta-analysis of randomized controlled trials (RCT) of 4 commonly used acupuncture therapies (electroacupuncture, fire needling, warming acupuncture and filiform needling) for shoulder hand syndrome (SHS) after stroke was performed. METHODS: The RCTs regarding electroacupuncture, fire needling, warming acupuncture and filiform needling for SHS after stroke before March 10, 2020 were searched in databases of CNKI, Wanfang, VIP, SinoMed, PubMed, EMbase and Cochrane Library. The included literature was screened and evaluated by Cochrane bias risk assessment tool, and the data analysis was performed by RevMan5.3, Gemtc0.14.3 and Stata14.2. RESULTS: A total of 21 RCTs were included, involving 1508 patients, 814 cases in the observation group and 694 cases in the control group. In term of effective rate and visual analogue scale (VAS) score, warming acupuncture, electroacupuncture and fire needling needling were superior to western medication and rehabilitation (P<0.05), and warming acupuncture was most likely to be the best treatment. In term of joint swelling score, warming acupuncture was superior to rehabilitation (P<0.05), and warming acupuncture was most likely to be the best treatment. In term of Fugl-Meyer assessment (FMA) score, fire needling was superior to western medication and rehabilitation (P<0.05), warming acupuncture was superior to filiform needling (P<0.05), fire needling was most likely to be the best treatment (P<0.05). CONCLUSION: The curative effect of 4 acupuncture therapies for SHS after stroke is better than the western medication and rehabilitation, and warming acupuncture has the best clinical efficacy.

The cell-impermeable Ru(II) polypyridyl complex as a potent intracellular photosensitizer under visible light irradiation via ion-pairing with suitable lipophilic counter-anions.

Developing the cell-impermeable Ru(II) polypyridyl cationic complexes as effective photosensitizers (PS) which have high cellular uptake and photo-toxicity, but low dark toxicity, is quite challenging. Here we found that the highly reactive singlet oxygen (1O2) can be generated by the irradiation of a typical Ru(II) polypyridyl complex Ru(II)tris(tetramethylphenanthroline) ([Ru(TMP)3]2+) under visible light irradiation by ESR with TEMPO (2,2,6,6-tetramethyl-4-piperidone-N-oxyl) as 1O2 probe. Effective cellular and nuclear delivery of cationic [Ru(TMP)3]2+ was achieved through our recently developed ion-pairing method, and 2,3,4,5-tetrachlorophenol (2,3,4,5-TeCP) was found to be the most effective among all chlorophenols tested. The accelerated cellular, especially nuclear uptake of [Ru(TMP)3]2+ results in the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and DNA strand breaks, caspase 3/7 activation and cell apoptosis in HeLa cells upon light irradiation. More importantly, compared with other traditional photosensitizers, [Ru(TMP)3]2+ showed significant photo-toxicity but low dark toxicity. Similar effects were observed when 2,3,4,5-TeCP was substituted by the currently clinically used anti-inflammatory drug flufenamic acid. This represents the first report that the cell-impermeable Ru(II) polypyridyl complex ion-paired with suitable lipophilic counter-anions functions as potent intracellular photosensitizer under visible light irradiation mainly via a 1O2-mediated mechanism. These findings should provide new perspectives for future investigations on other metal complexes with similar characteristics as promising photosensitizers for potential photodynamic therapy.

Bright bluish-green emitting Cu(I) complexes exhibiting efficient thermally activated delayed fluorescence.

Three strongly emissive Cu(i) complexes [Cu(tBupzmpy)(POP)]BF4(1), [Cu(Phpzmpy)(POP)]BF4(2) and [Cu(Adpzmpy)(POP)]BF4(3) (tBupzmpy = 2-(5-(tert-butyl)-1H-pyrazol-3-yl)-6-methylpyridine, Phpzmpy = 2-methyl-6-(5-phenyl-1H-pyrazol-3-yl)pyridine, Adpzmpy = 2-(5-((3R,5R)-adamantan-1-yl)-1H-pyrazol-3-yl)-6-methylpyridine, and POP = bis[2-(diphenylphosphino)phenyl]ether) were synthesized and characterized. These complexes exhibit bright bluish-green photoluminescence in the solid state with quantum yields of 91% (1), 71% (2) and 77% (3) and lifetimes of 13.4 µs (1), 32.9 µs (2) and 34.1 µs (3) at room temperature. The results of theoretical calculations, coupled with the temperature dependence of the spectroscopic properties and emission decay behaviors, reveal that the title Cu(i) complexes emit efficient thermally activated delayed fluorescence (TADF) from excited states involving metal-to-ligand charge transfer (MLCT) transitions and ligand-to-ligand charge transfer (LLCT) transitions. The emissive-state characteristics and emission properties of the investigated Cu(i) complexes were tuned effectively by changing the steric and electronic structures of the diimine ligands.

Structure-Activity Relationship Investigation on Reaction Mechanism between Chlorinated Quinoid Carcinogens and Clinically-Used Aldoxime Nerve-Agent Antidote under Physiological Condition.

Pyridinium aldoximes are best-known therapeutic antidotes used for clinical treatment of poisonings by organophosphorus nerve-agents and pesticides. Recently, we found that pralidoxime (2-PAM, a currently clinically used nerve-agent antidote) could also detoxify tetrachloro-1,4-benzoquinone (TCBQ), which is a carcinogenic quinoid metabolite of the widely used wood preservative pentachlorophenol under normal physiological conditions, via an unusually mild and facile Beckmann fragmentation mechanism accompanied by radical homolysis. However, it is not clear whether the less-chlorinated benzoquinones (CnBQs, n ≤ 3) act similarly; if so, what is the structure-activity relationship? In this study, we found that (1) The stability of reaction intermediates produced by different CnBQs and 2-PAM was dependent not only on the position but also the degree of Cl-substitution on CnBQs, which can be divided into TCBQ- and DCBQ (dichloro-1,4-benzoquinone)-subgroup; (2) The pKa value of hydroxlated quinones (Cn-1BQ-OHs, the hydrolysis products of CnBQs), determined the stability of corresponding intermediates, that is, the decomposition rate of the intermediates depended on the acidity of Cn-1BQ-OHs; (3) The pKa value of the corresponding Cn-1BQ-OHs could also determine the reaction ratio of Beckmann fragmentation to radical homolysis in CnBQs/2-PAM. These new findings on the structure-activity relationship of the halogenated quinoid carcinogens detoxified by pyridinium aldoxime therapeutic agents via Beckmann fragmentation and radical homolysis reaction may have broad implications on future biomedical and environmental research.

Ultrafast excited state dynamics and light-switching of [Ru(phen)2(dppz)]2+ in G-quadruplex DNA.

The triplet metal to ligand charge transfer (3MLCT) luminescence of ruthenium (II) polypyridyl complexes offers attractive imaging properties, specifically towards the development of sensitive and structure-specific DNA probes. However, rapidly-deactivating dark state formation may compete with 3MLCT luminescence depending on different DNA structures. In this work, by combining femtosecond and nanosecond pump-probe spectroscopy, the 3MLCT relaxation dynamics of [Ru(phen)2(dppz)]2+ (phen = 1,10-phenanthroline, dppz = dipyridophenazine) in two iconic G-quadruplexes has been scrutinized. The binding modes of stacking of dppz ligand on the terminal G-quartet fully and partially are clearly identified based on the biexponential decay dynamics of the 3MLCT luminescence at 620 nm. Interestingly, the inhibited dark state channel in ds-DNA is open in G-quadruplex, featuring an ultrafast picosecond depopulation process from 3MLCT to a dark state. The dark state formation rates are found to be sensitive to the content of water molecules in local G-quadruplex structures, indicating different patterns of bound water. The unique excited state dynamics of [Ru(phen)2(dppz)]2+ in G-quadruplex is deciphered, providing mechanistic basis for the rational design of photoactive ruthenium metal complexes in biological applications.

The critical role of superoxide anion radicals on delaying tetrachlorohydroquinone autooxidation by penicillamine.

We have recently found that penicillamine, a classic copper-chelating thiol-drug for Wilson's disease, can delay tetrachlorohydroquinone (TCHQ) autooxidation via a previously unrecognized redox-activity. However, its underlying molecular mechanism remains not fully understood. In this study, we found, interestingly and unexpectedly, that superoxide dismutase (SOD) can significantly shorten the delay of TCHQ autooxidation by penicillamine, but not by ascorbate; SOD can also markedly increase the yields of the oxidized form of penicillamine. Similar effects were observed with a recently-developed specific and sensitive superoxide anion radical (O2•-) probe CT-02H, which was also employed to successfully measure O2•- generated from both TCHQ and TCHQ/penicillamine systems for the first time. More importantly, addition of extra O2•- (KO2/18-crown-6) can further prolong the delaying effects by penicillamine and slow down penicillamine consumption. Taken together, an unexpected critical role of O2•- in TCHQ/penicillamine interaction was proposed: O2•- may regenerate penicillamine, thereby continuously reducing TCSQ•- to TCHQ and finally delaying TCHQ autooxidation; In contrast, if O2•- were eliminated, which can not only markedly change the reaction equilibrium, accelerate the rate of interaction, and ultimately shorten the delay of TCHQ autooxidation by penicillamine, but can also accelerate penicillamine oxidation to form its corresponding disulfide solely via redox reaction without any minor nucleophilic reaction. These findings not only further support our previously-proposed redox mechanism for the protection against TCHQ-induced cytotoxicity by penicillamine, but also reveal a new mode of action for O2•- in the inhibition of haloquinoids-induced toxicity by thiol antioxidants.