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As alternatives of perfluorooctanoic acid (PFOA), hexafluoropropylene oxide dimeric acid (HFPO-DA) and trimeric acid (HFPO-TA) have been detected increasingly in environmental media and even humans. They have been shown to exhibit reproductive toxicity to model species, but their effects on human remain unclear due to the knowledge gap in their mode of action. Herein, (anti-)androgenic effects of the two HFPOs and PFOA were investigated and underlying toxicological mechanism was explored by combining zebrafish test, cell assay and molecular docking simulation. Exposure of juvenile zebrafish to the chemicals during sex differentiation promoted feminization, with HFPO-TA acting at an environmental concentration of 1 μg/L. The chemicals inhibited proliferation of human prostate cells and transcriptional activity of human and zebrafish androgen receptors (AR), with HFPO-TA displaying the strongest potency. Molecular docking revealed that the chemicals bind to AR in a conformation similar to a known AR antagonist. Combined in vivo, in vitro and in silico results demonstrated that the chemicals disrupted sex differentiation likely by antagonizing AR-mediated pathways, and provided more evidence that HFPO-TA is not a safe alternative to PFOA.

Metalaxyl (MET) and myclobutanil (MYC) are two widely used chiral fungicides that may pose health risks to non-occupationally exposed populations. Here, the two fungicides were enantiomer-specific quantified in the dietary food and urine of residents in an Eastern China city, to determine the exposure and excretion of these contaminants in different populations. Results indicate that residues of MET and MYC varied with different food items at 0.42–0.86 ng/g fresh weight (FW) and 0.18–0.33 ng/g FW, respectively. In urine samples, the residual levels after creatinine adjusting (CR) ranged from 10.2 to 1715.4 ng/g CR for MET and were below the detection limit up to 320.7 ng/g CR for MYC. Significant age- and gender-related differences were separately found in urinary MET and MYC of different populations. Monte-Carlo simulations suggested that children had higher daily dietary intake (DDI) but lower urinary excretion (DUE) rates than youths, and thus may suffer higher body burdens. The residues of antifungally ineffective enantiomers (S-MET and R-MYC) were slightly higher than their antipodes in foods. Moreover, the enantiomer-selective urinary excretion resulted in higher retention of S-MET and R-MYC in the human body. Our results suggest that both dietary intake and urinary excretion should be enantiomer-specifically considered when assessing the exposure risk and body burden of chiral fungicides in the non-occupationally exposed population. Furthermore, substitutive application of enantiomer-enriched fungicide formulations can not only benefit the antifungal efficacy but also be safer for human health.

Several studies have indicated metabolic function disruption effects of bisphenol analogues through peroxisome proliferator-activated receptor (PPAR) alpha and gamma pathways. In the present study, we found for the first time that PPARβ/δ might be a novel cellular target of bisphenol analogues. By using the fluorescence competitive binding assay, we found seven bisphenol analogues could bind to PPARβ/δ directly, among which tetrabromobisphenol A (TBBPA, 18.38-fold) and tetrachlorobisphenol A (TCBPA, 12.06-fold) exhibited stronger binding affinity than bisphenol A (BPA). In PPARβ/δ-mediated luciferase reporter gene assay, the seven bisphenol analogues showed transcriptional activity toward PPARβ/δ. Bisphenol AF (BPAF), bisphenol F (BPF) and bisphenol B (BPB) even showed higher transcriptional activity than BPA, while TBBPA and TCBPA showed comparable activity with BPA. Moreover, in human liver HL-7702 cells, the bisphenol analogues promoted the expression of two PPARβ/δ target genes PDK4 and ANGPTL4. Molecular docking simulation indicated the binding potency of bisphenol analogues to PPARβ/δ might depend on halogenation and hydrophobicity and the transcriptional activity might depend on their binding affinity and hydrogen bond interactions. Overall, the PPARβ/δ pathway may provide a new mechanism for the metabolic function disruption of bisphenol analogues, and TBBPA and TCBPA might exert higher metabolic disruption effects than BPA via PPARβ/δ pathway.

Medical applications of nanotechnology are promising in creating efficient and targeted therapies. However, so far, nanodrug design has not taken into consideration possible effects on human microbiota. The beneficial functions of bacteria could be stimulated by nanodrugs while negative effects on beneficial bacteria could cause risks to human health. Here, simulated intestinal fluid (IF) was optimized for culturing a human commensal and probiotic bacterial strain, Lactobacillus casei, to study the effects of medically relevant NPs—Ag and hyaluronic acid-coated Au NPs (HA-Au NPs)—in conditions pertinent to the gastrointestinal tract. When cultivated either aerobically or anaerobically, the specific growth rates of L. casei were ~0.2 h−1 in IF and ~0.4 h−1 in the standard medium of lactobacilli (MRS). Ag NPs inhibited the growth of L. casei in IF at lower concentrations (EC50 ~ 65 and 15 mg/L in aerobic and anaerobic conditions, respectively) than in MRS (EC50 > 100 mg/L), likely caused by differences in the composition of the two media and different intrinsic growth rates of bacteria in IF and MRS. Ag NP dissolution in IF and MRS did not explain the differences in growth inhibition, implying NP-specific effects. HA-Au NPs were not growth-inhibitory to L. casei up to 250 mg/L. Still, both NPs at sub-growth-inhibitory concentrations suppressed the expression of bacteriocin genes in L. casei, suggesting an inhibitory effect of NPs on the probiotic properties of L. casei, i.e., its competitiveness in microbial communities. However, HA-Au NPs did not appear to affect or even stimulated the immunomodulatory properties of L. casei in human intestinal epithelial cells. Thus, medically relevant NPs at low, sub-bacteriostatic levels can affect the metabolism of beneficial human bacteria and potentially induce changes in the microbiota and immune signaling.

Abstract Cellular uptake and exocytosis of SWCNTs are fundamental processes determining their intracellular concentration and effects. Despite the great potential of acid-oxidized SWCNTs in biomedical field, understanding of the influencing factors on these processes needs to be deepened. Here, we quantitatively investigated uptake and exocytosis of SWCNTs in three lengths-630 (±171) nm (L-SWCNTs), 390 (±50) nm (M-SWCNTs), and 195 (±63) nm (S-MWCNTs) in macrophages. The results showed that the cellular accumulation of SWCNTs was a length-independent process and non-monotonic in time, with the most SWCNTs (3950 fg/cell) accumulated at 8 h and then intracellular SWCNTs dropped obviously with time. The uptake rate of SWCNTs decreased with increasing concentration, suggesting that intracellular SWCNTs accumulation is a saturable process. After refreshing culture medium, we found increasing SWCNTs in supernatant and decreasing intracellular SWCNTs over time, confirming the exocytosis occurred. Selective inhibition of endocytosis pathways showed that the internalization of SWCNTs involves several pathways, in the order of macropinocytosis> caveolae-mediated endocytosis> clathrin-dependent endocytosis. Intriguingly, clathrin-mediated endocytosis is relatively important for internalizing shorter SWCNTs. The dynamic processes of SWCNTs uptake and exocytosis and the mechanisms revealed by this study may render a better understanding on SWCNT toxicity and facilitate the design of CNT products with mitigated toxicity and desired functions.

Photoelectrochemcal sensors were developed for the rapid detection of oxidative DNA damage induced by titanium dioxide and polystyrene nanoparticles. Each sensor is a multilayer film prepared on a tin oxide nanoparticle electrode using layer- by-layer self assembly and is composed of separate layer of a photoelectrochemical indicator, DNA. The organic compound and heavy metals represent genotoxic chemicals leading two major damaging mechanisms, DNA adduct formation and DNA oxidation. The DNA damage is detected by monitoring the change of photocurrent of the indicator. In one sensor configuration, a DNA intercalator, Ru(bpy)2 (dppz)2+ [bpy=2, 2′ -bipyridine, dppz=dipyrido( 3, 2-a: 2′ 3′-c) phenazine], was employed as the photoelectrochemical indicator. The damaged DNA on the sensor bound lesser Ru(bpy)2 (dppz)2+ than the intact DNA, resulting in a drop in photocurrent. In another configuration, ruthenium tris(bipyridine) was used as the indicator and was immobilized on the electrode underneath the DNA layer. After oxidative damage, the DNA bases became more accessible to photoelectrochemical oxidation than the intact DNA, producing a rise in photocurrent. Both sensors displayed substantial photocurrent change after incubation in titanium dioxide / polystyrene solution in a time – dependent manner. According to the data, damage of the DNA film was completed in 1h in titanium dioxide / polystyrene solution. In addition, the titanium dioxide induced much more sever damage than polysterene. The results were verified independently by gel electrophoresis and UV-Vis absorbance experiments. The photoelectrochemical reaction can be employed as a new and inexpensive screening tool for the rapid assessment of the genotoxicity of existing and new chemicals.

The mechanistic aspects of the photoelectrochemical sensor are examined in order to improve the sensitivity of the sensor. The sensor configuration has provided a unique tool for examining the role of DNA-bound [Fe.sup.2+] in Fenton reaction and DNA damage and the results have shown that [Fe.sup.2+] ions associated with DNA has induced DNA damage in the presence of [H.sub.2][O.sub.2].

Redox reaction and binding of the metallointercalator Ru(bpy)2[(dppz).sup.2+] with DNA is investigated by DNA film voltammetry. The intercalation positions the metal complex in close contact with the guanines inside DNA resulting in fast electrocatalytic reaction, giving rise to a catalytic pre-peak.

BACKGROUND: Numerous studies have indicated the estrogenic effects of polybrominated diphenyl ethers (PBDEs) and hydroxylated PBDEs (OHPBDEs). However, the previous mechanistic studies focused on their estrogenic effects through genomic transcriptional activation of estrogen receptors. OBJECTIVE: The present study aimed to investigate the estrogenic effects of PBDEs and OH-PBDEs via nongenomic G protein-coupled estrogen receptor (GPER) pathways. METHODS: The binding affinities of 12 PBDEs and 18 OH-PBDEs with GPER were determined by a fluorescence competitive binding assay in a human breast cancer cell line (SKBR3). Molecular docking was performed to simulate the interactions. Their activities on GPER pathways were investigated by detecting calcium mobilization and cyclic adenosine monophosphate (cAMP) accumulation in SKBR3 cells. The effects on SKBR3 cell migration were investigated using Boyden chamber and wound-healing assays. RESULTS: Our results showed that 11 of the OH-PBDEs but none of the PBDEs bound to GPER directly. Relative binding affinities ranged from 1.3% to 20.0% compared to 17b-estradiol. Docking results suggested that the hydroxyl group played an essential role in the binding of OH-PBDEs to GPER by forming hydrogen bond interactions. Most of the OH-PBDEs activated subsequent GPER signaling pathways. Among them, 40-OH-BDE-049, 50-OH-BDE-099, and 30-OH-BDE-154 displayed the highest activity with lowest effective concentrations (LOECs) of 10-100 nM. These three OH-PBDEs also promoted SKBR3 cell migration via GPER pathways with LOECs of 0:1-1 lM. CONCLUSION: OH-PBDEs could bind to GPER, activate the subsequent signaling pathways, and promote SKBR3 cell migration via GPER pathways. OH-PBDEs might exert estrogenic effects by a novel nongenomic mechanism involving the activation of GPER at nanomolar concentrations. [ABSTRACT FROM AUTHOR]

Transformation of nanomaterials in aqueous environment has significant impact on their behavior in engineered application and natural system. In this paper, UV irradiation induced transformation of TiO2 nanoparticles in aqueous solutions was demonstrated, and its effect on the aggregation and photocatalytic reactivity of TiO2 was investigated. UV irradiation of a TiO2 nanoparticle suspension accelerated nanoparticle aggregation that was dependent on the irradiation duration. The aggregation rate increased from <0.001 nm/s before irradiation to 0.027 nm/s after 50 h irradiation, resulting in aggregates with a hydrodynamic diameter of 623 nm. The isoelectric point of the suspension was lowered from 7.0 to 6.4 after irradiation, indicating less positive charges on the surface. ATR-FTIR spectra displayed successive growth of surface hydroxyl groups with UV irradiation which might be responsible for the change of surface charge and aggregation rate. UV irradiation also changed the photocatalytic degradation rate of Rhodamine B by TiO2, which initially increased with irradiation time, then decreased. Based on the photoluminescence decay and photocurrent collection data, the change was attributed to the variation in interparticle charge transfer kinetics. These results highlight the importance of light irradiation on the transformation and reactivity of TiO2 nanomaterials. [ABSTRACT FROM AUTHOR]

Polybrominated diphenyl ethers (PBDEs) are used in large quantities as flame retardant additives in commercial products. Bio-monitoring data show that PBDE concentrations have increased rapidly in the bodies of wildlife and human over the last few decades. Based on the studies on experimental animals, the toxicological endpoints of exposure to PBDEs are likely to be thyroid homeostasis disruption, neurodevelopmental deficits, reproductive ineffectiveness and even cancer. Unfortunately, the available molecular toxicological evidence for these endpoints is still very limited. This review focuses on the recent studies on the molecular mechanisms of PBDE toxicities carried out through the hormone receptor pathways, including thyroid hormone receptor, estrogen receptor, androgen receptor, progesterone receptor and aryl hydrocarbon receptor pathways. The general approach in the mechanistic investigation is to examine the in vitro direct binding of a PBDE with a receptor, the in vitro recruitment of a co-activator or co-repressor by the ligand-bound receptor, and the participation of the ligand in the receptor-mediated transcription pathways in cells. It is hoped that further studies in this area would provide more insights into the potential risks of PBDEs to human health. [ABSTRACT FROM AUTHOR]

Exposure of DNA to oxidative stress conditions results in the generation of 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodGuo). 8-OxodGuo is genotoxic if left unrepaired. We quantified 8-oxodGuo lesions in double-stranded DNA films by using a photoelectrochemical DNA sensor in conjunction with a specific covalent labeling method. A lesion-containing DNA film was assembled on a SnO2 nanoparticle modified indium tin oxide electrode through layer-by-layer electrostatic adsorption. The lesions were covalently labeled with a biotin conjugated spermine derivative, and ruthenium tris(bipyridine) labeled streptavidin was introduced as the signal reporter molecule. Photocurrent increased with the number of lesions in the strand and decreased as the film was diluted with intact DNA. Quantification of 8-oxodGuo was achieved with an estimated detection limit of 1 lesion in 650 bases or 1.6 fmol of 8-oxodGuo on the electrode. Incubation of the film with a DNA base excision repair enzyme, E. coli formamidopyrimidine-DNA glycosylase (Fpg), resulted in complete loss of the signal, indicating efficient excision of the isolated lesions in the nucleotide. Oxidatively generated DNA damage to a double-stranded calf thymus DNA film by the Fenton reaction was then assessed. One 8-oxodGuo lesion in 520 bases was detected in DNA exposed to 50 μM Fe2+/200 μM H2O2. Treatment with Fpg reduced the photocurrent by 50%, indicating only partial excision of 8-oxodGuo. This suggests that tandem lesions, which are resistant to Fpg excision, are generated by the Fenton reaction. Unlike repair enzyme dependent methods, the sensor recognizes 8-oxodGuo in tandem lesions and can avoid underestimating DNA damage. [ABSTRACT FROM AUTHOR]

Halogenated phenols are widely used as biocides and are considered to be possibly carcinogenic to humans. In this report, a previously developed photoelectrochemical DNA sensor was employed to investigate DNA damage induced by tetra-halogenated quinones, the in vivo metabolites of halogenated phenols. The sensor surface was composed of a double-stranded DNA film assembled on a SnO2 semiconductor electrode. A DNA intercalator, Ru(bpy)2(dppz)2+, was allowed to bind to the DNA film and produce photocurrent upon light irradiation. After the DNA film was exposed to 300 μM tetrafluoro-1,4-benzoquinone (TFBQ), the photocurrent dropped by 20%. In a mixture of 300 μM TFBQ and 2 mM H2O2, the signal dropped by 40%. The signal reduction indicates less binding of Ru(bpy)2(dppz)2+ due to structural damage of ds-DNA in the film. Similar results were obtained with tetra-1,4-chlorobenzoquinone (TCBQ), although the signal was not reduced as much as TFBQ. Fluorescence measurement showed that TFBQ/H2O2 generated more hydroxyl radicals than TCBQ/H2O2. Gel electrophoresis proved that the two benzoquinones produced DNA strand breaks together with H2O2, but not by themselves. Using the photoelectrochemical sensor, it was also found that TCBQ covalently bound with DNA did not produce additional oxidative damage in the presence of H2O2. The combined photoelectrochemistry, gel electrophoresis, and fluorescence data revealed distinctive differences between TFBQ and TCBQ in terms of DNA adduct formation and hydroxyl radical generation. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Noncovalent interaction of polycyclic aromatic compounds (PACs) with DNA is the first step in their DNA-damaging actions. The binding interaction of 15 PACs with DNA was investigated by the fluorescence displacement method. A DNA-binding dye with known binding mode was employed as the fluorescence probe. Addition of a DNA-binding PAC into the dye/DNA conjugate sets up a competition between the probe and the PAC for DNA and results in a reduction in fluorescence signal. When thiazole orange, a DNA intercalator, was employed as the probe, the dissociation constants of 1-hydroxypyrene, 1-aminopyrene, and 1-pyrenebutyric acid with calf thymus DNA were determined to be 0.62, 1.1, and 4.7 μM, respectively. Other PACs, with two to five fused aromatic rings, showed displacement similar to that of 1-pyrenebutyric acid. When the DNA groove-binding agents Hoechst 33258 and 4',6-diamidino-2-phenylindole were used as the probe, none of the PACs exhibited any significant competition with the probe for DNA. The fluorescence data and the viscosity measurement revealed that these PACs interact with DNA predominantly by intercalation instead of the groove-binding mode. The results also suggested that the polar groups on the periphery of the PAC's aromatic ring play a more important role than the number of aromatic rings in determining the binding affinities with DNA. The fluorescence displacement method provides a convenient tool for rapidly investigating the relationship between PAC structure and its DNA-binding properties. [ABSTRACT FROM AUTHOR]

Protein phosphorylation plays an important role in many significant cellular processes, and has thus gained tremendous interest in the field of proteomics. The electro-active tyrosine residue, as an important receptor of phosphorylation in proteins, exhibits electro-inactivity after being phosphorylated on the hydroxy group of its aromatic ring. In this study, the electrochemical oxidation of tyrosine on indium tin oxide (ITO) electrodes was catalyzed with an electron mediator Os(bpy)32+(bpy = 2,2′-bipyridine) and was employed as a signal reporter to differentially detect non-phosphorylated and phosphorylated peptides. A short, tyrosine-containing peptide glu-glu-glu-glu-glu-tyr (EY-6) was immobilized on an ITO surface using the layer-by-layer self-assembly method, and was detected by cyclic voltammetry in an Os(bpy)32+solution. The limit of detection was about 0.23 μg mL−1EY-6 in solution. The phosphorylated peptide glu-glu-glu-glu-glu-tyr-OP (EY-6P) did not produce an appreciable oxidation current on the electrode. Surface plasmon resonance measurements revealed that the amount of EY-6 and EY-6P adsorbed on the sensor chip surface was 269 and 378 pg mm−2, respectively. The poly(glu, tyr) (4 : 1) peptide, a protein tyrosine kinase substrate, was also detected by the same approach, with a detection limit of 0.65 μg mL−1. This new approach offers the possibility of label-free and on-chip detection of protein tyrosine kinase activity. [ABSTRACT FROM AUTHOR]

Rapid and sensitive detection methods are in urgent demand for the screening of an overwhelming number of existing and new chemicals as potential DNA-damaging agents. In this study, two photoelectrochemistry-based DNA sensor configurations were employed in the detection of DNA damage caused by styrene oxide and Fe2+/H2O2. The organic compound and heavy metal represent genotoxic chemicals possessing two major damaging mechanisms, DNA adduct formation and DNA oxidation. In the first sensor configuration, a ruthenium tris(bipyridine)-labeled avidin film and a double-stranded calf thymus DNA (ds-DNA) film were assembled successively on tin oxide nanoparticle film electrodes. Photogenerated Ru(lll) oxidized guanidine and adenosine bases in DNA and gave rise to photocurrent. DNA damage was detected after the reaction of the DNA film with either styrene oxide or Fe2+/H2O2, which exposed more DNA bases for photooxidation and resulted in increased photocurrent. In the second configuration, an unlabeled avidin film and a ds-DNA film were assembled on the semiconductor electrode. A DNA intercalator, Ru- (bpy)2(dppz)2+ (bpy = 2,2′-bipyridine, dppz = dipyrido[3,2-a: 2′,3′-c]phenazine), was employed as the photoelectrochemical signal reporter. After the chemical reaction with the damaging agents, the DNA film bound less Ru(bpy)2(dppz)2+ accompanied by a drop in photocurrent. Both sensors were used to follow the reaction course in styrene oxide and Fenton reagents and produced similar results. According to the data, damage of the DNA film was complete in 1 h in Fenton reagents and in 3 h in styrene oxide. In addition, the Fenton reaction induced much more severe damage than styrene oxide. The results demonstrate for the first time that the photoelectrochemical DNA sensor can detect both DNA adduct formation and DNA oxidation. It has the potential of becoming a screening tool for the rapid assessment of the genotoxicity of existing and new chemicals. [ABSTRACT FROM AUTHOR]

DNA films immobilized on an indium tin oxide (ITO) electrode surface were detected and determined employing a high-affinity intercalator, Ru(bpy)2(dppz)2+ (bpy = 2,2′-bipyridine, dppz = dipyrido[3,2-a:2′,3′-c]phenazine), as a redox indicator, and oxalate as a sacrificial electron donor in solution to chemically amplify the voltammetric signal of the indicator. Nucleic acids were immobilized on ITO by layer-by-layer electrostatic adsorption, using avidin as the first layer and nucleic acid as the second layer. In quartz crystal microbalance (QCM) measurements on an avidin-coated gold surface, the amount of adsorption from a 200 µg mL−1 nucleic acid solution was found to be 3.2 ng mm−2 for both double-stranded (ds-) and single-stranded (ss-) calf-thymus DNA as well as polycytidylic acid (Poly-C). After binding with Ru(bpy)2(dppz)2+ (Ru-dppz), voltammetry of the ds-DNA film on ITO was carried out in an indicator-free phosphate buffer. An anodic peak at about 1.15 V was observed, and it was assigned to Ru-dppz oxidation. When measured in an oxalate buffer, however, a catalytic current was observed due to the oxidation of oxalate by electrochemically generated Ru(bpy)2(dppz)3+, resulting in a 120-fold increase in the signal. Since oxalate itself produces a very low oxidation current on ITO, catalytic voltammetry produces about a 14-fold improvement in the signal-to-blank ratio over the non-amplified determination. As a result, ds-DNA adsorbed from 20 ng mL−1 solution could be detected, which was estimated by QCM to be 160 pg mm−2 on the surface. The catalytic current of ds-DNA was substantially higher than that of ss-DNA and poly-C, indicative of selective binding of the redox indicator to ds-DNA. The results serve as a basis for the catalytic voltammetric detection of DNA hybridization in future work. [ABSTRACT FROM AUTHOR]

Protein folding has been studied extensively with an aim to better understanding of the relationship between protein sequence, structure, and function. A large variety of techniques have been developed and utilized to probe protein conformation and folding/unfolding transition. In this report, electrochemical monitoring of urea-induced unfolding of a large cofactor-free protein, bovine serum albumin (BSA), is described. Enhanced electrochemical oxidation of tyrosine and tryptophan in free amino acids and in BSA was achieved on an indium tin oxide electrode by using an electron mediator, Os(bpy)2dppz (bpy = 2,2′-bipyridine, dppz = dipyrido[3,2-a:2′,3′-e]phenazine). The oxidation current was used as a signal reporter in the monitoring of urea-induced BSA denaturation. At high urea concentrations, the electrochemical signal increased by 3-fold relative to the native protein. The increase is attributed to the closer contact between the oxidizable residues in the unfolded BSA and Os(bpy)2dppz. The degree of unfolding assessed by electrochemistry correlates well with the established fluorescence technique in the range of 0–10 M urea. The method can be used to investigate the unfolding process of other cofactor-free proteins. [ABSTRACT FROM AUTHOR]

Direct electrochemistry of site-specific mutants of yeast iso-1-cytochrome c (cyt c) and their complexes with bovine cytochrome b5 (cyt b5) has been investigated at edge-plane pyrolytic graphite (EPG) and bis(4-pyridyl)- disulphide-modified gold electrodes. Structure/function relationships have been investigated with the particular aim of clarifying the factors controlling the interactions of proteins at electrode/electrolyte interfaces and the determinants for direct electrochemistry in ternary protein/protein/electrode adducts, e.g. cyt c/cyt As/EPG. Investigations of the cyt c mutants alone revealed a variety of electrochemical responses: all the mutants show similar voltammetric reversibility at modified gold electrodes, whereas at EPG electrodes the reversibility follows the order: Asn52Ile-Cys102Thr « Cys102Thr « Asn52Ala-Cys102Thr. Mid-point potentials follow the order: Arg13Ile (+60 ± 5 mV vs. standard calomel electrode) « Cys102Thr (+40 ± 5 mV) « Lys27Gln (+30 ± 5mV) ≅ Lys72Asp(+30 ± 5mV) « Asn52Ala-Cys102Thr (+15 ± 5mV) « Asn52Ile-Cys102Thr (-10 ± 5 mV). The structural basis for these differences is briefly discussed. When these mutants are bound to cyt b5, the differences in electrochemical response are greatly enhanced in the ternary cyt c/cyt b5/EPG adducts. A minimal analysis of these differences supports a model of multiple overlapping binding and recognition domains on cyt c which may be finely tuned to allow ternary complex formation so that a single-site variation could modify or abolish direct electrochemistry in the ternary adduct. [ABSTRACT FROM AUTHOR]

The author discusses the health effects of haze and particulate matters (PM) pollution.

Selective photoelectrochemical oxidation of DNA was achieved by ruthenium tris(bipyridine) immobilized on a tin oxide nanoparticle electrode. The metal complex was covalently attached to a protein, avidin, which adsorbed strongly on the tin oxide electrode by electrostatic interaction. Upon irradiation with 473-nm light, anodic photocurrent was generated in a blank electrolyte and was enhanced significantly after addition of poly(guanadylic acid) (poly-G) into the electrolyte. The current increased progressively with the nucleotide concentration, suggesting the enhancement effect was related to poly-G. The action spectrum indicates that the photo current was initiated by light absorption of the ruthenium compound immobilized on the electrode. Among the various polynucleotides examined, poly-G produced the largest photocurrent increase, followed by poly-A, single-stranded DNA, chemically damaged DNA, and double-stranded DNA, whereas poly-C and poly-U showed little effect. The combined experimental data support the hypothesis that the photoexcited Ru2+* species injects an electron into the semiconductor and produces Ru3+, which is then reduced back to Ru2+ by guanine and adenine bases in DNA, resulting in the recycling of the metal complex and enhanced photocurrent. The photoelectrochemical reaction can be employed as a new method for the detection of DNA damage. [ABSTRACT FROM AUTHOR]

Quantitative detection of a biological affinity reaction, the biotin/avidin recognition, was achieved using our newly developed photoelecirochemical analytical system. The system is based on the operation mechanism of the well- developed dye-sensitized photoelectrochemical solar cells and comprises a ruthenium tris(2,2'-bipyridine) (Ru-bipy) derivative as the photoelectrochemical signal-generating molecule, oxalate as the sacrificial electron donor, and tin oxide nanoparticle as the semiconductor electrode material. To perform the affinity reaction, avidin was immobilized on SnO[SUB2] electrode by passive adsorption. Biolin-linked bovine serum albumin (BSA) was labeled with an NHS-ester derivative of Ru-bipy. After binding of BSA to the surface-immobilized avidin through biotin, photoelectrochemical measurement was carried out in the presence of oxalate. Anodic photocurrent was turned on and off repeatedly by control of incidental light. The action spectrum of the photocurrent resembled the absorption spectrum of Ru-bipy, proving the photocurrent was generated from the metal complex. A linear relationship between photocurrent and BSA concentration was obtained in the range of 1-100 μg/mL. This is the first case of quantitative photoelectrochemical detection of a biological affinity interaction. [ABSTRACT FROM AUTHOR]