Accurate standard hydrogen electrode potential and applications to the redox potentials of vitamin C and NAD/NADH

Gold Decoration and Photoresistive Response to Nitrogen Dioxide of WS2 Nanotubes

Composites of WS₂ nanotubes (NT-WS₂ ) and gold nanoparticles (AuNPs) were prepared using aqueous HAuCl₄ solutions and subjected to surface analysis. The obtained materials were jointly characterized by X-ray photoelectron (XPS), Raman scattering (RSS), and ultraviolet photoelectron (UPS) spectroscopies. Optical extinction spectroscopy and electron energy loss spectroscopy in the scanning transmission electron microscopy regime (STEM-EELS) were also employed to study plasmon features of the nanocomposite. It was found that AuNPs deposition is accompanied by a partial oxidative dissolution of WS₂ , whereas Au-S interfacial species could be responsible for the tight contact of metal nanoparticles and the disulfide. A remarkable sensitivity of n-type resistance of NT-WS₂ and Au-NT-WS₂ to the adsorption of NO₂ gas was also demonstrated at room temperature using periodical illumination by a 530 nm light-emitting diode. Au-NT-WS₂ nanocomposites are found to possess a higher photoresponse and enhanced sensitivity in the 0.25-2.0 ppm range of NO₂ concentration, as compared to the pristine NT-WS₂ . This behaviour is discussed within the physisorption-charge transfer model to explore sensing properties of the nanocomposites.

A computational scheme of pKa values based on the three-dimensional reference interaction site model self-consistent field theory coupled with the linear fitting correction scheme

A scheme for quantitatively computing the acid dissociation constant, pKa, of hydrated molecules is proposed. It is based on the three-dimensional reference interaction site model self-consistent field (3D-RISM-SCF) theory coupled with the linear fitting correction (LFC) scheme. In LFC/3D-RISM-SCF, pKa values of target molecules are evaluated using the Gibbs energy difference between the protonated and unprotonated states calculated by 3D-RISM-SCF and the parameters fitted by the LFC scheme to the experimental values of training set systems. The pKa values computed by LFC/3D-RISM-SCF show quantitative agreement with the experimental data.

Computational electrochemistry of a novel ferrocene derivative

In this study, the structural and redox properties of a novel ferrocene derivative in dichlomethane solvent were investigated. For this aim, various exchange-correlation functionals and basis sets in gas phase with different continuum solvation models and cavities in liquid phase were applied. The results indicated that UM06/6-31++G(d,p)/SDD level of theory successfully calculated bond lengths and angles with MADs = 0.02 Å and 0.78 deg., respectively. Also, its combination with CPCM-Pauling-UHF/6-31+G(d)/SDD level of theory in liquid phase effectively computed the redox potential with 0.06 V deviation from the experimental value. Moreover, transferability of the proposed method was studied through ferrocene molecule and its new synthesized derivative.

In situ plasmonic generation in functional ionic-gold-nanogel scaffold for rapid quantitative bio-sensing

Conventional analytical techniques, which have been developed for high sensitivity and selectivity for the detection and quantification of relevant biomarkers, may not be as suitable for medical diagnosis in resource scarce environments as compared to point-of-care devices (POC). We have developed a new reactive sensing material which contains ionic gold entrapped within an agarose gel scaffold for POC quantification of ascorbic acid (AA) in tear fluid. Pathologically elevated concentration of AA in human tear fluid can serve as a biomarker for full-thickness injuries to the ocular surface, which are a medical emergency. This reactive sensing material will undergo colorimetric changes, quantitatively dependent on endogenous bio-reductants that are applied, as the entrapped ionic gold is reduced to form plasmonic nanoparticles. The capacity for this reactive material to function as a plasmonically driven biosensor, called 'OjoGel' (ojo-eye), was demonstrated with the endogenous reducing agent, AA. Through applications of AA of varied concentrations to the OjoGel, we demonstrated a quantitative colorimetric relationship between red (R) hexadecimal values and concentrations of AA in said treatments. This colorimetric relationship is directly resultant of plasmonic gold nanoparticle formation within the OjoGel scaffold. Using a commercially available mobile phone-based Pixel Picker^® application, the OjoGel plasmonic sensing platform opens a new avenue for easy-to-use, rapid, and quantitative biosensing with low cost and accurate results.

Colorimetric Detection of Mercury(II) Ion in Aqueous Solution Using Silver Nanoparticles

Novel green-chemistry synthesis of silver nanoparticles (AgNPs) is introduced as a low-cost, rapid and easy-to-use analytical method for mercury ion detection. Aqueous fruit extract of water apple (Syzygium aqueum) was used for the first time as bioreductant to synthesize stable AgNPs. The prepared AgNPs have a yellowish-brown color with a surface plasmon resonance peak at 420 nm. The addition of Hg(II) ions then changes the AgNPs color to colorless. The color change was in proportion to the concentration of Hg(II) ions. The presence of other metal ions in the system was also evaluated. The proposed method shows good selectivity and sensitivity towards Hg(II) ions. Using UV-visible spectrophotometry, the detection limit of the developed method was 8.5 × 10^-7 M. The proposed method has been successfully applied for determination of Hg(II) ions in tap and lake water samples with precision better than 5%.

Vitamin K: Redox-modulation, prevention of mitochondrial dysfunction and anticancer effect

This review is directed to the redox-modulating properties and anticancer effect of vitamin K. The concept is focused on two aspects: (i) redox-cycle of vitamin K and its effect on the calcium homeostasis, “oncogenic” and “onco-suppressive” reactive oxygen species and the specific induction of oxidative stress in cancer; (ii) vitamin K plus C as a powerful redox-system, which forms a bypass between mitochondrial complexes II and III and thus prevents mitochondrial dysfunction, restores oxidative phosphorylation and aerobic glycolysis, modulates the redox-state of endogenous redox-pairs, eliminates the hypoxic environment of cancer cells and induces cell death. The analyzed data suggest that vitamin C&K can sensitize cancer cells to conventional chemotherapy, which allows achievement of a lower effective dose of the drug and minimizing the harmful side-effects. The review is intended for a wide audience of readers - from students to specialists in the field.

A theoretical study of ascorbic acid oxidation and HOO˙/O2˙- radical scavenging

Ascorbic acid is a well-known antioxidant and radical scavenger. It can be oxidized by losing two protons and two electrons, but normally loses only one electron at a time. The reactivity of the ascorbate radical is unusual, in that it can either disproportionate or react with other radicals, but it reacts poorly with non-radical species. To explore the oxidation mechanism of ascorbic acid, the pK_a's and reduction potentials have been calculated using the B3LYP/6-31+G(d,p) and CBS-QB3 levels of theory with the SMD implicit solvent model and explicit waters. Calculations show that the most stable form of dehydroascorbic acid in water is the bicyclic hydrated structure, in agreement with NMR studies. The possible oxidation reactions at different pH conditions can be understood by constructing a potential-pH (Pourbaix) diagram from the calculated pK_a's and standard reduction potentials. At physiological pH disproportionation of the intermediate radical is thermodynamically favored. The calculations show that disproportionation proceeds via dimerization of ascorbate radical and internal electron transfer, as suggested by Bielski. In the dimer, one of the ascorbate units cyclizes. Then protonation and dissociation yields the fully reduced and bicyclic fully oxidized structures. Calculations show that this mechanism also explains the reaction of the ascorbic acid radical with other radical species such as superoxide. Ascorbate radical combines with the radical, and intramolecular electron transfer followed by cyclization and hydrolysis yields dehydroascorbic acid and converts the radical to its reduced form.

Low-voltage driven portable paper bipolar electrode-supported electrochemical sensing device

Aiming to overcome the obstacles of power supply requirement and chip usefulness in practice, a low-cost and convenient portable electrochemical sensing device is introduced for the first time, featuring bipolar electrode system, LED read-out, laminated paper-based devices, and low-voltage button cells. The electric circuits of this practical device are constructed on laminating films with copper and conductive carbon tapes, and the reservoirs facilitating chemical reactions are made with chromatography paper. The device is sensitive to electrochemical responses, validated by the demonstrative hydrogen peroxide and enzyme-assisted glucose detection. The business-card-size chip achieves sensitive analyte detection by naked eyes as well as further image processing in both laboratory samples and human serum samples testing, featuring detection limit as low as 1.79 μM and a dynamic range from 10 μM to 10 mM. This new practical design of point-of-care sensing chip entails the properties of facile fabrication, simple usage, high robustness, low power consumption, and accurate sensing showing the attainability of fabricating a useful and portable analytical device.

A computational study of the Fenton reaction in different pH ranges

The mechanism of the Fenton reaction is pH dependent and four distinct reactive species have been identified and found to display quite different oxidation reactivities.

Electrochemical behaviors and relativistic DFT calculations to understand the terminal ligand influence on the [Re6(μ3-Q)8X6]4− clusters

A Born–Haber thermodynamic cycle was used to determine the redox potential in a series of rhenium(iii) clusters theoretical analysis at DFT level was considered to estimate the free energy of the reversible process ReIII6/ReIII5Re^IV.

A facile hydroxylation of arylboronic acids mediated by sodium ascorbate

A mild and selective method for the synthesis of phenols has been described.

Dendrite formation in silicon anodes of lithium-ion batteries

Rechargeable lithium-ion batteries require a vigorous improvement if we want to use them massively for high energy applications. Silicon and metal lithium anodes are excellent alternatives because of their large theoretical capacity when compared to graphite used in practically all rechargeable Li-ion batteries. However, several problems need to be addressed satisfactorily before a major fabrication effort can be launched; for instance, the growth of lithium dendrites is one of the most important to take care due to safety issues. In this work we attempt to predict the mechanism of dendrite growth by simulating possible behaviors of charge distributions in the anode of an already cracked solid electrolyte interphase of a nanobattery, which is under the application of an external field representing the charging of the battery; thus, elucidating the conditions for dendrite growth. The extremely slow drift velocity of the Li-ions of ∼1 mm per hour in a typical commercial Li-ion battery, makes the growth of a dendrite take a few hours; however, once a Li-ion arrives at an active site of the anode, it takes an extremely short time of ∼1 ps to react. This large difference in time-scales allows us to perform the molecular dynamics simulation of the ions at much larger drift velocities, so we can have valuable results in reasonable computational times. The conditions before the growth are assumed and conditions that do not lead to the growth are ignored. We performed molecular dynamics simulations of a pre-lithiated silicon anode with a Li : Si ratio of 21 : 5, corresponding to a fully charged battery. We simulate the dendrite growth by testing a few charge distributions in a nanosized square representing a crack of the solid electrolyte interphase, which is where the electrolyte solution comes into direct contact with the LiSi alloy anode. Depending on the selected charge distributions for such an anode surface, the dendrites grow during the simulation when an external field is applied. We found that dendrites grow when strong deviations of charge distributions take place on the surface of the crack. Results from this work are important in finding ways to constrain lithium dendrite growth using tailored coatings or pre-coatings covering the LiSi alloy anode.

Dendrite formation conditions on a SEI crack exposing the silicon anode to the electrolyte during the charging of a LIB.

Reducing Agent-Assisted Excessive Galvanic Replacement Mediated Seed-Mediated Synthesis of Porous Gold Nanoplates and Highly Efficient Gene-Thermo Cancer Therapy

Porous Au nanoplates (pAuNPs) were manufactured by a reducing agent-assisted galvanic replacement reaction on Ag nanoplates using a seed-mediated synthetic approach. Two core additives, poly(vinylpyrrolidone) and l-ascorbic acid, prevented fragmentation and proceeded secondary growth. By controlling the concentration of the additives and the amount of replacing ion AuCl₄^-, various nanostructures including nanoplates with holes, nanoframes, porous nanoplates, and bumpy nanoparticles with unity and homogeneity were synthesized. The present synthetic method is advantageous, because it can be used to manufacture pAuNPs with ease, robustness, and convenience. The prepared pAuNPs exhibited a highly efficient photothermal conversion effect and cargo loading capacity on exposed surfaces by Au-thiol linkage. By using dual cargo mixed loading of the hepatitis C virus (HCV) targeting gene drug DNAzyme and cell-penetrating peptide TAT onto the surface of the pAuNPs and photothermal conversion-mediated hyperthermic treatment, successful gene-thermo therapy against HCV genomic human hepatocarcinoma cells were demonstrated.

The effects of lipoic acid on redox status in brain regions and systemic circulation in streptozotocin-induced sporadic Alzheimer's disease model

While the deterioration of insulin-glucose metabolism (IGM), impaired redox homeostasis (IRH), β-amyloid accumulation was reported in Sporadic Alzheimer's Disease (SAD) model, aforementioned factors related to lipoic acid administration and anthropometric indexes (AIs) are not yet studied with integrative approach. β-amyloid accumulation, redox homeostasis biomarkers and AIs are investigated in SAD model. Streptozotocin-induced inhibition of insulin-signaling cascade but not GLUT-2 and GLUT-3 transporters takes a role in β-amyloid accumulation. Inhibition types are related to IRH in cortex, hippocampus and systemic circulation. Lipoic acid (LA) shows both antioxidant and prooxidant effect according to the anatomical location. LA administration also leads to improved AIs during GLUT-2 inhibition and cortical redox status in GLUT-3 inhibited group. Optimal LA action could be possible if its redox behavior is balanced to antioxidant effect. Diagnostic usage of systemic IRH parameters as biomarkers and their possible correlations with deteriorated IGM should be investigated. Graphical abstract ᅟ.

Monitoring Dynamic Cellular Redox Homeostasis Using Fluorescence-Switchable Graphene Quantum Dots

Monitoring cellular redox homeostasis is critical to the understanding of many physiological functions ranging from immune reactions to metabolism, as well as to the understanding of pathological development ranging from tumorigenesis to aging. Nevertheless, there is currently a lack of appropriate probes for this ambition, which should be reversibly, sensitively, and promptly responsive to a wide range of physiological oxidants and reductants. In this work, a redox-sensitive fluorescence-switchable probe is designed based on graphene quantum dots (GQDs) functionalized with a chelated redox Fe²⁺/Fe³⁺ couple. The underlying mechanism is investigated and discussed. The high sensitivity and fast response are attributable to the fact that the GQD's photoluminescence is highly sensitive to photon-induced electron transfer because of its ultrasmall size and associated prominent quantum confinement effect. Also taking advantages of GQDs' excellent photostability, biocompatibility, and readiness for cell uptake, our reversibly tunable fluorescence probe is employed to monitor in real time the triggered dynamic change of the intracellular redox state. This addition to the limited arsenal of available redox probes shall be useful to the still poorly understood redox biology, as well as for monitoring environment or chemical processes involving redox reactions.

Photo-enhanced oxidizability of tetrazolium salts and its impact on superoxide assaying

Herein, we report for the first time the enhanced oxidation properties of tetrazolium salts induced by UV-irradiation, and demonstrate that there is real deviation in the photo-induced superoxide anion radical assay based on tetrazolium salts.

Free Energies of Redox Half-Reactions from First-Principles Calculations

Quantitative prediction of the energetics of redox half-reactions is still a challenge for modern computational chemistry. Here, we propose a simple scheme for reliable calculations of vertical ionization and attachment energies, as well as of redox potentials of solvated molecules. The approach exploits linear response approximation in the context of explicit solvent simulations with spherical boundary conditions. It is shown that both vertical ionization energies and vertical electron affinities, and, consequently redox potentials, exhibit linear dependence on the inverse radius of the solvation sphere. The explanation of the linear dependence is provided, and an extrapolation scheme is suggested. The proposed approach accounts for the specific short-range interactions within hybrid DFT and effective fragment potential approach as well as for the asymptotic system-size effects. The computed vertical ionization energies and redox potentials are in excellent agreement with the experimental values.

Sequence-Dependent Photocurrent Generation through Long-Distance Excess-Electron Transfer in DNA

Given its well-ordered continuous π stacking of nucleobases, DNA has been considered as a biomaterial for charge transfer in biosensors. For cathodic photocurrent generation resulting from hole transfer in DNA, sensitivity to DNA structure and base-pair stacking has been confirmed. However, such information has not been provided for anodic photocurrent generation resulting from excess-electron transfer in DNA. In the present study, we measured the anodic photocurrent of a DNA-modified Au electrode. Our results demonstrate long-distance excess-electron transfer in DNA, which is dominated by a hopping mechanism, and the photocurrent generation is sequence dependent.

Thin-layer voltammetry of soluble species on screen-printed electrodes: proof of concept

Thin-layer diffusion conditions were accomplished on screen-printed electrodes by placing a controlled-weight onto the cast solution and allowing for its natural spreading.