Neutral Phosphate Buffer Research Articles

Simultaneous electrochemical detection of hydroquinone and catechol using MWCNT-COOH/CTF-1 composite modified electrode

In this present work, a carboxylated multi-walled carbon nanotubes (MWCNT-COOH) and covalent triazine framework (CTF-1) co-modified glassy carbon electrode (GCE) is prepared and used for simultaneous electrochemical detection of hydroquinone (HQ) and catechol (CC). Due to the synergistic effect between the high electrocatalytic activity and good conductivity of MWCNT-COOH and large surface area of CTF-1, the prepared modified electrode exhibits good selectivity and high sensitivity for the simultaneous determination of HQ and CC. In the neutral phosphate buffer, HQ and CC produce a pair of well-defined redox peaks on the MWCNT-COOH/CTF-1/GCE. The concentrations of CC and HQ show good linearity in the range of 2–280 μM and the detection limits of HQ and CC are 0.12 μM and 0.17 μM, respectively. The prepared electrochemical sensor can be employed to determine contents of HQ and CC in real samples. • The MWCNT-COOH/CTF-1 composite exhibits superior electrocatalytic performance towards hydroquinone and catechol detection. • The research paves a feasible way to unlock high performance CTF electrode materials. • The sensor showed excellent specificity, good stability, and desirable reproducibility.

Mechanism of water oxidation catalyzed by vitamin B12: Redox non-innocent nature of corrin ligand and crucial role of phosphate

Vitamin B12 (macrocyclic cobalamin) has been recently reported to be capable of electrochemically catalyzing water oxidation in a neutral phosphate buffer solution. In this work, density functional calculations were employed to elucidate the water oxidation mechanism catalyzed by vitamin B12. The calculations showed that the catalytic cycle starts from the L•-CoII-OH2 complex 1. A proton-coupled electron transfer process then leads to the formation of a L•-CoIII-OH complex 2, followed by another proton-coupled electron transfer event to afford a corrin ligand radical cation intermediate 3 (L•-CoIII-O•). The redox non-innocent nature of the corrin ligand plays an essential role in the oxidation process. 3 is capable of triggering the O-O bond formation via a water nucleophilic attack mechanism, in which a hydrophosphate dianion functions as a base to accept a proton from the water nucleophile. A dioxygen molecule is released after the oxidation of the CoIII-OOH intermediate. The rate-determining step was calculated to be the O-O bond formation with a total barrier of 16.5 kcal/mol. While the use of water molecules as the proton acceptor was found to be less feasible for the O-O bond formation, with a barrier of 31.2 kcal/mol, further highlighting the crucial of phosphate in water oxidation.

Developing a Fluorescent Hybrid Nanobiosensor Based on Quantum Dots and Azoreductase Enzyme forMethyl Red Monitoring.

Background:Azo dyes are the most widely used synthetic colorants in the textile, food, pharmaceutical, cosmetic, and other industries, accounting for nearly 70% of all dyestuffs consumed. Recently, much research attention has been paid to efficient monitoring of these hazardous chemicals and their related metabolites because of their potentially harmful effect on environmental issues. In contrast to the complex and expensive instrumental procedures, the detection system based on the QDs with the superior optochemical properties provides a new era in the pollution sensing and prevention. Methods:We have developed a QD-enzyme hybrid system to probe MR in aqueous solutions using a fluorescence quenching procedure. Results:The azoreductase enzyme catalyzed the reduction of azo group in MR, which can efficiently decrease the FRET between the QDs and MR molecules. The correlation between the QDs photoluminescence recovery and MR enzymatic decolorization at the neutral phosphate buffer permitted the creation of a fluorescence quenching-based sensor. The synthesized biosensor can be used for the accurate detection of MR in a linear calibration over MR concentrations of 5-84 μM, with the LOD of 0.5 μM in response time of three minutes. Conclusion:Our findings revealed that this fluorometric sensor has the potential to be successfully applied for monitoring a wide linear range of MR concentration with the relative standard deviation of 4% rather than the other method.

A Monochromophoric Approach to Succinct Ratiometric Fluorescent Probes without Probe-Product Crosstalk

Ratiometric probes facilitate quantitative studies via self-calibration and are cherished for bioimaging. Often, a small probe-product spectral separation leads to crosstalk, but the rational devel...

Improvement of the electrocatalytic performance of FeP in neutral electrolytes with Fe nanoparticles

Metal phosphides are promising electrocatalysts for hydrogen evolution reaction (HER). However, their applications are hindered by the low electronic conductivity and sluggish HER kinetics in neutral electrolytes. Here we report an approach to significantly improving the HER performance of hierarchical iron phosphide (pFeP) modified with metallic iron (Fe) in neutral phosphate buffer electrolytes. It was observed that the presence of Fe can accelerate the charge transport kinetics. As a result, a significant improvement on the proton-acceptor (negatively charged P sites) and hydride-acceptor (coordinated Fe sites) were achieved, therefore promoting proton adsorption to the electrocatalyst surface during water electrolysis. Specifically, the Fe modified FeP electrocatalyst (pFe/FeP) displayed high HER catalytic rates (e.g., −100 mA cm−2 at an overpotential of −380 mV), low onset potential (50 mV), and excellent long-term stability for 40 h in neutral electrolyte. This study provides a new approach to the design and synthesis of noble-metal-free electrocatalysts with excellent performance for hydrogen production in neutral electrolytes.

Study of pH-Responsive and Polyethylene Glycol-Modified Doxorubicin-Loaded Mesoporous Silica Nanoparticles for Drug Delivery.

Tumor-targeted drug delivery systems represent challenging and widely investigated strategies to enhance cancer chemotherapy. In this study, we introduce a novel high-hydrophilic mesoporous silica nanoparticle system with a pH-sensitive drug release. The resultant composite nanoparticles appear as spheres of uniform size (450±25 nm) with a porous structure, which enables a high drug-loading ratio. Through modification of chitosan and polyethylene glycol monomethyl ether, the modified mesoporous silica was non-toxic to normal cells, but effective at inducing tumor cell death. With regard to the characteristics of drug release, the modified mesoporous silica clearly displayed a pH-stimulated release of the model drug doxorubicin hydrochloride in an acidic phosphate buffer solution (pH 4.0 and 6.0). The release was much greater than that observed in neutral or alkaline phosphate buffer solutions (pH 7.3 and 8.0). Furthermore, the release behavior was in accordance with the Higuchi model, indicating that this modified mesoporous silica drug delivery system can exhibit controlled release. The above results imply that the modified mesoporous silica is an effective drug delivery system for cancer therapy.

Boosting the Activity and Stability of Copper Tungsten Nanoflakes toward Solar Water Oxidation by Iridium-Cobalt Phosphates Modification

Severe interfacial electron–hole recombination greatly limits the performance of CuWO4 photoanode towards the photoelectrochemical (PEC) oxygen evolution reaction (OER). Surface modification with an OER cocatalyst can reduce electron–hole recombination and thus improve the PEC OER performance of CuWO4. Herein, we coupled CuWO4 nanoflakes (NFs) with Iridium–cobalt phosphates (IrCo-Pi) and greatly improved the photoactivity of CuWO4. The optimized photocurrent density for CuWO4/IrCo-Pi at 1.23 V vs. reversible hydrogen electrode (RHE) rose to 0.54 mA∙cm−2, a ca. 70% increase over that of bare CuWO4 (0.32 mA∙cm−2). Such improved photoactivity was attributed to the enhanced hole collection efficiency, which resulted from the reduced charge-transfer resistance via IrCo-Pi modification. Moreover, the as-deposited IrCo-Pi layer well coated the inner CuWO4 NFs and effectively prevented the photoinduced corrosion of CuWO4 in neutral potassium phosphate (KPi) buffer solution, eventually leading to a superior stability over the bare CuWO4. The facile preparation of IrCo-Pi and its great improvement in the photoactivity make it possible to design an efficient CuWO4/cocatalyst system towards PEC water oxidation.

Improving solubility and intrinsic dissolution rate of ofloxacin API through salt formation via mechanochemical synthesis with diphenic acid

The study focusses on the effect of solubility and intrinsic dissolution rate on the pharmaceutical salt of ofloxacin, a new generation fluoroquinolone antibacterial marketed drug, with the organic acid coformer, diphenic acid produced via mechanochemical synthesis using liquid assisted grinding method. The synthesized cocrystal salt was characterized by single crystal and powder X-ray diffraction, differential scanning calorimetry, and infrared spectroscopy techniques. The crystal structure reveals that, there is proton migration from the coformer to the drug leading to the formation of salt via charge assisted N–H+···O hydrogen bond interactions. The aqueous solubility of the drug and its corresponding salt were determined in neutral phosphate buffer medium (pH = 7) at 25 °C using UV–Vis absorption spectroscopy, while dissolution experiments were carried out at 37 °C bath temperature and neutral phosphate buffer conditions. Interestingly it has been observed that the aqueous solubility and intrinsic dissolution rate of the salt form of ofloxacin has enhanced significantly compared to the parent drug and this is expected to have implications in the bioavailability of the drug in different formulations related to the utilization of this drug.

Electrocatalytic performance and cell voltage characteristics of 1st-row transition metal phosphate (TM-Pi) catalysts at neutral pH

Water electrolysis represents a clean and sustainable route for large-scale hydrogen generation. However, efficient water splitting is hindered by the kinetically sluggish oxygen evolution reaction (OER), which requires significant energy inputs to drive the reaction at sufficiently fast rates. Recently, an increasing number of applications have emerged that require water electrolysis at neutral pH and under ambient conditions. This requirement creates additional challenges as the electrolysis of water is favorable in acidic and alkaline conditions. In order to tackle these challenges, considerable efforts have been devoted to the development of earth-abundant, highly effective, and robust electrocatalysts for the OER at pH = 7. Of these catalysts, amorphous transition-metal phosphates have attracted wide attention because of their unique electrocatalytic properties. In this paper, the OER performance of a series of amorphous first-row transition metal phosphate (TM-Pi) catalysts, namely Co-Pi, NiFe-Pi and Fe-Pi prepared with different deposition strategies onto various substrates, is comparatively studied in a neutral phosphate buffer solution (PBS). Additionally, a simplified cell model is applied to analyze the current-voltage characteristics and quantitatively evaluate and compare the reversible, ohmic, and activation overvoltage components of the studied TM-Pi. It is found that TM-Pi catalysts deposited onto a highly ordered nickel foam (NF) substrate are competitive with commercial Pt and IrO2 catalysts in terms of OER activity and long-term stability.

Homogeneous Electrochemical Water Oxidation at Neutral pH by Water-Soluble NiII Complexes Bearing Redox Non-innocent Tetraamido Macrocyclic Ligands.

Water oxidation is the bottleneck reaction in artificial photosynthesis. Exploring highly active and stable molecular water oxidation catalysts (WOCs) is still a great challenge. In this study, a water-soluble NiII complex bearing a redox non-innocent tetraamido macrocyclic ligand (TAML) is found to be an efficient electrocatalyst for water oxidation in neutral potassium phosphate buffer. Controlled-potential electrolysis experiments show that it can sustain at a steady current of approximately 0.2 mA cm-2 for >7 h at 1.75 V versus normal hydrogen electrode (NHE) without the formation of NiOx . Electrochemical and spectroelectrochemical tests show that the redox-active ligand, as well as HPO4 2- in the buffer, participate in the catalytic cycle. More importantly, catalytically active intermediate [NiIII (TAML2- )-O. ] is formed via several proton-coupled electron transfer processes and reacts with H2 O with the assistance of base to release molecular oxygen. Thus, the employment of redox non-innocent ligands is a useful strategy for designing effective molecular WOCs.

The medium effect on electrodissolution of adsorbed or suspended Ag nanoparticles

Electrochemical behaviour of six types of Ag nanoparticles (three stabilised by citrate and three others stabilised by polymers) was studied on carbon screen-printed electrode and glassy carbon rotating disc electrode. A stationary electrode was used as a support for adsorbed nanoparticles, whereas the rotating disc electrode was applied for experiments in nanoparticles suspension. Peak shaped cyclic voltammograms obtained for immobilised nanoparticles indicate their electro-dissolution and electrodeposition of silver in the backward scan. The given peak shape and its position on potential scale depend both on the type of nanoparticles and the supporting electrolyte. When aggregation of Ag nanoparticles was detected by UV–vis spectroscopy, splitting of an anodic peak corresponding to electrodissolution of silver in neutral phosphate buffer or NaOH solution is seen. Injection of a fraction of microgram of Ag nanoparticles was detected in chronoamperometric experiments on rotating disc electrode. However, in the presence of H2O2, the effect of nanograms of silver was seen on voltammetric curve indicating electrocatalytic amplification.

The Immunological Study of Salmonella Infantis in white Mice Immunized with Killed Antigen

The present study was carried out to investigate the effect of formalin-killed antigen for Sallmonellainfantis in vivo with the study of cellular immune response through the study of cytokines.Sallmonellainfantis were isolated and diagnosed from local milk products (milk and cheese). 74 milk samples and 53 cheese samples were taken.The media were usedgeneral and special culture media as well as biochemical tests were used to diagnose the isolates and the diagnosis was confirmed by using API 20. Sallmonellainfantis antigens were used systemically. 50 Swiss white mice of both sexes were randomly divided into three groups. The first group prevented (20 mice) with the bacterial antigen killed by formalin in a dose (0.3) I.P for each animal. The group was injected with a booster dose and the same first immunization dose two weeks after the first dose. The second group (20 mice) and the third group (10 mice) were counted as positive and negative control groups respectively. The first group and the second group received a dose of 0.3 ml of stuck S.infantis containing (1×108 live cells / ml) I.P, while the third group injected 0.3 ml of neutral phosphate buffer solution under the skin. The results showed that 4 animals from the first group were killed and all the remaining animals from the first group were killed 20 days after the challenge dose and serum was taken to measure cellular immunity. The results of serological tests showed that the level of (IL-4 and IL-6) were (38.48 ± 2.1 and 31.81, 3.01) respectively, as well as the results of measurement of concentration (INF gamma and TNF-?) were (401 ± 2.12 and 173.421 ± 3.11) respectively.We conclude from the study that there was a high percentage of S.infantis isolated from milk products as well as we conclude that the formalinS.infantiskilledantigen partially protected against the infection.

Preparation of self-assembled collagen fibrillar gel from tilapia skin and its formation in presence of acidic polysaccharides

Fibrillar gel of pepsin-solubilized collagen from tilapia skin was prepared by self-assembly in neutral phosphate buffer at 28 °C. Then effects of acidic polysaccharides, such as sodium alginate (SA), chondroitin sulfate (CS), and hyaluronic acid (HA), on the formation and properties of self-assembled fibrillar gel were investigated. SA and CS prolonged gelling time, whereas HA had no obvious effect. SA made fibril network denser, while CS and HA induced the presence of larger ordered structures. All the acidic polysaccharides broadened the D-periodicity of fibrils. SA and HA increased the maximum mechanical strength of gel to 39.64 and 34.49 kN/m2, respectively, significantly higher than that of pure collagen gel (14.53 kN/m2), while that only 17.20 kN/m2 after CS introduced. HA had no evident effect on enzymatic resistance, while SA and CS decreased. Therefore, tilapia skin collagen with HA has a higher potential as a biomaterial than that with CS or SA.

One-step synthesis of Ni(OH)2/MWCNT nanocomposites for constructing a nonenzymatic hydroquinone/O2 fuel cell.

In this work, a H-type hydroquinone/O2 fuel cell was assembled and shows high energy density in neutral phosphate buffer solution at moderate temperature. The anodic material, Ni(OH)2/MWCNTs, was synthesized by a one-step hydrothermal synthesis method to oxidize hydroquinone. The cathode material, Pt/MWCNTs, was obtained by an electrodeposition method, and shows great oxygen reduction reaction (ORR) activity. The properties and the morphology of Ni(OH)2/MWCNT nanocomposites were characterized by TEM, XPS, EDS-mapping and electrochemical methods, like cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results show that Ni(OH)2/MWCNTs can effectively oxidize hydroquinone and play a dominant role in enhancing the fuel cell performance. The nonenzymatic fuel cell possesses a high power density of 0.24 mW cm−2 at a cell potential of 0.49 V.

Metallo‐Corroles Supported on Carbon Nanostructures as Oxygen Reduction Electrocatalysts in Neutral Media

In this work, we report the investigation of Fe and Co triphenylcorrole complexes supported on two different carbon supports as eletrocatalysts for the ORR in neutral pH media, comparing their performances with the corresponding tetraphenylporphyrin complexes. Cyclic voltammetry experiments were acquired in neutral phosphate buffer demonstrating that corroles exhibit a superior catalytic activity towards ORR than porphyrins, as demonstrated by more positive oxygen reduction peak potential (Epr) and half‐wave potential (E1/2) values of corroles. Also, iron complexes performed better than cobalt ones, showing an ORR activity even superior to that of platinum taken as reference, as demonstrated by RDE experiments. We investigated the role of the axial ligand on the ORR activity of the macrocycles, and we found that Epr and E1/2 values are more positive along the series: PPh3Co < py2Co = µ‐oxoFe2 < FeCl. By contrast, there was not much difference in activity supporting the porphyrinoids on carbon nanotubes or carbon black pearls, indicating that the effect of carbon support is less important to that of the axial ligand. The results allowed pointing at iron corroles as a promising class of molecular catalysts for application as cathodes in biolectrochemical systems at neutral pH, such as microbial fuel cells.

Investigation of surface topography of different root-end filling materials: An in vitro study

Aim: Although there are many materials that can be used for retrograde filling in surgical endodontics, none of them can be regarded as an ideal material yet. The purpose of this study was to compare the surface topography of three different root-end filling materials.Methods: 36 extracted single rooted human incisor teeth were cleaned and decoronated to standardized 10 mm root lengths. The root segments were prepared and 2 mm apical resection were performed. The samples were randomly separeted to three groups (Group A: Ca(OH)2, Group B: MTA Angelus, Group C: ProRoot MTA), each comprised of 12 roots. Materials were placed as 2 mm apical barriers and obturated with guttapercha and AH-Plus sealer. Each group dimidiated two subgroups (A1,A2,B1,B2,C1,C2). Groups A1,B1,C1 were stored in normal saline (NS), groups A2,B2,C2 were stored in neutral phosphate buffer saline (NPBS) solution and samples were incubated at 370C for 2 weeks. Stereomicroscope (32X) was used to photograph the root-end filling.Results: All specimens demonstrated white crystals formation and sediment over the root-end filling materials and on the superficial border of the root-end cavities’ wall as a white plague. A2,B2,C2 samples have more crystal sediment on root-end fillings than samples A1,B1,C1. Dissolution and corrosion were observed in groups A1, A2.Conclusions: The results of this study revealed that calcium hydroxide is more resorbable than MTA Angelus and ProRoot MTA. The crystals formation and precipitation were observed in neutral phosphate buffer saline solution was more than normal saline solution for all groups as a hydroxiapatite crystals.

Carbon nanodots chelated with metal ions as efficient electrocatalysts for enhancing performance of microbial fuel cell based on sulfate reducing bacteria

We report the electrocatalytic activity of a graphite electrode chemically coated with ultra-small nitrogen-doped carbon nanodots (N-doped C-dots), which formed an intermediate diazo-metal chelate phase. Its performance as cathode for enhanced current production was demonstrated in a dual-chamber microbial fuel cell (MFC) through synergistic cooperation with electroactive biofilm of sulfate-reducing bacteria (SRB) on the anode. For that purpose, the immobilized SRB biofilm on the anode facilitated direct transfer of electrons to the graphite surface by filaments network, known as nano-pili, which provided cell-to-cell link. A significantly improved acceleration of the electrons was measured on the cathode in the presence of chemically conjugated N-doped C-dots chelated with metal ions, because they acted as efficient electrocatalysts for oxygen reduction reaction (ORR) in a neutral phosphate buffer solution. As a result, the power density obtained from the occurred synergistic effect in MFC increased almost double higher than the initial value in the control experiment. The chemical resistance, exploitation life and the easy protocol for fabrication of the reported cathode coated with electrocatalytic nanolayer open up the possibility for new class cheap electrocatalytic electrodes with a wide practical applications in fuel cell engineering and technology.

Sonochemical synthesis of perovskite-type barium titanate nanoparticles decorated on reduced graphene oxide nanosheets as an effective electrode material for the rapid determination of ractopamine in meat samples

A simple and facile ultrasound based sonochemical method to incorporate Perovskite-type barium titanate (BaTiO3) nanoparticles inside the layered and reduced graphene oxide sheets (rGOs) is reported. BaTiO3@rGOs nanocomposite was characterized by FESEM, HRTEM, EDX, mapping, XRD, XPS and EIS. The results show that the decoration and also incorporation of BaTiO3 nanoparticles in the multi-layered and ultrasound reduced graphene oxide matrix. Non-enzymatic and differential pulse voltammetric sensor of ractopamine (food toxic) based on the BaTiO3@rGOs nanocomposite modified screen printed carbon electrode is developed. Compared with the original BaTiO3/SPCE and rGOs/SPCE, the BaTiO3@rGOs/SPCE displays excellent current response towards ractopamine and gives linearity in the range of 0.01–527.19 µM ractopamine in neutral phosphate buffer (pH 7.0). The BaTiO3@rGOs nanocomposite modified sensor also exhibits valuable ability of anti-interference to electroactive analytes. Furthermore, the as-prepared BaTiO3 NPs@rGOs/SPCE has been applied to the determination of ractopamine in pork and chicken samples.

Facile synthesis of mesoporous WS2 nanorods decorated N-doped RGO network modified electrode as portable electrochemical sensing platform for sensitive detection of toxic antibiotic in biological and pharmaceutical samples

We report a facile and ultrasound assisted sonochemical synthesis of a Tungsten disulfide nanorods decorated nitrogen-doped reduced graphene oxide based nanocomposite. The WS2 NRs/N-rGOs nanocomposite was characterized by FESEM, HRTEM, XRD, XPS and electrochemical methods and its application towards the electrochemical detection of organo-arsenic drug (coccidiostat). The WS2 NRs/N-rGOs modified SPCE was used for the electrochemical reduction of roxarsone (ROX) and it showed superior electrocatalytic performance in terms of reduction peak current and shift in overpotential when compared to those of WS2 NRs/SPCE, N-rGOs/SPCE and based SPCE. The WS2 NRs/N-rGOs modified SPCE showed an excellent sensing ability towards ROX in nitrogen saturated phosphate buffer (PB) then the other controlled modified and unmodified electrodes. The WS2 NRs/N-rGOs/SPCE displays high sensitive response towards ROX and gives wide linearity in the range of 0.1–442.6 µM ROX in neutral phosphate buffer (pH 7.0) and the sensitivity of the sensor is calculated as 14.733 µA µM−1 cm−2. The WS2 NRs/N-rGOs nanocomposite modified sensor also exhibits valuable ability of anti-interference to electroactive analytes. Furthermore, the as-prepared WS2 NRs/N-rGOs/SPCE has been applied to the determination of ROX in biological and pharmaceutical samples.

Quantum Chemical Study of the Mechanism of Water Oxidation Catalyzed by a Heterotrinuclear Ru2 Mn Complex.

The heterotrinuclear complex A {[RuII (H2 O)(tpy)]2 (μ-[MnII (H2 O)2 (bpp)2 ])}4+ [tpy=2,2':6',2''-terpyridine, bpp=3,5-bis(2-pyridyl)pyrazolate] was found to catalyze water oxidation both electrochemically and photochemically with [Ru(bpy)3 ]3+ (bpy=2,2'-bipyridine) as the photosensitizer and Na2 S2 O8 as the electron acceptor in neutral phosphate buffer. The mechanism of water oxidation catalyzed by this unprecedented trinuclear complex was studied by density functional calculations. The calculations showed that a series of oxidation and deprotonation events take place from A, leading to the formation of complex 1 (formal oxidation state of Ru1IV MnIII Ru2III ), which is the starting species for the catalytic cycle. Three sequential oxidations of 1 result in the generation of the catalytically competing species 4 (formal oxidation state of Ru1IV MnV Ru2IV ), which triggers the O-O bond formation. The direct coupling of two adjacent oxo ligands bound to Ru and Mn leads to the production of a superoxide intermediate Int1. This step was calculated to have a barrier of 7.2 kcal mol-1 at the B3LYP*-D3 level. Subsequent O2 release from Int1 turns out to be quite facile. Other possible pathways were found to be much less favorable, including water nucleophilic attack, the coupling of an oxo and a hydroxide, and the direct coupling pathway at a lower oxidation state (RuIV MnIV RuIV ).