Quercetin-rGO based mercury-free electrode for the determination of toxic Cd (II) and Pb (II) ions using DPASV technique.

Metal ion pollution poses serious threat to environment. Analysis of Cd (II) and Pb (II) ions using chemically modified mercury free electrode is a feasible routine analytical tool. Developing an electrode surface modified with conductive 2D carbon and metal complexing ligand created a synergetic effect towards sensitive and selective electrochemical determination of metal ions. The present study focused on green chemistry approach towards synthesis of reduced graphene oxide using a natural flavonoid (Quercetin) that acts as a reducing, functionalizing agent and also as metal complexing agent. This quercetin reduced graphene oxide (Q-rGO) was surface modified over paraffin wax impregnated graphite electrode. The resulting Q-rGO electrode was used as a mercury-free electrode for simultaneous analysis of Pb (II) and Cd (II) ions. Physico-chemical parameters of the synthesized Q-rGO and modified electrodes were characterized using X-ray diffraction, UV-Vis, FT-IR, and Raman spectrometer. The morphology of the material and surface topography of the modified electrode was observed using HR-TEM and FESEM, respectively. Cyclic voltammetry (CV) and AC impedance (EIS) were adopted for electrochemical characterization and Differential pulse anodic stripping voltammetry (DPASV) was chosen for simultaneous sensing of metal ions using Q-rGO electrode. Analytical parameters such as effect of electrolyte, effect of pH, preconcentration time and deposition potential were optimized. The experimental results suggested that the Q-rGO electrode is capable of sensing Pb (II) and Cd (II) ions individually and simultaneously. Inference from the calibration plot showed that the Q-rGO electrode was capable of sensing the concentration range of Cd (II) ion form 0.19 to 2.5 µgL-1 with LOD-0.05 µgL-1 and Pb (II) ions from 0.19 to 3.1 µgL-1 with LOD 0.06 µgL-1.

Electrochemical determination of 4-nitrophenol in environmental water samples using porous graphitic carbon nitride-coated screen-printed electrode.

We demonstrate a facile preparation of novel oxidized graphitic carbon nitride (O-gC3N4) applied as an efficient electrocatalyst for highly sensitive electrochemical detection of 4-nitrophenol (4-NP) in environmental water samples. As-prepared O-gC3N4 were characterized by attenuated total reflection infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction methods for the confirmation of different functional groups and structural phase of O-gC3N4. The surface morphology of the O-gC3N4 was characterized using field emission scanning electron microscopy and high-resolution transmission electron microscopy. Results revealed that the synthesized gC3N4 possessed acid functional groups, nanosheet with porous in nature. The O-gC3N4 was drop cast on the screen-printed electrode (SPE), and it was applied for electrochemical determination of 4-NP using cyclic voltammetry and differential pulse voltammetry (DPV) techniques. The O-gC3N4/SPE exhibited excellent electrocatalytic activity towards 4-NP detection. Under the optimized experimental conditions, the DPV response of O-gC3N4/SPE showed good linear range from 0.0033 to 0.313 µM with a detection limit (S/N = 3) of 0.075 µM. The developed electrode has successfully applied for the determination of 4-NP in different environmental water samples, and the results have shown satisfied.

Comparative evaluation of color stability of three composite resins in mouthrinse: An in vitro study.

AIM: The aim of this study was to compare the effect of chlorhexidine mouthrinse on the color stability between three different types of composites. MATERIALS AND METHODS: A total of 30 samples of size 10-mm length, 1-mm width, and 1-mm thickness were prepared on a customized microglass slide from each of the composite materials and immersed in 20 ml of distilled water followed by incubation at 37°C for 24 h. The samples were divided into three groups (n = 10) - Group I: A nanofilled composite, Filtek Z350XT (3M ESPE, St. Paul, USA); Group II: A microhybrid composite, Polofil Supra (Voco GmbH, Germany); and Group III: A nanoceramic composite, Ceram.x Sphere TEC (Dentsply, Konstanz, Germany). Baseline color values were recorded using a spectrophotometer (V-770 UV-Visible/NIR Spectrophotometer, Easton, Maryland, USA) according to the laboratory scale. After baseline color measurements, ten randomly selected specimens from each group were immersed in 20 ml of 0.2% chlorhexidine mouthrinse (Rexidin Plus, Aurangabad, India) for 24 h. The postimmersion color values of the samples were then recorded, respectively, using the same spectrophotometer. STATISTICAL ANALYSIS USED: The statistical analysis was done using one-way ANOVA followed by Tukey's post hoc test. RESULTS: Statistically significant difference was observed between the mean color change values in the three groups (P < 0.05) with the highest color change (delta E [ΔE]) in Group III (Nanoceramic composite). The ΔE for Group I (Nanofilled composite) was 3.16, Group II (Microhybrid composite) was 3.32, and Group III (Nanoceramic composite) was 3.51. CONCLUSION: All the three types of composites displayed color changes after immersion in mouthrinse, but the color shift depended on the material used, and the nanofilled composites (Filtek Z350XT, 3M ESPE, St. Paul, MN, USA) had higher color stability.

Synthesis, structural characterization and electrochemical studies switching of MWCNT/novel tetradentate ligand forming metal complexes on PIGE modified electrode by using SWASV.

A novel sensor of a square wave anodic stripping voltammetric (SWASV) determination of Pb(II) and Cd(II) with a Multiwall carbon nanotube MWCNT/(H2bpabza) novel tetradentate carboxamide ligand modified electrode is reported. The ligand was synthesized and prepared by the condensation of 2-pyridinecarboxylicacid and 2-aminobenzylamine, with triphenylphosphite as the activator and tetrabutylammonium bromide as the reaction medium. The ligand was characterized by UV-Visible spectroscopy, Fourier transform infrared spectroscopy, Raman studies, Nuclear magnetic resonance spectroscopy and scanning electron microscope methods. The ligand was characterized voltammetrically using redox couples Fe(CN)63-/4-, complemented with electrochemical impedance spectroscopy (EIS). The modified electrode has provided an electrochemical sensing platform for simultaneous determination of Pb(II) and Cd(II) ions in 0.1 M acetate buffer solution (ABS) (pH 4.5) have been evaluated. The detection limit of MWCNT/(H2bpabza) modified electrode toward Pb(II) and Cd(II) is 2.7 nM and 0.92 nM, (S/N = 3) respectively. The electrochemical parameters that exert influence on deposition and stripping of metal ions, such as supporting electrolytes, pH value and deposition time, were carefully studied. Linear response from 8.3 nM to 115 nM for both Pb(II) and Cd(II) metal ions were achieved with the modified electrode. The modified electrode was also successfully applied to the analysis of Pb(II) and Cd(II) in real sample with good recovery, ranging from 98.7-100%.

A nanocomposite consisting of porous graphitic carbon nitride nanosheets and oxidized multiwalled carbon nanotubes for simultaneous stripping voltammetric determination of cadmium(II), mercury(II), lead(II) and zinc(II).

A 3D nanocomposite consisting of porous graphitic carbon nitride nanosheets (p-g-C3N4-NSs) and oxidized multiwalled carbon nanotubes (O-MWCNTs) was prepared by simultaneous chemical oxidation of bulk g-C3N4 and bulk MWCNTs. This one-step oxidation results in the formation of acidic functional groups on the basal surfaces of both g-C3N4 and MWCNTs. Simultaneously, the O-MWCNTs are incorporated in-situ on the porous structure of p-g-C3N4. The acid functionalization and surface morphology of the nanocomposite were examined using attenuated total reflectance infrared spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy. The nanocomposite was used to modify a screen-printed electrode (SPE) which then was studied by using cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulse voltammetry. The modified SPE exhibits excellent sensitivity and selectivity towards the simultaneous detection of the heavy metal ions Cd(II), Hg(II), Pb(II) and Zn(II), typically at -0.78, +0.35, -0.5 and - 1.16 V (vs. Ag/AgCl). The detection limits (at S/N = 3) range between 8 and 60 ng L-1 under conditions of stripping analysis. The method was applied to the simultaneous detection of these ions in various (spiked) food samples. The results demonstrated the good accuracy and reproducibility of the method. Graphical abstract Schematic of a highly sensitive and selective electrochemical method for the simultaneous detection of four heavy metals. It is based on the use of a screen printed electrode (SPE) modified with 3D porous g-C3N4 and O-MWCNTs, and of anodic stripping voltammetry.

Interference of apex locator, pulp tester and diathermy on pacemaker function.

AIM: The purpose of this study was to evaluate the effects of three electronic apex locators (EAL), electric pulp tester (EPT) and diathermy on pacemaker function in vitro. MATERIALS AND METHODS: Three EALs: Root ZX (J. Morita Co., Tustin, CA, U.S.A.), Propex (Dentsply), Mini Apex locator (SybronEndo, Anaheim, CA, USA), EPT (Parkell pulp vitality tester Farmingdale, NY, USA) and Diathermy (Neomed 250 B) were tested for any interference with one pacemaker (A medtronic kappa KVDD901-serial number: PLE734632S). Directly connecting the pacemaker lead with the EAL/EPT/diathermy operating on a flat bench top, the telemetry wand was held directly over the pacemaker to monitor the pacing pattern for a period of 30 s. Pacemaker activity was continuously recorded on the telemetric programmer and electro gram (EGM) readings examined for pacer inhibition, noise reversion or inappropriate pacemaker pulses. RESULTS: All the three apex locators showed no pacing interference or background noise during its function or at rest. The EGM readings of EPT showed varying levels of background noise in between pacing however, this did not affect the normal pacing pattern and the pacing interval remained constant. EGM readings of diathermy showed an increase in the pacing interval (irregular pacing pattern) followed by complete inhibition of the pacing system. CONCLUSION: The tested EALs do not interfere with cardiac pacemaker function. The tested EPT showed varying levels of background noise but does not interfere with cardiac pacemaker function. Use of Diathermy interfered with the normal pacing, leading to complete inhibition of the pacing system.

Highly potential antifungal activity of quantum-sized silver nanoparticles against Candida albicans.

The antifungal activity of polyvinylpyrrolidone (PVP)-stabilized quantum-sized silver nanoparticles (SNPs) against the growth of Candida albicans has been demonstrated in the present study. C. albicans is a known opportunistic human pathogen causing superficial and systemic infections. Research data carried out on C. albicans so far have shown unequivocally that it develops resistance against conventional antifungal drugs and that the infections it causes are difficult to cure with conventional antifungal agents. Hence, it is urgent to find newer materials for the treatment of infections caused by C. albicans that must be safe for the host. PVP-capped SNPs were synthesized, and its surface plasmon band was observed at 410 nm. The growth of C. albicans was markedly inhibited when the cells were incubated with SNP. The minimum inhibitory concentration (MIC) of SNP was determined as 70 ng/ml, and this value is relatively lower when compared with the conventionally used antifungal drugs such as amphotericin B (0.5 µg/ml), fluconazole (0.5 µg/ml), and ketoconazole (8 µg/ml). The viability of SNP-treated cells was checked by measuring the metabolic activity using XTT assay. Field emission scanning electron microscopic (FE-SEM) and transmission electron microscopic (TEM) analyses of the cells treated with SNP have lost the structural integrity to a greater extent.

Synthesis and in vivo antidiabetic activity of novel dispiropyrrolidines through [3+2] cycloaddition reactions with thiazolidinedione and rhodanine derivatives.

The synthesis of a series of novel dispiropyrrolidines has been accomplished by 1,3-dipolar cycloaddition reaction with 5-arylidene-1,3-thiazolidine-2,4-dione and 5-arylidene-4-thioxo-1,3-thiazolidine-2-one derivatives as dipolarophiles. The structure and stereochemistry of the cycloadduct have been established by single crystal X-ray structure and spectroscopic techniques. Molecular docking studies were performed on 1FM9 protein. The synthesized compounds were screened for their antidiabetic activity on male Wistar rats.

A novel nanobiocomposite based glucose biosensor using neutral red functionalized carbon nanotubes.

The performance of a new glucose biosensor based on the combination of biocatalytic activity of glucose oxidase (GOx) with the electrocatalytic properties of CNTs and neutral red (NR) for the determination of glucose is described. This sensor is comprised of a multiwalled carbon nanotubes (MWNTs) conduit functionalized with NR and Nafion (Nf) as a binder and glucose oxidase as a biocatalyst. Neutral red was covalently immobilized on carboxylic acid groups of the CNTs via carbodiimide reaction. The functionalized MWNTs were characterized by microscopic, spectroscopic and thermal methods. The MWNT-NR-GOx-Nf nanobiocomposite was prepared by mixing the GOx solution with NR functionalized CNTs followed by mixing homogeneously with Nafion. The performance of the MWNT-NR-GOx-Nf nanobiocomposite modified electrode was examined by electrochemical impedance spectroscopy and cyclic voltammetry. The catalytic reduction of hydrogen peroxide liberated from the enzymatic reaction of glucose oxidase upon glucose with NR functionalized CNTs leads to the selective detection of glucose. The excellent electrocatalytic activity and the influence of nanobiocomposite film result in good characteristics such as low potential detection of glucose with a large determination range from 1 x 10(-8) to 1 x 10(-3)M with a detection limit of 3 x 10(-9)M glucose, a short response time (with 4s), good stability and anti-interferent ability. The improved electrocatalytic activity and stability made the MWNT-NR-GOx-Nf nanobiocomposite biosensor system a potential platform to immobilize different enzymes for other bioelectrochemical applications.

3-(4-Fluoro-phenyl)-1-[1'-(4-fluoro-phenyl)-2-oxo-5',6',7',7a'-tetra-hydro-1H-indole-3(2H)-spiro-3'(2'H)-1H'-pyrrol-izin-2'-yl]prop-2-en-1-one.

In the title compound, C(29)H(24)F(2)N(2)O(2), one of the pyrrolidine rings of the pyrrolizine system is disordered over two sites, with occupancy factors 0.734:0.266 (12). Both components of the disordered pyrrolidine ring adopt envelope conformations, whereas the other pyrrolidine ring adopts a twist conformation. The mol-ecules are linked into centrosymmetric dimers by N-H⋯O hydrogen bonds and the dimers are connected via C-H⋯π inter-actions. The crystal structure is also stabilized by inter-molecular C-H⋯F hydrogen bonds.

1-[2-Oxo-1'-phenyl-2',3',5',6',7',7a'-hexa-hydroindoline-3-spiro-3'-1'H-pyrrolizin-2'-yl]-3-phenyl-prop-2-en-1-one.

In the title compound, C(29)H(26)N(2)O(2), one of the pyrrolidine rings in the pyrrolizine system is disordered, with site occupancies of ca 0.55 and 0.45. Both components of the disordered pyrrolidine ring adopt envelope conformations, whereas the other pyrrolidine ring adopts a twist conformation. The mol-ecules are linked into centrosymmetric dimers by N-H⋯O hydrogen bonds and the dimers are connected via C-H⋯π inter-actions.

Amperometric hydrogen peroxide sensor based on a sol-gel-derived ceramic carbon composite electrode with toluidine blue covalently immobilized using 3-aminopropyltrimethoxysilane.

A carbon composite amperometric hydrogen peroxide sensor has been developed using a sol-gel technique. Toluidine blue (TB), which acts as the redox mediator, was covalently immobilized via glutaraldehyde crosslinking with an organically modified silane, namely 3-aminopropyltrimethoxysilane (APTMOS). Methyltrimethoxysilane (MTMOS) was used as the additional monomer; this controls the hydrophobicity of the electrode surface, thus limiting the wettability. The immobilization of TB within the sol-gel matrix was confirmed with FTIR studies. The sol-gel mixture containing TB immobilized in APTMOS and MTMOS was mixed with graphite powder in order to prepare the carbon composite electrode. The electrode was characterized using voltammetric techniques and its electrocatalytic activity for the reduction of hydrogen peroxide was also studied. The carbon composite electrode has the advantage of sensing H(2)O(2) at a lower potential and with a higher sensitivity, and interferences due to ascorbic acid, uric acid and acetaminophen were greatly minimized. The linear range for the determination of H(2)O(2) extends from 5.37 x 10(-6) to 6.15 x 10(-3) M, with a correlation coefficient of 0.9981. The detection limit was found to be 2.15 x 10(-6) M. The covalent immobilization of TB effectively prevents the leakage of the water-soluble mediator during measurements. The modified electrode, aside from electrocatalyzing the reduction of H(2)O(2), exhibits distinct advantages in terms of surface renewal in the event of surface fouling, as well as simple preparation, good chemical and mechanical stability, and good reproducibility.

Amperometric sensor for the determination of ascorbic acid based on Cobalt hexacyanoferrate modified electrode fabricated through a new route.

A new approach was attempted to prepare a chemically modified electrode using Cobalt hexacyanoferrate (CoHCF) as the redox mediator and to study its stability and electrocatalytic activity for ascorbic acid (AA) oxidation. The basic principle underlying the electrode modification is the coordination of cobalt ion with the amino nitrogen of aniline adsorbed on the surface of a graphite rod. This surface was subsequently derivatized with ferrocyanide to get CoHCF film on the electrode surface. The CoHCF modified electrode as prepared above was characterized using cyclic voltammetry. The effect of scan rate, supporting electrolyte and pH of the medium on the performance of the modified electrode was investigated. The CoHCF modified electrode exhibited good electrocatalytic activity towards the oxidation of ascorbic acid and gave a linear response from 5.52 x 10(-5) M to 3.23 x 10(-2) M with a correlation coefficient of 0.9929. The detection limit was found to be 3.33 x 10(-5) M. Hydrodynamic voltammetry and chronoamperometry studies for the oxidation of ascorbic acid were also carried out. The electrode was highly stable and exhibited good reproducibility. This modified electrode was also applied for the determination of ascorbic acid in commercial samples.