Highly sensitive determination of atropine using cobalt oxide nanostructures: Influence of functional groups on the signal sensitivity

This study describes sensitive determination of atropine using glassy carbon electrodes (GCE) modified with Co₃O₄ nanostructures. The as-synthesised nanostructures were grown using cysteine (CYS), glutathione (GSH) and histidine (HYS) as effective templates under hydrothermal action. The obtained morphologies revealed interesting structural features, including both cavity-based and flower-shaped structures. The as-synthesised morphologies were noted to actively participate in electro-catalysis of atropine (AT) drug where GSH-assisted structures exhibited the best signal response in terms of current density and over-potential value. The study also discusses the influence of functional groups on the signal sensitivity of atropine electro-oxidation. The functionalisation was carried with the amino acids originally used as effective templates for the growth of Co₃O₄ nanostructures. The highest increment was obtained when GSH was used as the surface functionalising agent. The GSH-functionalised Co₃O₄-modified electrode was utilised for the electro-chemical sensing of AT in a concentration range of 0.01–0.46 μM. The developed sensor exhibited excellent working linearity (R² = 0.999) and signal sensitivity up to 0.001 μM of AT. The noted high sensitivity of the sensor is associated with the synergy of superb surface architectures and favourable interaction facilitating the electron transfer kinetics for the electro-catalytic oxidation of AT. Significantly, the developed sensor demonstrated excellent working capability when used for AT detection in human urine samples with strong anti-interference potential against common co-existing species, such as glucose, fructose, cysteine, uric acid, dopamine and ascorbic acid.     

Kinetic and thermodynamic interplay of cation ingress and egress at a TCNQ-modified electrode in contact with aqueous electrolyte mixtures containing Co(II) and Ni(II) cations

In this study, kinetic and thermodynamic aspects associated with the selective uptake/release of divalent cations from/into an equimolar (0.1 M) aqueous electrolyte mixture of Co²⁺ and Ni²⁺ cations at TCNQ_(s)│electrode_(s)│electrolyte_(aq) triple phase boundary junction are probed. Results derived from cyclic voltammetry demonstrate that competitive insertion of either Co²⁺ _(aq) or Ni²⁺ _(aq) or both cations can be kinetically controlled and that the thermodynamic properties can be described in terms of midpoint potentials (E _m). The effect of voltammetric scan rate, electrolysis time, electrolyte concentration, temperature, and method of electrode modification on the preferential selection of Co²⁺ _(aq) or Ni²⁺ _(aq) cations have been explored. Importantly, the large separation in peak potential (ΔE _p observed for the redox-based TCNQ/[M(TCNQ)₂(H₂O)₂] solid–solid transformation; ΔE _p?=?250 mV for Co²⁺ vs 140 mV for Ni²⁺) under conditions of cyclic voltammetry are consistent with an electrochemically irreversible, but chemically reversible interconversion for both systems. The kinetic and/or thermodynamic implications of the ΔE _p values are discussed in terms of nucleation–growth and miscibility gap theories. From a thermodynamic perspective, the ~55 mV difference in E _m for the two systems suggests that TCNQ^?– prefers to accommodate Co²⁺ _(aq) cations so that the reaction [Ni(TCNQ)₂(H₂O)₂]_(s)?+?Co²⁺ _(aq) ? [Co(TCNQ)₂(H₂O)₂]_(s)?+?Ni²⁺ _(aq) is thermodynamically favored and the estimated equilibrium constant (K _eq?=?50) attests that the reaction lies in favor of the Co-TCNQ system. Atomic force microscopy (AFM) monitoring of the changes that accompany the TCNQ/[M(TCNQ)₂(H₂O)₂] transformations reveals that the morphology and crystal size of electrochemically generated Co- and Ni-TCNQ systems are substantially different from each other and from the parent TCNQ crystals with the kinetically favored [Ni(TCNQ)₂(H₂O)₂] needles being much shorter than the thermodynamically favored [Co(TCNQ)₂(H₂O)₂] analogue, thereby enabling their facile identification in AFM images.

Tuning the electrocrystallization parameters of semiconducting Co[TCNQ]2-based materials to yield either single nanowires or crystalline thin films

Electrocrystallization of single nanowires and/or crystalline thin films of the semiconducting and magnetic Co[TCNQ]2(H2O)2 (TCNQ=tetracyanoquinodimethane) charge-transfer complex onto glassy carbon, indium tin oxide, or metallic electrodes occurs when TCNQ is reduced in acetonitrile (0.1 M [NBu4][ClO4]) in the presence of hydrated cobalt(II) salts. The morphology of the deposited solid is potential dependent. Other factors influencing the electrocrystallization process include deposition time, concentration, and identity of the Co2+(MeCN) counteranion. Mechanistic details have been elucidated by use of cyclic voltammetry, chronoamperometry, electrochemical quartz crystal microbalance, and galvanostatic methods together with spectroscopic and microscopic techniques. The results provide direct evidence that electrocrystallization takes place through two distinctly different, potential-dependent mechanisms, with progressive nucleation and 3-D growth being controlled by the generation of [TCNQ]*- at the electrode and the diffusion of Co2+(MeCN) from the bulk solution. Images obtained by scanning electron microscopy reveal that electrocrystallization of Co[TCNQ]2(H2O)2 at potentials in the range of 0.1-0 V vs Ag/AgCl, corresponding to the [TCNQ]0/*- diffusion-controlled regime, gives rise to arrays of well-separated, needle-shaped nanowires via the overall reaction 2[TCNQ]*-(MeCN)+Co2+(MeCN)+2H2O right harpoon over left harpoon {Co[TCNQ]2(H2O)2}(s). In this potential region, nucleation and growth occur at randomly separated defect sites on the electrode surface. In contrast, at more negative potentials, a compact film of densely packed, uniformly oriented, hexagonal-shaped nanorods is formed. This is achieved at a substantially increased number of nucleation sites created by direct reduction of a thin film of what is proposed to be cobalt-stabilized {(Co2+)([TCNQ2]*-)2} dimeric anion. Despite the potential-dependent morphology of the electrocrystallized Co[TCNQ]2(H2O)2 and the markedly different nucleation-growth mechanisms, IR, Raman, elemental, and thermogravimetric analyses, together with X-ray diffraction, all confirmed the formation of a highly pure and crystalline phase of Co[TCNQ]2(H2O)2 on the electrode surface. Thus, differences in the electrodeposited material are confined to morphology and not to phase or composition differences. This study highlights the importance of the electrocrystallization approach in constructing and precisely controlling the morphology and stoichiometry of Co[TCNQ]2-based materials.     

Synthesis of Sheet Like Nanostructures of NiO Using Potassium Dichromate as Surface Modifying Agent for the Sensitive and Selective Determination of Amlodipine Besylate (ADB) Drug

The monitoring of hypertension drugs is very critical and important to sustain a healthy life. In this study, we have synthesized nickel oxide (NiO) nanostructures using potassium dichromate as surface modifying agent by hydrothermal method. These NiO nanostructures were found highly active for the oxidation of ADB besylate (ADB). The unit cell structure and morphology were investigated by scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) techniques. The SEM study has confirmed the nano sheet like morphology and XRD analysis has described the cubic unit arrays of NiO. After the physical characterization, NiO nanostructures were used to modify the surface of glassy carbon electrode (GCE) by drop casting method. Then cyclic voltammetry (CV) was used to characterize the electrochemical activity of NiO nanostructures in the0.1 M phosphate buffer solution of pH 10.0 and a well resolved oxidation peak was identified at 0.70 V. The linear range for the NiO nanostructures was observed from 20–90 nM with a regression coefficient of 0.99 using CV. The calculated limit of detection (LOD) was 2.125 nM and the limit of quantification (LOQ) was 4.08 nM. Further to validate the CV calibration plot, an amperometry experiment was performed on the NiO nanostructures and sensors exhibited a linear range of 10 nM to 115 nM with LOD of 1.15 nM. The proposed approach was successfully used for the determination of ADB from commercial tablets and it reveals that the sensor could be capitalized to monitor ADB concentrations from pharmaceutical products. The use of potassium dichromate as a surface modifying agent for the metal oxide nanostructures may be of great interest to manipulate their crystal and surface properties for the extended range of biomedical and energy related applications.     

Enzymes and phytochemicals from neem extract robustly tuned the photocatalytic activity of ZnO for the degradation of malachite green (MG) in aqueous media

The malachite green (MG) is very difficult to degrade in water; thus, it needs an efficient photocatalyst. In this study, neem extract was used to tune the surface and crystal properties of ZnO nanostructures for the photodegradation of MG. The biosynthesized ZnO samples were prepared by hydrothermal method in the presence of 5, 10 and 15 mL of neem extract. The structural characterization has shown nanoparticle like morphology of ZnO as revealed by scanning electron microscopy (SEM) and hexagonal phase was confirmed by powder X-ray diffraction (XRD) technique. The XRD analysis has shown a shift in the 2 theta towards lower angle for ZnO with increasing amount of neem extract. Also, the crystallite particle size of ZnO was decreased with increasing neem extract. The UV–visible spectroscopy has shown the decrease in the optical band gap of ZnO, and the lowest band gap is possessed by ZnO sample produced with 15 mL of neem extract. The ZnO sample obtained with 15 mL of neem extract has shown approximately 99% degradation efficiency for MG for 70 min in aqueous solution. The superior photocatalytic activity of ZnO sample with 15 mL of neem extract could be attributed from the decrease in charge recombination rate due to the decreased optical band gap and particle size.

     

Copper vanadate nanowires-based MIS capacitors: synthesis,characterization, and their electrical charge storage applications

Dielectric properties of porous glass nanocomposites with TGS crystals embedded into six porous matrices with average pore size from 5 to 312 nm were investigated in the temperature range from 280 to 380 K at selected frequencies. The results are discussed based on the effect of the particle size on the phase transition temperature of TGS nanocomposites. Temperature–size phase diagram of TGS composites was derived. Non-monotonic character of the temperature-driven phase transition (T _p) with the decreasing particle size was determined. The nature of the T _p variation can be ascribed to the size-effect theoretically predicted by Zhong et al. (Phys Rev B 50:698–703, 1994).     

A window-space-directed assembly strategy for the construction of supertetrahedron-based zeolitic mesoporous metal–organic frameworks with ultramicroporous apertures for selective gas adsorption

Despite their scarcity due to synthetic challenges, supertetrahedron-based metal–organic frameworks (MOFs) possess intriguing architectures, diverse functionalities, and superb properties that make them in-demand materials. Employing a new window-space-directed assembly strategy, a family of mesoporous zeolitic MOFs have been constructed herein from corner-shared supertetrahedra based on homometallic or heterometallic trimers [M₃(OH/O)(COO)₆] (M₃ = Co₃, Ni₃ or Co₂Ti). These MOFs consisted of close-packed truncated octahedral cages possessing a sodalite topology and large β-cavity mesoporous cages (∼22 Å diameter) connected by ultramicroporous apertures (∼5.6 Å diameter). Notably, the supertetrahedron-based sodalite topology MOF combined with the Co₂Ti trimer exhibited high thermal and chemical stability as well as the ability to efficiently separate acetylene (C₂H₂) from carbon dioxide (CO₂).

A series of supertetrahedron (ST)-based sodalite (sod)-topology zeolitic MOFs specimens ST-sod-MOFs featuring ultramicroporous square windows and a mesoporous sodcage have been synthesized via a window-space-directed assembly approach.     

Chiral Frustrated Lewis Pair@Metal-Organic Framework as a New Platform for Heterogeneous Asymmetric Hydrogenation

Asymmetric hydrogenation, a seminal strategy for the synthesis of chiral molecules, remains largely unmet in terms of activation by non-metal sites of heterogeneous catalysts. Herein, as demonstrated by combined computational and experimental studies, we present a general strategy for integrating rationally designed molecular chiral frustrated Lewis pair (CFLP) with porous metal–organic framework (MOF) to construct the catalyst CFLP@MOF that can efficiently promote the asymmetric hydrogenation in a heterogeneous manner, which for the first time extends the concept of chiral frustrated Lewis pair from homogeneous system to heterogeneous catalysis. Significantly, the developed CFLP@MOF, inherits the merits of both homogeneous and heterogeneous catalysts, with high activity/enantio-selectivity and excellent recyclability/regenerability. Our work not only advances CFLP@MOF as a new platform for heterogeneous asymmetric hydrogenation, but also opens a new avenue for the design and preparation of advanced catalysts for asymmetric catalysis.     

Synthesis and characterization of microstructured sheets of semiconducting Ca[TCNQ]2 via redox-driven solid-solid phase transformation of TCNQ microcrystals

Microstructured sheets of semiconducting Ca[TCNQ]₂ (TCNQ = 7,7,8,8-tetracyanoquinodimethane) have been synthesized via electrochemically driven (TCNQ)/Ca[TCNQ]₂ solid-solid phase transformation that occurs upon one-electron reduction of solid TCNQ, mechanically attached to an electrode surface, in the presence of an aqueous Ca²⁺ _(aq) electrolyte solution. Voltammetric probing of the electrochemically irreversible TCNQ/Ca[TCNQ]₂ interconversion revealed that it is highly dependent on scan rate and Ca²⁺ _(aq) electrolyte concentration. This voltammetric behavior, supported by double potential-step chronoamperometric evidence, clearly attests that formation of Ca[TCNQ]₂ takes place via a rate-determining nucleation/growth process, which involves ingress of Ca²⁺ _(aq) cations into the TCNQ^·? crystal lattice at the triple phase TCNQ/TCNQ^·? _(s)│GC_(s)│Ca²⁺ _(aq) electrolyte junction. The overall redox process associated with this chemically reversible solid-solid transformation can be described by the equation: TCNQ⁰ _(S)?+?2e^??+?Ca²⁺ _(aq) ? {Ca[TCNQ]₂}_(S). SEM characterization of the morphology of the generated Ca[TCNQ]₂ material showed the formation of microstructured sheets, which are substantially different from those of parent TCNQ crystals and the needle-shaped crystals of group I cations (M⁺?=?Li, Na, K, Rb, and Cs). The kinetic and thermodynamic implications of the ΔE _p and E _m values as a function of scan rate are discussed in terms of nucleation–growth and their relevance to those reported for the conceptually related group I cations and binary M[TCNQ]₂ (M²⁺?=?Mn, Fe, Co, and Ni)-based coordination polymers.     

Novel Cr (III), Fe (III) and Ru (III) Vanillin Based Metallo‐Pharmaceuticals for Cancer and Inflammation Treatment: Experimental and Theoretical Studies

In this study, three novel complexes comprising trivalent Cr (III), Fe (III) and Ru (III) with imine ligand derived from 2‐amino‐3‐hydroxypyridine and o‐vanillin (H₂L) have been synthesized and characterized via wide range of spectroscopic and analytical tools such as ¹H NMR and ¹³C NMR, infrared (IR) and UV–Vis spectrophotometry, conductivity and magnetic measurements. The obtained results along with DFT data confirmed a 1:1 (metal: ligand) stoichiometry with non‐planner geometries for the three complexes. The binding action and the docking study of the prepared metal‐complexes to calf thymus DNA was also studied by absorption spectra and viscosity technique, which revealed that the three complexes interact strongly with DNA through intercalative binding mode. Significantly, these metal‐imine complexes showed strong and efficient anti‐inflammatory and antimicrobial activities against various gram‐positive (Microccus luteus), gram‐negative (Escherichia coli and Serratia marcescence) bacteria, and three strains of fungus. Moreover, all complexes exhibited more potent cytotoxicity effect on the outgrowth of different types of carcinoma cells, including human colon (HCT‐116 cell line), breast (MCF‐7 cell line), and hepatic cellular (HepG‐2), than the clinically‐proven Vinblastine standard.