Development and characterization of hydroquinone-loaded nanofiber for topical delivery: effect of chitosan

Hydroquinone (HQ) loaded polymer solution was electrospun for its topical application. Nanofibers were then investigated in terms of stability, drug release, and antifungal activity. The effect of chitosan (CS) was investigated on the viscosity, stability, drug release, and antifungal activity of the developed formulation. Results indicate a significantly stable HQ-loaded nanofiber formulation. The addition of CS caused hydration of the drug delivery system and enhanced drug release but reduced its stability. HQ-loaded nanofiber mat showed significant antifungal activity, however, there was no inhibition zone in samples containing CS.     

The Cu-MOF-199/single-walled carbon nanotubes modified electrode for simultaneous determination of hydroquinone and catechol with extended linear ranges and lower detection limits

A novel electrochemical sensor based on Cu-MOF-199 [Cu-MOF-199 = Cu₃(BTC)₂ (BTC = 1,3,5-benzenetricarboxylicacid)] and SWCNTs (single-walled carbon nanotubes) was fabricated for the simultaneous determination of hydroquinone (HQ) and catechol (CT). The modification procedure was carried out through casting SWCNTs on the bare glassy carbon electrode (GCE) and followed by the electrodeposition of Cu-MOF-199 on the SWCNTs modified electrode. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) were performed to characterize the electrochemical performance and surface characteristics of the as-prepared sensor. The composite electrode exhibited an excellent electrocatalytic activity with increased electrochemical signals towards the oxidation of HQ and CT, owing to the synergistic effect of SWCNTs and Cu-MOF-199. Under the optimized condition, the linear response range were from 0.1 to 1453 μmol L⁻¹ (R_HQ = 0.9999) for HQ and 0.1–1150 μmol L⁻¹ (R_CT = 0.9990) for CT. The detection limits for HQ and CT were as low as 0.08 and 0.1 μmol L⁻¹, respectively. Moreover, the modified electrode presented the good reproducibility and the excellent anti-interference performance. The analytical performance of the developed sensor for the simultaneous detection of HQ and CT had been evaluated in practical samples with satisfying results.     

聚吡咯/纳米SiO_2复合材料的制备及氧化性能

采用化学氧化法制备聚吡咯/纳米Si O2(PPy/n Si O2)复合材料,通过扫描电子显微镜和红外光谱对其进行表征,并将其应用到对苯二酚的氧化反应中.结果表明,PPy/n Si O2复合材料中,PPy较均匀地负载在纳米Si O2表面.在弱酸性介质中,PPy/n Si O2对对苯二酚具有很好的氧化性能.反应2 h内,对苯二酚的氧化过程符合表观一级反应动力学.结合紫外-可见光谱法分析表明,聚吡咯通过与对苯二酚之间的氢键相互作用形成聚吡咯活性中间体,将对苯二酚氧化为对苯醌,聚吡咯具有氧化剂和催化剂的双重功能.     

全氟磺酸功能化碳纳米管的制备及其催化性能

采用全氟磺酸-全氟乙烯共聚物的液相沉积方法制备了全氟磺酸功能化碳纳米管催化剂,利用N2吸附、扫描电子显微镜、透射电子显微镜、傅里叶变换红外光谱以及酸碱滴定等方法对材料的结构和酸性进行了表征,考察了温度和溶剂对催化剂稳定性的影响.结果表明,催化剂在极性和非极性溶液中均十分稳定,并且具有良好的热稳定性,使用温度可达300°C.该催化剂在对苯二酚与叔丁醇的烷基化反应中表现出优异的催化性能,其催化活性与稳定性均高于聚苯乙烯磺酸功能化的碳纳米管催化剂.     

Enhanced Sensitive Electrochemical Sensor for Simultaneous Catechol and Hydroquinone Detection by Using Ultrasmall Ternary Pt-based Nanomaterial

The simple and effective method for the novel synthesis of Pt-based nanoparticle was presented with high efficiency. The sensitive catalyst for the simultaneous detection of catechol and hydroquinone was prepared by depositing ternary metal complex on fluorine-doped tin-oxide (FTO). The composition and morphology of nanomaterials were characterized by TEM, HRTEM, XRD, XPS, and EDS (energy dispersive spectroscopy). The size of the Pt-based nanomaterial was about 5±1 nm. The electrochemical performance of the modified catalyst was studied by CV, DPV, and EIS. The modified PtNiCu@FTO catalyst possessed good electro-oxidation activity for hydroquinone and catechol and used for simultaneous detection of catechol and hydroquinone at scan rate of 20 mV s⁻¹ (vs. Ag/AgCl). Detection responses were found in the ranges of 5–2900 μM for hydroquinone and 5–3000 μM for catechol. The detection limits (LOD) for HQ and CC were observed as 0.35 and 0.29 μM, respectively. The sensitivity of HQ and CC were 1515.55 and 1485 μA mM⁻¹ cm⁻², respectively. The prepared nanomaterial were effectively applied for the determination of CC and HQ in real samples.     

Imidazolium Based Surface Active Ionic Liquids as Novel Micellar Media for Simultaneous and Sensitive Electrochemical Detection of Dopamine and Ascorbic Acid

Surface active ionic liquid (SAIL) micelle assisted, simultaneous and highly sensitive electrochemical sensing of dopamine (DA) and ascorbic acid (AA) is presented. Results presented herein establish that SAILs viz.1‐dodecyl‐3‐methyl imidazolium chloride ([DDMIM][Cl]), 1‐octyl‐3‐methyl imidazolium chloride ([OMIM][Cl]) and 1‐butyl‐3‐methyl imidazolium chloride ([BMIM][Cl]) exhibit a probe and SAIL nature/concentration specific impact on the redox behaviour of hydroquinone (H₂Q), dopamine (DA) and ascorbic acid (AA). To our observations, the electrochemical behaviour of DA and AA is affected oppositely by SAILs with the apparent effects being more appreciable in presence of [DDMIM][Cl]. In the presence of [DDMIM][Cl] micelles, the electro‐oxidation of AA was observed to occur at potentials about 350 mV less positive than required for electrooxidation of DA, an important advantage that minimises the interference of former in sensing of the later. The peak to peak potential separation of 350 mV observed in presence of [DDMIM][Cl] micelles is the largest to be reported so far. The DPV signal for DA and AA displayed a linear response in the concentration range of 6.6 to 99.9 μM and 6.6 to 131.5 μM respectively. Very low detection limits of 0.0161 μM for DA in presence of 39.8 μM AA and 0.0227 μM for AA in presence of 39.8 μM DA were estimated in micellar phase of [DDMIM][Cl].     

Synthesis of size tunable monodispersed silver nanoparticles and the effect of size on SERS enhancement

Spherical and monodispersed silver nanoparticles (AgNPs) are ideal for fundamental research as the contribution from size and shape can be accounted for in the experimental design. In this paper a seeded growth method is presented, whereby varying the concentration of sodium borohydride-reduced silver nanoparticle seeds, different sizes of stable spherical nanoparticles with a low polydispersity nanoparticles are produced using hydroquinone as a selective reducing agent. The surface-enhanced Raman scattering (SERS) enhancement factor for each nanoparticle size produced (17, 26, 50, and 65 nm) was then assessed using three different analytes, rhodamine 6G (R6G), malachite green oxalate (MGO) and thiophenol (TP). The enhancement factor gives an indication of the Raman enhancement effect by the nanoparticle. Using non-aggregated conditions and two different laser excitation wavelength (633 nm and 785 nm) it is shown that an increase in particle size results in an increased enhancement for each analyte used.     

Surface characterization and catalytic evaluation of copper-promoted Al-MCM-41 toward hydroxylation of phenol

The Mobil Composition of Matter No. 41 (MCM-41) containing Cu and Al with Si/Al ratios varying from 100 to 10 and 1 to 6 wt.% of Cu was synthesized under hydrothermal and impregnation conditions, respectively. The samples were characterized by nitrogen adsorption–desorption measurements, X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS), temperature-programmed reduction (TPR), temperature-programmed desorption (TPD), and ²⁹Si and ²⁷Al magic-angle spinning–nuclear magnetic resonance (MAS–NMR) spectra. X-ray diffraction patterns indicate that the modified materials retain the standard MCM-41 structure. TPR patterns show the two-step reduction of Cu species. TPD study shows that Cu-impregnated Al-MCM-41 samples are more acidic than Al-MCM-41. From the MAS–NMR it was confirmed that most of the Al atoms are present tetrahedrally within the framework and some are present octahedrally in extraframework position. Impregnation of Cu shifted Al to the extraframework position. The catalytic activity of the samples toward hydroxylation of phenol in aqueous medium was evaluated using H₂O₂ as the oxidant at 80 °C. The effects of reaction parameters such as temperature, catalyst amount, amount of H₂O₂, and solvent were also investigated. Sample containing 4 wt.% copper-loaded Al-MCM-41-100 showed high phenol conversion (78%) with 68% catechol and 32% hydroquinone selectivity.     

Real-time probing of the growth dynamics of nanoparticles using potentiometric ion-selective electrodes

This Communication demonstrates the ability of potentiometric ion-selective electrodes (ISE) to probe the growth dynamics of metal nanoparticles in real-time. The new monitoring capability is illustrated using a solid-contact silver ISE for monitoring the hydroquinone-induced precipitation of silver on gold nanoparticle seeds. Potential-time recordings obtained under different conditions are used to monitor the depletion of the silver ion during the nanoparticle formation and shed useful insights into the growth dynamics of the nanoparticles. Such potentiometric profiles correlate well with the analogous optical measurements. The new real-time electrochemical probing of the particle growth process reflects the direct, rapid and sensitive response of modern ISE to changes in the level of the precipitated metal ion from the bulk solution and holds considerable promise for probing the preparation of different nanoscale materials.     

Discrimination and simultaneous determination of hydroquinone and catechol by tunable polymerization of imidazolium-based ionic liquid on multi-walled carbon nanotube surfaces

Tunable polymerization of ionic liquid on the surfaces of multi-walled carbon nanotubes (MWCNTs) was achieved by a mild thermal-initiation-free radical reaction of 3-ethy-1-vinylimidazolium tetrafluoroborate in the presence of MWCNTs. Successful modification of polymeric ionic liquid (PIL) on MWCNTs surfaces (PIL-MWCNTs) was demonstrated by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy. The resulting PIL-MWCNTs possessed unique features of high dispersity in aqueous solution and tunable thickness of PIL layer, due to positive imidazole groups along PIL chains and controllable ionic liquid polymerization by tuning the ratio of precursor. Based on cation-π interaction between the positive imidazole groups on PIL-MWCNTs surface and hydroquinone (HQ) or catechol (CC), excellent discrimination ability toward HQ and CC and improved simultaneous detection performance were achieved. The linear range for HQ and CC were 1.0 × 10⁻⁶ to 5.0 × 10⁻⁴ M and 1.0 × 10⁻⁶ to 4.0 × 10⁻⁴ M, respectively. The detection limit for HQ was 4.0 × 10⁻⁷ M and for CC 1.7 × 10⁻⁷ M (S/N = 3), correspondingly.