Measuring local pH in electrochemistry

Localized pH measurements are important in various areas of electrochemistry, from corrosion to bio-electrochemistry and electrocatalysis. Different techniques are available to perform these measurements and offer numerous possibilities in terms of spatial and temporal resolution, sensitivity, and precision. In this brief review we present the recent progress made and summarize the main techniques available for localized pH measurements in electrochemistry such as scanning probe techniques (SECM, SICM, SIET), laser (confocal) fluorescence microscopy, rotating ring-disc electrode (RRDE) voltammetry, and infra-red spectroscopy, among others.     

In Vitro Cytotoxic Protective Effect of Alginate-Encapsulated Capsaicin Might Improve Skin Side Effects Associated with the Topical Application of Capsaicin

Chronic neuropathic pain, particularly peripheral pain, is a cause of great concern for diabetic patients. Current treatments include numerous agents such as capsaicinoids, a known deterrent of neuropathic pain despite the inconvenience associated with local side effects. In this context, the current work aims to elucidate the potential mechanisms involved in cytotoxicity by capsaicin and proposes an efficient formulation of capsaicin in alginate microcapsules, which significantly reduces side effects from capsaicin topical administration. For this, human dermal fibroblast cells were treated with alginate-microencapsulated capsaicin extracts and screened for potential cytotoxic effects produced by the treatment. Cell viability and morphology were examined, as well as oxidative stress status and anti-inflammatory potential. Our results show that the alginate encapsulated formulation of capsaicin exerted lower cytotoxic effects on human dermal fibroblasts as measured by cell viability and reactive oxygen species (ROS) production. Furthermore, the expression profiles of inflammatory cytokines were significantly altered by the treatment as compared with the control culture.     

Identification of a Prenyl Chalcone as a Competitive Lipoxygenase Inhibitor: Screening,Biochemical Evaluation and Molecular Modeling Studies

Cyclooxygenase (COX) and lipoxygenase (LOX) are key targets for the development of new anti-inflammatory agents. LOX, which is involved in the biosynthesis of mediators in inflammation and allergic reactions, was selected for a biochemical screening campaign to identify LOX inhibitors by employing the main natural product library of Brazilian biodiversity. Two prenyl chalcones were identified as potent inhibitors of LOX-1 in the screening. The most active compound, (E)-2-O-farnesyl chalcone, decreased the rate of oxygen consumption to an extent similar to that of the positive control, nordihydroguaiaretic acid. Additionally, studies on the mechanism of the action indicated that (E)-2-O-farnesyl chalcone is a competitive LOX-1 inhibitor. Molecular modeling studies indicated the importance of the prenyl moieties for the binding of the inhibitors to the LOX binding site, which is related to their pharmacological properties.     

Zn(ferulate)-LSH Systems as Multifunctional Filters

Excessive UV solar radiation exposure causes human health risks; therefore, the study of multifunctional filters is important to skin UV protective ability and also to other beneficial activities to the human organism, such as reduction of reactive oxygen species (ROS) responsible for cellular damages. Potential multifunctional filters were obtained by intercalating of ferulate anions into layered simple metal hydroxides (LSH) through anion exchange and precipitation at constant pH methods. Ultrasound treatment was used in order to investigate the structural changes in LSH-ferulate materials. Structural and spectroscopic analyses show the formation of layered materials composed by a mixture of LSH intercalated with ferulate anions, where carboxylate groups of ferulate species interact with LSH layers. UV-VIS absorption spectra and in vitro SPF measurements indicate that LSH-ferulate systems have UV shielding capacity, mainly UVB protection. The results of reactive species assays show the ability of layered compounds in capture DPPH^•, ABTS^•+, ROO^•, and HOCl/OCl⁻ reactive species. LSH-ferulate materials exhibit antioxidant activity and singular optical properties that enable their use as multifunctional filters.     

Wet-Chemically Prepared Porphyrin Layers on Rutile TiO2(110)

Porphyrins are large organic molecules that are interesting for different applications, such as photovoltaic cells, gas sensors, or in catalysis. For many of these applications, the interactions between adsorbed molecules and surfaces play a crucial role. Studies of porphyrins on surfaces typically fall into one of two groups: (1) evaporation onto well-defined single-crystal surfaces under well-controlled ultrahigh vacuum conditions or (2) more application-oriented wet chemical deposition onto less well-defined high surface area surfaces under ambient conditions. In this study, we will investigate the wet chemical deposition of 5-(monocarboxyphenyl)-10,15,20-triphenylporphyrin (MCTPP) on well-defined rutile TiO₂(110) single crystals under ambient conditions. Prior to deposition, the TiO₂(110) crystals were also cleaned wet-chemically under ambient conditions, meaning none of the preparation steps were done in ultrahigh vacuum. However, after each preparation step, the surfaces were characterized in ultrahigh vacuum with X-ray photoelectron spectroscopy (XPS) and the result was compared with porphyrin layers prepared in ultrahigh vacuum (UHV) by evaporation. The differences of both preparations when exposed to zinc ion solutions will also be discussed.     

A Novel Carbon Nitride Nanosheets-based Electrochemical Sensor for Determination of Hydroxychloroquine in Pharmaceutical Formulation and Synthetic Urine Samples

This study introduces modified carbon paste electrodes with carbon nitride nanosheets (CNNS) and outlines their application for the determination of hydroxychloroquine sulfate (HCQ) in tablets and synthetic urine samples. CNNS were synthesized by hydrothermal route (200 °C, 10 h) using melamine and citric acid as their precursors. The carbon nitride nanosheets-based electrode (CNNS/E) presented a linear dynamic range for HCQ (LDR), ranging from 10.0 nmol l⁻¹ to 6.92 μmol l⁻¹, and detection (LOD) and quantification limits (LOQ) of 0.16 nmol l⁻¹ and 0.52 nmol l⁻¹, respectively. LOD and LOQ were calculated by the equations: LOD=3(S_d/b), and LOQ=10(S_d/b). The modified sensor presented excellent relative standard deviations for parameters such as repeatability (2.39 % and 1.87 %) and reproducibility (3.22 % and 2.32 %) in HCQ oxidation peaks (1 and 2). The CNNS/E has not shown significant variations in its anodic signal intensity in the presence of some organic and inorganic substances. It is worth bearing in mind that CNNS/E can be easily manufactured and the sensor has the lowest HCQ detection limits reported so far. The proposed sensor was successfully applied for HCQ determination in tablets and synthetic urine, showing good recovery values and an error of 0.60 % about comparative method in tablet samples, assuring the quality of the method.     

Characterization of a Robust CoII Fluorescent Complex Deposited Intact On HOPG

The new diimine fluorescent ligand ACRI‐1 based on a central acridine yellow core is reported along with its coordination complex [Co₂( ACRI‐1 )₂] ( 1 ), a fluorescent weak ferromagnet. Due to the strong fluorescence of the acridine yellow fluorophore, it is not completely quenched when the ligand is coordinated to Co^II. The magnetic properties of bulk complex 1 and its stability in solution have been studied. Complex 1 has been deposited on highly ordered pyrolitic graphite (HOGP) from solution. The thin films prepared have been characterized by AFM, time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS), grazing incidence X‐ray diffraction (GIXRD), X‐ray absorption spectroscopy (XAS), X‐ray magnetic circular dichroism (XMCD) and theoretical calculations. The data show that the complex is robust and remains intact on the surface of graphite.     

Immunosensor for Detection of the Textile Dye Disperse Orange 1 Based on Non‐conventional Competitive Assay

Textile dyes appear as an important class of compounds that has become a matter of public concern and a serious challenge for scientists and environmentalists due to their large‐scale production and extensive application. In this work, a non‐conventional competitive‐type amperometric immunosensor was successfully developed for detection of the textile dye Disperse Orange 1 (DO1). The DO1 was magnetically captured and separated from the sample solution using magnetic particles (MP) functionalized with the antibody anti‐DO1 and with HRP and gold electrodes were modified with the conjugate DO1‐BSA. Molecules of DO1 immobilized on the electrode surface and DO1 captured by MP compete for antibody binding sites. As a result, the amperometric signal decreases with increasing target DO1 concentration at the capture step, because this decreases, the attachment between the HRP coated MP and the electrode. This strategy allowed us to determine DO1 at the low detection limit of 0.87 ng mL^?1 with great specificity. Also, there were good recoveries for detection of the textile dye in river water samples without the need of sample pre‐treatment. The competitive amperometric immunosensor shows applicability for the determination of small molecules that cannot be determined by conventional competitive or sandwich immunosensors.     

Optimal Control of an Evolution Problem Involving Time-Dependent Maximal Monotone Operators

Journal of Optimization Theory and Applications - We consider a control problem in a finite-dimensional setting, which consists in finding a minimizer for a standard functional defined by way of...     

Nanostructures of sodium titanate/zirconium oxide

In this work is reported the synthesis of nanotubes and nanoribbons from mixed oxides (Ti_1−x Zr _x O₂·nH₂O), employing hydrothermal treatment in a highly alkaline medium. The morphology and crystal structure of the products obtained via hydrothermal treatment depend on the value of x. For example, for x equal to 0 and 0.50 were observed the presence of nanotubes (diameter around 9 nm) and nanoribbons (diameter around 200 nm), respectively. However, for x values above 0.50, there was no morphological change. Regarding the crystalline structure of these samples, for x equal to 0 was observed the sodium titanate phase; already for x values up to 0.50, we observed the presence of two crystalline phases: sodium titanate and tetragonal ZrO₂. For x values above 0.50, only tetragonal ZrO₂ was observed. Furthermore, only the product obtained from x equal to 0.15 was observed the presence of three-dimensional flower-like arrangements. The results obtained by the characterization techniques showed the segregation of zirconium after hydrothermal treatment of precursors with x less or equal to 0.50. Thus, we describe the important role that Ti/Zr molar ratio of the precursor plays on the morphology and crystalline phase of the products formed by hydrothermal treatment.