Search

AbstractAn electrochemical sensor for the electrocatalytic oxidation of cysteine was designed based upon a 2-(2,5-dihydroxy-phenyl)-naphtho[1,2-d] oxazole-5-sulfonic acid (DHPNOS) and cerium oxide nanoparticle (CN) modified carbon paste electrode (CPE). An investigation of the redox properties of this modified electrode indicates a reduction in oxidative overvoltage and an intense increase in the analytical current. The pH, modifier, and nanoparticles were optimized to 7, 4% weight percent, and 5% weight percent, respectively. The apparent charge transfer rate constant (ks) and transfer coefficient for electron transfer between modifier and electrode were 2.776 s−1 and 0.47, respectively. Using differential pulse voltammetry, a linear range from 1 to40 µM with a detection limit of 0.33 µM was observed in phosphate buffer (pH 7.0). This work introduces a simple approach for selective determination of L-cysteine in the presence of uric acid. Also, based on chronoamperometry, the diffusion coefficient was determined to be 2.61 × 10−5 cm2 s−1. The effect of interferences on L-cysteine peak current were studied. The repeatability and reproducibility of the designed sensor were also measured with relative standard deviation values of 1.00% and 4.45%, respectively. The constructed sensor was employed for the determination of L-cysteine in acetylcysteine tablets. [ABSTRACT FROM AUTHOR]

Titanium is the optimal biomaterial for orthopedic and dental applications. Due to its biocompatibility and superior mechanical properties, it is more suitable for implant applications than other metals. However, due to its bio-inertness, the surface of titanium must be modified for human bone tissue. Various techniques can be used to construct titanium dioxide (TiO2) nanoparticles (TNPs), but anodizing is the most often used because of its portability and low cost. Due to the high similarity of hydroxyapatite to the mineral components of bone and dentin, metal implants are coated with bone-conducting biomaterials such as hydroxyapatite (HA) to enable better bone bonding. In this study, copper and chitosan were used because of their excellent antimicrobial properties. Electrochemical impedance tests show that an HA/Cu/Drug/chitosan (Chit) coating has a polarization resistance of 300,000 Ω because the copper coating on the titanium dioxide nanoparticle (TNP) increases corrosion resistance. A potentiodynamic polarization test shows that the current of corrosion of the HA/Cu/Drug/chitosan sample is 2.1719 x 10-6 A. The antibacterial activity of the HA/Drug, HA/Drug/Chit, and HA/Cu/Drug/Chit coatings was evaluated in vitro against Staphylococcus aureus ATCC 29737, and it is found that the HA/Cu/Drug/Chit coating presents high antibacterial activity due to the presence of copper and chitosan. Its optical density is 0.78, which is lower than that of all the other samples. Cell viability is highest for the TNP samples containing chitosan. Regarding the TNP sample containing HA/Drug (99.4%), it is observed that the percentage of cell viability is higher than that of the TNP sample containing HA/Cu/Drug (97.54%) due to the toxicity of copper. This study shows that the modification of the titanium implants can be used to control drug release and enhance corrosion resistance, antibacterial properties, and cell viability. [ABSTRACT FROM AUTHOR]

Due to the biological effects of phenolic acid components, polyphenol-rich foods are a significant part of human and animal diets. In this study, the acidity constants of caffeic acid (3,4-dihydroxycinnamic acid) in binary mixtures of ethanol–water were determined spectrophotometrically using the introduced net analyte signal (NAS) algorithm and an ab initio quantum mechanical method. The NAS is an efficient chemometric algorithm for analysis of acid–base equilibrium systems by a spectrophotometric method. At different pH values, the distribution of acid species is obtained from an absorption data matrix and this procedure enabled the pKa of caffeic acid to be obtained alternatively. The results showed that pKa1 (4.02, 4.26, 4.39, 4.57 and 5.11) and pKa2 (8.43, 8.68, 8.79, 9.00 and 9.34) were increased by increasing the percent ethanol in water (0, 10, 20, 30 and 40 vol. %) and these results were in agreement with the results of the Gaussian method. The ab initio calculated Gibbs energy change showed that para-hydroxy group is more acidic than meta-hydroxy group. The red shifts of different species of caffeic acid obtained using the ab initio quantum mechanical method are in good agreement with the results of UV–Vis spectroscopy.

A mefenamic acid sensor was prepared by the modification of a glassy carbon electrode (GCE) with graphene nano-sheets (Gr) and multi wall carbon nanotubes (MWCNT). The designed sensor (MWCNT/Gr/GCE) indicated an electrocatalytic behaviour when applied for mefenamic acid (MFA) oxidation due to good conductivity, low electron transfer resistance and catalytic effect. The suggested sensor revealed a lower overvoltage and enhanced current compared with bare GCE for the oxidation of MFA. The observations indicated that the oxidation potential of MFA is decreased more than 200 mV using the designed sensor. The percentages of MWCNTs and Gr nano materials, and pH solution were optimized. Under the optimum conditions, some kinetic parameters, such as surface coverage in a 0.5 mM [Fe(CN)6]3-/4- solution was obtained by cyclic voltammetric method. The diffusion coefficient of MFA (D) was calculated to be 2.88×10-6 cm2 s-1 by chronoamperometeric technique. The MWCNT/Gr/GCE sensor exhibited a linear dynamic range for MFA (2– 100 μM) with a detection limit of 0.66 μM by differential pulse voltammetry (DPV) technique. This sensor revealed a suitable applicability for determination of MFA in real samples (drug samples and serum solutions).