The inhibitory ability of an oxazinoquinoxaline derivative (OAQX) against the corrosion of AISI 1018 mild steel induced by aqueous 0.6 mol L-1 NaCl solution is herein evaluated. Linear polarization resistance studies showed the inhibitory efficiency of OAQX varying from 62.75% to 75.93% with OAQX concentration ranged from 0.259 x 10-4 mol L-1 to 3.243 x 10-4 mol L-1. Aiming at to investigate the Tafel curves on the OAQX electrochemical behavior at saline (0.6 mol L-1 NaCl) aqueous media the linear Tafel segments of anodic and cathodic curves were extrapolated to the intersection point which afforded corrosion potential (Ecorr) and corrosion current density (icorr) data. By applying Tafel approach the efficiency of OAQX ranges from 55.30% to 87.60%. In both analysis Langmuir isotherm lead to optimized adsorption parameter. The adsorption mechanism of OAQX is proposed from FTIR experiments and quantum calculations. The theoretical employed method is hybrid B3LYP combined with 6-311++G(d,p). Theoretical results showed OAQX as a promising inhibitor that form a stable protective metal-ligand film on metal surfaces, and differs from several heterocyclic compounds due to its solubility in small amount of DMSO (0.627 x 10-4 mol L-1) which is resistant to a saline aqueous media (0.6 mol L-1 NaCl).

The use of digital image analysis as an analytical tool is a reality nowadays, and the use of smartphones stands out due to its high accessibility and practicality. Ascorbic acid (AA) is a natural and essential vitamin available as a supplement as a result of its use in preventing and treating several pathologies. This paper reports a simple, fast and low cost method using smartphone image analysis for quantification of AA based on its interfering effect in the enzymatic colorimetric detection of glucose. Commercial vitamin C tablets were used as prediction set for AA quantification, showing very satisfactory results (relative errors < 4%), where no statistical difference at a 95% confidence level was observed between the AA content estimated by the imaging method and the labeled reference values. As advantages, this method does not use expensive reagents neither laborious procedures to carry out the analysis.

This paper presents a low-cost reflectometer for selective detection of Cu2+. The reflectometer is based on an emission light source using five light-emitting diodes at different wavelengths and a detector using a webcam. The samples were prepared using a filter paper-based colorimetric sensor with ascorbic acid-based quinoxaline derivative. Video analysis using gray color intensity was used to perform both copper ion screening (Cu2+, Pb2+, Cr+3, Ni2+, Fe2+, Sn2+, Mg2+, Cd2+, Ag+ and Co2+) and quantification of Cu2+ in spiked samples. In addition, a multivariate validation was performed. The system proved to be selective to Cu2+ among the screened ions, and its quantification was performed using partial least square regressions. Good linearity (R2 = 0.979, coefficient of determination), low root-mean-square error of prediction (RMSEP = 5.20 × 10-3 mol L-1) and high recovery (93.39-128.64%) were achieved. This method has potential to be employed for rapid and selective determination of Cu2+ in water using low-cost instrumentation.

This paper describes the use of digital imaging acquired from a conventional desktop scanner for characterization of newly synthesized amino-nitroquinoxaline dyes. The synthetic protocol was based on reactions of building block 2,3-dichloro-6,7-dinitroquinoxaline with aliphatic amines and experiments based on image analysis were carried out with compounds in solution (96-microwell plates) and/or adsorbed on silica (thin-layer chromatography (TLC) plates). Three main goals were achieved: firstly, compounds 2-chloro-6,7-dinitro-3-pyrrolidinoquinoxaline and 6,7-dinitro-2,3-dipyrrolidinoquinoxaline had their concentration predicted in dimethyl sulfoxide (DMSO) solution, as a mixture. Secondly, TLC studies were performed to build a kinetic profile in attempt to monitor reaction involving conversion of 2-chloro-6,7-dinitro-3-pyrrolidinoquinoxaline into 6,7-dinitro-2,3-dipyrrolidinoquinoxaline. Lastly, image analysis and UV-Vis spectroscopy were applied to study the interaction of 2,3-di-n-butylamino-6,7-dinitroquinoxaline with hydroxide anion in DMSO. These approaches based on digital image characterization were successfully implemented in qualitative and quantitative analysis of organic dyes.

Bioorganic and biological chemistry have been found to be highly motivating to undergraduate students and in this context, biochemical blood parameter analysis emerges as highly attractive content. In this proposal, several aspects related to analyses of glucose, cholesterol and triglycerides using the enzymatic colorimetric method were involved, and the findings have at least two relevant implications: i) introducing students to connections between organic chemistry and biology based on enzymatic processes, including reactivity and mechanistic aspects; ii) performing a micro scale bioassay analysis. The proposal requires two theoretical classes (2 h per class) and one practical class (4 h).