A comparative application of two-way and three-way analysis to three-dimensional voltammetric dataset for the pKa determination of vanillin

2-Methoxyethyl Nitrite as a Reagent for Chemoselective On-Water Nitration

An on-water approach has been developed that allows a nitration of tyrosines and phenols under mild conditions. We envisioned that the assembly of tyrosine/tyrosyl radical couples with interfacial water molecules would realize a biomimetic stacking hydrogen atom transfer (HAT) transition state to facilitate the electron-transfer process. The optimal organic nitrite, 2-methoxyethyl nitrite, resulted in rapid coupling of the tyrosyl radicals with •NO 2 at the oil-water interface to afford the nitrated phenols. Many characteristics found in our on-water strategy are distinct from other complementary systems that include radical nitration. These enticing roles of water in the reaction process introduce new avenues to explore in the design of synthetic organic chemistry systems.

Electrochemical determination of vanillin in cookies at mediated AuNPs/GR nanocomposites modified glassy carbon electrode

Background:

Currently, carbon nanomaterials and carbon nanomaterials-based electrodes have illustrated significant electrocatalytic abilities.

Methods:

An electrochemical sensor was developed for vanillin using graphene (GR) decorated with gold nanoparticles (AuNPs) on a glassy carbon electrode (GCE) with two steps. AuNPs/GR/GCE, as the electrochemical sensor for determination of vanillin, included dropping GR onto the electrode and then electrodepositing AuNPs on GR/GCE. The structure and morphology of the synthesized nanocomposites (AuNPs/GR) on the electrode were confirmed by scanning electron microscopy (SEM).

Results:

Electrochemical studies revealed that modification of the electrode surface with AuNPs/GR nanocomposites significantly increases the oxidation peak currents of vanillin. The peak currents in differential pulse voltammetry (DPV) of vanillin increased linearly with their concentration in the range of 5-120 µM. The limit of detection was found to be 1.7 µM for vanillin. Also, the effect of some interfering compounds, such as NaCl, KCl, glucose, alanine, phenylalanine, glycine, and others, on the determination of vanillin was evaluated, and none of them had a significant effect on the assay recovery

Conclusions:

A new electrochemical biosensor was fabricated with AuNPs/GR nanocomposites. The sensor was successfully used to detect vanillin in cookie samples.

PARAFAC and MCR-ALS approaches to the pKa determination of benzoic acid and its derivatives

In general, the identification of biological activities of a molecule requires the observation of its physicochemical characteristics with its molecular interactions in an organism. The acid-base ionization constant (or pKa) is one of the key parameters that shows the physicochemical behaviors of molecules used in pharmaceuticals, foods, cosmetics etc. Therefore, the development of new methods (or approaches) is necessary to get simple, rapid, inexpensive and reliable determination of the acidity constants of active and inactive ingredients used in commercial products. In this paper, new UV spectroscopic methods were developed for the first time, by applying parallel factor analysis (PARAFAC) and multivariate curve resolution-alternating least squares (MCR-ALS) to the pH-UV spectral data arrays for determining the pKa values of benzoic acid and its five derivatives (4-fluorobenzoic acid, thiosalicylic acid, anthranilic acid, phthalic acid, 4-aminobenzoic acid). The pH profiles obtained by the PARAFAC and MCR-ALS decomposition of the pH-UV data arrays were used for the quantitative estimation of the acid-base ionization constants for the investigated compounds without classical titration procedure. We concluded that the proposed PARAFAC and MCR-ALS provided us an opportunity for simple and rapid pKa determination of relevant compounds, which have functional importance in pharmaceutical and food industries.

Three-dimensional voltammetry: Use of chronoamperometric E-t-i data to achieve second-order advantage

This work studied the use of three-dimensional voltammetry, particularly potential-time-current (E-t-i) data, on the development of electroanalytical methods. E-t-i data was obtained by taking chronoamperograms at potentials applied as pulses on a staircase waveform. By using this three-way kind of data and appropriate calibration algorithms, the possibility of achieving the second-order advantage was evaluated in the determination of ferrocyanide in the presence of the uncalibrated interference hydroquinone as a model system. The determination of acetaminophen in urine samples, where ascorbic acid and uric acid play the major roles as interferents was also studied. Parallel factor analysis (PARAFAC) and multivariate curve resolution alternating least-squares (MCR-ALS) were the algorithms employed in this work. Both algorithms successfully achieved the second-order advantage by correctly predicting the concentrations of the validation synthetic samples. Excellent predictions were obtained in the direct analysis of acetaminophen-spiked urine samples by E-t-i data and MCR-ALS.

Nitrite-Mediated Photooxidation of Vanillin in the Atmospheric Aqueous Phase

Nitrite (NO₂^-) and its conjugate acid, nitrous acid (HNO₂), have long been recognized as a ubiquitous atmospheric pollutant as well as an important photochemical source of hydroxyl radicals (·OH) and reactive nitrogen species (·NO, ·NO₂, ·N₂O₃, etc.) in both the gas phase and aqueous phase. Although NO₂^-/HNO₂ plays an important role in atmospheric chemistry, our understanding on its role in the chemical evolution of organic components in atmospheric waters is rather incomplete and is still in dispute. In this study, the nitrite-mediated photooxidation of vanillin (VL), a phenolic compound abundant in biomass burning emissions, was investigated under pH conditions relevant for atmospheric waters. The influence of solution pH, dissolved oxygen, and ·OH scavengers on the nitrite-mediated photooxidation of VL was discussed in detail. Our study reveals that the molecular composition of the products is dependent on the molar ratio of NO₂^-/VL in the solution and that nitrophenols are the major reaction products. We also found that the light absorbance of the oxidative products increases with increasing pH in the visible region, which can be attributed to the deprotonation of the nitrophenols formed. These results contribute to a better understanding of methoxyphenol photooxidation mediated by nitrite as a source of toxic nitrophenols and climatically important brown carbon in atmospheric waters.