Toward Food Freshness Monitoring: Coordination Binding–Based Colorimetric Sensor Array for Sulfur-Containing Amino Acids

Herein, a self-assembled colorimetric chemosensor array composed of off-the-shelf catechol dyes and a metal ion (i.e., Zn2+) has been used for the sulfur-containing amino acids (SCAAs; i.e., glutathione, glutathione disulfide, L–cysteine, DL–homocysteine, and L–cystine). The coordination binding–based chemosensor array (CBSA) fabricated by a competitive assay among SCAAs, Zn2+ ions, and catechol dyes [i.e., pyrocatechol violet (PV), bromopyrogallol red (BPR), pyrogallol red (PR), and alizarin red S (ARS)] yielded fingerprint-like colorimetric changes. We succeeded in the qualification of SCAAs based on pattern recognition [i.e., a linear discrimination analysis (LDA)] with 100% correct classification accuracy. The semiquantification of reduced/oxidized forms of SCAAs was also performed based on LDA. Furthermore, we carried out a spike test of glutathione in food samples using the proposed chemosensor array with regression analysis. It is worth mentioning that we achieved a 91–110% recovery rate in real sample tests, which confirmed the accuracy of the constructed model. Thus, this study represents a step forward in assessing food freshness based on supramolecular analytical methods.

Kinetics of Electron Exchange between Bromopyrogallol Red and Periodate Ion in Aqueous Acidic Medium

The kinetics of the electron transfer reaction between Bromopyrogallol (BPR2-) and periodate ion in aqueous acidic solution has been studied in the acid range 0.1 — 10-4 ≤ [H+] ≤ 2 — 10-4 mol dm-3, ionic strength 0.01 ≤ [I] ≤ 0.18 mol dm-3 (NaCl) and T = 29 ± 1.ºC. The reaction shows a first order dependence on reductant and half order on oxidant concentration respectively. It displayed an inverse dependence on the acid concentration of the reaction medium. The reaction conforms to the rate law: -d[BPR2-]/dt = k2[BPR2-][IO4-]1/2[H+]-1/2 The stoichiometry of the reaction is 1:1. Added anions had no effect on the rate of the reaction. Spectroscopic investigation indicates that an intermediate complex is probably formed in the course of this reaction. The reaction is believed to proceed via the innersphere mechanistic pathway.

Kinetics of the Oxidation of Bromopyrogallol Red by Nitrite Ion in Aqueous Acidic Medium

The kinetics of the electron transfer reaction between Bromopyrogallol (BPR2-) and nitrite ion in aqueous acidic solution has been studied in the acid range 0.1 × 10-4 ≤ [H+] ≤ 2 × 10-4 mol dm-3, ionic strength 0.01 ≤ ≤ 0.18 mol dm-3 (NaCl) and T = 29 ± 1.°C. The reaction shows a first order dependence on oxidant and reductant concentration respectively. The rate of the reaction increases with increase in [H+]. Plot of k2 versus [H+] was linear with a positive intercept. The overall reaction conforms to the rate law: -d[BPR2-]/dt = (a + b[H+])[BPR2][NO2-]. The stoichiometry of the reaction is 1:1 (BPR2- : NO2-). Added anions had no effect on the rate of the reaction. The results of spectroscopic investigation indicate that no intermediate complex is probably formed in the course of this reaction. The reaction is believed to proceed via the outersphere mechanistic pathway.

Ultrafast excited state dynamics of S2 and S1 states of triphenylmethane dyes

Excited state dynamics of S2 and S1 states for a series of TPM dyes, pyrogallol red (PGR), bromopyrogallol red (Br-PGR) and aurin tricarboxylic acid (ATC), have been monitored by using ultrafast transient absorption and fluorescence up-conversion techniques.