Due to dopamine's chemical structure and the fact that it has three pKa values, its deprotonation process, in aqueous solution, may involve different chemical species. For instance, the first deprotonation step, from the fully protonated dopamine molecule (H3DA+) to the neutral one (H2DA), will result in zwitterionic species if a proton from one of the OH groups in the catechol ring is lost or into a neutral species if the proton is lost from the amino group. Given that the interaction of such a product with its environment will be quite different depending on its nature, it is very important, therefore, to have an accurate knowledge of which is the dopamine chemical species that results after each deprotonation step. In order to gain a better understanding of dopamine chemistry and to establish a plausible dopamine deprotonation pathway, the optimized geometries of the aforementioned species were calculated in this work by means of the density functionals theory (B3LYP/6-311+G(d,p)) in both cases: in vacuo and with solvent effect, to assess, among other theoretical criteria, the proton affinities of the different dopamine species. This permitted us to propose the following reaction pathway: [reaction in text]. Moreover, the calculations of the chemical shift (NMR-GIAO) modeling the effect of the solvent with a continuum method (PCM) was in agreement with the 13C NMR experimental spectra, which confirmed even further the proposed deprotonation pathway.

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e noncompetitive inhibition of laccase by mercury ions is reported, in particular focusing their effect over the enzyme catalytic activity. e enzymatic kinetics were obtained for different substrates (caffeic acid, gallic acid, and catechol), where caffeic acid displayed the greatest enzymatic activity. e laccase inhibition by mercury ions permitted to establish the inhibition effect through a mixed model (that actually displayed a behavior closer to that of the noncompetitive inhibitors) when evaluated by means of UV-Vis spectrophotometry, using caffeic acid as an electron donor. A mercury concentration of 2 mM led to 35% enzymatic inhibition after only a 2-minute incubation period. is method was used for quantification of mercury ions in aqueous solution, showing a detection limit of 15 ± 1 ppm. erefore, this work presented a novel perspective for the determination of the toxic Hg(II) ions that can be readily implemented into environmental remediation methods.

Potentiometric studies are presented here on solid contact ion-selective electrodes, based on neutral carriers comprising structural sulfur−donating groups and an aliphatic chain, where the latter confers stability to the molecule for the formation of metal complexes. As result, an ISE was obtained for the potentiometric determination of mercury. This sensor allowed continuous mercury determinations at nanomolar levels within a wide concentration interval (1.0 × 10 −9 to 1.0 × 10 −1 ) molL −1 , with a detection limit of (9.1 ± 0.8) × 10 −10 molL −1 and a Nernstian response of (29.8 ± 0.4) mV decade −1 . This ISE can be used in the 0-6 pH interval, exhibiting a high selectivity toward the mercury ions even in the presence of interferents, and be used as an indicating electrode during potentiometric mercury titration with EDTA, because it is comparable with the commercial electrodes, within its same class. The main advantage of the ISE reported here is its nM LOD and that it does not require an internal reference.

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