Enantioselective Dynamic Exchange Reactions of Imines

One-step removal of hexavalent chromium in wide pH range using thiourea dioxide: the role of reactive species

One-step removal of hexavalent chromium in a wide pH range is of great significance. In this paper, a single thiourea dioxide (TD) and two-components thiourea dioxide/ethanolamine (MEA) were used as a green reducing agent for the efficient removal of Cr(vi), respectively. The reduction of Cr(vi) and the precipitation of Cr(iii) were carried out simultaneously under this reaction system. The experimental results proved that TD was activated by amine exchange reaction with MEA. In other words, MEA promoted the generation of an active isomeride of TD by changing the equilibrium position of the reversible reaction. After adding MEA, the removal rate of Cr(vi) and total Cr could reach industrial water discharge standards in a wide pH range of 8-12. The change of pH, reduction potential and the decomposition rate of TD were investigated in the reaction processes. Meanwhile, reductive and oxidative reactive species were produced simultaneously during this reaction process. Further, oxidative reactive species (O₂˙^- and ¹O₂) were beneficial for the decomplexation of Cr(iii) complexes and the formation of Cr(iii) precipitation. The experimental results also demonstrated that TD/MEA was effective in practical industrial wastewater. Hence this reaction system has a significant industrial application prospect.

A Non-Hydrolysis Reaction-Based Imine for Fluorescence Response toward Al3+ Ions with Extremely High Selectivity

Designing an imine-based fluorescent probe capable of greatly suppressing the tendency of intrinsic hydrolysis reaction is an attractive topic in the field of chemo-/biosensing. In this work, hydrophobic 1,1'-binaphthyl-2,2'-diamine containing two amine groups was introduced to synthesize probe R-1 bearing two imine bonds linked by two salicylaldehyde (SAs). The hydrophobicity of binaphthyl moiety and the unique clamp-like structure formed from double imine bonds and from ortho-OH on SA part make probe R-1 is able to function as an ideal receptor to coordinate with Al³⁺ ions, leading to the fluorescence originated from the complex rather than from the assumed hydrolyzed fluorescent amine is turned on. Further study revealed that, when Al³⁺ ions were introduced, both the hydrophobic binaphthyl moiety and the clamp-like double imine structure in the designed imine-based probe showed important contributions to suppress the intrinsic hydrolysis reaction, resulting in generating a stable coordination complex with an extremely high selectivity in fluorescence response.

Modulating Dual Fluorescence Emissions in Imine-Based Probes to Distinguish D2O and H2O

How to distinguish D₂O and H₂O and determine the trace H₂O content in D₂O solvent, by using molecule-based spectral probes, is an intriguing topic in analytical chemistry, yet considerably few examples remain up to now, likely due to the very similar physical/chemical properties between D₂O and H₂O. In this work, we found that both the hydrolysis reactions to release fluorescent amines and aggregation-induced emission (AIE) of imines, functioning as dual fluorescence signals to distinguish D₂O and H₂O, could be modulated by changing the imine structures. The hydrophobicity of imines showed an important contribution to the ability of modulating the hydrolysis reactions and AIE, demonstrating a significant difference on fluorescence signals in D₂O and H₂O solvents. Among all tested imines, probe 3, condensed from 2-naphthylamine and salicylaldehyde, was found to have the potential ability to act as an ideal candidate for probing the H₂O content in D₂O solvent, particularly in a low H₂O content range, using the ratiomeric emission signals.