Thiourea Organocatalysts as Emerging Chiral Pollutants: En Route to Porphyrin-Based (Chir)Optical Sensing

Abstract

Environmental pollution with chiral organic compounds is an emerging problem requiring innovative sensing methods. Amino-functionalized thioureas, such as 2-(dimethylamino)cyclohexyl-(3,5-bis(trifluoromethyl)phenyl)thiourea (Takemoto’s catalyst), are widely used organocatalysts with virtually unknown environmental safety data. Ecotoxicity studies based on the Vibrio fischeri luminescence inhibition test reveal significant toxicity of Takemoto’s catalyst (EC50 = 7.9 mg/L) and its NH2-substituted analog (EC50 = 7.2–7.4 mg/L). The observed toxic effect was pronounced by the influence of the trifluoromethyl moiety. En route to the porphyrin-based chemosensing of Takemoto-type thioureas, their supramolecular binding to a series of zinc porphyrins was studied with UV-Vis and circular dichroism (CD) spectroscopy, computational analysis and single crystal X-ray diffraction. The association constant values generally increased with the increasing electron-withdrawing properties of the porphyrins and electron-donating ability of the thioureas, a result of the predominant Zn⋯N cation–dipole (Lewis acid–base) interaction. The binding event induced a CD signal in the Soret band region of the porphyrin hosts—a crucial property for chirality sensing of Takemoto-type thioureas.

Aminocatalysts are More Environmentally Friendly than Hydrogen‐Bonding Catalysts

“…Therefore, for some of the compounds the EC 50 values were predicted from the EC 20 values (the concentrations causing a 20 % inhibitory effect compared to the control) using the factor 2.0 derived from the 11 compounds presented in Table 1 for which both EC 20 and EC 50 values were obtained from dose–response curves. The conversion factor used (2.0) was also in line with the data from one of our previous study on the toxicity of thiourea organocatalysts on V. fischeri [18] . To increase the solubilization of the organocatalysis studied, dimethyl sulfoxide (DMSO) was added as a solubilization vehicle (2.5 % in the final test environment), to allow at least the EC 20 value to be determined.…”

“…The conversion factor used (2.0) was also in line with the data from one of our previous study on the toxicity of thiourea organocatalysts on V. fischeri. [18] To increase the solubilization of the organocatalysis studied, dimethyl sulfoxide (DMSO) was added as a solubilization vehicle (2.5 % in the final test environment), to allow at least the EC 20 value to be determined. In Table 1 the toxicity (EC 50 and EC 20 values) is presented on a mg L À 1 basis as well as in μm.…”

“…There are only sporadic examples: nonchiral functionalized thioureas proved toxic to human cell lines in vitro (half maximal effective concentration EC 50 ranging from 6 to 32 μ m ) [17] . Also, Takemoto's chiral catalyst proved toxic in a bioluminescence inhibition assay with Vibrio fischeri (EC 50 =7.9 mg L −1 =19 μ m ) [18] . The cytotoxicity of cinchona alkaloid organocatalysts was determined for multidrug‐resistant uterine sarcoma cell lines [19] .…”

“…[17] Also, Takemoto's chiral catalyst proved toxic in a bioluminescence inhibition assay with Vibrio fischeri (EC 50 = 7.9 mg L À 1 = 19 μm). [18] The cytotoxicity of cinchona alkaloid organocatalysts was determined for multidrug-resistant uterine sarcoma cell lines. [19] It is important to note that novel chemicals and/or materials form the cornerstone of progress contributing to society's exponentially growing needs for energy, health care, food, housing, and so on.…”

Mixed Oxime-Functionalized IL/16-s-16 Gemini Surfactants System: Physicochemical Study and Structural Transitions in the Presence of Promethazine as a Potential Chiral Pollutant

“…The increasing concern about chiral pharmaceutical pollutants is connected to environmental contamination causing both chronic and acute harmful effects on living organisms. It is a problem of direct importance to detect chiral compounds [1], including chiral pollutants of different natures [2]. Using surfactants for increasing analytical signals and, consequently, reducing the detection concentration of the pollutants is one of the attractive strategies in chemical analysis [3,4] since it may ensure selective binding of one of the components, providing more reliable detection in the cases when the structurally similar compounds are present in the mixture.…”