A new class of silica-supported chromo-fluorogenic chemosensors for anion recognition based on a selenourea scaffold

Abstract

The development of optical chemosensors for neutral and charged species recognition has been one of the most active research field in Supramolecular Chemistry in the last 20 years. 1-6 A vast library of chemosensors has been proposed so far, but only recently organoselenium and organotellurium compounds have been used for this purpose. 7,8,9 Heavy chalcogen-containing derivatives, and in particular those containing selenium, are of great interest because selenium compounds play an important role as enzymatic antioxidants participating in the conversion of hydrogen peroxides in water in biological systems. 10 In the particular case of seleniumcontaining chemosensors, the formation of highly stable selenoxides is often the event that triggers the optical recognition of analytes such as reactive oxygen species (ROS) superoxide, 11 hypochlorite 12 or reactive nitrogen species (RNS, for instance peroxynitrate). 13 However, very few examples of selenium-containing optical chemosensors for "classic" anions such as fluoride 14 or carboxylates 15 have been described. In reported selenium-containing probes, the sensing mechanism of fluoride is based on a deprotonation event of an amino group, while carboxylate recognition depends on the formation of hydrogen bonds between the guest and pyrimidine and amide protons of the receptor. However, in both cases, selenium is contained in a selenodiazole moiety and do not actively participate to the sensing event.One of the most common strategy for the design of anion chemosensors is the use of hydrogen-bond donor groups such as urea or thiourea. In the case of thiourea-based chemosensors, due to the more acidic nature of the NHs protons (compared to those of the analogous urea derivatives), the recognition event is often caused by the deprotonation of the receptor that usually leads to a remarkable modification in the electronic properties of the system resulting in colour or emission changes. However, in this scenario, and, to the best of our knowledge, examples of selenourea-based anion sensors have never been reported in the literature to date despite selenoureas are interesting organoseleno compounds that show anticancer activity, antioxidant properties, enzyme inhibition, and DNA binding properties. [16][17][18][19][20] Taking these concepts into account and following our interest in anion recognition and sensing [21][22][23][24][25] we decided to explore the potential use of selenoureas as a new scaffold for the design of anion chemosensors.In particular, here, we describe the ability of the asymmetric 1-(4-methyl-2-oxo-2H-chromen-7-yl)-3-phenylselenourea (L) to act as a colorimetric and/or fluorescent sensor for S 2-and CNrecognition. L was obtained according to the reaction shown in Scheme 1.Scheme 1. Synthesis of 1-(4-methyl-2-oxo-2H-chromen-7-yl)-3-phenylselenourea (L).Phenylisoselenocyanate was synthesised following a literature procedure. 26 Reaction with 7-amino-4-methylcoumarin in DCM/EtOH (1:1, v/v) at 40°C for 3 hours under N2 atmosphere (Fig. 1) and CN -(see ESI...

Selenium‐NMR Spectroscopy in Organic Synthesis: From Structural Characterization Toward New Investigations

“…In this sense, Caltagirone and co‐workers have prepared a selenourea derivative to act as a colorimetric and/or fluorescent anion‐sensor (Scheme 40). [172] The probe was evaluated for distinct anions, as HSO 4 − , H 2 PO 4 − , NO 3 − , Br − , I − , ClO 4 − , and others, being effective only for S 2− and CN − anions. In order to identify the molecular changes in the selenium‐based probe, 77 Se NMR spectroscopy and HRMS analysis were designed.…”

Discussions of Fluorescence in Selenium Chemistry: Recently Reported Probes, Particles, and a Clearer Biological Knowledge

“…Although it is not soluble in water, alternatively, they formed L by loading modified mesoporous nanosilica with trimethylsilyl as a hydrophobic outer side and PEG as a hydrophobic inner side. By that, L can discriminate the S 2− ion over CN − ion by a “turn–off” fluorescence change mechanism [ 55 ].…”

“…Although it is not soluble in water, alternatively, they formed L by loading modified mesoporous nanosilica with trimethylsilyl as a hydrophobic outer side and PEG as a hydrophobic inner side. By that, L can discriminate the S 2− ion over CN − ion by a "turn-off" fluorescence change mechanism [55]. Gao et al designed a near-infrared (NIR) chemosensor based on an azo-BODIPY and diphenylselenol (BD-di-SeH) system for the detection of sulfane sulfur under hypoxic conditions.…”

Interfacial Assembly of Mesoporous Silica‐Based Optical Heterostructures for Sensing Applications

“…Anion species such as phosphate, fluoride, sulfion, cyanide ion, intractable anion, and superoxide anion could also be detected using mesoporous silicas materials. In a report by Caltagirone and co‐workers, S 2− selective mesoporous silica NP loaded with fluorescent chemosensor containing a selenourea moiety was developed (Figure c,d) …”