Host–Guest Chemosensor Ensembles based on Water-Soluble Sulfonated Calix[n]arenes and a Pyranoflavylium Dye for the Optical Detection of Biogenic Amines

Biogenic amines (BAs) are biologically active nitrogen-containing compounds formed during the food spoilage process and are often related as key markers of food quality, safety, and freshness. Because their presence in foods at high levels can cause significant health problems, researchers have been focused on developing novel strategies and methods for early detection and capture of these analytes. Herein, water-soluble sulfonated calix­[n]­arene macrocycles (SC4, SC6, and SC8) and a pH-sensitive dye (4′-hydroxy-10-methylpyranoflavylium) were investigated as host–guest systems for BA sensing. The hosts were able to bind the flavylium cation of the dye with association constants of 10³ to 10⁴ M^–1. The dye complexation also allowed tuning its pK_a from 6.72 (free) toward high values: 7.68 (SC4), 7.79 (SC6), and 8.45 (SC8). These data were crucial to optimize the host–guest complexes as optical sensing systems for putrescine/tyramine (pH 7.2–7.6), yielding a colorimetric redshift from yellow to red. The BA sensing was also demonstrated by fluorescence quenching for the calix­[n]­arene/dye complexes and fluorescence recovery after the addition of BAs. ¹H NMR spectroscopy was used to demonstrate the interaction mode, confirming an encapsulation-driven mechanism. Overall, these host–guest systems demonstrated great potential for the detection of BAs, one of the main key markers of food spoilage.