Colorimetric pH-Responsive Biomaterials Based on Pyranoflavylium-Biopolymer Hybrid Conjugates
Ana Sofia Pires, Vânia Gomes, Dina Neves, Nuno Mateus, Víctor de Freitas, Luís Cruz
Abstract
The conjugation of functional molecules into marine-origin biopolymers has been extensively used toward the creation of new (bio)materials for applications in food and biomedical areas. Herein, two chitosan (CHT) and alginate (ALG) biobased conjugates functionalized with pH-dyes were successfully developed to be integrated as smart labels and tags in biocompatible packaging materials for food spoilage sensing. For that, two pyranoflavylium-based pH-indicator dyes, Pyflav (4) and Pyflav (5), were designed, synthesized, and then grafted onto CHT and ALG scaffolds via EDC/NHS carbodiimide coupling chemistry with substitution degrees of 14 and 1.2%, respectively. Afterward, the conjugates were fully characterized by Fourier transform infrared, 1H NMR, and dynamic light scattering techniques, and their acidity constants were determined by UV–vis spectroscopy, yielding a great color variation (from orange to purple, pKa 6.43 ± 0.04, for Pyflav-CHT (6) and from pink to purple, pKa 7.17 ± 0.02, for Pyflav-ALG (7) and compatible with the food spoilage pH range of many perishable foods (pH between 5.8 and 7.4).