Identification of Molecular Fluorophore as a Component of Carbon Dots able to Induce Gelation in a Fluorescent Multivalent-Metal-Ion-Free Alginate Hydrogel

Abstract

We introduce a simple approach to fabricate fluorescent multivalent metal ion-free alginate hydrogels, which can be produced using carbon dots accessible from natural sources (citric acid and L-cysteine). Molecular fluorophore 5-oxo-2,3-dihydro-5H-[1,3]-thiazolo[3,2-a] pyridine-3,7-dicarboxylic acid (TPDCA), which is formed during the synthesis of carbon dots, is identified as a key segment for the crosslinking of hydrogels. The crosslinking happens through dynamic complexation of carboxylic acid groups of TPDCA and alginate cages along with sodium ions. The TPDCA derived hydrogels are investigated regarding to their thermal, rheological and optical properties, and found to exhibit characteristic fluorescence of this aggregated molecular fluorophore. Moreover, gradient hydrogels with tunable mechanical and optical properties and controlled release are obtained upon immersion of the hydrogel reactors in solutions of divalent metal ions (Ca2+, Cu2+, and Ni2+) with a higher affinity to alginate.

Molecular Fluorophores Self-Organize into C-Dot Seeds and Incorporate into C-Dot Structures

“…19 Thus, it has been suggested that these aggregates may affect the overall fluorescence properties of a C-dot solution. [29][30][31][32] These findings are consistent with the fact that planar conjugated materials tend to form aggregates in solutions/suspensions. [33][34][35] Self-assemblies of polyaromatic hydrocarbons (PAHs) used as building blocks display PL properties resembling those of C-dots, and the properties of C-dots can be tuned by changing the composition of individual PAH building blocks.…”

Research Progress Review of Preparation and Applications of Fluorescent Hydrogels

“…In addition, the most common forms of alginate are its gel and polyvalent metal ions, but in practical application, gels without any polyvalent metal ions are welcome [33]. Recently, Kasak et al [34] have prepared polyvalent nonmetal alginate fluorescent hydrogels by dynamic complexing method. Crosslinking occurs through the dynamic complexation of 5-oxo-2, 3-dihydro-5H- [1,3]-thiazolo[3, 2-a] pyridine-3, 7-dicarboxylic acid (TPDCA), carboxylic acid groups in alginate cages and sodium ions (Figure 5).…”

“…Figure5: Schematic diagram of synthesis of crosslinked alginate fluorescent hydrogels. Among them, the picture on the right was shot under the excitation of ultraviolet lamp (reprinted from[34]). …”

Fluorescent Zn(II)-Based Metal-Organic Framework: Interaction with Organic Solvents and CO2 and Methane Capture

“…In the reaction of citric acid with natural amino acid L-cysteine, 5-oxo-2,3-dihydro-5H- [1,3]-thiazolo [3,2-a]pyridine-3,7-dicarboxylic acid (TPDCA) [42,43] has been synthesized and further applied as a component of fluorescent biodegradable polymers [44,45] and other soft materials [46][47][48][49]. TPDCA also has been identified as a key component for induction of gelation of natural polysaccharide-alginate [50] and related carbon dots [51,52]. In this work, TPDCA was employed as a ligand for the formation of different MOF structures.…”