Carbohydrate-Conjugated Amino Acid-Based Fluorescent Block Copolymers: Their Self-Assembly, pH Responsiveness, and/or Lectin Recognition

An effective strategy has been documented to combine both carbohydrate and amino acid biomolecules in a single synthetic polymeric system via a reversible addition–fragmentation chain transfer (RAFT) polymerization technique. The resultant unique block copolymer was engineered to form uniform micelles with the desired projection of either selective or both amino acid/sugar residues on the outer surface with multivalency, providing pH-based stimuli-responsiveness and/or lectin recognition. The self-assembly process was studied in detail by field emission scanning electron microscopy (FE-SEM), dynamic light scattering (DLS), and UV–visible spectroscopy. The enhanced lectin binding behavior was observed for glyconanoparticles with both amino acid/sugar entities on the shell as compared to the only glycopolymer nanoparticle because of the higher steric hindrance factor in the case of only the glycopolymer nanoparticle. Fluorophore conjugation by postpolymerization functionalization was further exploited by fluorescence spectroscopy for evidencing the lectin recognition process

Supramolecular Interaction-Assisted Fluorescence and Tunable Stimuli-Responsiveness of l‑Phenylalanine-Based Polymers

Supramolecular host–guest interactions between randomly methylated β-cyclodextrin (RM β-CD) and side-chain phenylalanine (Phe) and Phe–Phe dipeptide-based homopolymers have been employed for the amplification of fluorescence emission of otherwise weakly fluorescent amino acid Phe. The host–guest complex has been characterized by ¹H and ¹³C NMR spectroscopy, two-dimensional rotating-frame overhauser spectroscopy, Fourier-transform infrared spectroscopy, UV–visible spectroscopy, and fluorescence spectroscopy. To gain insights into the origin of fluorescence in homopolymers, density functional theory calculations were performed where phenyl moieties inside the less polar core of β-CD were observed to form a π–π coupled complex resulting in an enhanced emission. Furthermore, the complex-forming ability of Phe, the guest molecule, has been employed in tuning the cloud point temperature (<i>T</i>_CP) of statistical copolymers derived from side-chain Phe/Phe–Phe-based methacrylate monomers and <i>N</i>-isopropylacrylamide. By varying the co-monomer feed ratios in the statistical copolymer and hence the concentration of RM β-CD throughout the polymer chain, host–guest interaction-assisted broad tunability in <i>T</i>_CP of the supramolecular polymeric complex has been achieved