Agarose functionalization: Synthesis of PEG-agarose amino acid nano-conjugate – its structural ramifications and interactions with BSA in a varying pH regime

• PEGylated agarose amino acid (PEG-AAE) was synthesised and characterised.
• Nanosize protein like PEG-AAE (331.2 kDa) had pH-dependent properties.
• The new PEG-AAE derivative formed triple helix structure at pH 8 (ORD).
• It showed pH-dependent complexation and decomplexation with BSA (CD).
• PEG-AAE may have applications in biologics, drug delivery and sensors.

In a rapid one-step method protein-mimicking large agarose amino acid framework (AAE; GPC 156.7 kDa) was conjugated with polyethylene glycol (PEG 9 kDa) affording nano-sized PEGylated amphoteric agarose (PEG-AAE; <10 nm; DLS) containing amino, carboxyl and ester groups [overall degree of substitution (DS) 0.91]. The PEG groups were at the residual free carboxylic acid groups of succinate half-ester moiety at C-6 positions of the 1, 3 β-d-galactopyranose moieties of AAE. This new nano-sized PEG-AAE performed like a giant protein conjugate (GPC 331.2 kDa) and exhibited pH-responsive interconversion between the triple helix and single-stranded random structures (optical rotatory dispersion) presenting a mixed solubility pattern like random coil (soluble), helical (soluble) and aggregate (precipitation) formations. Circular dichroism studies showed its pH-dependent complexation and decomplexation with bovine serum albumin (BSA). Such pH-responsive PEG-conjugate may be of pronounced therapeutic potential in the area of pharmacology as well as in sensing applications.