Tailoring agar's dual helix formation and physicochemical properties via side-chain modification with succinic...

This study investigated the influence of different derivatives of succinic anhydride on the structure and properties of anhydride-modified agar, using molecular dynamics simulations to visualize self-assembly. Fourier transform infrared spectroscopy and physicochemical analyses revealed that branched 2,2-dimethylsuccinic anhydride (DMSA) only mono-succinylates agar, whereas succinic anhydride (SA), 2-methylsuccinic anhydride (MSA), and 2-methylenesuccinic anhydride (MESA) are capable of mono-succinylation and cross-linking agar (SA-modified agar [SAG]). Mono-succinylation significantly improved the gel transparency of agar (MESAG reached a maximum of 91.8 %, which was 73.2 % higher than that of native agar) but reduced gel strength (SAG decreased to 206.9 g/cm², which was an 87.4 % reduction). High-temperature-induced cross-linking (40 °C-70 °C) significantly boosted gel strength (up to 356.7 % for SAG) and maintained transparency (>80 %). As branching in the anhydride side chains (from no methyl groups in SA to two methyl groups in DMSA) increased, the gel strength of mono-succinylated agar improved, whereas transparency and DS decreased, and the cross-linking degree weakened (SAG > MESAG > MSAG > DMSAG). Molecular dynamics simulations showed that increased side-chain branching prolonged the time required for agar chains to form a stable double helix and altered self-assembly pathways by disrupting hydrogen bonding, leading to spherical aggregates. The capacity for double-helix formation adhered to the following order: Native agar > SAG > MESAG > MSAG > DMSAG > Agar-hexanoate. This study provides insights into the gelling mechanism of anhydride-modified agar and offers theoretical support for its design and modification.