NMR analysis of fractionated irradiated κ-carrageenan oligomers as plant growth promoter

The optimum plant growth promoting effect in irradiated κ-carrageenan is known to be of Mw<10,000. This is obtained by irradiating κ-carrageenan at a dose of 100 kGy in solid and at 2 kGy in 1% aqueous solution. Kappa carrageenan irradiated at these doses was fractionated at different Mw ranges. The isolated fraction with a Mw of 3–10 kDa was analyzed by NMR. The chemical shifts of 13C and 1H spectra indicated that the basic functional structure of κ-carrageenan (alternating d-galactose-4-sulfate and 3,6-anhydro-d-galactose dimer) remains intact at a Mw of 3–10 kDa. No radiolytic products were detected at this range.

► Irradiated κ-carrageenan fractions with Mw<3 kDa contained higher carbonyl bonds.
► 1H NMR and 13C spectra of irradiated κ-carrageenan were similar to references.
► κ-Carrageenan oligomers with Mw of 3–10 kDa may be suitable as plant growth promoter.