Preparation Of Inclusion Compound Of Gibberellin A₃ With Hydroxypropyl-?? Cyclodextrin And Assay Of Its Stability

Gibberellin A3(GA3)is a kind of endogenous plant hormones controlling various aspects of growth and development,such as seed germination,stem elongation,root growth,leaf shape and shoot de-etiolation,flowering and fruit development.At present,GA3 has been widely used in crop cultivation and gardening,and have a significant role in breaking seed dormancy,promoting the elongation of steams,the growth of leaves,the differentiation of flower bud and fuit growth.However,GA3 is only soluble in organic solvents such as alcohol but insoluble in water.Thus,in agricultural exercises,GA3 is usually dissolved with organic solvents and then diluted to the usage dosage with water.Due to the special arrangement in the molecule and the unstable property of the functional groups,GA3 is easily isomerized to iso-GA3 in aqueous solutions resulting in the loss of biological activity.The insolubility of GA3 also brings lots of inconvenience in practical applications.Due to the individual structure with hydrophobic central cavity,hydroxypropyl-?-cyclodextrin(HP-?-CD)can selectively bind different guest molecules to form inclusion complexes.Therefore,in order to over the weaknesses of GA3 such as poor water-solubility and decompose in aqueous solution easily,inclusion compound of GA3 with hydroxypropyl-?-cyclodextrin was prepared to enhance the stability and bioactivity GA3 in the aqueous solution.The form of inclusion compound and physiological effects were used as a criterion in the study.The optimal conditions with single-factor test were established with ethyl alcohol as a solvent.The inclusion solution with the same mole ratio of HP-?-CD and GA3 was stirred about 2 h at 35 ?.Then inclusion compound was prepared in diethanolamine solutions and the 40%glycerol aqueous solutions.The inclusion rate under this condition was 81.7%and 78.7%.Moreover,the stability of the GA3-HP-?-CD was evaluated using the biological test on pea's stem elongation and quantitated by the Ultra Performance Liquid Chromatography(UPLC).The results exhibited that nearly all GA3 molecules in aqueous solution were degraded and lost the biological activity after 15 d at 55 ?,whereas,the GA3-HP-?-CD that used diethanolamine as the solvent only showed an degration rate of 34%and used glycerol as the solvent only showed an degration rate of 38.9%at the same condition.Above data suggested the inclusion of GA3 with HP-?-CD should be an effective way to raise GA3 stability in aqueous solutions.