Preparation And Properties Of A Series Of Cyclodextrin-Perilla Aldehyde Inclusion Complexes

Cyclodextrins are a class of cyclic compounds linked by ?-1,4 glycosidic bonds between D-glucopyranose units,which are produced from polysaccharides or starches by catalyzation of glucosyltransferases.Natural cyclodextrins are well known as ?-,?and y-cyclodextrin.Due to its special structure of "hydrophilic outer wall and hydrophobic inner cavity",cyclodextrins can form host-guest supramolecular inclusion complexes with lots of small organic molecules,which can improve the physical and chemical properties of organic molecules,such as improving the water solubility and so increasing the stability of organic molecules in the aqueous phase,thus effectively increase the availability of organic molecules,make them to be more widely used in medicine or food.Perilla aldehyde is a natural active substance extracted from plant perilla.It has potential medical value,such as anti-tumor,anti-cancer,anti-inflammatory,anti-oxidation,anti-allergic,helpful to the diastole of blood vessel and nerve protection.However,Perilla aldehyde has been limited in those applications due to its poor water solubility,high susceptibility to oxidation and poor stability at room temperature.In this paper,using ?-,?-,?-class natural cyclodextrin as host molecules and purified perilla aldehyde as a guest molecule,a series of host-guest compounds were respectively synthesized such as ?-cyclodextrin-perilla aldehyde,?-cyclodextrin-perilla aldehyde and ?-cyclodextrin-perilla aldehyde.These supramolecular inclusion complexes have been studied intensively on their inclusion mechanism as well as their properties.Main researches are as follows:(1)Synthesis of inclusion complex:Perilla aldehyde was purified by column chromatography with a purified yield of 70.48%.Then a series of inclusion complexes,?-cyclodextrin-perilla aldehyde,?-cyclodextrin-perilla aldehyde and?-cyclodextrin-perilla aldehyde,were respectively prepared by coprecipitation method using purified cyclodextrins and perilla aldehyde.(2)Structural characterization of inclusion complexes:FTIR,1H NMR,PXRD,SEM,TGA and DSC were used to study the structure of these inclusion complexes.All the results confirmed that their physical mixtures are only a simple superposition of the host compound and the guest compound,while the host-guest supramolecular inclusion compounds of cyclodextrin and perilla aldehyde were successfully synthesized by the coprecipitation method.(3)Studies on the inclusion mechanism:In-depth studies by 1H NMR revealed that(?)in the ?-cyclodextrin-perilla aldehyde inclusion complex and the?-cyclodextrin-perilla aldehyde inclusion complex,the guest molecule perilla aldehyde was stuck at the big mouth of the host cyclodextrin;(?)in the?-cyclodextrin-perilla aldehyde inclusion complex,there is a phenomenon of dynamic equilibrium of perilla aldehyde in the aqueous solution of the inclusion complex.At the same time,both the inclusion constants and inclusion ratios of?-cyclodextrin-perilla aldehyde and ?-cyclodextrin-perilla aldehyde were calculated by the phase solubility method.The inclusion constants are respectively 342 L/mol for the former and 160 L/mol for the latter,while the inclusion ratios of these two inclusion compounds are 1:1.These results indicated that perilla aldehyde can be interacted with ?-cyclodextrin better than with ?-cyclodextrin,probably due to the cavity size of ?-cyclodextrin is smaller than ?-cyclodextrin and so can be better matched with the size of perilla aldehyde.At the same time,the cavity size of?-cyclodextrin is the largest among these three kinds of cyclodextrins,so that the perilla aldehyde molecule enters the cavity of y-cyclodextrin but then can also easily escapes from this large cavity,forming a dynamic equilibrium system and resulting in an unstable formation of ?-cyclodextrin-perilla aldehyde inclusion complex,which is consistent with the results of the1H NMR study.(4)Studies on the application properties of inclusion complexes:(?)Firstly,the phase solubility method was used to study the water solubility of perilla aldehyde before and after inclusion of cyclodextrin.The aqueous solution containing different concentrations of cyclodextrin was added to the aqueous solution of perilla aldehyde.As the concentration of ?-cyclodextrin increased,the concentration of perilla aldehyde increased linearly,indicating that ?-cyclodextrin has a solubilizing effect on Perilla aldehyde in aqueous solution.Results showed ?-cyclodextrin has a similar solubilizing effect on perilla aldehyde.However,y-cyclodextrin reduces the solubility of perilla aldehyde in aqueous solution.The reason may be that in aqueous solution,perilla aldehyde cannot be stably included into the cavity of ?-cyclodextrin.(?)The antioxidant properties of the inclusion complexes were investigated by DPPH method.Results showed that the anti-oxidation effect of both ?-cyclodextrin-perilla aldehyde and ?-cyclodextrin-perilla aldehyde are better than that of perilla aldehyde itself,while the antioxidant property of ?-cyclodextrin-perilla aldehyde is similar to that of the unencapsulated perilla aldehyde molecule.(?)The sustained-release properties of the inclusion complexes were studied by means of dialysis compartment.It was found that the release rates of perilla aldehyde were slowed down in all these three types of cyclodextrin inclusions,indicating that the inclusion interaction can achieve the release control of perilla aldehyde,which is helpful to prolong the action of perilla aldehyde in vivo.