Characterization Method Of The Cavity Size Of Amylodextrin And Method Application

Amylodextrin(AD)has hydrophobic inside and hydrophilic outside in solution,which is similar to amylose.With regard to this unique property,AD can be used as a wall material for embedding the object molecules.The cavity size of AD can be changed according to the size of the object molecules,therefore,AD has flexible cavity structure like spring,and the cavity size of AD is the basis of accommodating guest molecules and forming inclusion complexes.At present,the study on AD cavity mainly focus on hydrophobic qualitative analysis,and researches about method of quantitative analysis of AD cavity size range are absent.The study on AD cavity size provides direct evaluation for the encapsulation,so as to expand application of AD in the field of embedding.Based on this,carbon nanotubes(CNTs)with a set of fixed sizes were introduced into AD helix.AD fractions were prepared and three of AD with representative chain length were selected,different chain lengths AD-CNTs were tested to determine whether they formed complexes or not,thus the spring cavity size of AD with different chain lengths could be confirmed,and the characterization method of AD cavity size was established,and the application of this method was carried out.Furthermore,it will provide guidance of AD encapsulating of macromolecular guests.AD with different chain length was prepared and characterized.AD_3:1(the volume ratio of alcohol to water was 3:1,the same below),AD_2:1,AD_1:1,AD_1:2,AD_1:5,and AD_>1:5(the precipitated part after adding alcohol solution with a volume ratio of ethanol to water at 1:5)were prepared by pullulanase enzymatic hydrolysis of waxy corn starch combined with gradient ethanol dissolution method.AD_3:1 and AD_2:1 were hygroscopic,and absorption peaks of the two could not be observed after iodine staining.While the absorption peaks of other AD samples were red shifted,indicating that the chain length of each AD presented an increasing trend.High performance gel filtration chromatography and high performance anion exchange chromatography were used to measure the average molecular weight and the chain length distribution of AD,the results showed that the weight-average molecular weight of AD_1:1,AD_1:2,AD_1:5,and AD_>1:5 were 1450,1957,1971,and 2436,respectively,and the average degree of polymerization(DP)were 14.53,15.98,16.20,and 25.25,respectively.The particle size distribution results of AD showed micron size.X-ray diffraction results exhibited that the diffraction peaks of AD were 5.7°,17.3°,22.4°,and 24°,showing B-type crystallization.And¹H nuclear magnetic resonance results showed the peak strength of?-1,4 glycosidic bond at5.4 ppm was high,it proved that AD had straight chain with helical structure.The thermal stability analysis showed that AD had good thermal stability.The characterization method of the cavity size of AD was established.AD_1:1,AD_1:5,and AD_>1:5 with representative DP were selected to combine with single-walled carbon nanotubes with an outer diameter of 0.6?0.8 nm(SWNTs_0.6-0.8),single-walled carbon nanotubes with an outer diameter of 1?2 nm(SWNTs_1-2)and multi-walled carbon nanotubes with an outer diameter of 2?4 nm(MWNTs_2-4)under the action of ultrasonic wave,and the nine composite systems were judged wether formed inclusion complexes or not.After iodine stain reaction,it was found that the ultraviolet absorption spectra of AD_1:1-MWNTS_2-4 and AD_1:5-MWNTS_2-4were not significantly different from corresponding AD_1:1 and AD_1:5 without adding carbon nanotubes(CNTs),while the absorption of other seven groups were decreased.The attenuated total reflection-Fourier transform infrared spectroscopy,laser confocal micro-Raman spectroscopy and differential scanning calorimeter analysis showed that AD_1:1-MWNTs_2-4 and AD_1:5-MWNTs_2-4 did not form the complexes,while the other seven groups formed the complexes.X-ray diffraction analysis was used to verify the V-type single helix structure of seven complexes,which indicated that CNTs entered the inner cavity of AD and formed inclusion compounds.Therefore,the cavity sizes of AD_1:1,AD_1:5,and AD_>1:5 were 0.6?2,0.6?2,and 0.6?4 nm,respectively.The DP of AD_1:1 and AD_1:5 were not same,but they had same cavity size ranges.It could be seen that the cavity size of AD was not completely proportional to the chain length.The key influencing factors of the cavity size characterization method of AD were analysed.The influences of concentration of dimethyl sulfoxide(DMSO)and preparation temperature on the helix cavity of AD were investigated.Iodine was used as the probe.High absorption value indicated that the complex ability of AD with iodine was strong,and the corresponding complex ability with CNTs was weak.As the volume fraction of DMSO increased to 55%,AD changed from loose and discontinuous helical to rigid helical,and with the temperature rising to 100°C,the loose and discontinuous helical structure of AD was gradually destroyed.The absorbance values of AD-CNTs complexes were increased gradually under the two conditions,it was indicated that neither rigid helical structure nor complete extension of molecular chain was favorable conditions to form AD-CNTs complexes.On the contrary,the loose and discontinuous helix was more suitable for CNTs into AD cavity.The application feasibility of cavity size characterization method of AD was verified.AD-V_E with different cavity sizes were studied,no inclusion compound was formed in B-type crystal of AD_1:1 and AD_1:5,and the V_E molecule could stay between the chains of AD;AD_>1:5-V_E showed V-type structure,indicating V_E could enter into AD helical cavity and form inclusion compound.This phenomenon could be explained by the cavity size range of AD.AD_1:1 and AD_1:5 formed small cavity size,V_E could not enter into the cavity,while AD_>1:5 could form large helical cavity,V_E molecules could enter into the inside of the helical cavity.Futhermore,thermal stability and photostability of AD-V_E complex,the loading and inclusion rate of AD to V_E were basically consistent with the changing trend of cavity size of AD.Selecting of AD with appropriate cavity size could protect the guest molecule to reduce the damage caused by heat and light by maximum extent.Therefore,the characterization method of the cavity size of AD was of great guidence significance to the embedding of macromolecular guest by AD.