Preparation Of Cellulose Lyotropic Liquid Crystals And Application For The Measurement Of RDC

Cellulose has attracted more and more attention as natural polymers with the advantages of wide variety,good biocompatibility and biodegradability.Cellulose nanocrystals(CNCs)prepared by sulfuric acid hydrolysis have sulfate groups on their surface.The CNCs are rod-shaped particles with high axis ratio,high crystallinity and large specific surface area.In addition,their surfaces are rich with groups that can be chemically modified.Therefore,CNCs have broad application prospects such as optical materials,compound material and biomedical materials et al.It is worth noting that the rod-shaped CNCs suspensions can spontaneously shear-induced orientation to form lyotropic liquid crystals after reaching a certain concentration.The lyotropic liquid crystals can induce the solute to align.Due to the characteristics of their large molecule,no signal is produced in the liquid nuclear magnetic resonance(NMR).It may be used in the determination of residual dipolar coupling(RDC)parameters in NMR.Therefore,in this dissertation,cellulose was chosen as the research object,and cellulose aqueous liquid crystals(TCNCs and CNCs)and organic liquid crystals(CNC-g-AA)were prepared.The main contents are as follows:(1)In order to obtain a low critical concentration of cellulose liquid crystals,the ascidian was chosen as the experimental material,according to its contained a large aspect ratio.Firstly,cellulose was extracted from the ascidian by bleaching and deproteinizing.Then the TCNCs liquid crystals were prepared by sulfuric acid hydrolysis.Average TCNCs particle size was obtained by hydrolysis with different treatment time and ultrasonic time.The optimum reaction parameters were analyzed by scanning electron microscopy and ²H NMR.The low concentration of 20.0 mg/m L was obtained with hydrolysis time 6 hours and ultrasonic 120 min.At this time,the length of cellulose is 100-600 nm and the diameter is 20-30 nm.(2)To detect and improve the splitting of the water signal in one-dimensional ²H NMR spectra,we have systematically explored the effect of reaction time,ultrasonic time and ionic strength on CNCs liquid crystals.The well-ordered alignment of CNCs liquid crystals was further uncovered by ²H NMR spectrum,with the residual quadrupolar coupling(RQC)splitting of ca.9.92 Hz at 98.0 mg/m L and p H 8.6.The experimental results show that liquid crystals have good stability by testing the thermostability of alignment and measuring the RDCs of proline.So that CNCs liquid crystals can as an aligned medium for the measurement of RDC in biomolecular NMR studies.(3)To improve its compatibility with organic solvents,weaken the effect of hydrogen bond and reduce the ability of gelation,further modifications were carried out by grafting polymer brushes onto cellulose crystallite using free radical polymerization that was achieved with acrylic acid as the monomer.To access the alignment of CNC-g-AA liquid crystals in DMSO-d₆,1D ²H NMR spectra were measured.And the birefringence of CNC-g-AA liquid crystals was further observed under polarizer.The result indicated that the modified cellulose could form liquid crystals in DMSO.Furthermore,to show the compatibility and applicability of the CNC-g-AA liquid crystals as an aligned medium,the RDCs of artemisinin,gibberellin and oridonin were determined.The Q values were all less than 0.1,indicating that CNC-g-AA as a suitable aligned medium to measure the RDC in DMSO-d₆.