Study On Langmuir Film Of Amphiphilic Chitosan And The Property Of Chitosan-based Selfassemble Vesicles

Our group has researched the properties of the self-assembled vesicles andLangmuir films of N, N-dilauryl chitosan （DLCS）, which distinctive works attractedcounterpart attention. Here, we hope to synthesize N-methyl-N, N-dilauryl chitosanquaternary ammonium salt （MDLCQ） to further study the properties of theLangmuir film and the self-assembled vesicles of chitosan derivatives.High-substituted N,N-dilauryl chitosan （DLCS） had a good organic solventsolubility. After introducing a methyl to the amino group of DLCS, MDLCQ couldbe obtained and could be dissolved in new organic solvents such as methanol,ethanol, and diethyl ether, but still not dissolved in water. This property provided amore convenient way to prepare self-assembled vesicles by the ethanol injectionmethod. The results of IR spectroscopy, elemental analysis showed that the targetproducts were successfully synthesized.The experimental results of MDLCQ Langmuir film showed a clear liquid-solidtransition platform under pure water subphase. Compared with DLCS film, thecollapse pressure （πc） of MDLCQ was increased, the limit molecular area （Aex） wasdecreased. Dropped the subphase pH, the π-A isotherm of DLCS shifted to the leftafter the solid-liquid conversion platform, the limit molecular area （Aex） decreased（pH7at74.4A², pH1at50.2A²）. At the same condition the π-A isotherm ofMDLCQ shifted to left overally, the limit molecular area （Aex） decreasedsignificantly （pH7at59.82, pH1at28.92）. The experimental results indicateddifferent subphase ions (Na⁺, Ca²⁺, Cl^-, SO₄^2-) had no effect to the behaviors of theDLCS Langmuir films, but the cations had little effct to MDLCQ Langmuir films.When the charge of the anionic increases, the Langmuir films of MDLCQ becamedenser （Cs-1became larger）.The behaviors of MDLCQ/cholesterol Langmuir film was studied in the paperas well. The experimental results indicated that when the content of MDLCQ wasbetween50%⁶0%, the liquid-solid transition platform of the π-A isotherms of mixed film disappeared and the πcbecame bigger than both pure MDLCQ andcholesterol. When MDLCQ content exceeded60%, the π-A isotherms of the mixedmonolayer were similar to the pure MDLCQ, but the limit molecular area （Aex） wasincreased as the content of MDLCQ increased. When the content of cholesterolexceeded50%, the π-A isotherms of the mixed monolayer were similar to the purecholesterol, and the limit molecular area （Aex） was decreased as the content ofcholesterol increased. Above experimental results were similar to the smallmolecular systems, such as DPPC/HD mixed monolayers. The method of the excessmolecular area testified that the MDLCQ/cholesterol mixed monolayer met rigiditypercolation theory.The MDLCQ selfassembled vesicles were prepared by the ethanol injectionmethod and using vitamin B12as hydrophilic model drug and ketoprofen ashydrophobic model drug. The experimental results indicated the Zeta potentials ofthe vesicles were between39.5and46mV, the particle sizes between50and100nm,polydispersity index between0.17and0.26. They could keep stable in30days. Thedrug-load content and the encapsulation efficiency of the vesicles was increased asthe pH decreased （The drug-loaded content:0.08g/g at pH7,0.11g/g at pH1.2forB12;0.25g/g at pH7,0.28g/g at pH1.2for ketoprofen; the encapsulation efficiency:9.83%at pH7,13.87%at pH1.2for B12;79.21%at pH7,83.46%at pH1.2forketoprofen）. Environmental pH had little effect on drug release of the vesciles. Theequilibrium rates of drug release were decreased as the preparation medium pHdecreased （44%at pH7,32.4%at pH1.2for ketoprofen;57.4%at pH7,46.2%atpH1.2for B12）. The drug releasing behaviors of the vesicles were consistent withthe study of the Langmuir films.