The Influences Of Cyclodextrins On The Micellization Of Several Amino Acid Surfactant Mixed Systems And The Study Of The Host-guest Interactions

The cyclodextrin host molecules can form supramolecular self-assembly systems with surfactant guest molecules.They are one typical kind of"supramolecular cyclodextrin amphiphilic molecules",and are widely used in many fields such as cosmetics,detergents,and drug release.In this thesis,cyclodextrins were selected as the host molecules,and amino acid surfactants or gemini ester quat surfactants were selected as the guest molecules.The influences of cyclodextrins with different cavity sizes on the micellization of several amino acid surfactant mixed systems,and the corresponding host-guest interactions were systematically explored by using some methods such as surface tension method,conductivity method,dynamic light scattering（DLS）,nuclear magnetic resonance spectroscopy（¹H NMR）,transmission electron microscopy（TEM）,and molecular dynamics（MD）simulations,combined with relevant formulas and theoretical model calculations.1.The influences of cyclodextrins（α-CD,β-CD,γ-CD）with different molalities and different cavity sizes on the micellization of surfactant mixed systems composed of N（α）-palmitoyl-lysine methyl ester hydrochlorate（PLM）and sodium N-lauroylsarcosinate（SLS）have been investigated at 298.15 K.The experimental results indicated that the effective molalities of surfactants were reduced due to the formation of different types of inclusion complexes between cyclodextrins and surfactant molecules,leading to the increase of the CMC values of the PLM/SLS mixed systems.The increasing order of CMC values of the mixed systems caused by cyclodextrins is:γ-CD<β-CD<α-CD.The compositions and interaction parameters of the mixed micelles were calculated using the thermodynamic model of mixed micellization.The calculation results indicate that the order of the synergistic effect for the mixed systems from strong to weak after the addition of cyclodextrin is:γ-CD>β-CD>α-CD.The measurement results of zeta potential indicate that when the molar ratio of PLM to SLS in the mixed system is 3:7,the mixed micelles are positively charged.This is because,in comparison with SLS,the CMC of PLM with longer tail chain is lower,and its micelle formation ability is stronger,leading to a larger proportion of PLM ions in the mixed micelles.For the PLM/SLS mixed system,the inclusion complexes with inclusion ratio of 1:2 were manually constructed,and then MD simulations were performed.MD simulation results illustrate that the inclusion complexesα-orβ-CD₁@（PLM₁+SLS₁）are unstable.During the simulation process,one surfactant ion was expelled out of the cavity of cyclodextrin,andα-orβ-CD₁@（PLM₁+SLS₁）was transformed into inclusion complexesα-orβ-CD₁@PLM₁（or SLS₁）.Whereas,forγ-CD with a larger cavity size,the inclusion complexγ-CD₁@（PLM₁+SLS₁）is stable.In addition,MD simulations were performed for the self-assembly process ofβ-CD、PLM and SLS molecules randomly distributed in the simulation box.The simulation results indicate that inclusion complexesβ-CD₁@PLM₁ andβ-CD₁@SLS₁ of type 1:1 and inclusion complexβ-CD₂@PLM₁ of type 2:1 form,there is no inclusion complexes of type 1:2,andβ-CD and the three inclusion complexes participate the formation of mixed micelles.2.At 298.15 K,the gemini ester quat surfactants(C₁₀DEG₃ and C₁₀DEG₆)with different spacer length were used to mix with SLS,respectively.The influence ofβ-CD on the micellization of C₁₀DEG₃/SLS and C₁₀DEG₆/SLS mixed systems was investigated.The results show that,for the C₁₀DEG₃ molecules with shorter spacer,the formation of micelles is easier due to smaller steric hindrance.Therefore,for the two mixed systems with water orβ-CD aqueous solution as solvent,the increasing order of CMC values is:C₁₀DEG₃/SLS<C₁₀DEG₆/SLS,and the order of the synergistic effect from strong to weak is:C₁₀DEG₃/SLS>C₁₀DEG₆/SLS.β-CD can form inclusion complexes with C₁₀DEG₃ and C₁₀DEG₆,and the inclusion complexes are mainly mixtures of 2:1 type and1:1 type.The experimental results of zeta potential illustrate that the mixed micelles are positively charged when the molar ration of C₁₀DEG₃ to SLS is 3:7.This is because the positive charged ionic headgroup of gemini surfactant C₁₀DEG₃ is divalent,and its micelle formation ability is stronger than that of SLS.3.The N（α）-fatty acyl-L-lysine methyl ester hydrochlorides（decanoyl DLM,lauroyl LLM,and myristoyl MLM）with different chain length were used to mix with SLS,respectively.The influence ofβ-CD on the micellization of DLM/SLS,LLM/SLS,MLM/SLS mixed systems was investigated.The results show that the CMC values of N（α）-fatty acyl-L-lysine methyl ester hydrochlorides decrease with the increase of the chain length when water orβ-CD aqueous solution is used as solvent.β-CD can form inclusion complexes with DLM,LLM and MLM,and the inclusion complexes are mainly mixtures of 1:1 type and 2:1 type.For the cationic/anionic surfactant mixed systems,the increasing order of CMC values is:LLM/SLS<MLM/SLS<DLM/SLS.It illustrates that for this kind of mixed systems,the higher symmetry of the chain lengths is more conducive to the formation of mixed micelles.In addition,for the mixed systems with asymetric chain lengths,the longer the total chain length of the surfactants,the stronger the ability to form mixed micelles.The order of the synergistic effect from strong to weak is:LLM/SLS≈DLM/SLS>MLM/SLS.