Interactions Of Proteins With Binary Monolayers Through Metal Coordination And Stimuli-responsive Controlled Release Of Pillararene Supramolecular Nanovalves

The development of biomedical functional materials are closed related to the development of bioscience.Both of them are the focuses of current scientific research.Protein-biomembrane interactions and stimuli-responsive nanoparticle-based drug delivery systems are the important content of the research of bioscience and the exploitation of biomedical functional materials,respectively.This thesis has two focuses,of which the research content are briefly summarized as:1)the multi-site binding of myoglobin(Mb)to the binary monolayers at the air-water interface surface through metal coordination and the interactions between Mb and the monolayers,2)the synthesis and host-guest chemistry of water-soluble pillararenes and the self-assembly and stimuli-responsive controlled release of pillararene nanovalves based on mesoporous silica nanoparticles.Many important cellular activities involve protein-membrane interactions,which are usually multivalent.Moreover,the fluidity of cell membranes play an important role in biological functions.The studies of protein-membrane interactions are helpful for not only the understanding of the biological processes but also the development of new biosensors.Langmuir monolayers at the air/water interface are a good model system for biological membranes.The molecular structures of the monolayers and the secondary structures of adsorbed proteins can be analyzed in situ by infrared reflection absorption spectroscopy(IRRAS).Coordination interactions of lipids,metal ions,and proteins are able to precisely control the specific interactions between lipids and proteins and are widely used in the studies of protein-membrane interactions or protein-protein interactions occuring on membrane surfaces.Due to the complexity of the cell membraneres,studies of complex systems help to obtain a full picture of the interactions between proteins and lipids.Stimuli-responsive nanoparticle-based drug delivery systems can improve therapeutic efficacy of drugs,reduce toxic side effects,and target drug delivery,which is one of hot research topics.Mesoporous silica nanoparticles(MSN)have emerged as an ideal drug container owing to high specific surface area,large pore volume,tunable pore size,good biocompatibility,and easy and diverse functionalization.Supramolecular nanovalved-MSN drug delivery system is an important branch of stimuli-responsive nanoparticle-based drug delivery systems.The introduction of new host-gest complexes and the development of diverse stimuli-responsive strategies help to broaden the application prospect of drug delivery systems.In recent years,pillararenes,as an emerging macrocyclic host,have received much attention.Pillararenes have been widely applied to develop new functional materials owing to their highly symmetrical structures,easy synthesis and functionalization etc.1.Metal Coordination Interactions between Mb and Binary Monolayers at Air/Water InterfaceSimilar to iminodiacetic acid(IDA),nitrilotriacetic acid(NTA)can specifically bind proteins with surface exposed histidine residues in the presence of transition metal ions.1,2-dioleoyl-sn-glycero-3-[(N-(5-amino-1-carboxypentyl)iminodiacetic acid)succinyl](DOGS-NTA),with two unsaturated hydrocarbon chains and one NTA headgroup,was mixed with 1,2-dioleoyl-sn-glycero-3-phosphocholine(DOPC),1,2-dihexadecyl-glycero-3-triethylene glycol(DPE)and 1,2-dihexadecyl glycerol(DPG)respectively to form three binary monolayers at air-water interface:DOGS-NTA&DOPC,DOGS-NTA&DPE,and DOGS-NTA&DPG.The miscibility and phase separation behaviors of these binary monolayers were analyzed with surface pressure-area(π-A)isotherms and IRRAS spectra.Due to the identical unsaturated hydrocarbon chains,DOGS-NTA and DOPC were miscible in their binary monolayers.Both of DPE and DPG have saturated hydrocarbon chains,but their headgroups were different in length,which made them show different π-A isotherms.Thus,the DOGS-NTA&DPE and DOGS-NTA&DPG binary monolayers also showed different miscibility.The IRRAS spectra studies indicate no Mb binding to the monolayers of DOPC,DPE,or DPG in the presence of Ni2+(or Cu2+)and DOGS-NTA in the absence of Ni2+(or Cu2+)at the surface pressure 30 mN/m but significant myoglobin binding to the DOGS-NTA monolayer in the presence of Ni2+(or Cu2+)because of the formation of ternary complexes of NTA-Cu2+-His.Compared with Ni2+,in the presence of Cu2+ with a stronger coordination ability,the amount of adsorbed Mb on the monolayer surface was ca.5 times higher than that in the former case。Fully extended length of the headgroup of DOPC is shorter than that of DOGS-NTA,and the PC headgroups might take a flat orientation which would result in further reduction of the length.Part aminoacid residues of Mb protrude the plane defined by multi surface exposed His residues.In the DOGS-NTA&DOPC binary monolayers,the increase of surface densities of NTA(XNTA),on one hand,would facilitate multi-site binding of Mb,however,on the other hand,the surrounding extending NTA headgroups were unfavorable for the access of surface exposed histidine residue of Mb to the NTA headgroups,resulting in increase of steric hindrance for multi-site binding.The amount of bound Mb increased with the increase of XNTA in the presence of Cu2+ with a stronger coordination ability,but first nearly unchanged and then increased in the presence of Ni2+.In the cases of phase-separated binary monolayers(DOGS-NTA&DPE and DOGS-NTA&DPG),protein binding occurred in the DOGS-NTA domains.Multi-site protein binding occurred with insertion of protein segment into the headgroup regions of the monolayers.The steric repulsion between inserted aminoacid residues and headgroups would result in the decrease of lipid packing density,and the increase the surface pressure of monolayers which would further result in the decrease of tilt angle of the hydrocarbon chains in the ordered phase.Multi-site protein binding occurred on the boundary of the disordered phase induced lateral rearrangement to reduce the expulsion between bound proteins and the headgroups of monolayers.Multi-site binding of Mb to phase-separated binary monolayers related to metal ion,XNTA and length of headgroups.The difference of headgroup length in the DOGS-NTA&DPG binary monolayers were bigger than that in the DOGS-NTA&DPG binary monolayers.The protein-directed lateral rearrangement of the DOGS-NTA&DPG binary monolayers could minimized the repulsion to the headgroup regions of the binary monolayers owing to the multi-site protein binding.Compared with Ni2+,in the presence of Cu2+,stronger coordination interaction facilitated multi-site protein binding by overcoming steric hindrince,resulting in the increase of bound proteins.2.Carboxylatte-Substituted Pillar[6]arene-Valved Mesoporous Silica Drug Delivery System for Multiresponsive Controlled ReleaseThe synthesis and host-guest chemistry of pillararene(PA)derivatives are a hot research topic,and the applications of PAs in relevant research fields are essential to explore.Carboxy late-substituted pillar[6]arene(CPA[6])and a new guest,1,3-dimethyl-2-methylmercaptobenzimidazolium(DMBI-SM)were synthesized and could form a 1:1 inclusion complex with a high binding affinity.1H NMR titration studies indicated that the association constant between them was(2.82±1.83)×105 M-1.CPA[6]-valved MSN vehicles functionalized with dimethylbenzimidazolium(DMBI)or bipyridinium(BP)as stalks were constructed,respectively,for multiresponsive controlled release.CPA[6]encircled the DMBI or BP stalks to develop supramolecular nanovalves for encapsulation of cargo within the MSN pores.The release of cargo was triggered by acidic pH or competitive binding for the dethreading of CPA[6]and the opening of the nanovalves;moreover,coordination chemistry was the first strategy to activate CPA nanovalves by metal chelating with the carboxylate groups of CPA for cargo release.The controlled release of the CPA[6]-valved MSN delivery systems can meet diverse requirements and has promising biological applications in targeted drug therapy.3.Phosphonate-Substituted Pillar[5]arene-Valved Mesoporous Silica Nano Delivery System for Stimuli-Responsive Controlled ReleaseA new watersoluble pillararene,phosphonate-substituted pillar[5]arene(PPA[5])was firstly synthesized.Supramolecular nanovalves could be assembled on the basis of the host-guest complex between PPA[5]and choline(Ch)(or pyridium(Py))functionalized on the MSN surfaces.The dissociation constant of phosphonic acid groups of PPA[5]was larger than that of carboxylic acid groups of CPA,resulting the response of PPA[5]nanovalves to a smaller extent than that of CPA nanovalves upon trigger of pH.Moreover,the PPA[5]-valved MSN functionalized with different stalks(Ch or Py)displayed different stimuli-responsive performances.Thus,The stimuli-responsive performances of the pillararene nanovalves can be tuned by altering the stalks on the MSN surface and pillararene derivatives for diverse requirements.Moreover,the controlled release of PPA[5]-valved MSN drug delivery systems could be activated by the competitive binding of Methyl viologen and the coordination of Zn2+.