Small Molecule Peptide Self-assembled Ordered Media For The Measurement Of Anisotropic Nuclear Magnetic Parameters Of Biomolecules

Nuclear magnetic resonance spectroscopy(NMR)plays a pivotal role in the analysis and identification of organic molecular structures.Among them,anisotropic NMR parameters such as molecular residual dipolar coupling(RDC)and chemical shift anisotropy(RCSA)can be effectively used to analyze molecular configurations and dominant conformations,which provides significant supplementary information for conventional NMR methods(such as the generation distance of the Overhauser nuclear effect(NOE)),and has been favored by researchers in recent years.However,in order to effectively obtain the relevant parameters of the measured molecules,it is necessary to provide a weakly oriented medium to restrict the molecular movement of and therefore induce its orientation.As a consequence,it is of great significance to construct a simple,practical and controllable orientation medium for the extraction of anisotropic NMR parameters of organic molecules.This thesis focuses on the preparation of new lyotropic liquid crystals self-assembled from small molecular-weight peptides for the measurement of NMR anisotropy parameters.In the first chapter of the thesis,the common methods for structural analysis of organic molecules and the advantages and main principles of the application of nuclear magnetic anisotropy parameters are introduced,and the development history,advantages and disadvantages of the oriented media used for anisotropy parameter measurement are summarized;The new type of small molecule peptide self-assembly orientation medium is described in detail;finally,the specific application of NMR anisotropy parameters in the identification of organic molecular structure is summarized.In the second chapter,we designed a new type of amphiphilic small molecule peptide,which constructed a multi-solvent compatible liquid crystal medium through self-assembly,which can be used for the accurate measurement of RDC of organic molecules simply and quickly.The amphiphilic small molecule peptide C₁₅H₃₁-CONH-VVVVKKK-CONH₂(OPA1)was synthesized by solid-phase organic synthesis technology.OPA1 can quickly self-assemble to form a lyotropic liquid crystal medium in three solvents:water,methanol,and dimethyl sulfoxide(DMSO).Select 7 kinds of organic molecules with different biological activities and solubility(gibberellin,triptolide,San Daonian,(-)-huperzine A,oridonin,estrone and(-)-proline Acid)as a model,the quaternary split value(RQC)measurement shows that the small molecule peptide self-assembled liquid crystal has good orientation performance.The C-H coupling spectra of 7 kinds of molecules were further collected,and larger RDCs values were obtained,and the spectra had almost no background peaks,which effectively improved the accuracy of the analysis.Through calculation and fitting by density functional theory and other theories,a very small Q value is obtained.In addition,the orientation ability of the peptide liquid crystal is almost not affected by the purity of the peptide,and a better map can be obtained with crude peptide as the medium.The chiral camphor molecule was selected as the model,and it was found that OPA1/DMSO-d6 medium showed certain enantiomeric discrimination characteristics.In order to further control the degree of media anisotropy,in Chapter 3,we designed and synthesized an amphipathic small molecule peptide C₁₅H₃₁-CONH-AAAAAKKE-CONH₂(OPA2),and adjusted the peptide assembly in DMSO by adding a small amount of water.Orderliness of nanofibers.Scanning electron microscopy(SEM)tests show that the arrangement of OPA2 nanofibers can be transformed from a random network structure to an ordered nanofiber by changing the water content and assembly time.The dependence of order on water content was further tracked by polarized light microscope(POM)and 1D ²H NMR spectroscopy,and it was found that with the increase of water content,the enhancement of birefringence area and the increase of split value can be observed.When 2%(v/v)water was added to 4wt%OPA2/DMSO-d6,the quaternary split value was observed to be 20 Hz.This medium is used for the measurement of residual dipole coupling of estrone molecule,and a smaller Q value is obtained by linear fitting of RDCs calculated by experiment and theory.In the study,it was found that the residual four-level coupling value(RQC)increased with time,indicating that the orientation ability of the medium changes with time.Therefore,this medium is expected to be used for the measurement of organic molecules RCSA in DMSO system.