| Chirality is one of the fundamental properties in nature,and it is also one of the most prominent characteristics of life.Many biological macromolecules are chiral such as polysaccharides,nucleic acids and proteins,which are the important basis of life activities.In addition to playing a very critical role in life activities,chirality also plays a very important role in human production and life.There are many ways to obtain homochiral molecules,among which,asymmetric synthesis is one of the effective means to obtain a large number of enantiomers.In this process,determining the configuration and enantiomeric composition of the object chiral molecules plays a key role to measure and feedback the efficiency of asymmetric synthesis.In recent years,in order to meet the needs of high-throughput chirality analysis with the rapid development of asymmetric synthesis,a variety of efficient spectroscopy-based chirality sensors have been developed.Among them,circular dichroism(CD)spectroscopy can not only be used for quantitative analysis,but also directly identify the configuration of the analyte according to the spectral characteristics.Therefore,chiral sensing method based on CD spectroscopy has received extensive attention.Although a large number of chiral sensing systems based on CD spectroscopy have been successfully developed,the chiral transfer mechanism is either localized transfer with specific stoichiometric ratios(the advantage is enabling a wide range of detection concentrations,the disadvantage is low sensitivity)or chirality transfer with nonlinear amplification effect(the advantage is high detection sensitivity,the disadvantage is the narrow detection concentration range),therefore,achieving high sensitivity detection and quantification in a wide concentration range is still a serious challenge.In addition,there are few systematic studies on the synthesis methods,detection methods,and material scalability of the existing sensing bodies,and the comprehensive properties are still far from practicality,so it is urgently needed to develop new sensing systems and chiral transfer mechanism.Au(?)-thiolate two-dimensional assemblies(hereafter referred to as assemblies)can be viewed as layered assembly arranged by two-dimensional Au(?)-thiolate linear coordination polymer chain structures through lateral aurophilic interactions.The middle structure of its single-layer is a gold-sulfur inorganic framework,which has high structural stability,and high-density functional groups are integrated on the upper and lower surfaces,providing abundant interaction sites for sensing and detection;Although the gold-sulfur framework has good crystallinity,the surface functional groups have disordered interactions,so the ligands have certain conformational freedom,which avoid the long-range chirality transfer on the surface of assembly,providing the basis for new chiral transfer behaviors.In this paper,we used Au(?)-thiolate 2D assemblies as achiral hosts to adsorb chiral guest molecules through non-covalent and covalent bonds,respectively,and investigated their behaviors and laws of chirality transfer on the surface of the assembly.And we have realized CD chirality sensing on two-dimensional surfaces for the first time.The specific research results are as follows:First,we used carboxylic acid-functionalized assemblies(Au(?)-MPA)and chiral1,2-diamino cyclohexanes with amino functional groups as model research systems to explore the feasibility and laws of CD sensing.In this process,we determined the chiral sensing method that the chiral molecules interact with the ligands on the surface of the assembly,thereby making the assembly produce supramolecular chirality;new laws were found that the CD signal of the assembly increase linearly and then nonlinearly with the concentration of diamino cyclohexanes.Utilizing the high asymmetry factor and the existence of a wide linear response region of the assembly,we realized the quantitative detection to diamino cyclohexanes with high sensitivity and a wide concentration range;using the nonlinear region,the determination of the enantiomeric composition in a slight excess was realized.Above all,it was overcomed that the difficulty of completing high sensitivity and quantitative detection in a wide range at the same time in the previous system.Second,we revealed a new class of supramolecular chirality and a new chirality transfer mechanism on the surface of 2D assemblies by the in-depth study of the Au(?)-MPA assembly-diamino cyclohexanes system.A new form of supramolecular chirality was established,which does not depend on the twist or helix of positional features of the continuous building blocks,but depends on the asymmetric conformational distribution of ligand molecules on the surface of the two-dimensional assembly.It was proved that at low diamino cyclohexane concentration,one diamino cyclohexane can induce multiple ligands to undergo conformational changes to form discrete chiral amplification regions.At this point,the CD signal of the assembly increases linearly with the concentration of diamino cyclohexane.When the concentration of diamino cyclohexane exceeded the critical value,the discrete chiral amplification regions overlapped,and the two-dimensional confined space occupied by the ligand was gradually compressed by the bound diamino cyclohexane,and the interaction of chiral transfer is gradually enhanced,which leads to the nonlinear improvement of the chiral transfer efficiency and the nonlinear growth of the chiral signal,resulting that the chiral transfer behavior change from linear growth to nonlinear growth.The research results enrich the existence forms and chiral transfer behaviors of supramolecular chirality.This chiral transfer behavior with both linear amplification and nonlinear amplification also provides a new strategy for establishing efficient chiral sensing systems.Finally,the functional groups on the surface of the assembly were modified by the co-assembly method,which expanded the detection range of the assembly.We successfully synthesized Au(?)-MPA-MPBA assemblies by introducing the functional ligand 4-mercaptophenylboronic acid(MPBA)into the assemblies by co-assembly method.Then,sugar alcohols and sugar amine molecules were adsorbed on the surface of the assemblies by the covalent reaction of polyhydroxy chiral molecules and boronic acid,and chiral transfer was realized.And the high sensitivity detection over a wide concentration range of these chiral guest molecules was completed.The research results prove that the detection range can be expanded by introducing functional molecules in Au(?)-thiolate layered assembly under the induced model unchanged,which provides a basis for the development of a general-purpose chiral sensing system.In summary,using this two-dimensional Au(?)-thiolate assembly with both ordered and disordered characteristics as a material system,we established a method for generating supramolecular chirality by the interaction between chiral inducers and ligands on the surface of the assembly to induce a relatively distorted conformation of ligands,thereby making the assembly produce.A new form of supramolecular chirality with asymmetric conformational distribution of surface ligands are confirmed,which not rely the twist or helix positional features between the continuous building elements.Combined with a variety of research methods and analytical techniques,we revealed and elucidated the special chiral transfer behavior existing on the two-dimensional confined surface,that is,under the condition of low chiral inducer concentration,it exhibits linearly amplified chirality transfer behavior,while under the condition of high chiral inducer concentration,it has nonlinearly amplified chiral transfer behavior.The high-sensitivity and wide-range detection of chiral small molecules have been achieved by using this behavior,and the extendibility of the assembly in the detection range is verified.The assembly exhibit high stability,reusability,and solid-state detection possibilities with potential for practical applications.Therefore,the research in this paper provides a new idea for the construction of stable and high-performance chiral sensing systems. |
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