Cucurbit[7] Uril Host-guest And O…S Weak Interactions Based On Single Molecule Conductance

Single-molecule conductivity measurement,a technique for measuring the electrical properties of individual molecules,has shown great potential not only in molecular electronics but also in physical chemistry,analytical chemistry,biosensing,and gene sequencing.The hydrogen bonds,coordination bonds of metal ions,π-π interactions,and such weak interactions between cucurbiturate hosts and guests and between O…S in individual molecules have important effects on the regulation of carrier mobility,and it is necessary to conduct systematic and in-depth studies on the weak interactions of various non-covalent bonds between molecules at the single-molecule level by using single-molecule conductivity measurement techniques that are highly sensitive to electron transport paths.At present,the weak interactions between cucurbituran hosts and objects are mainly studied at the single-molecule level using optical and mechanical methods,which are complicated to detect.And single-molecule conductivity measurement technique as a precise single-molecule detection means,has the advantages of real-time,accurate and rapid.Cucurbit[7]urea(CB[7])is a supramolecular macrocyclic compound that can wrap different guest molecules to form host-guest complexes with excellent molecular recognition properties.This project will systematically investigate the weak interactions between cucurbituril molecules and their guest molecules under domain-limited conditions using single-molecule conductivity measurements.This research can advance the application of single-molecule conductivity measurement techniques in basic physical chemistry,as well as promote basic research and practical applications of cucurbituride supramolecules in the medical field.While the study of weak interactions between the host and guest of CB [7] using single-molecule conductance measurement techniques is still in the exploratory stage,the measurement of single-molecule conductance is influenced by three parts: the gold electrode,the molecule,and the anchoring group,and changes in any of its constituent structures can have significant effects on the electron transport properties.In addition to these internal effects,there are also many external environmental influences;for example,pH,bias,light,solvents,etc.Our study of the CB[7] host-guest complex revealed that the recognition molecular system is more complex and has more influencing factors.In order to be able to discuss the weak interactions of molecules in more depth,we designed and synthesized another organic conjugated molecule with a simple system containing weak interactions between O…S for the study.First,in order to confirm the reliability of the scanning tunneling microscopy solidification method(STM-FJ),simple carbon chain molecules with stable conformations were used for the tests;then the influence of the weak interactions between the host-guest and O…S interactions of cucurbit [7] urea on the charge transport was investigated at the single molecule level.The following conclusions were obtained.(1)The conductivity values of CB[7] and the host-guest complex of CB[7] wrapped with amantadine hydrochloride were examined separately using STM-FJ,and it was found that the wrapping of amantadine hydrochloride decreased the conductivity value of CB[7] by about 33%,which was due to the weak interaction between the amino group of the guest molecule and CB[7] that interfered with the electronic coupling between the electrodes.(2)The competitive reaction of Hoechst 33258 pentahydrate with 1,5-pentanediamine in CB[7] was examined by adjusting the pH and using STM-FJ.It was found that the guest molecule 1,5-pentanediamine encapsulated in CB[7] was replaced by Hoechst 33258 pentahydrate upon pH change,resulting in a decrease in conductivity value of about 78%,which was mainly caused by the change in weak interaction between the two guest molecules and CB[7].(3)Conductance measurements of three organic conjugated molecules(DT-B,DTCB and DT-OB)synthesized by in-house design using STM-FJ showed that the conductance of DT-CB and DT-OB increased by a factor of 2 and 3.5,respectively,compared to that of DT-B.This is caused by the weak O…S interactions in DT-CB and DT-OB,i.e.,non-covalent conformational locking,indicating that the weak O…S interactions in organic conjugated molecules have a significant enhancement of charge transport.