Construction And Properties Of Cucurbit Ring Supramolecular System Based On Metal Ion/pH Response

Cucurbit[n]urils(Q[n]s)is a type of macrocyclic host,which has a rigid hydrophobic cavity and two negatively charged carbonyl ports.Therefore,the cucurbit[n]urils can not only pass through the cavity and the guest molecule to form inclusions,but also coordinate with metal ions through carbonyl oxygen ports.In view of the characteristics of weak intramolecular interaction of cucurbituril host-guest complex,some external stimulus,such as pH,temperature,humidity,light,redox,metal ions,etc.,can be used to dynamically control the non-covalent bond interaction between the systems to give the flexible stimuli-response characteristics of supramolecular systems will have potential applications in chemical sensing and the design of certain responsive smart materials.In this paper,cucurbit[7]uril(Q[7])and cucurbit[8]uril(Q[8])are selected as host molecules,and Hoechst33342(H33342),rhodamine B(Rh B)and berberine hydrochloride(BER)are selected as guest molecules.Firstly,the H33342@Q[7]supramolecular system that responds to pH-stimuli is constructed,forming a reversible"ON-OFF"fluorescent switch;then,H33342@Q[7]and H33342@Q[8]supramolecules that respond to Hg²⁺are constructed system,through the action of Hg²⁺can change the mode of action of the supramolecular system;finally constructed Rh B@Q[7],H33342@2Q[7]and BER@Q[7]these three supramolecular systems and composed them into fluorescence transmission sensing array,therefore achieves the purpose of detecting multiple metal ions(Ba²⁺,Hg²⁺,Fe²⁺,Fe³⁺,Pb²⁺,Al³⁺,Cr³⁺)at the same time.The main research contents and conclusions are as follows:The supramolecular effects of H33342 and Q[7]under four different conditions of pH 2.0,pH 4.5,pH 7.0 and pH 10.0 were investigated.Under the conditions of pH 2.0and pH 4.5,H33342 and Q[7]first formed H33342@Q[7](1:1)complex,with the increase of Q[7],H33342@Q[7](1:2)complex,the system exhibits strong fluorescence;under the conditions of pH 7.0 and pH 10.0,H33342 and Q[7]mainly form H33342@Q[7](1:1)complex,the system fluorescence is more weak.Therefore,a fluorescent molecular switch based on pH response was designed:by adjusting H⁺(pH 4.5)and OH^-(pH 7.0),the interaction ratio between H33342 and Q[7]can be changed,which can be in H33342@Q[7](1:1)and H33342@Q[7](1:2)to switch back and forth;At the same time,a reversible"on-off"fluorescent switch can also be formed between H33342?2H⁺@2Q[7](strong fluorescence)and H33342?H⁺@Q[7](weak fluorescence).The supramolecular effects of H33342 and Q[8]under four different conditions of pH 2.0,pH 4.5,pH 7.0 and pH 10.0 were investigated,and it was found that the equilibrium states of H33342 and Q[8]were 1:1,1:2 and 2:1.Taking pH 4.5 as an example,combined with the content of Chapter 2,two types of supramolecular systems that respond to Hg²⁺are designed:(1)Hg²⁺is added to the host-guest complex formed by Q[7]and H33342,and Hg²⁺will affect Q[7]Push from the piperidine ring to the benzimidazole position and the second Q[7]will be pushed to the ethyl group,which provides a certain idea for chemical sensing;(2)Add Hg²⁺to Q[8]and H33342 to form In the complex of Hg²⁺,Hg²⁺ions can disrupt the balance of the system through its interaction with H33342 itself and the ion dipole of Q[8],so that both Q[8]and H33342 are oriented in a 1:2 ratio.This may have potential applications in the design of molecular devices and the design of some special ion-responsive smart materials.The supramolecular interactions of three guest molecules of H33342,Rh B and BER with Q[7]were studied,and three host-guest complexes of Rh B@Q[7],H33342@Q[7]and BER@Q[7]were constructed.It can be used as three sensing elements to form a supramolecular fluorescence sensor array to simultaneously detect Ba²⁺,Hg²⁺,Fe²⁺,Fe³⁺,Pb²⁺,Al³⁺,Cr³⁺.First,linear discriminant analysis(LDA)was performed in ultrapure water to evaluate the ability of the sensor array to recognize the above-mentioned metal ions;secondly,a series of Pb²⁺with different concentrations was selected as the model analyte,and the quantitative analysis of the metal ion concentration of the array was investigated.Then,using Huaxi River water instead of ultrapure water(as actual samples),the sensor array's ability to recognize the above-mentioned metal ions was evaluated through linear discriminant analysis(LDA).These results are encouraging and further show the versatility of the sensor array,which can qualitatively and quantitatively detect and identify the seven metal ions Ba²⁺,Hg²⁺,Fe²⁺,Fe³⁺,Pb²⁺,Al³⁺,and Cr³⁺.