Spectrometric Studies Of Supramolecular Host Based On P-sulfonated Calix[n]arenes

Calixarene is well known as the third generation supramolecularhost compound followed crown ether and eyelodextrin. Thesupramolecular chemistry based on calixarene host is one of themost active areas of research. Calixarene, which has a cavity can beadjusted to changes in conformation, easy chemical modification,etc., is widely used in the life sciences, materials science,pharmacology and supramolecular chemistry research that show awide range of applications. This paper studies on the interactions ofwater-soluble p-sulfonated calix[n]arene as the host supramolecularhost and some guest molecules, basing on the supramolecularchemistry, pharmaceutical analysis and chemical thermodynamics,using fluorescent spectrophotometry, UV spectrophotometry,1H NMRspectrum and density functional theory calculations. It is establishedmolecular models and elaborated formation mechanism of inclusioncomplexes by the means of experimental and theoretical methodsthat provide a theoretical basis for the application of drugs to improvebioavailability and fluorescent sensors. Details are as follows:1. The general respect of supramolecular chemistry was described briefly. The development process of calixarene wasreviewed and calixarene structure characteristics and mechanism ofits derivatives interaction with guest molecules were introduced.Moreover, the important results and research status on molecularrecognition, molecular assembly and thermodynamics of calixarenesand its derivatives were reviewed.2. The supramolecular interactions between a homologousseries of p-sulfonated calix[n]arenes (SCnA, n=4,6,8) as hosts andlomefloxacin (LFLX) were studied by spectrofluorimetry and1H NMR.LFLX was found to react with SCnA to produce a1:1host-gueststable complex, respectively, and the fluorescence intensity of thecomplexes decreased gradually with increasing SCnAconcentration. The effects of the inclusion process factors andforces were examined in detail from pH and temperature, etc.,confirmed the electrostatic interaction and structure matchingeffect played effective roles in the formation of inclusion complexes.The results show that different stability constants of the complexwere obtained under different pH and temperature. And in the sameconditions, the complex stability constant monotonically increasedwith the number of phenolic units in the calixarene ring. At T=298K, the stability constant of the inclusion complex was7.49×104,2.38×105, and3.96×105L/mol at pH6.00in Britton-Robinson buffersolution upon the addition of SC4A, SC6A, and SC8A, respectively.At the same time, enthalpy (ΔH) and entropy changes (ΔS) can bedetermined from the Van′t Hoff equation. Therefore, thecorresponding free energy change (ΔG) can also be obtained. Thenegative sign of free energy illustrated that the complex formation process is spontaneous. In addition,1H NMR studies and densityfunctional theory (DFT) calculations to explain the mechanism ofinteraction and the establishment of a molecular model ofhost-guest inclusion.3. The inclusion interaction between procaine (PC) andp-sulfonated calix[6]arene (SC6A) was investigated via fluorescenceand1H NMR spectroscopy. The effects of pH, temperature, ionicstrength, and SC6A concentration were examined in detail. In aBritton–Robinson solution with a pH of7.5, the fluorescence of PCsignificantly quenched upon the addition of SC6A, which revealed theformation of inclusion complexes between PC and SC6A. Thestoichiometric ratio of1:1was obtained via the continuous variationmethod. The inclusion constant of PC–SC6A complexes was1.29×104L/mol, which was obtained via the nonlinear curve fitting method. The1H NMR spectra verified that the aliphatic chain of PC may be partiallypenetrated into the hydrophobic cavity of SC6A. This finding wasconfirmed by density functional theory calculations.4. Supramolecular inclusion interactions of three different ionicliquids with p-sulfonated calix[4]arene were studied via a new type offluorescent probe titration method. Coptisine (COP) emits weakfluorescence in acidic (pH=2) aqueous solution. However, aremarkable increase in fluorescence intensity is observed whenp-sulfonated calix[4]arene (SC4A) is added to the aqueous solution.With the addition of ionic liquid, the aqueous solution of COP-SC4Acomplexes considerably quenches fluorescence intensity. Thesupramolecular interactions of SC4A with three types of1-butyl-3-methylimidazolium ionic liquids (C4MIm+) were examined based on this fluorescent probe system. This phenomenon explainsthat the inclusion behavior were occurred between the three ionicliquids and SC4A through competitive effects. And complexes bindingconstants were calculated by linear equations.1H NMR spectrumconfirmed the1-butyl-imidazolium moiety of ionic liquid wasembedded in the SC4A cavity, and the counter anion slightly affectedthe binding capacity of the ionic liquid. molecular modelingtheoretical calculations established the molecular model of inclusioncomplexes.