Theoretical Study On The Interaction Of Cyclodextrin With Organic Small-molecules

In this paper, the theory of quantum chemistry calculation was carried out to study theinteractions between the cyclodextrin with different small molecule.Firstly, PM3semi-empirical and density functional theory (DFT) methods were carriedout to study the interaction of ferulic acid (FA) with α-cyclodextrin (α-CD). First, all theinitial structures of structured inclusion complex were optimized by PM3semi-empiricalmethod, the result point out the two lowest energy structures formed from a different side ofα-CD. Second, two most energetically favorable inclusion complexes were reoptimized byDFT B3LYP/6-31G*method and then analysis their geometries, binding energy, Müllikencharge transfer and frontier molecular orbital. The calculated results showed that FA enteringinto the cavity of α-CD from wide side was more stable than from narrow side.Secondly, the inclusion complex of1-methylcyclopropene (1-MCP) with α-cyclodextrin(α-CD) is studied by density functional theory (DFT) and PM3semiempirical methods in thepaper. Firstly, DFT B3LYP/6-31G*method is used to optimize geometries of isolated α-CDand1-MCP. Secondly, PM3method is performed on the all inclusion complexes from aninitial geometry optimization, the results point out two inclusion complexes of the lowestenergy which1-MCP entering into α-CD from different sides. Thirdly, DFT method is used toperform analysis of energies, hydrogen bond interactions, Mülliken charge transfers andfrontier molecular orbitals (FMO) of two most energetically favorable inclusion complexes atB3LYP/6-31G*level. The calculated results show that1-MCP entering into the cavity ofα-CD from its wide side has a lower energy. Finally, to know whether infrared (IR) spectrumis suitable for the detection of1-MCP/α-CD, IR spectrum of the inclusion complex iscalculated by DFT B3LYP/6-31G*method.Thirdly, in order to investigate the interaction of difluorobenzocyclooctyne (DIFBO)with β-cyclodextrin (β-CD), this work carries out hybrid density functional theory (DFT) andhybrid method our own n-layered integrated molecule orbit and molecule mechanics(ONIOM). ONIOM method is performed on the all inclusion complexes from an initialgeometry optimization. This work aims to find out two inclusion complexes of the lowestenergy which DIFBO entering into β-CD from different sides. DFT B3LYP/6-31G*method isused to optimize geometries of β-CD and DIFBO. In both the gas phase and water, this workcalculates the HF (heats of formation) single point energies of two favorable inclusion complexes using DFT B3LYP/6-31G*method. Two the most energetically favorablestructures are used to perform analysis of energies, natural bond orbital (NBO), Müllikencharge transfer and frontier molecular orbital (FMO) at B3LYP/6-31G*level. The calculatedresults indicate that DIFBO entering into the cavity of β-CD from its wide side is more stablethan narrow side. Besides, infrared (IR) spectrum of the inclusion complex is calculated byDFT B3LYP/6-31G*method. The results demonstrate that IR spectrum may be suitable forthe detection of β-CD/DIFBO.Fourthly, in this work, the interaction of n-octyl β-D-glucopyranoside (OGP) into thecavity of α-cyclodextrin (α-CD) had been investigated by using hybrid density functionaltheory (DFT) and hybrid our own n-layered integrated molecule orbit and moleculemechanics (ONIOM) methods. ONIOM method was performed on the all inclusioncomplexes from an initial geometry optimization, two inclusion complexes of the lowestenergy which OGP entering into the cavity of β-CD from different sides were obtained.Analysis of the structures, energies, solvent effect and natural bond orbital (NBO) werecarried out at B3LYP level. The calculated results indicated that OGP entering into the cavityof α-CD from its narrow side was more stable than wide side. Moreover, the inclusionprocess of OGP into α-CD was investigated by means of infrared (IR) and Ramanspectroscopy at B3LYP/6-31G*level. The calculated vibrational spectrum indicated that IRand Raman spectroscopy may be suitable for the detection of α-CD/OGP.