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Supramolecular Recognition Mechanism and Its Application Based on Calixarene Coated QCMs

Author: DaiYunLin
Tutor: CaoZhong
School: Changsha University of Science and Technology
Course: Physical and chemical
Keywords: QCM Methanol Ethanol Isopropanol Host-Guest Recognition C–H…π
CLC: TP212.2
Type: Master's thesis
Year: 2011
Downloads: 10
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Abstract


With high sensitivity and selectivity, coated quartz crystal microbalance (QCM) sensors have become an important research direction for online monitoring the industrial toxic gases and environmental air pollutants. The coating materials for recognition of gas molecules with good performance were large-ring molecules and functional polymers, especially, calixarene was an oligomeric macrocycle compound by condensation of the alkyl phenol and formaldehyde, possessing high sensitivity and selectivity for recognition of small molecules, has become a very important area in supramolecular recognition fields. In this thesis, four calixarene supramolecular compounds (RCT, MRCT, PCT, TBCA8) were employed as the adsorption coating materials of QCMs for responding to trace harmful small molecule alcohol gases, and the sensors’performance and recognition mechanism were discussed in this paper. It was found that RCT was the most effective active absorption coating material to methanol and isopropanol, MRCT was the most effective coating material to ethanol, and were optimized to obtain the most amount of film as respect to each small molecule alcohol gases. The coated QCM devices had good sensitivity, reproducibility and stability when used for alcohol molecular detection. With rapid test time, good reproducibility, selectivity and stability, the RCT coated QCM sensor could be used for the detection of methanol samples with a recovery of 97.83～103.66%, which agreed well with those obtained by gas chromatography, showing its potential application on the determination of methanol gas in atmospheric environment. In addition, the kinetics processes for adsorption and desorption of guest molecules such as methanol on RCT have been fitted well, that the initial speeds of the adsorption and desorption processes were obtained as -0.2110 Hz/s and 0.09497 Hz/s, respectively.The single crystal of RCT-MeOH was prepared and subject to X-ray diffraction analyis, showing that the recognition mechanism was based on the formation of C–H?πbond interaction between the methyl group of the methanol molecule and the phenyl ring of the calixarene. The further examination showed that the RCT interacted with the methyl of the methanol molecule through the large negativeπ* electron center which was formed by the four molecularπelectronic center structure in its cavity. Similarly, the supromolecular mechanisms for ethanol and isopropanol have also been discussed. The recognition mechanism for RCT to isopropanal was based onπ* electrostatic attraction to C-H. But for recognition of ethanol by MRCT, there exsiting a strong interaction between the hydroxyl groups of the calixarene molecule and the hydroxyl group of the ethanol molecule, which could form stronger hydrogen bonds than the C—H---π, because the ethanol molecule only have two C-H.By means of structural analysis of X-ray single crystal diffraction’s data, the study will provide theoretical guidance for sensitive active substances’s selection and design in the new kinds chemical and biological sensors, showing their important theoretical value and research significance in the field of supramolecular sensing recognition.

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