Elucidation of Retention Mechanism with Distinct Functional Groups on Polysaccharide-Based by Means of Thermodynamics /Infrared Spectroscopy/Molecular Simulations.

• Main Authors: ANG-YEH LIN, 林昂曄
• Other Authors: Hung-Weu Tsui
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/22rd3t

碩士 === 國立臺北科技大學 === 化學工程與生物科技系化學工程碩士班 === 106 === Polysaccharide derivative-based sorbents have been widely used for chiral separation for a long time. However, it remained unclear how the chiral stationary phase interact with the molecules associated with different functional groups. This research was divided into two approaches to analyze the retention mechanism. The effects of the different molecular interaction between solutes and polysaccharide-based chiral sorbents were discussed in the first part. The adsorption enthalpy changes of the adsorption process and the functional groups which can interact with sorbents were investigated by density functional theory (DFT), fourier-transform infrared spectrometer (FTIR) and high performance liquid chromatography (HPLC). Results indicated that the functional groups C=O, COC and phenyl groups of solutes showed considerably different interaction mechanisms with the sorbent. The DFT simulations and IR spectra indicated that alcohol molecules may simultaneously form two H-bonds with the sorbent. However, ketone molecules and ether molecules may form one H-bonds with the iv sorbent. H-bonds formed between the NH groups of sorbent and the C=O groups of ketone molecules, and between the NH groups of sorbent and the O groups of ether molecules. The effect of the side chain on the different molecular structure of two commercially important polysaccharide-based chiral sorbents-amylose tris (3,5-dimethlphenylcarbamate) (IA) and amylose tris (3,5-dichlorophenylcarbamate) (IE) were investigated by molecular dynamic (MD), DFT and HPLC. For IE, the H-bond strengths of the NH groups were stronger than that for IA. The cellulose backbone and amylose backbone were left-handed helical structure can be investigated by MD and DFT simulation. The second part was to change the environmental condition. Retention factor of aromatic solutes was affected by both electrostatic force and dispersion force, which caused the U-shaped retention curves. Van’t Hoff plots have been widely used for investigating the thermodynamic properties of adsorption processes in various chromatography systems. By measuring the retention factor k over a certain temperature range, the plot of ln k versus 1/T often yields a straight line with a slope of −ΔHvH/R. Although this method provides information on adsorption enthalpy changes,its theoretical basis did not account for the effect of the solvent. In this study, the results revealed that two key dimensionless groups controled the van’t Hoff enthalpic curves: the fractions of solute molecules bound to modifier molecules and adsorption sites occupied by modifier molecules. The new model was thus demonstrated to be more reliable than the current model for examining the thermodynamic properties of retention mechanisms. The results have theoretical and partical implications for the understanding of retention mechanism.