Chemical and Biomolecular Engineering - Research Publications
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ItemFabrication of Chiral Stationary Phases via Continuous Assembly of Polymers for Resolution of Enantiomers by Liquid Chromatography(WILEY-V C H VERLAG GMBH, 2014-11)Precise stereochemical determination of chiral molecules is highly important, especially in the pharmaceutical industry where one enantiomer may have a therapeutic effect while the other has detrimental effects. Herein, the continuous assembly of polymers (CAP) mediated via ring‐opening metathesis polymerization (ROMP) is used to fabricate immobilized‐type chiral stationary phases (CSPs) – as cross‐linked thin films on solid supports – for enantiomeric separation. Optically active polysaccharides (chitosan and amylose) with aromatic substituents were pre‐functionalized with pendent norbornene groups and subsequently employed as macrocross‐linkers in the CAPROMP process, building cross‐linked films from initiator‐functionalized mesoporous silica particles. The immobilized cross‐linked films on mesoporous silica particles can act as CSPs. Therefore, the chiral recognition abilities of the CSPs were explored by liquid chromatography (LC). It was found that CSPs with higher amount of polysaccharide cross‐linked films – made from multiple CAP reactions – have better chiral separation capabilities. This work demonstrates the versatility of the CAP approach to fabricate CSPs to tailor specific separation needs.
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ItemNo Preview AvailableContinuous assembly of polymers via solid phase reactions(ROYAL SOC CHEMISTRY, 2014-09)
The formation of cross-linked polymer films, with tunable thickness, proceeds directionally from the substrate surface by controlled polymerization in the solid state.
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ItemNo Preview AvailableDynamic Performance of Duolayers at the Air/Water Interface. 1. Experimental Analysis(AMER CHEMICAL SOC, 2014-09-18)Understanding, and improving, the behavior of thin surface films under exposure to externally applied forces is important for applications such as mimicking biological membranes, water evaporation mitigation, and recovery of oil spills. This paper demonstrates that the incorporation of a water-soluble polymer into the surface film composition, i.e., formation of a three-duolayer system, shows improved performance under an applied dynamic stress, with an evaporation saving of 84% observed after 16 h, compared to 74% for the insoluble three-monolayer alone. Canal viscometry and spreading rate experiments, performed using the same conditions, demonstrated an increased surface viscosity and faster spreading rate for the three-duolayer system, likely contributing to the observed improvement in dynamic performance. Brewster angle microscopy and dye-tagged polymers were used to visualize the system and demonstrated that the duolayer and monolayer system both form a homogeneous film of uniform, single-molecule thickness, with the excess material compacting into small floating reservoirs on the surface. It was also observed that both components have to be applied to the water surface together in order to achieve improved performance under dynamic conditions. These findings have important implications for the use of surface films in various applications where resistance to external disturbance is required.
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ItemNo Preview AvailableDynamic Performance of Duo layers at the Air/Water Interface. 2. Mechanistic Insights from All-Atom Simulations(AMER CHEMICAL SOC, 2014-09-18)The novel duolayer system, comprising a monolayer of ethylene glycol monooctadecyl ether (C18E1) and the water-soluble polymer poly(vinylpyrrolidone) (PVP), has been shown to resist forces such as wind stress to a greater degree than the C18E1 monolayer alone. This paper reports all-atom molecular dynamics simulations comparing the monolayer (C18E1 alone) and duolayer systems under an applied force parallel to the air/water interface. The simulations show that, due to the presence of PVP at the interface, the duolayer film exhibits an increase in chain tilt, ordering, and density, as well as a lower lateral velocity compared to the monolayer. These results provide a molecular rationale for the improved performance of the duolayer system under wind conditions, as well as an atomic-level explanation for the observed efficacy of the duolayer system as an evaporation suppressant, which may serve as a useful guide for future development for thin films where resistance to external perturbation is desirable.