ABSTRACT
In this study, the chiral separation mechanisms of Dansyl amino acids, including Dansyl-Leucine (Dans-Leu), Dansyl-Norleucine (Dans-Nor), Dansyl-Tryptophan (Dans-Trp) and Dansyl-Phenylalanine (Dans-Phe) binding to poly-sodium N-undecanoyl-(L)-Leucylvalinate, poly(SULV), were investigated using molecular dynamics simulations. Micellar electrokinetic chromatography (MEKC) has previously shown that when separating the enantiomers of these aforementioned Dansyl amino acids, the L- enantiomers bind stronger to poly(SULV) than the D- enantiomers. This study aims to investigate the molecular interactions that govern chiral recognition in these systems using computational methods. This study reveals that the computationally-calculated binding free energy values for Dansyl enantiomers binding to poly(SULV) are in agreement with the enantiomeric order produced in experimental MEKC studies. The L- enantiomers of Dans-Leu, Dans-Nor, Dans-Trp, and Dans-Phe binding to their preferred binding pockets in poly(SULV) yielded binding free energy values of -21.8938, -22.1763, -21.3329 and -13.3349 kJ·mol-1, respectively. The D- enantiomers of Dans-Leu, Dans-Nor, Dans-Trp, and Dans-Phe binding to their preferred binding pockets in poly(SULV) yielded binding free energy values of -14.5811, -15.9457, -13.6408, and -12.0959 kJ·mol-1, respectively. Furthermore, hydrogen bonding analyses were used to investigate and elucidate the molecular interactions that govern chiral recognition in these molecular systems.
ABSTRACT
The purpose of this study was to determine the comparative environmental impacts of coupled seawater desalination and water reclamation using a novel hybrid system that consist of an osmotically driven membrane process and established membrane desalination technologies. A comparative life cycle assessment methodology was used to differentiate between a novel hybrid process consisting of forward osmosis (FO) operated in osmotic dilution (ODN) mode and seawater reverse osmosis (SWRO), and two other processes: a stand alone conventional SWRO desalination system, and a combined SWRO and dual barrier impaired water purification system consisting of nanofiltration followed by reverse osmosis. Each process was evaluated using ten baseline impact categories. It was demonstrated that from a life cycle perspective two hurdles exist to further development of the ODN-SWRO process: module design of FO membranes and cleaning intensity of the FO membranes. System optimization analysis revealed that doubling FO membrane packing density, tripling FO membrane permeability, and optimizing system operation, all of which are technically feasible at the time of this publication, could reduce the environmental impact of the hybrid ODN-SWRO process compared to SWRO by more than 25%; yet, novel hybrid nanofiltration-RO treatment of seawater and wastewater can achieve almost similar levels of environmental impact.
