Chiral separation using a novel combination of cooling crystallization and a membrane barrier: Resolution of DL-glutamic acid

l-Cysteine-Modified Graphene Oxide-Based Membrane for Chiral Selective Separation

A novel chiral separation membrane was fabricated by assembling l-cysteine (l-Cys)-modified graphene oxide sheets. l-Cys modification leads to an enantiomer separation membrane with an accessible interlayer spacing of 8 Å, which allows high solvent permeability. In the racemate separation experiments under isobaric conditions, the enantiomeric excess (ee) values of alanine (Ala), threonine (Thr), tyrosine (Tyr), and penicillamine (Pen) racemates in the permeation solution were 43.60, 44.11, 27.43, and 46.44%, respectively. In the racemate separation experiments under negative pressure, the separation performances of Ala, Thr, and Tyr were still maintained, and the enantiomeric excess (ee) values of the filtrate after separation were 56.80, 54.57, and 32.34%, respectively. These results indicate that the as-prepared GO-Cys membrane has a great practical value in the field of enantiomer separation.

β-Cyclodextrin Functionalized Nanoporous Graphene Oxides for Efficient Resolution of Asparagine Enantiomers

Efficient resolution of racemic mixture has long been an attractive but challenging subject since Pasteur separated tartrate enantiomers in 19^th  century. Graphene oxide (GO) could be flexibly functionalized by using a variety of chiral host molecules and therefore, was expected to show excellent enantioselective resolution performance. However, this combination with efficient enantioselective resolution capability has been scarcely demonstrated. Here, nanoporous graphene oxides were produced and then covalently functionalized by using a chiral host material-β-cyclodextrin (β-CD). This chiral GO displayed enantioselective affinity toward the l-enantiomers of amino acids. In particular, >99 % of l-asparagine (Asn) was captured in a racemic solution of Asn while the adsorption of d-enantiomer was not observed. This remarkable resolution performance was subsequently modelled by using an attach-pull-release dynamic method. We expect this preliminary concept could be expanded to other chiral host molecules and be employed to current membrane separation technologies and finally show practical use for many other racemates.

An Autobiography of Ronald W. Rousseau

This article provides a synopsis of my professional career, from the decision to study chemical engineering to leadership of one of the top academic programs in that field. I describe how I chose to devote my research to phenomena associated with crystallization as practiced for separation and purification and then made the transition to leader of an academic program. Embedded in the coverage are descriptions of research advances coming from exploration of secondary nucleation, especially how collisions of crystals in supersaturated environments dominate the behavior of industrially relevant crystallization processes. I recount some of the challenges associated with becoming a school chair and how the program I led grew. The story illuminates the contributions of my many mentors, colleagues, and students.

Advances and New Directions in Crystallization Control

The academic literature on and industrial practice of control of solution crystallization processes have seen major advances in the past 15 years that have been enabled by progress in in-situ real-time sensor technologies and driven primarily by needs in the pharmaceutical industry for improved and more consistent quality of drug crystals. These advances include the accurate measurement of solution concentrations and crystal characteristics as well as the first-principles modeling and robust model-based and model-free feedback control of crystal size and polymorphic identity. Research opportunities are described in model-free controller design, new crystallizer designs with enhanced control of crystal size distribution, strategies for the robust control of crystal shape, and interconnected crystallization systems for multicomponent crystallization.