Special Report system with continuous recovery of chiral amines. Three liquid phases are: a reaction phase, an organic solvent phase (where the poorly water soluble ketone substrate was supplied), an aqueous extraction phase for continuous product recovery. Synthesis of (S)-1-methyl3-phenylpropylamine was taken as model substance. Under optimal conditions 85% of the product formed was extracted. Advantages and drawbacks are pointed out. (Chem Cat Chem, 2019; DOI: 10.1002/cctc.201902056).
Overcoming work-up limitations of biphasic biocatalytic reaction mixtures through liquid-liquid segmentated flow process N. Adebar et al have referred to the attention the biphasic systems for biocatalytic processes have received. These have relevance in the pharma industry. These authors have presented a segmented flow system using a biphasic MTBE/ buffer mixture. A hydrophobic ketone was used in the presence of an alcohol dehydrogenase as an enzyme. Two different enzymes as well as different substrates are referred. Acetophenone and 2,2,2-trifluoroacetophenone were used. (Chem Cat Chem, 2019; DOI: 10.1002/cctc.201901107).
Reaction engineering for the industrial implementation of biocatalysis J.M. Woodley (This author has many papers on biocatalysis and some have been covered in this column) has referred to the use of one or more enzymes based processes as more sustainable ones and particularly in the pharma industry. While the selection and evolution of enzymes is very important this will also demand smart reaction engineering. This requires an evaluation of the thermodynamics and Chemical Weekly April 28, 2020
reaction kinetics, as well as the stability of the biocatalyst. An example of biological oxidation was taken to illustrate the type of work that is required to be undertaken. (Topics in Catalysis, 2019, 62, Issues 17-20, 1202-1207).
iron oxide was responsible for stable and active oxidation of CO. Perez-Ramirez, Mitchell and co-workers have worked on single Pd atom, supported on carbon nitride, for the Suzuki coupling reaction.
Catalytic and biophysical inves- There is a challenge to develop thermally tigation of Rh-hydroformylase stable catalysts. Attempts are being made (RHF) to overcome this problem. H.T. Imam et al have referred to the use of Rh-containing artificial metalloenzymes based on two mutants of sterol carrier protein_2L (SCP_2L). These have shown significant activity and unexpectedly high selectivity for a range of olefins. Modifications through directed mutagenesis is reported, along with studies of biophysical properties of these catalysts. Single methionine mutants of SCP_2L were studied using advanced spectroscopic methods. Selected mutants are reported. (Catalysis Sci. Technology, 2019; DOI: 10.1039/C9CY01679A).
One-atom wonder! [We seem to moving from nano (e.g. gold) catalysts to one-atom!]. A. Extance has covered this subject in a very lucid way. Work of Maria FlytzaniStephanopoulos is covered which was concerned with Au and Pt supported on ceria for the water-gas shift reaction of great importance in making H2 and NH3. It was observed that softer gold was leached with a cyanide the catalyst was still active, which indicated that a small amount of gold remained associated with ceria and this indicated these were single atoms! Another example of the selective hydrogenation of alkynes to alkenes is referred. The existence of single atoms has been confirmed through aberration-corrected scanning transmission electron spectroscopy. Work of T. Zhang and co-workers is cited wherein Pt atoms on surface of
Example of selective dehydrogenation of butane to butene at 400°C in referred with Pt-CuSAA. Greenhouse gas CO2 electroreduction is under study. Hydrogen fuel cell is under study by Marc-Olivier Coppens. They are drawing analogy with the functioning of lungs. The strategy is to reduce the noble metal content by an order of magnitude. Reference is to hierarchical nanoporous structure. Cui and co-workers are drawing analogy with the alveolous structure in mammalian lungs. The idea is for the gas to reach the catalyst surface straight even though there is a liquid where solubility is low. They have developed gold-polyethylene membranes with high gas permeability that allow water through reluctantly. This strategy has been developed for CO2 to CO. (Chemistry World, 2019, Nov., 52-55).
From directed evolution to computational enzyme engineering R. Chowdhury and C.D. Maranas have reviewed this subject. Enzymes have applications over a wide range from molecular nitrogen fixation to synthesis of hormones, to targeted chemical conversions. References are made to proteolytic enzymes in detergents, amylases for excess bleach removal from textiles, proteases in meat tenderization, and lactoperoxidases in dairy products. An overview of enzyme science and engineering milestones is given. (AIChE Jl., 2019; DOI: 10.1002/ aic.16847). 129