Employing lipase of candida antarctica (calb) as catalyst in the acetylation of para-aminophenol in aqueous and water-free medium

Candida antarctica lipase B (CaLB) is one of lipase classes enzymes that has many advantages to be used in the process of synthesizing organic compounds. In this study, some experiments were conducted to examine the ability of CaLB as a catalyst in the para-aminophenol (PAP) acetylation to produce paracetamol as the result. Two types of research have been carried out, the first one is to utilize CaLB to catalyze acetylation of PAP in a water-free reaction medium, and the second one is to use CaLB as catalyst in aqueous medium through oxidative amidation reaction. Reaction in water free system was held in ethyl catalyst acetate as solvent that also act as the acyl donor, while in the aqueous medium, acetylacetone was used as acyl donor and ethyl acetate as source to produce peracid that will be used as oxidator. Analysis was done by HPLC and TLC densitometric to follow the amount of paracetamol produced. The results of CaLB-catalyzed acylation in water free system showed that the enzyme could accept PAF and ethyl acetate as a substrate in a nucleophilic substitution reaction, resulting in paracetamol as a product. However, the yield from the acylation of PAP is still not satisfactory. In the reaction in aqueous medium, CaLB has been proven to show its activity to catalyze the acylation of PAP with acetylacetone, as well as the reaction of peracid formation from ethyl acetate. The results show that this strategy can work well and give better yields than the other reaction in water-free medium.

One-dimensional cobalt oxide nanotubes with rich defect for oxygen evolution reaction

For the electrochemcial hydrogen production, the oxygen evolution reaction (OER) is a pivotal half-reaction in water splitting. However, OER suffers sluggish kinetics and high overpotential, leading to the increase of overall energy consumption and decrease of the energy efficiency. In this work, high-quality cobalt oxide porous nanotubes (Co3O4-PNTs) are easily obtained by simple self-template approach. One-dimensional (1D) porous structure provides the large specific surface area, enough abundant active atoms and effective mass transfer. In addition, Co3O4-PNTs also own self-stability of 1D architecture, benefitting the their durability for electrocatalytic reaction. Thus, Co3O4-PNTs with optimal annealing temperature and time reveal the attractive alkaline OER performance (Tafel slope of 56 mV dec-1 and 323 mV overpotential at 10 mA cm-2), which outperform the Co3O4 nanoparticles and benchmark commercial RuO2 nanoparticles. Furthermore, Co3O4-PNTs also exhibit excellent OER durability for least 10 h at the 10 mA cm-2. Overall, Co3O4-PNTs with low cost can be serve as a highly reactive and economical catalyst for OER.

Untethering sparteine: 1,3-diamine ligand for asymmetric synthesis in water

Chiral ligands are the toolbox for asymmetric synthesis to access 3D molecular world. Enabling efficient asymmetric reaction in water is a big challenge. As moisture/air stable and strong binding moieties, amines, compared to imine and phosphine ligands, are ideal candidates to accommodate asymmetric transformations in water. Known amine ligands like Proline analogues and Cinchona alkaloids showed excellent asymmetric induction. Sparteine, an alkaloid studied originated in 1968, had never been considered as a privileged catalyst due to its structure defection which led to poor reaction compatibility and unsatisfactory stereoselectivity. Here, we report the design of a chiral diamine catalyst untethering one of the sparteine rings. The diamine catalyst was easily accessed in two steps on 100 gram-scale. This chiral ligand was proved to be efficient for addition reactions in water providing products with excellent yields and enantiomeric ratios. This pluripotent catalyst has also shown good reactivity/enantioselectivity under organocatalysis, Cu and Pd-catalysed conditions. We anticipate that the ligand would allow further development of other catalysts for important yet challenging green stereoselective transformations.

Catalytic Descriptors to Investigate Catalytic Power in the Reaction of Haloalkane Dehalogenase Enzyme with 1,2-Dichloroethane

Enzymes play a fundamental role in many biological processes. We present a theoretical approach to investigate the catalytic power of the haloalkane dehalogenase reaction with 1,2-dichloroethane. By removing the three main active-site residues one by one from haloalkane dehalogenase, we found two reactive descriptors: one descriptor is the distance difference between the breaking bond and the forming bond, and the other is the charge difference between the transition state and the reactant complex. Both descriptors scale linearly with the reactive barriers, with the three-residue case having the smallest barrier and the zero-residue case having the largest. The results demonstrate that, as the number of residues increases, the catalytic power increases. The predicted free energy barriers using the two descriptors of this reaction in water are 23.1 and 24.2 kcal/mol, both larger than the ones with any residues, indicating that the water solvent hinders the reactivity. Both predicted barrier heights agree well with the calculated one at 25.2 kcal/mol using a quantum mechanics and molecular dynamics approach, and also agree well with the experimental result at 26.0 kcal/mol. This study shows that reactive descriptors can also be used to describe and predict the catalytic performance for enzyme catalysis.