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The conformational stability and activity of Candida antarctica lipase B (CALB) in the polar and nonpolar organic solvents were investigated by molecular dynamics and quantum mechanics/molecular mechanics simulations. The conformation change of CALB in the polar and nonpolar solvents was examined in two aspects: the overall conformation change of CALB and the conformation change of the active site. The simulation results show that the overall conformation of CALB is stable in the organic solvents. In the nonpolar solvents, the conformation of the active site keeps stable, whereas in the polar solvents, the solvent molecules reach into the active site and interact intensively with the active site. This interaction destroys the hydrogen bonding between Ser 105 and His 224 . In the solvents, the activation energy of CALB and that of the active site region were further simulated by quantum mechanics/molecular mechanics simulation. The results indicate that the conformation change in the region of active sites is the main factor that influences the activity of CALB.Because of its high enantioselectivity and catalytic activity, wide range of substrates, and thermal stability, Candida antarctica lipase B (CALB) 3 is widely used in many industrial applications and scientific researches (1). CALB is composed of 317 amino acid residues and has a molecular mass of 33 K (2). Similar to other serine hydrolyzes, a serine-histidine-asparate catalytic triad is responsible for the catalytic activity of CALB. The mechanism is outlined in Fig. 1. It is a two-step mechanism with an acylation step and a deacylation step separated by a covalent acyl-enzyme intermediate (3).The activity of the enzymes is strongly affected by the choice of solvent (4 -7). As a matter of fact, even reversal of substrate specificity (8, 9) and enantiopreference (10, 11) has been reported. A higher thermostability and altered stereoselectivity for CALB in organic solvents have also been observed (12, 13). Many researchers have put effort into elucidating the underlying mechanisms responsible for the observed solvent effects. The most widely accepted model was described by Laane (14), who summarized the influence of organic solvents on the enzymatic reactions and concluded that the enzyme activity is higher in the environment surrounded by nonpolar and midpolar solvents, whereas the lowest activity is expressed in polar solvents. The Laane model has been widely used in solvent selection in enzymatic reactions. However, the Laane model does not describe the mechanisms of solvent effect on a molecular level.Molecular dynamics simulations have been proven to be a useful tool in understanding protein structure and have been used to get insights into the structure and behavior of the enzymes (15-18). The effect of solvents on the activity of CALB might be the results of the conformational change around the activity site or some particular area. In this work, the overall conformational change of CALB and the local conformational change around the active site in ...

We present herein the first visible-light-driven hydrocarboxylation as well as carbocarboxylation of alkynes using CO via an iridium/cobalt dual catalysis. Such transformations provide access to various pharmaceutically important heterocycles in a one-pot procedure from readily available alkynes. Coumarins, 2-quinolones, and 2-benzoxepinones were directly accessed through a one-pot alkyne hydrocarboxylation/alkene isomerization/cyclization sequence in which the Ir photocatalyst serves a dual role to promote single-electron transfer in alkyne hydrocarboxylation and energy transfer in the subsequent alkene isomerization. Moreover, an unprecedented cobalt carboxylation/acyl migration cascade enables alkyne difunctionalization to introduce γ-hydroxybutenolides with high efficiency. We expect that this cascade strategy will inspire new perspectives for alkyne and alkene difunctionalization.

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We report a new strategy to synthesize the hierarchical mesoporous zeolite through design of mesoscale cationic surfactant cetyltrimethylammonium bromide (CTAB) micelle with cosolvent tertbutyl alcohol (TBA) and the 1,3,5-trimethylbenzene (TMB) additive, by which the formation of hierarchical mesostructure arose from the condensing of zeolite fragments on the mesoscale surfactant micelles. The hierarchical mesoporous silica with zeolite Y or sodalite fragment is synthesized for the first time, which exhibited both the mesostructure and the typical diffraction of zeolite. XRD, N 2 adsorption-desorption, 27 Al MAS NMR, FTIR, and NH 3 -TPD techniques were employed to characterize the resulting samples, and the adsorption of NPYR (N-nitrosopyrrolidine) and NNN (N-nitrosonornicotine) were performed to assess the adsorptive capability of the zeolitic mesoporous materials. The MS3-4t-5b sample synthesized by assembling zeolite gel exhibited the adsorptive capacity comparable to NaY zeolite for trapping NPYR in airflow but four times superior to NaY for adsorbing bulky nitrosamine NNN in solution because of its hierarchical mesostructure.