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The scope of thermolytic, N-Boc deprotection was studied on 26 compounds from the Pfizer compound library, representing a diverse set of structural moieties. Among these compounds, 12 substrates resulted in clean (≥95% product) deprotection, and an additional three compounds gave ≥90% product. The thermal de-Boc conditions were found to be compatible with a large number of functional groups. A combination of computational modeling, statistical analysis, and kinetic model fitting was used to support an initial, slow, and concerted proton transfer with release of isobutylene, followed by a rapid decarboxylation. A strong correlation was found to exist between the electrophilicity of the N-Boc carbonyl group and the reaction rate.
The hierarchical equations of motion (HEOM) theory is in principle exact for describing the dissipative dynamics of quantum systems linearly coupled to Gaussian environments. In practice, the hierarchy needs to be truncated at a finite tier. We demonstrate that, for general systems described by the fermionic HEOM, the (n+L̃)th-tier truncation with L̃=2NN yields the exact density operators up to the nth tier. Here, N = 2 for fermionic systems and N is the system degrees of freedom. For noninteracting systems, L̃ is further reduced by half. Such an exact termination pattern originates from the Pauli exclusion principle for fermions, and it holds true regardless of the system-environment coupling strength, the number of coupling reservoirs, or the specific scheme employed to unravel the environment memory contents. The relatively small L̃ emphasizes the nonperturbative nature of the HEOM theory. We also propose a simplified HEOM approach to further reduce the memory cost for practical calculations.
The time-dependent wavepacket diffusive method [X. Zhong and Y. Zhao, J. Chem. Phys. 138, 014111 (2013)] is extended to investigate the energy relaxation and separation of a hot electron-hole pair in organic aggregates with incorporation of Coulomb interaction and electron-phonon coupling. The pair initial condition generated by laser pulse is represented by a Gaussian wavepacket with a central momentum. The results reveal that the hot electron energy relaxation is very well described by two rate processes with the fast rate much larger than the slow one, consistent with experimental observations, and an efficient electron-hole separation is accomplished accompanying the fast energy relaxation. Furthermore, although the extra energy indeed helps the separation by overcoming the Coulomb interaction, the width of initial wavepacket is much sensitive to the separation efficiency and the narrower wavepacket generates the more separated charges. This behavior may be useful to understand the experimental controversy of the hot carrier effect on charge separation.
A kind of low-calorie structured lipid (LCSL) was obtained by interesterification of tributyrin (TB) and methyl stearate (St-ME), catalyzed by a commercially immobilized 1,3-specific lipase, Lipozyme RM IM from Rhizomucor miehei . The condition optimization of the process was conducted by using response surface methodology (RSM). The optimal conditions for highest conversion of St-ME and lowest content LLL-TAG (SSS and SSP; S, stearic acid; P, palmitic acid) were determined to be a reaction time 6.52 h, a substrate molar ratio (St-ME:TB) of 1.77:1, and an enzyme amount of 10.34% at a reaction temperature of 65 °C; under these conditions, the actually measured conversion of St-ME and content of LLL-TAG were 78.47 and 4.89% respectively, in good agreement with predicted values. The target product under optimal conditions after short-range molecular distillation showed solid fat content (SFC) values similar to those of cocoa butter substitutes (CBS), cocoa butter equivalent (CBE), and cocoa butters (CB), indicating its application for inclusion with other fats as cocoa butter substitutes.
Biocatalytic reductive amination
catalyzed by engineered imine
reductase (RedAms) is a new and powerful tool for the synthesis of
substituted chiral amines. Herein, we describe a streamlined synthesis
of compound 3, a key intermediate to a CDK 2/4/6 inhibitor 1, relying on the enzymatic reductive amination of a hydroxyketone
to introduce the chiral secondary amine with high diastereoselectivity.
The improved synthesis of the hydroxyketone precursor by a titanium-catalyzed
reductive cyclization and the process development for two SNAr reactions en route to 3 are also presented.
Herein, we demonstrate for the first time that the enantio-selective polymerization of DA monomers could be realized upon irradiation with circularly polarized visible light (CPVL), which could effectively provide chiral order in the propagating step of a polymerization reaction.
Although the carriers in organic semiconductors commonly follow the hopping-type motions caused by strong carrierphonon interactions, they can also present a band-like behavior in well-performed organic crystals. In this article, we review a unified model to describe the carrier dynamics covering from the hopping-type to band-like motions, the timedependent wavepacket diffusion method proposed in our group recently. In the method, the effects of vibrational motions of organic molecules and inter or intramolecular electronic couplings are considered as the fluctuations to the carrier dynamics. Numerical simulations demonstrate that the computational cost of present method is similar to that of mixed quantum-classical methods, but it overcomes the deficiency in those methods that the detailed balance principle is not satisfied. We further present how to combine electronic structure calculations and molecular dynamics simulations with the present model to reveal the carrier dynamics in realistic organic semiconductors.
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