Second-Layer Chiral Environment-Induced Steric Hindrance Enables Catalyst Conformation Lockdown in Enantioselective Hypervalent Iodine Organocatalysis

A class of confined chiral hypervalent iodines have been designed and developed by incorporating two sterically demanding BINOL-derived units, which form the second-layer chiral environment, into the iodine-containing molecules to lock down the conformation of the catalyst and indirectly create a compact chiral environment around the active site. Good-to-excellent enantioselectivities have been achieved with these catalysts for the α-oxysulfonylation of ketones (up to 97.5:2.5 er) and the oxidative cyclization of 5-oxo-5-arylpentanoic acids to γ-butyrolactones (up to 98:2 er), thereby demonstrating the utility of this strategy for catalyst design

Second-Layer Chiral Environment-Induced Steric Hindrance Enables Catalyst Conformation Lockdown in Enantioselective Hypervalent Iodine Organocatalysis

A class of confined chiral hypervalent iodines have been designed and developed by incorporating two sterically demanding BINOL-derived units, which form the second-layer chiral environment, into the iodine-containing molecules to lock down the conformation of the catalyst and indirectly create a compact chiral environment around the active site. Good-to-excellent enantioselectivities have been achieved with these catalysts for the α-oxysulfonylation of ketones (up to 97.5:2.5 er) and the oxidative cyclization of 5-oxo-5-arylpentanoic acids to γ-butyrolactones (up to 98:2 er), thereby demonstrating the utility of this strategy for catalyst design

Mild Hydrodeoxygenation of Aromatic Ketones by Pd/H_<i>x</i>WO_3–<i>y</i> with Plasmonic Features Assisted by Visible-NIR Light Irradiation

Hydrodeoxygenation (HDO) reactions are important processes in the fields of bioenergy and biorefining, as they enable the conversion of biomass into valuable products that can replace fossil fuels and reduce greenhouse gas emissions. The efficient utilization of solar energy for boosting HDO reactions is of great significance for achieving ecological chemistry in a sustainable manner. However, the application of photocatalysts is severely restricted by inadequate utilization of the solar spectrum, rapid recombination of photogenerated carriers, and slow catalytic kinetics. Here, we demonstrate that the Pd/HxWO3–y catalyst prepared by a facile H2 reduction process displays efficient catalytic activity in the HDO of benzophenone to diphenylmethane with the aid of light irradiation owing to its surface plasmon resonance (SPR) effect. The H2 reduction process forms a large number of hydroxyl groups and a trace of oxygen defects on the Pd/WO3 surface, and the intercalated H atoms enrich the Pd/HxWO3–y surface with a large number of free electrons, resulting in plasmonic absorption under visible-NIR irradiation. Photoelectrochemical characterization and in situ Fourier transform infrared (FT-IR) spectroscopy indicate the photogenerated hot electron generation and electric field enhancement effect on the catalyst surface during the photoassisted reaction, which promotes H2 activation and CO bond activation to enhance the HDO reaction’s efficiency. This experiment establishes a feasible approach to effectively utilize solar energy in the HDO reaction of ketones under mild conditions by creating an intriguing field of catalysis on Pd/HxWO3–y with plasmonic features

Positive feedback stabilizes the induced state.

<p>(A-C) Extremely slow operon-state switching is necessary to induce purely stochastic bistability without positive feedback. (D-F) In the presence of positive feedback, the induced state is stabilized, and a bimodal distribution emerges, even when operon-state switching rates are within the physiological region.</p

Bistability with and without stochastic operon-state switching.

<p>(A) Deterministic bifurcation diagram for wild-type cells. There are two saddle-node bifurcations occurring around <i>I</i>_<i>e</i> = 10<i>μ</i>M and 59<i>μ</i>M. (B) Deterministic bifurcation diagram containing both the active transcriptional rate <i>k</i>_<i>M</i> and the extracellular inducer concentration <i>I</i>_<i>e</i>. The wild-type cells exhibit deterministic bistability inside the parameter region between the blue and brown lines and exhibit monostability otherwise. (C) Deterministic bifurcation diagram of the mutant cells without positive feedback. (D)(E) Deterministic bifurcation diagrams with different association constants for the repressor bound to the operon in the absence of a DNA loop: 5 <i>molec.</i>⁻¹ (D), 8 <i>molec.</i>⁻¹ (E). (F) Stochastic hysteresis response of the probability of induction for wild-type cells. Initial conditions: uninduced (blue line) or fully induced (red line) cells with a period of <i>T</i> = 2000 min. The extracellular inducer concentration must exceed over 350<i>μ</i>M to completely activate initially uninduced cells, whereas it must decrease below 10<i>μ</i>M to completely deactivate the initially induced cells. See <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1006051#pcbi.1006051.s001" target="_blank">S1 Text</a> for parameter values.</p

Overview of the model.

(A) Regulatory mechanism of the lac operon. Expression of permease increases the intracellular concentration of the inducer TMG (thiomethyl β-D-galactoside), which removes the repressor LacI from the promoter, leading to increased expression of permease. Hence the repressor LacI and permease LacY form a positive feedback loop. (B) Cartoon showing the dynamics of operon states. (C) Diagram of the Markovian jumping process of operon states. The O state denotes the free operon; the O*R state denotes the operon bound to the repressor at the auxiliary lac operator O2 or O3(partial dissociation); the OR state denotes the repressor bound to the operon at both the major and auxiliary lac operators; the O*RIm state denotes the repressor bound to the operon at the auxiliary lac operator O2 or O3 and to the inducer.</p

Transition rates between phenotypic states and the phenomenon of resonance.

<p>(A) Phenotypic landscape <i>ϕ</i>(<i>x</i>) in the region of deterministic bistability. (B) Phenotypic landscape <i>ϕ</i>(<i>x</i>) outside the region of deterministic bistability. (C) The rate formula <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1006051#pcbi.1006051.e003" target="_blank">(2)</a> is valid for the parameter region of deterministic bistability with the fitted positive barrier <i>V</i>₁₂ = 0.0550. (D) When the switching rates among different gene states are sufficiently rapid, the phenotype transition from the uninduced state to the induced state must occur through the accumulation of many complete dissociation events, rather than through a single dissociation event in wild-type cells, within the parameter region of deterministic bistability. (E) The transition rate increases and is finally saturated when the operon-state switching rate increases in the region of purely stochastic bistability. (F) The mean phenotype transition time varies with the operon-state switching rates at <i>I</i>_<i>e</i> = 25<i>μ</i>M.</p

Major transit pathways and transition rates between fully repressed and fully dissociated operon states.

<p>(A, B) The major transit pathways between fully repressed and fully dissociated operon states in the uninduced and induced phenotypic states. (C-F) Transition rates between fully repressed and fully dissociated operon states in the uninduced and induced phenotypic states with very low and high intracellular inducer concentrations respectively. The transition rates from the fully repressed operon state to the fully dissociated state in the uninduced phenotypic state are the lowest, which stabilizes the uninduced state, even outside of the parameter range of deterministic bistability.</p

Probability of induction by a single large burst and quasi-steady state.

<p>(A)Two typical single-cell time traces of permease levels. The first shows induction by a single full dissociation event of the repressor from the operon (left), while the second shows a failure to induce (right). (B) The large burst size in the presence of positive feedback is remarkably prolonged compared with the case without positive feedback. (C) Successful probability of induction by a complete dissociation event as a function of the extracellular inducer concentration. (D-G) Probability of induction within different time windows starting from uninduced cells (blue) or induced cells (red); we determined the stochastic threshold through mathematical fitting in the form of for these curves. The deterministic threshold is approximately 20(<i>molec.</i>), while the stochastic thresholds are larger and decrease when the time window is extended. The extracellular inducer concentration, <i>I</i>_<i>e</i>, is set to 40<i>μ</i>M.</p

CO₂ Hydrogenation to Methanol over a Pt-Loaded Molybdenum Suboxide Nanosheet with Abundant Surface Oxygen Vacancies

Hydrogenation of carbon dioxide (CO2) using CO2-free hydrogen (H2) to produce methanol (CH3OH) is a promising reaction that can alleviate both carbon emissions and the dependence on fossil fuels. Nonstoichiometric molybdenum suboxide coupled with Pt nanoparticles (NPs) acts as a promising catalyst for this reaction, in which surface oxygen vacancies (VO) and the redox ability of Mo in molybdenum suboxide are the keys to transforming CO2 into the CO intermediate and further to afford CH3OH. In this study, a series of molybdenum oxides with different morphologies, including bulk, nanosheet, nanobelt, and rod morphologies, are used as catalysts, and the effects of particle morphologies on the catalytic performance toward CO2 hydrogenation are examined. A Pt-loaded molybdenum suboxide nanosheet (Pt/HxMoO3–y(Sheet)) with a high specific surface area affords 1.35 times greater CO2 conversion and CH3OH yield in liquid-phase CO2 hydrogenation compared with the corresponding bulk analog under relatively mild reaction conditions (total 4.0 MPa, 200 °C). Experiments and comprehensive analyses, including X-ray diffraction and in situ X-ray absorption fine structure studies, reveal that the enhanced activity of Pt/HxMoO3–y(Sheet) is attributable to a high concentration of surface-exposed VO sites, which are introduced in the (010) plane during the H2 reduction due to the high surface-to-volume ratio of the nanosheet-structured MoO3. In addition, the nanosheet-structured catalyst exhibits better reusability because of its antiaggregation behavior for Pt NPs compared with the conventional bulk analog