Molecular oxidation-reduction junctions for artificial photosynthetic overall reaction.

Constructing redox semiconductor heterojunction photocatalysts is the most effective and important means to complete the artificial photosynthetic overall reaction (i.e., coupling CO2 photoreduction and water photo-oxidation reactions). However, multiphase hybridization essence and inhomogeneous junction distribution in these catalysts extremely limit the diverse design and regulation of the modes of photogenerated charge separation and transfer pathways, which are crucial factors to improve photocatalytic performance. Here, we develop molecular oxidation-reduction (OR) junctions assembled with oxidative cluster (PMo12, for water oxidation) and reductive cluster (Ni5, for CO2 reduction) in a direct (d-OR), alternant (a-OR), or symmetric (s-OR) manner, respectively, for artificial photosynthesis. Significantly, the transfer direction and path of photogenerated charges between traditional junctions are obviously reformed and enriched in these well-defined crystalline catalysts with monophase periodic distribution and thus improve the separation efficiency of the electrons and holes. In particular, the charge migration in s-OR shows a periodically and continuously opposite mode. It can inhibit the photogenerated charge recombination more effectively and enhance the photocatalytic performance largely when compared with the traditional heterojunction models. Structural analysis and density functional theory calculations disclose that, through adjusting the spatial arrangement of oxidation and reduction clusters, the energy level and population of the orbitals of these OR junctions can be regulated synchronously to further optimize photocatalytic performance. The establishment of molecular OR junctions is a pioneering important discovery for extremely improving the utilization efficiency of photogenerated charges in the artificial photosynthesis overall reaction.

Calix[4]arene-Functionalized Titanium-Oxo Compounds for Perceiving Differences in Catalytic Reactivity Between Mono- and Multimetallic Sites.

While the difference in catalytic reactivity between mono- and multimetallic sites is often attributed to more than just the number of active sites, still few catalyst model systems have been developed to explore more underlying causal factors. In this work, we have elaborately designed and constructed three stable calix[4]arene (C4A)-functionalized titanium-oxo compounds, Ti-C4A, Ti4-C4A, and Ti16-C4A, with well-defined crystal structures, increasing nuclearity, and tunable light absorption capacity and energy levels. Among them, Ti-C4A and Ti16-C4A can be taken as model catalysts to compare the differences in reactivity between mono- and multimetallic sites. Taking CO2 photoreduction as the basic catalytic reaction, both compounds can achieve CO2-to-HCOO- conversion with high selectivity (close to 100%). Moreover, the catalytic activity of multimetallic Ti16-C4A is up to 2265.5 µmol g-1 h-1, which is at least 12 times higher than that of monometallic Ti-C4A (180.0 µmol g-1 h-1), and is the best-performing crystalline cluster-based photocatalyst known to date. Catalytic characterization combined with density functional theory calculations shows that in addition to the advantage of having more metal active sites (for adsorption and activation of more CO2 molecules), Ti16-C4A can effectively reduce the activation energy required for the CO2 reduction reaction by completing the multiple electron-proton transfer process rapidly with synergistic metal-ligand catalysis, thus exhibiting superior catalytic performance to that of monometallic Ti-C4A. This work provides a crystalline catalyst model system to explore the potential factors underlying the difference in catalytic reactivity between mono- and multimetallic sites.

Theoretical study of NiI-NiIII cycle mediated by heterogeneous zinc in C-N cross-coupling reaction.

Photoredox/transition-metal dual catalysis could efficiently construct C-N bonds by a cross-coupling reaction. The limitations of low recovery, low utilization rate and high cost have hindered the application and development of low-cost and efficient transition metal catalytic cycles. The integration of heterogeneous metal and transition metal catalysis is an appealing alternative to realize the oxidation state modulation of active species. With the support of density functional theory (DFT) calculation, we have explored the mechanistic details of Ni-catalyzed C-N cross-coupling of aryl bromide and cyclic amine assisted by zinc powder. Zinc successfully regulates the oxidation state of NiII → NiI, thus achieving the NiI-NiIII-NiI catalytic cycle in the absence of light. In comparison, when the Ni(0) complex is employed as the initial catalyst, organic zinc reagents can still be involved in the transmetalation process to accelerate the cross-coupling reaction. We hope that such computational studies can provide theoretical reference for the design and development of low-cost and efficient catalytic systems for C-N cross-couplings.

Superiority of Iridium Photocatalyst and Role of Quinuclidine in Selective α-C(sp3)-H Alkylation: Theoretical Insights.

Recent experimental work reported that visible-light photoredox catalysis coupled with primary sulfonamides and electron-deficient alkenes could efficiently construct C-C bonds at the α-position of primary amine derivatives under mild conditions. Here, a systematic study was conducted to explore the non-negligible excited-state single-electron-transfer (SET) processes and the catalytic cycle. Hydrogen atom transfer (HAT) catalysis containing different site-selective functionalization, involved as a critical process during the reaction, was computationally characterized. The superiorities of iridium-based photoredox catalysts in terms of photoabsorption properties, phosphorescence rates, and electron-transfer rates for SET processes were focused on. In addition, the function of quinuclidine in the entire photocatalytic reaction was also probed. These intrinsic properties and detailed insights into the mechanism are supposed to be helpful to the understanding of the C-C bond functionalization reaction and the future application of the iridium-based photoredox catalyst.

Photocatalytic aerobic oxidation of C(sp3)-H bonds.

In modern industries, the aerobic oxidation of C(sp3)-H bonds to achieve the value-added conversion of hydrocarbons requires high temperatures and pressures, which significantly increases energy consumption and capital investment. The development of a light-driven strategy, even under natural sunlight and ambient air, is therefore of great significance. Here we develop a series of hetero-motif molecular junction photocatalysts containing two bifunctional motifs. With these materials, the reduction of O2 and oxidation of C(sp3)-H bonds can be effectively accomplished, thus realizing efficient aerobic oxidation of C(sp3)-H bonds in e.g., toluene and ethylbenzene. Especially for ethylbenzene oxidation reactions, excellent catalytic capacity (861 mmol g cat-1) is observed. In addition to the direct oxidation of C(sp3)-H bonds, CeBTTD-A can also be applied to other types of aerobic oxidation reactions highlighting their potential for industrial applications.

Bridging the Homogeneous and Heterogeneous Catalysis by Supramolecular Metal-Organic Cages with Varied Packing Modes.

Integrating the advantages of homogeneous and heterogeneous catalysis has proved to be an optimal strategy for developing catalytic systems with high efficiency, selectivity, and recoverability. Supramolecular metal-organic cages (MOCs), assembled by the coordination of metal ions with organic linkers into discrete molecules, have performed solvent processability due to their tunable packing modes, endowing them with the potential to act as homogeneous or heterogeneous catalysts in different solvent systems. Here, the design and synthesis of a series of stable {Cu3} cluster-based tetrahedral MOCs with varied packing structures are reported. These MOCs, as homogeneous catalysts, not only show high catalytic activity and selectivity regardless of substrate size during the CO2 cycloaddition reaction, but also can be easily recovered from the reaction media through separating products and co-catalysts by one-step work-up. This is because that these MOCs have varied solubilities in different solvents due to the tunable packing of MOCs in the solid state. Moreover, the entire catalytic reaction system is very clean, and the purity of cyclic carbonates is as high as 97% without further purification. This work provides a unique strategy for developing novel supramolecular catalysts that can be used for homogeneous catalysis and recycled in a heterogeneous manner.

Photochromic radical states in 3D covalent organic frameworks with zyg topology for enhanced photocatalysis.

Covalent-organic frameworks (COFs) with photoinduced donor-acceptor (D-A) radical pairs show enhanced photocatalytic activity in principle. However, achieving long-lived charge separation in COFs proves challenging due to the rapid charge recombination. Here, we develop a novel strategy by combining [6 + 4] nodes to construct zyg-type 3D COFs, first reported in COF chemistry. This structure type exhibits a fused Olympic-rings-like shape, which provides a platform for stabilizing the photoinduced D-A radical pairs. The zyg-type COFs containing catalytically active moieties such as triphenylamine and phenothiazine (PTZ) show superior photocatalytic production rates of hydrogen peroxide (H2O2). Significantly, the photochromic radical states of these COFs show up to 400% enhancement in photocatalytic activity compared to the parent states, achieving a remarkable H2O2 synthesis rate of 3324 µmol g-1 h-1, which makes the PTZ-COF one of the best crystalline porous photocatalysts in H2O2 production. This work will shed light on the synthesis of efficient 3D COF photocatalysts built on topologies that can facilitate photogenerating D-A radical pairs for enhanced photocatalysis.

Green synthesis of bifunctional phthalocyanine-porphyrin cofs in water for efficient electrocatalytic CO2 reduction coupled with methanol oxidation.

Electrocatalytic CO2 reduction (ECR) coupled with organic oxidation is a promising strategy to produce high value-added chemicals and improve energy efficiency. However, achieving the efficient redox coupling reaction is still challenging due to the lack of suitable electrocatalysts. Herein, we designed two bifunctional polyimides-linked covalent organic frameworks (PI-COFs) through assembling phthalocyanine (Pc) and porphyrin (Por) by non-toxic hydrothermal methods in pure water to realize the above catalytic reactions. Due to the high conductivity and well-defined active sites with different chemical environments, NiPc-NiPor COF performs efficient ECR coupled with methanol oxidation reaction (MOR) (Faradaic efficiency of CO (FECO) = 98.12%, partial current densities of CO (jCO) = 6.14 mA cm-2 for ECR, FEHCOOH = 93.75%, jHCOOH = 5.81 mA cm-2 for MOR at low cell voltage (2.1 V) and remarkable long-term stability). Furthermore, experimental evidences and density functional theory (DFT) calculations demonstrate that the ECR process mainly conducts on NiPc unit with the assistance of NiPor, meanwhile, the MOR prefers NiPor conjugating with NiPc. The two units of NiPc-NiPor COF collaboratively promote the coupled oxidation-reduction reaction. For the first time, this work achieves the rational design of bifunctional COFs for coupled heterogeneous catalysis, which opens a new area for crystalline material catalysts.

Different Protonic Species Affecting Proton Conductivity in Hollow Spherelike Polyoxometalates.

Polyoxometalates (POMs), which possess strong acidity and chemical stability, are promising solid proton conductors and potential candidates for proton exchange membrane fuel cell applications. To investigate how factors such as proton concentration and carrier affect the overall proton conduction, we have synthesized new compounds HImMo132 (Im, imidazole), HMeImMo132, ILMo132, and TBAMo132 with hollow structures and HImPMo12 with a solid spherelike structure. These crystal models were prepared by encapsulating POM with organic molecules with different proton contents. Among them, the single-crystal sample of the hollow structure HImMo132 containing more proton sources shows a high proton conductivity of 4.98 × 10-2 S cm-1, which was approximately 1 order of magnitude greater than that of the solid cluster HImPMo12 with the same proton sources and 3 orders of magnitude greater than that of the proton-free organic cation-encapsulated giant ball TBAMo132. This study provides a theoretical guidance toward designing and developing new-generation proton conductors and studying their performances at the molecular level.

Orthogonal reactivity of Ni(i)/Pd(0) dual catalysts for Ullmann C-C cross-coupling: theoretical insight.

Dual catalysis has become a desirable alternative because of the synergetic effect of two distinct catalysts, but little is known about the mechanism of dual catalysis and its effect on the high reactivity and selectivity. Here, a novel Ullmann C-C cross-coupling of bromobenzene and 4-methoxyphenyltriflate via nickel/palladium dual catalysis has been investigated using density functional theory. The orthogonal reactivity of NiI/Pd0 combination is the precondition and foundation of achieving such a Ullmann cross-coupling reaction. In the present dual catalysis, the NiI complex acts as the primary catalyst, while the Pd0 catalyst plays a decisive role in the cross-selectivity.

[Modified type I thyroplasty for treating unilateral vocal cord paralysis].

OBJECTIVE: To explore a new surgical approach for treating unilateral vocal cord paralysis. METHODS: Five cases of unilateral vocal cord paralysis due to various causes were treated with modified type I thyroplasty. Laryngostroboscopy and electroglottography were performed before and after the operations. RESULTS: The vocal cords were shifted very close to the median line in all the 5 cases postoperatively as shown by laryngostroboscopy and electroglottography. Complete closure of the glottis was achieved. The patients had almost normal results of electroglottography, and the vocal sound nearly recovered normal or was significantly improved. CONCLUSION: Modified type I thyroplasty is effective, safe and easy in treating unilateral vocal cord paralysis.

[Perioperative management of severe obstructive sleep apnea hypopnea syndrome].

OBJECTIVE: To investigate the perioperative management of severe obstructive sleep apnea hypopnea syndrome (OSAHS). METHODS: Fifty-three patients with severe OSAHS received uvulopalatopharyngoplasty with uvula preservation and radiofrequency tongue base reduction. All the patients were treated with automated continuous positive airway pressure (CPAP) for 3-7 days before operation and automated antibiotic therapy administered in the oropharynx, with 24 h ECG monitoring postoperatively. Polysomnography were carried out before and 6 months after surgery. RESULTS: The preoperative apnea hypopnea index (AHI) and lowest SaO(2) (LSaO(2)) were 58.4-/+5.1/h and 0.650-/+0.059, respectively, which were 15.5-/+3.2/h and 0.864-/+0.064 at 6 months after surgery, respectively, showing significant changes after surgery (P<0.01). Dyspnea occurred in 2 cases after operation, intraoperative bleeding in 1 case, primary bleeding in 2 cases and hypertension crisis in 1 case. CONCLUSION: Severe OSAHS patients are subject to great surgical risk. Application of auto-CPAP before operation can significantly improve the patients' tolerance of surgery and anesthesia, and reduce the surgical risks and preoperative complications.