Computational Studies on the Mechanism and Origin of the Different Regioselectivities of Manganese Porphyrin-Catalyzed C-H Bond Hydroxylation and Amidation of Equilenin Acetate.

The manganese porphyrin-catalyzed C-H bond hydroxylation and amidation of equilenin acetate developed by Breslow and his co-worker have been investigated with density functional theory (DFT) calculations. The hydroxylation of C(sp2)-H bond of equilenin acetate leading to the 6-hydroxylated product is more favorable than the hydroxylation of C(sp3)-H bond of equilenin acetate, leading to the 11ß-hydroxylation product. The computational results suggest that the C(sp2)-H bond hydroxylation of equilenin acetate undergoes an oxygen-atom-transfer mechanism, which is more favorable than the C(sp3)-H bond hydroxylation undergoing the hydrogen-atom-abstraction/oxygen-rebound (HAA/OR) mechanism by 1.6 kcal/mol. That is why, the 6-hydroxylated product is the major product and the 11ß-hydroxylated product is the minor product. In contrast, the 11ß-amidated product is the only observed product in manganese porphyrin-catalyzed amidation reaction. The benzylic amidation undergoes a hydrogen-atom-abstraction/nitrogen-rebound (HAA/NR) mechanism, in which hydrogen atom abstraction is followed by nitrogen rebound, leading to the 11ß-amidated product. The benzylic C(sp3)-H bond amidation at the C-11 position is more favorable than aromatic amidation at the C-6 position by 4.9 kcal/mol. Therefore, the DFT computational results are consistent with the experiments that manganese porphyrin-catalyzed C-H bond hydroxylation and amidation of equilenin acetate have different regioselectivities.

Highly Efficient Phosphorescent Tetradentate Platinum(II) Complexes Containing Fused 6/5/6 Metallocycles.

A series of neutral tetradentate Pt(II) complexes with fused 6/5/6 metallocycles and biphenyl (bp)-containing ligands have been designed and synthesized. All bridging atoms adopt nitrogens designed as an acridinyl group (Ac), an aza acridinyl group (AAc), and an aza carbazolyl group (ACz), which can effectively tune their LUMO energy levels. Their HOMO energy levels can be well-controlled through molecular modifications on the bp moieties with electron-donating and electron-withdrawing groups. These molecular modifications also have profound effects on the electrochemical and photophysical properties and photostabilities of the Pt(II) complexes. The ground-states and excited states are systematically studied by density functional theory (DFT), time-dependent density functional theory (TD-DFT), and natural transition orbital (NTO) calculations. All the Pt(II) complexes exhibit admixed 3(LC/MLCT) characters in T1 states with various proportions, which are strongly structure-dependent. These 6/5/6 Pt(II) complexes demonstrate high quantum efficiencies in dichloromethane solutions (ΦPL = 27-51%) and in doped PMMA films (ΦPL = 36-52%) at room temperature with short luminescence lifetimes of 1.6-9.5 µs and 7.6-9.0 µs, respectively. They emit green light with dominant peaks of 512-529 nm in solutions and 512-524 nm in doped PMMA films, respectively. Importantly, Pt(bp-2) exhibits highly stable emission colors with the same dominant peaks at 512 nm in various matrixes and also demonstrates a long photostability lifetime, LT80, at 80% of initial luminance, of 190 min, which is doped in polystyrene films (5 wt %) excited by UV light of 375 nm at 500 W/m2. These studies indicate that these 6/5/6 Pt(II) complexes can act as good phosphorescent emitters for OLED applications and should provide a viable route for the development of efficient and stable Pt(II)-based phosphorescent emitters.

Tuning the Excited State of Tetradentate Pd(II) Complexes for Highly Efficient Deep-Blue Phosphorescent Materials.

Deep-blue-light-emitting materials are urgently desired in high-performance organic light-emitting diodes (OLEDs) for full-color display and solid-state lighting applications. However, the development of stable and efficient deep-blue emitters remains a great challenge. Herein, a series of stable and efficient tetradentate Pd(II)-complex-based deep-blue emitters with rigid 5/6/6 metallocycles and no F atom were designed and synthesized. These deep-blue emitters employ various isoelectronic five-membered heteroaryl-ring-containing ligands to exhibit extremely narrow emission spectra peaking at 439-443 nm with a full width at half-maximum (fwhm) of only 22-38 nm in 2-methyltetrahydrofuran at room temperature. In particular, the design of an intramolecular hydrogen bond enabled the 1-phenyl-1,2,3-trazole-based Pd(II) complexes to achieve CIEy < 0.1 (0.069-0.078; CIE is Commission Internationale de L'Eclairage). Theoretical calculation and natural transition orbital analysis reveal that these deep-blue materials emit light exclusively from their ligand (carbazole)-centered (3LC) states. Moreover, the triplet excited-state property can be efficiently regulated through ligand modification with isoelectronic oxazole and thiazole rings or pyridine rings, resulting in sky-blue-to-yellow materials, which emit light originating from an admixture of metal-to-ligand charge-transfer (3MLCT) and intraligand charge-transfer states. The newly developed Pd(II) complexes are strongly emissive in various matrixes with a quantum efficiency of up to 51% and also highly thermally stable with a 5% weight-reduction temperature (ΔT5%) of up to 400 °C. Deep-blue OLEDs with CIEy < 0.1 employing Pd(II) complexes as emitters were successfully fabricated for the first time. This study demonstrates that the Pd(II) complexes can act as excellent phosphorescent light-emitting materials through rational molecular design and also provide a valuable method for the development of Pd(II)-complex-based efficient and stable deep-blue emitters.

Understanding the structures and aromaticity of heteroporphyrins with computations.

Heteroporphyrins are porphyrin derivatives with replacement of the pyrrolic NH moiety by other heteroatom-containing groups, such as PH, AsH, SiH2, O, S, etc. For all studied heteroporphyrins, the macrocycle structure is distorted due to the presence of large heteroatoms. The HOMO-LUMO gap of heteroporphyrins is generally decreased compared to regular porphyrins. Both nucleus independent chemical shifts values and visualized anisotropy of induced current density were computed to describe the aromaticity of heteroporphyrins. The plots of anisotropy of induced current density suggest that the ring current diverged into an outer and an inner pathway at each ring. The current mainly passes through the outer path at the pyrrolic rings with inner hydrogen and through the inner path at the pyrrolic rings without inner hydrogen. In both regular porphyrin and O-substituted heteroporphyrins, the aromatic pathway is mainly contributed by the 22π-electron aromatic route model. Heteroatoms such as PH, AsH, S, Se and Te have little contribution to the aromaticity of heteroporphyrins. In addition, the π conjugation is also interrupted at the CH2 and SiH2 moiety, and the ring current mainly passes through the outer path of the heteroporphyrins with CH2 and SiH2 replacing the pyrrolic NH moiety. Therefore the 18π-[18]annulene model is dominated in PH-, AsH-, S-, Se-, Te-, CH2- and SiH2-substituted heteroporphyrins. These computational studies shed new light on the aromatic characters of heteroporphyrins, and will facilitate the further development of various novel heteroporphyrins.

Mechanism and stereoselectivity of benzylic C-H hydroxylation by Ru-porphyrin: a computational study.

The mechanism and origin of the stereoselectivity of asymmetric benzylic C-H hydroxylation by Ru-porphyrin were elucidated with density functional theory calculations. The reaction proceeds via a hydrogen-atom abstraction/oxygen-rebound pathway, wherein a high-valent ruthenium-oxo species abstracts a hydrogen atom from ethylbenzene to generate a radical pair intermediate, followed by the oxygen-rebound process to form 1-phenylethanol. The hydrogen-atom abstraction step is the rate- and stereoselectivity-determining step. Based on the mechanistic model, the computed stereoselectivity is in agreement with the experimental observations. Analysis of the distortion/interaction model suggests that stereoselectivity is determined by both the distortion energy of the ethylbenzene and the interaction energy between the ethylbenzene and the chiral Ru-porphyrin. The steric repulsion between the phenyl group of ethylbenzene and the bulky substituent of Ru-porphyrin is the leading cause of chiral induction.

Computational Exploration of Chiral Iron Porphyrin-Catalyzed Asymmetric Hydroxylation of Ethylbenzene Where Stereoselectivity Arises from π-π Stacking Interaction.

The mechanism and origins of stereoselectivity of chiral iron porphyrin-catalyzed asymmetric hydroxylation of ethylbenzene were explored with density functional theory. The hydrogen atom abstraction is the rate- and stereoselectivity-determining step. In good agreement with experimental results, the formation of the (R)-1-phenylethanol product is found to be the most favorable pathway. The transition state of hydrogen atom abstraction which leads to the (S)-1-phenylethanol product is unfavorable by 1.7 kcal/mol compared to the corresponding transition state which leads to the (R)-1-phenylethanol product. Enantioselectivity arises from an attractive π-π stacking interaction between the phenyl group of ethylbenzene substrate and the naphthyl group of the porphyrin ligand.

Metal-Assisted Delayed Fluorescent Pd(II) Complexes and Phosphorescent Pt(II) Complex Based on [1,2,4]Triazolo[4,3-a]pyridine-Containing Ligands: Synthesis, Characterization, Electrochemistry, Photophysical Studies, and Application.

The synthesis and photophysical characterization of a series of tetradentate cyclometalated M(tzpPh-O-CzPy-R) complexes and their analogues are reported, where M is palladium or platinum and a tetradentate cyclometalating ligand contains tzpPh (3-phenyl-[1,2,4]triazolo[4,3-a]pyridine) and CzPy (carbazolylpyridine) moieties linked with an oxygen atom. Variations of the σ-electron-donating group R on the ligand significantly affect the photophysical properties of the complexes. By using the strong electron-withdrawing tzp portion as an acceptor and the carbazole portion as a donor, a series of Pd(II)-based metal-assisted delayed fluorescence (MADF) materials was developed. Electrochemical analysis demonstrates the irreversible reduction process occurs on the tzp ring and the irreversible oxidation process mainly occurs on the metal-phenyl moiety. This is in agreement with the HOMO and LUMO distributions by the DFT calculations, which also shows that the Pt(II) complex has more metal orbital character than those of the Pd(II) complexes. Most of the Pd(II) complexes reported here are highly emissive at 77 K in 2-MeTHF with luminescent lifetimes in the millisecond range (τ = 1.96-2.36 ms) and λmax = 488-499 nm; however, the luminescent lifetimes are shortened to the microsecond range (τ = 26.7-152.9 µs in solution and 57.0-109.9 µs in thin film respectively) at room temperature. The quantum efficiency of the Pd(II) complexes can be increased by more than 8-fold through structure modification with σ-donating groups on the ligand. Especially, the Pd(tzp-3) has a small ΔEST of 0.228 eV and exhibits strong typical MADF in PMMA film. The Pt(II) complex Pt(tzp-2) exhibits high thermal stability (ΔT0.5% = 440 °C) and high quantum efficiency (Φ = 50.1%) in dichloromethane solution with τ of 15.8 µs. The Pt(tzp-2) based bright green OLED achieved a peak EQE of 8.7% and a maximum brightness of 28280 cd/m2 using an unoptimized device structure.

An interventional implementation project: hand hygiene improvement.

BACKGROUND: Good hand hygiene is the most effective basic measure for preventing hospital-acquired infections. This research project, which originated from a project report on improving hand hygiene at a general hospital in Hangzhou, Zhejiang, China, aimed to investigate the effectiveness of hand hygiene improvement among the hospital staff. METHODS: Since 2017, a hand hygiene improvement project involving the staff of a 2,500-bed general teaching hospital in Zhejiang, China, has been carried out. This study summarized the implementation and effectiveness of the project, which is based on the five factors of systematic evaluation. The research summary was divided into three phases: phase I (December 2017 to August 2018), phase 2 (September 2018 to April 2019), and phase 3 (May 2019 to December 2019). The data of hand hygiene compliance rates of different groups of professionals in the different research periods were statistically analyzed. RESULTS: The results showed that continuous intervention led to a gradual increasing trend (Ptrend<0.001) in the hand hygiene implementation rate with as the intervention time and phases progressed. The hand hygiene compliance rates differed significantly during different phases (76.61%, 79.95%, and 83.34% in phases 1, 2, and 3, respectively, P<0.001). At the same time, the compliance rates of hand hygiene at each phase differed significantly between different professions (P<0.001, the compliance rate of hand hygiene among nurses was the highest and lowest among workers). The compliance rate of hand hygiene for different professions during the three phases were: nurses, 84.73%; doctors, 78.35%; interns, 77.62%; and other hospital workers, 72.79%. CONCLUSIONS: The hand hygiene compliance rate was effectively improved among the hospital staff after the implementation of the hand hygiene improvement project. In this hospital, the project yielded remarkable results. Hand hygiene must be continuously practiced and improved to develop good habits. Effective and detailed planning as well as key factors, such as hand hygiene facilities, information monitoring, the active participation and response of employees, training and education, and supervision and feedback, could help to guarantee the effectiveness of the project.

Characteristics of fecal gut microbiota in patients with colorectal cancer at different stages and different sites.

Numerous studies have revealed that the gut microbiota serves an important role in the pathogenesis of colorectal cancer (CRC). The present study aimed to investigate the populations present in the gut microbiota in patients with CRC of different stages and at different sites. Fecal samples were obtained from 67 CRC patients and 30 healthy controls, which were analyzed by sequencing the V3-V4 region of the 16S rRNA gene. Increased diversity of the fecal gut microbiota in patients with CRC was reported compared with the healthy controls. In the present study, at the genus level, the relative abundances of Prevotella, Collinsella and Peptostreptococcus in the gut microbiota of CRC patients were substantially increased compared with healthy controls, while the relative abundance of Escherichia-Shigella was significantly lower. In addition, differences in the fecal gut microbiota were also compared between patients with stage I-IV CRC and healthy controls. The results revealed that the abundances of the genera Peptostreptococcus, Collinsella and Ruminococcus were significantly increased in patients with CRC stage I compared with the healthy controls, while Alistipes was enriched in patients with stage III CRC compared with patients with stage IV. Furthermore, the present study reported that the genera Veillonella and Coprobacter were more abundant in the proximal segments than in the distal segments of the colon. In conclusion, despite the low number of samples employed in the present study, a signature of genera indicating dysbiosis of the gut microbiota of patients with stage I-IV CRC patients was proposed, which may provide insight into the mechanisms underlying the progression of CRC. These findings are also valuable for developing novel fecal diagnostic methods and therapeutic strategies for the treatment of CRC.