Catalytic C(sp3)−H functionalization can convert abundant feedstock hydrocarbons into value‐added products in an atom‐ and step‐economic manner and is a powerful tool in organic synthesis. However, ...the intrinsic chemical inertness of ubiquitous aliphatic C−H bonds of alkanes and cycloalkanes makes their direct and selective functionalization extremely challenging. Recently, some elegant strategies have been developed to solve the problems based on the merger of photocatalyzed hydrogen atom transfer (HAT) with transition metal catalysis. Light‐induced HAT processes are employed to initiate the alkyl radical generation, which is synergistic with metal catalysis involving for example nickel, copper, cobalt, cerium, chromium, or manganese. The different metal catalysts provide redox adjustment, Lewis acid activation or other functionalities and tune the reactivity and selectivity of the radical‐mediated sequences, allowing the development of diverse chemo‐, site‐, and/or stereoselective synthetic reactions. In this minireview, we offer a brief summary of the recent advances in dual photo‐induced HAT and transition metal catalysis for C−H functionalization of alkanes and cycloalkanes. We expect that these methodologies will stimulate the applications in catalysis, pharmaceuticals, and other related fields.
Catalytic C(sp3)−H functionalization of alkanes and cycloalkanes is a useful tool to convert abundant chemical feedstocks into value‐added products but remains a challenging task. In this review, recent advances relying on dual photo‐induced hydrogen atom transfer and transition metal catalysis are summarized.
The axon initial segment (AIS) is located at the proximal axon and is the site of action potential initiation. This reflects the high density of ion channels found at the AIS. Adaptive changes to the ...location and length of the AIS can fine‐tune the excitability of neurons and modulate plasticity in response to activity. The AIS plays an important role in maintaining neuronal polarity by regulating the trafficking and distribution of proteins that function in somatodendritic or axonal compartments of the neuron. In this review, we provide an overview of the AIS cytoarchitecture, mechanism of assembly, and recent studies revealing mechanisms of differential transport at the AIS that maintain axon and dendrite identities. We further discuss how genetic mutations in AIS components (i.e., ankyrins, ion channels, and spectrins) and injuries may cause neurological disorders.
In this review, we provide an overview of the AIS cytoarchitecture, mechanism of assembly, and recent studies revealing mechanisms of differential transport at the AIS that maintain axon and dendrite identities. We further discuss how genetic mutations in AIS components (i.e., ankyrins, ion channels, and spectrins) and injuries may cause neurological disorders.
Polycystic ovary syndrome (PCOS) is a complex endocrine and metabolic disorder. Typically, it is characterized by hirsutism, hyperandrogenism, ovulatory dysfunction, menstrual disorders and ...infertility. To date, its pathogenesis remains unclear. However, insulin resistance (IR) is considered as the primary pathological basis for its reproductive dysfunction. On the other hand, a condition in which insulin is over-secreted is called hyperinsulinemia. IR/Hyperinsulinemia is associated with chronic inflammation, hormonal changes, follicular dysplasia, endometrial receptivity changes, and abortion or infertility. Additionally, it increases incidence of complications during pregnancy and has been associated with anxiety, depression, and other psychological disorders. Gut microbiota, the "second genome" acquired by the human body, can promote metabolism, immune response through interaction with the external environment. Gut microbiota dysbiosis can cause IR, which is closely linked to the occurrence of PCOS. This article reviewed recent findings on the roles of gut microbiota in the development of insulin resistance and the mechanism underlying polycystic ovary syndrome.
Efficient charge separation and utilization are critical factors in photocatalysis. Herein, it is demonstrated that the complete spatial separation of oxidation and reduction cocatalysts enhances the ...efficacy of charge separation and surface reaction. Specifically, a Pt@NH2‐UiO‐66@MnOx (PUM) heterostructured photocatalyst with Pt and MnOx as cocatalysts is designed for the optimization of the NH2‐UiO‐66 photocatalyst. Compared with the pristine NH2‐UiO‐66, Pt@NH2‐UiO‐66 (PU), and NH2‐UiO‐66@MnOx (UM) samples, the PUM sample exhibits the highest hydrogen production activity. As cocatalysts, Pt favors trapping of electrons, while MnOx tends to collect holes. Upon generation from NH2‐UiO‐66, electrons and holes flow inward and outward of the metal–organic framework photocatalyst, accumulating on the corresponding cocatalysts, and then take part in the redox reactions. The PUM photocatalyst greatly prolongs the lifetime of the photogenerated electrons and holes, which favors the electron–hole separation. Furthermore, the PUM sample facilitates overall water splitting in the absence of sacrificial agents, thereby demonstrating its potential as a modification method of MOF‐type semiconductors for the overall water‐splitting reaction.
A heterostructured photocatalyst, Pt@NH2‐UiO‐66@MnOx (PUM), is constructed based on the rational optimization of NH2‐UiO‐66 with spatially separated Pt and MnOx nanoparticles as cocatalysts. The optimization results in a long lifetime of the photogenerated electrons and holes in the composite, which can drive overall water splitting in the absence of sacrificial agents.
Development of practical deuteration reactions is highly valuable for organic synthesis, analytic chemistry and pharmaceutic chemistry. Deuterodehalogenation of organic chlorides tends to be an ...attractive strategy but remains a challenging task. We here develop a photocatalytic system consisting of an aryl-amine photocatalyst and a disulfide co-catalyst in the presence of sodium formate as an electron and hydrogen donor. Accordingly, many aryl chlorides, alkyl chlorides, and other halides are converted to deuterated products at room temperature in air (>90 examples, up to 99% D-incorporation). The mechanistic studies reveal that the aryl amine serves as reducing photoredox catalyst to initiate cleavage of the C-Cl bond, at the same time as energy transfer catalyst to induce homolysis of the disulfide for consequent deuterium transfer process. This economic and environmentally-friendly method can be used for site-selective D-labeling of a number of bioactive molecules and direct H/D exchange of some drug molecules.
In the HSS iteration methods proposed by Bai, Golub and Ng Z.-Z. Bai, G.H. Golub, M.K. Ng, Hermitian and skew-Hermitian splitting methods for non-Hermitian positive definite linear systems, SIAM. J. ...Matrix Anal. Appl. 24 (2003) 603–626, the determination of the optimal parameter is a tough task when solving a non-Hermitian positive definite linear system. In this paper, a new and simple strategy for obtaining the optimal parameter is proposed, which computes the optimal parameter by solving a cubic polynomial equation. The coefficients of this polynomial are determined by several traces of some matrices related to the symmetric and skew-symmetric parts of the coefficient matrix of the real linear system. Numerical experiments show that our new strategy is very effective for approximating the optimal parameter in the HSS iteration methods as it leads to fast convergence of the method.
While the relationship between state ownership and firm performance has been widely researched, the empirical evidence has provided mixed results. This study applies panel data regression techniques ...to 10,639 firm-year observations of nonfinancial Chinese listed firms during 2003–2010 to examine the relationship between state ownership and firm performance. The results show that state ownership has a U-shaped relationship with firm performance. The Split Share Structure Reform in2005–2006 played a positive role in enhancing the relationship between state ownership and firm profitability ratios. Although state ownership decreased significantly after 2006, it remains high in strategically important industry sectors such as the oil, natural gas and mining sector and the publishing, broadcasting and media sector. The findings reveal that a higher level of state ownership is superior to a dispersed ownership structure due to the benefits of government support and political connections. The Split Share Structure Reform made previously nontradable shares legally tradable, improving corporate governance and reducing the negative effect of non-tradable state shares.
Abstract We perform a direct search for an isotropic stochastic gravitational-wave background (SGWB) produced by cosmic strings in the Parkes Pulsar Timing Array (PPTA) Data Release 2 (DR2). We find ...no evidence for such an SGWB, and therefore place a 95% confidence level upper limit on the cosmic string tension, G μ , as a function of the reconnection probability, p , which can be less than 1 in the string-theory-inspired models or pure Yang–Mills theory. The upper bound on the cosmic string tension is G μ ≲ 5.1 × 10 −10 for p = 1, which is about five orders of magnitude tighter than the bound derived from the null search of individual gravitational-wave bursts from cosmic string cusps in the PPTA DR2, and comparable to previous bounds derived from the null search of the SGWB from cosmic strings.
More reliable biomarkers using near-patient technologies are needed to improve early diagnosis and intervention for patients with renal disease. Infrared (IR) vibrational ...spectroscopy/microspectroscopy is an established analytical method that was first used in biomedical research over 20 years ago. With the advances in instrumentation, computational and mathematical techniques, this technology has now been applied to a variety of diseases; however, applications in nephrology are just beginning to emerge. In the present study, we used attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy to analyze urine samples collected from rodent models of inflammatory glomerulonephritis (GN) as well as from patients with crescentic GN, with the aim of identifying potential renal biomarkers; several characteristic mid-IR spectral markers were identified in urine samples. Specifically, a 1545 cm
band increased in intensity with the progression and severity of GN in rats, mice and humans. Furthermore, its intensity declined significantly in response to corticosteroid treatment in nephritic rats. In conclusion, our results suggest that specific urinary FTIR biomarkers may provide a rapid, sensitive and novel non-invasive means of diagnosing inflammatory forms of GN, and for real-time monitoring of progress, and response to treatment.
Photo‐Induced C−H Methylation Reactions Li, Qian‐Yu; He, Yuhang; Lin, Yu‐Mei ...
Chemistry : a European journal,
December 22, 2023, Letnik:
29, Številka:
72
Journal Article
Recenzirano
Direct C−H methylation is a highly valuable approach for introducing methyl groups into organic molecules, particularly in pharmaceutical chemistry. Among the various methodologies available, ...photo‐induced methylation stands out as an exceptional choice due to its mild reaction conditions, energy efficiency, and compatibility with functional groups. This article offers a comprehensive review of photochemical strategies employed for the direct and selective methylation of C(sp3)−H, C(sp2)−H, and C(sp)−H bonds in various organic molecules. The discussed methodologies encompass transition‐metal‐based photocatalysis, organophotocatalysis, as well as other metal‐free approaches, including electron donor‐acceptor (EDA)‐enabled transformations. Importantly, a wide range of easily accessible agents such as tert‐butyl peroxide, methanol, DMSO, methyl tert‐butyl ether, TsOMe, N‐(acetoxy)phthalimide, acetic acid, methyl halides, and even methane can serve as effective methylating reagents for modifying diverse targets. These advancements in photochemical C−H methylation are anticipated to drive further progress in the fields of organic synthesis, photocatalysis, and pharmaceutical development, opening up exciting avenues for creating novel organic molecules and discovering new drug compounds.
In this review, we present a concise overview of recent breakthroughs in photochemical C−H methylation. These advancements encompass a variety of methodologies, including transition metal‐based photocatalysis, organophotocatalysis, and various metal‐free approaches, such as electron donor‐acceptor ‐enabled processes.
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