Selective cleavage and functionalization of C−C bonds have important applications in organic synthesis and biomass utilization. However, functionalization of C−C bonds by controlled cleavage remains ...difficult and challenging because they are inert. Herein, we describe an unprecedented efficient protocol for the breaking of successive C−C bonds in alcohols to form esters with one or multiple carbon atoms less using heterogeneous cobalt nanoparticles as catalyst with dioxygen as the oxidant. A wide range of alcohols including inactive long‐chain alkyl aryl alcohols undergo smoothly successive cleavage of adjacent −(C−C)n− bonds to afford the corresponding esters. The catalyst was used for seven times without any decrease in activity. Characterization and control experiments disclose that cobalt nanoparticles are responsible for the successive cleavage of C−C bonds to achieve excellent catalytic activity, while the presence of Co‐Nx has just the opposite effect. Preliminary mechanistic studies reveal that a tandem sequence reaction is involved in this process.
Cobalt nanoparticles‐catalyzed aerobic oxidative cleavage of adjacent −(C−C)n− bonds in succession in a wide range of alcohols as well as inactive long‐chain alkyl aryl alcohols to afford esters was developed. Control experiments disclose that metallic cobalt nanoparticles are responsible for the outstanding catalytic performance rather than single atom cobalt.
An in situ formed porphyrin-inspired iron complex that catalyzes asymmetric epoxidation of di- and trisubstituted enones is described. The reaction provides highly enantioenriched α,β-epoxyketones ...(up to 99% ee). The practical utility of the new catalyst system is demonstrated by the gram-scale synthesis of optically pure epoxide. Hammett analysis suggests that the transition state of the reaction is electron-demanding and the active oxidant is electrophilic.
A novel strategy for catalytic asymmetric epoxidation of a wide variety of olefins by a porphyrin-inspired chiral manganese complex using H2O2 as a terminal oxidant in excellent yield with up to ...greater than 99% ee has been successfully developed.
An unprecedented efficient protocol is developed for the oxidative cleavage of C≡C bonds in alkynes to produce structure-diverse esters using heterogeneous cobalt nanoparticles as catalyst with ...molecular oxygen as the oxidant. A diverse set of mono- and multisubstituted aromatic and aliphatic alkynes can be effectively cleaved and converted into the corresponding esters. Characterization analysis and control experiments indicate high surface area and pore volume, as well as nanostructured nitrogen-doped graphene-layer coated cobalt nanoparticles are possibly responsible for excellent catalytic activity. Mechanistic studies reveal that ketones derived from alkynes under oxidative conditions are formed as intermediates, which subsequently are converted to esters through a tandem sequential process. The catalyst can be recycled up to five times without significant loss of activity.
Display omitted
•Esterification of alkynes via oxidative cleavage of C≡C bonds•Heterogeneous cobalt nanoparticles as catalyst and oxygen as oxidant•Excellent functional group compatibility, facile scalability, and a broad substrate scope•A significant advancement in developing heterogeneous catalyst for unsaturated hydrocarbons
Organic synthesis; Interface science
Desferrioxamine (DFO), an iron chelator, can stimulate osteogenesis and angiogenesis by stabilizing hypoxia-inducible factor 1α. We postulate that a bone graft substitute combined with DFO is ...beneficial to the reconstruction of bone defects.
We implanted pure true bone ceramic (TBC) and DFO-loaded TBC (DFO/TBC) scaffolds into 15-mm rabbit radial defects for 8 weeks. The bone segments were examined with X-ray, micro-CT and histology.
Radiographs showed that the DFO/TBC scaffold became radiopaque, and the gaps between the scaffold and radial cut ends were often invisible. Variables from micro-CT, including the bone volume fraction (BV/TV), trabecular thickness (Tb.Th) and trabecular number (Tb.N), were significantly increased in pure TBC and DFO/TBC scaffolds that had been implanted for 8 weeks compared to unimplanted TBC scaffolds (p values <0.05-0.001). Between the former two groups, BV/TV and Tb.Th were significantly increased in DFO/TBC scaffolds (p < 0.001), but Tb.N did not show significant differences. Histological examinations showed considerably increased new bone and decreased TBC trabecular remnants in DFO/TBC scaffolds compared to pure TBC scaffolds. Many cavities in the new bone area in DFO/TBC scaffolds were occupied by bone marrow elements and blood vessels. Percent of new bone with tetracycline labeling was significantly greater in DFO/TBC scaffolds than in pure TBC scaffolds (p < 0.001).
This preliminary study reveals that DFO can effectively induce new bone growing into TBC scaffolds, suggesting that the DFO/TBC composite is a promising bone graft substitute for the treatment of bone defects.
What are the key points of bibliometrics? Li, Xincheng; Li, Guosong; Huang, Jie
International journal of surgery (London, England),
07/2024, Volume:
110, Issue:
7
Journal Article
It is important to investigate the constitutive behavior of high density polyethylene (HDPE) under cyclic loading since it is widely used for industrial applications. However, there are only a few ...preliminary investigations on the constitutive behavior of HDPE under cyclic loading. This work aims at investigating the deformation mechanism, developing the constitutive model especially for the cyclic-loading behavior, and proposing an efficient approach for model calibration. Firstly, the deformation mechanism was successfully explored by conducting a special designed relaxation-unloading test by which the time-independent elastic-plastic behavior was decoupled from the time-dependent overall deformation behavior. Then, a nonlinear elastic-viscoplastic constitutive model was developed based on the parallel rheological framework (PRF) composed of an elastic-plastic network in parallel with multiple nonlinear viscoelastic networks. Finally, an approach was proposed to calibrate the constitutive model by means of relaxation-unloading tests and material parameter optimizations. The agreement between the prediction and the test data successfully demonstrated that the model could be used to precisely simulate the constitutive behavior of HDPE under static, quasi-static and dynamic cyclic loading. The developed constitutive model is beneficial to the long-term durability evaluation of HDPE. The methodology for exploring the deformation mechanism and calibrating the constitutive model may also be applicable to other polymers.
•The elastic-plastic behavior is identified from overall elastic-viscoplastic behavior by the relaxation-unloading test.•The parallel rheological framework is developed to predict cyclic-loading behavior of high density polyethylene.•An approach is proposed based on tests and parameters optimization to calibrate the constitutive model accurately.
Radical hydroboration reactions have only recently been reported and are still rare. Here we describe a photoredox radical hydroboration of α,β-unsaturated esters, amides, ketones, and nitriles with ...NHC-boranes that uses only an organocatalyst and visible light. The conditions are mild, the substrate scope is broad, and the α/β regioselectivity is high. The reaction requires only the organocatalyst; there is no costly metal, and there are no other additives (base, cocatalyst, initiator).
The oxidative cleavage and functionalization of C–C bonds in 1,2-diols have become a rapidly growing field of chemical transformations. However, achieving it in a direct and selective manner, ...especially using metal-free-based catalysts, remains challenging because of the inherent kinetic inertness and thermodynamic stability of C–C bonds. Herein, we describe a general and efficient metal-free N-doped porous carbon material that enables the synthesis of nitriles from 1,2-diols. A broad array of structurally distinct mono- and multisubstituted 1,2-diols can smoothly undergo cleavage of C–C bonds to obtain nitriles using O2 as the oxidant and aq. NH3 as the nitrogen source. Notably, the oxidative cleavage and amidation of 1,2-diols to deliver amides can also be achieved with NH4OAc as a nitrogen source. A series of control experiments verify that the preference of selectivity for amides stems from the synergistic effect of the carboxylic acid group in catalysts and carboxylate anions. This protocol exhibits easy scalability, broad substrate scope, remarkable functional group tolerability, and recyclable catalyst. Characterization analysis and experimental data reveal that the high catalytic activity of the N-doped carbon materials is mainly attributed to graphitic-N species and the large specific surface area.
Purpose: MicroRNAs (miRNAs or miRs) play an important role in the initiation and development of chondrosarcoma (CS). However, the role of miR-21-5p in CS progression and its underlying molecular ...mechanisms remains unclear.
Materials and Methods: miR-21-5p expression was measured by qRT-PCR. Cell proliferation, migration, and invasion were detected by CCK-8 and Transwell assay. Dual-luciferase reporter assay was used to validate the target of miR-21-5p. Western blot was applied to explore the expressions of CCR7 and EMT biomarkers. Then, the xenograft model was established to confirm the effects of miR-21-5p.
Results: miR-21-5p was significantly downregulated in CS tissues and cells and negatively correlated with grade, recurrence, and 5-year overall survival. In vitro, miR-21-5p caused G0/G1 cell cycle arrest and induced apoptosis by decreasing cyclin D1 expression and Bcl-2/Bax ratio. miR-21-5p suppressed cell migration and invasion of CS cells by inhibiting epithelial-mesenchymal transition (EMT). In vivo, miR-21-5p inhibited xenograft tumor formation of SW1353 cells. Mechanistically, miR-21-5p targeted the 3'-UTR of C-C chemokine receptor 7 (CCR7) mRNA to inhibit its expression. Overexpression of CCR7 reversed the inhibitory effects of miR-21-5p on CS cell behaviors. However, the silencing of CCR7 enhanced the inhibitory effects of miR-21-5p on CS cells. Besides, the overexpression of miR-21-5p or silencing of CCR7 obviously reduced the expression levels of p-STAT3, p-p56, and p-IκBα.
Conclusion: miR-21-5p targeted CCR7 expression to inhibit the STAT3 and NF-κB signaling, thereby suppressing cell proliferation, migration, invasion, and EMT in CS cells, which might be a novel mechanistic study for CS therapy.
Abbreviations: 3'-UTR: 3'-untranslated region; CCR7: C-C chemokine receptor type 7; CS: chondrosarcoma; DMEM: dulbecco's modified eagle's medium; EMT: epithelial-mesenchymal transition; HEK-293T: human embryonic kidney-293T; miR-21-5p: microRNA-21-5p; miR-NC: negative control miRNA; SD: standard deviation; si-CCR7: CCR7 siRNAs
