Herein we report a protocol for the generation of alkyl carbon radicals from alkylboronic acids wherein photoexcited 4‐nitropyridine N‐oxide biradical features a catalyst to promote the ...nucleo‐homolytic substitution of boronic acids. With a wide range of readily available aliphatic boronic acids, including methyl boronic acid, the developed catalytic system demonstrates broad applicability for alkylation, amination, and cyanation.
Photoexcited 4‐nitropyridine N‐oxide biradical was found to catalyze the carbon radical generation from alkylboronic acids with blue LED irradiation without exogenous photocatalysts. With a wide range of readily available aliphatic boronic acids, including methyl boronic acid, the developed catalytic system allowed simple and robust applicability for alkylation, amination, and cyanation reactions.
The needs of everyday life, such as counting and measuring, are roots of theoretical mathematics. I believe these roots are why mathematical ideas ground research so amazingly well within many ...scientific fields. Initially trained as a theoretical mathematician and having collaborated with non-mathematicians in the field of bone research, I address the advantages and challenges of collaborations across fields of research among investigators trained in different disciplines. I report on the mathematical ideas that have guided my research on the mechanics of bone tissue. I explain how the mathematical ideas of local vs. global properties influence my research. Polarized light microscopy (PLM) is a tool that I use consistently, in association with other microscopy techniques, to investigate bone in its healthy state and in the presence of bone disease, in humans and in animal models. I review the results that I and investigators around the world have obtained with PLM. Applied to thin bone sections, PLM yields extinct (black) and bright (white) signals that are interpreted in terms of the orientation of collagen type I, by means of other microscopy techniques. Collagen type I is an elementary component of bone tissue. Its orientation is important for the mechanical function of bone. Images obtained by PLM at a specific bone site yield big data sets regarding collagen orientation. Multiple data sets in respect of multiple sites are often needed for research because the bone tissue differs by location in response to the distinct forces acting on it. Mathematics, defined by philosophers as the theory of patterns, offers the backdrop for pattern identification in the big data sets regarding collagen orientation. I also discuss the computational aspect of the research, pursuant to which the patterns identified are incorporated in simulations of mechanical behaviors of bone. These mathematical ideas serve to understand the role of collagen orientation in bone fracture risk.
•Research progress benefits from cross-field collaborations.•Concepts of theoretical mathematics guide the study of bone biomechanics.•Polarized light microscopy is key to the study of bone tissue.•Images obtained by polarized light microscopy yield big data sets.•The patterns of big data sets are included in simulations of bone mechanics.
Readily available and facilely tunable pyridine N-oxides have been developed as effective photoinduced hydrogen-atom-transfer (HAT) catalysts for site-selective C–H functionalizations of a broad ...range of C–H substrates, including unactivated alkanes. Pyridine N-oxide radicals, catalytically generated from N-oxides by photoredox catalyzed single-electron oxidation, are the key intermediates that enable an effective HAT process for carbon radical generation to achieve alkylation, amination, azidation, allylation, and cyanation. Additionally, the fine-tuning of reactivity and selectivity of pyridine N-oxides through operationally simple structural modification was investigated and showed promising capability for selective functionalization of unactivated C(sp3)–H bonds.
The first multi-messenger detection of a binary neutron star merger, GW170817, brought to the forefront the structured jet model as a way to explain multiwavelength observations taken more than a ...year after the event. Here, we show that the high-latitude emission from a structured jet can naturally produce an X-ray plateau in gamma-ray burst (GRB) light curves, independent of the radiation from an external shock. We calculate the radiation from a switched-off shell featuring an angular structure in both its relativistic bulk motion and intrinsic brightness. Our model is able to explain the shallow decay phase (plateau) often observed in GRB X-ray light curves. We discuss the possible contribution of the structured jet high-latitude emission to other distinctive features of GRB X-ray light curves, and its capability to explain the chromatic optical/X-ray light-curve properties.
Haptoglobin (Hp) reacts with dimeric hemoglobin (Hb), shifts the equilibrium in favor of the αβ dimer and displays heme-based catalysis. Here, kinetics of peroxynitrite scavenging by ferric human ...haptoglobin1-1:hemoglobin and haptoglobin2-2:hemoglobin complexes (Hp1-1:Hb(III) and Hp2-2:Hb(III), respectively) is reported between pH 6.2 and 8.3 at 20.0 °C. The reactivity of Hp1-1:Hb(III) and Hp2-2:Hb(III) against peroxynitrite is similar to that of tetrameric Hb(III), reflecting the R-like structure of the αβ dimers of Hb(III) bound to Hp. To investigate the protective role of Hp1-1:Hb(III) and Hp2-2:Hb(III) against peroxynitrite-mediated nitration, the relative yield of nitro-l-tyrosine formed by the reaction of peroxynitrite with free l-tyrosine was determined. Interestingly, both Hp1-1:Hb(III) and Hp2-2:Hb(III) impair peroxynitrite-mediated nitration of free l-tyrosine. Therefore, Hp:Hb complexes could participate to the detoxification of reactive nitrogen and oxygen species in vivo, contributing to prevent extra-erythrocytic Hb-induced damage during hemolytic crisis.
The Front Cover represents the photoinduced generation of alkyl carbon radicals from alkylboronic acids through nucleo‐homolytic substitution catalyzed by blue light excited 4‐nitropyridine N‐oxide ...biradical. In their Research Article, Y. Deng and co‐workers demonstrated the biradical nature of the photoexcited pyridine N‐oxides and the synthetic applications for alkyl carbon radical generation from organoboronic acid allowing simple and robust protocols for alkylation, amination, and cyanation reactions. This work is an example of great opportunities for the development of aromatic N‐oxides based new photocatalysts. More information can be found in the Research Article by Y. Deng and co‐workers.
We consider φ⁎TP3, the pull-back of TP3 (the tangent bundle to P3) via a generically one-to-one parametrization φ of a rational curve D of degree dD≥3 and spanning P3. We study the splitting of φ⁎TP3 ...as direct sum of line bundles in terms of ancillary curve(s) of degree strictly smaller than dD and spanning Pr with r≤3. The degrees of these line bundles are determined by (i) the largest multiplicity of D at a point (if the largest multiplicity is greater than or equal to ⌊dD/2⌋) and (ii) the largest multiplicities at a non-coplanar quadruple of points (if all the multiplicities of D are strictly smaller than ⌊dD/2⌋).
This work investigates how changes in cortical bone microstructure alter the risk of fragility fractures. The secondary osteons of non-osteoporotic (by DXA) women with fragility fractures have ...reduced lamellar width and greater areas of birefringent brightness in transverse sections, a pathological condition. We used hierarchical finite element (FE) models of the proximal femur of two women aged 67 and 88 (younger and older) during one-legged stance. At specific locations of the anterior-inferior neck (ROI), we analyzed micro-models containing osteons comprised of alternating birefringent extinct and bright lamellae. The plane of lamellar isotropy (XY) was transverse to the osteon longitudinal axis (Z) which was parallel to the femoral neck axis. To evaluate changes in fracture risk with changes in microstructure, we investigated principal and von Mises stresses, and planar stress measures that accounted for transverse isotropy. For both younger and older femurs, 48% to 100% of stress measures were larger in models with healthy architecture than in models with pathological architecture, while controlling for type of lamella and osteon. These findings suggest that bone adaptation reduces stress at most pathological lamellar sites. However, in the bright lamellae of the younger femur, the pathological tensile, compressive and distortional stresses in the transverse plane and distortional stress in the longitudinal planes were larger than the non-negligible corresponding stresses in 6 of the 28 osteon models with healthy architecture, in 5 of the 7 locations. Therefore, a minority of sites with pathological architecture present greater stress, and therefore, greater fracture risk.
Human serum albumin (HSA), the most prominent protein in plasma, binds different classes of ligands at multiple sites. The globular domain structural organization of monomeric HSA is at the root of ...its allosteric properties which are reminiscent of those of multimeric proteins. Here, both functional and structural aspects of the allosteric modulation of heme and drug (e.g., warfarin and ibuprofen) binding to HSA and of the drug-dependent reactivity of HSA-heme are reviewed.
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