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The enantioselective total syntheses of (+)-peniciketals A and B, two members of a family of architecturally complex spiroketals, have been achieved. Key synthetic transformations comprise Type I Anion Relay Chemistry (ARC) to construct the benzannulated [6,6]-spiroketal skeleton, a Negishi cross-coupling/olefin cross-metathesis reaction sequence to generate the trans-enone structure, and a late-stage large fragment union exploiting our recently developed photoisomerization/cyclization tactic.

Cells exposed with irradiation can induce different biological effects in non-irradiated cells due to the cell-cell interactions. Herein, we investigated the bystander effect of different types of irradiation including gamma irradiation (GR) and lithium heavy ion irradiation (LR) on the model human neuroblastoma cell line (SH-SY5Y). The gamma and lithium ion irradiation induced different bystander effects on the SH-SY5Y cell line. The bystander effect induced by gamma irradiation promoted the cell proliferation through activating the ERK and AKT signaling pathways, but it could slightly influence the cell cycle of non-irradiated SH-SY5Y cells. Whereas, the bystander effect induced by lithium heavy ion irradiation inhibited the cell proliferation, arrested the cell cycle and activated the process of pro-apoptosis. The findings of this study confirm the diversified bystander effects of various irradiation on the non-irradiated cells, therefore it highlights the importance of revised strategy for clinical radiotherapy and radioprotection to reduce the damages caused by bystander effects. Further, the in-depth mechanism research on the cell proliferation influenced by the bystander effect of radiation will also be useful to understand the biological effects of radiation.

Multi-component union tactics in which three or more fragments are rapidly assembled are highly prized in the construction of architecturally complex natural products. Anion Relay Chemistry (ARC), a multi-component union tactic, has just such potential to elaborate structurally diverse scaffolds in a single operation with excellent stereochemical control. Conceptually, the ARC tactic can be divided into two main classes: “Through-Bond”, by the relay of negative charge through the bonding system of a molecule; and “Through-Space”, by the migration of negative charge across space by a transfer agent. “Through-Space” Anion Relay Chemistry, the focus of this Account, can be further subdivided into two types: Type I ARC, originated from Tietze-Schaumann-Smith coupling reaction, which for the first time permits controllable Brook rearrangements to construct unsymmetrical adducts, and as such has been successfully employed in the total syntheses of diverse natural products, including the mycoticins, bryostatin 1, spongistatins, rimocidin, indolizidine alkaloids, and enigmazole A; and Type II ARC, central to which is the design of novel bifunctional linchpins that enable rapid assembly of linear and cyclic fragments with diverse architectural features, ranging from polyols, spiroketals and polyenes to polypropionate scaffolds. Recently, the Type II ARC tactic has been exploited as the key construction tactic in the total syntheses of the spirastrellolides, the cryptocarya acetates, secu’amamine A, mandelalide A and nahuoic acid C(i) (B(ii)). This Account will present the evolution of both the Type I and Type II Anion Relay tactics, in conjunction with some prominent applications. [Image: see text]

Microwave-assisted catalysis offers great promise as an “intensified” technology for chemical processing. The present study investigates microwave-assisted direct conversion of methane with focus on the design and evaluation of microwave-sensitive H-(Fe)ZSM-5 catalysts for the existence of hotspot formation. Isomorphous substituted H-(Fe)ZSM-5 catalysts are tuned to identify key design parameters that control their microwave sensitivity. Increasing the amount of Al and Fe substitution in the zeolite lattice is found to result in higher microwave sensitivity due to improved dielectric properties and hence facilitated microwave heating of the catalyst bed. Comparison between the performance of these catalysts in a conventional thermally-heated (CH) fixed-bed and a microwave (MW) reactor allows identification of the effect of microwave irradiation on the catalyst activity. Methane conversion is drastically enhanced at MW conditions (from 3% at CH conditions to 40% at MW conditions), indicating accelerated methane activation over the metal site and hence suggesting a hot metal site despite much lower catalyst bulk temperature measured in the microwave reactor. The existence of metal hotspot formation is further supported by the reaction product distribution and spent catalyst analysis. At MW conditions, C2 (ethane and ethylene) and coke (mainly carbon nanotubes and nanofibers) selectivity are much higher at the cost of aromatics make compared to CH conditions. This can be explained by reduced aromatization activity at the Bronsted acid sites of the zeolite due to its lower relative temperature of the zeolite. The much-enhanced metal aggregation observed in the spent catalyst from the MW reactor along with the distribution of coke species further confirms the existence of selective heating (i.e. hotspot formation) occurring at the active metal site in the catalyst at MW conditions.

A convergent total synthesis of (−)-nahuoic acid Ci(Bii) (3), a novel cis-decalin polyketide, has been achieved. Key synthetic transformations include Type II Anion Relay Chemistry (ARC) to construct the polyol chain, a Ti-catalyzed asymmetric Diels–Alder reaction to generate the cis-decalin skeleton, and a late-stage large fragment union exploiting a Micalizio alkoxide-directed alkyne–alkene coupling tactic.

Based on 5 requirements which are essential for stable OAM mode transmission, we propose an OAM fiber family based on a structure of circular photonic crystal fiber (C-PCF). The proposed C-PCF in the family is made of pure silica, with a big round air hole at the center, several rings of air-hole array as the cladding, and a ring shaped silica area in between as the core where the OAM modes propagate. We also provide a design strategy with which the optimized C-PCF can be obtained with optimum number of high quality OAM modes (up to 42 OAM modes), large effective index separation for corresponding vector modes over a wide bandwidth, relative small and flat dispersion, and low nonlinear coefficient compared with a conventional single mode fiber. The designed fiber can be used in MDM communications and other OAM applications in fibers.

Three catalyst-dependent divergent reaction pathways for reactions of propargyl aryldiazoacetates are disclosed. Transition metal catalysts including those of rhodium(II), palladium(0 and II), silver(I), mercury(II), copper(I and II), platinum(II), and cationic gold(I) are effective for reactions that proceed through dinitrogen extrusion, carbene/alkyne metathesis, and aromatic substitution to form fused indeno-furanones, and use of tetrakis(acetonitrile)copper(I) provides indeno-furanones in the highest product yields. A Lewis acid catalyzed pathway that forms furan-2-ones is uncovered with FeCl3, ZnBr2, and BF3·Et2O as catalysts that proceed through activation of the aryldiazoacetate ester for arylpropargyl cation dissociation followed by recombination through cation addition to the diazo carbon. Neutral gold catalysts selectively activate the triple bond of propargyl aryldiazoacetates, resulting in the formation of allenic aryldiazoesters that further undergo uncatalyzed rearrangement.

International audience; The hydroxylation of phenols into polyphenols, which are valuable chemicals and pharmaceutical products, is a challenging reaction. The search for green synthetic processes has led to considering microorganisms and pure hydroxylases as catalysts for phenol hydroxylation. Herein, we report the structural and functional characterization of the flavin adenine dinucleotide (FAD)‐dependent 4‐hydroxyphenylacetate 3‐monooxygenase from Escherichia coli, named HpaB. It is shown that this enzyme enjoys a relatively broad substrate specificity, which allows the conversion of a number of non‐natural phenolic compounds, such as tyrosol, hydroxymandelic acid, coumaric acid, hydroxybenzoic acid and its methyl ester, and phenol, into the corresponding catechols. The reaction can be performed by using a simple chemical assay based on formate as the electron donor and the organometallic complex [Rh(bpy)Cp*(H2O)]2+ (Cp*: 1,2,3,4,5‐pentamethylcyclopentadiene, bpy: 2,2′‐bipyridyl) as the catalyst for FAD reduction. The availability of a crystal structure of HpaB in complex with FAD at 1.8 Å resolution opens up the possibility of the rational tuning of the substrate specificity and activity of this interesting class of phenol hydroxylases.

DFT exploration of 1,5- and 1,6-hydrogen atom transfers (HAT), radical addition, and relay to alkene is reported. The reactivity of 1,5- and 1,6-HAT are similar. We also explored reactions involving a multiple radical transferring process. Initially generated radicals undergo a multiple HAT process to form multiple bonds in a “relay” fashion, provided by exquisitely balanced rates.

Visible-light-induced generation of dithianyl and dioxolanyl radicals via selective hydrogen atom transfer (HAT) has been achieved. This radical relay tactic enables remote C(sp(3))—H functionalization to permit rapid access to polyol and spiroketal segments, and in turn has been exploited as a key synthetic construct in the total synthesis of the danshenspiroketallactones. The conformational stability of the danshenspiroketallactones has also been defined via experiments and DFT calculations.

We report herein a transition-metal-free coupling reaction of arylboronic acids with benzyl halides and mesylates for the construction of C(sp2)C(sp3) bonds. A unique feature of this coupling reaction is the formation regioisomers in some cases. Mechanistic studies suggest that this reaction may proceed via an unprecedented Friedel–Crafts-type reaction pathway under base conditions with the assistance of boronic acid moiety.

In this work, the interactive process between separation bubble and impinging leading-edge vortices, which is superimposed in unsteady separated and reattaching flows over a finite blunt plate, was experimentally determined. We used an effective recognition strategy based on an offline data analysis by dynamic mode decomposition (DMD) and online DMD computation in a field-programmable gate array (FPGA). The approach was established for phase-locking particle image velocimetry (PIV) measurements of the underlying vortex dynamics. The DMD mode coefficients of wall-pressure fluctuations following the temporal evolution of the corresponding unsteady events clearly reflected the interactive process, in which three consecutive impinging vortices appeared in one period of the separation bubble. The global interactive process between the separation bubble and the impinging vortices was classified into three consecutive processes: an amplification process, a transition process and a preparation process. The phase-averaged PIV measurements revealed the following: (a) During the amplification process, the separation bubble and impinging vortices are in a synchronous enlargement process beginning from the shortest position of the separation bubble at x / D = 3.00 . (b) In both the transition and preparation processes, the interaction was characterized by a flapping separation bubble (which enlarged in the first half of the period and then shrank in the second half of the period) and by the impinging vortices constantly shedding to the downstream region. Finally, the underlying shear layer instabilities and vortex movements of these three interactive processes were analyzed.

Many models have been created and attempted to describe the temperature-dependent viscosity of glass-forming liquids, which is the foundational feature to lay out the mechanism of obtaining desired glass properties. Most viscosity models were generated along with several impact factors. The complex compositions of commercial glasses raise challenges to settle these parameters. Usually, this issue will lead to unsatisfactory predicted results when fitted to a real viscosity profile. In fact, the introduction of the reliable viscosity-temperature data to viscosity equations is an effective approach to obtain the accurate parameters. In this paper, the Eyring viscosity equation, which is widely adopted for molecular and polymer liquids, was applied in this case to calculate the viscosity of glass materials. On the basis of the linear variation of molar volume with temperature during glass cooling, a modified temperature-dependent Eyring viscosity equation was derived with a distinguished mathematical expression. By means of combining high-temperature viscosity data and the glass transition temperature (Tg), nonlinear regression analysis was employed to obtain the accurate parameters of the equation. In addition, we have demonstrated that the different regression methods exert a great effect on the final prediction results. The viscosity of a series of glasses across a wide temperature range was accurately predicted via the optimal regression method, which was further used to verify the reliability of the modified Eyring equation.

Pointing accuracy and pointing stability play an important role in gravitational wave detection spacecraft. This paper presents dynamics model, pointing accuracy and stability analysis of a payload-spacecraft system connected using umbilical and non-contact actuators. Accurate model of payload-umbilical-spacecraft is proposed which takes into account the translational stiffness and damping effects, as well as the torsional stiffness effect. The Lagrangian approach is applied to derive the rigid-flexible coupling dynamics model. Both of the open-loop and closed-loop simulation studies are conducted to investigate the pointing accuracy and stability of the payload. The results indicate that the umbilical significantly degrades the vibration isolation performance of the payload at low frequencies between 0.01 Hz and 1 Hz. Simulation of two other cases, the payload without umbilical and the payload with umbilical considering only the translational stiffness effect, are also performed. The results of these three cases show that the umbilical greatly degrades the pointing accuracy of the payload and lowers the pointing stability. The torsional stiffness also has a slight effect on the pointing accuracy of the payload.

Oxidative [1,2]-Brook rearrangements via hypervalent silicon intermediates induced by photoredox-catalyzed single-electron transfer have been achieved, permitting the formation of reactive radical species that can engage in alkylations and arylations.

We propose a new orbital angular momentum (OAM) erbium-doped fiber amplifier based on a circular photonic crystal fiber, which can support a total of 18 modes (14 OAM modes) over C-band. A correction factor is proposed to modify the overlap factor, with the aim of evaluating the performance of the amplifier more accurately. We found that the confined doping profile can help optimize the differential model gain (DMG). Numerical simulations suggest that the proposed OAM fiber amplifier can provide a gain larger than 20 dB for all 14 OAM modes, with the small DMG less than 0.2 dB and the noise figure lower than 3.5 dB across the C-band.

α-Halo-N-tosylhydrazones are employed as reagents for the formation of multiple carbon–carbon bonds in the three-component reactions. In this transformation, a strategy has been designed to generate the diazo intermediate by using a nucleophile to react with the azoalkene intermediate generated in situ from the α-halo-N-tosylhydrazone. The diazo intermediate thus generated further undergoes transition-metal-free C–C bond forming reaction with arylboronic acids.

Vortex dynamics and aeroacoustic energy transfer, which play essential roles in vortex-excited acoustic resonance inside straight channels with coaxial side-branches, were investigated by phase-locked particle image velocimetry (PIV) and Howe’s acoustic analogy. In the experiments, the periodic acoustic pressure fluctuations at the endplates of the side branches were used to trigger PIV via a field-programmable gate array control system. The results revealed that the spatiotemporal evolution of vortex shedding can be classified into three regions in response to the acoustic standing-wave propagations: the formation region, the convection region, and the collapse region, along with the flapping recirculation zone and the intermittent vertical flow streaks that occur inside the side branches. Further investigation was performed in terms of phase-dependent quantities such as the shear and normal stresses; the normal stress production, which was attributed to the evolution of vortex shedding, was found to be the major contributor to the kinematics and energetics of the self-sustained flow. Finally, Howe’s acoustic analogy was used to determine the instantaneous acoustic power and the accumulated aeroacoustic energy during one acoustic resonance cycle. The aeroacoustic energy extracted from the acoustic standing-wave propagations contributed to the formation and subsequent growth of the shedding vortex, whereas the decreased turbulent kinetic energy of the shedding vortex was transferred to the acoustic standing waves to maintain the longitudinal wave propagations.

The influence of vortex-excited acoustic resonance on flow dynamics in a straight channel with coaxial side branches was experimentally determined. The energetic vortex structures superimposed in the shear layer, formed at the intersection between the straight channel and the side-branches, are closely coupled with the natural acoustic modes of the side-branches, resulting in significantly intensified acoustic standing waves in the side-branches. Two configurations with symmetric (length-to-diameter ratio: L1/D = L2/D = 10) and asymmetric (L1/D = 10, L2/D = 5) arrangements of the side-branches were used to investigate the clearly different flow dynamics with and without acoustic resonance. In the experiments, wall pressure measurements and acoustic modal analyses were first conducted to determine the frequency lock-on range of the vortex-excited acoustic resonance. Subsequently, the flow fields in two configurations were measured with planar particle image velocimetry. The results indicated that the vortex-excited acoustic resonance resulted in significant flow fluctuations inside the branches together with expanded shear layers and the enlarged vortex structures. Vorticity fluctuations and Reynolds shear stresses were also increased significantly when subjected to acoustic modulation. In terms of the proper orthogonal decomposition analysis, two different motions of the energetic flow structures were identified as interacting with the acoustic resonance: the vertical synchronous oscillation mode and the streamwise vortex-shedding mode. Correspondingly, the phase-averaged low-order flow fields, determined by the mode coefficients of these two correlative modes, clearly indicated the flapping motion of the mainstream and the periodic oscillation of the shear layer.

It is of great significance to design glasses with satisfactory mechanical properties predictively through modeling. Among various modeling methods, data-driven modeling is such a reliable approach that can dramatically shorten research duration, cut research cost and accelerate the development of glass materials. In this work, the ridge regression (RR) analysis was used to construct regression models for predicting the compositional dependence of CaO-Al2O3-SiO2 glass elastic moduli (Shear, Bulk, and Young's moduli) and hardness based on the ternary diagram of the compositions. The property prediction over a large glass composition space was accomplished with known experimental data of various compositions in the literature, and the simulated results are in good agreement with the measured ones. This regression model can serve as a facile and effective tool for studying the relationship between the compositions and the property, enabling high-efficient design of glasses to meet the requirements for specific elasticity and hardness.

The orbital angular momentum (OAM) of light can be another physical dimension that we exploit to make multiplexing in the spatial domain. The design of the OAM mode supporting fiber attracts many attentions in the field of the space division multiplexing (SDM) system. This paper reviews the recent progresses in photonic crystal fiber (PCF) supporting OAM modes, and summarizes why a PCF structure can be used to support stable OAM transmission modes. The emphasis is on the circular PCFs, which possess many excellent features of transmission performance, such as good-quality OAM modes, enough separation of the effective indices, low confinement loss, flat dispersion, a large effective area, and a low nonlinear coefficient. We also compare the transmission properties between the circular PCF and the ring core fiber, as well as the properties between the OAM EDFA based on circular PCF and the OAM EDFA based on the ring core fiber. At last, the challenges and prospects of OAM fibers based on the PCF structure are also discussed.