Hydrogels are investigated broadly in flexible sensors which have been applied into wearable electronics. However, further application of hydrogels is restricted by the ambiguity of the sensing mechanisms, and the multi-functionalization of flexible sensing systems based on hydrogels in terms of cost, difficulty in integration, and device fabrication remains a challenge, obstructing the specific application scenarios. Herein, cost-effective, structure-specialized and scenario-applicable 3D printing of direct ink writing (DIW) technology fabricated two-dimensional (2D) transition metal carbides (MXenes) bonded hydrogel sensor with excellent strain and temperature sensing performance is developed. Gauge factor (GF) of 5.7 (0 − 191% strain) and high temperature sensitivity (−5.27% °C−1) within wide working range (0 − 80 °C) can be achieved. In particular, the corresponding mechanisms are clarified based on finite element analysis and the first use of in situ temperature-dependent Raman technology for hydrogels, and the printed sensor can realize precise temperature indication of shape memory solar array hinge.

Selective amination of σ and π entities such as C–H and CC bonds of substrates remains a challenging endeavor for current catalytic methodologies devoted to the synthesis of abundant nitrogen-containing chemicals. The present work addresses an approach toward discriminating aromatic over aliphatic alkenes in aziridination reactions, relying on the use of anionic metal reagents (M = Mn, Fe, Co, Ni) to attenuate reactivity in a metal-dependent manner. A family of MnII reagents bearing a triphenylamido-amine scaffold and various pendant arms has been synthesized and characterized by various techniques, including cyclic voltammetry. Aziridination of styrene by PhINTs in the presence of each MnII catalyst establishes a trend of increasing yield with increasing MnII/III anodic potential. The FeII, CoII, and NiII congeners of the highest-yielding MnII catalyst have been synthesized and explored in the aziridination of aromatic and aliphatic alkenes, exhibiting good to high yields with para-substituted styrenes, low to modest yields with sterically congested styrenes, and invariably low yields with aliphatic olefins. CoII mediates faster styrene aziridination in comparison to MnII but is less selective than MnII in competitive aziridinations of conjugated versus nonconjugated olefins. Indeed, MnII proved to be highly selective even versus well-established copper and rhodium aziridination reagents. Mechanistic investigations and computational studies indicate that all metals follow a two-step styrene aziridination pathway (successive formation of two N–C bonds), featuring a turnover-limiting metal–nitrene addition to an olefinic carbon, followed by product-determining ring closure. Both steps exhibit activation barriers in the order Fe > Mn > Co, most likely stemming from relevant metal–nitrene electrophilicities and MII/III redox potentials. The aziridination of aliphatic olefins follows the same stepwise path, albeit with a considerably higher activation barrier and a weaker driving force for the formation of the initial N–C bond, succeeded by ring closure with a miniscule barrier.

Accumulating evidence suggests significant biological effects caused by extremely low frequency electromagnetic fields (ELF-EMF). Although exo-endocytosis plays crucial physical and biological roles in neuronal communication, studies on how ELF-EMF regulates this process are scarce. By directly measuring calcium currents and membrane capacitance at a large mammalian central nervous synapse, the calyx of Held, we report for the first time that ELF-EMF critically affects synaptic transmission and plasticity. Exposure to ELF-EMF for 8 to 10 days dramatically increases the calcium influx upon stimulation and facilitates all forms of vesicle endocytosis, including slow and rapid endocytosis, endocytosis overshoot and bulk endocytosis, but does not affect the RRP size and exocytosis. Exposure to ELF-EMF also potentiates PTP, a form of short-term plasticity, increasing its peak amplitude without impacting its time course. We further investigated the underlying mechanisms and found that calcium channel expression, including the P/Q, N, and R subtypes, at the presynaptic nerve terminal was enhanced, accounting for the increased calcium influx upon stimulation. Thus, we conclude that exposure to ELF-EMF facilitates vesicle endocytosis and synaptic plasticity in a calcium-dependent manner by increasing calcium channel expression at the nerve terminal.

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Solution-state dynamic nuclear polarization (DNP) is a powerful tool for hyperpolarization and the study of intermolecular interactions in solution.

Temperature reflects the balance between production and dissipate of heat. Flexible temperature sensors are primary sensors used for temperature monitoring. To obtain real-time and accurate information of temperature, different flexible temperature sensors are developed according to the principle of flexible resistance temperature detector (FRTC), flexible thermocouple, flexible thermistor and flexible thermochromic, showing great potential in energy conversion and storage. In order to obtain high integration and multifunction, various flexible temperature sensors are studied and optimized, including active-matrix flexible temperature sensor, self-powered flexible temperature sensor, self-healing flexible temperature sensor and self-cleaning flexible temperature sensor. This review focuses on the structure, material, fabrication and performance of flexible temperature sensors. Also, some typical applications of flexible temperature sensors are discussed and summarized.

The C-H bond activation of methane using PDI-M≡N [PDI = 2,6-(PhN═CMe)CHN] (M = V, Mn, Fe, Co, Ni, Al, or P) has been studied via three reaction pathways: [2 + 2] addition, hydrogen atom abstraction (HAA), and direct insertion. The activating ligand is a nitride/nitridyl (N), with diiminopyridine (PDI) as the supporting ligand. Calculations show reasonable C-H activation barriers for Co, Ni, Al, and P PDI nitrides, complexes that favor an HAA pathway. ElectrophilicPDI nitride complexes of the earlier metals with a nucleophilic actor ligand-V, Mn, Fe-follow a [2 + 2] addition pathway for methane activation. Free energy barriers for methyl migration, PDI-M(CH)═NH → PDI-M-N(H)CH, are also interesting in the context of alkane functionalization; discriminating factors in this mechanistic step include the strengths of the σ-bond and metal-actor ligand π-bond that are broken and the electrophilicity of the actor ligand to which methyl migrates.

Although vesicle replenishment is critical in maintaining exo-endocytosis recycling, the underlying mechanisms are not well understood. Previous studies have shown that both rapid and slow endocytosis recycle into a very large recycling pool instead of within the readily releasable pool (RRP), and the time course of RRP replenishment is slowed down by more intense stimulation. This finding contradicts the calcium/calmodulin-dependence of RRP replenishment. Here we address this issue and report a three-pool model for RRP replenishment at a central synapse. Both rapid and slow endocytosis provide vesicles to a large reserve pool (RP) ~42.3 times the RRP size. When moving from the RP to the RRP, vesicles entered an intermediate pool (IP) ~2.7 times the RRP size with slow RP-IP kinetics and fast IP-RRP kinetics, which was responsible for the well-established slow and rapid components of RRP replenishment. Depletion of the IP caused the slower RRP replenishment observed after intense stimulation. These results establish, for the first time, a realistic cycling model with all parameters measured, revealing the contribution of each cycling step in synaptic transmission. The results call for modification of the current view of the vesicle recycling steps and their roles.