Positive cooperative binding, a phenomenon prevalent in biological processes, holds great appeal for the design of highly sensitive responsive molecules and materials. It has been demonstrated that ...metal–organic frameworks (MOFs) can show positive cooperative adsorption to the benefit of gas separation, but potential binding cooperativity is largely ignored in the study of sensory MOFs. Here, we report the first demonstration of positive cooperative protonation of a MOF and the relevant pH response in fluorescence and proton conduction. The MOF is built of Zr–O clusters and bipyridyl-based tetracarboxylate linkers and has excellent hydrolytic stability. It shows a unique pH response that features two synchronous abrupt turn-off and turn-on fluorescent transitions. The abrupt transitions, which afford high sensitivity to small pH fluctuations, are due to cooperative protonation of the pyridyl sites with a Hill coefficient of 1.6. The synchronous dual-emission response, which leads to visual color change, is ascribable to proton-triggered switching between (n, π*) and (π, π*) emissions. The latter emission can be quenched by electron donating anion-dependent through photoinduced electron transfer and ground-state charge transfer. Associated with cooperative protonation, the proton conductivity of the MOF is abruptly enhanced at low pH by two orders, but overhigh acid concentration is adverse because excessive anions can interrupt the conducting networks. Our work shows new perspectives of binding cooperativity in MOFs and should shed new light on the development of responsive fluorescent MOFs and proton conductive materials.
The automatic dependent surveillance-broadcast (ADS-B) system adopts an open communication mode, and the lack of designed-in security measures in the ADS-B system makes it vulnerable to various types ...of attacks (jamming, spoofing, etc.). In view of the low-bandwidth and less-data-bit features of the ADS-B, this paper studies the integrity and authenticity of information by signing messages and proposes an ADS-B message authentication method based on certificateless short signature. This method uses short signature and does not require certificate management and has efficient performance. Compared with the existing approach, the computation costs of the proposed method in the signature phase are reduced by 1/2, and the signature length is reduced by 3/4. Additionally, we used the extended NS2 simulation platform to simulate 1090ES data link in different scenarios of the network; the simulation results show that our solution is suitable for minimum operational performance standard of ADS-B.
We report the first dark matter search results using the commissioning data from PandaX-4T. Using a time projection chamber with 3.7 tonne of liquid xenon target and an exposure of 0.63 tonne·year, ...1058 candidate events are identified within an approximate nuclear recoil energy window between 5 and 100 keV. No significant excess over background is observed. Our data set a stringent limit to the dark matter-nucleon spin-independent interactions, with a lowest excluded cross section (90% C.L.) of 3.8×10^{-47} cm^{2} at a dark matter mass of 40 GeV/c^{2}.
Bulk chemical 2‐methyl‐2‐butene, one of the main C5 distillates of the petrochemical industry, has scarcely been utilized directly in synthesizing high‐value‐added fine chemicals. Herein, we use ...2‐methyl‐2‐butene as the starting material to develop a palladium‐catalyzed highly site‐ and regio‐selective C‐3 dehydrogenation reverse prenylation of indoles. This synthetic method features mild reaction conditions, a broad substrate scope, atom‐ and step‐economies.
An efficient C‐3 regioselective dehydrogenation reverse prenylation of indoles has been developed by use of 2‐methyl‐2‐butene as the prenylation reagent. The protocol is of atom‐ and step‐economies.
•Cl isotope composition is powerful in identifying input of magmatic fluids directly.•Rehai hot springs with the lowest δ37Cl values indicated a magmatic fluid input.•Acidic Rehai hot springs ...enriched in 37Cl had little to do with magmatic fluids.•δ37Cl values of some Rehai hot springs were severely altered by reservoir processes.•Hydrochemistry was used subsidiarily for evaluating the effects of magmatic fluids.
Identification of hydrothermal systems affected by magmatic fluid input is relevant for geothermal energy development. Thus, an approach for identifying such systems based on chlorine isotope composition and auxiliary hydrochemical indices was proposed. The approach enabled us to distinguish Rehai, a magmatic hydrothermal area in the Tengchong volcanic region of China, from several other typical non-magmatic hydrothermal areas in Tengchong: Menglian, Shiqiang, and Jietou. The hot springs in the non-Rehai areas featured high δ37Cl values, reflecting an exclusive contribution of chlorine from hostrock leaching. By contrast, some hot springs with much lower δ37Cl values occurred in Rehai, all of which were nearly fully equilibrated waters with respect to reservoir hostrocks, rich in chloride and bromide. These springs should have the closest relationship with the fluids released from the underlying magma chamber. Notably, the potential reservoir processes that geothermal waters may undergo after receiving an input of magmatic fluids can further alter their chlorine isotope compositions to various degrees. Therefore, a deep understanding of these processes would help improve the use of the proposed approach based primarily on chlorine isotopes. Regarding Rehai, all the neutral to alkaline hot springs with δ37Cl values ranging from −0.44 ‰ to 0.31 ‰ evolved from a parent geothermal fluid that received an input of magmatic fluids—via adiabatic cooling, conductive cooling, mixing with low-temperature shallow groundwaters, or a combination of some of these processes. By contrast, the acidic Rehai hot springs with the highest δ37Cl values (up to 1.12 ‰) were essentially locally perched groundwaters heated by geothermal steam separated from underlying geothermal fluids upon their adiabatic cooling; thus, they were much less to do with the parent geothermal fluid than the neutral to alkaline springs were. Hence, only the neutral to alkaline Rehai hot springs not strongly affected by the mixing of shallow groundwaters and adiabatic cooling can reflect the chlorine isotope characteristics of intrusive magmatic fluids. Overall, chlorine isotope composition in combination with hydrochemistry has proven to be a robust tool for identifying a magmatic fluid-affected hydrothermal system.
We describe an efficient method for α‐functionalization of N‐aryl‐tetrahydroisoquinolines under visible‐light‐irradiation catalyzed by organic photocatalyst. This protocol provides a concise and ...environmental approach for the rapid allylation and benzylation of N‐aryl‐tetrahydroisoquinolines, and shows broad substrate scope. Stable organoboron reagents have shown their ability in the construction of challenging Csp3−Csp3 bond. The load of the photocatalyst is low and the oxidant is inexpensive and less toxic.
This work disclosed a concise and environmental approach for the rapid alkylation of N‐aryl‐tetrahydroisoquinolines, providing a new route to versatile intermediates of tetrahydroisoquinoline derivatives. Stable organoboron reagents have shown their ability in the photoinduced aerobic cross‐coupling reactions, allowing the construction of challenging Csp3−Csp3 bond.
A new class of electrophilic monofluoromethylselenolation reagents, Se‐(fluoromethyl) benzenesulfonoselenoates, has been developed. They can be readily prepared from sodium benzenesulfinates, Se ...powder and ClCFH2 in one step under mild reaction conditions. Se‐(fluoromethyl) benzenesulfonoselenoates are efficient electrophilic monofluoromethylselenolation reagents for a wide range of nucleophiles including indole, 6‐azaindole, pyrrole, thiophene, electron‐rich arene, aryl boronic acid and alkyne. The monofluoromethylselenolation approach features mild and environmentally friendly reaction conditions, good tolerance of various functional groups, and broad substrate scope.
A new class of electrophilic monofluoromethylselenolation reagents, Se‐(fluoromethyl) benzenesulfonoselenoates 2, has been developed, which can be facilely prepared in one step and enable the monofluoromethylselenolation for a wide range of nucleophiles including indole, 6‐azaindole, pyrrole, thiophene, electron‐rich arene, aryl boronic acid and alkyne under mild reaction conditions.
The assembly of two tripyridinium‐tricarboxylate ligands and different metal ions leads to seven isostructural MOFs, which show novel 2D→2D supramolecular entanglement featuring catenane‐like ...interlocking of tricyclic cages. The MOFs show tripyridinium‐afforded and metal‐modulated photoresponsive properties. The MOFs with d10 metal centers (1‐Cd, 1‐Zn, 2‐Cd, 2‐Zn) show fast and reversible photochromism and concomitant fluorescence quenching, 1‐Ni displays slower photochromism but does not fluoresce, and 1‐Co and 2‐Co are neither photochromic nor fluorescent. It is shown here that the network entanglement dictates donor‐acceptor close contacts, which enable fluorescence originated from interligand charge transfer. The contacts also allow photoinduced electron transfer, which underlies photochromism and concomitant fluorescence response. The metal dependence in fluorescence and photochromism can be related to energy transfer through metal‐centered d‐d transitions. In addition, 1‐Cd is demonstrated to be a potential fluorescence sensor for sensitive and selective detection of UO22+ in water.
Organo‐originated and metal‐modulated photoresponsive properties were elucidated for a family of isostructural MOFs with tripyridinium‐tricarboxylate likers. Supramolecular entanglement between 2D networks dictates electron donor‐acceptor close contacts, which not only allow photoluminescence through interligand charge‐transfer excitation/emission but also cause photochromism through photoinduced electron transfer. Transition metal centers can weaken or prevent the photoresponsive properties because of energy transfer through d‐d transitions. The MOFs also show highly sensitive and selective fluorescence quenching response to UO22+ in water.
A two-dimensional Cd(ii) metal-organic framework (MOF) was constructed from a tris(pyridinium)-based hexacarboxylate zwitterionic ligand. The MOF shows a novel fashion of 2-fold 2D → 2D parallel ...entanglement. It is the entanglement that dictates close interlayer contacts between carboxylate (electron donor) and pyridinium (acceptor), which in turn impart the MOF with reversible photochromic properties through photoinduced electron transfer (PET). This is an extension of PET-based photochromism from bipyridinium to multipyridinium compounds. Thanks to the photoresponsive behaviour, the fluorescence of the MOF can be reversibly modulated or switched by photoirradiation. Besides, the fluorescence of the water-stable MOF in aqueous dispersion is very sensitive to nitrofuran antibiotics with high selectivity, and therefore the MOF is a good candidate of efficient and regenerable sensing material for determination of the antibiotics in water media.
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