Polyol‐substituted cyclic ethers are fundamental building blocks of biomolecules. The position and stereochemistry of multiple hydroxy substituents of cyclic ethers play a central role in their ...biological function. Current methods for the synthesis of such structures are limited to “naked” ring products with no or few substituents. Here we describe a general route to medium‐sized polyol cyclic ethers using a migratory ether formation strategy. In contrast to the common pathway of direct opening of epoxides, Me3Al was found to promote an unprecedented ether addition reaction, opening a neighboring epoxide. The resulting oxonium intermediate triggers a 1,3‐methyl shift to yield 2‐deoxyribital products. When the hemiacetal auxiliary is a monosaccharide, the sugar ring is expanded by four atoms to give the corresponding 9‐ to 11‐membered analogues. This method provides an entry into the untapped chemical space of medium‐sized sugar mimetics.
Biomolecular building blocks: In a general route to medium‐sized polyol cyclic ethers, Me3Al promotes an unprecedented intramolecular epoxide‐opening by an ether addition reaction. The resulting oxonium intermediate triggers a 1,3‐methyl shift to yield 2‐deoxyribital products. When the hemiacetal auxiliary is a monosaccharide, the sugar ring is expanded by four atoms to give the 9‐ to 11‐membered analogues.
The detailed mechanism of the Pd-catalyzed annulative chlorophenylene dimerization (ACD) has been elucidated and the roles of the base have been identified. It is shown that the initial steps of this ...reactionthe active catalyst formation and the C–Cl bond activationproceed via the “base-assisted oxidative addition” mechanism and require only a 16.2 kcal/mol barrier. The following steps of the reaction are palladacycle and Pd–aryne formations, among which the former is favorable: it proceeds with a moderate C–H activation barrier and is slightly exergonic. Although the Pd–aryne formation requires a slightly lower energy barrier, it is highly endergonic. It is shown that the base plays important roles also in the palladacycle formation and facilitates the driving of the reaction forward by removing a proton to the solution via the bicarbonate-to-carbonate exchange mechanism. Addition of the second C–Cl bond to the thermodynamically favorable palladacycle, i.e., Pd(II)/Pd(IV) oxidation, is a rate-limiting step of the entire Pd-catalyzed and Cs-carbonate-mediated ACD reactions: it occurs with a 35.8 kcal/mol energy barrier and is exergonic by 25.1 kcal/mol. The following polycyclic aromatic hydrocarbon (PAH) formation is a multistep process and requires a lesser energy barrier. An alternative pathway, namely, cyclooctatetraene (COT) formation, requires a higher energy barrier and is not feasible. This finding is consistent with experiments that show no COT product in the utilized conditions. The calculations also indicate that the observed diminishing of the yield of the Pd-catalyzed ACD reaction upon the use of Na2CO3 instead of Cs2CO3 is the result of not only the poor solubility of Na-carbonate in the used experimental conditions but also a prohibitively large free-energy barrier required for the second C–Cl activation.
Bioinspired superwettable micropatterns that combine superhydrophobicity and superhydrophilicity have been proved to exhibit outstanding capacity in controlling and patterning microdroplets and ...possessed new functionalities and possibilities in emerging sensing applications. Here, we introduce a flexible tape-based superhydrophilic–superhydrophobic tape toward on-site heavy metals monitoring. On such a superwettable tape, capillarity-assisted superhydrophilic microwells allow directly anchoring indicators in fixed locations and sampling into a test zone via simple dip-pull from an origin specimen solution. In contrast, the superhydrophobic substrate could confine the microdroplets in the superhydrophilic microwells for reducing the amount of analytical solution. The tape-based microchip also displays excellent flexibility against stretching, bending, and torquing for expanding wearable and portable sensing devices. Qualitative and quantitative colorimetric assessments of multiplex heavy metal analyses (chromium, copper, and nickel) by the naked eye are also achieved. The superwettable tape-based platforms with a facile operation mode and accessible signal read-out represent unrevealed potential for on-site environmental monitoring.
One-dimensional Pt nanostructures are of considerable interest for the development of highly stable and sensitive electrochemical sensors. This paper describes a self-interconnecting Pt nanowire ...network electrode (PtNNE) for the detection of hydrogen peroxide (H2O2) and glucose with ultrahigh sensitivity and stability. The as-prepared PtNNE consists of polycrystalline nanowires with high-index facets along the side surface which provides more active surface atoms on kinks and steps, those ultralong nanowires being interconnected with each other to form a free-standing network membrane. The excellent structural features of the PtNNE promoted its performance as a Pt-based electrochemical sensor both in terms of electrocatalytic activity and stability. Amperometric measurements towards hydrogen peroxide were performed; the PtNNE sensor showed an extremely high sensitivity of 1360 μA mM(-1) cm(-2). This excellent sensitivity is mainly attributed to the high-index facets of the nanowires resulting in their superior electrocatalytic activity towards H2O2, and the interconnected nanowire network forming an "electron freeway" transport model, which could provide multiple electron pathways and fast electron transport on the electrode, leading to rapid reaction and sensitive signal detection. The as-prepared PtNNE also holds promise as an oxidase-based biosensor. As a proof of concept, a PtNNE-based glucose biosensor also showed an outstanding sensitivity as high as 114 μA mM(-1) cm(-2), a low detection limit of 1.5 μM, and an impressive detection range from 5 μM to 30 mM.
The basement of the North China craton (NCC) can be divided into eastern and western blocks separating the Trans-North China orogen on the basis of petrologic associations, structures, metamorphic ...processes, and isotopic ages. Aluminous gneiss khondalites occur in the western block, and record a clockwise metamorphic P-T history characterized by nearly isothermal decompression following peak metamorphism at ca. 1.3 GPa and 825°C. Four metamorphic stages are recognized based on mineral assemblages. The early prograde metamorphic assemblage contains Ky+Bt+Ms+Grt+Pl+Qtz. The peak metamorphic mineral assemblage is characterized by Grt+Sil+Bt+Kfs+Pl+Qtz and the formation of cordierite after garnet, leading to a retrograde assemblage of Grt+Sil+Crd+Pl+Kfs+Qtz. Garnet retrogrades to biotite and the formation of pervasive matrix muscovite define a final metamorphic stage, inferred at ca. < 0.6 GPa and 700°C. Quantified metamorphic stages and a related clockwise P-T path derived from pseudosection analysis in the KMASH system suggest collision of the north Yinshan block with the South Ordos block at 1.92 Ga, before final suturing of the entire NCC basement.
The clinopyroxene amphibolite from the Bailang terrane is located in the central section of the Yarlung Zangbo suture zone (YZSZ), southern Tibet. The study of it is expected to provide important ...clues for the subduction of the Neo-Tethyan Ocean below the Asian Plate and thus for better understanding of the development of the India-Asia collision zone. Based on integrated textural, mineral compositional, metamorphic reaction history and geothermobarometric studies of the clinopyroxene amphibolite within a serpentinite mélange, four overprinted metamorphic stages are established. They are the first metamorphic record of M1 stage indicated by a relict assemblage of plagioclase+clinopyroxene+amphibole, an early M2 stage characterized by an assemblage of medium-grained clinopyroxene+amphibole+plagioclase+quartz as well as rutile inclusion in titanite, which is formed during burial process, an isobaric cooling M3 stage which is characterized by an assemblage of clinopyroxene+amphibole+plagioclase+titanite, and a decomposing retrograde stage M4, which is represented by the amphibolite+plagioclase symplectite+titanite+ rutile+quartz. By applying the THERMOCALC (versions 6.2 and 6.3) technique in the NCFMASHTO system, the
P-T
conditions estimated from M1 to M4 stages are ca. 8.6 kbar/880 °C, 10.8-13.4 kbar/800-840 °C, 12.7-13.2 kbar/650-660 °C and <11.2 kbar/640 °C, respectively. The mineral assemblages and their
P-T
conditions define a counterclockwise
P-T
path for the clinopyroxene amphibolite of the Xigaze ophiolite, suggesting that the rocks underwent a cooling process during burial from magmatic protolith, and a decompressing stage after the pressure peak metamorphic conditions, which implies that the Bailang terrane of the Xigaze ophiolite may have experienced subduction/collision-related tectonic processes. The peak metamorphism reaches to the transitional
P-T
conditions among amphibolite facies, granulite facies and eclogite facies with a burial depth of 30–40 km. After exhumation of the ophiolitic unit to the shallow crustal levels, the clinopyroxene amphibolite exposes to a high
f
O2
condition on the basis of the stable epidotebearing assemblage in the
T
-MO
2
diagrams. A late subgreenschist facies overprinting subsequently occurs, the relevant mineral assemblage is prehnite+albite+chlorite+epidote+quartz.
A pH‐responsive free‐blockage release system was achieved through controlling the hydrophobic/hydrophilic conversion of mesoporous silica nanopores. This system further presented pulsatile release ...with changing pH values between 4.0 and 7.0 for several cycles. This free‐blockage release system could also release antitumor agents to induce cell death after infecting tumor cells and could have the ability of continuous infection to tumor cells with high drug‐delivery efficiency and few side effects.
An open and shut case: A pH‐responsive free‐blockage release system was achieved through controlling the hydrophobic/hydrophilic conversion of mesoporous silica nanopores (see figure). This system could have the ability of continuous infection to tumor cells with high drug‐delivery efficiency and few side effects.
The aggregation of Aβ peptides is a crucial factor leading to Alzheimer's disease (AD). Inhibiting the Aβ peptide aggregation has become one of the most essential strategies to treat AD. In this ...work, efficient and low-cytotoxicity inhibitors, graphene quantum dots (GQDs) are reported for their application in inhibiting the aggregation of Aβ peptides. Compared to other carbon materials, the low cytotoxicity and great biocompatibility of GQDs give an advantage to the clinical research for AD. In addition, the GQDs may cross the blood-brain barrier (BBB) because of the small size. It is believed that GQDs may be therapeutic agents against AD. This work provides a novel insight into the development of Alzheimer's drugs.
Paleoproterozoic banded iron formation (BIF) iron ore of the Zhengjiapo region of the Changyi metallogenic belt, Eastern Block of North China Craton contains abundant coexisting antiperthite and ...mesoperthite textures. The antiperthite and mesoperthite occur in felsic domains of the Zhengjiapo BIF ore and enable derivation of peak temperature metamorphic conditions. Thermodynamic phase modeling shows that equilibrium conditions of corresponding textures, considering the related mineral assemblage of Pl + Qz + Kfs + Mag + Opx + L, are in the range of 870–940 °C and 5.0–6.8 kbar. Ternary feldspar thermometry using reintegrated compositions of antiperthite and mesoperthite in the felsic domain of the studied BIF iron ore reveals even higher peak metamorphic temperatures of 1045–1080 °C. The ultra-high temperature–low pressure conditions of Precambrian BIF have not yet been reported from the North China Craton. The documented ultra-high temperature metamorphism of the Zhengjiapo BIF iron ore in the Changyi metallogenic belt indicates that the BIF was involved in the collision-related tectonic process during Paleoproterozoic to have occurred in the Jiao-Liao-Ji orogenic belt.
Pelitic granulite from the Huangtuyao area, occurrs in the Huai’an Complex, is located in the Trans-North China Orogen of the North China Craton. On the basis of petrolography, mineral component, and ...phase equilibrium modeling studies, the
P
-
T
conditions and mineral assemblages of pelitic granulites can be divided into four metamorphic stages: the prograde metamorphic stage M1 defined by the stable mineral assemblage of Grt
1
(garnet core)+Pl+Bt+Kfs+Qz+Rt, the peak pressure
P
max
stage M2 indicated by Grt
2
(garnet mantle)+Kfs±(Ky)+Rt+Qz+Liq (melt), peak temperature
T
max
stage M3 characterized by Grt
3
(garnet rim)+Sill+Pl+Kfs+Qz+Ilm+Liq, and retrograde stage M4 represented by Grt (in matrix)+Kfs+Sill+Bt+Pl+Qz+Ilm. By using the THERMOCALC V340, the
P
-
T
conditions are estimated at ~13.8−14.1 kbar and ~840−850 °C at stage M2, and 7–7.2 kbar and 909–915 °C for the
T
max
stage M3, indicating an ultra-high temperature (UHT) metamorphic overprinting during decompression and heating process after high pressure granulite facies metamorphism. The mineral assemblages and their
P
-
T
conditions presented a clockwise
P
-
T
trajectory for the Huangtuyao pelitic granulites. The major metamorphic events at ~1.95 and ~1.88 Ga obtained by the zircon U-Pb dating suggest that pelitic granulites from the Huangtuyao area has undergone HP granulite metamorphism which probably occurred in the prograde metamorphism and related to the collision between the Ordos and the Yinshan blocks, and afterwards UHT metamorphism is related to crustal extension after continental-continental collision.
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