Isospin Pomeranchuk effect in twisted bilayer graphene.

In condensed-matter systems, higher temperatures typically disfavour ordered phases, leading to an upper critical temperature for magnetism, superconductivity and other phenomena. An exception is the Pomeranchuk effect in 3He, in which the liquid ground state freezes upon increasing the temperature1, owing to the large entropy of the paramagnetic solid phase. Here we show that a similar mechanism describes the finite-temperature dynamics of spin and valley isospins in magic-angle twisted bilayer graphene2. Notably, a resistivity peak appears at high temperatures near a superlattice filling factor of -1, despite no signs of a commensurate correlated phase appearing in the low-temperature limit. Tilted-field magnetotransport and thermodynamic measurements of the in-plane magnetic moment show that the resistivity peak is connected to a finite-field magnetic phase transition3 at which the system develops finite isospin polarization. These data are suggestive of a Pomeranchuk-type mechanism, in which the entropy of disordered isospin moments in the ferromagnetic phase stabilizes the phase relative to an isospin-unpolarized Fermi liquid phase at higher temperatures. We find the entropy, in units of Boltzmann's constant, to be of the order of unity per unit cell area, with a measurable fraction that is suppressed by an in-plane magnetic field consistent with a contribution from disordered spins. In contrast to 3He, however, no discontinuities are observed in the thermodynamic quantities across this transition. Our findings imply a small isospin stiffness4,5, with implications for the nature of finite-temperature electron transport6-8, as well as for the mechanisms underlying isospin ordering and superconductivity9,10 in twisted bilayer graphene and related systems.

Rational Design of a Highly Sensitive Carboxylesterase Probe and Its Application in High-Throughput Screening for Uncovering Carboxylesterase Inhibitors.

Tracking carboxylesterases (CESs) through noninvasive and dynamic imaging is of great significance for diagnosing and treating CES-related metabolic diseases. Herein, three BODIPY-based fluorescent probes with a pyridine unit quaternarized via an acetoxybenzyl group were designed and synthesized to detect CESs based on the photoinduced electron transfer process. Notably, among these probes, BDPN2-CES exhibited a remarkable 182-fold fluorescence enhancement for CESs within 10 min. Moreover, BDPN2-CES successfully enabled real-time imaging of endogenous CES variations in living cells. Using BDPN2-CES, a visual high-throughput screening method for CES inhibitors was established, culminating in the discovery of an efficient inhibitor, WZU-13, sourced from a chemical library. These findings suggest that BDPN2-CES could provide a new avenue for diagnosing CES-related diseases, and WZU-13 emerges as a promising therapeutic candidate for CES-overexpression pathological processes.

Metal Effect on the Proton Conduction of Three Isostructural Metal-Organic Frameworks and Pseudo-Capacitance Behavior of the Cobalt Analogue.

Three isostructural transition metal-organic frameworks, [M(bta)0.5(bpt)(H2O)2]·2H2O (M = Co (1), Ni (2), Zn (3), H4bta = 1,2,4,5-benzenetetracarboxylic acid, bpt = 4-amino-3,5-bis(4-pyridyl)-1,2,4-triazole), were successfully constructed using different metal cations. These frameworks exhibit a three-dimensional network structure with multiple coordinated and lattice water molecules within the framework, contributing to high stability and a rich hydrogen-bond network. Proton conduction studies revealed that, at 333 K and 98% relative humidity, the proton conductivities (σ) of MOFs 1-3 reached 1.42 × 10-2, 1.02 × 10-2, and 6.82 × 10-3 S cm-1, respectively. Compared to the proton conductivity of the initial ligands, the σ values of the complexes increased by 2 orders of magnitude, with the activation energies decreasing from 0.36 to 0.18 eV for 1, 0.09 eV for 2, and 0.12 eV for 3. An in-depth analysis of the correlation between different metal centers and proton conduction performance indicated that the varying coordination abilities of the metal cations and the water absorption capacities of the frameworks might account for the differences in conductivity. Additionally, the potential of 1 as a supercapacitor electrode material was assessed. 1 exhibited a specific capacitance of 61.13 F g-1 at a current density of 0.5 A g-1, with a capacitance retention of 82.4% after 5000 cycles, making it a promising candidate for energy storage applications.

Synthesis of 1-Aminoisoquinolines and Their Application in a Host-Guest Doped Strategy To Construct Ultralong Room-Temperature Phosphorescence Materials for Bioimaging.

Organic ultralong room-temperature phosphorescence (RTP) materials have attracted great attention for their wide applications in optoelectronic devices and bioimaging. However, the development of these materials remains a challenging task, partially due to the lack of rational molecular design strategies and unclear luminescence mechanisms. Herein, we present a method for facile access to structurally diverse substituted 1-aminoisoquinoline derivatives through a copper-catalyzed one-pot three-component coupling reaction that provides a promising approach to rapidly assemble a library of 1-aminoisoquinolines for exploring the regularity of the host-guest doped system. A series of host-guest RTP materials with wide-ranging lifetimes from 4.4 to 299.3 ms were constructed by doping various substituted isoquinolines derivatives into benzophenone (BP). Furthermore, 4 r/BP nanoparticles could be used for in-vivo imaging with a signal-to-noise ratio value as high as 32, revealing the potential of the isoquinoline framework for the construction of high-performance RTP materials.

Two Stable Bifunctional Zinc Metal-Organic Frameworks with Luminescence Detection of Antibiotics and Proton Conduction.

Functionalized crystalline solids based on metal-organic frameworks (MOFs) enable efficient luminescence detection and high proton conductivity, making them crucial in the realms of environmental monitoring and clean energy. Here, two structurally and functionally distinct zinc-based MOFs, [Zn(TTDPa)(bodca)]·H2O (1) and [Zn(TTDPb)(bodca)]·H2O (2), were successfully designed and synthesized using 3,6-di(pyridin-4-yl)thieno[3,2-b]thiophene (TTDPa) and 2,5-di(pyridin-4-yl)thieno[3,2-b]thiophene (TTDPb) as ligands, in the presence of bicyclo[2.2.2]octane-1,4-dicarboxylic acid (H2bodca). Both 1 and 2 display a three-dimensional (3D) structure with 5-fold interpenetration, and notably, 2 forms a larger one-dimensional pore measuring 17.16 × 10.81 Å2 in size. Fluorescence experiments demonstrate that 1 and 2 can function as luminescent sensors for nitrofurantoin (NFT) and nitrofurazone (NFZ) with low detection limits, remarkable selectivity, and good recyclability. A comprehensive analysis was conducted to investigate the differing sensing effects of compounds 1 and 2 and to explore potential sensing mechanisms. Additionally, at 328 K and 98% relative humidity, 1 and 2 exhibit proton conductivity values of 2.13 × 10-3 and 4.91 × 10-3 S cm-1, respectively, making them suitable proton-conducting materials. Hence, the integration of luminescent sensing and proton conductivity in monophasic 3D Zn-MOFs holds significant potential for application in intelligent multitasking devices.

Rational Design of a Near-Infrared Ratiometric Probe with a Large Stokes Shift: Visualization of Polarity Abnormalities in Non-Alcoholic Fatty Liver Model Mice.

Tracking liver polarity with noninvasive and dynamic imaging techniques is helpful to better understand the non-alcoholic fatty liver (NAFL). Herein, a novel near-infrared (NIR) fluorescent probe Cy-Mp is constructed using a "symmetry collapse" strategy. The structure modification leads to the conversion of locally excited state fluorescence to charge transfer state fluorescence. Cy-Mp emits at near-infrared (NIR) wavelengths with high photostability as well as a large Stokes shift. Cy-Mp exhibits a ratiometric response to polarity, providing more accurate analysis of intracellular polarity via the built-in internal reference correction. Most importantly, the in vivo studies indicate that Cy-Mp can accumulate in the liver and the decreased polarity in the liver of mice with NAFL is verified by the ratiometric imaging, implying the great potential of Cy-Mp in the diagnosis of NAFL.

Dysprosium(III) Metal-Organic Framework Demonstrating Ratiometric Luminescent Detection of pH, Magnetism, and Proton Conduction.

A multifunctional metal-organic framework, (Hdmbpy)[Dy(H2dobdc)2(H2O)]·3H2O (Dy-MOF, H4dobdc = 2,5-dihydroxyterephthalic acid, dmbpy = 4,4'-dimethyl-2,2'-bipyridine), was synthesized and structurally characterized. The metal center DyIII is connected by four carboxyl groups to form the [Dy2(CO2)4] binuclear nodes, which are further interconnected by eight separate H2dobdc2- ligands to form a three-dimensional (3D) framework including hydrophilic triangular channels and abundant hydrogen-bonding networks. Dy-MOF has good stability in aqueous solution as well as in harsh acidic or alkaline solutions (pH range: 2.0-12.0). Furthermore, the luminescence signal of Dy-MOF undergoes a visualized color change as the acidity of the solution alters, which is the typical behavior of pH ratiometric probe. At a 100% relative humidity, Dy-MOF exhibits a high proton conductivity σ (1.70 × 10-4 S cm-1 at 303 K; 1.20 × 10-3 S cm-1 at 343 K) based on the proton hopping mechanism, which can be classified as a superionic conductor with σ exceeding 10-4 S cm-1. Additionally, the ferromagnetic interaction and magnetic relaxation behavior are simultaneously achieved in Dy-MOF. Herein, the combination of luminescence sensing, magnetism, and proton conduction in a single-phase 3D MOF may offer great potential applications in smart multitasking devices.

Rare-Earth Metal Tetrathiafulvalene Carboxylate Frameworks as Redox-Switchable Single-Molecule Magnets.

Using the redox-active tetrathiafulvalene tetrabenzoate (TTFTB4- ) as the linker, a series of stable and porous rare-earth metal-organic frameworks (RE-MOFs), [RE9 (µ3 -OH)13 (µ3 -O)(H2 O)9 (TTFTB)3 ] (1-RE, where RE=Y, Sm, Gd, Tb, Dy, Ho, and Er) were constructed. The RE9 (µ3 -OH)13 (µ3 -O) (H2 O)9 ](CO2 )12 clusters within 1-RE act as segregated single-molecule magnets (SMMs) displaying slow relaxation. Interestingly, upon oxidation by I2 , the S=0 TTFTB4- linkers of 1-RE were converted into S= 1 / 2 TTFTB.3- radical linkers which introduced exchange-coupling between SMMs and modulated the relaxation. Furthermore, the SMM property can be restored by reduction in N,N-dimethylformamide. These results highlight the advantage of MOFs in the construction of redox-switchable SMMs.

ZnO nanoparticles: recent advances in ecotoxicity and risk assessment.

The widespread application of zinc oxide nanoparticles (nano-ZnO) has received increasing attention because of their potential risks to human health and the environment. This review summarizes the relationship between the toxic effects and physicochemical properties of nano-ZnO and the underlying toxicity mechanisms of nano-ZnO. This study presents the possible human health hazards posed by nano-ZnO exposure and the biotoxicity to bacteria, algae, higher plants, aquatic animals, terrestrial invertebrates and vertebrates in vitro and in vivo. The advances in research on the ecotoxicity of nano-ZnO and the potential risks to human health are discussed. Finally, the current research deficiencies in this area are identified, and recommendations for future research are proposed.

Modulating Magnetic Property of Phthalocyanine Supported MII-DyIII (M = Ni, Zn) Heterodinuclear Complexes.

Three heterometallic dinuclear compounds, [MIIDyIII(L)(Pc)(ROH)]·ROH (R = CH3, M = Ni (1), Zn (2); R = C2H5, M = Zn (3)), were stepwise synthesized based on phthalocyanine (H2Pc) and one tripodal Schiff-base ligand 1,1,1-tris[(salicylideneamino)methyl]ethane (H3L). All of them have been studied structurally and magnetically. The six-coordinate MII ion and the seven-coordinate DyIII ion are bridged by two phenolic oxygen atoms to form an MII-LnIII heterodinuclear unit. Magnetic measurements indicate that the ferromagnetic NiII-DyIII interaction is operative in compound 1 and all three compounds exhibit the field-induced slow relaxation of magnetizations. In particular, compounds 2 and 3 have the improved magnetic performance. Ab initio calculations indicate that the weak NiII-DyIII interaction decreases the energy barrier, while the replacement of the paramagnetic NiII ion by the diamagnetic ZnII in compound 2 and 3 not only controls the magnetic interaction but also alters the local magnetic axes of DyIII ions to optimize the magnetic relaxation behavior.

A Two-Dimensional Iron(II) Coordination Polymer with Synergetic Spin-Crossover and Luminescent Properties.

A composite material, {[Fe(L)(TPPE)0.5 ]⋅3 CH3 OH}n , has been constructed by integrating the spin-crossover (SCO) subunit FeII {diethyl(E,E)-2,2'-[1,2-phenyl-bis(iminomethylidyne)]bis(3-oxobutanoate)-(2-)-N,N',O3 ,O3 '} and the highly luminescent connector 1,1,2,2-tetrakis(4-(pyridin-4-yl)phenyl)-ethene. Its structure contains four staggered 4×4 layers and intercalated methanol. The packing is dominated by considerable H-bonds either between adjacent layers and between layers and guests. A crystal-structure transformation was detected upon removal of the guest molecules. The SCO transition of the solvated crystals is centered at ca. 215 K with a non-symmetrical hysteresis of 25 K wide, and the desolvated [Fe(L)(TPPE)0.5 ]n exhibits gradual SCO without hysteresis. Intriguingly, the intensity of the fluorescence at 460 nm for the latter is maximized at the SCO transition. The energy transfer between luminescent and SCO entities is achievable as confirmed by theoretical calculations.

Modulating the Magnetic Interaction in New Triple-Decker Dysprosium(III) Single-Molecule Magnets.

A new type of dinuclear dysprosium(III) complex based on phthalocyanine and salicylaldehyde derivatives (HL-R), [Dy2(Pc)2(L-R)2(H2O)]·2THF (R = OCH3 (1), OC2H5 (2); H2Pc = phthalocyanine; HL-OCH3 = 2-hydroxy-3-methoxybenzaldehyde; HL-OC2H5 = 3-ethoxy-2-hydroxybenzaldehyde), was successfully synthesized and structurally characterized. Complex 1 features a sandwich-type triple-decker structure, where two coplanar L-OCH3 ligands lie in the middle layer shared by two eight-coordinated DyIII ions and two Pc ligands are located in the outer layer. In 2, the introduction of an ethoxy group generates a noncoordination mode for the Oalkoxy atom. Magnetic studies indicate that complex 1 behaves as a zero-field single-molecule magnet with a higher energy barrier, while 2 exhibits a fast tunneling relaxation process. Theoretical calculations revealed that changes in the ligand field environment around DyIII ions can significantly affect the arrangement of the main magnetic axes and further result in distinct magnetic interactions as well as different relaxation behaviors.

Enhancing low-field magnetoresistance in magnetite nanoparticles via zinc substitution.

We report a strategy to enhance the room temperature low-field magnetoresistance (LFMR) behavior of Fe3O4 nanoparticle (NP) assemblies by controlled Zn-substitution. The Zn-substituted 7 nm ZnxFe3-xO4, (x = 0 to 0.4) NPs are prepared by thermal decomposition of metal acetylacetonates (M(acac)n, M = Fe2+, Fe3+, and Zn2+). The substitution increases NP magnetic susceptibility (χ) and makes the magnetic moment more sensitive to low magnetic fields. As a result, the Zn0.3Fe2.7O4 NP assembly with NPs separated by tridecanoate exhibits a large magnetoresistance (MR) ratio of -14.8% at 300 K under a 4.5 kOe magnetic field. The demonstrated approach to control NP substitution to enhance low-field magnetoresistance of the NP assemblies provides an attractive new strategy to fabricate Fe3O4-based magnetic NP assemblies with desirable transport properties for sensitive spintronic applications.

Parental transfer of perfluorooctane sulfonate and ZnO nanoparticles chronic co-exposure and inhibition of growth in F1 offspring.

Perfluorooctane sulfonate (PFOS) and ZnO nanoparticles (Nano-ZnO) are two kinds of environmental contaminants that have been frequently detected in natural waters. The potential joint toxicity of PFOS and nano-ZnO remains to be fully elucidated. The objective of this study was to evaluate co-exposure effects of PFOS and nano-ZnO on growth in initial generation (F0) zebrafish after chronic exposure and to examine possible parental transfer of PFOS and nano-ZnO transgenerational effects on the growth of first generation (F1) larvae. When zebrafish (2 h after incubation) were exposed to single- and co-exposure groups for 120 days, bioconcentration resulted in significantly less growth as measured by body length and body weight, higher mortality, and less spawning in the F0 generation. These effects were possibly due to the down-regulation of the expression of Vtg1 genes along with a sex hormone (T/E2) involved in the hypothalamus-pituitary-gonad (HPG) axis. Furthermore, after long-term exposure, less fertilization, less hatching, greater mortality and more malformation were found in the F1 generation. The down-regulation of genes and hormones might be responsible for transgenerational toxicity. This study suggested that chronic exposure to PFOS and nano-ZnO adversely impacts development, reproduction in the F0 generation, and offspring embryonic growth.

A review on silver nanoparticles-induced ecotoxicity and the underlying toxicity mechanisms.

Silver nanoparticles (Ag-NPs) are increasingly being applied in many consumer products due to their unique properties. Widespread use of Ag-NPs leads to an increasing human exposure to Ag-NPs in many different pathways. This review summarized the toxicity mechanisms of Ag-NPs based on various environmentally relevant test species, such as bacteria, cells, plants, aquatic animals and mammals, in both in vitro and in vivo experiments. Nanoparticles were usually exposed to combination chemicals but to single chemicals in the environment and thereby exert combined toxicities to the organisms. Therefore, the joint effects of nanomaterials and their co-existing characteristics were also discussed. The current knowledge gaps and safe product designs of Ag-NPs have been discussed in detail. The limited and existing data implied that understanding the toxicity mechanisms is crucial to the future research development of nanomaterials.

Magnetic Anisotropy along a Series of Lanthanide Polyoxometalates with Pentagonal Bipyramidal Symmetry.

Magneto-structural correlations in a series of lanthanide polyoxometalates (POMs) with pentagonal bipyramidal symmetry, namely, [Ln2(NMP)12(PW12O40)][PW12O40] (NMP is N-methyl pyrrolidone), were studied in detail experimentally combined with theoretical calculations. Furthermore, two types of Dy-based complexes with pentagonal bipyramidal symmetry were built to discuss the dependence of the theoretical energy barriers with the axial Dy-O bond lengths when the magnetic axes in ground Kramers doublet are along the axial orientation or on the equatorial plane. A meaningful conclusion was put forward for designing such Dy-based SIMs with high performance.

Modulating Single-Molecule Magnetic Behavior of a Dinuclear Erbium(III) Complex by Solvent Exchange.

[Er2(thd)4Pc]·2C6H6 (1) (Hthd = 2,2,6,6-tetramethylheptanedione), obtained as green crystals from the reaction of [Er(thd)3]·2H2O with lithium phthalocyanine, Li2Pc, is a stable dinuclear complex with two ErIII centers. Its lattice benzene solvent can be exchanged by soaking the crystals in dichloromethane to give [Er2(thd)4Pc]·2CH2Cl2 (2). The magnetic susceptibility data suggest different coupling interactions for the two complexes. While 1 exhibits fast relaxation and an estimated energy barrier of Ea = 2.6 cm-1 under 600 Oe dc field, the single-molecule magnet behavior of 2 is field-induced and the energy barrier is higher at 34.3 cm-1. Ab initio calculations were performed to understand the nature of the coupling interaction between two ErIII ions bridged by the phthalocyanine and the origin of different magnetic behavior. Importantly, the single-molecule magnetic properties can be reversibly tuned through the exchange of solvent molecules, confirmed by further measurements on the reverse solvated complexes 1-re and 2-re. This subtle control of relaxation by lattice solvents is rarely observed in single-molecule magnets, especially for ErIII-based complexes.

Photo- and Electronically Switchable Spin-Crossover Iron(II) Metal-Organic Frameworks Based on a Tetrathiafulvalene Ligand.

A major challenge is the development of multifunctional metal-organic frameworks (MOFs), wherein magnetic and electronic functionality can be controlled simultaneously. Herein, we rationally construct two 3D MOFs by introducing the redox active ligand tetra(4-pyridyl)tetrathiafulvalene (TTF(py)4 ) and spin-crossover FeII centers. The materials exhibit redox activity, in addition to thermally and photo-induced spin crossover (SCO). A crystal-to-crystal transformation induced by I2 doping has also been observed and the resulting intercalated structure determined. The conductivity could be significantly enhanced (up to 3 orders of magnitude) by modulating the electronic state of the framework via oxidative doping; SCO behavior was also modified and the photo-magnetic behavior was switched off. This work provides a new strategy to tune the spin state and conductivity of framework materials through guest-induced redox-state switching.

Modulating band structure through introducing Cu0/CuxO composites for the improved visible light driven ammonia synthesis.

The photocatalytic performance of ceria-based materials can be tuned by adjusting the surface structures with decorating the transition-metal, which are considered as the important active sites. Herein, cuprous oxide-metallic copper composite-doped ceria nanorods were assembled through a simple hydrothermal reduction method. The photocatalytic ammonia synthesis rates exhibit an inverted "V-shaped" trend with increasing Cu0/CuxO mole ratio. The best ammonia production rate, approximately 900 or 521 µmol·gcal-1·h-1 under full-spectra or visible light, can be achieved when the Cu0/CuxO ratio is approximately 0.16, and this value is 8 times greater than that of the original sample. The absorption edge of the as-prepared samples shifted towards visible wavelengths, and they also had appropriate ammonia synthesis levels. This research provides a strategy for designing noble metal-free photocatalysts through introducing the metal/metallic oxide compositesto the catalysts.

A well-resolved cyclic water tetramer in a dinuclear CuII coordination complex based on 1,2-bis(pyridin-3-yloxy)ethane and capped by pyridine-2,6-dicarboxylic acid.

µ-1,2-Bis(pyridin-3-yloxy)ethane-κ(2)N:N'-bis[aqua(pyridine-2,6-dicarboxylato-κ(3)O(2),N,O(6))copper(II)] tetrahydrate, [Cu2(C7H3NO4)2(C12H12N2O2)(H2O)2]·4H2O, (I), is a C-shaped molecule based on 1,2-bis(pyridin-3-yloxy)ethane (L) and Cu(II) in the presence of pyridine-2,6-dicarboxylic acid (H2pydc). The two five-coordinated Cu(II) centres are chelated by terminal pydc(2-) ligands and bridged by an L spacer. The molecules are arranged in a two-dimensional sheet via 15 O-H...O hydrogen bonds, and C-H...O interactions further bridge neighbouring sheets into a three-dimensional supermolecular architecture. The structure includes a well-resolved cyclic water tetramer, which acts as a subunit to form a larger aggregate. A thermogravimetric analysis of complex (I) was also carried out.