Ferroelectricity and Thermochromism in a 2D Dion-Jacobson Organic-Inorganic Hybrid Perovskite.

2D organic-inorganic hybrid perovskites (OIHPs) have become one of the hottest research topics due to their excellent environmental stability and unique optoelectronic properties. Recently, the ferroelectricity and thermochromism of 2D OIHPs have attracted increasing interests. Integrating ferroelectricity and thermochromism into perovskites can significantly promote the development of multichannel intelligent devices. Here, a novel 2D Dion-Jacobson OIHP of the formula (3AMP)PbI4 (where 3AMP is 3-(aminomethyl)pyridinium) is reported, which has a remarkable spontaneous polarization value (Ps) of 15.6 µC cm-2 and interesting thermochromism. As far it is known, such a large Ps value is the highest for 2D OIHPs recorded so far. These findings will inspire further exploration and application of multifunctional perovskites.

Selectively Probing the Magnetic Resonance Signals of γ-Aminobutyric Acid in Human Brains In Vivo.

BACKGROUND: Gamma-aminobutyric acid (GABA) is an inhibitory neurotransmitter in human brains, playing a role in the pathogenesis of various psychiatric disorders. Current methods have some non-neglectable shortcomings and noninvasive and accurate detection of GABA in human brains is long-term challenge. PURPOSE: To develop a pulse sequence capable of selectively detecting and quantifying the 1 H signal of GABA in human brains based on optimal controlled spin singlet order. STUDY TYPE: Prospective. SUBJECTS/PHANTOM: A phantom of GABA (pH = 7.3 ± 0.1) and 11 healthy subjects (5 females and 6 males, body mass index: 21 ± 3 kg/m2 , age: 25 ± 4 years). FIELD STRENGTH/SEQUENCE: 7 Tesla, 3 Tesla, GABA-targeted magnetic resonance spectroscopy (GABA-MRS-7 T, GABA-MRS-3 T), magnetization prepared two rapid acquisition gradient echoes sequence. ASSESSMENT: By using the developed pulse sequences applied on the phantom and healthy subjects, the signals of GABA were successfully selectively probed. Quantification of the signals yields the concentration of GABA in the dorsal anterior cingulate cortex (dACC) in human brains. STATISTICAL TESTS: Frequency. RESULTS: The 1 H signals of GABA in the phantom and in the human brains of healthy subjects were successfully detected. The concentration of GABA in the dACC of human brains was 3.3 ± 1.5 mM. DATA CONCLUSION: The developed pulse sequences can be used to selectively probe the 1 H MR signals of GABA in human brains in vivo. EVIDENCE LEVEL: 1 TECHNICAL EFFICACY STAGE: 1.

Atomic Ruthenium-Promoted Cadmium Sulfide for Photocatalytic Production of Amino Acids from Biomass Derivatives.

Amino acids are the building blocks of proteins and are widely used as important ingredients for other nitrogen-containing molecules. Here, we report the sustainable production of amino acids from biomass-derived hydroxy acids with high activity under visible-light irradiation and mild conditions, using atomic ruthenium-promoted cadmium sulfide (Ru1/CdS). On a metal basis, the optimized Ru1/CdS exhibits a maximal alanine formation rate of 26.0 molAla ⋅ gRu -1 ⋅ h-1, which is 1.7 times and more than two orders of magnitude higher than that of its nanoparticle counterpart and the conventional thermocatalytic process, respectively. Integrated spectroscopic analysis and density functional theory calculations attribute the high performance of Ru1/CdS to the facilitated charge separation and O-H bond dissociation of the α-hydroxy group, here of lactic acid. The operando nuclear magnetic resonance further infers a unique "double activation" mechanism of both the CH-OH and CH3-CH-OH structures in lactic acid, which significantly accelerates its photocatalytic amination toward alanine.

Direct observation of geometric and sliding ferroelectricity in an amphidynamic crystal.

Sliding ferroelectricity is a recently observed polarity existing in two-dimensional materials. However, due to the weak polarization and poor electrical insulation in these materials, existing experimental evidences are indirect and mostly based on nanoscale transport properties or piezoresponse force microscopy. We report the direct observation of sliding ferroelectricity, using a high-quality amphidynamic single crystal (15-crown-5)Cd3Cl6, which possesses a large bandgap and so allows direct measurement of polarization-electric field hysteresis. This coordination polymer is a van der Waals material, which is composed of inorganic stators and organic rotators as determined by X-ray diffraction and NMR characterization. From density functional theory calculations, we find that after freezing the rotators, an electric dipole is generated in each layer driven by the geometric mechanism, while a comparable ferroelectric polarization originates from the interlayer sliding. The net polarization of these two components can be directly measured and manipulated. Our finding provides insight into low-dimensional ferroelectrics, especially control of the synchronous dynamics of rotating molecules and sliding layers in solids.

Distinguishing glutamate and glutamine in in vivo 1 H MRS based on nuclear spin singlet order filtering.

PURPOSE: The signals of glutamate (Glu) and glutamine (Gln) are often significantly overlapped in routine 1 H-MR spectra of human brain in vivo. Selectively probing the signals of Glu and Gln in vivo is very important for the study of the metabolisms in which Glu and Gln are involved. METHODS: The Glu-/Gln- targeted pulse sequences are developed to selectively probe the signals of Glu and Gln. The core part of the Glu-/Gln- targeted pulse sequences lies on the preparation of the nuclear spin singlet orders (SSOs) of the five-spin systems of Glu and Gln. The optimal control method is used to prepare the SSOs of Glu and Gln with high efficiency. RESULTS: The Glu-/Gln- targeted pulse sequences have been applied on phantoms to selectively probe the signals of Glu and Gln. Moreover, in the in vivo experiments, the signals of Glu and Gln in human brains of healthy subjects have been successfully probed separately. CONCLUSION: The developed Glu-/Gln- targeted pulse sequences can be used to distinguish the 1 H-MR signals of Glu and Gln in human brains in vivo. The optimal control method provides an effective way to prepare the SSO of a specific spin system with high efficiency and in turn selectively probe the signals of a targeted molecule.

Performance of Artificial Intelligence-Aided Diagnosis System for Clinically Significant Prostate Cancer with MRI: A Diagnostic Comparison Study.

BACKGROUND: The high level of expertise required for accurate interpretation of prostate MRI. PURPOSE: To develop and test an artificial intelligence (AI) system for diagnosis of clinically significant prostate cancer (CsPC) with MRI. STUDY TYPE: Retrospective. SUBJECTS: One thousand two hundred thirty patients from derivation cohort between Jan 2012 and Oct 2019, and 169 patients from a publicly available data (U-Net: 423 for training/validation and 49 for test and TrumpeNet: 820 for training/validation and 579 for test). FIELD STRENGTH/SEQUENCE: 3.0T/scanners, T2 -weighted imaging (T2 WI), diffusion-weighted imaging, and apparent diffusion coefficient map. ASSESSMENT: Close-loop AI system was trained with an Unet for prostate segmentation and a TrumpetNet for CsPC detection. Performance of AI was tested in 410 internal and 169 external sets against 24 radiologists categorizing into junior, general and subspecialist group. Gleason score >6 was identified as CsPC at pathology. STATISTICAL TESTS: Area under the receiver operating characteristic curve (AUC-ROC); Delong test; Meta-regression I2 analysis. RESULTS: In average, for internal test, AI had lower AUC-ROC than subspecialists (0.85 vs. 0.92, P < 0.05), and was comparable to junior (0.84, P = 0.76) and general group (0.86, P = 0.35). For external test, both AI (0.86) and subspecialist (0.86) had higher AUC than junior (0.80, P < 0.05) and general reader (0.83, P < 0.05). In individual, it revealed moderate diagnostic heterogeneity in 24 readers (Mantel-Haenszel I2  = 56.8%, P < 0.01), and AI outperformed 54.2% (13/24) of readers in summary ROC analysis. In multivariate test, Gleason score, zonal location, PI-RADS score and lesion size significantly impacted the accuracy of AI; while effect of data source, MR device and parameter settings on AI performance is insignificant (P > 0.05). DATA CONCLUSION: Our AI system can match and to some case exceed clinicians for the diagnosis of CsPC with prostate MRI. EVIDENCE LEVEL: 3 TECHNICAL EFFICACY: Stage 2.

Organic enantiomeric high-Tc ferroelectrics.

For nearly 100 y, homochiral ferroelectrics were basically multicomponent simple organic amine salts and metal coordination compounds. Single-component homochiral organic ferroelectric crystals with high-Curie temperature (Tc) phase transition were very rarely reported, although the first ferroelectric Rochelle salt discovered in 1920 is a homochiral metal coordination compound. Here, we report a pair of single-component organic enantiomorphic ferroelectrics, (R)-3-quinuclidinol and (S)-3-quinuclidinol, as well as the racemic mixture (Rac)-3-quinuclidinol. The homochiral (R)- and (S)-3-quinuclidinol crystallize in the enantiomorphic-polar point group 6 (C6) at room temperature, showing mirror-image relationships in vibrational circular dichroism spectra and crystal structure. Both enantiomers exhibit 622F6-type ferroelectric phase transition with as high as 400 K [above that of BaTiO3 (Tc = 381 K)], showing very similar ferroelectricity and related properties, including sharp step-like dielectric anomaly from 5 to 17, high saturation polarization (7 µC/cm2), low coercive field (15 kV/cm), and identical ferroelectric domains. Their racemic mixture (Rac)-3-quinuclidinol, however, adopts a centrosymmetric point group 2/m (C2h), undergoing a nonferroelectric high-temperature phase transition. This finding reveals the enormous benefits of homochirality in designing high-Tc ferroelectrics, and sheds light on exploring homochiral ferroelectrics with great application.

Cooperative Motion in Water-Methanol Clusters Controls the Reaction Rates of Heterogeneous Photocatalytic Reactions.

Detailed information about the influences of the cooperative motion of water and methanol molecules on practical solid-liquid heterogeneous photocatalysis reactions is critical for our understanding of photocatalytic reactions. The present work addresses this issue by applying operando nuclear magnetic resonance (NMR) spectroscopy, in conjunction with density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations, to investigate the dynamic behaviors of heterogeneous photocatalytic systems with different molar ratios of water to methanol on rutile-TiO2 photocatalyst. The results demonstrate that methanol and water molecules are involved in the cooperative motions, and the cooperation often takes the form of methanol-water clusters that govern the number of methanol molecules reaching to the active sites of the photocatalyst per unit time, as confirmed by the diffusion coefficients of the methanol molecule calculated in the binary methanol-water solutions. Nuclear Overhauser effect spectroscopy experiments reveal that the clusters are formed by the hydrogen bonding between the -OH groups of CH3OH and H2O. The formation of such methanol-water clusters is likely from an energetic standpoint in low-concentration methanol, which eventually determines the yields of methanol reforming products.

Role of Organic Fluoride Salts in Stabilizing Niobium Oxo-Clusters Catalyzing Epoxidation.

We present here that easily available organic salts can stabilize/modify niobium (Nb) oxo-clusters. The as-synthesized Nb oxo-clusters have been characterized by various methods. These Nb oxo-clusters were catalytically active for the epoxidation of allylic alcohols and olefins with H2O2 as an oxidant. Notably, Nb-OC@TBAF-0.5 appeared as highly dispersed nanosized particles and showed the highest catalytic activity, which can be attributed to the following reasons on the basis of characterization. First, the strong coordination of fluorine ions with Nb sites and the steric protection with bulky organic cations led to high stabilization and dispersion of the oxo-clusters in the course of the reaction. Second, a hydrogen-bond interaction between the coordinated fluorine atom and the -OH group of allylic alcohol favored the epoxidation reaction. Third, the electron density of Nb sites decreased due to the strong electron-withdrawing ability of F- adjacent to Nb sites, thus promoting the electrophilic oxygen transfer to the C═C bond.

Dynamic heterogeneity in homogeneous polymer melts.

Chain entanglement behaviors were studied by 1H Hahn echo nuclear magnetic resonance (NMR) and 1H double-quantum (DQ) NMR experiments. Poly(ethylene oxide) (PEO) was chosen to investigate the chain entanglement behaviors. The 1H Hahn echo NMR results demonstrate that the critical molecular weight of PEO is approximately 6 kg mol-1. Above this critical molecular weight, chain entanglements start to occur in the melts resulting in anisotropic motions of polymer chain. The 1H DQ NMR observations establish that PEO melts with molecular weights above the critical value exhibit dynamical entanglements. The entangled networks, formed by PEO with a molecular weight of 480 kg mol-1 (PEO480), present slow mobility and rather homogeneously distributed chain entanglements, while the entangled networks, formed by PEO with a molecular weight of 255 kg mol-1 (PEO255), present fast mobility and obvious dynamic heterogeneity in the distribution of chain entanglement. Short chain PEOs like that with a molecular weight of 2 kg mol-1 are demonstrated to function like solvents when being added in an appropriate concentration to PEO480, and the dilution effect increases the chain mobility of PEO480. Moreover, properly diluted PEO480 networks exhibit dynamic heterogeneity similar to that observed in PEO255.

Accurate and Real-Time Temperature Monitoring during MR Imaging Guided PTT.

Photothermal therapy (PTT) is an efficient approach for cancer treatment. However, accurately monitoring the spatial distribution of photothermal transducing agents (PTAs) and mapping the real-time temperature change in tumor and peritumoral normal tissue remain a huge challenge. Here, we propose an innovative strategy to integrate T1-MRI for precisely tracking PTAs with magnetic resonance temperature imaging (MRTI) for real-time monitoring temperature change in vivo during PTT. NaBiF4: Gd@PDA@PEG nanomaterials were synthesized with favorable T1-weighted performance to target tumor and localize PTAs. The extremely weak susceptibility (1.04 × 10-6 emu g-1 Oe1-) of NaBiF4: Gd@PDA@PEG interferes with the local phase marginally, which maintains the capability of MRTI to dynamically record real-time temperature change in tumor and peritumoral normal tissue. The time resolution is 19 s per frame, and the detection precision of temperature change is approximately 0.1 K. The approach achieving PTT guided by multimode MRI holds significant potential for the clinical application.

A clinical-radiomics nomogram for the preoperative prediction of lymph node metastasis in colorectal cancer.

BACKGROUND: Accurate lymph node metastasis (LNM) prediction in colorectal cancer (CRC) patients is of great significance for treatment decision making and prognostic evaluation. We aimed to develop and validate a clinical-radiomics nomogram for the individual preoperative prediction of LNM in CRC patients. METHODS: We enrolled 766 patients (458 in the training set and 308 in the validation set) with clinicopathologically confirmed CRC. We included nine significant clinical risk factors (age, sex, preoperative carbohydrate antigen 19-9 (CA19-9) level, preoperative carcinoembryonic antigen (CEA) level, tumor size, tumor location, histotype, differentiation and M stage) to build the clinical model. We used analysis of variance (ANOVA), relief and recursive feature elimination (RFE) for feature selection (including clinical risk factors and the imaging features of primary lesions and peripheral lymph nodes), established classification models with logistic regression analysis and selected the respective candidate models by fivefold cross-validation. Then, we combined the clinical risk factors, primary lesion radiomics features and peripheral lymph node radiomics features of the candidate models to establish combined predictive models. Model performance was assessed by the area under the receiver operating characteristic (ROC) curve (AUC). Finally, decision curve analysis (DCA) and a nomogram were used to evaluate the clinical usefulness of the model. RESULTS: The clinical-primary lesion radiomics-peripheral lymph node radiomics model, with the highest AUC value (0.7606), was regarded as the candidate model and had good discrimination and calibration in both the training and validation sets. DCA demonstrated that the clinical-radiomics nomogram was useful for preoperative prediction in the clinical environment. CONCLUSION: The present study proposed a clinical-radiomics nomogram with a combination of clinical risk factors and radiomics features that can potentially be applied in the individualized preoperative prediction of LNM in CRC patients.

Preparation of Long-Lived States in a Multi-Spin System by Using an Optimal Control Method.

The lifetime Ts of a long-lived nuclear spin state (LLS) could be much longer than the longitudinal order T1 . Many spin systems were used to produce long-lived states, including two or more homonuclear spins that couple to each other. For multiple homonuclear spins with rather small chemical shift difference, normally it is difficult to selectively control the spins and then to prepare a LLS. Herein, we present a scheme that prepares different spin orders in a multi-spin system by using optimal control and numerical calculation. By experimentally measuring the lifetime of the states, we find that for a three-spin physical system, although there are many forms of state combinations with different spin orders, each component has its own lifetime.

Ionic Liquid Stabilized Niobium Oxoclusters Catalyzing Oxidation of Sulfides with Exceptional Activity.

We present here a new class of niobium oxoclusters that are stabilized effectively by carboxylate ionic liquids. These functionalized ILs are designated as [TBA][LA], [TBA][PA], and [TBA][HPA] in this work, in which TBA represents tetrabutylammonium and LA, PA, and HPA refer to lactate, propionate, 3-hydroxypropionate anions, respectively. The as-synthesized Nb oxoclusters have been characterized by use of elemental analysis, NMR, IR, XRD, TGA, HRTEM. It was found that [TBA][LA]-stabilized Nb oxoclusters (Nb-OC@[TBA][LA]) are uniformly dispersed with an average particle size of 2-3 nm and afforded exceptionally high catalytic activity for the selective oxidation of various thioethers. The turnover number with Nb-OC@[TBA][LA] catalyst was over 56 000 at catalyst loading as low as 0.0033 mol % (1 ppm). Meantime, the catalyst also showed the high activity for the epoxidation of olefins and allylic alcohols by using only 0.065 mol % of catalyst (50 ppm). The characterization of 93 Nb NMR spectra revealed that the Nb oxoclusters underwent structural transformation in the presence of H2 O2 but regenerated to their initial state at the end of the reaction. In particular, the highly dispersed Nb oxoclusters can absorb a large amount of polar organic solvents and thus were swollen greatly, which exhibited "pseudo" liquid phase behavior, and enabled the substrate molecules to be highly accessible to the catalytic center of Nb oxocluster units.

A Small Lattice Change Induces Significant Dynamic Changes of CH3NH3+ Caged in Hybrid Perovskite Crystals: Toward Understanding the Interplay between Host Lattices and Guest Molecules.

Two perovskite-type compounds, (MA)2[B'Co(CN)6] (MA = methylammonium, B' = K(I) and Na(I)), have very similar structures, but exhibit marked differences in the phase and dielectric transitions. Solid state 2H NMR studies reveal the detailed dynamic changes of the caged methylammonium (MA) cations before and after the phase transitions, which are correlated with the different dielectric states of the compounds. Using solid state 59Co NMR, the dynamic changes of the host lattices before and after the transitions, which accompany the changes in the dynamics of the caged MA cations, are unveiled, demonstrating the intriguing interplay between the MA cations and the host lattices. On the basis of these observations, the molecular origins of the dielectric transitions are discussed in detail.

Fast Lithium-Ion Transportation in Crystalline Polymer Electrolytes.

Fast lithium-ion transportation is found in the crystalline polymer electrolytes, α-CD-PEOn /Li+ (n=12, 40), prepared by self-assembly of α-cyclodextrin (CD), polyethylene oxide (PEO) and Li+ salts. A detailed solid-state NMR study combined with the X-ray diffraction technique reveals the unique structural features of the samples, that is, a) the tunnel structure formed by the assembled CDs, providing the ordered long-range pathway for Li+ ion transportation; b) the all-trans conformational sequence of the PEO chains in the tunnels, attenuating significantly the coordination between Li+ and the EO segments. The origin of the fast lithium-ion transportation has been attributed to these unique structural features. This work demonstrates the first example in solid polymer electrolytes (SPEs) for "creating" fast ion transportation through material design and will find potential applications in the design of new ionconducting SPE materials.

Ionic conductivity of ß-cyclodextrin-polyethylene-oxide/alkali-metal-salt complex.

Highly conductive, crystalline, polymer electrolytes, ß-cyclodextrin (ß-CD)-polyethylene oxide (PEO)/LiAsF6 and ß-CD-PEO/NaAsF6 , were prepared through supramolecular self-assembly of PEO, ß-CD, and LiAsF6 /NaAsF6 . The assembled ß-CDs form nanochannels in which the PEO/X(+) (X=Li, Na) complexes are confined. The nanochannels provide a pathway for directional motion of the alkali metal ions and, at the same time, separate the cations and the anions by size exclusion.

A chemically triggered and thermally switched dielectric constant transition in a metal cyanide based crystal.

A dielectric constant transition is chemically triggered and thermally switched in (HPy)2[Na(H2O)Co(CN)6] (2, HPy=pyridinium cation) by single-crystal-to-single-crystal transformation and structural phase transition, respectively. Upon dehydration, (HPy)2[Na(H2O)2Co(CN)6] (1) transforms to its semi-hydrated form 2, accompanying a transition from a low-dielectric state to a high-dielectric state, and vice versa. This dielectric switch is also realized by a structural phase transition in 2 that occurs between room- and low-temperature phases, and which corresponds to high- and low-dielectric states, respectively. The switching property is due to the variation in the environment surrounding the HPy cation, that is, the hydrogen-bonding interactions and the crystal packing, which exert predominant influences on the dynamics of the cations that transit between the static and motional states.

Uniaxial movements of a metal-cyanide framework switched by weak interactions through dehydration and rehydration.

A metal-cyanide framework undergoes a dehydration-rehydration triggered reversible single-crystal-to-single-crystal transformation. The resulting accordion-like contraction-expansion corresponds to a size change along the c axis as much as 24 %. This anisotropic response arises from the cooperativity among the water molecules, K ions, and CN groups between the unique two-dimensional bimetallic layers through weak interactions of hydrogen bonds and electrostatic (ionic) interactions. The key role of the water molecules in the dehydration-rehydration process is revealed by solid-state (1)H NMR spectroscopy and dielectric measurements.

Transferring lithium ions in nanochannels: a PEO/Li⁺ solid polymer electrolyte design.

A new category of crystalline polymer electrolyte prepared by the supramolecular self-assembly of polyethylene oxide (PEO), α-cyclodextrin (α-CD), and LiAsF6 is reported. The polymer electrolyte consists of the nanochannels formed by α-CDs in which the PEO/Li(+) complexes are confined. The nanochannels formed by α-CD provide the pathway for the directional motion of Li(+) ions and at the same time prevent the access of the anions by size exclusion, resulting in good separation of the Li(+) ions and the anions. The conductivity of the reported material is 30 times higher than that of the comparable PEO/Li(+) complex crystal at room temperature. By using state-of-art solid-state NMR spectroscopy, the structure and dynamics of the material were investigated in detail. The dynamics of the Li(+) ions was studied and correlated to the ionic conductivity of the material.