Organoboron flank-substituted donor-acceptor polymer anode with ultra-long cycling stability for lithium ion batteries.

The tunable structure and other properties of organic materials suggest that they can potentially solve the shortcomings of traditional anodes such as graphite. We successfully introduced an organoboron unit into the thiophene-based polymer PBT-2 to construct a donor-acceptor polymer anode. The charge delocalization and LUMO energy level resulting from the unique structure of this material enabled good redox activity and a very stable electrochemical performance in electrochemical tests, with a reversible capacity of 262 mA h g-1 at 0.5 A g-1 and >10 000 cycles at 1 A g-1 with a decay of 0.056‰ per cycle. Accordingly, targeted structural design to overcome the shortcomings of active units such as thiophene can effectively regulate their electrochemical performance, providing a solution for the development of high-performance anode materials for use in lithium ion batteries.

Monomer-Promoting Asymmetric Kinetic Resolution-Alternating Copolymerization To Afford AAB-Type Copolyesters.

Living copolymerization of mixed monomers can enrich the diversity of copolymer materials with well-defined performance via controlling both monomers and stereosequences. However, periodic sequence-controlled living copolymerization of same-type monomers with more than two components in synthetic polymer science remains a challenge. In this work, a new method of monomer-promoting asymmetric kinetic resolution-alternating copolymerization can let a tricomponent mixture of l-lactide (S,S-LA or l-LA) and two enantiomeric isomers of racemic tropic acid cyclic esters (tropicolactone) be polymerized into sequence-controlled -(ASASBS)n- type biodegradable copolyesters (the subscript S presents the configuration and A and B present lactic acid units and tropic acid units, respectively), and diblock copolymers of -(ASASBS)n-b-(ARARBR)n- can further be obtained upon addition of R,R-LA (d-LA). Compared to previous asymmetric kinetic resolutions of racemic chemicals via polymerization or organic reactions, no enantiopure catalyst/initiator is required in this system. After the resolution and alternating copolymerization of S,S-LA and rac-tropicolactone, the ee value of unreacted tropicolactone can reach 99.4%. The alternating probability between tropicolactone and lactide monomers is more than 96% in periodic sequence polymers of -(ASASBS)n-. The tetracomponent mixture of rac-lactide and rac-tropicolactone can be copolymerized into an alternating copolymer with a -((ASASBS)x-ran-(ARARBR)y)n- structure, in which the stereoselective linkage probability of 95% after S,S-lactide (R,R-lactide) followed by S-tropicolactone (R-tropicolactone) keeps very high too.

Replacing CC Unit with B←N Unit in Isoelectronic Conjugated Polymers for Enhanced Photocatalytic Hydrogen Evolution.

Three linear isoelectronic conjugated polymers PCC, PBC, and PBN are synthesized by Suzuki-Miyaura polycondensation for photocatalytic hydrogen (H2 ) production from water. PBN presented an excellent photocatalytic hydrogen evolution rate (HER) of 223.5 µmol h-1 (AQY420  = 23.3%) under visible light irradiation, which is 7 times that of PBC and 31 times that of PCC. The enhanced photocatalytic activity of PBN is due to the improved charge separation and transport of photo-induced electrons/holes originating from the lower exciton binding energy (Eb ), longer fluorescence lifetime, and stronger built-in electric field, caused by the introduction of the polar B←N unit into the polymer backbone. Moreover, the extension of the visible light absorption region and the enhancement of surface catalytic ability further increase the activity of PBN. This work reveals the potential of B←N fused structures as building blocks as well as proposes a rational design strategy for achieving high photocatalytic performance.

Two-Step Redox in Polyimide: Witness by In Situ Electron Paramagnetic Resonance in Lithium-ion Batteries.

Organic materials are promising candidates for future rechargeable batteries, owing to their high natural abundance and rapidly redox reaction. Elaborating the charge/discharge process of organic electrode is critical to unveil the fundamental redox mechanism of lithium-ion batteries (LIBs), but monitoring of this process is still challenging. Here, we report a nondestructive electron paramagnetic resonance (EPR) technique to real-time detect the electron migration step within polyimide cathode. From in situ EPR tests, we vividly observe a classical redox reaction along with two-electron transfer which only shows one pair of peaks in the cyclic voltammetry curve. The radical anion and dianion intermediates are detailed delineation at redox sites in EPR spectra, which can be further confirmed through density functional theory calculations. This approach is especially crucial to elaborate the correlation behind electrochemical and molecular structure for multistep organic-based LIBs.

Tetrabutylammonium Halides as Selectively Bifunctional Catalysts Enabling the Syntheses of Recyclable High Molecular Weight Salicylic Acid-Based Copolyesters.

To synthesize high molecular weight poly(phenolic ester) via a living ring-opening polymerization (ROP) of cyclic phenolic ester monomers remains a critical challenge due to serious transesterification and back-biting reactions. Both phenolic ester bonds in monomer and polymer chains are highly active, and it is difficult so far to distinguish them. In this work, an unprecedented selectively bifunctional catalytic system of tetra-n-butylammonium chloride (TBACl) was discovered to mediate the syntheses of high molecular weight salicylic acid-based copolyesters via a living ROP of salicylate cyclic esters (for poly(salicylic methyl glycolide) (PSMG), Mn =361.8 kg/mol, Ð<1.30). Compared to previous catalysis systems, the side reactions were suppressed remarkably in this catalysis system because phenolic ester bond in monomer can be selectively cleaved over that in polymer chains during ROP progress. Mechanistic studies reveal that the halide anion and alkyl-quaternaryammonium cation work synergistically, where the alkyl-quaternaryammonium cation moiety interacts with the carbonyl group of substrates via non-classical hydrogen bonding. Moreover, these salicylic acid-based copolyesters can be recycled to dimeric monomer under solution condition, and can be recycled to original monomeric monomers without catalyst under sublimation condition.

Synthesis of Linear to Cyclic Polylactide via a One-Pot Step-Wise Ring-Opening Polymerization and Back-Biting Reaction of Ring Closure Using Magnesium Complexes.

The controllable synthesis of cyclic polylactide remains a challenging topic so far. In this work, a new strategy of one-pot step-wise ring-opening polymerization (ROP) followed by a back-biting reaction of ring closure was reported, in which one magnesium atrane-like complex {N,N-bis[3,5-di-cumyl-2-benzyloxy]-[2-(2-aminoethoxy)ethoxy]magnesium} was utilized to initiate the ROP of lactide using 4-dimethylaminopyridine as a co-catalyst; then, macrocyclic polylactides were liberated out via increasing temperature after complete depletion of the monomer in which a back-biting reaction was utilized as a ring-closure method. The living feature at the first ROP stage can be proved well by the controllable molecular weights ranging from 3.10 to 34.70 kDa and narrow molecular weight distributions of linear polylactides obtained after quenching the reaction. The final cyclic polylactides with molecular weights (vs polystyrene) ranging from 2.50 to 16.10 kDa can be achieved too after the back-biting reaction of ring closure. Although a shoulder peak at the gel permeation chromatography profile appears when the ratio of monomer:initiator is high up to 100:1 or 200:1, this system is suitable for the controllable syntheses of cyclic polylactides with desirable modest molecular weights.

Piperlongumine increases the sensitivity of bladder cancer to cisplatin by mitochondrial ROS.

BACKGROUND: The development of cisplatin resistance often results in cisplatin inefficacy in advanced or recurrent bladder cancer. However, effective treatment strategies for cisplatin resistance have not been well established. METHODS: Gene expression was measured by qRT-PCR and Western blotting. CCK-8 assay was performed to detect cell survival. The number of apoptotic cells was determined using the Annexin V-PI double-staining assay. The level of reactive oxygen species (ROS) was measured using 2',7'-dichlorodihydrofluorescein diacetate fluorescent dye, and the ATP level was detected using an ATP measurement kit. RESULTS: The expression of receptor-interacting protein kinase 1 (RIPK1), a key regulator of necroptosis, gradually decreased during cisplatin resistance. We first used piperlongumine (PL) in combination with cisplatin to act on cisplatin-resistant BC cells and found that PL-induced activation of RIPK1 increased the sensitivity of T24 resistant cells to cisplatin treatment. Furthermore, we revealed that PL killed T24 cisplatin-resistant cells by triggering necroptosis, because cell death could be rescued by the mixed lineage kinase domain-like (MLKL) protein inhibitor necrotic sulfonamide or MLKL siRNA, but could not be suppressed by the apoptosis inhibitor z-VAD. We further explored the specific mechanism and found that PL activated RIPK1 to induce necroptosis in cisplatin-resistant cells by stimulating mitochondrial fission to produce excessive ROS. CONCLUSIONS: Our results demonstrated the role of RIPK1 in cisplatin-resistant cells and the sensitization effect of the natural drug PL on bladder cancer. These may provide a new treatment strategy for overcoming cisplatin resistance in bladder cancer.

Reductive Alkylation of Alkenyl Acetates with Alkyl Bromides by Nickel Catalysis.

Catalytic alkylation of stable alkenyl C-O electrophiles is synthetically appealing, but studies to date have typically focused on the reactions with alkyl Grignard reagents. We report herein a cross-electrophile reaction of alkenyl acetates with alkyl bromides. This work has enabled a new method for the synthesis of aliphatic alkenes from alkenyl acetates to be established that can be used to add more structural complexity and molecular diversity with enhanced functionality tolerance. The method allows for a gram-scale reaction and modification of biologically active molecules, and it affords access to useful building blocks. Preliminary mechanistic studies reveal that the NiI species plays an essential role for the success of the coupling of these two reactivity-mismatched electrophiles.

Isotactic-Alternating, Heterotactic-Alternating, and ABAA-Type Sequence-Controlled Copolyester Syntheses via Highly Stereoselective and Regioselective Ring-Opening Polymerization of Cyclic Diesters.

Synthesizing different types of sequence-controlled copolyesters can enrich the diversity of copolyesters and modify their properties more precisely, but it is still a challenge to synthesize a complicated sequence-controlled copolyester using different hydroxy acids in a living polymerization manner. In this work, a highly regioselective and stereoselective catalytic system was developed to synthesize biorenewable and biodegradable copolyesters of mandelic acid and lactic acid with isotactic-alternating, heterotactic-alternating, and ABAA-type precise and complicated sequences. Because of the regular incorporation of mandelic acid into polylactide, these sequence-controlled copolymers of mandelic acid and lactic acid show higher glass-transition temperatures than polylactide and a random copolymer. A stereocomplexation interaction between two opposite enantiomeric isotactic polymer chains was also discovered in the isotactic-alternating copolymer.

Nanostructured Lateral Boryl Substitution Conjugated Donor-Acceptor Oligomers for Visible-Light-Driven Hydrogen Production.

Poor charge separation is the main factor that limits the photocatalytic hydrogen generation efficiency of organic conjugated polymers. In this work, a series of linear donor-acceptor (D-A) type oligomers are synthesized by a palladium-catalyzed Sonogashira-Hagihara coupling of electron-deficient diborane unit and different dihalide substitution sulfur functionalized monomers. Such diborane-based A unit exerts great impact on the resulting oligomers, including distinct semiconductor characters with isolated lowest unoccupied molecular orbital (LUMO) orbits locating in diborane-containing fragment, and elevated LUMO level higher than water reduction potential. Relative to A-A type counterpart, the enhanced dipole polarization effect in D-A oligomers facilitates separation of photogenerated charge carriers, as evidenced by notably prolonged electron lifetime. Owing to π-π stacking of rigid backbone, the oligomers can aggregate into an interesting 2D semicrystalline nanosheet (≈2.74 nm), which is rarely reported in linear polymeric photocatalysts prepared by similar carbon-carbon coupling reaction. Despite low surface area (30.3 m2 g-1 ), such ultrathin nanosheet D-A oligomer offers outstanding visible light (λ > 420 nm) hydrogen evolution rate of 833 µmol g-1 h-1 , 14 times greater than its A-A analogue (61 µmol g-1 h-1 ). The study highlights the great potential of using boron element to construct D-A type oligomers for efficient photocatalytic hydrogen generation.

Ring-Opening Alternating Copolymerization of O-Carboxyanhydrides of Lactic Acid and Malic Acid Using Hafnium Alkoxide Initiators with Different Stereo Selectivities and Activities.

Monomer sequence controllable syntheses of copolymers, including copolyesters, remain a challenge in polymer science. Although alternating sequence-controlled copolymerization of O-carboxyanhydrides (OCAs) can be achieved via using syndioselective initiators, the alternating copolymerization of lactic acid-derived O-carboxyanhydride (LacOCA) with other monomers still suffers from a lack of highly syndioselective initiators. In this work, a highly syndioselective system for the ring-opening polymerization (ROP) of LacOCA was achieved using a bulky amine tris(phenolate) hafnium alkoxide initiator with a high Pr value of 0.91. However, the stereoselectivities of amine tris(phenolate) hafnium alkoxide initiators for the ROP of malic acid O-carboxyanhydride (MalOCA) change to be modestly or lowly isoselective. Interestingly, despite the different stereoselectivities of this system for the two different monomers, the high syndioselectivity of the initiator for the ROP of LacOCA and the low activity of MalOCA in the ROP allow comparatively high rates of cross-propagation; consequently, the ring-opening alternating copolymerization (ROAP) of LacOCA and MalOCA was achieved successfully.

Isoselective Polymerization of rac-Lactide Catalyzed by Ion-Paired Potassium Amidinate Complexes.

Three potassium crown ether complexes supported with bulky amidinate ligands were synthesized for the ring-opening polymerization (ROP) of rac-lactide. The side polymerization reaction initiated directly by ligand anion was suppressed well in the presence of alcohol as our design, and the synthesis of linear polylactide with a molecular weight as high as 117.7 kg/mol was successful together with an isoselectivity value of Pm = 0.88 at -70 °C. In this system, lactide can be deprotonated by amidinate anion to give lactide enolate, which can initiate the ROP of lactide as a side reaction in the absence of alcohol; however, this side reaction can also be suppressed well in the presence of alcohol by a decrease in temperature. An interesting anti-Arrhenius-like behavior in the polymerization was discovered, which can be attributed to the fact that the active catalyst can be converted to a less active lactide enolate potassium complex at a high temperature.

MIMIIP3O9 (MI = Rb, MII = Cd, Mg, Ca; MI = Cs, MII = Pb, Sr; MI = K, MII = Mg): Cation Substitution Application in Cyclophosphate Family and Nonlinear Optical Properties.

By the application of cation substitution, five new members of cyclophosphates, RbCdP3O9, CsPbP3O9, CsSrP3O9, RbMgP3O9, and RbCaP3O9, were obtained by a high-temperature melt method and structurally analyzed. The five compounds have identical stoichiometries, and all of them feature a three-dimensional network, which consists of MIIO6 (MII = Cd, Mg, Ca, Pb, Sr) octahedra and cyclic P3O9 units, while alkali-metal atoms are located within the network. However, RbCdP3O9 and CsPbP3O9 belong to the asymmetric space groups P6̅ c2 and Pna21, respectively, and the other three compounds belong to orthorhombic space group Pnma. Detailed structure comparisons in the MI-MII-P-O and (MIMIIP3O9) n ( n = 1, 2, 6) systems are discussed. Remarkably, KMgP3O9 as one of the cyclophosphate members exhibits a second harmonic generation (SHG) intensity about 0.2 times that of KH2PO4 (KDP), RbCdP3O9, and CsPbP3O9 also show SHG responses 0.1 times that of KDP. In addition, the related optical properties are discussed. Furthermore, theoretical calculations and dipole moments were calculated to explain the relation of structure and optical properties.

Synthesis of Bis-Cycloborate Olefin and Butatriene Derivatives through the Reduction of Alkynyl-Bridged Diboryl Compounds.

A series of bis-cycloborate olefin and butatriene derivatives were synthesized from alkynyl-bridged diboryl compounds using a simple reduction strategy. In the reduction route of 1,2-bis[2-(dimesitylboranyl)phenyl]ethyne (1), bis-cycloborate olefin (4) to diborate-bridged stilbene (5) can be obtained selectively by varying the reaction temperature. In addition, a thermal isomerization from 4 to 5 was found as a result of the rearrangement of double bonds. The generality of this reaction was further verified in similar reduction reactions. In the direduction of 1,2-bis[8-(dimesitylboranyl)naphthalen-1-yl]ethyne (2), the bis-cycloborate olefin (6) was isolated in high yield and demonstrated no thermal isomerization. In the two-electron reduction of 1,8-bis{[2-(dimesitylboranyl)phenyl]ethynyl}naphthalene (3), the bis-cycloborate butatriene (7) was obtained unexpectedly because of the departure of the naphthyl group. When using Na as the reductant and diethyl ether as the solvent, 1,2-bis[( Z)-2-(dimesitylboranyl)benzylidene]-1,2-dihydroacenaphthylene (8) was isolated after adding 1 or 2 drops of H2O to the reduction reaction filtrates. Meanwhile, the related mechanisms for radical cyclization, thermal isomerization, and formation of bis-cycloborate butatriene were also discussed.

Diradical Anion of Potassium Aggregate: Reduction of Dimer Boroxide Complex.

Crystalline aggregates containing metal cation clusters "wrapped" by reduced hydrocarbon anions have been presented. Initially, a dimeric complex (2) possessing a bimetallic K2O2 core was synthesized from the reaction between an anthracene substituted boronic acid (2-(anthracen-9-yl)phenyl)(hydroxy)(mesityl)borane (1-H) and KN(SiMe3)2 in THF solution. The B-O bond length (1.281(4) Å) in complex 2 is comparable to those observed in oxoboranes, indicating this may be a double bond, which is supported by its Wiberg bond order (1.9) predicted by density functional theory calculations. Subsequently, potassium aggregate complexes, diradical 3 and dihydro anion 4, were obtained through the reduction reactions of dimeric complex 2 and 1-H, respectively. They exhibit similar K3O2B2 aggregate structures, but differ significantly in the geometry of the anthracene units. Complex 3 features a triplet diradical character with planar anthracene units that carry the unpaired electrons, while the anthracene groups in complex 4 display a puckered structure due to the addition of hydrogen atoms.

Stereoselective Alkali-Metal Catalysts for Highly Isotactic Poly(rac-lactide) Synthesis.

A high degree of chain end control in the isoselective ring-opening polymerization (ROP) of rac-lactide is a challenging research goal. In this work, eight highly active sodium and potassium phenolates as highly isoselective catalysts for the ROP of rac-lactide are reported. The best isoselectivity value of Pm = 0.94 is achieved. The isoselective mechanism is chain-end control through the analysis of the stereoerrors in the microstructure of a final polymer; thus, isotactic multiblock structure polymers are obtained, and the highest melt point can reach 192.5 °C. The donating group in phenolate can clearly accelerate the ROP reaction, potassium complexes are more active than the analogous sodium complexes, and the big spacial hindrance of the ligand can decrease the activity. The high isoselectivities of these complexes mostly result from their sandwich structure constructed by the plane of the crown and the plane of the anthryl group.

Dependency of cardiac rubidium-82 imaging quantitative measures on age, gender, vascular territory, and software in a cardiovascular normal population.

OBJECTIVES: Recent technological improvements to PET imaging equipment combined with the availability of software optimized to calculate regional myocardial blood flow (MBF) and myocardial flow reserve (MFR) create a paradigm shifting opportunity to provide new clinically relevant quantitative information to cardiologists. However, clinical interpretation of the MBF and MFR is entirely dependent upon knowledge of MBF and MFR values in normal populations and subpopulations. This work reports Rb-82-based MBF and MFR measurements for a series of 49 verified cardiovascularly normal subjects as a preliminary baseline for future clinical studies. METHODS: Forty-nine subjects (24F/25M, ages 41-69) with low probability for coronary artery disease and with normal exercise stress test were included. These subjects underwent rest/dipyridamole stress Rb-82 myocardial perfusion imaging using standard clinical techniques (40 mCi injection, 6-minute acquisition) using a Siemens Biograph 40 PET/CT scanner with high count rate detector option. List mode data was rehistogrammed into 26 dynamic frames (12 × 5 seconds, 6 × 10 seconds, 4 × 20 seconds, 4 × 40 seconds). Cardiac images were processed, and MBF and MFR calculated using Siemens syngo MBF, PMOD, and FlowQuant software using a single compartment Rb-82 model. RESULTS: Global myocardial blood flow under pharmacological stress for the 24 females as measured by PMOD, syngo MBF, and FlowQuant were 3.10 ± 0.72, 2.80 ± 0.66, and 2.60 ± 0.63 mL·minute(-1)·g(-1), and for the 25 males was 2.60 ± 0.84, 2.33 ± 0.75, 2.15 ± 0.62 mL·minute(-1)·g(-1), respectively. Rest flows for PMOD, syngo MBF, and FlowQuant averaged 1.32 ± 0.42, 1.20 ± 0.33, and 1.06 ± 0.38 mL·minute(-1)·g(-1) for the female subjects, and 1.12 ± 0.29, 0.90 ± 0.26, and 0.85 ± 0.24 mL·minute(-1)·g(-1) for the males. Myocardial flow reserves for PMOD, syngo MBF, and FlowQuant for the female normals were calculated to be 2.50 ± 0.80, 2.53 ± 0.67, 2.71 ± 0.90, and 2.50 ± 1.19, 2.85 ± 1.19, 2.94 ± 1.31 mL·minute(-1)·g(-1) for males. CONCLUSION: Quantitative normal MBF and MFR values averaged for age and sex have been compiled for three commercial pharmacokinetic software packages. The current collection of data consisting of 49 subjects resulted in several statistically significant conclusions that support the need for a software specific, age, and sex-matched database to aid in interpretation of quantitative clinical myocardial perfusion studies.

Iso-selective ring-opening polymerization of rac-lactide catalyzed by crown ether complexes of sodium and potassium naphthalenolates.

Two crown ether complexes of sodium and potassium naphthalenolates were synthesized and entirely characterized. The two complexes can iso-selectively catalyze the ring-opening polymerization (ROP) of rac-lactide at room temperature and afford polylactides with desired molecular weights and narrow PDIs; the best isotacticity (Pm) achieved was 0.73.

Stepwise Reduction of 9,10-Bis(dimesitylboryl)anthracene.

Stepwise reduction of 9,10-bis(dimesitylboryl)anthracene afforded an radical anion and a dianion, accompanied by stepwise changes of the aromaticity of the anthracene moiety. The radical has a planar semiquinoidal structure, while the dianion has a puckered quinoidal structure. The alteration of the geometries of the 9,10-bis(dimesitylboryl)anthracene upon reduction is rationalized by the nature of the bonding. These results have been confirmed by cyclic voltammetry, X-ray crystallography, NMR, EPR, and UV-vis-NIR spectroscopy, as well as DFT calculations.

A crystalline phosphaalkene radical anion.

Salts containing phosphaalkene radical anions have been isolated and characterized by electron paramagnetic resonance (EPR) spectroscopy, UV-vis absorption spectroscopy, and single-crystal X-ray diffraction. The radical anions feature elongated P-C bonds and an aromatization of fulvene compared to the neutral phosphaalkene. Their EPR spectra and theoretical calculations indicate the spin density of the radicals mainly resides on phosphorus atoms. This work provides the first example of a crystalline phosphaalkene radical anion.