Sb‐Triggered β‐to‐α Transition: Solvothermal Synthesis of Metastable α‐Cu2Se

Control over phase stabilities during synthesis processes is of great importance for both fundamental studies and practical applications. We describe herein a facile strategy for the synthesis of Cu₂Se with phase selectivity through a simple solvothermal method. In the presence and absence of SbCl₃, monoclinic α‐Cu₂Se and cubic β‐Cu₂Se can be synthesized, respectively. The formation of α‐Cu₂Se requires optimization of the Cu/Se molar ratio in the starting reagents, the reaction temperature, as well as the timing for the addition of SbCl₃. Differential scanning calorimetry of the synthesized α‐Cu₂Se has shown that a part of it undergoes a phase transition to β‐Cu₂Se at 135 °C, and that this phase transition is irreversible on cooling to ambient temperature. Kinetic studies have revealed that in the presence of Sb species the kinetically favored β‐Cu₂Se transforms to the thermodynamically favored α‐Cu₂Se. In this β‐to‐α phase transition process, the distribution of Cu ions in β‐Cu₂Se, as determined by the Cu/Se ratio and temperature, is likely to play a crucial role.     

Achieving High‐Temperature Stability of Metastable α‐MoC1‐x by Suppressing Phase Transformation with Mounted Atoms for Lithium Storage Performance

Despite a significant advancement in preparing metastable materials, one common problem is the strict and precious reaction conditions due to their metastable structures. Herein, we achieved the preparation of high‐temperature stabilized metastable α‐MoC_1?x by mounting zinc atoms into its lattice structure. Such a structural construction could suppress the phase transformation from α‐MoC_1?x to β‐Mo₂C through restricting the displacement of Mo atoms upon increased temperature. The resultant metastable α‐MoC_1?x can be stabilized up to 1000 °C and this stability temperature is the highest for the metastable α‐MoC_1?x so far. Synchrotron X‐ray absorption spectroscopy (XAS) and X‐ray photoelectron spectroscopy (XPS) confirm the structure of Zn‐mounted α‐MoC_1?x. Density functional theory (DFT) calculations reveal that the introduction of the Zn atoms in the lattice structure of α‐MoC_1?x could significantly decrease the energy difference (ΔE) between α‐MoC_1?x and β‐Mo₂C, thus effectively suppressing the phase transformation from α‐MoC_1?x to β‐Mo₂C and accordingly maintaining the high‐temperature stability of α‐MoC_1?x. This novel strategy can be used as a universal method to be extended to synthesize metastable α‐MoC_1?x from different precursors or other mounted elements. Moreover, the optimal product exhibits excellent lithium storage performances in terms of the cycling stability and rate performance.     

An interaction potential to study the thermal structure evolution of a thermoelectric material: β‐Cu2Se

An interaction potential model has been developed, for the first time, for β‐Cu₂Se using the ab initio derived data. The structure and elastic constants of β‐Cu₂Se using the derived force‐field are within a few percent of DFT derived structure and elastic constants and reported experimental structure. The derived force‐field also shows remarkable ability to reproduce temperature dependent behavior of the specific heat and thermal expansion coefficient. The thermal structure evolution of the β‐Cu₂Se is studied by performing the molecular dynamic simulations using the derived force‐field. The simulation results demonstrate that the Cu ions moves around the equilibrium lattice position within the temperature range of 500–800 K. However, at a temperature > 800 K, the Cu ions starts diffusing within the material, while the Se ions remains in their lattice position. The evaluated thermodynamic properties such as free energy and excess entropy, show that the increased Cu–Se interaction with the temperature makes the system more thermodynamically stable. © 2017 Wiley Periodicals, Inc.     

Enantioselective Synthesis of α‐Hydroxy Amides and β‐Amino Alcohols from α‐Keto Amides

Synthesis of enantiomerically enriched α‐hydroxy amides and β‐amino alcohols has been accomplished by enantioselective reduction of α‐keto amides with hydrosilanes. A series of α‐keto amides were reduced in the presence of chiral Cu^II/(S)‐DTBM‐SEGPHOS catalyst to give the corresponding optically active α‐hydroxy amides with excellent enantioselectivities by using (EtO)₃SiH as a reducing agent. Furthermore, a one‐pot complete reduction of both ketone and amide groups of α‐keto amides has been achieved using the same chiral copper catalyst followed by tetra‐n‐butylammonium fluoride (TBAF) catalyst in presence of (EtO)₃SiH to afford the corresponding chiral β‐amino alcohol derivatives.     

Quantum mechanical studies on model α‐pleated sheets

Pauling and Corey proposed a pleated‐sheet configuration, now called α‐sheet, as one of the protein secondary structures in addition to α‐helix and β‐sheet. Recently, it has been suggested that α‐sheet is a common feature of amyloidogenic intermediates. We have investigated the stability of antiparallel β‐sheet and two conformations of α‐sheet in solution phase using the density functional theoretical method. The peptides are modeled as two‐strand acetyl‐(Ala)₂‐N‐methylamine. Using stages of geometry optimization and single point energy calculation at B3LYP/cc‐pVTZ//B3LYP/6‐31G* level and including zero‐point energies, thermal, and entropic contribution, we have found that β‐sheet is the most stable conformation, while the α‐sheet proposed by Pauling and Corey has 13.6 kcal/mol higher free energy than the β‐sheet. The α‐sheet that resembles the structure observed in molecular dynamics simulations of amyloidogenic proteins at low pH becomes distorted after stages of geometry optimization in solution. Whether the α‐sheets with longer chains would be increasingly favorable in water relative to the increase in internal energy of the chain needs further investigation. Different from the quantum mechanics results, AMBER parm94 force field gives small difference in solution phase energy between α‐sheet and β‐sheet. The predicted amide I IR spectra of α‐sheet shows the main band at higher frequency than β‐sheet. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Hydrothermal Synthesis and Properties of Controlled α‐Fe2O3 Nanostructures in HEPES Solution

A facile, template‐free, and environmentally friendly hydrothermal strategy was explored for the controllable synthesis of α‐Fe₂O₃ nanostructures in HEPES solution (HEPES=2‐[4‐(2‐hydroxyethyl)‐1‐piperazinyl]ethanesulfonic acid). The effects of experimental parameters including HEPES/FeCl₃ molar ratio, pH value, reaction temperature, and reaction time on the formation of α‐Fe₂O₃ nanostructures have been investigated systematically. Based on the observations of the products, the function of HEPES in the reaction is discussed. The different α‐Fe₂O₃ nanostructures possess different optical, magnetic properties, and photocatalytic activities, depending on the shape and size of the sample. In addition, a novel and facile approach was developed for the synthesis of Au/α‐Fe₂O₃ and Ag/α‐Fe₂O₃ nanocomposites in HEPES buffer solution; this verified the dual function of HEPES both as reductant and stabilizer. This work provides a new strategy for the controllable synthesis of transition metal oxide nanostructures and metal‐supported nanocomposites, and gives a strong evidence of the relationship between the property and morphology/size of nanomaterials.     

Silica‐Protection‐Assisted Encapsulation of Cu2O Nanocubes into a Metal–Organic Framework (ZIF‐8) To Provide a Composite Catalyst

The integration of metal/metal oxide nanoparticles (NPs) into metal–organic frameworks (MOFs) to form composite materials has attracted great interest due to the broad range of applications. However, to date, it has not been possible to encapsulate metastable NPs with high catalytic activity into MOFs, due to their instability during the preparation process. For the first time, we have successfully developed a template protection–sacrifice (TPS) method to encapsulate metastable NPs such as Cu₂O into MOFs. SiO₂ was used as both a protective shell for Cu₂O nanocubes and a sacrificial template for forming a yolk–shell structure. The obtained Cu₂O@ZIF‐8 composite exhibits excellent cycle stability in the catalytic hydrogenation of 4‐nitrophenol with high activity. This is the first report of a Cu₂O@MOF‐type composite material. The TPS method provides an efficient strategy for encapsulating unstable active metal/metal oxide NPs into MOFs or maybe other porous materials.     

Completely Green Synthesis of Colloid Adams’ Catalyst α‐PtO2 Nanocrystals and Derivative Pt Nanocrystals with High Activity and Stability for Oxygen Reduction

We report a first solution strategy for controlled synthesis of Adams’ catalyst (i.e., α‐PtO₂) by a facile and totally green approach using H₂PtCl₆ and water as reactants. The prepared α‐PtO₂ nanocrystals (NCs) are ultrasmall in size and have very “clean” surfaces, which can be reduced to Pt NCs easily in ethanol under ambient conditions. Such Adams’ catalysts have been applied as electrocatalysts beyond the field of heterogeneous catalysis. Noticeably, the water‐only synthesized α‐PtO₂ NCs and their derivative Pt NCs all exhibit much higher oxygen reduction reaction (ORR) activities and stabilities than that of the state‐of‐art Pt/C electrocatalysts. This study provides an example on the organics‐free synthesis of α‐PtO₂ and Pt NCs as promising cathode catalysts for fuel cell applications and, particularly, this simple, straightforward method may open a new way for the synthesis of other “clean” functional nanomaterials.     

A facile synthetic strategy for hyperbranched polymer via combining free radical telomerization and polycondensation

A facile strategy combining free radical telomerization and polycondensation to prepare hyperbranched polymers was developed. By selecting a suitable telogen and a vinyl monomer, the product obtained by telomerization could be regarded as an AB_n type monomer for preparing a hyperbranched polymer via conventional polycondensation. The principles for selecting vinyl monomers and telogens were proposed. The feed ratio of vinyl monomer to telogen was discussed in the theory. For demonstrating the strategy, methyl (meth)acrylate (MA or MMA) and 2‐mercaptoethanol were used as a vinyl monomer and a telogen, respectively. The two‐unit adduct of MA or MMA obtained after purifying was regarded as a model ABB′ monomer. The sequential transesterification demonstrated that the carboxylate group at the terminal unit has higher reactivity than that at penultimate unit because of the different substituents at the respective α‐positions, resulting in lower degree of branching (DB) of obtained polymer. As substitutes, 2‐hydroxyethyl (meth)acrylate and thioglycolic acid were used as a vinyl monomer and a telogen, respectively. The results showed that the hyperbranched polymer obtained by using pseudo one‐pot approach had moderate DB. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7543–7555, 2008     

Cyclodextrin‐overhanging hyperbranched core‐double‐shell miktoarm architectures: Synthesis and gradient stimuli‐responsive properties

We report the synthesis and gradient stimuli‐responsive properties of cyclodextrin‐overhanging hyperbranched core‐double‐shell miktoarm architectures. A ionic hyperbranched poly(β‐cyclodextrin) (β‐CD) core was firstly synthesized via a convenient “A₂+B₃” approach. Double‐layered shell architectures, composed of poly(N‐isopropyl acrylamide) (PNIPAm) and poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) miktoarms as the outermost shell linked to poly(N,N‐diethylaminoethyl methacrylate) (PDEAEMA) homoarms which form the inner shell, were obtained by a sequential atom transfer radical polymerization (ATRP) and parallel click chemistry from the modified hyperbranched poly(β‐CD) macroinitiator. The combined characterization by ¹H NMR, ¹³C NMR, ¹H‐²⁹Si heteronuclear multiple‐bond correlation (HMBC), FTIR and size exclusion chromatography/multiangle laser light scattering (SEC/MALLS) confirms the remarkable hyperbranched poly(β‐CD) core and double‐shell miktoarm architectures. The gradient triple‐stimuli‐responsive properties of hyperbranched core‐double‐shell miktoarm architectures and the corresponding mechanisms were investigated by UV–vis spectrophotometer and dynamic light scattering (DLS). Results show that this polymer possesses three‐stage phase transition behaviors. The first‐stage phase transition comes from the deprotonation of PDEAEMA segments at pH 9–10 aqueous solution under room temperature. The confined coil‐globule conformation transition of PNIPAm and PDMAEMA arms gives rise to the second‐stage hysteretic cophase transition between 38 and 44 °C at pH 10. The third‐stage phase transition occurs above 44 °C at pH = 10 attributed to the confined secondary conformation transition of partial PDMAEMA segments. This cyclodextrin‐overhanging hyperbranched core‐double‐shell miktoarm architectures are expected to solve the problems of inadequate functionalities from core layer and lacking multiresponsiveness for shell layers existing in the dendritic core‐multishell architectures. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Two‐Dimensional CuSe Nanosheets with Microscale Lateral Size: Synthesis and Template‐Assisted Phase Transformation

Semiconducting nanosheets with microscale lateral size are attractive building blocks for the fabrication of electronic and optoelectronic devices. The phase‐controlled chemical synthesis of semiconducting nanosheets is of particular interest, because their intriguing properties are not only related to their size and shape, but also phase‐dependent. Herein, a facile method for the synthesis of phase‐pure, microsized, two‐dimensional (2D) CuSe nanosheets with an average thickness of approximately 5 nm is demonstrated. These hexagonal‐phased CuSe nanosheets were transformed into cubic‐phased Cu_2?xSe nanosheets with the same morphology simply by treatment with heat in the presence of Cu^I cations. The phase transformation, proposed to be a template‐assisted process, can be extended to other systems, such as CuS and Cu_1.97S nanoplates. Our study offers a new method for the phase‐controlled preparation of 2D nanomaterials, which are not readily accessible by conventional wet‐chemical methods.     

Palladium‐Catalyzed Aerobic Intermolecular Cyclization of Acrylic Acid with 1‐Octene to Afford α‐Methylene‐γ‐butyrolactones: The Remarkable Effect of Continuous Water Removal from the Reaction Mixture and Analysis of the Reaction by Kinetic,ESI‐MS,and XAFS Measurements

Further study of our aerobic intermolecular cyclization of acrylic acid with 1‐octene to afford α‐methylene‐γ‐butyrolactones, catalyzed by the Pd(OCOCF₃)₂/Cu(OAc)₂ ? H₂O system, has clarified that the accumulation of water generated from oxygen during the reaction causes deactivation of the Cu cocatalyst. This prevents regeneration of the active Pd catalyst and, thus, has a harmful influence on the progress of the cyclization. As a result, both the substrate conversion and product yield are efficiently improved by continuous removal of water from the reaction mixture. Detailed analysis of the kinetic and spectroscopic measurements performed under the condition of continuous water removal demonstrates that the cyclization proceeds in four steps: 1) equilibrium coordination of 1‐octene to the Pd acrylate species, 2) Markovnikov‐type acryloxy palladation of 1‐octene (1,2‐addition), 3) intramolecular carbopalladation, and 4) β‐hydride elimination. Byproduct 2‐acryloxy‐1‐octene is formed by β‐hydride elimination after step 2). These cyclization steps fit the Michaelis–Menten equation well and β‐hydride elimination is considered to be a rate‐limiting step in the formation of the products. Spectroscopic data agree sufficiently with the existence of the intermediates bearing acrylate (Pd? O bond), η³‐C₈H₁₅ (Pd? C bond), or C₁₁H₁₉O₂ (Pd? C bond) moieties on the Pd center as the resting‐state compounds. Furthermore, not only Cu^II, but also Cu^I, species are observed during the reaction time of 2–8 h when the reaction proceeds efficiently. This result suggests that the Cu^II species is partially reduced to the Cu^I species when the active Pd catalytic species are regenerated.     

Lithiation of Copper Selenide Nanocrystals

The search for ion‐conductive solid electrolytes for Li⁺ batteries is an important scientific and technological challenge with economic and sustainable energy implications. In this study, nanocrystals (NCs) of the ion conductor copper selenide (Cu_2?ySe) were doped with Li by the process of cation exchange. Li_2xCu_2?2xSe alloy NCs were formed at intermediate stages of the reaction, which was followed by phase segregation into Li₂Se and Cu₂Se domains. Li‐doped Cu_2?ySe NCs and Li₂Se NCs exhibit a possible SI phase at moderately elevated temperatures and warrant further ion‐conductance tests. These findings may guide the design of nanostructured super‐ionic electrolytes for Li⁺ transport.     

Light‐Induced Chiral Iron Copper Selenide Nanoparticles Prevent β‐Amyloidopathy In Vivo

The accumulation and deposition of β‐amyloid (Aβ) plaques in the brain is considered a potential pathogenic mechanism underlying Alzheimer's disease (AD). Chiral l/d ‐Fe_xCu_ySe nanoparticles (NPs) were fabricated that interfer with the self‐assembly of Aβ42 monomers and trigger the Aβ42 fibrils in dense structures to become looser monomers under 808 nm near‐infrared (NIR) illumination. d ‐Fe_xCu_ySe NPs have a much higher affinity for Aβ42 fibrils than l ‐Fe_xCu_ySe NPs and chiral Cu_2?xSe NPs. The chiral Fe_xCu_ySe NPs also generate more reactive oxygen species (ROS) than chiral Cu_2?xSe NPs under NIR‐light irradiation. In living MN9D cells, d ‐NPs attenuate the adhesion of Aβ42 to membranes and neuron loss after NIR treatment within 10 min without the photothermal effect. In‐vivo experiments showed that d ‐Fe_xCu_ySe NPs provide an efficient protection against neuronal damage induced by the deposition of Aβ42 and alleviate symptoms in a mouse model of AD, leading to the recovery of cognitive competence.     

Sulfonamide‐Promoted Palladium(II)‐Catalyzed Alkylation of Unactivated Methylene C(sp3)?H Bonds with Alkyl Iodides

The alkylation of unactivated β‐methylene C(sp³) H bonds of α‐amino acid substrates with a broad range of alkyl iodides using Pd(OAc)₂ as the catalyst is described. The addition of NaOCN and 4‐Cl‐C₆H₄SO₂NH₂ was found to be crucial for the success of this transformation. The reaction is compatible with a diverse array of functional groups and proceeds with high diastereoselectivity. Furthermore, various β,β‐hetero‐dialkyl‐ and β‐alkyl‐β‐aryl‐α‐amino acids were prepared by sequential C(sp³) H functionalization of an alanine‐derived substrate, thus providing a versatile strategy for the stereoselective synthesis of unnatural β‐disubstituted α‐amino acids.     

Sulfonamide‐Promoted Palladium(II)‐Catalyzed Alkylation of Unactivated Methylene C(sp3)H Bonds with Alkyl Iodides

The alkylation of unactivated β‐methylene C(sp³)? H bonds of α‐amino acid substrates with a broad range of alkyl iodides using Pd(OAc)₂ as the catalyst is described. The addition of NaOCN and 4‐Cl‐C₆H₄SO₂NH₂ was found to be crucial for the success of this transformation. The reaction is compatible with a diverse array of functional groups and proceeds with high diastereoselectivity. Furthermore, various β,β‐hetero‐dialkyl‐ and β‐alkyl‐β‐aryl‐α‐amino acids were prepared by sequential C(sp³)? H functionalization of an alanine‐derived substrate, thus providing a versatile strategy for the stereoselective synthesis of unnatural β‐disubstituted α‐amino acids.     

One‐Pot Halogen Dance/Negishi Coupling of Dibromothiophenes for Regiocontrolled Synthesis of Multiply Arylated Thiophenes

One‐pot halogen dance/Negishi cross‐coupling of readily available 2,5‐dibromothiophenes is described. A lithium diisopropylamide (LDA)‐mediated halogen dance reaction resulted in the formation of thermodynamically stable α‐lithiodibromothiophenes, which were transmetalated with ZnCl₂ and subjected to Negishi cross‐coupling to provide the corresponding arylated dibromothiophenes in one pot. The resultant β‐bromo group was much less reactive than the remaining α‐bromo group, which was used in a one‐pot double Suzuki–Miyaura cross‐coupling, enabling facile synthesis of multiply arylated thiophenes.     

Facile Fabrication of Near‐Infrared‐Responsive and Chitosan‐Functionalized Cu2Se Nanoparticles for Cancer Photothermal Therapy

Photothermal therapy has attracted much interest for use in cancer treatment in recent years. In this study, Cu₂Se nanoparticles as a novel photothermal agent modified by chitosan (CS‐Cu₂SeNPs) were successfully synthesized through a facile route at room temperature. The as‐synthesized CS‐Cu₂SeNPs exhibited good water solubility and significant stability. CS‐Cu₂SeNPs can efficiently convert near‐infrared (NIR) light into heat and exhibit excellent thermostability. In vitro experiments showed that CS‐Cu₂SeNPs had selective cellular uptake between cancer and normal cells and expressed clear anticancer activity on A375 and HeLa human cancer cells. In addition, the anticancer activity was increased to about 400 % by combination with a laser at 808 nm, which acted through induction of apoptosis with the involvement of intrinsic and extrinsic pathways. CS‐Cu₂SeNPs irradiated with a laser effectively triggered the intracellular reactive oxygen species (ROS) overproduction that promoted cell apoptosis. Therefore, the developed CS‐Cu₂SeNPs could be used as a novel phototherapeutic agent for the photothermal therapy of human cancers.     

A New Class of Tunable Dendritic Diphosphine Ligands: Synthesis and Applications in the Ru‐Catalyzed Asymmetric Hydrogenation of Functionalized Ketones

A series of tunable G₀–G₃ dendritic 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (BINAP) ligands was prepared by attaching polyaryl ether dendrons onto the four phenyl rings on the P atoms. Their ruthenium complexes were employed in the asymmetric hydrogenation of β‐ketoesters, α‐ketoesters, and α‐ketoamides to reveal the effects of dendron size on the catalytic properties. The second‐ and third‐generation catalysts exhibited excellent enantioselectivities, which are remarkably higher than those obtained from the small molecular catalysts and the first‐generation catalyst. Molecular modeling indicates that the incorporation of bulky dendritic wedges can influence the steric environments around the metal center. In addition, the ruthenium catalyst bearing a second‐generation dendritic ligand could be recycled and reused seven times without any obvious decrease in enantioselectivity.     

Regioselective Monoacetylation of Methyl Pyranosides of Pentoses and 6‐Deoxyhexoses by Acetic Anhydride in the Presence of MoCl5

Convenient regioselective syntheses of 3‐acetates of methyl pyranosides of α‐L‐rhamnose, α‐ and β‐L‐arabinose, α‐D‐fucose, α‐D‐lyxose, and β‐D‐ribose with good yields have been attained using MoCl₅ as catalyst. Methyl β‐L‐rhamnopyranoside under this conditions gave 2‐acetate.