We report the comparative studies of Me₂(CH₂Cl) SiCN and Me₃SiCN in the catalytic enantioselective cyanation reactions of aldehydes,which were catalyzed by the merger of 5 mol% Jacobsen's catalyst (salen) AlCl (R,R)-1 and 6 mol% ylide 2a,and are conducted at -50℃ using i-Pr2O as the solvent.This was based on our recent finding that (R,R)-1 could be effectively activated by ylide to form an enhanced chiral Lewis acid.Generally,the use of Me₂(CH₂Cl) SiCN as the cyanating reagent afforded obviously higher activity in the reaction of all the aldehydes we examined,along with by-and-large similar enantioselectivity.This further suggested that Me₂(CH₂Cl) SiCN might be useful cyanating reagent to develop reaction involving the use of less active substrates.Under the indicated condition,aromatic aldehydes worked well to give the desired adducts in up to 99% yield and 94% ee,but the reactions of vinyl aldehydes and aliphatic aldehydes were not successful.All the reactions were performed by the following general procedure.To a 4 mL vial were successively added complex (R,R)-1(30.3 mg,0.05 mmol),ylide 2a (22.6 mg,0.06 mmol) and i-Pr₂O (1.0 mL).The resulting solution was stirred at -50℃ for 0.5 h before the addition of aldehydes (1.0 mmol) and the cyanating reagent,Me₂(CH₂Cl) SiCN or Me₃SiCN (250 μL,2.0 mmol).After TLC analysis indicated the full consumption of the aldehydes,the reaction mixture was filtrated with a pad of silica gel and eluted with Et₂O.The filtrate is concentrated under reduced pressure to give a crude residue for column chromatography purification.In contrast,when Me₂(CH₂Cl) SiCN is used,both cyanohydrins and its silyl ethers were obtained,so a further deprotection by p-TsOH is adopted to obtain free cyanohydrins as the only product.

Using transmission electron microscopy (TEM) to directly observe a dynamic chemical reaction process in liquid-phase environment is a big challenge because it is difficult to keep liquid reactants under vacuum.In this work,we reported a liquid-based cell that enables in-situ observation of a solution reaction process under TEM.The novel liquid cell design not only realizes the self-alignment of top/bottom windows,but also achieves an adjustable liquid layer thickness down to nanometer scale.The cell consists of top and bottom frames,both of which are fabricated from silicon wafers using conventional micro-fabrication techniques.The transparent observation windows are made of silicon nitride (SiNx) membranes.In a typical assembling process,an ethanol solution containing silver nanowires and an ethanol solution containing saturated sulfur were sequentially dropped into the liquid tank of the bottom-frame of a liquid cell by using 1 mL syringe.Then,the liquid tank was covered by the top-frame with a window direction of 90 degrees,and an epoxy was used to seal the edge between the top-frame and bottom-frame.Using this assembled liquid cell,we performed in-situ TEM observation of the chemical reaction between Ag nanowires and sulfur in ethanol solution.Additional ex-situ X-ray diffraction (XRD) and Raman spectroscopy were also performed to study the reaction intermediates and final products.Instead of a simple reaction process in which sulfur diffuses into Ag to form the final product of Ag₂S,we found that the real reaction process involves the formation of a soluble intermediate phase (Ag₂S₄),which led to a partial dissolution of Ag nanowires in ethanol solution during reaction.These results well demonstrate that the in-situ TEM technique is a powerful tool to reveal the "real" chemical reaction mechanism.The experimental technique developed here could also be used to study a broad range of dynamic phenomena in liquid environment.

Metal-organic frameworks (MOFs) are synthesized via the self-assembling combination of organic ligands and inorganic metals or metal-oxo units (secondary building units,SBUs) using strong bonds to form a porous open crystalline.Because of their outstanding thermal stability,chemical stability and designability,MOFs are successfully applied in various fields,such as gas absorption,separation,purification,catalysis,as well as templates for various functional materials.MOFs are also used as column materials for gas or liquid chromatography separation.In this paper,the studies about MOFs used as stationary phases in gas chromatography and high-performance liquid chromatography were reviewed according to the separated various analytes.We summarized the separation effects of different MOFs for different substances,especially focusing on the separation mechanism of MOFs.The key influence factors on the chromatographic separation,such as pore diameter,functional groups and unsaturated metal sites of MOFs,were expounded.Then,the challenges of MOFs as stationary phases in gas and high-performance liquid chromatography were discussed,which include the mechanism,chiral separation,the limited MOFs in chromatographic separation.The future research in this field should focus on defining separation mechanism,improving their stability and synthesizing the MOFs with special function.

Extensive density functional theoretical (DFT) and ab initio[CCSD (T)]calculations were combined to investigate the geometric and electronic structure of a series of dinuclear hafnium oxide clusters,Hf₂O_n^-/0(n=1~6).DFT calculations were performed to search for the lowest energy structures for both the anionic clusters and the neutral counterparts.The search for the global minima was performed using analytical gradients with the Stuttgart relativistic small core potential and the valence basis sets augmented with two f-type and one g-type polarization functions for Hf and the aug-cc-pVTZ basis set for oxygen.The relative energies of the low-lying structures (within ca.0.35 eV) were further evaluated via single-point calculations at the coupled cluster[CCSD (T)]level with the Hf/Stuttgart+2f1g/O/aug-cc-pVTZ basis sets at the B3LYP geometries.Generalized Koopmans' theorem (GKT) was applied to predict VDEs and simulate the anion photoelectron spectra (PES).The trends of structural evolution and the behavior of sequential oxidation of the Hf₂O_n^-(n=1~6) clusters were observed.For the anionic species,starting from the C_2v triangular structure Hf₂O^-,the next O atom in the Hf₂O₂^- cluster was again bridge-bonded,forming a rhombus structure.The third O atom occupied the terminal site.The fourth O atom favored the bridging site and the fifth O atom occupied the terminal site.In Hf₂O₆^-,the additional O atom was bonded to a terminal site.Molecular orbital analyses were performed to elucidate the chemical bonding and the structural evolution in Hf₂O_n^-(n=1~4) clusters.Spin density analyses revealed oxygen radical,diradical and superoxide characters in the oxygen-rich clusters,except for the singlet Hf₂O₅ cluster.We showed that Hf₂O₃ contains a localized Hf²⁺ site,which can readily react with O₂ to form the Hf₂O₅ cluster.The Hf₂O₆^- and Hf₂O₆ clusters,which can be viewed to be formed by the interaction of Hf₂O₄^-/0 and O₂,may be utilized as molecular models to understand dioxygen activation on Hf₂O₄^- and Hf₂O₄ clusters.

In recent years,photodynamic therapy (PDT) technology,as a noninvasive method of treating malignant tumors and age-related macular degeneration,which is different from the traditional cancer treatments,has drawn more and more attention of scientists.PDT treatment relies on the combination of photosensitizer,oxygen and light,when the photosensitizer is irradiated by special light,it can generate singlet oxygen,which is a cytotoxic agent can eradicate tumors via vasculature damage and cell damage,and sometimes the response of immune system.Due to its special advantages,i.e small traumatic,low toxicity,good compatibility,collaborative surgical treatment and repeatable treatment etc.,PDT is widely used in many kinds of tumor treatments.Current practice of photodynamic therapy is limited to a few functionalized photosensitizers,for example porphyrins,however these compounds has several disadvantageous properties such as low absorption in the tissue transparency window (650~900 nm),prolonged skin photosensitivity,and slow clearance rate from body.This has inspired efforts to develop more effective PDT photosensitizers with improved photophysical characteristics and special targeting advantages.So in this review,the authors briefly outline the theories of PDT as well as the development process of photosensitizer,and summarize the characteristics of ideal photosensitizer.At present,the third generation photosensitizers mainly based on phthalocyanines have become a research highlight in PDT.However,how to improve the targeting of photosensitizer so as to achieve precise photodynamic efficiency is still an urgent problem to be solved.Therefore,this review mainly summarizes the recent research on phthalocyanine based targeting photosensitizers.In addition,the development of key research directions in the future has also been pointed out.According to the present researches,in the aspects of PDT,overcoming the limitation of cancer hypoxic microenvironment,developing Type I independently from oxygen,and penetrating more deeply targeting photosensitizers possess enormous potential,and they may become a kind of photosensitizer with excellent performance in the field of photodynamic therapy.

Herein,we reported the synthesis and self-assembly of a novel temperature-responsive polyamide.The temperature-responsive polyamides (APA) was synthesized by forming-salts and solution-melt polycondensation based on the hexanedioic acid and temperature-responsive poly (propylene glycol) bis (2-aminopropyl ether).The polyamide structures of as-prepared polyamides were ascertained by Fourier transform infrared spectroscopy (FT-IR) measurement.And the gel permeation chromatography (GPC) curve showed that the as-prepared temperature-responsive polyamide possessed a distribution with a number-average molecular weight of 17800 Da and a polydispersity of 2.91.The micro differential scanning calorimetry (Micro-DSC) and UV results showed that the APA possessed a LCST of 33℃.Then a direct hydration method was used to induce the self-assembly of APA by putting polymers into deionized water with a concentration of 1.0 mg/mL at room temperature.On the other hand,we also prepared the other self-assemblies through the same direct hydration method while the temperature is at 60℃,which is beyond the LCST of as-prepared APA.The transmission electron microscope (TEM) images ascertained that the as-prepared APA should self-assemble into normal fibers at room temperature (c=1.0 mg/mL).And the formation of these long fibers are attributed to the aggregation and fusion of the primary polyamide micelles.However,very interesting,when the temperature was increased to 60℃,the atomic force microscope (AFM) and TEM results showed that the original fibers have transformed into helical fibers with more than 5 μm length.And the average helix pitch was about 35 nm.This fascinating morphology transformation should be attributed to the solubility change of PPG segments in APA fibers.When the temperature was increased to 60℃ beyond the LCST of APA,the solubility of PPG segments would decrease,and the PPG segments would also collapse.And what's more,due to an alternating hydrophilic/hydrophobic structure of APA,and the PPG segments on the surface of the APA fibers should twist.Finally,the helical APA fibers have been obtained.The present work represents a new progress for macromolecular self-assembly.

The perovskite-type NaNbO₃ were prepared through a solvothermal process under a moderate condition followed by calcinations at high temperature.The Fe³⁺-doping inside the NaNbO₃ lattice and the heterojunctions between α-Fe₂O₃ and NaNbO₃ were acquired synchronously in a similar process by treating NaNbO₃ with ferric nitrates.The photocatalytic activity of catalysts was evaluated from the photodegradation of Rhodamine B (RhB) in aqueous solution under UV light irradiation and the significant enhancement of degradation rate of aqueous RhB on modified NaNbO₃ was observed,with the degradation ratio of RhB reached as high as 95% within 1 h,and the quasi-first-grade rate constant of the RhB degradation reaction over the modified NaNbO₃ reached almost 7 times of the pristine one under the experimental conditions.Characterizations by X-ray diffraction (XRD),scanning electron microscopy (SEM),X-ray photoelectron spectroscopy (XPS),UV-vis diffuse reflectance spectrophotometry (DRS),adsorption-desorption of N₂ at low temperature (BET calculation),photoluminescence spectroscopy (PL),electron spin resonance spectroscopy (ESR) and photocurrent measurement were performed.The compositions and structures of the as-prepared raw and modified catalysts were carefully identified.It is found that the optimal mass fraction of Fe in modified catalysts is around 2.5%,with about 30% of it exists as Fe³⁺ inside the lattice of NaNbO₃ and the remainder as α-Fe₂O₃ outside the NaNbO₃ lattice.The results of characterizations or measurements suggest that a moderate Nb⁵⁺ in NaNbO₃ can be substituted by Fe³⁺ while the perovskite-type structure of NaNbO₃ remains unchanging.The moderate Fe-doping into the lattice of NaNbO₃ improved the photocatalytic performance of NaNbO₃ by the donor level of impurities,charge capturing and adsorption of dissolved oxygen.A fitting amount of α-Fe₂O₃ cooperates harmoniously with NaNbO₃ in degradation of RhB by enhancing the light quantum efficiency through the migration and jumping of electrons or holes between α-Fe₂O₃ and NaNbO₃.It is proposed that the modification (i) promotes the excitation of photocatalysts indicated by an improved light adsorption of modified catalysts on DRS,(ii) suppresses the recombination of photogenerated charge carriers revealed by PL spectra,and (iii) promotes the charge transfer founded by photocurrent measurements.

Formamidinium lead halide perovskite FAPbI₃(FA=HC(NH₂)₂⁺) has drawn wide attention as efficient photoelectronic conversion material.First-principles calculations were performed by using the Vienna ab initio simulation package (VASP) based on density functional theory.The structure configuration,electronic property,absorption spectrum,and bonding energy were analyzed to elucidate the structural and photoelectronic properties of trigonal and hexagonal FAPbI₃ perovskites.Results showed that the crystal deformation from trigonal to hexagonal crystal would distort the PbI₃ framework,change the covalent/ionic Pb-I bonds,and eventually alter the semiconductor bandgaps.The trigonal and hexagonal FAPbI₃ perovskites are both direct-bandgap semiconductors.The direct-bandgap nature of trigonal crystal locates at Z (0,0,0.5) symmetry point with the ideal bandgap of ca.1.50 eV;the direct-bandgap nature of hexagonal crystal locates at Γ(0,0,0) symmetry point with the wide bandgap of ca.2.50 eV.For the both crystals,the main contributions to VBM (valence band maximum) are I 5p orbitals with a little overlapping of Pb 6s orbitals,and the main components of CBM (conduction band minimum) are Pb 6p orbitals.The FA cations do not directly participate into the electron transition process,just acting as charge donors to supply PbI₃ framework with more than 0.7 e.There exists both covalent and ionic interactions between Pb and I ions.Compared with the hexagonal crystal,the trigonal FAPbI₃ possesses smaller electron and hole effective masses.It exhibits dramatic red shifted absorption spectrum and a better absorption efficiency than hexagonal FAPbI₃ and tetragonal MAPbI₃(MA=CH₃NH₃⁺) perovskites.Bonding energy analyses showed that the hexagonal FAPbI₃ was more stable than the trigonal crystal,and interaction between FA and PbI₃ framework was stronger than that between MA and PbI₃ framework.Our results could provide theoretical guidance for the experimental design and synthesis of FAPbI₃ perovskite solar cells.