3-和4-苯基香豆素化合物的电子结构及光谱性质的理论研究

采用从头算、密度泛函和单激发组态相互作用理论方法研究3-和4-苯基香豆素化合物的电子结构和光谱性质,并用极化连续模型考虑了溶剂对光谱性质的影响.结果发现,在3-苯基香豆素的7-位引入给电子基团甲氧基或吸电子基团氰基均使它们的吸收光谱和荧光光谱产生红移,4-苯基香豆素的衍生物的吸收光谱和荧光光谱均产生蓝移.3-苯基香豆素衍生物与4-苯基香豆素的衍生物的基态和激发态的电子转移方向相反.计算的结果与实验结果吻合的很好.     

Temperature-induced chiral nematic phase changes of suspensions of poly(N,N-dimethylaminoethyl methacrylate)-grafted cellulose nanocrystals

Temperature-induced copolymers of poly(N,N-dimethylaminoethyl methacrylate)-grafted cellulose nanocrystals (PDMAEMA-grafted CNC) were synthesized by surface-initiated atom transfer radical polymerization (ATRP). The graft copolymers were characterized by thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR), and gel permeation chromatography (GPC). The size of the original CNC was 10–40 nm in width and 100–400 nm in length, as characterized by atomic force microscopy (AFM). The liquid-crystalline properties of the graft copolymers were investigated by using polarizing optical microscopy (POM). The graft copolymers exhibited fingerprint texture in lyotropic state. The temperature-induced fingerprint texture changes of PDMAEMA-grafted CNC aqueous suspensions were investigated at various temperatures. With increasing temperature, the spacing of the fingerprint lines decreases. Temperature-induced changes of PDMAEMA polymer chains result in changes of fingerprint texture.     

Investigation of the toxic effect of a QDs heterojunction on the interactions between small molecules and plasma proteins by fluorescence and resonance light-scattering spectra

The effect of a ZnO#ZnS QDs heterojunction (O#SQDs) on the binding affinities of flavonoid glycosides for bovine serum albumin (BSA) was investigated. The fluorescence intensities of BSA decreased remarkably with increasing concentration of O#SQDs. The magnitudes of the binding constants of flavonoid glycosides for BSA in the presence of O#SQDs were in the range of 10(5)-10(7) L mol(-1), and the number of binding sites per BSA (n) was determined as 1.24 ± 0.17. O#SQDs increased the affinities of flavonoid glycosides for BSA by about 2.96% to 114.68% depending on their structures. O#SQDs in blood will enhance the transportation of flavonoid glycosidegs in blood and improve their pharmacology effects. From this point, O#SQDs are a perfect candidate for flavonoid glycosides delivery applications.     

Synthesis of 2-(polyfluoroaryl)benzofurans via a copper(I)-catalyzed reaction of 2-(2,2-dibromovinyl)phenol with polyfluoroarene

A novel and efficient route for the synthesis of 2-(polyfluoroaryl)benzofurans via a copper(I)-catalyzed tandem reaction of 2-(2,2-dibromovinyl)phenol with polyfluoroarene is reported. The corresponding products are generated in good yields. During the reaction process, a copper-catalyzed intramolecular C-O bond formation and a C-H activation are involved.     

Polymeric coatings on silver nanoparticles hinder autoaggregation but enhance attachment to uncoated surfaces

The propensity of silver nanoparticles (AgNPs) having two different polymer coatings (poly(vinylpyrrolidone), PVP, or gum arabic, GA) to aggregate, or to deposit to a reference surface (silica), was explored as a basis for differentiating the effect of surface coating on the stability of nanoparticles in aggregation and in deposition. Surface polymeric coatings stabilize nanoparticles against aggregation as shown by either an increased critical coagulation concentration as for PVP-coated AgNPs (AgPVP) or the absence of observable aggregation even at a high ionic strength as for GA-coated AgNPs (AgGA). In experiments of AgNPs deposition in a silica porous medium, dissimilar surfaces favored deposition, such as the case where polymer coatings were present on the AgNPs but were absent on the porous medium. The increased affinity of the AgNPs for the porous medium in this case may be explained by a shifted contact frontier where electrical double layer interaction is weaker. When coating polymers were introduced to the porous medium and allowed to preadsorb to the silica surfaces, the attachment efficiencies for both the AgPVP and AgGA were reduced due to steric and electrosteric stabilization, respectively. The results suggest that polymeric coatings that are usually deemed as stabilizers (as they indeed are in the case of autoaggregation) might not necessarily stabilize nanoparticles against deposition unless the collector surfaces are also coated with polymer.     

Flame synthesis of hierarchical nanotubular rutile titania derived from natural cellulose substance

Hierarchical nanotubular rutile titania material was fabricated by facile flame burning of ultrathin titania gel film coated cellulose nanofibres of commercial cellulose substance (filter paper), which possesses efficient photocatalytic performance for degradation of organic dye (methylene blue) under ultraviolet irradiation.     

DFT and TD-DFT studies on symmetrical squaraine dyes for nanocrystalline solar cells

Abstract  

The ground-state geometries, electronic structures, and electronic absorption spectra of symmetrical squaraine dyes SQ1–SQ4 were investigated using density functional theory and time-dependent DFT at the B3LYP level. The calculated geometries indicate that strong conjugation effects occur in the dyes. The highest occupied molecular orbital energy levels were calculated to be −4.95, −5.22, −5.09, and −5.06 eV, and the lowest unoccupied molecular orbital energies were −2.72, −3.05, −2.80, and −2.80 eV for SQ1–SQ4, respectively. Taking the conduction band energy of TiO₂ into account, these data reveal the sensitized mechanism: the interfacial electron transfer between the semiconductor TiO₂ electrode and the dye sensitizers SQ1–SQ4 are electron-injection processes from excited dyes to the semiconductor conduction band. The intense calculated absorption bands are assigned to π → π* transitions, which exhibit appreciable blue-shift compared with the experimental absorption maxima due to the inherent approximations in the TD-DFT.     

Unique Thia‐Baeyer–Villiger‐Type Oxidation of Dibenzothiophene Sulfoxides Derivatives

The present research has demonstrated that selective C?S bond cleavages of dibenzothiophene and its derivatives are feasible by thia‐Baeyer–Villiger type oxidation, i. e. the oxygen insertion process within a sulfoxide‐carbon linkage, in the presence of porphyrin iron (III) and by ultraviolet irradiation originating from sunlight, high pressure Hg‐lamp or residentially germicidal ultraviolet lamp under very mild conditions. This reaction with tert‐butylhydroperoxide at 30.0 °C leads to dibenzo[1,2]oxathiin‐6‐oxide ( PBS ) in 83.2 % isolated yield or its hydrated products, 2‐(2‐hydroxyphenyl)‐benzenesulfinic derivatives ( HPBS ) in near 100 % yield based HPLC data. PBS and HPBS are a type of biological products detected on the C?S bond cleavage step through various oxidative biodesulfurization ( OBDS ) pathways, and are useful synthetic intermediates and fine chemicals. These observations may contribute on understanding delicately molecular aspect of OBDS in the photosynthesis system, expanding the C‐S cleavage chemistry of S‐heterocyclic compounds and approaching toward biomemic desulfurization with respect to converting sulfur contaminants to chemically beneficial blocks as needed and performing under the ambient conditions.     

Lanthanide‐Catalyzed Reversible Alkynyl Exchange by Carbon–Carbon Single‐Bond Cleavage Assisted by a Secondary Amino Group

Lanthanide‐catalyzed alkynyl exchange through C?C single‐bond cleavage assisted by a secondary amino group is reported. A lanthanide amido complex is proposed as a key intermediate, which undergoes unprecedented reversible β‐alkynyl elimination followed by alkynyl exchange and imine reinsertion. The in situ homo‐ and cross‐dimerization of the liberated alkyne can serve as an additional driving force to shift the metathesis equilibrium to completion. This reaction is formally complementary to conventional alkyne metathesis and allows the selective transformation of internal propargylamines into those bearing different substituents on the alkyne terminus in moderate to excellent yields under operationally simple reaction conditions.