Reactivity insight into reductive coupling and aldol cyclization of chalcones by visible light photocatalysis

The reductive coupling and cyclization of chalcones to generate cyclopentanol derivatives in up to 84% yield by visible light photoredox catalysis is described. This reaction involves radical anion homocoupling, monoprotonation, and intramolecular cyclization cascade.     

New insight into photochemistry of ferrioxalate

Optical spectroscopy and nanosecond flash photolysis (Nd:YAG laser, 355 nm, pulse duration 5 ns, mean energy 5 mJ/pulse) were used to study the photochemistry of Fe(III)(C2O4)3(3-) complex in aqueous solutions. The main photochemical process was found to be intramolecular electron transfer from the ligand to Fe(III) ion with formation of a primary radical complex [(C2O4)2Fe(II)(C2O4(*))](3-). The yield of radical species (i.e., CO2(*-) and C2O4(*-)) was found to be less than 6% of Fe(III)(C2O4)3(3-) disappeared after flash. [(C2O4)2Fe(II)(C2O4(*))](3-) dissociates reversibly into oxalate ion and a secondary radical complex, [(C2O4)Fe(II)(C2O4(*))](-). The latter reacts with the initial complex and dissociates to Fe(II)(C2O4) and oxalate radical. In this framework, the absorption spectra and rate constants of the reactions of all intermediates were determined.     

SiO2/COPs的合成及其在光催化反应中的协同效应

共价有机聚合物(COPs)是一类由轻质元素(C,H,O,N和B等)通过共价键的方式连接而成的有机多孔材料.COPs的共轭结构赋予其优异的可见光吸收特性,已经在光催化水分解制氢、二氧化碳还原、有机合成和污染物降解等领域显示出巨大的应用潜力.虽然COPs具有能带结构易调控和高孔隙率等优点,但其光催化活性仍有待提升.使用助催化剂是提升COPs的光催化活性,促进表面反应普遍采用的策略.此外,底物活化官能团的引入和光催化剂表面性质的调控也是提高光催化剂反应活性的有效方法.虽然可以通过改变COPs单体种类、化学键的类型和拓扑结构来调控COPs的组成,但要同时兼顾COPs的结构和亲疏水性的调控以及底物活化官能团的引入仍十分困难.与纯COPs相比,与其他材料进行杂化为扩大COPs的化学组成和功能性提供了更多可能.迄今为止,在COPs纳米孔中封装分子、纳米颗粒或将COPs涂覆在其他固体材料上是制备基于COPs复合材料的常用策略.但是,考虑到COPs和无机材料合成条件的不相容性,在纳米尺度精确控制复合材料的组分、结构和形貌仍然是一项艰巨的任务.本文制备了稳定在十六烷基三甲基溴化铵(CTAB)疏水核中的COPs胶体,其粒度分布在16 nm左右.通过溶胶-凝胶法在CTAB周围水解聚合四乙氧基硅烷,得到SiO2/COPs复合材料.表征结果表明,COPs均匀分布在氧化硅的骨架中.该复合材料具有分别来自于SiO2和COPs的介孔和微孔结构.与纯COPs相比,复合材料的表面疏水性降低.SiO2/COPs具有可见光响应特性,其吸收带边随COPs含量的增加而红移,表明在复合材料中COPs在高含量时发生团聚.SiO2/COPs作为光催化剂,可高效催化α-溴代苯乙酮的还原脱卤反应(汉斯酯为还原剂),其催化活性和SiO2/COPs比例相关,在COPs含量为22.6 wt％时达到最优.SiO2/COPs的催化活性较COPs有大幅度提高.在优化的SiO2/COPs比例下,SiO2/COPs的TOF是COPs的近12倍.控制实验表明,SiO2中的羟基对汉斯酯为还原剂有活化作用.此外,本文研究发现,复合材料的活性与SiO2/COPs的比值呈火山型曲线,表明在光催化反应中SiO2和COPs之间存在协同效应.由此可见,将光催化剂和反应物活化材料耦合是提高光催化反应活性的有效策略.     

An insight into phenomenal optical non‐linearities arising from synergistic relationship between selected BODIPYs and noble metal nanoparticles

Materials with large and quick non‐linear optical response, excellent photo thermal stability, cost effectiveness and off resonant non‐linear absorption (NLA) are essential requirements for a good optical limiting (OL). Among them, organic systems and π‐conjugated polymers are getting special interest because of their flexibility in structural modification that leads to the tuning of optical and electronic properties that are suitable for working under large bandwidth. Here, we report a drastic enhancement of non‐linear optical activity and exceptional OL action of two organic–inorganic hybrid system based on BODIPY and Au and Ag nanoparticles (NPs). The organic system taken was certain set of BODIPYs with different substitution at the para and meta positions. All the compounds were found to be exhibiting good reverse saturable absorption (RSA) behaviour and negative non‐linear refraction property. An attempt was made to improve the non‐linear optical (NLO) property of the BODIPY by forming nanohybrids with Au and Ag NPs, and the best NLO active candidate among the studied system was chosen for it. A significant enhancement in NLO property was observed on hybrid system formation. The optical limiting (OL) threshold of the hybrid (1 J/cm²) was reduced almost 1/5 times than that of the parent compound (5.2 J/cm²), and this value is comparable with the benchmark OL materials like C₆₀. The mechanism behind the NLA is found to be the combination of excited state absorption (ESA) and two‐photon absorption (TPA). The enhanced NLA and OL action of C? Ag/Au nanohybrids are attributed to the synergetic effect among the two parent components as well as the local field effects of NPs. Enhancement in non‐linear optical property is found to be stronger in hybrid system with Au NPs and is due to the resonant charge transfer and intense local field effect on exciting with 532‐nm pulse compared with that of Ag NPs. Both the parent compounds and the nanohybrids exhibit negative non‐linearity, and the non‐linear refraction is also found to be enhanced. The improved NLA and OL property of hybrid system guarantees successful usage of the strategy in OL applications.     

Engineering oxygen into ultrathin graphitic carbon nitride: synergistic improvement of electron reduction and charge carrier dynamics for efficient photocatalysis

The fast separation rate of photogenerated carriers and the high utilization of sunlight are still a major challenge that restricts the practical application of carbon nitride (g-C₃N₄) materials in the field of photocatalytic hydrogen (H₂) evolution. Here, ultrathin oxygen (O) engineered g-C₃N₄ (named UOCN) was successfully obtained by a facial gaseous template sacrificial agent-induced bottom-up strategy. The synergy of O doping and exfoliating bulk into an ultrathin structure is reported to simultaneously achieve high-efficiency separation of photogenerated carriers, enhance the utilization of sunlight, and improve the reduction ability of electrons to promote photocatalytic H₂ evolution of UOCN. As a proof of concept, UOCN affords enhanced photocatalytic H₂ evolution (93.78 μmol h^?1) under visible light illumination, which was significantly better than that of bulk carbon nitride (named CN) with the value of 9.23 μmol h^?1. Furthermore, the H₂ evolution rate of UOCN at a longer wavelength (λ = 450 nm) was up to 3.92 μmol h^?1 due to its extended light absorption range. This work presents a practicable strategy of coupling O dopants with ultrathin structures about g-C₃N₄ to achieve efficient photocatalytic H₂ evolution. This integrated engineering strategy can develop a unique example for the rational design of innovative photocatalysts for energy innovation.     

New insight into modeling non-covalently imprinted polymers

Three series of polymers were carefully formulated with increasing amounts of template while keeping the polymer components constant. The number of binding sites (N) and the number average association constant (K(n)()) were calculated for each polymer in a series, using equations adapted from the literature describing molecularly imprinted polymers (MIPs). The trends of N and K(n)() for each series of polymers, which were graphed versus percent template, suggest multiple functional monomers in the binding sites of noncovalent MIPs. This new insight has implications for understanding the underlying mechanisms for the formation of binding sites in the MIPs studied.     

New insight into the discrimination between omeprazole enantiomers by cyclodextrins in aqueous solution

We report results regarding the use of ¹H-NMR spectroscopy in the study of the conformational behaviour and optical activity of omeprazole. Changes in the chemical shifts of chosen atoms reveal that the conformational behaviour of omeprazole is temperature and pH sensitive. Separation and identification of omeprazole enantiomers in the presence of natural and derivative cyclodextrins, such as β-cyclodextrin (βCD) and methyl-β-cyclodextrin (MβCD) are achieved using ¹H-NMR spectroscopy, with information from molecular dynamics simulation. This work shows that βCD includes preferentially R-(–)-omeprazole, acting as a chiral selector. This discrimination of omeprazole enantiomers by cyclodextrins allows development of pharmaceutical formulations with a better bioavailability profile.     

New insight into the pathways of methanol oxidation

Methanol electrooxidation at Pt(1 1 1) is extremely sensitive to the nature of the supporting electrolyte. Much lower currents for methanol oxidation are observed in H₂SO₄ than in HClO₄ solutions, specific adsorption of sulfate being responsible for the inhibitory effect. While this effect is largely known, its fundamental consequences for the reaction mechanism were not evident till now. This is the subject of the present paper. The analysis of data on the yields of soluble products using both supporting electrolytes throws new light on the important question of the mechanism of parallel pathways during methanol oxidation reaction.     

Evidence for the hydration effect at the semiconductor phospholipid-bilayer interface by TiO2 photocatalysis

The interactions of TiO2 with phospholipid bilayers found in cell membrane walls were observed to perturb the bilayer structure under UVA light irradiation. The structure changes in the phospholipid bilayers upon contact with TiO2 under light and in the dark were followed by X-ray diffraction. Hydration effects at the semiconductor-phospholipid interface played an important role in the degradation of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) bilayers taken as cell wall lipid bilayer models. Evidence is provided that the fluidity of the phospholipid bilayers plays a significant role when interacting in the dark with the TiO2 or in processes mediated by TiO2 under light irradiation.     

Interaction between GUVs and catanionic nanocontainers: new insight into spontaneous membrane fusion

Spontaneous receptor-free membrane fusion with pure lipid systems, used as a cell membrane model, is demonstrated with easy-to-handle lactose-derived catanionic vesicles. This fusion, mediated and controlled by phospholipids, emphasizes the great value of these nanovesicles for enhanced direct cytosolic drug delivery without the shortcomings linked with endocytic pathways.     

New synthesis and insight into the structure of blue ultramarine pigments

A new and easy method for preparing blue sodalite pigments which involves high-temperature calcination of sodalite samples synthesized with aluminum sulfate and an organic template, is presented. Calcination generated the S(3)(-) and S(2)(-) radicals, and the effects of the Al/Si ratio and the calcination temperature on the nature and amounts of the radicals were examined. The radicals were characterized in detail by continuous wave and pulsed EPR at X- and W-band frequencies (approximately 9 and 95 GHz, respectively) complemented by UV-vis measurements. The high-field electron-paramagnetic resonance (EPR) measurements allowed us to clearly resolve the g anisotropy of S(3)(-) and W-band electron nuclear double resonance (ENDOR) measurements detected strong coupling with extra-framework (23)Na cations and weak coupling with framework (27)Al. On the basis of the spectroscopic results and density functional theory (DFT) calculations of the g-tensors of S(3)(-) and S(2)(-) radicals, the EPR signals were attributed to three different radicals, all with the open structure C(2v), that are located within the sodalite beta cages. While two of these radicals are well isolated, the third one is associated with an exchange-narrowed signal originating from S(3)(-) radicals in nearby sodalite cages.     

New insight into mesoporous silica for nano metal-organic framework

In this paper the particle volume fraction and temperature dependence of the dynamic viscosity of highly concentrated transformer oil based magnetic nanofluids was investigated in the absence of an external magnetic field. The solid particle volume fraction dependence of the relative viscosity was found to be very well fitted by the Krieger-Dougherty formula, whence the mean ellipticity of the colloidal particles and the effective surfactant layer thickness were obtained. Using the information on the particles' size and shape statistics obtained from TEM, DLS and magnetogranulometry investigations, it was concluded that the magnetite nanoparticles agglomerate in small clusters of about 1.3 particles/cluster, due to the van der Waals interactions. The effective thickness of the oleic acid surfactant layer was estimated as about 1.4 nm, in very good agreement with the value resulted from previous SANS investigations.     

Bioanalytics: detailed insight into bioprocesses

The principles of bioanalytical systems for an on-line bioprocess monitoring are described within this paper. These sensor systems can be interfaced to the bioprocess in different ways according to the needs of the single bioprocess. Modular systems are necessary, which can fit exactly to the needs of the single process. Invasive as well as non-invasive bioanalytical tools are described and discussed in detail. Immunosensors give the possibility to monitor high molecular weight components within short time intervals. Non-invasive optical sensors allow the direct monitoring of various analytes such as oxygen pH for the complex fluorescence behavior of the bioprocess medium. These so-called fluorescence sensors offer the possibility to monitor intra- as well as extracellular components without interfering with the bioprocess. An industrial example for the application of bioanalytical tools for a process optimization are presented in this application. Here a biosensor system is used to optimize the downstreaming of molasses on a technical scale. The economic as well ecological advantages are discussed.     

New insight into the mechanisms of reactions between some anionic nucleophiles and phenyl acetate in the gas phase

Experiments carried out in an ion cyclotron resonance (ICR) drif cell, an ICR trapped ion cell and a flowing afterglow (FA) system show that in the gas phase phenyl acetate reacts with a variety of clustered and unclustered nucleophiles to yield mainly the product ion C₆H₅O^?.     

New insight into the soot nanoparticles in a candle flame

Using anodic aluminium oxide films as collectors, all four well known carbon forms, diamond, graphitic, fullerenic and amorphous particles, are identified inside a candle flame, suggesting a new nucleation mechanism for diamond growth and fullerene formation in a combustion synthesizing process.     

A novel insight into the inductive effect in silicon chemistry

A revision of quantitative literature data for the reactivity of organosilicon compounds in light of conceptions stemmed from organic chemistry has been carried out. It has been found that in structure-reactivity analysis for organosilicon compounds, differently of carbon compounds, the inductive effect of substituents, at least in nucleophilic displacement reactions at silicon, must be expressed by two terms involving that for electronegativity. A protocol for the correlation analysis in organosilicon chemistry is now available.     

TiO2 photocatalysis for the degradation of pollutants in gas phase: From morphological design to plasmonic enhancement

TiO₂-based photocatalysis has become a viable technology in various application fields such as (waste)water purification, photovoltaics/artificial photosynthesis, environmentally friendly organic synthesis and remediation of air pollution. Because of the increasing impact of bad air quality worldwide, this review focuses on the use and optimization of TiO₂-based photocatalysts for gas phase applications. Over the past years various specific aspects of TiO₂ photocatalysis have been reviewed individually. The intent of this review is to offer a broad tutorial on (recent) trends in TiO₂ photocatalyst modification for the intensification of photocatalytic air treatment. After briefly introducing the fundamentals of photocatalysis, TiO₂ photocatalyst modification is discussed both on a morphological and an electronic level from the perspective of gas phase applications. The main focus is laid on recent developments, but also possible opportunities to the field. This review is intended as a solid introduction for researchers new to the field, as well as a summarizing update for established investigators.     

New insight into solid-state molecular dynamics: mechanochemical synthesis of azobenzene/triphenylphosphine palladacycles

Solid-state reactions of dicyclopalladated azobenzenes and triphenylphosphine lead to the thermodynamically favorable bridged complexes. It was demonstrated for the first time that very complex molecular dynamics involving a series of structural transformations is also feasible in the solid state.     

New insight into the gas-phase bimolecular self-reaction of the HOO radical

The singlet and triplet potential energy surfaces (PESs) for the gas-phase bimolecular self-reaction of HOO*, a key reaction in atmospheric environments, have been investigated by means of quantum-mechanical electronic structure methods (CASSCF and CASPT2). All the reaction pathways on both PESs consist of a first step involving the barrierless formation of a prereactive doubly hydrogen-bonded complex, which is a diradical species lying about 8 kcal/mol below the energy of the reactants at 0 K. The lowest energy reaction pathway on both PESs is the degenerate double hydrogen exchange between the HOO* moieties of the prereactive complex via a double proton transfer mechanism involving an energy barrier of only 1.1 kcal/mol for the singlet and 3.3 kcal/mol for the triplet at 0 K. The single H-atom transfer between the two HOO* moieties of the prereactive complex (yielding HOOH + O2) through a pathway keeping a planar arrangement of the six atoms involves a conical intersection between either two singlet or two triplet states of A' and A" symmetries. Thus, the lowest energy reaction pathway occurs via a nonplanar cisoid transition structure with an energy barrier of 5.8 kcal/mol for the triplet and 17.5 kcal/mol for the singlet at 0 K. The simple addition between the terminal oxygen atoms of the two HOO* moieties of the prereactive complex, leading to the straight chain H2O4 intermediate on the singlet PES, involves an energy barrier of 7.3 kcal/mol at 0 K. Because the decomposition of such an intermediate into HOOH + O2 entails an energy barrier of 45.2 kcal/mol at 0 K, it is concluded that the single H-atom transfer on the triplet PES is the dominant pathway leading to HOOH + O2. Finally, the strong negative temperature dependence of the rate constant observed for this reaction is attributed to the reversible formation of the prereactive complex in the entrance channel rather than to a short-lived tetraoxide intermediate.     

New insight into the electrochemical desorption of alkanethiol SAMs on gold

A combination of Polarization Modulation Infrared Reflection Absorption Spectroscopy (PMIRRAS) under electrochemical control, Electrochemical Scanning Tunneling Microscopy (ECSTM) and Molecular Dynamics (MD) simulations has been used to shed light on the reductive desorption process of dodecanethiol (C12) and octadecanethiol (C18) SAMs on gold in aqueous electrolytes. Experimental PMIRRAS, ECSTM and MD simulations data for C12 desorption are consistent with formation of randomly distributed micellar aggregates stabilized by Na(+) ions, coexisting with a lying-down phase of molecules. The analysis of pit and Au island coverage before and after desorption is consistent with the thiolate-Au adatoms models. On the other hand, PMIRRAS and MD data for C18 indicate that the desorbed alkanethiolates adopt a Na(+) ion-stabilized bilayer of interdigitated alkanethiolates, with no evidence of lying down molecules. MD simulations also show that both the degree of order and tilt angle of the desorbed alkanethiolates change with the surface charge on the metal, going from bilayers to micelles. These results demonstrate the complexity of the alkanethiol desorption in the presence of water and the fact that chain length and counterions play a key role in a complex structure.