Showing papers in "Chemistry-an Asian Journal in 2011"

Click Chemistry: 1,2,3‐Triazoles as Pharmacophores

Abstract: The copper(I)-catalyzed 1,2,3-triazole-forming reaction between azides and terminal alkynes has become the gold standard of 'click chemistry' due to its reliability, specificity, and biocompatibility. Applications of click chemistry are increasingly found in all aspects of drug discovery; they range from lead finding through combinatorial chemistry and target-templated in vitro chemistry, to proteomics and DNA research by using bioconjugation reactions. The triazole products are more than just passive linkers; they readily associate with biological targets, through hydrogen-bonding and dipole interactions. The present review will focus mainly on the recent literature for applications of this reaction in the field of medicinal chemistry, in particular on use of the 1,2,3-triazole moiety as pharmacophore.

New Design Tactics in OLEDs Using Functionalized 2‐Phenylpyridine‐Type Cyclometalates of Iridium(III) and Platinum(II)

Abstract: As a result of their outstanding attributes, organic light-emitting diodes (OLEDs) and white organic light-emitting diodes (WOLEDs) have been recognized in recent years as the most promising candidates for future flat-panel display technologies and next generation solid-state energy-saving lighting sources New advancements in the area of high performance triplet emitters become vital for realizing more practical applications In this regard, several critical issues must be carefully identified and addressed, and these include the ways to enhance device efficiency and suppress efficiency roll-off, to achieve versatile color tuning and simple device manufacture, as well as to obtain high-quality white light from WOLEDs It has been shown that some functionalized phosphorescent Ir(III) and Pt(II) ppy-type cyclometalated complexes (ppy = 2-phenylpyridine) possess unique features that are suitable for solving these difficult and challenging tasks In this Focus Review, we will highlight the recent design tactics adopted for these functional metallophosphors and the critical roles they may play in developing more realistic devices

Piezofluorochromism of an aggregation-induced emission compound derived from tetraphenylethylene.

Abstract: The development of organic fluorescence materials is of great interest for both fundamental research and practical applications. The modification or alteration of molecular chemical structures is the most-common approach for controlling fluorescence properties. However, there are a limited number of effective materials for the dynamic control of solid-state fluorescence with high efficiency and reversibility, because most chemical reactions in the solid state involve insufficient conversion and irreversible reactions, or result in the loss of fluorescence capability. To overcome this problem, a very attractive approach is proposed which dynamically controls solid fluorescence properties by altering the mode of solid-state molecular stacking without changing the chemical structure of the constituting molecules. Found recently, piezofluorochromism is a change in the fluorescence color induced by mechanical stress, accompanied with a reversion to the original fluorescent color by heating, recrystallization, or exposure to solvent vapor. Many piezochromic materials have been reported based on the change in absorption characteristics under pressure. Fluorescence can be detected with high sensitivity, thus enabling materials with piezofluorochromism to have a wide variety of applications in optical recording and strainor pressure-sensing systems. However, organic piezofluorochromic materials are exceedingly rare. Recently, many aggregation-induced emission (AIE) compounds with various chemical structures have been synthesized in our laboratory, and it is very interesting to find that almost all of these compounds are piezofluorochromic materials. We would thus suggest calling these compounds piezofluorochromic aggregation-induced emission (PAIE) materials as they possess both piezofluorochromic and aggregation-induced emission properties. Aggregation-induced emission materials, first reported by Tang and co-workers, are one of an important class of luminescent materials and exhibit many special properties, such as strong solid emission, excellent device performance, and highly stimuli-sensitive fluorescence. PAIE materials have the advantages of both piezofluorochromic materials and aggregation-induced emission materials and can be more-widely used. However, to the best of our knowledge, there has been only one compound (DBDCS, Scheme 1 c) that has both piezofluorochro-

What kind of "soft materials" can we design from molecular gels?

Abstract: Since their discovery, over the years, molecular gels have been constantly drawing the attention of chemists from various scientific fields. Their structural softness together with the orderliness at the molecular level provides such molecules immense potential for the amplification of their properties. Using this chemistry, one can easily realize a macroscopic outcome from a molecular level modulation. This phenomenon is governed by the principle of supramolecular interactions that introduce a unique "reversibility" to the system. The new generation of gel chemistry is now tending more towards the development of new attractive functions to create smart materials for achieving outstanding response or unprecedented selectivity over a process. However, for the successful implementation of this mission, it is really essential to correlate gel functions with their structures. This focus review is an attempt to find such a correlation, which can motivate and stimulate this existing field towards precisely designing molecular gels for the desired functions.

Supramolecular Chemical Sensors Based on Pyrene Monomer–Excimer Dual Luminescence

Abstract: The past ten years have seen a spectacular development of chemical sensors based on the monomer-excimer dual luminescence of aromatic systems, such as pyrene. Either in the form of integrated or multicomponent molecular devices these chemosensors have been attracting a high interest above all because of their unique ratiometric properties. This review will focus on the latter systems, which can be classified into two classes: Firstly, the assembly of receptor-effector conjugates is triggerred by the analyte of interest. As a result, the sensor shows monomer to excimer fluorescence switching upon substrate binding. Secondly, the supramolecular assembly that constitutes the sensor is perturbed by interaction with the analyte. This induces a conformational change or the exchange of a component of the system, which is the cause of the luminescence switch effect.

Sulfonyl and Phosphoryl Azides: Going Further Beyond the Click Realm of Alkyl and Aryl Azides

Abstract: Whereas alkyl and aryl azides readily react with terminal alkynes to afford 1,4-disubstituted-1,2,3-triazoles in excellent yields and selectivity in the presence of a copper catalyst, sulfonyl, phosphoryl, and certain acyl azides allow additional chemistry upon ring-opening of the corresponding copper–triazole intermediates. The amazingly versatile new chemistry stems from the high reactivity of a ring-opened ketenimine intermediate, with which a wide range of nucleophiles react to give multicomponent products. Among those nucleophiles, amines, alcohols, water, and heterocyclic compounds are especially capable of being involved in this new chemistry.

An Evaluation of UiO-66 for Gas-Based Applications

Abstract: In addition to its high thermal stability, repetitive hydration/dehydration tests have revealed that the porous zirconium terephthalate UiO-66 switches reversibly between its dehydroxylated and hydroxylated versions. The structure of its dehydroxylated form has thus been elucidated by coupling molecular simulations and X-ray powder diffraction data. Infrared measurements have shown that relatively weak acid sites are available while microcalorimetry combined with Monte Carlo simulations emphasize moderate interactions between the UiO-66 surface and a wide range of guest molecules including CH4, CO, and CO2. These properties, in conjunction with its significant adsorption capacity, make UiO-66 of interest for its further evaluation for CO2 recovery in industrial applications. This global approach suggests a strategy for the evaluation of metal–organic frameworks for gas-based applications.

Aerobic oxidations catalyzed by colloidal nanogold.

Abstract: Recently, dispersions of gold nanoclusters in liquid media (colloidal nanogold) have been extensively used as quasi-homogeneous catalysts for various aerobic oxidation reactions. This review describes recent progress in such reactions, with a focus on our comprehensive studies on gold clusters (<2 nm) stabilized by poly(N-vinyl-2-pyrrolidone) and their participation in oxidation reactions of alcohols, α-hydroxylation reactions of benzylic ketones, and homocoupling reactions of organoboronates, as well as formal Lewis acidic reactions, such as intramolecular hydroalkoxylation and hydroamination reactions of nonactivated alkenes. Mechanistic studies have shown that a partial electron transfer from the gold clusters to O(2) generates superoxide- or peroxide-like species and Lewis acidic centers, both of which play essential roles in the catalytic reactions.

Oxazolones in Organocatalysis, New Tricks for an Old Reagent

Abstract: Oxazolones or azlactones are among the most-common starting materials for the synthesis of quaternary amino acids. Since the seminal works of Steglich and co-workers until the recent examples from Ooi and co-workers, azlactones have been the focus of intense research. Oxazolones are also widely used in organometallic chemistry; however, with the "renaissance" of organocatalysis, this reagent has emerged as an important starting material for a broad range of new organocatalytic asymmetric methodologies. In this Focus Review, we aim to cover all of these new organocatalytic methodologies. We begin by discussing the dynamic kinetic resolution reactions developed with azlactones. Then, we disclose the organocatalytic rearrangements. Finally, we focus on the use of oxazolones as nucleophiles in organocatalytic processes.

Molecular Logic Gate Arrays

Abstract: Chemists are now able to emulate the ideas and instruments of mathematics and computer science with molecules. The integration of molecular logic gates into small arrays has been a growth area during the last few years. The design principles underlying a collection of these cases are examined. Some of these computing molecules are applicable in medical- and biotechnologies. Cases of blood diagnostics, ‘lab-on-a-molecule’ systems, and molecular computational identification of small objects are included.

Piezofluorochromic and aggregation-induced-emission compounds containing triphenylethylene and tetraphenylethylene moieties.

Abstract: New fluorescent compounds containing triphenylethylene and tetraphenylethylene moieties were synthesized, and their piezofluorochromic and aggregation-induced emission behaviors were investigated. The results show that all compounds exhibit aggregation-induced emission characteristics and only the crystalline compound possesses piezofluorochromic properties. The color, emission spectra, and morphological structures of the one piezofluorochromic compound exhibit reversibility upon grinding and annealing (or fuming) treatments. The piezofluorochromic behaviors are caused by a change between different modes of solid state molecular packing under external pressure. The single crystal X-ray diffraction analysis reveals that the twisted conformation of the aggregation-induced emission compound leads to the formation of metastable crystal lattice with cavity which is readily destroyed under external pressure. A possible mechanism of piezofluorochromic phenomenon has been proposed.

Two-photon fluorescent probes for metal ions.

Abstract: Two-photon microscopy (TPM) has become an indispensible tool in biology and medicine owing to the capability of imaging the intact tissue for a long period of time. To make it a versatile tool in biology, a variety of two-photon probes for specific applications are needed. In this context, many research groups are developing two-photon probes for various applications. In this Focus Review, we summarize recent results on model studies and selected examples of two-photon probes that can detect intracellular free metal ions in live cells and tissues to provide a guideline for the design of useful two-photon probes for various in vivo imaging applications.

10 Years of Click Chemistry: Synthesis and Applications of Ferrocene‐Derived Triazoles

Abstract: Click chemistry has played a significant role as a rapid and versatile strategy for conjugating two molecular fragments under very mild reaction conditions. Introduction of ferrocene-derived triazole systems using click chemistry has attracted enormous interest in various fields due to its potential applications in electrochemical techniques for detection and sensing. The present discussion focuses on the synthesis of ferrocene-triazole and the importance of using a CuAAC reaction for such conjugation. Applications of ferrocene-based click reactions in conjugate chemistry, asymmetric catalysis, medicinal chemistry, host-guest interactions, and materials chemistry have been highlighted.

Adsorption of N719 dye on anatase TiO2 nanoparticles and nanosheets with exposed (001) facets: equilibrium, kinetic, and thermodynamic studies.

Abstract: Anatase TiO2 nanosheets (TiO2 NS) with dominant (001) facets and TiO2 nanoparticles (TiO2 NP) with dominant (101) facets are fabricated by hydrothermal hydrolysis of Ti(OC4H9)4 in the presence and absence of hydrogen fluoride (HF), respectively. Adsorption of N719 onto the as-prepared samples from ethanol solutions is investigated and discussed. The adsorption kinetic data are modeled using the pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetics equations, and indicate that the pseudo-second-order kinetic equation and intraparticle diffusion model can better describe the adsorption kinetics. Furthermore, adsorption equilibrium data of N719 on the as-prepared samples are analyzed by Langmuir and Freundlich models; this suggests that the Langmuir model provides a better correlation of the experimental data. The adsorption capacities (qmax) of N719 on TiO2 NS at various temperatures, determined using the Langmuir equation, are 65.2 (30 °C), 68.2 (40 °C), and 76.6 (50 °C) mg g−1, which are smaller than those on TiO2 NP, 92.4 (30 °C), 100.0 (40 °C), and 108.2 (50 °C) mg g−1, respectively. The larger adsorption capacities of N719 for TiO2 NP versus NS are attributed to its higher specific surface areas. However, the specific adsorption capacities (qmax/SBET) at various temperatures are 1.5 (30 °C), 1.6 (40 °C), and 1.7 (50 °C) mg m−2 for TiO2 NS, which are otherwise higher than those for NP, 0.9 (30 °C), 1.0 (40 °C), and 1.1 (50 °C) mg m−2, respectively. The larger specific adsorption capacities of N719 for TiO2 NS versus NP are because the (001) surface is more reactive for dissociative adsorption of reactant molecules compared with (101) facets. Notably, the qmax and qmax/SBET for both TiO2 samples increase with increasing temperature, suggesting that adsorption of N719 on the TiO2 surface is an endothermic process, which is further confirmed by the calculated thermodynamic parameters including free energy, enthalpy, and entropy of adsorption process. The present work will provide a new understanding on the adsorption process and mechanism of N719 molecules onto TiO2 NS and NP, and this should be of great importance for enhancing the performance of dye-sensitized solar cells.

Fabrication and Functionalization of Hydrogels through “Click” Chemistry

Abstract: Hydrogels are crosslinked polymeric materials that play a vital role in many biomedical areas such as drug delivery, sensor technology, and tissue engineering. Increasing demand of these materials for such advanced applications has necessitated the development of hydrogels with complex chemical compositions such as incorporating small molecules and biomolecules that provide the functional attributes. This Focus Review highlights the tremendous impact of click chemistry on the design, synthesis, and functionalization of hydrogels. The high efficiency and fidelity of the click reactions have enabled rapid and modular synthesis of hydrogels with near-ideal network structures. Efficient incorporation of biomolecular building blocks, such as peptide sequences either during or after the fabrication of hydrogels, have been achieved through various click reactions. Utilization of these efficient reactions has led to the fabrication of many stimuli-responsive or 'smart' hydrogels in recent years.

Synthesis and spectroscopic properties of fused-ring-expanded aza-boradiazaindacenes.

Abstract: A series of fused-ring-expanded aza-boradiazaindacene (aza-BODIPY) dyes have been synthesized by reacting arylmagnesium bromides with phthalonitriles or naphthalenedicarbonitriles. An analysis of the structure-property relationships has been carried out based on X-ray crystallography, optical spectroscopy, and theoretical calculations. Benzo and 1,2-naphtho-fused 3,5-diaryl aza-BODIPY dyes display markedly red shifted absorption and emission bands in the near-IR region (>700 nm) due to changes in the energies of the frontier MOs relative to those of 1,3,5,7-tetraaryl aza-BODIPYs. Only one 1,2-naphtho-fused aza-BODIPY of the three possible isomers is formed due to steric effects, and 2,3-naphtho-fused compounds could not be characterized because the final BF(2) complexes are unstable in solution. The incorporation of a -N(CH(3))(2) group at the para-positions of a benzo-fused 3,5-diaryl aza-BODIPY quenches the fluorescence in polar solvents and results in a ratiometric pH response, which could be used in future practical applications as an NIR "turn-on" fluorescence sensor.

A BODIPY‐Based Probe for the Selective Detection of Hypochlorous Acid in Living Cells

Abstract: Reactive oxygen species (ROS) are essential for a wide range of biological and pathological events. [1] During infection and inflammation, the phagocytic leukocytes, including neutrophils, monocytes, and macrophages generate reactive oxygen species (ROS) to kill invading bacteria and pathogens. [2] Among ROS, hypochlorous acid (HOCl/OCl )i s a highly reactive oxygen species produced from hydrogen peroxide (H2O2) and chloride ions (Cl ) by the enzyme myeloperoxidase (MPO), which is secreted by activated neutrophils. [3] Although hypochlorous acid plays important roles in the human immune-defense system, overproduction of ROS in living organism has detrimental effects on biological molecules, including nucleic acids, lipids, and proteins, resulting in the inhibition of various protein functions, and contributes to the progression of numerous human diseases, such as atherosclerosis, cancer, cardiovascular diseases, and rheumatoid arthritis. [4] Despite its importance in human health and disease, not as much is known about the mechanism of action and specific roles of HOCl in living systems in comparison with other ROS, owing to slower progress in the development of suitable probes. Several fluorescence probes for the detection and visualization of HOCl in living cells have recently been developed on the basis of the strong oxidizing properties of HOCl. [5–7] HOCl-induced oxidation reactions were employed in the design of fluorescent probes in which the fluorescence properties were regulated by the conversion of the spirocyclic form of rhodamine fluorophores into their ringopened form, [5] or through photoinduced-electron-transfer processes. [6] To facilitate practical applications of such probes, next-generation designs should emphasize higher analyte selectivity, limit susceptibility to autooxidation, and avoid demanding multistep syntheses. Herein, we report the facile synthesis and properties of a new boron-dipyrromethene (BODIPY) dye bearing a methylthioether group, and its biological application as a highly sensitive and selective

Revisiting Keteniminium Salts: More than the Nitrogen Analogs of Ketenes

Abstract: Keteniminium salts are powerful electrophilic heterocumulene reagents well-known for their selectivity and stereocontrol in [2+2] cycloadditions to olefins and carbonyl derivatives. Furthermore, they are readily accessible from stable and simple precursors under a variety of different conditions. Herein, we present the chemistry of keteniminium salts with the hindsight of time, describe preparation methods, recent [2+2] chemistry, mechanistic studies, and assorted applications that significantly extend the scope of utility of these unique electrophilic heterocumulenes.

Self-Assembled Gels for Biomedical Applications

Abstract: Natural and synthetic gel-like materials have featured heavily in the development of biomaterials for wound healing and other tissue-engineering purposes. More recently, molecular gels have been designed and tailored for the same purpose. When mixed with, or conjugated to therapeutic drugs or bioactive molecules, these materials hold great promise for treating/curing life-threatening and degenerative diseases, such as cancer, osteoarthritis, and neural injuries. This focus review explores the latest advances in this field and concentrates on self-assembled gels formed under aqueous conditions (i.e., self-assembled hydrogels), and critically compares their performance within different biomedical applications, including three-dimensional cell-culture studies, drug delivery, and tissue engineering. Although stability and toxicity issues still need to be addressed in more detail, it is clear from the work reviewed here that self-assembled gels have a bright future as novel biomaterials.

Sulfated Ligands for the Copper(I)‐Catalyzed Azide–Alkyne Cycloaddition

Abstract: The copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC), the prototypical reaction of click chemistry, is accelerated by tris(triazolylmethyl)amine-based ligands. Herein, we compare two new ligands in this family--3-[4-({bis[(1-tert-butyl-1H-1,2,3-triazol-4-yl)methyl]amino}methyl)-1H-1,2,3-triazol-1-yl]propanol (BTTP) and the corresponding sulfated ligand 3-[4-({bis[(1-tert-butyl-1H-1,2,3-triazol-4-yl)methyl]amino}methyl)-1H-1,2,3-triazol-1-yl]propyl hydrogen sulfate (BTTPS)--for three bioconjugation applications: 1) labeling of alkyne-tagged glycoproteins in crude cell lysates, 2) labeling of alkyne- or azide-tagged glycoproteins on the surface of live mammalian cells, and 3) labeling of azides in surface proteins of live Escherichia coli. Although BTTPS exhibits faster kinetics than BTTP in accelerating the CuAAC reaction in in vitro kinetic measurements, its labeling efficiency is slightly lower than BTTP in modifying biomolecules with a significant amount of negative charges due to electrostatic repulsion. Nevertheless, the negative charge conferred by the sulfate at physiological conditions significantly reduced the cellular internalization of the coordinated copper(I), thus making BTTPS-Cu(I) a better choice for live-cell labeling.

Synthesis of Ordered Porous Graphitic-C3N4 and Regularly Arranged Ta3N5 Nanoparticles by Using Self-Assembled Silica Nanospheres as a Primary Template

Abstract: Uniform-sized silica nanospheres (SNSs) assembled into close-packed structures were used as a primary template for ordered porous graphitic carbon nitride (g-C(3)N(4)), which was subsequently used as a hard template to generate regularly arranged Ta(3)N(5) nanoparticles of well-controlled size. Inverse opal g-C(3)N(4) structures with the uniform pore size of 20-80 nm were synthesized by polymerization of cyanamide and subsequent dissolution of the SNSs with an aqueous HF solution. Back-filling of the C(3)N(4) pores with tantalum precursors, followed by nitridation in an NH(3) flow gave regularly arranged, crystalline Ta(3)N(5) nanoparticles that are connected with each other. The surface areas of the Ta(3)N(5) samples were as high as 60 m(2) g(-1), and their particle size was tunable from 20 to 80 nm, which reflects the pore size of g-C(3)N(4). Polycrystalline hollow nanoparticles of Ta(3)N(5) were also obtained by infiltration of a reduced amount of the tantalum source into the g-C(3)N(4) template. An improved photocatalytic activity for H(2) evolution on the assembly of the Ta(3)N(5) nanoparticles under visible-light irradiation was attained as compared with that on a conventional Ta(3)N(5) bulk material with low surface area.

Synthesis, characterization, and physical properties of a conjugated heteroacene: 2-methyl-1,4,6,7,8,9-hexaphenylbenz(g)isoquinolin-3(2H)-one (BIQ).

Abstract: We report the synthesis and characterization of a novel, stable and blue heteroacene, 2-methyl-1,4,6,7,8,9-hexaphenylbenz(g)isoquinolin-3(2H)-one (BIQ ). BIQ , with its relatively small π framework, has an absorption λmax at 620 nm, which is larger than that of pentacene (λmax=582 nm), but BIQ is more stable. The solutions of BIQ are observed without any noticeable photobleaching on the order of days. In the solid state, it is very stable at ambient conditions and can be stored indefinitely. Owing to its pyridone end unit, BIQ can display different resonance structures in different solvents (aprotic and protic) or Lewis acids to give different colors. The attractive stability exhibited by BIQ is very desirable in organic semiconductor devices. Herein, we investigated a simple heterojunction photovoltaic device based on BIQ as an electron donor and [6,6]-phenyl-C61 butyric methyl ester as an electron acceptor. Our results show that this type of heteroacene could be a good candidate as a charge-transport material in organic semiconductor devices.

Cytocompatible Poly(ethylene Glycol)-Co-Polycarbonate Hydrogels Cross-Linked by Copper-Free, Strain-Promoted Click Chemistry

Abstract: Strategies to encapsulate cells in cytocompatible three-dimensional hydrogels with tunable mechanical properties and degradability without harmful gelling conditions are highly desired for regenerative medicine applications. Here we reported a method for preparing poly(ethylene glycol)-co-polycarbonate hydrogels through copper-free, strain-promoted azide-alkyne cycloaddition (SPAAC) click chemistry. Hydrogels with varying mechanical properties were formed by "clicking" azido-functionalized poly(ethylene glycol)-co-polycarbonate macromers with dibenzocyclooctyne-functionalized poly(ethylene glycol) under physiological conditions within minutes. Bone marrow stromal cells encapsulated in these gels exhibited higher cellular viability than those encapsulated in photo-cross-linked poly(ethylene glycol) dimethacrylate. The precise control over the macromer compositions, cytocompatible SPAAC cross-linking, and the degradability of the polycarbonate segments make these hydrogels promising candidates for scaffold and stem cell assisted tissue repair and regeneration.

A mechanistic study on the formation of silver nanoplates in the presence of silver seeds and citric acid or citrate ions.

Abstract: The world on a plate: In addition to their role as a capping agent that selectively binds to the {l_brace}111{r_brace} faces of silver, the carboxylate group can coordinate with Ag+ ions to form complexes and thus substantially reduce the reduction rate of Ag+ ions, leading to the formation of silver seeds with both twin planes and stacking faults.

I2‐Catalyzed Indole Formation via Oxidative Cyclization of N‐Aryl Enamines

Abstract: The indole moiety exists in a wide variety of natural products and pharmaceuticals. Its importance has stimulated considerable interest in developing reactions for their synthesis. Until now, the Fischer indole synthesis is still one of the most-powerful synthetic methods to construct the indole skeleton. However, its drawbacks are also apparent in view of today s drive towards sustainable chemistry. Consequently, chemists are endeavoring to develop new reactions for synthesizing indoles by applying environmentally benign oxidative-coupling strategies, which has been documented in the literatures. For examples, Glorius and co-workers have reported an efficient oxidative synthesis of indoles from Naryl enamines using PdACHTUNGTRENNUNG(OAc)2 as a catalyst. Jiao and coworkers disclosed a practical indole synthesis using the palladium-catalyzed reactions of simple anilines and alkynes using dioxygen as the oxidant. Preliminary mechanistic studies showed that the reaction was comprised of two sequential steps: the addition of aniline to alkyne and the intramolecular oxidative coupling of the thus-formed N-aryl enamine. Very recently, Cacchi and co-workers have developed an efficient copper-catalyzed multisubstituted indole synthesis from N-aryl enaminoes. Moreover, the intramolecular oxidative-coupling method was also applied to construct the oxindole skeleton using stoichoimetric amounts of copper salts. Even though the power of transition metal catalysis has been well-demonstrated in synthesis, we believe that, if a reaction catalyzed by transition metals can be replaced by a metal-free analogue with the same efficiency, the non-metalcatalyzed reaction will have greater advantage in synthesis. With this in mind, we wanted to investigate whether some transition-metal-catalyzed reactions can be adapted to their metal-free versions. As such, we decided to whether the above-mentioned transition-metal-catalyzed synthesis of indoles can be modified to its metal-free variant. Recently, Zhao and co-workers have reported an oxidative synthesis of indoles from enamines, in which hyperiodides instead of transition metals were used. Even though this process is metal-free, stoichiometric quantities of expensive iodobenzene diacetate was consumed. We hypothesized that iodine, which is cheap and less toxic, could also function as the catalyst for this oxidative indole synthesis and we undertook an investigation of this possibility in order to develop a better way to indole synthesis. Herein, we report a novel and efficient iodine-catalyzed indole synthesis. (Z)-Ethyl 3-phenyl-3-(phenylamino)acrylate (1 a) was used as a model substrate for optimization of the reaction conditions (Table 1). The desired product, ethyl 2-phenylindole-3-carboxylate (2 a), was obtained in 6 % yield in the

Determination of explosives using electrochemically reduced graphene.

Abstract: A graphene-based electrochemical sensing platform for sensitive determination of explosive nitroaromatic compounds (NACs) was constructed by means of electrochemical reduction of graphene oxide (GO) on a glassy carbon electrode (GCE). The electrochemically reduced graphene (ER-GO) adhered strongly onto the GCE surface with a wrinkled morphology that showed a large active surface area. 2,4-Dinitrotoluene (2,4-DNT), as a model analyte, was detected by using stripping voltammetry, which gave a low detection limit of 42 nmol L(-1) (signal-to-noise ratio=3) and a wide linear range from 5.49×10(-7) to 1.1×10(-5) M. Further characterizations by electrochemistry, IR, and Raman spectra confirmed that the greatly improved electrochemical reduction signal of DNT on the ER-GO-modified GC electrode could be ascribed to the excellent electrocatalytic activity and high surface-area-to-volume ratio of graphene, and the strong π-π stacking interactions between 2,4-DNT and the graphene surface. Other explosive nitroaromatic compounds including 1,3-dinitrobenzene (1,3-DNB), 2,4,6-trinitrotoluene (TNT), and 1,3,5-trinitrobenzene (TNB) could also be detected on the ER-GO-modified GC electrode at the nM level. Experimental results showed that electrochemical reduction of GO on the GC electrode was a fast, simple, and controllable method for the construction of a graphene-modified electrode for sensing NACs and other sensing applications.

Photoinduced electron transfer in a distyryl BODIPY-fullerene dyad.

Abstract: A novel distyryl BODIPY-fullerene dyad is prepared. Upon excitation at the distyryl BODIPY moiety, the dyad undergoes photoinduced electron transfer to give a charge-separated state with lifetimes of 476 ps and 730 ps in polar (benzonitrile) and nonpolar (toluene) solvents, respectively. Transient absorption measurements show the formation of the triplet excited state of distyryl BODIPY in the dyad, which is populated from charge-recombination processes in both solvents.

Solid-state electrochemistry of graphene oxides: absolute quantification of reducible groups using voltammetry.

Abstract: The quantification of various oxygen-containing groups in graphene oxides is of very high importance as these groups have strong influences on the physical, chemical, and material properties of graphene oxides. All current methods provide only relative quantification. Herein, we present a powerful electrochemical technique for the absolute quantification of selected oxygen-containing groups on graphene oxide. Since its discovery in 2004, graphene has captured the imaginations of many scientists. Likewise, graphene-related materials have also attracted the attention of chemists, physicists, and materials scientists alike owing to their interesting properties. Graphene-related materials can be prepared by various methods. The mainstream methods mainly consist of 1) mechanical exfoliation of graphite, 2) Chemical-vapour deposition (CVD) growth of graphene, and 3) chemical oxidation of graphite to graphite oxide followed by consequent exfoliation and modifications leading to the formation of various types of graphene oxides. The third preparation procedure is the most-popular method used for the manufacturing of bulk quantities of graphenerelated materials. This procedure typically involves the oxidation of graphite by a mixture of nitric acid and strong oxidants (i.e. KClO3 or KMnO4), which yields graphite oxide. The structure of graphite oxide consists of graphite layers with significant increment in their interlayer spacing owing to the presence of functional groups on the basal planes of the individual graphene sheets that are introduced through oxidative treatment. The functional groups are a mixture of various oxygen-containing groups (C/O ratio of graphite oxide is ca. 1.9:1), such as hydroxy, carbonyl, aldehyde, carboxy, epoxide, peroxy, ether, and ester groups. Consequently, graphite oxide is exfoliated by thermal or sono-exfoliation to give graphene oxide (GO). With the use of reducing agents such as hydrazine or sodium tetrahydroborate, GO is often reduced to yield “graphene”. Such chemically reduced graphene possesses different structural and chemical features when compared to the pristine graphene obtained by methods (1) or (2). To distinguish pristine graphene from graphene oxide and chemically reduced graphene oxide (CRGO), graphene oxide and CRGO are generally termed as chemically modified graphenes. The exact quantification of various types of oxygen-containing groups on graphene-related materials is a very challenging issue. Whilst the total amount of oxygen in graphene oxides is easily accessible by chemical analysis, the absolute quantification of these particular oxygen-containing groups, such as hydroxy, aldehyde, carbonyl, carboxy, peroxy, ether, or ester groups is currently practically impossible. Spectroscopic methods are often used in an attempt to elucidate the relative ratio of the particular types of oxygencontaining groups. However, the most widely used spectroscopic methods, such as the Fourier transform infrared spectroscopy (FTIR) or X-ray photoelectron spectroscopy (XPS), suffer from the fact that graphene is actually a heterogeneous material where there is no homogenous distribution of these oxygen-containing groups on its surface. This problem is worsened by the fact that graphene oxides are capable of forming multilayer structures when their suspensions in solutions are dried prior to spectroscopic analyses. In addition, the FTIR and XPS data are often misinterpreted as the vibration/rotation modes of several functional groups overlap each other (in the case of FTIR) or their binding energies are too close that artificial deconvolution is needed (in the case of XPS). This misinterpretation resulted in the assignment of the signals that belong to the same energy levels to different groups, in different journals (for FTIR and XPS, see Ref. [14] and Ref. [13], respectively, and references within). This confusion consequently raises doubts regarding the reliability of these spectroscopic techniques in the identification and quantification of specific oxygen-containing groups. In addition, because there is no standard material at the moment, all of these methods can [a] E. L. K. Chng, Prof. M. Pumera Division of Chemistry & Biological Chemistry School of Physical and Mathematical Sciences Nanyang Technological University Singapore 637371 (Singapore) Fax: (+65) 6791-1961 E-mail : pumera@ntu.edu.sg

Visible light-triggered photoswitchable diarylethene-based iridium(III) complexes for imaging living cells.

Abstract: A novel diarylethene-based iridium(III) complex was synthesized as a phosphorescence probe for monitoring living cells. The switchable phosphorescence complex in solution and within living cells was controlled by two distinguishable visible-light irradiations, which suggests that this complex can be developed as a promising probe with weak photodamage for biological samples.