Reaction of 1,6‐Dioxo‐2,4‐Diene with Aziridine and Secondary Amine

The (2E,4E)‐ and (2E,4Z)‐1‐phenyl‐1,6‐dioxo‐hepta‐2,4‐diene reacts with aziridine to give aziridinecyclopentenol 3. This product arises from an intermolecular Michael addition of a nitrogen lone pair to the less reactive enone, followed by an intramolecular aldol reaction of the enol with ketone. Furthermore, the initially formed enol did not undergo nucleophilic attack onto the aziridine ring to form heterocycles. Interestingly, the reaction with secondary amine did not give the cyclopentenol adduct, and this only leads to the isomerization of (2E,4Z)‐1‐phenyl‐1,6‐dioxo‐hepta‐2,4‐diene to the more stable (2E,4E)‐1‐phenyl‐1,6‐dioxo‐hepta‐2,4‐diene by addition to the more reactive enone.     

Facile and Versatile Chemoenzymatic Synthesis of Enterobactin Analogues and Applications in Bacterial Detection

Siderophores, such as enterobactin (Ent), are small molecules that can be selectively imported into bacteria along with iron by cognate transporters. Siderophore conjugates are thus a promising strategy for delivering functional reagents into bacteria. In this work, we present an easy‐to‐perform, one‐pot chemoenzymatic synthesis of functionalized monoglucosylated enterobactin (MGE). When functionalized MGE is conjugated to a rhodamine fluorophore, which affords RhB‐Glc‐Ent, it can selectively label Gram‐negative bacteria that utilize Ent, including some E. coli strains and P. aeruginosa. V. cholerae, a bacterium that utilizes linearized Ent, can also be weakly targeted. Moreover, the targeting is effective under iron‐limiting but not iron‐rich conditions. Our results suggest that the RhB‐Glc‐Ent probe is sensitive not only to the bacterial strain but also to the iron condition in the environment.     

Decreased Turn‐On Times of Single‐Component Light‐Emitting Electrochemical Cells by Tethering an Ionic Iridium Complex with Imidazolium Moieties

We report a significant decrease in turn‐on times of light‐emitting electrochemical cells (LECs) by tethering imidazolium moieties onto a cationic Ir complex. The introduction of two imidazolium groups at the ends of the two alkyl side chains of [Ir(ppy)₂(dC6‐daf)]⁺(PF₆)^? (ppy=2‐phenylpyridine, dC6‐daf=9,9′‐dihexyl‐4,5‐diazafluorene) gave the complex [Ir(ppy)₂(dC6MIM‐daf)]³⁺[(PF₆)^?]₃ (dC6MIM‐daf=9,9‐bis[6‐(3‐methylimidazolium)hexyl]‐1‐yl‐4,5‐diazafluorene). Both complexes exhibited similar photoluminescent/electrochemical properties and comparable electroluminescent efficiencies. The turn‐on times of the LECs based on the latter complex, however, were much lower than those of devices based on the former. The improvement is ascribed to increased concentrations of mobile counterions ((PF₆)^?) in the neat films and a consequent increase in neat‐film ionic conductivity. These results demonstrate that the technique is useful for molecular modifications of ionic transition‐metal complexes (ITMCs) to improve the turn‐on times of LECs and to realize single‐component ITMC LECs compatible with simple driving schemes.     

Electrochemistry and electrogenerated chemiluminescence of 3,6-di(spirobifluorene)-N-phenylcarbazole

We report here the electrochemistry, luminescence, and electrogenerated chemiluminescence (ECL) of 3,6-dispirobifluorene-N-phenylcarbazole (DSBFNPC). DSBFNPC contains two spirobifluorene groups covalently attached to the N-phenylcarbazole core. The optimized geometry as determined from semiempirical MNDO calculations shows that the phenyl group is twisted 89 degrees from the plane of central carbazole, indicating a lack of electron delocalization between these groups. However, the two fluorene rings of each spirobifluorene group are twisted 58 degrees relative to each other and two spirobifluorene groups are twisted 64 degrees from the N-phenylcarbazole ring, suggesting some charge delocalization among these groups. The cyclic voltammetry of this compound shows two reversible oxidation waves (assigned to the formation of the cation and dication) and a two-electron reduction wave that becomes reversible at higher scan rates (assigned to formation of anion). Digital simulations were carried out to obtain details of the electrochemical processes, and electrochemical behavior was compared to that of phenylcarbazole (PC). Upon cycling between the oxidation and reduction waves, ECL is produced by radical ion annihilation. The photophysical properties of DSBFNPC show a strong resemblance to the parent compound, PC, and the ECL spectrum produced via radical ion annihilation shows good agreement with the fluorescence emission spectrum of DSBFNPC.     

The Mesomeric Effect of Thiazolium on non‐Kekulé Diradicals in Pichia stipitis Transketolase

It is theoretically plausible that thiazolium mesomerizes to congeners other than carbene in a low effective dielectric binding site; especially given the energetics and uneven electronegativity of carbene groups. However, such a phenomenon has never been reported. Nine crystal structures of transketolase obtained from Pichia stipitis (TKps) are reported with subatomic resolution, where thiazolium displays an extraordinary ring‐bending effect. The bent thiazolium congeners correlate with non‐Kekulé diradicals because there is no gain or loss of electrons. In conjunction with biophysical and biochemical analyses, it is concluded that ring bending is a result of tautomerization of thiazolium with its non‐ Kekulé diradicals, exclusively in the binding site of TKps. The chemophysical properties of these thiazolium mesomers may account for the great variety of reactivities carried out by thiamine–diphosphate‐containing (ThDP) enzymes. The stability of ThDP in living systems can be regulated by the levels of substrates, and hydration and dehydration, as well as diradical‐mediated oxidative degradation.     

Using a Multi‐Shelled Hollow Metal–Organic Framework as a Host to Switch the Guest‐to‐Host and Guest‐to‐Guest Interactions

A bio‐inspired design of using metal–organic framework (MOF) microcrystals with well‐defined multi‐shelled hollow structures was used as a matrix to host multiple guests including molecules and nanoparticles at separated locations to form a hierarchical material, mimicking biological structures. The interactions such as energy transfer (ET) between different guests are regulated by precisely fixing them in the MOF shells or encapsulating them in the cavities between the MOF shells. The proof‐of‐concept design is demonstrated by hosting chromophore molecules including rhodamine 6G (R6G) and 7‐amino‐4‐(trifluoromethyl)coumarin (C‐151), as well as metal nanoparticles (Pd NPs) into the multi‐shelled hollow zeolitic imidazolate framework‐8 (ZIF‐8). We could selectively establish or diminish the guest‐to‐framework and guest‐to‐guest ET. This work provides a platform to construct complex multifunctional materials, especially those need precise separation control of multi‐components.     

A Convenient Modified Short Route for the Preparation of [32]ane‐N8 Hydrochloride

A convenient modified short‐cut route for the preparation of a 32‐membered octaazamacrocyclic molecule, 1,5,9,13,17,21,25,29‐octaazacyclodotriacontane hydrochloride, [32]ane‐N₈·8HCl has been described. The proper tetramine has been contemplated to go this new pathway which propagates [32]‐N8·8HCl more effectively.     

Ion transport properties of mechanically stable symmetric ABCBA pentablock copolymers with quaternary ammonium functionalized midblock

Anion exchange membranes (AEMs) are a promising class of materials for applications that require selective ion transport, such as fuel cells, water purification, and electrolysis devices. Studies of structure–morphology–property relationships of ion‐exchange membranes revealed that block copolymers exhibit improved ion conductivity and mechanical properties due to their microphase‐separated morphologies with well‐defined ionic domains. While most studies focused on symmetric diblock or triblock copolymers, here, the first example of a midblock quaternized pentablock AEM is presented. A symmetric ABCBA pentablock copolymer was functionalized to obtain a midblock brominated polymer. Solution cast films were then quaternized to obtain AEMs with resulting ion exchange capacities (IEC) ranging from 0.4 to 0.9 mmol/g. Despite the relatively low IEC, the polymers were highly conductive (up to 60 mS/cm Br^? at 90 °C and 95%RH) with low water absorption (<25 wt %) and maintained adequate mechanical properties in both dry and hydrated conditions. X‐ray scattering and transmission electron microscopy (TEM) revealed formation of cylindrical non‐ionic domains in a connected ionic phase. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 612–622     

Biomimetic Taste Receptors with Chiral Recognition by Photoluminescent Metal–Organic Frameworks Chelated with Polyaniline Helices

The adsorption of phenylaniline (Phe) enantiomers on (+)‐polyaniline (PAN)‐chelated [In(OH)(bdc)]_n microcrystals was carefully designed and studied by using the Job titration, circular dichroism, X‐ray photoelectron spectroscopy, and photoluminescence to mimic heterotrimeric guanine nucleotide‐binding protein (G protein)‐coupled receptors in selective, but not specific, ligand binding with chiral recognition and signal transduction. Six essential working principles across different length scales are unraveled: 1) a chiral (+)‐PAN (host), 2) specific sites for Phe‐(+)/PAN (guest–host) binding, 3) a conformational change of (+)‐PAN after binding with Phe enantiomers, 4) different degrees of packing for (+)‐PAN, 5) interactions between (+)‐PAN and the underlying signal‐generating framework (i.e., [In(OH)(bdc)]_n microcrystals), and 6) a systematic photoluminescent signal combination by using principal‐component analysis from the other three polymer‐chelated metal–organic frameworkds (MOFs), such as poly(acrylic acid) (PAA), sodium alginate (SA), and polyvinylpyrrolidone (PVP) to enhance the selectivity and discrimination capabilities.     

Photoresponsive and fluorescence behaviors of azobenzene‐containing amphiphilic block copolymers

The effects of solvency and mole fraction of azobenzene moieties (f_PAzoMA) on the photoresponsive and fluorescence behaviors of poly(acrylic acid)‐block‐poly(6‐[4‐(4′‐methoxyphenylazo)phenoxy]hexyl methacrylate) (PAA‐PAzoMA) amphiphilic diblock copolymers were investigated using UV–vis spectroscopy and fluorescence spectroscopy. The photoresponsive behavior depended strongly on the solvency and f_PAzoMA. When dissolved in a PAA‐selective solvent, PAA‐PAzoMA formed micelles with PAzoMA in the micelle core. The confinement of azobenzene moieties caused a steric hindrance, thereby markedly reducing the kinetics of photoisomerization compared with that of the unconfined PAA‐PAzoMA in a nonselective solvent. Additionally, PAA‐PAzoMA dissolved in the PAA‐selective solvent caused a blue shift of the maximum absorbance, suggesting the formation of H‐aggregates of azobenzene mesogens. The high H‐aggregate content substantially reduced the fluorescence emission. Consequently, the fluorescence emission of PAA‐PAzoMA in the nonselective solvent was more intense than that in the PAA‐selective solvent. Upon UV irradiation, the enhanced bent‐shaped cis isomers disturbed the compact packing of azobenzene mesogens, which substantially enhanced the fluorescence emission. Both the photoisomerization rate and fluorescence emission decreased with an increase in f_PAzoMA. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 793–803