Tetrathiafulvalene–Oligo(para‐phenyleneethynylene) Conjugates: Formation of Multiple Mixed‐Valence Complexes upon Electrochemical Oxidation

Short monodisperse oligo‐ (para‐phenyleneethynylene) (pOPE) units bearing laterally attached tetrathio‐substituted tetrathiofulvalene (TTF) units have been synthesised from functionalised aromatic building blocks by using the Sonogashira cross‐coupling methodology. The unusual redox properties of these TTF–pOPE conjugates were observed by employing electrochemical methods, such as cyclic voltammetry and exhaustive electrolysis. We found that formally one half of the TTF units in the pOPE monomer 1 , dimer 2 , and trimer 3 (with 2, 4, and 6 TTF units, respectively) are electrochemically silent during the first‐step oxidation at 0.49 V. We propose the formation of persistent mixed‐valence complexes from the TTF and TTF^+. units present in an equal ratio. Such mixed‐valence dyads (single or multiple in the partially oxidised 1 – 3 ) exhibit an unusual stability towards oxidation until the potential of the second oxidation at 0.84 V is achieved. This finding suggests that below this potential the oxidation of the respective mix‐valence complexes is extremely slow.     

Label‐ and modification‐free‐based in situ selection of bovine serum albumin specific aptamer

Systematic evolution of ligands by exponential enrichment is a traditional approach to select aptamer, which has a great potential in biosensing field. However, chemical modifications of DNA library or targets before selection might block the real recognition and binding sites between aptamers and their targets. In this study, a label‐ and modification‐free‐based in situ selection strategy was developed to overcome this limitation. The strategy is an attempt to screen bovine serum albumin aptamers according to the principle of electrophoretic mobility shift assay, and allowed single‐stranded DNA sequence to be fully exposed to interact with bovine serum albumin which was mixed with the agarose gel beforehand. After eight rounds of selection, specific aptamer with low dissociation constant (K_d) value of 69.44 ± 7.60 nM was selected and used for subsequent establishment of fluorescence biosensor. After optimization, the optimal aptasensor exhibited a high sensitivity toward bovine serum albumin with a limit of detection of 0.24 ng/mL (linear range from 1 to 120 ng/mL). These results indicated that the label‐ and modification‐free‐based in situ selection strategy proposed in this work could effectively select specific aptamer to develop aptasensor for sensitive detection of bovine serum albumin or other targets in actual complicated samples.     

Avidin and Glucose Oxidase‐non‐covalently Functionalized Multi‐walled Carbon Nanotubes: A New Analytical Tool for Building a Bienzymatic Glucose Biosensor

We report an innovative supramolecular architecture for bienzymatic glucose biosensing based on the non‐covalently functionalization of multi‐walled carbon nanotubes (MWCNTs) with two proteins, glucose oxidase (GOx) (to recognize glucose) and avidin (to allow the specific anchoring of biotinylated horseradish peroxidase (b‐HRP)). The optimum functionalization was obtained by sonicating for 10 min 0.50 mg mL^?1 MWCNTs in a solution of 2.00 mg mL^?1 GOx+1.00 mg mL^?1avidin prepared in 50 : 50 v/v ethanol/water. The sensitivity to glucose for glassy carbon electrodes (GCE) modified with MWCNTs‐GOx‐avidin dispersion and b‐HRP (GCE/MWCNTs‐GOx‐avidin/b‐HRP), obtained from amperometric experiments performed at ?0.100 V in the presence of 5.0×10^?4 M hydroquinone, was (4.8±0.3) μA mM^?1 (r²=0.9986) and the detection limit was 1.2 μM. The reproducibility for 5 electrodes using the same MWCNTs/GOx‐avidin dispersion was 4.0 %, while the reproducibility for 3 different dispersions and 9 electrodes was 6.0 %. The GCE/MWCNT‐GOx‐avidin/b‐HRP was successfully used for the quantification of glucose in a pharmaceutical product and milk.     

Zeptomole Detection of Streptavidin Using Carbon Paste Electrode and Square‐Wave Voltammetry

We compared the suitability of avidin and streptavidin for avidin‐biotin technology in view of the sensitivity of the analysis using square‐wave voltammetry. We found out during our preliminary experiments that streptavidin gave approximately 100 times higher electrochemical response in comparison with avidin at the same experimental conditions and concentration. Thus, we used two approaches for streptavidin determination – analysis directly in electrochemical cell and analysis by adsorptive transfer technique (AdTS). Ten minutes long accumulation on carbon paste electrode surface was ascertained as optimal in both cases. Limits of detection were 0.3 aM (electrochemical cell) and 30 aM (AdTS).     

Designing superhydrophobic surface based on fluoropolymer–silica nanocomposite via RAFT‐mediated polymerization‐induced self‐assembly

Superhydrophobic surfaces (SHS) find versatile applications as coatings due to their very high water‐repellency, self‐cleaning, and anti‐icing properties. This investigation describes the preparation of a SHS from surfactant‐free hybrid fluoropolymer latex. In this case, reversible addition‐fragmentation chain transfer (RAFT) polymerization was adopted to prepare a copolymer of 4‐vinyl pyridine (4VP) and vinyl triethoxysilane (VTES), where the pyridine units were quaternized to make the copolymer soluble in water. The copolymer was further used as a macro‐RAFT agent to polymerize 2,2,2‐trifluoroethyl methacrylate (TFEMA) in a surfactant‐free emulsion via polymerization‐induced self‐assembly (PISA). The macro‐RAFT agent contained a small amount of VTES as co‐monomer which was utilized to graft silica nanoparticles (SNPs) onto the P(TFEMA) spheres. The film prepared using the nanocomposite latex exhibited a nano‐structured surface as observed by SEM and AFM analyses. Surface modification of the film with fluorinated trichlorosilane produced an SHS with a water contact angle (WCA) of 151.5°. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 266–275     

Offset‐compensated and zero‐quantum suppressed ROESY provides accurate 1H–1H distances in small to medium‐sized molecules

A robust version of the off‐resonance ROESY pulse scheme is suggested for the measurement of proton–proton distances or slow chemical exchange in small to medium‐sized molecules. The method implements adiabatic ramps to establish a pair of opposite frequency off‐resonance spin lock fields – with optionally randomized duration – and adiabatic inversion pulses with simultaneous gradients for efficient zero‐quantum suppression. The amended pulse sequence yields pure absorption cross‐peaks and works safely for small to medium‐sized molecules. The applicability of the method has been demonstrated using small, rigid molecules (strychnine and codeine) and was also applied for a cyclic peptide and a small protein. We found that the pure phase cross‐peaks of the new ROESY version are beneficial for distance measurements. The one‐dimensional (selective) version of the new method is also powerful for measuring selected pair‐wise interactions and distance determination. Copyright © 2016 John Wiley & Sons, Ltd.     

One‐Pot,Step‐Wise,Alternative Syntheses of Quinoline‐Substituted Bis(Indolyl)Methanes Using a Green Approach

A green and highly efficient protocol for one‐pot, step‐wise, alternative syntheses of quinoline‐substituted bi(indolyl)methanes has been described by the condensation of N‐methyl or N‐ethyl quinolone‐4‐one‐3‐carbaldehydes 1a and b with indole 2a – f in water containing a catalytic amount of l ‐proline to afford the title compounds 5a – l in high yields and in shorter reaction times. This reaction involves easy workup without using column chromatography.     

On the use of the observation‐wise k‐fold operation in PCA cross‐validation

Cross‐validation (CV) is a common approach for determining the optimal number of components in a principal component analysis model. To guarantee the independence between model testing and calibration, the observation‐wise k‐fold operation is commonly implemented in each cross‐validation step. This operation renders the CV algorithm computationally intensive, and it is the main limitation to apply CV on very large data sets. In this paper, we carry out an empirical and theoretical investigation of the use of this operation in the element‐wise k‐fold (ekf) algorithm, the state‐of‐the‐art CV algorithm. We show that when very large data sets need to be cross‐validated and the computational time is a matter of concern, the observation‐wise k‐fold operation can be skipped. The theoretical properties of the resulting modified algorithm, referred to as column‐wise k‐fold (ckf) algorithm, are derived. Also, its performance is evaluated with several artificial and real data sets. We suggest the ckf algorithm to be a valid alternative to the standard ekf to reduce the computational time needed to cross‐validate a data set. Copyright © 2015 John Wiley & Sons, Ltd.     

Enhanced β‐phase in PVDF polymer nanocomposite and its application for nanogenerator

Harvesting energy from the ambient mechanical energy by using flexible piezoelectric nanogenerator is a revolutionary step toward achieving reliable and green energy source. Polyvinylidene fluoride (PVDF), a flexible polymer, can be a potential candidate for the nanogenerator if its piezoelectric property can be enhanced. In the present work, we have shown that the polar crystalline β‐phase of PVDF, which is responsible for the piezoelectric property, can be enhanced from 48.2% to 76.1% just by adding ZnO nanorods into the PVDF matrix without any mechanical or electrical treatment. A systematic investigation of PVDF‐ZnO nanocomposite films by using X‐ray diffractometer, Fourier transform infrared spectroscopy, and polarization‐electric field loop measurements supports the enhancement of β‐phase in the flexible nanocomposite polymer films. The piezoelectric constant (d₃₃) of the PVDF‐ZnO (15 wt%) film is found to be maximum of approximately −1.17 pC/N. Nanogenerators have been fabricated by using these nanocomposite films, and the piezoresponse of PVDF is found to enhance after ZnO loading. A maximum open‐circuit voltage ~1.81 V and short‐circuit current of 0.57 μA are obtained for 15 wt% ZnO‐loaded PVDF nanocomposite film. The maximum instantaneous output power density is obtained as 0.21 μW/cm² with the load resistance of 7 MΩ, which makes it feasible for the use of energy harvesting that can be integrated to use for driving small‐scale electronic devices. This enhanced piezoresponse of the PVDF‐ZnO nanocomposite film‐based nanogenerators attributed to the enhancement of electroactive β‐phase and enhanced d₃₃ value in PVDF with the addition of ZnO nanorods.     

1,8‐Naphthalimide‐Substituted BODIPY Dyads: Synthesis,Structure, Properties,and Live‐Cell Imaging

A set of 1,8‐naphthalimide (NPI)‐substituted 4,4‐difluoroboradiaza‐s‐indacene (BODIPY) dyads 1 a – 1 c were designed and synthesized by the Pd‐catalyzed Sonogashira cross‐coupling reaction of ethynyl substituted NPI 1 with the meso‐, β‐, and α‐halogenated BODIPYs a , b , and c , respectively. The BODIPY 1 c exhibits redshifted absorption, which suggests better electronic communication with substitution at the α‐position of BODIPY compared with at the meso and β positions, which was further supported by time‐dependent DFT calculations. The optical band gap follows the order 1 a > 1 b > 1 c . The single‐crystal X‐ray structures of dyads 1 a – 1 c are reported, which reflect planar orientations of the BODIPY units with respect to the NPIs. The DFT‐optimized structures show good correlation with the experimental data obtained from the single‐crystal X‐ray structures. The packing diagram of 1 a shows a sheet‐like arrangement, 1 b forms a ladder‐like structural motif, and 1 c forms a complex 3D structural arrangement. The dyads 1 a – 1 c show low cytotoxicity (IC₅₀>100 μm ). The confocal microscopy studies with HeLa and A375 cells (when treated with dyads 1 a – 1 c ) show that all the dyads easily enter the cell membrane and show significant multicolor intracellular fluorescence covering the entire visible range with clear emissions in blue, green, and red channels.     

A Simple Synthesis of 5‐(2‐Aminophenyl)‐1H‐pyrazoles

A four‐step synthesis of 1‐substituted 5‐(2‐aminophenyl)‐1H‐pyrazoles 5 as a novel type of histamine analogs and versatile building blocks for further transformations was developed. The synthesis starts from commercially available 2‐nitroacetophenone ( 12 ), which is converted into the enamino ketone 13 as the key intermediate. Cyclization of the key intermediate 13 with monosubstituted hydrazines 14a – 14l afforded the 5‐(2‐nitrophenyl)‐1H‐pyrazoles 17a – 17l . Finally, catalytic hydrogenation of the nitro compounds 17a, 17c – 17e , and 17g – 17j furnished the title compounds 5a, 5c – 5e , and 5g – 5j , respectively, in good yields. As demonstrated by some further transformations, additional functionalization of compounds 17 and 5 is feasible, either by electrophilic substitution at C(4) of the pyrazole ring, or at the NH₂ group.     

Sequence‐based prediction of protein–peptide binding sites using support vector machine

Protein–peptide interactions are essential for all cellular processes including DNA repair, replication, gene‐expression, and metabolism. As most protein – peptide interactions are uncharacterized, it is cost effective to investigate them computationally as the first step. All existing approaches for predicting protein – peptide binding sites, however, are based on protein structures despite the fact that the structures for most proteins are not yet solved. This article proposes the first machine‐learning method called SPRINT to make Sequence‐based prediction of Protein – peptide Residue‐level Interactions. SPRINT yields a robust and consistent performance for 10‐fold cross validations and independent test. The most important feature is evolution‐generated sequence profiles. For the test set (1056 binding and non‐binding residues), it yields a Matthews’ Correlation Coefficient of 0.326 with a sensitivity of 64% and a specificity of 68%. This sequence‐based technique shows comparable or more accurate than structure‐based methods for peptide‐binding site prediction. SPRINT is available as an online server at: http://sparks-lab.org/ . © 2016 Wiley Periodicals, Inc.     

Cross‐linked Polymer‐Blend Gate Dielectrics through Thermal Click Chemistry

New cross‐linking reagents were synthesized and mixed with polystyrene (PS) in solution to form a blend. Thin‐films were spin‐coated from the blend and then cross‐linked by thermal activation at relatively low temperature (100 °C) to form cross‐linked gate dielectrics. This new method is compatible with plastic substrates in flexible electronics. The azide and alkyne cross‐linking reagents are kinetically stable at room temperature, so any premature cross‐linking is avoided during processing. This method also significantly improved the dielectric performances of PS thin films. Solution‐processed top‐gate organic field‐effect transistor devices with indacenodithiophene–benzothiadiazole copolymer as semiconductor layer and the cross‐linked PS blend as dielectric layer showed improved performances with lower gate leakages and higher operation stabilities than devices with neat PS film as dielectric layer.     

Direct Cross‐Couplings of Propargylic Diols

[Pd(PPh₃)₄] catalyzes a Suzuki–Miyaura‐like twofold cross‐coupling sequence between underivatized propargylic diols and either aryl or alkenyl boronic acids to furnish highly substituted 1,3‐dienes. Thus, 2,3‐diaryl‐1,3‐butadienes and their dialkenic congeners ([4]dendralenes) are delivered in a (pseudo)halogen‐free, single‐step synthesis which supersedes existing methods. Allenols are also readily formed. Treatment of these single‐ and twofold cross‐coupled products with acid leads to remarkably short syntheses of highly‐substituted benzofulvenes and aryl indenes, respectively.     

Benzimidazolin‐2‐ylidene–palladium‐catalysed coupling reactions of aryl halides

The in situ prepared three‐component system Pd(OAc)₂–1,3‐dialkylbenzimidazolium chlorides ( 2a – f ) and Cs₂CO₃ catalyses, quantitatively, the Suzuki cross‐coupling of deactivated aryl chlorides and Heck coupling reactions of aryl bromide and iodide substrates. The 1,3‐dialkylbenzimidazolium salts ( 2a – f ) were characterized by conventional spectroscopic methods and elemental analysis. Copyright © 2005 John Wiley & Sons, Ltd.     

Surface‐Modifiable Free‐Floating Films Formed by Multiway Connection of Collagen‐Like Triple‐Helical Peptides

Square‐millimeter‐sized free‐floating translucent films are formed in physiological buffer by multiway connections between biotinylated collagen‐like triple‐helical peptides and avidin. Although the compositions of the films are almost constant, regardless of the ratios of the components loaded, their thicknesses can be controlled by the concentrations of the components. The film surfaces can be further modified by taking advantage of exposed biotin (or avidin) functionalities. The self‐assembled films could serve as novel materials in biomedical and biosensing applications.     

Transition‐Metal‐Free BF3‐Mediated Oxidative and Non‐Oxidative Cross‐Coupling of Pyridines

We report a BF₃‐mediated direct alkynylation of pyridines at C(2) by using a variety of alkynyllithium reagents (oxidative cross‐coupling). Moreover, we have developed a novel transition‐metal‐free cross‐coupling method between alkylmagnesium reagents and 4‐substituted pyridines, such as isonicotinonitrile and 4‐chloropyridine, by employing BF₃?OEt₂ as a promoter. The combination of these methods enabled us to efficiently prepare a range of di‐, tri‐, and tetrasubstituted pyridines.     

Graphene‐Oxide‐Catalyzed Direct CH−CH‐Type Cross‐Coupling: The Intrinsic Catalytic Activities of Zigzag Edges

The development of graphene oxide (GO)‐based materials for C?C cross‐coupling represents a significant advance in carbocatalysis. Although GO has been used widely in various catalytic reactions, the scope of reactions reported is quite narrow, and the relationships between the type of functional groups present and the specific activity of the GO are not well understood. Herein, we explore CH?CH‐type cross‐coupling of xanthenes with arenes using GO as real carbocatalysts, and not as stoichiometric reactants. Mechanistic studies involving molecular analogues, as well as trapped intermediates, were carried out to probe the active sites, which were traced to quinone‐type functionalities as well as the zigzag edges in GO materials. GO‐catalyzed cross‐dehydrogenative coupling is operationally simple, shows reusability over multiple cycles, can be conducted in air, and exhibits good functional group tolerance.