Double Functionalization of Carbon Nanotubes with Purine and Pyrimidine Derivatives

Herein, we have developed a synthetic strategy for the covalent double functionalization of single‐walled carbon nanotubes (SWCNTs) with a combination of purine–pyrimidine and purine–purine nucleobase systems. The nucleobases were introduced on the sidewall of oxidized SWCNTs through 1,3‐dipolar cycloaddition and by amidation of the carboxylic acids located at the tips and defect sites of the nanotubes. The new nanohybrids were characterized by transmission electron microscopy, thermogravimetric analysis, FTIR and Raman spectroscopy, magic‐angle spinning NMR spectroscopy, and Kaiser test. The nucleobase/SWCNT conjugates can be envisaged for the modulation of the interactions with nucleic acids by means of base pairing, thereby opening new possibilities in the development of DNA/CNT nanobioconjugates.     

Capillary electrophoresis of covalently functionalized single‐chirality carbon nanotubes

We demonstrate the separation of chirality‐enriched single‐walled carbon nanotubes (SWCNTs) by degree of surface functionalization using high‐performance CE. Controlled amounts of negatively charged and positively charged functional groups were attached to the sidewall of chirality‐enriched SWCNTs through covalent functionalization using 4‐carboxybenzenediazonium tetrafluoroborate or 4‐diazo‐N,N‐diethylaniline tetrafluoroborate, respectively. Surfactant‐ and pH‐dependent studies confirmed that under conditions that minimized ionic screening effects, separation of these functionalized SWCNTs was strongly dependent on the surface charge density introduced through covalent surface chemistry. For both heterogeneous mixtures and single‐chirality‐enriched samples, covalently functionalized SWCNTs showed substantially increased peak width in electropherogram spectra compared to nonfunctionalized SWCNTs, which can be attributed to a distribution of surface charges along the functionalized nanotubes. Successful separation of functionalized single‐chirality SWCNTs by functional density was confirmed with UV‐Vis‐NIR absorption and Raman scattering spectroscopies of fraction collected samples. These results suggest a high degree of structural heterogeneity in covalently functionalized SWCNTs, even for chirality‐enriched samples, and show the feasibility of applying CE for high‐performance separation of nanomaterials based on differences in surface functional density.     

In Situ Synthesis of a Novel Quinone Imine Self‐Assembled Monolayer and Consideration of Its Reactivity with L‐Arginine

In situ functionalization of a 4‐aminothiophenol (4ATP) self‐assembled monolayer (SAM) on a Au electrode (4ATP/Au SAM) by the Michael addition reaction is considered. Under optimized conditions, the nucleophilic attack of the amino group of 4ATP/Au SAM to give an electrogenerated ortho‐quinone produced a novel electroactive SAM (ESAM). The ESAM could be oxidized to quinone‐imine SAM (QI SAM) for the covalent immobilization of L ‐arginine monolayers. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Fourier transform infrared (FTIR) spectroscopy are employed to characterize these systems.. The apparent heterogeneous rate constant (k_s^app) for ESAM/Au and the rate constant (k′) of the pseudo‐first order Michael addition reaction of L ‐arginine and ESAM/Au are calculated.     

Functionalization of single-walled carbon nanotubes with (R-)oxycarbonyl nitrenes

Sidewall functionalization of single-walled carbon nanotubes (SWCNTs) via the addition of (R-)oxycarbonyl nitrenes allows for the covalent binding of a variety of different groups such as alkyl chains, aromatic groups, dendrimers, crown ethers, and oligoethylene glycol units. Such additions lead to a considerable increase in the solubility in organic solvents such as 1,1,2,2-tetrachloroethane (TCE), dimethyl sulfoxide (DMSO), and 1,2-dichlorobenzene (ODCB). The highest solubilities of 1.2 mg/mL were found for SWCNT adducts with nitrenes containing crown ether of oligoethylene glycol moieties in DMSO and TCE, respectively. The presence of chelating donor groups within the addends allowed for the complexation of Cu(2+) and Cd(2+). Atomic force microscopy (AFM) and transmission electron microscopy (TEM) revealed that the functionalized tubes form thin bundles with typical diameters of 10 nm. The presence of thin bundles in solution is supported by (1)H NMR spectroscopy. The elemental composition of the functionalized SWCNT was determined by X-ray photoelectron spectroscopy (XPS). The use of Raman and electron absorption spectroscopy (UV/Vis-nIR) showed that the electronic properties of the SWCNTs are mostly retained after functionalization, indicating a low degree of addition within this series of SWCNT derivatives.     

Poly(γ‐benzyl‐L‐glutamate)‐functionalized single‐walled carbon nanotubes from surface‐initiated ring‐opening polymerizations of N‐carboxylanhydride

Single‐walled carbon nanotubes (SWCNTs) have been functionalized with poly(γ‐benzyl‐L ‐glutamate) (PBLG) by ring‐opening polymerizations of γ‐benzyl‐L ‐glutamic acid‐based N‐carboxylanhydrides (NCA‐BLG) using amino‐functionalized SWCNTs (SWCNT‐NH₂) as initiators. The SWCNT functionalization has been verified by FTIR spectroscopy and transmission electron microscopy. The FTIR study reveals that surface‐attached PBLGs adopt random‐coil conformations in contrast to the physically absorbed or bulk PBLGs, which exhibit α‐helical conformations. Raman spectroscopic analysis reveals a significant alteration of the electronic structure of SWCNTs as a result of PBLG functionalization. The PBLG‐functionalized SWCNTs (SWCNT‐PBLG) exhibit enhanced solubility in DMF. Stable DMF solutions of SWCNT‐PBLG/PBLG with a maximum SWCNTs concentration of 259 mg L^?1 can be readily obtained. SWCNT‐PBLG/PBLG solid composites have been characterized by differential scanning calorimetry, thermogravimetric analysis, wide/small‐angle X‐ray scattering (W/SAXS), scanning electron microscopy, and polarized optical microscopy for their thermal or morphological properties. Microfibers containing SWCNT‐PBLG and PBLG can also be prepared via electrospinning. WAXS characterization reveals that SWCNTs are evenly distributed among PBLG rods in solution and in the solid state where PBLGs form a short‐range nematic phase interspersed with amorphous domains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2340–2350, 2010     

“Smart” molecularly imprinted monoliths for the selective capture and easy release of proteins

A new thermally switchable molecularly imprinted monolith for the selective capture and release of proteins has been designed. First, a generic poly(glycidyl methacrylate‐co‐ethylene dimethacrylate) monolith reacted with ethylenediamine followed by functionalization with 2‐bromoisobutyryl bromide to introduce the initiator for atom transfer radical polymerization. Subsequently, a protein‐imprinted poly(N‐isopropylacrylamide) layer was grafted onto the surface of the monolithic matrix by atom transfer radical polymerization. Scanning electron microscopy and energy‐dispersive X‐ray spectroscopy of the cross‐sections of imprinted monoliths confirmed the formation of dense poly(N‐isopropylacrylamide) brushes on the pore surface. The imprinted monolith exhibited high specificity and selectivity toward its template protein myoglobin over competing proteins and a remarkably large maximum adsorption capacity of 1641 mg/g. Moreover, this “smart” imprinted monolith featured thermally responsive characteristics that enabled selective capture and easy release of proteins triggered only by change in temperature with water as the mobile phase and avoided use of stronger organic solvents or change in ionic strength and pH.     

Direct Electrochemistry of Hemoglobin on Single‐Walled Carbon Nanotubes Modified Carbon Ionic Liquid Electrode and Its Electrocatalysis

In this article we report on the fabrication of a carbon ionic liquid electrode (CILE) by using a room temperature ionic liquid of 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF₆) as binder. It was further modified by single‐walled carbon nanotubes (SWCNTs) to get a SWCNTs modified CILE denoted as SWCNTs/CILE. The redox protein of hemoglobin (Hb) was further immobilized on the surface of SWCNTs/CILE with the help of Nafion film. UV‐vis and FT‐IR spectra indicated that the immobilized Hb retained its native conformation in the composite film. The direct electrochemistry of Hb on the SWCNTs/CILE was carefully studied in pH 7.0 phosphate buffer solution (PBS). Cyclic voltammetric results indicated that a pair of well‐defined and quasireversible voltammetric peaks of Hb heme Fe(III)/Fe(II) was obtained with the formal potential (E°') at ?0.306 V (vs. SCE). The electrochemical parameters such as the electron transfer coefficient (α), the electron transfer number (n) and the apparent heterogeneous electron transfer rate constant (k_s) were calculated as 0.34, 0.989 and 0.538 s^?1, respectively. The fabricated Hb modified electrode showed good electrocatalytic ability to the reduction of trichloroacetic acid (TCA) in the concentration range from 20.0 to 150.0 mmol/L with the detection limit of 10.0 mmol/L (3σ).     

Redox-active electrolyte supercapacitors using electroactive ionic liquids

Here we present redox ionic liquid supercapacitors (RILSCs) which use electrolytes made from ionic liquids modified with an electroactive function to increase the energy density of activated carbon electrodes via faradaic reactions. More specifically, two different ionic liquids were made by modifying either the imidazolium cation or the bis(trifluoromethanesulfonyl)imide anion with ferrocene in order to determine the importance of the electroactive ion's polarity. The functionalization of an ionic liquid with ferrocene led to high concentrations of redox moieties in the electrolyte (2.4 M) and a large maximum operating voltage (2.5 V). An energy density of up to 13.2 Wh per kg (both electrodes) was obtained which represents an 83% increase vs. the unmodified ionic liquid. When the ionic liquid's anion is modified with ferrocene, the self-discharge at the positive electrode is fully suppressed due to the deposition of a film on the electrode. The results presented herein demonstrate that electroactive ionic liquids constitute a promising alternative to conventional solute in solvent electrolytes found in energy storage devices, and are particularly well-suited for redox-active electrolyte supercapacitors.     

Covalent Inter‐Carbon‐Allotrope Architectures Consisting of the Endohedral Fullerene Sc3N@C80 and Single‐Walled Carbon Nanotubes

Using a reductive sidewall functionalization concept, we prepared for the first time a covalent inter‐carbon‐allotrope hybrid consisting of single‐walled carbon nanotubes (SWCNTs) and the endohedral fullerene Sc₃N@C₈₀. The new compound type was characterized through a variety of techniques including absorption spectroscopy, Raman spectroscopy, TG‐MS, TG‐GC‐MS, and MALDI‐TOF MS. HRTEM investigations were carried out to visualize this highly integrated architecture.     

Synthesis of trans‐dihydrofurans using bis (1(3‐trimethoxysilylpropyl)‐3‐methyl‐imidazolium) nickel tetrachloride tethered to colloidal silica nanoparticles

An efficient multicomponent synthesis of dihydrofurans is described by a one‐pot condensation reaction of 4‐bromophenacyl bromide, aromatic aldehydes, and dimedone using an ionic liquid tethered to colloidal silica nanoparticles under reflux conditions in acetonitrile. The ionic liquid tethered to colloidal silica nanoparticles is characterized by ¹H NMR spectroscopy, scanning electron microscopy, energy‐dispersive spectroscopy, thermogravimetric analysis, and dynamic light scattering. Atom economy, a wide range of products, high catalytic activity, excellent yields in short reaction times, diastereoselective synthesis, reusability of the catalyst, and low catalyst loading are some of the important features of this protocol.     

Synthesis of Cyclic Carbonate Catalyzed by DBU Derived Basic Ionic Liquids

In this work, 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU), 1,5‐diazabicyclo[4.3.0]‐5‐nonene (DBN), and imidazole (MIM)‐derived bromide ionic liquids (ILs) were synthesized and used to catalyze the cycloaddition reactions of carbon dioxide (CO₂) with several kinds of epoxides to form cyclic carbonates. The DBU derived bromide ionic liquid system was found to have the best catalytic activity among all the tested ILs. The influences of reaction conditions (including temperature, pressure and reaction time) on the reaction of CO₂ to propylene oxide (PO) were studied to show the best conditions of 120 °C, 1 MPa, 2.5 h catalyzed by 2 mol% DBU‐derived bromide ionic liquid, with the conversion of PO and the selectivity of propylene carbonate (PC) reaching 99% and 99%, respectively. Under the optimum reaction conditions, the ionic liquid system could be reused at least five times without decrease in selectivity and conversion. NMR spectroscopy and DFT calculations were used to reveal the hydrogen‐bond interaction between ionic liquids and reagent, based on which the reaction mechanism was proposed.     

Residual Metal Impurity Aids Facile In Situ Electrochemical Surface Derivatization of Single‐Walled Carbon Nanotubes

Residual metal impurities were exploited as reactants in the functionalization of the surface of single‐walled carbon nanotubes (SWCNT) with nickel hexacyanoferrate (NiHCF) by simple electrochemical cycling in ferricyanide solutions. This facile in situ electrochemical modification process provides intimate contact between NiHCF and SWCNTs that improves the stability of the redox property and reactivity of NiHCF. The characteristic redox behavior of NiHCF on SWCNT surfaces can be used as an electrochemical probe to access qualitative and quantitative information on unknown electroactive metal impurities in SWCNTs. Significantly, the NiHCF‐modified SWCNTs exhibit pseudocapacitive behavior, and the calculated specific capacitances are 710 and 36 F g^?1 for NiHCF‐SWCNTs and SWCNTs respectively. Furthermore, NiHCF‐SWCNTs were transformed into Ni(OH)₂/SWCNTs and used for enzymeless glucose oxidation.     

Selective polycarboxylation of semiconducting single-walled carbon nanotubes by reductive sidewall functionalization

The efficient and controllable synthesis, the detailed characterization, and the chemical postfunctionalization of polycarboxylated single-walled carbon nanotubes SWCNT(COOH)(n) are reported. This innovative covalent sidewall functionalization method is characterized by (a) the preservation of the integrity of the entire σ-framework of SWCNTs; (b) the possibility of achieving very high degrees of addition; (c) control of the functionalization degrees by the variation of the reaction conditions (reaction time, ultrasonic treatment, pressure); (d) the identification of conditions for the selective functionalization of semiconducting carbon nanotubes, leaving unfunctionalized metallic tubes behind; (e) the proof that the introduced carboxylic acid functionalities can serve as versatile anchor points for the coupling to functional molecules; and (f) the application of a subsequent thermal degradation step of the functionalized semiconducting tubes leaving behind intact metallic SWCNTs. Functional derivatives have been characterized in detail by means of Raman, UV-vis/nIR, IR, and fluorescence spectroscopy as well as by thermogravimetric analysis combined with mass spectrometry, atomic force microscopy, and zeta-potential measurements.     

Efficient Chemical Modification of Carbon Nanotubes with Metallacarboranes

As‐produced single‐walled carbon nanotubes (SWCNTs) tend to aggregate in bundles due to π–π interactions. Several approaches are nowadays available to debundle, at least partially, the nanotubes through surface modification by both covalent and noncovalent approaches. Herein, we explore different strategies to afford an efficient covalent functionalization of SWCNTs with cobaltabisdicarbollide anions. Aberration‐corrected HRTEM analysis reveals the presence of metallacarboranes along the walls of the SWCNTs. This new family of materials presents an outstanding water dispersibility that facilitates its processability for potential applications.     

Synthesis and characterization of polyethylene chains grafted onto the sidewalls of single‐walled carbon nanotubes via copolymerization

Polyethylene (PE) chains grafted onto the sidewalls of SWCNTs (SWCNT‐g‐PE) were successfully synthesized via ethylene copolymerization with functionalized single‐walled carbon nanotubes (f‐SWCNTs) catalyzed by rac‐(en)(THInd)₂ZrCl₂/MAO. Here f‐SWCNTs, in which α‐alkene groups were chemically linked on the sidewalls of SWCNTs, were synthesized by Prato reaction. The composition and microstructure of SWCNT‐g‐PE were characterized by means of ¹H NMR, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, thermogravimetric analyses (TGA), field‐emission scanning electron microscope (FESEM), and transmission electron microscope (TEM). Nanosized cable‐like structure was formed in the SWCNT‐g‐PE, in which the PE formed a tubular shell and several SWCNTs bundles existed as core. The formation of the above morphology in the SWCNT‐g‐PE resulted from successfully grafting of PE chains onto the surface of SWCNTs via copolymerization. The grown PE chains grafted onto the sidewall of the f‐SWCNTs promoted the exfoliation of the mass nanotubes. Comparing with pure PE, the physical mixture of PE/f‐SWCNTs and in situ PE/SWCNTs mixture, thermal stability, and mechanical properties of SWCNT‐g‐PE were higher because of the chemical bonding between the f‐SWCNTs and PE chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5459–5469, 2007     

A fully conjugated TTF-π-TCAQ system: synthesis, structure, and electronic properties

The synthesis of the first fully conjugated tetrathiafulvalene–tetracyano‐p‐quinodimethane ((TTF)–TCNQ)‐type system has been carried out by means of a Julia–Kocienski olefination reaction. In particular, a tetracyanoanthraquinodimethane (TCAQ) formyl derivative and two new sulfonylmethyl‐exTTFs (exTTF=2‐[9‐(1,3‐dithiol‐2‐ylidene)anthracen‐10(9H)‐ylidene]‐1,3‐dithiole)—prepared as new building blocks—were linked. A variety of experimental conditions reveal that the use of sodium hexamethyldisilazane (NaHMDS) as base in THF afforded the E olefins with excellent stereoselectivity. Theoretical calculations at the B3LYP/6‐31G** level point to highly distorted exTTF and TCAQ that form an almost planar stilbene unit between them. Although calculations predicted appreciable electronic communication between the donor and the acceptor, cyclic voltammetric studies did not substantiate this effect. It was only in photophysical assays that the electronic communication emerged in the form of a charge‐transfer (CT) absorption and emission. Once photoexcited (i.e., the locally excited state or excited charge‐transfer state), an ultrafast, subpicosecond charge separation leads to a radical ion pair state in which the spectroscopic features of the radical cation of exTTF as well as the radical anion of TCAQ are discernable. The radical ion pair is metastable and undergoes a fast ((1.0±0.2) ps) charge recombination to reconstitute the electronic ground state. Such ultrafast charge separation and recombination processes come as a consequence of the very short vinyl linkage between the two electroactive units.     

Direct Electrochemistry and Electrocatalysis of Myoglobin Immobilized on Graphene‐CTAB‐Ionic Liquid Nanocomposite Film

This paper describes the direct electrochemistry and electrocatalysis of myoglobin immobilized on graphene‐cetylramethylammonium bromide (CTAB)‐ionic liquid nanocomposite film on a glassy carbon electrode. The nanocomposite was characterized by transmission electron microscopy, scanning electron microscopy, X‐ray photoelectron spectroscopy, and electrochemistry. It was found that the high surface area of graphene was helpful for immobilizing more proteins and the nanocomposite film could provide a favorable microenvironment for MB to retain its native structure and activity and to achieve reversible direct electron transfer reaction at an electrode. The ionic liquid may play dual roles here: it keeps the protein's activity and improves stability of the nanocomposite film; it also serves as a binder between protein and electrode, therefore, enhancing the electron transfer between the protein and the electrode. The nanocomposite films also exhibit good stability and catalytic activities for the electrocatalytic reduction of H₂O₂.     

Multipurpose Nature of Rapid Covalent Functionalization on Carbon Nanotubes

In the vast field of functionalization routes to carbon nanoforms, the fulfillment of such critical requirements as quick and nonharsh methods, good dispersibility, introduction of reactive groups, short reaction time, and low cost can be quite challenging. Traditional thermally induced diazonium chemistry on single‐walled carbon nanotubes (SWCNTs) is revisited by using commercial anilines and providing useful insight into the versatility of this approach. Functionalized SWCNTs with multiple controllable features, such as degree (and ratio) of coverage, orthogonalization, doping, and high water dispersibility, are obtained by introducing benzenesulfonic acid and benzylamine moieties. The scenario opens up an avenue to address relevant applications in which most functionalization methods could not be applied in a straightforward way.     

Electrochemical polymerization of imidazolum‐ionic liquids bearing a pyrrole moiety

A series of imidazolium‐based ionic liquid monomers bearing a terminal pyrrole moiety were synthesized and electrochemically polymerized. It is found that the polymerizability of the synthesized ionic liquids is strongly dependent on the type of the counteranions. Although bromide monomer is not polymerizable, well‐defined polymeric films can be formed on various substrates in the cases of flour‐containing anions (BF₄^?, PF₆^?). The performed characterizations show that all resulting polypyrrole films are electroactive, and the imidazolium‐based ionic liquid moieties are correctly incorporated in polymer films during the electropolymerization process. This work not only provides a facile new method to immobilize ionic liquids on solid surface. Interestingly, without use of any template unique “knit” morphology and nanostructure, even hierarchical structures could also be produced by the electropolymerization of these new functionalized pyrrole monomers. We found that the properties of the pendant ionic liquid units on the surface of the formed polymer films preserved, and by simple anion exchange their surface energy and tension could be easily tuned without loss of the electrical, optical properties, and morphology of the polypyrrole films. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4151–4161, 2008     

Amino acid ionic liquid‐based titanomagnetite nanoparticles: An efficient and green nanocatalyst for the synthesis of 1,4‐dihydropyrano[2,3‐c]pyrazoles

The amino acid ionic liquid tetrabutylammonium asparaginate (TBAAsp) was immobilized on titanomagnetite (Fe_3?xTi_xO₄) nanoparticles in a facile one‐pot process using an organosilane compound (TMSP) as spacer. The modified Fe_3?xTi_xO₄@TMSP@TBAAsp magnetic nanoparticles were characterized using Fourier transform spectroscopy, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, vibrating sample magnetometry and thermogravimetric analysis. The resulting analytical data clearly verified the successful immobilization of the ionic liquid on the magnetic substrate. The magnetic ionic liquid‐based nanoparticles exhibited high catalytic activity in the synthesis of 1,4‐dihydropyrano[2,3‐c]pyrazole derivatives via a one‐pot three‐component reaction under mild reaction conditions. The catalyst was easily recycled and reused for at least six runs without any considerable loss of activity.