Reversible electrochemistry of DNA on multi-walled carbon nanotube modified electrode

Calf thymus DNA was electrochemically oxidized at a multi-walled carbon nanotube modified electrode. The potentials for DNA oxidation at pH 7.0 were 0.71 and 0.81 V versus SCE, corresponding to the oxidation of guanine and adenine residues, respectively. The initial 6e-oxidation of adenine, observed in the first scan, resulted a quasi-reversible 2e-redox process of the oxidation product in the following scans.     

Electrochemical detection of DNA methylation using a glassy carbon electrode modified with a composite made from carbon nanotubes and β-cyclodextrin

We describe a method for detecting DNA methylation. It is based on direct oxidation of DNA bases at a glassy carbon electrode (GCE) modified with film of a multiwalled carbon nanotube-β-cyclodextrin composite. This nano-structured film causes a strong enhancement on the oxidation current of DNA bases due to its large effective surface area and extraordinary electronic properties. Well-defined peaks were obtained as a result of electro-oxidation of guanine (at 0.67 V), adenine (at 0.92 V), thymine (at 1.11 V), cytosine (at 1.26 V), and 5-methylcytosine (at 1.13 V; all data vs. saturated calomel electrode (SCE)). The potential difference between 5-methylcytosine and cytosine (130 mV) is large enough to enable reliable simultaneous determination and analysis. The interference by thymine can be eliminated by following the principle of complementary pairing between purine and pyrimidine bases in DNA. The modified electrode was successfully applied to the evaluation of 5-methylcytosine in a fish sperm DNA, the methylation level of cytosine was found to be 7.47 %, and the analysis process took less than 1 h.     

Interfacing cytochrome c to electrodes with a DNA – carbon nanotube composite film

Multi-walled carbon nanotube (MWCNT) is successfully immobilized on the surface of platinum electrode by mixing with DNA. The DNA/MWCNT modified electrodes are characterized by electrochemical impedance spectroscopy and cyclic voltammetry. Further research indicates that cytochrome c can strongly adsorbed on the surface of the modified electrode, and forms an approximate monolayer. The immobilized MWCNT can promote the redox of horse heart cytochrome c which gives reversible redox peaks with a formal potential of 81 mV vs SCE.     

The preparation of functionalized single walled carbon nanotubes as high efficiency DNA carriers

The positively charged single walled carbon nanotubes (SWNTs~ ) were prepared by conjugating with-CONH-C_6H_(12)-NH_3~ . The double strand DNA(dsDNA) chains were loaded onto SWNTs~ via the electrostatic interactions.SWNTs~ shows improved loading efficiency (353.5μg/mg) toward dsDNA compared with that of charged free single walled carbon nanotubes (SWNTs) (82.9μg/mg).     

Investigation of lipase-catalyzed Michael-type carbon–carbon bond formations

Conjugate additions of carbon nucleophiles to appropriate acceptor molecules were investigated with respect to the synthetic potential and stereochemistry of the products. Reactions of short-chain α,β-unsaturated ketones and mono-substituted nitroalkenes with CH-acidic carboxylic ester derivatives were catalyzed by various immobilized lipases. Using methyl nitroacetate complete conversion with methyl vinyl ketone and trans-β-nitrostyrene was obtained. The reactions proceeded without enantioselectivity. Evidence for enzyme catalysis is provided by the observation that after denaturation of Candida antarctica lipase B or inhibition no reaction took place. Docking studies with the chiral addition product methyl 2-methyl-2-nitro-5-oxohexanoate did not reveal any specific binding mode for this reaction product, which would have been the requirement for stereoselective additions. These results support the experimental findings that the conjugate addition takes place without enantiopreference.     

Electrochemiluminescence DNA biosensor based on the use of gold nanoparticle modified graphite-like carbon nitride

The authors describe an electrochemiluminescent (ECL) DNA biosensor that is based on the use of gold nanoparticles (AuNPs) modified with graphite-like carbon nitride nanosheets (g-C₃N₄ NSs) and carrying a DNA probe. In parallel, nanoparticles prepared from gold-platinum (Au/Pt) alloy and carbon nanotubes (CNTs) were placed on a glassy carbon electrode (GCE). Once the g-C₃N₄ NHs hybridize with DNA-modified AuNPs, they exhibit strong and stable cathodic ECL activity. The Au/Pt-CNTs were prepared by electrochemical deposition of Au/Pt on the surface of the CNTs in order to warrant good electrical conductivity. On hybridization of immobilized capture probe (S₁), target DNA (S₂) and labeled signal probe (S₃), a sandwich-type DNA complex is formed that produces a stable ECL emission at a typical applied voltage of ?1.18 V and in the presence of peroxodisulfate. Under optimized conditions, the method has a response to target DNA that is linearly related to the logarithm of its concentration in the range between 0.04 f. and 50 pM, with a 0.018 f. detection limit.

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Graphical abstract Schematic presentation of an electrochemiluminescent DNA biosensor based on two-dimensional graphite-like carbon nitride nanosheets (g-C₃N₄ NSs) hybridized with gold nanoparticles. Abbreviations: MCH: 6-mercapto-1-hexanol; S1: Capture probe; S2: target DNA. 

     

A carbon–carbon hybrid – immobilizing carbon nanodots onto carbon nanotubes

The thrust of this work is to integrate small and uniformly sized carbon nanodots (CNDs) with single-walled carbon nanotubes (SWCNT) of different diameters as electron donors and electron acceptors, respectively, and to test their synergetic interactions in terms of optoelectronic devices. CNDs (denoted pCNDs, where p indicates pressure) were prepared by pressure-controlled microwave decomposition of citric acid and urea. pCNDs were immobilized on single-walled carbon nanotubes by wrapping the latter with poly(4-vinylbenzyl trimethylamine) (PVBTA), which features positively charged ammonium groups in the backbone. Negatively charged surface groups on the CNDs lead to attractive electrostatic interactions. Ground state interactions between the CNDs and SWCNTs were confirmed by a full-fledged photophysical investigation based on steady-state and time-resolved techniques. As a complement, charge injection into the SWCNTs upon photoexcitation was investigated by ultra-short time-resolved spectroscopy.     

Metal free amide synthesis via carbon–carbon bond cleavage

A metal-free oxidative coupling of methyl ketones and primary amines to amides has been developed. The reaction tolerates a variety of functional groups, and is operationally simple. The reaction is proposed to go through a radical pathway to form the triiodomethyl ketone intermediate and the amide is formed by the nucleophilic attack of amine on triiodomethyl ketone carbonyl.     

Highly active ferrocenylamine-derived palladacycles for carbon–carbon cross-coupling reactions

{[(N-Methyl-N-p-R-benzyl)amino]benzyl}ferrocenes 4a–c (R = H(a), OCH₃(b), CH₃(c)) were synthesized by N-methylation of the corresponding sec-amines 3a–cwith the reagent CH₃I-t-BuOK. Treatment of 4a–c with Na₂PdCl₄ in the presence of NaOAc produced a pair of palladacycles σ-Pd[(η⁵-C₅H₅)Fe(η⁵- C₅H₃CH(C₆H₅)N(CH₃)CH₂-C₆H₄-R)]Cl(PPh₃) 5a–c (R = same as before) consisting of R_NR_P and S_NS_P configurations. The structure of 5a was determined by single crystal X-ray analysis. High catalytic activities of 5a–c for the Suzuki coupling of aryl chlorides with phenylboronic acid and the Heck reaction of bromobenzene with styrene were observed.     

Ni-catalyzed carbon–carbon bonds cleavage of mixed polyolefin plastics waste

The inert carbon–carbon(C–C) bonds cleavage is a main bottleneck in the chemical upcycling of recalcitrant polyolefin plastics waste. Here we develop an efficient strategy to catalyze the complete cleavage of C–C bonds in mixed polyolefin plastics over non-noble metal catalysts under mild conditions. The nickelbased catalyst involving Ni₂Al₃ phase enables the direct transformation of mixed polyolefin plastics into natural gas, and the gas carbon yield reaches up to 89.6%. R...     

The influence of interunit carbon–carbon linkages during lignin upgrading

The cleavage of β-O-4 linkages in lignin can generate monomers with a phenyl propane structure that can easily be upgraded into valuable hydrocarbon biofuels and renewable aromatic chemicals. High-yield lignin monomer production from extracted (or technical) lignin that is produced in a practical way could facilitate the productivity and profitability of biomass conversion processes. However, interunit carbon–carbon (C–C) linkages present in native lignin or formed during lignin condensation in biomass pretreatments dramatically reduce lignin monomer yields. Here, we present a perspective on biological and chemical strategies that have been successfully used to reduce the formation of C–C linkages in native or technical lignin. We analyze the mechanisms involved in these strategies and offer our views on improving the quality of technical lignin resulting from biomass conversion in order to achieve high-yield lignin monomer production.     

Copper Catalysts based on carbon–carbon fiburous materials for ethanol dehydrogenation

The possibility of using new carbon–carbon composites as supports for a copper catalyst for ethanol dehydrogenation was demonstrated. The composites, which represented carbon nanostructures (single-walled carbon nanotubes or carbon nanofibers) attached to the surface of carbon microfibers, were prepared by essentially different procedures. Copper catalysts deposited on these supports exhibited different activity in the ethanol conversion, which is associated with the distribution and size of copper particles.     

The application of β-cyclodextrin derivative functionalized aligned carbon nanotubes for electrochemically DNA sensing via host-guest recognition

We functionalized aligned carbon nanotubes (ACNTs) electrode with a new kind of β-cyclodextrin (β-CD) derivative through diazotization reaction. The resulting β-CD/ACNTs electrode was used to detect DNA hybridization in homogeneous solution based on host–guest recognition technology. In the sensing protocol, one special DNA probe was designed with a stem-loop structure and both ends modified, which we called dually labeled DNA probe (DLP). One end of the DLP was labeled with dabcyl as guest molecule for β-CD/ACNTs electrode capture, and the other end was labeled with a CdS nanoparticle as an electrochemical tag to indicate the occurrence of DNA hybridization. In the absence of the target DNA sequence, the DLP maintains its hairpin structure in solution phase and would not be captured and detected by the β-CD/ACNTs electrode. In the presence of the complementary target sequence, the conformational structure of the DLP was altered and a double-stranded DNA (dsDNA) molecule was formed by the hybridization of DLP and complementary DNA sequence. Consequently, the dsDNA was captured by the β-CD/ACNTs electrode owing to guest–host recognition between β-CD and dabcyl. The electrochemical signal from the CdS nanoparticle–dsDNA/β-CD/ACNTs was then measured. Under optimized detection conditions, the proposed method showed high sensitivity and selectivity with a detection limit of 5.0 × 10⁻¹³ M for complementary DNA sequence.     

Recent advances in carbon nanostructures prepared from carbon dioxide for high-performance supercapacitors

The burgeoning global economy during the past decades gives rise to the continuous increase in fossil fuels consumption and rapid growth of CO₂ emission,which demands an urgent exploration into green and sustainable devices for energy storage and power management.Supercapacitors based on activated carbon electrodes are promising systems for highly efficient energy harvesting and power supply,but their promotion is hindered by the moderate energy density compared with batteries.Therefore,scalable conversion of CO₂ into novel carbon nanostructures offers a powerful alternative to tackle both issues:mitigating the greenhouse effect caused by redundant atmospheric CO₂ and providing carbon materials with enhanced electrochemical performances.In this tutorial review,the techniques,opportunities and barriers in the design and fabrication of advanced carbon materials using CO₂ as feedstock as well as their impact on the energy-storage performances of supercapacitors are critically examined.In particular,the chemical aspects of various Cv2 conversion reactions are highlighted to establish a detailed understanding for the science and technology involved in the microstructural evolution,surface engineering and porosity control of CO₂-converted carbon nanostructures.Finally,the prospects and challenges associated with the industrialization of CO₂ conversion and their practical application in supercapacitors are also discussed.     

Metal-free carbon–carbon cross-couplings between the ion pairs in sulfonium tetraphenylborates

A series of sulfonium tetraphenylborates can be readily prepared by the metathesis of sulfonium halides with sodium tetraphenylborates. After heating at 120–150 °C, the sulfonium tetraphenylborates can smoothly undergo the cross-couplings between the tetraphenylborate anions and the sulfonium cations in the absence of a metal catalyst. For carbonylmethyl-, benzyl-, and allylsulfoniums, the corresponding carbonylmethyl–phenyl, benzyl–phenyl, and allyl–phenyl cross-coupling products can be obtained in 22–76% yields. An interionic electron-transfer mechanism for this cross-coupling reaction is proposed.     

Novel carboncarbon bond formation induced by depalladation of organometallic compounds

Two internal alkynes undergo insertion at 20°C into the PdC bond of the cyclopalladated derivative of dimethylaminomethylferrocene to give new organometallic compounds. When the reaction with diphenylacetylene is performed at higher temperatures, depalladation occurs readily to give six- and seven-membered ortho-fused rings through new annulation reactions of phenyl groups, formation of one of these involving also the cleavage of a CN bond.     

Investigating detailed mechanism of hydrogen molecules adsorbing on single-wall carbon nanotubes using fitted force field parameters containing carbon–carbon interactions

The nonbonded and bonded force field parameters for carbon atoms in single-wall carbon nanotubes (SWNT) are fitted by means of quantum chemistry calculations with considering the periodic boundary conditions. The nonbonded parameters between carbon atoms and hydrogen atoms are fitted as well. All the fitted parameters are verified by comparing to quantum chemistry results and by calculating Young's modulus. Adsorption of Hydrogen molecules are then carried out on a bundle of self-assembled SWNTs. The adsorption isotherms are consistent to the Freundlich equation. Both hydrogen molecules adsorbed outside and inside the SWNTs are counted. According to our result, hydrogen molecules adsorbed inside the SWNTs are more stable at a relatively high temperature and are playing an important part in total amount of the adsorbed molecules. While C(10,10) have the highest adsorption capacities in most of the temperatures, hydrogen molecules inside C(5,5) are the most stable of all the four kinds of SWNTs. Thus, balancing adsorption capacities and strength of interaction can be important in choosing SWNT for gas adsorption. Besides, we deduct an equation that can describe the relation between hydrogen pressure and amount of SWNTs based on our simulation results. The hydrogen pressure may decrease by adding SWNTs in the system. The fitting method in our system is valid to SWNTs and can be tested in further studies of similar systems. © 2018 Wiley Periodicals, Inc.     

Ring-opening of cyclic ethers with carbon–carbon bond formation by Grignard reagents

The ring-opening of cyclic ethers with concomitant C–C bond formation was studied with a number of Grignard reagents. The transformation was performed in a sealed vial by heating to ∼160 °C in an aluminum block or at 180 °C in a microwave oven. Good yields of the product alcohols were obtained with allyl- and benzylmagnesium halides when the ether was tetrahydrofuran or 3,3-dimethyloxetane. Lower yields were obtained with substituted tetrahydrofurans while no ring-opening was observed with tetrahydropyran. Only highly reactive allyl and benzyl Grignard reagents participated in the transformation while no reaction occurred with other alkylmagnesium halides.     

Solubility of monocrotaline in supercritical carbon dioxide and carbon dioxide—ethanol mixtures

The solubility of monocrotaline, a chemotherapeutic drug precursor, in supercritical carbon dioxide and carbon dioxide—ethanol mixtures has been measured from 308.15 to 328.15 K and from 8.86 to 27.41 MPa. The solubility ranges from 6.0 × 10⁻⁶ to 2.21 × 10⁻⁴ mol fraction increasing up to 25-fold with the addition of ethanol. A new method for the estimation of the sublimation pressure of monocrotaline was developed based on the measured solubilities of monocrotaline in water. The sublimation pressure was then used in the compressed gas model to correlate the behavior of carbon dioxide—monocrotaline and carbon dioxide—ethanol—monocrotaline systems with reasonable success.