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.     

The characterisation and evaluation of activated carbon in a cigarette filter

Cigarette smoke is an ever changing and extremely complex mixture of over 5000 chemicals. When the cigarette burns, thousands of chemical substances are generated, and these are distributed between the gas phase and the particles which constitute the smoke aerosol. Activated carbon when used in a filter can selectively remove a number of the vapour phase compounds to varying degrees of efficiency. Carbons of different activities (50–60% CTC and 90–100% CTC) have been characterised using nitrogen adsorption and also the sorption of a number of different vapours with different properties, using a dynamic gravimetric adsorption technique. Surface areas, pore volumes, diffusivities and heats of adsorption were calculated using nitrogen, benzene, heptane, ethyl acetate and water as the probe molecules. Smoke chemistries were measured using a screening approach on the characterised carbons as filter additives. It was seen that the higher activity carbon results in increased retention in the majority of the measured vapour phase smoke constituents.     

The migratory insertion of carbon monoxide and methyl isocyanide into zirconium–carbon and titanium–carbon bonds anchored to a calix[4]arene moiety: a dynamical density functional study

The energetics and reaction mechanism of the migratory insertion of carbon monoxide and methyl isocyanide into the zirconium–carbon and titanium–carbon bonds in [calix[4](OMe)₂(O)₂–M–Me₂], (M=Zr, Ti), have been investigated by combining static and dynamic density functional calculations. Two steps have been characterized: the coordination of the incoming nucleophilic moiety leading to relatively stable facial adducts; its subsequent insertion into the M–C bond, leading to ²-bound acyl or iminoacyl complexes, providing a rationale for the different behavior of CO and MeNC towards both insertion and deinsertion reactions. Our results indicate that the rate-determining step for the overall MeNC insertion into the M–C bond is its coordination to the electron-deficient metal center, with the titanium system featuring a higher energy barrier (12.7 versus 5.5 kcal mol^–1). Ab initio molecular dynamics simulations have been performed on the Zr system by means of the Car–Parrinello method, to study the hitherto inaccessible mechanistic features of the insertion reactions.Contribution to the Björn Roos Honorary Issue     

Dispersion of single-walled carbon nanotubes in dimethylacetamide and a dimethylacetamide–cholic acid mixture

A way of dispersing single-walled carbon nanotubes in preparing stable suspensions with high concentrations of individual nanotubes in amide solvents is described. The obtained suspensions are studied via Raman spectroscopy. The dependence of the degree of single-walled carbon nanotube (SWNT) dispersion in individual and mixed amide solvents on the type of solvent, the mass of nanotubes, and the concentration of cholic acid is established. A technique for processing spectral data to estimate the diameters and chiralities of individual nanotubes in suspension is described in detail.     

Insertion of cyclopropanes between a carbonyl carbon and an α-carbon of carbonyl compounds with cyclopropylmagnesium carbenoids

The reaction of the lithium enolates of α-aryl carbonyl compounds with cyclopropylmagnesium carbenoids, derived from 1-chlorocyclopropyl p-tolyl sulfoxides with i-PrMgCl at low temperature, resulted in the formation of β-aryl carbonyl compounds bearing a cyclopropane ring at the α-position with one-carbon homologation in variable yields. The reaction was found to be highly stereospecific with respect to the stereochemistry of the cyclopropylmagnesium carbenoids. Mechanism and origin of the stereospecificity of the reaction are also discussed. This is the first example for the insertion of cyclopropanes in between a carbonyl carbon and an α-carbon of carbonyl compounds.     

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.     

Electrochemical methods for simultaneous determination of trace amounts of dopamine and uric acid using a carbon paste electrode incorporated with multi-wall carbon nanotubes and modified with α-cyclodextrine

In this work, we investigate the electrochemical activity of dopamine (DA) and uric acid (UA) using both a bare and a modified carbon paste electrode as the working electrode, with a platinum wire as the counter electrode and a silver/silver chloride (Ag/AgCl) as the reference electrode. The modified carbon paste electrode consists of multi-walled carbon nanotubes (>95%) treated with α-cyclodextrine, resulting in an electrode that exhibits a significant catalytic effect toward the electro-chemical oxidation of DA in a 0.2-M Britton–Robinson buffer solution (pH 5.0). The peak current increases linearly with the DA concentration within the molar concentration ranges of 2.0 × 10⁻⁶ to 5.0 × 10⁻⁵ M and 5.0 × 10⁻⁵ to 1.9 × 10⁻⁴ M. The detection limit (signal to noise >3) for DA was found to be 1.34 × 10⁻⁷ M, respectively. In this work, voltammetric methods such as cyclic voltammetry, chronoamperometry, chronocuolometry, differential pulse and square wave voltammetry, and linear sweep and hydrodynamic voltammetry were used. Cyclic voltammetry was used to investigate the redox properties of the modified electrode at various scan rates. The diffusion coefficient (D, cm² s⁻¹ = 3.05 × 10⁻⁵) and the kinetic parameters such as the electron transfer coefficient (α = 0.51) and the rate constant (k, cm³ mol⁻¹ s⁻¹ = 1.8 × 10³) for DA were determined using electrochemical approaches. By using differential pulse voltammetry for simultaneous measurements, we obtained two peaks for DA and UA in the same solution, with the peak separation approximately 136 mV. The average recovery was measured at 102.45% for DA injection.     

Kinetics and mechanistic study of pyridinium hydrobromide perbromide-induced carbon–carbon bond scission

The title investigation shows that pyridinium hydrobromide perbromide (PHPB) induced electron transfer reaction in pentaamminecobalt(III) complexes of α-hydroxy acids

Influence of carbon and nitrogen sources and temperature on hyperproduction of a thermotolerant β-glucosidase from synthetic medium by Kluyveromyces marxianus

The effect of carbon source and its concentration, inoculum size, yeast extract concentration, nitrogen source, pH of the fermentation medium, and fermentation temperature on β-glucosidase production by Kluyveromyces marxianus in shake-flask culture was investigated. These were the independent variables that directly regulated the specific growth and β-glucosidase production rate. The highest product yield, specific product yield, and productivity of β-glucosidase occurred in the medium (pH 5.5) inoculated with 10% (v/v) inoculum of the culture. Cellobiose (20 g/L) significantly improved β-glucosidase production measured as product yield (Y _P/S ) and volumetric productivity (Q _P ) followed by sucrose, lactose, and xylose. The highest levels of productivity (144 IU/[L·h]) of β-glucosidase occurred on cellobiose in the presence of CSL at 35°C and are significantly higher than the values reported by other researchers on almost all other organisms. The thermodynamics and kinetics of β-glucosidase production and its deactivation are also reported. The enzyme was substantially stable at 60°C and may find application in some industrial processes.     

Electrochemical determination of acetaminophen at a carbon electrode modified in the presence of β-cyclodextrin: role of the activated glassy carbon and the electropolymerised β-cyclodextrin

Acetaminophen is a well-known drug commonly used to provide pain relief, but it can also lead to acute liver failure at high concentrations. Therefore, there is considerable interest in monitoring its concentrations. Sensitive and selective acetaminophen electrochemical sensors were designed by cycling a glassy carbon electrode (GCE) to high potentials in the presence of β-CD in a phosphate electrolyte, or by simply activating the GCE electrode in the phosphate solution. Using cyclic voltammetry, adsorption-like voltammograms were recorded. The acetaminophen oxidation product, N-acetyl benzoquinone imine, was protected from hydrolysis, and this was attributed to the adsorption of acetaminophen at the modified GCE. The rate constants for the oxidation of acetaminophen were estimated as 4.3 × 10^–3 cm² s^–1 and 3.4 × 10^–3 cm² s^–1 for the β-CD-modified and -activated electrodes, respectively. Using differential pulse voltammetry, the limit of detection was calculated as 9.7 × 10^–8 M with a linear concentration range extending from 0.1 to 80 μM. Furthermore, good selectivity was achieved in the presence of caffeine, ascorbic acid and aspirin, enabling the determination of acetaminophen in a commercial tablet. Similar electrochemical data were obtained for both the β-CD-modified and activated GCE surfaces, suggesting that the enhanced detection of acetaminophen is connected mainly to the activation and oxidation of the GCE. Using SEM, EDX and FTIR, no evidence was obtained to indicate that the β-CD was electropolymerised at the GCE.

     

Synthesis of a novel gelatin–carbon nanotubes hybrid hydrogel

This letter focuses on the first result the preparation and its swelling behavior of a novel hybrid gelatin hydrogel with carbon nanotubes. A novel hybrid gelatin hydrogel with carbon nanotubes was synthesized by physical mixing method. The structure of the novel hydorgel obtained was characterized by SEM. Besides, the swelling behavior of the hydrogel synthesized was measured at different temperature. The results indicated that carbon nanotubes added could maintain the stability of the hybrid hydrogel at 37 °C. This suggests that the hybrid gelatin hydrogel with carbon nanotubes could be used in biomedical field. Besides, its application in protein concentrating has been discussed.     

Synthesis and properties of [9]cyclo-1,4-naphthylene: a π-extended carbon nanoring

The first synthesis of a π-extended carbon nanoring, [9]cyclo-1,4-naphthylene ([9]CN), has been achieved. Careful structure-property analyses uncovered a number of unique features of [9]CN that are quite different from those of [9]CPP, a simple carbon nanoring.     

Electrochemical chiral recognition of tryptophan using a glassy carbon electrode modified with β-cyclodextrin and graphene

We report on a method for electrochemical enantioselective recognition of tryptophan (Trp) enantiomers. It is based on competitive host-guest interaction between a deoxy-(2-aminoethylamino)-β-cyclodextrin (CD) bound to graphene nanosheets and the Cu(II) complexes of the Trp enantiomers via a ligand exchange mechanism. Chiral recognition was investigated via cyclic voltammetry and electrochemical impedance spectroscopy. The results reveal that the CD bound to graphene displays a stronger interaction with the Cu(II) complex of L-Trp than to that of D-Trp. The method was applied to the determination of the ratio of Trp enantiomers in mixtures.

Metal-free and selective cleavage of unstrained carbon–carbon single bonds: Synthesis of β-ketosulfones from β-chlorohydrins and sodium sulfinates

A metal-free protocol for the selective cleavage of unstrained C–C single bonds was developed. Under the catalysis of KI and in the presence of NaHCO₃, the readily available α-chloro-β-hydroxy ketones underwent bond breaking and sulfonylation smoothly to afford β-ketosulfones with high efficiency and broad substrate scope. Mechanism investigations, both experimental and theoretical, showed that a retro-aldol cleavage/nucleophilic substitution sequence might be involved.     

Constructing a hierarchical graphene–carbon nanotube architecture for enhancing exposure of graphene and electrochemical activity of Pt nanoclusters

Stacking of individual graphene sheets (GS) is effectively inhibited by introducing one-dimensional carbon nanotubes to form a 3-D hierarchical structure which enhances the utilization of GS-based composites. From SEM images, CNTs are useful nanospacers for diminishing the face-to-face aggregation of GS. The specific electrochemically active surface area (SECSA) and specific double-layer capacitance (C_S,DL) of Pt/GS–CNTs (127.9 m²/g, 171.3 F/g) is much higher than that of Pt/GS (105.4 m²/g, 104.7 F/g) and Pt/CNTs (51.5 m²/g, 37.1 F/g), revealing the synergistic effects between GS and CNTs on enhancing the electrochemical activity of Pt nanoparticles and electrolyte-accessible surface area.     

Non-enzymatic sensing of hydrogen peroxide using a glassy carbon electrode modified with a composite consisting of chitosan‐encapsulated graphite and platinum nanoparticles

We report on a non-enzymatic hydrogen peroxide (H₂O₂) sensor which makes use of a nanocomposite consisting of platinum nanoparticles (PtNPs) and chitosan-encapsulated graphite (graphite-CS). The composite was prepared by sonication of pristine graphite in chitosan (CS) in 5 % acetic acid. The PtNP decorated graphite-CS (graphite-CS/PtNPs) composite was prepared by electrodeposition of PtNPs on the graphite-CS modified glassy carbon electrode. The graphite-CS/PtNP composite was characterized by scanning electron microscopy, elemental analysis and FTIR spectroscopy. The modified electrode displays an enhanced reduction peak current for H₂O₂ when compared with electrodes modified with graphite/PtNPs and PtNPs. The modified electrode exhibits excellent electrocatalytic activity towards the reduction of H₂O₂, and the amperometric response is linear over the concentration range from 0.25 to 2890 μM. The sensitivity and the detection limit are 0.465 μA?μM￣¹ ? cm￣² and 66 nM, respectively. The sensor shows fast response (3 s) in detecting H₂O₂. It is also highly selective in the presence of potentially interfering compounds, and may therefore be used as a feasible platform for sensing H₂O₂ in real samples.

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Graphical abstract Preparation of graphite-CS/PtNP composite, and its application to electrochemical reduction of H₂O₂.

     

Evolution of the composition and structure of PAN carbon fiber during preoxidation

Using scanning electronic microscope, X-ray diffraction analysis, PYR-GCMS and IR etc., we studied the evolving process of the composition and structure of PAN carbon fiber during preoxidation. In the initial stage of preoxidation, PAN filament tows disappear and become semi-thaw. At first, reactions happen between the copolymers and esters disappear. The molecules annularly crosslink and the index of cyclation slowly increases. It is easy to fix the structure and form defects during the initial and the medium stages, which are most reactive. More traction is advised in these stages to minimize the structural deficiencies. In the medium stage of preoxidation, the fiber was reshaped into new sheet stacks and gradually changed to sheet sectors, and this structure tends to be stable in the final stage. Induced by acid and ester copolymer, PAN fiber forms a very stable cycle structure in the final stage. Besides, monomer, dimmer and trimer obviously decrease. In the final stage of the preoxidation, there exi     

Photosolvolysis of a carboncarbon bond. The photolysis of n,n-dimethyl- 2,2-diphenylethylamine in methanol.1

The title compound is photolyzed in methanol to give good yields (ca. 50%) of diphenylmethane indicating that the CC bond undergoes a formal heterolytic cleavage from the excited state as predicted from the measured redox potentials of the two ions.