Quantum chemical studies on addition reactions of carbene with carbon monoxide and formaldehyde

MNDO method has been employed to study the reaction paths and to optimize the structures of the reactants, products and transition states of the addition reactions of carbene with carbon monoxide and formaldehyde available. Mechanisms have been obtained.     

Synthesis of arylglycine and mandelic acid derivatives through carboxylations of α-amido and α-acetoxy stannanes with carbon dioxide

Incorporation reactions of carbon dioxide (CO(2)) with N-Boc-α-amido and α-acetoxy stannanes were developed using CsF as a mild tin activator. Monoprotected α-amido stannanes could be used, and the corresponding arylglycine derivatives were obtained in moderate-to-high yields under 1 MPa (10 atm) of CO(2) pressure. α-Acetoxy stannanes also underwent carboxylation to afford mandelic acid derivatives in excellent yields under ambient CO(2) pressure. Both transformations enabled the synthesis of α-tertiary and α-quaternary carboxylic acid derivatives. In addition, the chirality of (S)-N-tert-butylsulfonyl-α-amido stannanes was transferred with up to 90% inversion of configuration at 100 °C.     

Combination self-assembly of β-sheet peptides and carbon nanotubes: functionalizing carbon nanotubes with bioactive β-sheet block copolypeptides

Understanding the self-assembly behavior of β-sheet peptides is important, not only in constructing bioactive peptide nanostructures, but also in inhibiting uncontrollable protein aggregation in protein-misfolding diseases. Here, the first systematic investigation of combination self-assembly between β-sheet block copolypeptides and CNTs is presented, demonstrating the presence of several different association modes during the combination self-assembly process. Bioactive β-sheet block copolypeptides can self-assemble by themselves, or can be used to functionalize CNT hybrids depending on the situation. This behavior may be important both for fabricating bioactive peptide/CNT hybrids and for controlling/inhibiting protein-misfolding diseases.     

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.     

Electrocatalytic interaction of nano-engineered palladium on carbon nanofibers with hydrogen peroxide and β-NADH

The growing demands for reagentless hydrogen peroxide (H₂O₂) and β-nicotinamide adenine dinucleotide (β-NADH) sensors from food, pharmaceutical, chemical, and biochemical fields have stimulated extensive research interest on nano-engineered Pd. In this paper, Pd/carbon composite nanofibers were prepared by electrodepositing Pd onto electrospun carbon nanofibers to act as a catalyst toward the electrocatalytic redox reactions of H₂O₂ and β-NADH. The morphology of nano-engineered Pd was controlled by selectively adjusting the electrodeposition time and potential. Scanning electron microscopy and transmission electron microscopy results showed that nanocactus- and nanoflower-like Pd depositions were obtained on the surface of carbon nanofibers. Electrocatalytic analysis demonstrated a high electrocatalytic activity of the composite nanofibers for the redox of H₂O₂ and oxidation of β-NADH.     

Reaction of β-trifluoroethoxy vinamidinium salts with carbon nucleophiles

β-Trifluoroethoxy vinamidinium salts 1 reacted smoothly with various types of the carbanions, generated by treatment of ketones, esters, amide and nitriles with LDA, to give the corresponding trifluoroethoxylated multifunctional dienamine derivatives 3 in moderate to good yields. On the other hand, the reaction of 1 with lithium acetylide and other carbanions derived from methyl compounds bearing sulfonyl, sulfinyl, and phosphonyl groups produced the corresponding α,β-unsaturated aldehydes 5 in good yields.     

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.     

Synthesis and properties of novel aliphatic polycarbonate from carbon dioxide with 1,2-butylene oxide and ε-caprolactone

A new degradable aliphatic poly(butylene-co-e-caprolactone carbonate) (PBCL) was synthesized through the terpolymerization of carbon dioxide, 1,2-butylene oxide (BO) and e-caprolactone (CL), a polymer supported bimetallic complex (PBM) was used as a catalyst. The terpolymers prepared were characterized by FT-IR,1H NMR, 13C NMR, WXRD and DSC. The hydrolysis tests were carried out to appraise the degradability of the copolymers.     

Determination of cadmium(II) using glassy carbon electrodes modified with cupferron, ß-naphthol, and multiwalled carbon nanotubes

We report on a simple and reliable method for the determination of trace cadmium ion using a glassy carbon electrode (GCE) modified with cupferron, ß-naphthol and MWCNTs. The operational mechanism consists of several steps: first, the ligand cupferron on the modified electrode reacts with Cd²⁺ ion to form a chelate compound. Next, this chelate is adsorbed by the carrier ß-naphthol following the principle of organic co-precipitation. Finally, the coprecipitated complex is detected by the GCE. This scheme is interesting because it combines preconcentration and electrochemical detection. Two linear responses are obtained, one in the concentration range of 5.0?×?10^?11 to 1.6?×?10^?8 M, the other in the range of 1.6?×?10^?8 to 1.42?×?10^?6 M, with a lower detection limit of 1.6?×?10^?11 M. This modified GCE does not suffer from significant interferences by Cu(II), Hg(II), Ag(I), Fe(III), Pb(II), Cr(III), Zn(II), NO^3?, Cl^?, SO ₄ ^2? ions and EDTA. The response of the electrode remained constant for at least 3 weeks of successive operation. The method presented here provides a new way for the simultaneous separation, enrichment, and electrochemical detection of trace cadmium ion.

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.     

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

Electrochemical oxidation behavior of guanosine-5��-monophosphate on a glassy carbon electrode modified with a composite film of graphene and multi-walled carbon nanotubes, and its amperometric determination

The electrochemical oxidation of guanosine-5??-monophosphate (GMP) was studied with a glassy carbon electrode modified with a composite made from graphene and multi-walled carbon nanotubes. GMP undergoes an irreversible oxidation process at an oxidation peak potential of 987?mV in phosphate buffer solution. Compared to other electrodes, the oxidation peak current of GMP with this electrode was significantly increased, and the corresponding oxidation peak potential negatively shifted, thereby indicating that the modified material exhibited electrochemical catalytic activity towards GMP. Chronocoulometry demonstrates that the material also effectively increases the surface area of the electrode and increases the amount of GMP adsorbed. Under the optimum conditions, the oxidation current is proportional to the GMP concentration in the range from 0.1 to 59.7???M with a correlation coefficient of 0.9991. The detection limit is 0.025???M (at S/N?=?3).

Defect-rich and ultrathin nitrogen-doped carbon nanosheets with enhanced peroxidase-like activity for the detection of urease activity and fluoride ion

Although carbon nanozymes have attracted great interest due to their good biocompatibility, low cost,and high stability, designing high-active carbon nanozymes still faces great challenges. Herein, ultrathin nitrogen-doped carbon nanosheets with rich defects(d-NC) were prepared through a high-temperature annealing process, using potassium chloride and ammonium chloride as templates. Owing to the large specific surface area, rich defects and the high exposure of active sites, the proposed d-NC na...     

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.

An amperometric penicillin biosensor with enhanced sensitivity based on co-immobilization of carbon nanotubes, hematein, and β-lactamase on glassy carbon electrode

An amperometric penicillin biosensor with enhanced sensitivity was successfully developed by co-immobilization of multi-walled carbon nanotubes (MWCNTs), hematein, and β-lactamase on glassy carbon electrode using a layer-by-layer assembly technique. Under catalysis of the immobilized enzyme, penicillin was hydrolyzed, decreasing the local pH. The pH change was monitored amperometrically with hematein as a pH-sensitive redox probe. MWCNTs were used as an electron transfer enhancer as well as an efficient immobilization matrix for the sensitivity enhancement. The effects of immobilization procedure, working potential, enzyme quantity, buffer concentration, and sample matrix were investigated. The biosensor offered a minimum detection limit of 50 nM (19 μg L⁻¹) for penicillin V, lower than those of the conventional pH change-based biosensors by more than two orders of magnitude. The electrode-to-electrode variation of the response sensitivity was 7.0% RSD.     

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.     

Self-regeneration of activated carbon modified with palladium catalyst for electrochemical dechlorination

Catalyst regeneration and the retention of high catalytic activity are still the critical issues in environmental application.A novel fluidized gas-liquid-solid electrochemical reactor was developed to simultaneously remove chlorinated pollutants and in situ regenerate the spent catalyst.Activated carbon modified with palladium catalyst (AC-Pd) was prepared for electrochemical dechlorination.For the 4-chloropbenol wastewater of initial concentration 200 mg L~(-1),the removal efficiency could nearly reach 100% in less than 30 min.Catalytic activity of AC-Pd catalyst was preserved effectively even in consecutive cycling run without special regeneration.OH radicals,generated by electrochemical reaction,played a critical role in self-regeneration of AC-Pd.High catalytic activity of spent AC-Pd catalyst provided an attractive alternative in wastewater treatment.     

Photo-promoted carbonylation of chloroalkanes with carbon monoxide by non-precious metal catalysts

The photo-promoted carbonylation of chloroalkanes with carbon monoxide was carried out under ambient conditions with copper and cadmium salts catalysts. The results indicated that the corresponding esters were produced with three salt catalysts, i.e. CuBr2, CuCl2 and CdI2. Among these catalysts, CdI2 was the most efficient in terms of ester yield and selectivity, particularly, 60% yield and 75% selectivity in the carbonylation of chlorocyclohexane were achieved. Furthermore, the yield and selectivity of the ester can be improved greatly by adding tri-n-butylamine in the CuBr2 and CuCl2 catalyst systems. On the other hand, the carbonylation did not proceed with single CdCl2, however, the catalytic activity of CdCl2 was increased greatly with NaIá2H2O as additive. As a result, we suggest that iodide ion plays an important role in the catalyst system of the cadmium salts.