Carbon Nanoparticle Surface Electrochemistry: High‐Density Covalent Immobilisation and Pore‐Reactivity of 9,10‐Anthraquinone

2‐Bromomethyl‐9,10‐anthraquinone is covalently bound to carbon nanoparticle surfaces (Emperor 2000, Cabot Corp., with sulphonamide groups, ca. 9 to 18 nm diameter) with a coverage of ca. 250 anthraquinone molecules per particle (ca. 180 Ų per anthraquinone). The resulting hydrophobic carbon particles are dispersed in ethanol and coated onto glassy carbon electrodes. Electrochemical experiments are reported demonstrating the effect of surface coverage, scan rate, and pH. A linear shift in reversible potential of ca. 59 mV per pH unit from pH 2 to 12 is observed consistent with the reversible 2‐electron 2‐proton reduction of anthraquinone. High density of anthraquinone in carbon nanoparticle aggregates causes buffer capacity effects. Binding of hydrophobic tetraphenylborate anions into carbon nanoparticle aggregate pores is demonstrated. Applications in buffer characterisation and pH‐sensing are discussed.     

Magnetic retrieval of graphene: extraction of sulfonamide antibiotics from environmental water samples

A new technique of retrieving graphene from aqueous dispersion was proposed in the present study. Two-dimensional planar graphene sheets were immobilized onto silica-coated magnetic microspheres by simple adsorption. The graphene sheets were used as adsorbent material to extract six sulfonamide antibiotics (SAs) from water samples. After extraction, they were conveniently separated from the aqueous dispersion by an external magnetic field. Under the optimal conditions, a rapid and effective determination of SAs in environmental water samples was achieved. The limits of detection for six SAs ranged from 0.09 to 0.16 ng/mL. Good reproducibility was obtained. The relative standard deviations of intra- and inter-day analysis were less than 10.7% and 9.8%, respectively.     

Detection and Quantification of Sulfonamide Antibiotic Residues in Milk Using Scanning Electrochemical Microscopy

The use of scanning electrochemical microscopy (SECM) for the qualitative and quantitative determination of sulfapyridine (SPY) in milk is described. A direct competitive immunoassay was performed involving an antibiotic horseradish peroxidase (HRP)‐labeled analog and using selective capture antibodies immobilized on the surface of Protein G‐modified glassy carbon plates. SECM detection was accomplished by means of the sample generator/tip collector (GC) mode involving the reduction of benzoquinone (BQ) generated upon the HRP‐catalyzed oxidation of hydroquinone (HQ) at the modified substrate surface in the presence of H₂O₂. The detection limit for SPY in milk samples was as low as 0.13 ng mL^?1.     

Facile preparation of N-protected 2-alkylidene-1,3-imidazolidines

Stereoselective preparation of unsymmetrically protected 2-alkylidene-1,3-imidazolidines was achieved by the reaction of N,N′-protected ethylenediamine, bromopropynamide, and K₃PO₄ in hot DMF. When N-protected aminoethanol was used in place of the protected ethylenediamine, an oxazolidine derivative was produced.     

Nitroso group transfer from N-nitrososulfonamides to thiolate ions. Intrinsic reactivity

The nitroso group transfer from N-nitrososulfonamides to thiolate ions was studied. Based on the results, the reaction rate is strongly dependent on the nature of the leaving group (αlg≈−1.30), but virtually independent of the basicity of the thiol (βnuc≈0.10). This dependence is ascribed to the presence of a nucleophile desolvation equilibrium (βd) that is followed by the attack of the thiolate ion on the nitroso group via a concerted mechanism. The equilibrium constants for the loss of a nitroso group from a nitrosothiol and an N-nitrososulfonamide were used to obtain the equilibrium constants for the different reactions involved. By using rate-equilibrium correlations, the parameters , βd, and were obtained.