An electrochemical sensor prepared by sonochemical one-pot synthesis of multi-walled carbon nanotube-supported cobalt nanoparticles for the simultaneous determination of paracetamol and dopamine.

Multi-walled carbon nanotubes (MWCNTs) functionalized by cobalt nanoparticles were obtained using a single step chemical deposition method in an ultrasonic bath. The composite material was characterized using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The electroactivity of the cobalt-functionalized MWCNTs was assessed in respect to the electrooxidation of paracetamol (PAR) and dopamine (DA). It was found that the carbon nanotube supported cobalt nanoparticles have significantly higher catalytic properties. The proposed electrode has been applied for the simultaneous determination of PAR and DA. The modified electrode could resolve the overlapped voltammetric waves of PAR and DA into two well-defined voltammetric peaks with peak to peak separation of about 203 mV. On the other hand, the presence of potential drug interfering compounds AA and UA did not affect the voltammetric responses of PAR and DA. The current of oxidation peaks showed a linear dependent on the concentrations of PAR and DA in the range of 5.2×10(-9)-4.5×10(-7) M (R(2)=0.9987) and 5.0×10(-8)-3.0×10(-6) M (R(2)=0.9999), respectively. The detection limits of 1.0×10(-9) M and 1.5×10(-8) M were obtained for PAR and DA, respectively. The proposed electrode showed good stability (peak current change: 4.9% with and RSD of 2.6% for PAR; 5.5% with and RSD of 3.0% for DA over 3 weeks), reproducibility (RSD 2.3% for PAR and RSD 1.5% for DA), repeatability (RSD 2.25% for PAR and RSD 2.50% for DA) and high recovery (99.7% with an RSD of 1.3% for PAR; 100.8% with an RSD of 1.8% for DA). The proposed method was successfully applied to the determination of PAR and DA in pharmaceuticals.

Synthesis, spectroscopy, magnetic and redox behaviors of copper(II) complexes with tert-butylated salen type ligands bearing bis(4-aminophenyl)ethane and bis(4-aminophenyl)amide backbones.

New salen type ligands, N,N'-bis(X-3-tert-butylsalicylidene)-4,4'-ethylenedianiline [(X=H (1), 5-tert-butyl (2)] and N,N'-bis(X-3-tert-butylsalicylidene)-4,4'-amidedianiline [X=H (3), 5-tert (4)] and their copper(II) complexes 5-8, have been synthesized. Their spectroscopic (IR, (1)H NMR, UV/vis, ESR) properties, as well as magnetic and redox-reactivity behavior are reported. IR spectra of 7 and 8 indicate the coordination of amide oxygen atoms of 3 and 4 ligands to Cu(II). The solid state ESR spectra of 5-8 exhibits less informative exchange narrowed isotropic or anisotropic signals with weak unresolved low field patterns. The magnetic moments of 5 (2.92 µ(B) per Cu(II)) and 6 (2.79 µ(B) per Cu(II)) are unusual for copper(II) complexes and considerably higher than those for complexes 7 and 8. Cryogenic measurements (300-10 K) show weak antiferromagnetic exchange interactions between the copper(II) centers in complexes 6 and 8. The results of electrochemical and chemical redox-reactivity studies are discussed.

Spectroscopic and electron-transfer reactivity studies of bulky bis(N-cycloalkyl-3,5-tBu2-salicylaldiminato)copper(II) complexes: generation of uncoordinated and coordinated phenoxyl radicals.

This work summarizes the results of our studies on the spectral, magnetic, electrochemical and chemical redox properties of N-cycloalkyl-3,5-(t)Bu(2)-salicylaldimine ligands [cycloalkyl=cyclo-C(5)H(9)(HL(1)), cyclo-C(6)H(11) (HL(2)), cyclo-C(7)H(13) (HL(3)), cyclo-C(8)H(15) (HL(4)), 1-adamantyl (HL(5)), 2-adamantyl (HL(6))] and their copper(II) complexes (1-6). The compounds have been characterized by IR, (1)H NMR, UV-vis, EPR spectroscopy, electrochemical and magnetic susceptibility measurements. The geometry of 1-6, according to their EPR (g(II) and g(II)/A(II)) and visible spectral data, exhibit a significant amount distortion from slightly distorted square-planar to pseudo-tetrahedral. The cyclic voltammetric studies of 1-6 reveal that as the extent of the tetrahedral distortion of Cu(II) center increases on going from 1 to 5, the values of Cu(II)/Cu(I) potentials became more negative. The compounds have been oxidized electrochemically and chemically and the generated relatively stable uncoordinated phenoxyl [HL(x)](*+) and coordinated Cu(II)-phenoxyl radical [1-6](*+) species have been characterized by UV/vis and EPR spectroscopy.

Electrocatalytic Oxidation of Isoproterenol and its Voltammetric Determination in Pharmaceuticals and Urine Samples Using a Poly(1-methylpyrrole)-DNA Modified Electrode.

Determination of isoproterenol (ISP) was carried out using a DNA incorporated poly(1-methylpyrrole) modified glassy carbon electrode (GCE). The poly(1-methylpyrrole)-DNA/GCE showed an excellent electrocatalytic effect on the oxidation of ISP. The poly(1-methypyrrole)-DNA/GCE also accelerated the rate of electron transfer reaction of ISP. Compared with a bare GCE, the poly(1-methylpyrrole)-DNA/GCE exhibits a distinct shift of the oxidation potential of ISP in the cathodic direction and a marked enhancement of the current response. A linear calibration plot was obtained covering the concentration range from 2.0 × 10-6 to 6.0 × 10-5 M with a detection limit of 1.60 × 10-7 M by cyclic voltammetry. The electrode system has also successfully resolved the overlapping anodic peak of ISP and uric acid (UA) into two well-defined voltammetric peaks in cyclic voltammetry at 0.416 V and 0.552 V for ISP and UA, respectively. The poly(1-methypyrrole)-DNA/GCE has successfully been utilised for the determination of ISP in pharmaceutical preparations. The validity of the proposed method was also assured by the recovery of ISP and UA in urine samples.

A poly(3-acetylthiophene) modified glassy carbon electrode for selective voltammetric measurement of uric acid in urine sample.

A reliable and reproducible method for the determination of uric acid in urine samples has been developed. The method is based on the modification of a glassy carbon electrode by 3-acetylthiophene using cyclic voltammetry. The poly(3-acetylthiophene) modified glassy carbon electrode showed an excellent electrocatalytic effect towards the oxidation of uric acid in 0.1 m phosphate buffer solution (PBS) at pH 7.2. Compared with a bare glassy carbon electrode (GCE), an obvious shift of the oxidation peak potential in the cathodic direction and a marked enhancement of the anodic current response for uric acid were observed. The poly(3-acetylthiophene)/GCE was used for the determination of uric acid using square wave voltammetry. The peak current increased linearly with the concentration of uric acid in the range of 1.25 x 10(-5)-1.75 x 10(-4) M. The detection limit was 5.27 x 10(-7) M by square wave voltammetry. The poly(3-acetylthiophene)/GCE was also effective to determine uric acid and ascorbic acid in a mixture and resolved the overlapping anodic peaks of these two species into two well-defined voltammetric peaks in cyclic voltammetry at 0.030 V and 0.320 V (vs. Ag/AgCl) for ascorbic acid and uric acid, respectively. The modified electrode exhibited stable and sensitive current responses toward uric acid and ascorbic acid. The method has successfully been applied for determination of uric acid in urine samples.