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Multi-walled carbon nanotubes (MWCNTs) were grown by chemical vapor deposition. The effect of the composition of carbon paste electrode on its voltammograms was evaluated in basic solution with 5.0×10 −5 M tryptophan (Trp). It was found that addition of MWCNTs to the carbon paste would generate the peak current of Trp because of its catalytic effect on the redox process. The pH strongly affects the peak potential of Trp. The best analytical response was obtained at pH 13.0. The anodic peak currents were proportional to Trp concentrations in the range of 1.0×10 −9 -1.0×10 −4 M under the optimized experimental conditions. The detection limit was 2.2×10 −10 M. The effect of potential scan rate on the peak potential and peak current of tryptophan was investigated. The correlation of the peak currents against v 1/2 (v is the scan rate) is linear, which is very similar to a diffusion-controlled process. The proposed biosensor was applied to the determination of Trp in pharmaceuticals formulations successfully.

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The stability constants of the complexes of dioxovanadium(V) ion with some sulphur containing amino acids (L-cysteine, N-acetyl-L-cysteine, and DL-penicillamine) were determined in acidic solution at 25 °C and 0.1 mol dm" 3 ionic media with high ligand-to-metal ratios, using a combination of Potentiometrie and spectrophotometric techniques. Sodium Perchlorate solution was used to maintain the ionic strength. The compositions of the formed complexes were determined and it was shown that dioxovanadium(V), V0 2 \ forms two mononuclear 1:1 and 1:2 (metal-toligand ratios) species of the types V0 2 H 2 L + and V02(H 2 L) 2 + with the ligands, where L represents the fully dissociated form of each ligand. The logarithms of the cumulative stability constants, ß xy " of the complexes, [(oxometal ion) x (H) y (ligand) z ], are logß 12 i and logßi 42 as: 4.82, 6.26 (for cysteine), 5.14, 6.56 (for N-acetylcysteine), and 5.56, 8.06 (for penicillamine).

The interaction of magnesium hydrate at the phosphate oxygen atoms of the purine nucleotides (AMP, GMP, IMP) were studied at the Hartree-Fock level Theory. We used LANL2DZ basis set for Mg and 6-3 lg* basis set for other atoms. The basis set superposition error (BSSE) begins to converge for used method/basis set. NBO calculations were performed to the second-order; perturbative estimates of donor-acceptor (bonding-antibonding) interactions have been done. The gauge-invariant atomic orbital (GIAO) method was employed to calculate isotropic atomic shielding of the nucleotides using HF/6-31g** level. INTRODUCTION:All of the reactions involving nucleic acids in biological systems, such as those involving ATP or dinucleotide coenzymes, are mediated by metal ions. Metal ions are known to have an effect on the stability of both DNA and RNA in vivo. Physiologically, the important complexes are those involving Mg +2 . There is, however considerable discord as to the structure of these metal-nucleotide complexes /1-6/.A nucleotide consists of three main subunits, the nucleobase residue (purine or pyrimidine ), the sugar part and the phosphate group(s). The structures of the three common purine-nucleoside 5'-monophosphates are shown in Fig 1 /7Nuclear magnetic resonance techniques applied to poly-or mononucleotides can be directly used to detect the effects caused by the binding of a metal ion on these molecules in aqueous solutions. Hammes, Maciel, and Waugh found in 1961 that addition of Mg +2 and Ca +2 did not change the H(2) and H(8) resonance positions and therefore the metals did not bind to the ring III. Happe and Morales concluded from 1S N NMR chemical shifts that Mg +2 does not bind to the ring 161.The NMR shielding tensor σ can be all written as second derivatives of the energy σ =(<52E/dB0m)B.o,m-o, where Ε is the energy of the molecule, Β external magnetic field, Ε electric intensity, and n, m nuclear magnetic moments. Scalar parameter and σ observable for an isotropic medium are defined as 1/3 of the traces of the tensors J and σ, respectively /7/.Electronic structures were analyzed with the natural bond order method /9/ (NBO). In the NBO method, the aim is to optimally transform a given wave function into localized form, corresponding to the one-center (lone pair) and two-center (bond) elements of the chemist's Lewis structure picture. This is carried out by examining all possible interactions between filled (donor) Lewis type NBOs and empty (acceptor) non Lewis NBOs and estimating their energetic importance by two second-order perturbation theory. SLLJ-/Brought to you by | Carleton University OCUL Authenticated Download Date | 6/13/15 7:30 AM Vol. 28, No. 2, 2005 Structural Studies and Investigation of NMR Shielding Tensors Coordination of Magnesium Hydrate to Purine at distances ranging form 1.912 to 2.150, values that were in agreement with the available experimental results (2.02A°and 2.11A°) /14/.The latter kind of structure was also described for the Mg(II)-hydrate complexes of the 5'monophosphates. Int...