Minimum energy geometries, harmonic vibrational frequencies, and stepwise binding energies have been obtained for the cluster ions NO + ‚(H 2 O) n , n ) 1-4. From systematic ab initio calculations on the lighter NO + ‚(H 2 O) n complexes (n ) 1-2) at MPn, CCSD, and CCSD(T) levels of electron correlation with different basis sets, it was found that the MP2/6-311++G(2d,p) level of theory was reliable for the calculation of minimum-energy geometries and harmonic vibrational frequencies. Relative electronic energies were evaluated at the MP2/aug-cc-pVTZ//MP2/6-311++G(2d,p) level. The inclusion of zero point energy (ZPE) corrections, as well as counterpoise corrections for basis set superposition errors (BSSE), in the calculation of binding energies was essential to obtain the correct energy ordering for the different isomers of a cluster ion. The nature of the stepwise hydration processes was discussed based on the isomeric structures obtained. A reaction route for nitrous acid (HONO) formation when a water molecule is added to NO + ‚(H 2 O) 3 has been established.

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Flutamide is a nonsteriodal anti-androgen drug, which is commonly used in the treatment of advanced prostate cancer. Based on the reduction of the nitro organic moiety of the drug molecule in acetate buffer of pH 5 at the hanging mercury drop electrode, three adsorptive cathodic stripping voltammetric procedures were optimized for determination of flutamide in bulk, tablets, and human serum applying linear-sweep, differential-pulse, and square-wave waveforms. The achieved limits of detection of the bulk drug were 1.9 × 10–7, 8.7 × 10–8, and 9.7 × 10–9 mol L–1 by using the optimized differential-pulse, linear-sweep, and square-wave adsorptive stripping voltammetric procedures, respectively. Repeatability of the results was studied for 1 × 10–6 mol L–1 of the drug and the recoveries obtained were 98.51 ± 1.56% (LSV), 98.89 ± 0.87% (DPV), and 99.21 ± 1.03% (SWV). The proposed procedures were successfully applied to the determination of the drug in pharmaceutical formulation (Eulexin® tablets) and human serum. The detection limits of the drug in bulk, pharmaceutical formulation, and human serum achieved by means of the proposed procedures showed that the square-wave mode was more reliable for determination of the drug especially in its low concentration levels.Key words: flutamide, linear-sweep, differential-pulse, square-wave, cathodic adsorptive stripping voltammetry, determination, Eulexin® tablets, human serum.

Ab initio molecular orbital calculations have been used to compute thermodynamic constants (ΔH°, ΔS°, ΔG°) for the stepwise hydration reactions of NO+(H2O) n and for the competing rearrangement reaction which produces HONO and H+(H2O) n (for n ≤ 4). Geometry optimizations and harmonic frequency calculations were performed at the MP2/6-311++G(2d,p) level, and relative energies were computed at the MP2/aug-cc-pVTZ level with MP2/6-311++G(2d,p) optimized geometries. The geometry changes and energetics of these competing solvation and rearrangement reactions have been studied, and reasons are proposed to explain why NO+(H2O) n +1 formation is the dominant process for n = 1 and n = 2 but HONO + H+(H2O) n formation contributes for n = 3 and becomes more important for n = 4.