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.
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 × 107, 8.7 × 108, and 9.7 × 109 mol L1 by using the optimized differential-pulse, linear-sweep, and square-wave adsorptive stripping voltammetric procedures, respectively. Repeatability of the results was studied for 1 × 106 mol L1 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.
The photophysical and photochemical properties of the merocyanine dye 1-methyl-2-(4-hydroxystyryl)pyridinium betaine (M) have been studied in aqueous solution at the PM3-SCRF (SCRF = self-consistent
reaction field) level of theory. The trans isomer is more stable than the cis one by 6 kcal/mol, and the energy
gap decreases upon protonation to 2.4 kcal/mol. Protonation on nitrogen is energetically unfavorable and
costs at least 31 kcal/mol more energy than protonation on oxygen. The acidity of the O-protonated form
(MH+) soars up on excitation as inferred from the decrease in the proton affinity values. Potential energy
surfaces (PES) for the ground and lowest excited states for the O-protonated (MH+) and unprotonated (M)
forms of the dye have been constructed to explore the deactivation pathways of the excited states. Upon
excitation the protonated form adopts the quinonoid geometry of the central single bond, and the trans ⇌ cis
photoisomerization goes through a minimum, referred to as the phantom state, of 90° twisted molecular
architecture located on the potential energy surface of its first excited singlet state. For the unprotonated
form (M), the cis → trans isomerization is a downhill process of a quite negligible energy barrier, surmountable
thermally at room temperature. The photochemical/protolytic cycle Mtrans ⇌ MH+
trans ⇌ MH+
cis ⇌ Mcis →
Mtrans could be utilized in the storage of information and its subsequent carrier retrieval. The optical transitions
are xy-plane polarized π−π* transitions and are expected at 372 nm (experiment, 364 nm) and 428 nm
(experiment, 426 nm) for MH+ and M, respectively, in aqueous medium. Within the framework of the SCRF
model, the unprotonated form (M) exhibits a slight positive solvatochromism. The hydrogen bond donor
ability of the solvent is likely the key factor behind the experimentally observed negative solvatochromism.
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