Indirect Determination of Sulfide by Cold Vapor Atomic Absorption Spectrometry

A method for the determination of sulfide based on its interference with the determination of Hg by cold vapor atomic absorption spectrometry is described. The decrease in mercury absorbance at 253.7nm is proportional to the concentration of sulfide over the range of 10–320ngmL^–1. The limit of detection was found to be 7ngmL^–1 and the relative standard deviation (R.S.D.) for the determination of different concentrations of sulfide was in the range of 1.8–2.2%. This method was applied to the determination of sulfide in whole human blood after gas-phase separation.     

Kinetic study of the oxidation of some catecholamines by digital simulation of cyclic voltammograms

Electrochemical oxidation of some catecholamines such as dopamine ( 1 ), L ‐dopa ( 2 ), and methyldopa ( 3 ) has been studied in various pH values, using cyclic voltammetry. The results indicate participation of catecholamines ( 1–3 ) in intramolecular cyclization reaction to form the corresponding o‐quinone derivatives ( 1d–3d ). In various pHs, based on ECE mechanism, the observed homogeneous rate constants (k_obs) of cyclization reaction were estimated by comparing the experimental cyclic voltammetric responses with the digital‐simulated results. Also, the cyclization rate constants (k_cyc) were calculated using microscopic acidic dissociation constant of ammonium groups. The significant differences in electrochemical behavior, k_obs and k_cyc, of L ‐dopa ( 2 ) and methyldopa ( 3 ) with dopamine ( 1 ) are due to the effects of the side chain carboxyl group. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 17–24, 2005     

Spectrophotometric determination of fluoxetine by batch and flow injection methods

A rapid, simple, and accurate spectrophotometric method is presented for the determination of fluoxetine by batch and flow injection analysis methods. The method is based on fluoxetine competitive complexation reaction with phenolphthalein-beta-cyclodextrin (PHP-beta-CD) inclusion complex. The increase in the absorbance of the solution at 554 nm by the addition of fluoxetine was measured. The formation constant for fluoxetin-beta-CD was calculated by non-linear least squares fitting. Fluoxetine can be determined in the range 7.0 x 10(-6)-2.4 x 10(-4) mol l(-1) and 5.0 x 10(-5)-1.0 x 10(-2) mol l(-1) by batch and flow methods, respectively. The limit of detection and limit of quantification were respectively 4.13 x 10(-6) mol l(-1) and 1.38 x 10(-5) mol l(-1) for batch and 2.46 x 10(-5) mol l(-1) and 8.22 x 10(-5) mol l(-1) for flow method. The sampling rate in flow injection analysis method was 80+/-5 samples h(-1). The method was applied to the determination of fluoxetine in pharmaceutical formulations and after addition to human urine samples.     

‘Click Synthesis’ of Some Novel O‐Substituted Oximes Containing 1,2,3‐Triazole‐1,4‐diyl Residues as New Analogs of β‐Adrenoceptor Antagonists

The ‘click synthesis’ of some novel O‐substituted oximes, 7a – 7t , which contain 1,2,3‐triazolediyl residues, as new analogs of β‐adrenoceptor antagonists is described (Schemes 1–4). The synthesis of these compounds was achieved in four to five steps. The formation of oximes of 9H‐fluoren‐9‐one and benzophenone, i.e., 9a and 9b , respectively, followed by their reaction with propargyl bromide, afforded O‐propargyl oximes 10a and 10b , respectively, which by a subsequent CuI‐catalyzed Huisgen cycloaddition with prepared β‐azido alcohols 11a – 11j (Schemes 2 and 3), led to the target compounds 7a – 7t in good yields.     

Removal of numerical instability in the solution of an inverse heat conduction problem

In this paper, we consider an inverse heat conduction problem (IHCP). A set of temperature measurements at a single sensor location inside the heat conduction body is required. Using a transformation, the ill-posed IHCP becomes a Cauchy problem. Since the solution of Cauchy problem, exists and is unique but not always stable, the ill-posed problem is closely approximated by a well-posed problem. For this new well-posed problem, the existence, uniqueness, and stability of the solution are proved.     

Synthesis of Acyclic Nucleosides with N‐[(Benzyloxy)(aryl)methyl] Substituents as Potential HEPT,EBPU, and TNK‐651 Analogues

The syntheses of the novel acyclic nucleosides 5a – 5m , carrying different N‐[(benzyloxy)(aryl)methyl] substituents, are described (Scheme). These compounds could be prepared in medium‐to‐good yields by either direct or silyl‐assisted coupling of the electrophiles 6 with either purine or pyrimidine nucleobases, or with different imidazole derivatives. The reactivity of the positively charged electrophilic intermediates derived from 6 upon Cl^? abstraction was rationalized by ab initio HF/6‐311G quantum‐mechanic calculations. The positive charge was found to be dispersed differently, depending on the electronic properties of the aryl substituents.     

Interaction of β‐Cyclodextrin with Cetyltrimethylammonium Bromide in the Presence of Neutral Red and Its Application to the Spectrophotometric Determination of β‐Cyclodextrin

The effects of addition of β‐cyclodextrin (β‐CD) to the neutral red‐cetyltrimethylammonium bromide (CTAB) associates in pH 7 phosphate buffer solutions were investigated. Addition of β‐CD to neutral red‐CTAB association causes decomposition of the associate by displacement of neutral red with β‐CD. The inclusion complex of CTAB with β‐CD is more stable than that with neutral red. The results indicate that formation of inclusion complex of CTAB with β‐CD prevents its association with neutral red, and inclusion complex formation of β‐CD and neutral red in the presence of CTAB takes place after total consumption of CTAB. The competition of β‐CD and neutral red on the interaction with CTAB can be used for the simple, rapid and sensitive spectrophotometric determination of β‐CD.     

Optical and MRI investigations of an optimized acrylamide-based polymer gel dosimeter

The first purpose of this research was improvement of sensitivity of the normoxic acrylamide-based polymer gel dosimeter. Another aim of this study was investigation of the absorbance of the irradiated gels as well as their relaxation rate variations. In addition, a new optical parameter, area under the absorbance spectrum (AUS), was investigated. Sensitivity improvement was performed by adding glucose and urea to the previously reported acrylamide-based polymer gel formulation and new formulation was named PAGATUG. The formulation which gives the nearest tissue elemental composition has been determined to be 3 % bis, 3 % AA, 5 % gelatine, 5 mM THPC, 0.01 mM HQ, 8.5 % glucose, and 3 % urea. The differences in electron density, number of electrons per gram and effective atomic number of PAGATUG gel were no more than 1, 0.5, and 0.8 % of the corresponding values for the soft tissue respectively. PAGATUG gels were irradiated by ⁶⁰Co radiotherapy unit photon beams with different doses and imaged using a 1.5T Siemens Avanto MRI scanner for different post irradiation times. In addition, the absorbance of the irradiated gels were evaluated using a double beam spectrophotometer. We found that the R ₂-sensitivity of polymer gel was improved by a factor of more than 2.6 in respect of the previously reported PAGAT polymer gel. Dose–absorbance sensitivity was obtained as 0.89 Au Gy^?1 and the results showed more stable response in respect of R ₂ investigation. An AUS-sensitivity of 107.7 Au nm Gy^?1 indicated to steep response variation. This read out parameter showed an acceptable linearity and dynamic dose range.