Theoretical calculations of the relative pKa values of some selected aromatic arsonic acids in water using density functional theory
, Online first: October 2015
Behzad Khalili and Mehdi Rimaz PDF (230 K)
Abstract: With the focus on calculating the equilibrium constant (Ka) of arsonic acids (RAsO(OH)2) in aqueous media, the behavior of both neutral and negatively charged species of some arsonic acids have been considered through the isodesmic reaction scheme with polarized continuum model of solvation. The relative pKa values of a number of arsonic acids were calculated using density functional theory (DFT), with methylarsonic acid (CH3AsO(OH)2) used as a reference molecule. Various basis sets such as (6-31G(d), 6-31+G(d), 6-311++G(d,p) and 6-311++G(2d,2p)) in conjunction with B3LYP computational method were examined. Finally the latter one was found to give better results. The results of applied B3LYP 6-311++G(2d,2p) method for pKa values of 25 arsonic acids in aqueous media showed good agreement with corresponding experimental pKa values. In this level of theory the average error was less than 0.3 pKa units. The type of substituent affected the acid strength, with electron withdrawing substituents lowering the pKa and electron releasing groups increasing it.
Keywords: Arylarsonic acid, Relative pKa, DFT study, Aqueous media
Anhydrous ZnCl2: A Highly Efficient Reagent for Facile and Regioselective Conversion of Epoxides to β-Chlorohydrins
, Online first: October 2015
Ronak Eisavi, Behzad Zeynizadeh and Mehri Kouhkan PDF (230 K)
Abstract: Facile conversion of structurally different epoxides to the corresponding β-chlorohydrins was carried out successfully with anhydrous ZnCl2 in CH3CN. The reactions were carried out within 10-50 min to give β-chlorohydrins with perfect regioselectivity and high yields (80-97%).
Keywords: Anhydrous ZnCl2, β-Chlorohydrin, Epoxide, Regioselective
A green HPLC technique with a 100% water mobile phase for detecting imidacloprid and its metabolite 6-chloronicotinic acid
, Online First: September 2015
Naoto Furusawa PDF (230 K)
Abstract: This paper describes a harmless HPLC technique for detecting imidacloprid (ICP) and its metabolite, 6-chloronicotinic acid (6CA), using an isocratic 100 % water mobile phase. Chromatographic separations were performed a Daisopak® SP-200-3-C1-P with water mobile phase and a photodiode-array detector. The total run time was < 6 min. The system suitability was well within the international acceptance criteria. The detection limits were 0.018 μg/ml for ICP and 0.005 μg/ml for 6CA, respectively. A harmless HPLC method for simultaneous detecting ICP and 6CA was developed and may be further applied to the quantification in animal-derived foods.
Keywords: International harmonized analytical method, Imidacloprid, 6-Chloronicotinic acid, 100 % water mobile phase, HPLC
Potentiometric determination of piroxicam and oxfendazole in pharmaceuticals
, Online first: September 2015
Nagaraju Rajendraprasad and Kanakapura Basavaiah PDF (230 K)
Abstract: Piroxicam (POC) and oxfendazole (OFA) are two widely used veterinary non-steroidal anti-inflammatory and anthelmintic medicines, respectively. Simple, precise and accurate and cost-effective methods for the determination of POC and OFZ in bulk drug and in its dosage forms have been developed and validated. The methods are based on the potentiometric titration of compound with acetous perchloric acid in glacial acetic acid medium using modified glass-saturated calomel electrode system. The methods are applicable over the ranges 1.5 - 15 mg and 7.5-15 mg, for POC and OFA, respectively. The proposed methods were successfully applied to the determination of active substances in their pharmaceutical dosage forms. A statistical comparison was made on the results of proposed methods with those obtained for reference method. The intra-day and inter-day precision and accuracy values obtained were satisfactory with RSD and RE values less than 3%. Excipients in tablets did not interfere to the assay as shown by the recovery study via standard addition technique with mean percentage recoveries in the range 97.8 – 100.6%.
Keywords: Piroxicam, Oxfendazole, Potentiometry, Pharmaceuticals, Development, Validation
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