Mohamed H Assaleh - Academia.edu (original) (raw)

Papers by Mohamed H Assaleh

Thiocarbohydrazones (TCHs) and structurally related molecules are versatile organic compounds whi... more Thiocarbohydrazones (TCHs) and structurally related molecules are versatile organic compounds which exert antioxidant, anticancer, and other beneficial health effects. The combination of UV/Vis, NMR spectroscopy, and quantum chemical calculations
was used to rationalize the experimentally observed increase in the radical scavenging activity upon the addition of water in DMSO solution of TCHs. Mono- and bis(salicylaldehyde) TCHs (compounds 1 and 2) undergo water-induced E-to-Z
isomerization which is followed by disruption of intramolecular hydrogen bond, ground state destabilization, and 11 kcal/mol decrease in the bond dissociation enthalpy (BDE). Electron spin delocalization is more pronounced in Z-isomers of 1 and 2. On
the other hand, 2-acetylpyridine TCHs (compounds 3 and 4) undergo thione-to-thiol tautomerism which also decreases the BDE and facilitates the hydrogen atom transfer to 2,2-diphenyl-1-picrylhydrazyl radical (DPPH∙). The appearance of thiolic –SH group
as another reactive site toward free radicals improves the antioxidant activity of 3 and 4. The spin density of 3- and 4-thiol radicals is delocalized over the entire thiocarbohydrazide moiety compared to more localized spin of thione radicals. Additional stabilization of thiol radicals corroborates with the increased antioxidant activity. This study provides the new insights on the solution structure of TCHs, and also highlights the importance of solution structure determination when studying the structure-antioxidant relationships of isomerizable compounds.

A high performance liquid chromatography mass spectrometric method for the estimation of clopidog... more A high performance liquid chromatography mass spectrometric method for the estimation of clopidogrel (CLP), in human plasma in positive ion mode was developed and validated using clopidogrel D3 (CLPD) as internal standard (IS). Sample preparation was accomplished by liquid-liquid extraction technique. The reconstituted samples were chromatographed on Kromasil 100-5C18, 100×4.6 mm, 5µm column using a mobile phase consisting of HPLC grade Acetonitrile: Milli Q/HPLC grade water (90:10, v/v). The method was validated over a concentration range of0.0101 to 5.0315 ng/mL for CLP. This validation report provides the results of selectivity, matrix effect, sensitivity determinations, calibration standards and quality control samples data, precision and accuracy data, the results of recovery, various stabilities, run size evaluation and dilution integrity along with all pertinent supporting documentation.

A reverse phase high performance liquid chromatographic method was developed for the simultaneous... more A reverse phase high performance liquid chromatographic method was developed for the simultaneous determination of gemifloxacin and ambroxol in tablet dosage forms. Separation of both gemifloxacin and ambroxol was achieved within 7 min with required resolution, accuracy and precision thus enabling the utility of the method for routine analysis. Chromatographic separation was achieved on a BDS Hypersil C 18 column (250 × 4.6 mm, 3.5μ) using a mobile phase consisting of phosphate buffer pH 5.8 and acetonitrile in the ratio of 40:60 at a flow rate of 1.2 mL per min. The detection was made at 246 nm. The retention time of gemifloxacin and ambroxol were 2.553 and 3.546 min respectively. The method was found linear over the range of 50-90 μg/mL for gemifloxacin and 11.7-21 μg/mL for ambroxol. The proposed method was validated as per the ICH guidelines.

The aim of the present work is to develop a precise, accurate, simple and reliable, less time con... more The aim of the present work is to develop a precise, accurate, simple and reliable, less time consuming, RP-HPLC method for the simultaneous estimation of Amlodipine besylate and Hydrochlorothiazide in pharmaceutical formulation. First of all, maximum absorbance was found to be at 245 nm and the peaks purity was excellent. Injection volume was selected to be 20 μl which gave a good peak area. The column used for study was Hypersil C18, BDS chosen good peak shape. Ambient temperature was found to be suitable for the nature of drug solution. The flow rate was fixed at 1.0 mL/min because of good peak area and satisfactory retention time. Different ratios of mobile phase were studied, mobile phase with ratio of 50:50 Water: Acetonitrile was fixed due to good symmetrical peaks and for good resolution. The present recovery was found to be 98.0-101.5 was linear and precise over the same range. Both system and method precision was found to be accurate and well within range. Detection limit was found to be 0.77 for Amlodipine and 0.35 for Hydrochlorthiazide. The analytical method was found linearity over the range of 20-80 ppm of the target concentration for both the drugs. The analytical passed both robustness and ruggedness tests. On both cases, relative standard deviation was well satisfactory.

Thiocarbohydrazones (TCHs) and structurally related molecules are versatile organic compounds whi... more Thiocarbohydrazones (TCHs) and structurally related molecules are versatile organic compounds which exert antioxidant, anticancer, and other beneficial health effects. The combination of UV/Vis, NMR spectroscopy, and quantum chemical calculations
was used to rationalize the experimentally observed increase in the radical scavenging activity upon the addition of water in DMSO solution of TCHs. Mono- and bis(salicylaldehyde) TCHs (compounds 1 and 2) undergo water-induced E-to-Z
isomerization which is followed by disruption of intramolecular hydrogen bond, ground state destabilization, and 11 kcal/mol decrease in the bond dissociation enthalpy (BDE). Electron spin delocalization is more pronounced in Z-isomers of 1 and 2. On
the other hand, 2-acetylpyridine TCHs (compounds 3 and 4) undergo thione-to-thiol tautomerism which also decreases the BDE and facilitates the hydrogen atom transfer to 2,2-diphenyl-1-picrylhydrazyl radical (DPPH∙). The appearance of thiolic –SH group
as another reactive site toward free radicals improves the antioxidant activity of 3 and 4. The spin density of 3- and 4-thiol radicals is delocalized over the entire thiocarbohydrazide moiety compared to more localized spin of thione radicals. Additional stabilization of thiol radicals corroborates with the increased antioxidant activity. This study provides the new insights on the solution structure of TCHs, and also highlights the importance of solution structure determination when studying the structure-antioxidant relationships of isomerizable compounds.

A high performance liquid chromatography mass spectrometric method for the estimation of clopidog... more A high performance liquid chromatography mass spectrometric method for the estimation of clopidogrel (CLP), in human plasma in positive ion mode was developed and validated using clopidogrel D3 (CLPD) as internal standard (IS). Sample preparation was accomplished by liquid-liquid extraction technique. The reconstituted samples were chromatographed on Kromasil 100-5C18, 100×4.6 mm, 5µm column using a mobile phase consisting of HPLC grade Acetonitrile: Milli Q/HPLC grade water (90:10, v/v). The method was validated over a concentration range of0.0101 to 5.0315 ng/mL for CLP. This validation report provides the results of selectivity, matrix effect, sensitivity determinations, calibration standards and quality control samples data, precision and accuracy data, the results of recovery, various stabilities, run size evaluation and dilution integrity along with all pertinent supporting documentation.

A reverse phase high performance liquid chromatographic method was developed for the simultaneous... more A reverse phase high performance liquid chromatographic method was developed for the simultaneous determination of gemifloxacin and ambroxol in tablet dosage forms. Separation of both gemifloxacin and ambroxol was achieved within 7 min with required resolution, accuracy and precision thus enabling the utility of the method for routine analysis. Chromatographic separation was achieved on a BDS Hypersil C 18 column (250 × 4.6 mm, 3.5μ) using a mobile phase consisting of phosphate buffer pH 5.8 and acetonitrile in the ratio of 40:60 at a flow rate of 1.2 mL per min. The detection was made at 246 nm. The retention time of gemifloxacin and ambroxol were 2.553 and 3.546 min respectively. The method was found linear over the range of 50-90 μg/mL for gemifloxacin and 11.7-21 μg/mL for ambroxol. The proposed method was validated as per the ICH guidelines.

The aim of the present work is to develop a precise, accurate, simple and reliable, less time con... more The aim of the present work is to develop a precise, accurate, simple and reliable, less time consuming, RP-HPLC method for the simultaneous estimation of Amlodipine besylate and Hydrochlorothiazide in pharmaceutical formulation. First of all, maximum absorbance was found to be at 245 nm and the peaks purity was excellent. Injection volume was selected to be 20 μl which gave a good peak area. The column used for study was Hypersil C18, BDS chosen good peak shape. Ambient temperature was found to be suitable for the nature of drug solution. The flow rate was fixed at 1.0 mL/min because of good peak area and satisfactory retention time. Different ratios of mobile phase were studied, mobile phase with ratio of 50:50 Water: Acetonitrile was fixed due to good symmetrical peaks and for good resolution. The present recovery was found to be 98.0-101.5 was linear and precise over the same range. Both system and method precision was found to be accurate and well within range. Detection limit was found to be 0.77 for Amlodipine and 0.35 for Hydrochlorthiazide. The analytical method was found linearity over the range of 20-80 ppm of the target concentration for both the drugs. The analytical passed both robustness and ruggedness tests. On both cases, relative standard deviation was well satisfactory.