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A New Method for the Microdetermination of Para Aminophenol in Generic Brands of Paracetamol Tablets
(Taylor & Francis Group,, 2019) Adegoke, O. A.; Thomas, O. E.; Amao, S. A.; Agboola, S. O.; Omotosho, A. E.
In Nigeria, paracetamol is readily available in several retail outlets where the conditions of storage can be poor leading to elevated levels of para-aminophenol (PAP), which is known to be nephrotoxic and hepatotoxic. However, the routine analysis of PAP is mostly by chromatographic separation which requires expensive instrumentation not often available in developing countries. The objective of this research was to develop a sensitive colorimetric method for the quantification of PAP in paracetamol. The method was based on the diazo coupling reaction between diazotised PAP and chromotropic acid. Various reaction parameters critical for optimal detector response were optimized. The validation of the new method was done following the determination of parameters including repeatability, reproducibility and selectivity using current ICH guidelines. The new method was also applied to the assay of PAP in 14 paracetamol tablet samples. The calibration was linear between 0.0297 and 0.2229 mg/mL at 470nm with limits of detection and quantification of 0.0061 and 0.0185 mg/mL, respectively. The recovery was in the range of 95.96 and 102.21 while intra- and inter-day precisions at three different concentrations did not exceed 4.03%. The new method was successfully applied to quantify PAP in paracetamol with percent content varying from 0.14 to 0.21%w/w. A simple and reliable method for the quantification of PAP has been developed and successfully employed to report, for the first time, the presence of the degradation product at levels beyond the allowable limits in paracetamol dosage forms in Nigeria.
A new spectrophotometric method for the determination of gabapentin usingchromotropic acid
(Istanbul Medipol University, 2018) Adegbolagun, O. M.; Thomas, O. E.; Aiyenale, E. O.; Adegoke, O.A.
The purpose was to develop a colorimetric method for determining gabapentin. The method was based on the diazo coupling reaction between diazotized gabapentin and chromotropic acid. The method was validated using ICH guidelines before its application to generic brands of gabapentin. Coupling reaction generated an orange azo adduct whose absorbance was linearly correlated with concentration in the range of 1-6 μg/mL at 470 nm. The method was accurate and precise with recovery range of 97.6-103.1%; intra- and inter-day precisions (%RSD) were less than 0.65% and showed no statistical difference when compared with reference method in the analysis of the dosage forms. The 3D optimization of the adduct revealed an E-type configuration around the azo linkage which would contribute to its stability. The new method can serve as a reliable alternative to the official method for the routine analysis of gabapentin in bulk and dosage forms.
Antimicrobial and pharmaceutical properties of the seed oil of leucaena leucocephala (Lam.) de wit (Leguminosae)
(2011-01) Aderibigbe, S. A.; Adetunji, O. A.; Odeniyi, M. A.
The seed oil of Leuconia leucocephala was investigated for its antimicrobial activity and the pharmaceutical properties of its lotion formulation determined. The oil was extracted from the pulverised dried seeds of the Leuconia leucocephala plant by cold maceration in n-hexane. The oil was tested against four bacteria (Staphylococcus aureus, Esherichia coli, Bacillus subtilis and Pseudomonas aeruginosa) and four fungi (Aspergilus niger, Rhizopus stolon, Penicillum notatum and Candida albicans) isolates. Gentamycin and tioconazole were the reference drugs respectively. The oil was later formulated as a lotion and the pharmaceutical properties of the formulation determined.The oil was found to have a concentration-dependent activity against both Gram-positive and Gram-negative bacteria, while showing no activity against the fungi tested. The lotion formulation of the oil containing oleic acid had good pharmaceutical properties and was stable over the test period. Leucaena leucocephala seed oil extract had a concentration-dependent activity against both Gram-positive and Gram-negative bacteria and the lotion formulation had good pharmaceutical properties.
Characterization, antimicrobial and catalytic activities of silver nanoparticles biosynthesized using Aqueous extract of Euphorbia graminea
(Istanbul Medipol University, 2023) Thomas, O. E.; Alabi, S. O.; Osharode, P.E.
Phytosynthesis of silver nanoparticles (AgNPs) is not only affordable and ecofriendly but provides a means of synthesizing phytochemical capped AgNPs with predefined characteristics. The objective of this study was the green synthesis of AgNPs that possess antimicrobial and catalytic activities using aqueous extract of Euphorbia graminea. Reactions parameters critical to the yield, size and morphology of the biosynthesized AgNPs were optimized using UV spectroscopy. The UV-visible spectra analysis of the biosynthesized AgNPs showed surface plasmon resonance occurred at 462 nm. Scanning Electron Microscopy with Energy dispersive X-ray analysis revealed the characteristic absorption band of AgNPs at 3 KeV and confirmed 73.66% composition of particles as metallic silver. The AgNPs appeared as well-separated, quasi-spherical particles with narrow size distribution of 6.77±0.89 nm when examined with Transmission electron microscopy. X-ray diffraction confirmed the crystallinity of the AgNPs with mean crystallite size of 7.65 nm. The biosynthesized AgNPs showed broad-spectrum antimicrobial activity against bacteria and fungi. The rate constant of the degradation of methylene blue in the presence of as-synthesized AgNPs was increased several folds to sec-1 from sec-1 in its absence. The prepared AgNPs could find applications as therapeutic.
Colorimetric determination of Olanzapine via charge-transfer complexation with Chloranilic Acid.
(Elsevier B.V., 2016) Adegoke, O. A.; Thomas, O. E.; Emmanuel, S. N.
The charge-transfer complexation (CTC) formed between olanzapine and chloranilic acid have been studied and used as a sensitive colorimetric method for the determination of olanzapine. Evidence for the formation of the CTC between chloranilic acid (CAA) and olanzapine (OLP) was established by spot tests and TLC. Method development was carried out through selection of analytical wavelength, optimization and validation studies. Physicochemical parameters such as energy of transition, transition dipole, oscillator frequency and ionization energies were estimated and related to the stability of the formed CT band. Thermodynamic properties of the CT band at four temperature levels were also estimated and their inter-relationship established. The reaction was completed at room temperature within 10 min with the evidence of formation of purple-coloured solution with CAA that absorbed maximally at 520 nm. Linearity was obtained in the concentration range of 2–40 µg/mL for OLP (r = 0.9977) with a limit of detection of 1.57 µg/mL. Estimates of accuracies and precisions gave error values less than 2% for both intra- and inter-day assessments. The transition energies were of the order of 2.303 eV. The Gibbs energy varied with the temperature and room temperature values favoured formation of stable complexes. The thermodynamic studies revealed small positive entropy for slightly negative enthalpy change. The method was successfully applied to estimate OLP in tablets and the method was found to be of equivalent accuracy with the Indian Pharmacopoeia’s HPLC method (p > 0.05). The method could find application as a rapid and sensitive determination technique for olanzapine.
Comparison of the Calf Thymus DNA Binding Interactions of 5-hydroxymethylfurfural and its Synthesized Derivative, 5, 5’[oxy-bis(methylene)]bis-2-furfural: Experimental, DFT and Docking Studies.
(Taylor & Francis, 2023) Thomas, O. E.; Oduwole, R. T.; Akin-Taylor, A.
In this study, the in vitro DNA-binding interactions of the food/drug additive, 5-hydroxymethylfurfural (HMF) and its major degradant, 5, 5’[oxy-bis(methylene)]bis-2-furfural (OBMF) were investigated. OBMF was synthesized and characterized using IR, NMR and mass spectrometry. Photometric titrations revealed OBMF induced more extensive perturbations in the 258nm band of DNA and exhibited binding constants that were 5–12-folds higher than those of HMF. The greatest net changes in viscosity of DNA induced by HMF and OBMF were 10.5 and 8.9%, respectively which confirmed both compounds as minor groove binders. Docking revealed that OBMF and HMF bound to the guanine–cytosine regions of minor groove of DNA with global binding energies of −36.36 and −26.12 kcal/mol, respectively. DFT calculations revealed the higher electrophilicity of OBMF contributed to its increased interaction with the negatively charged DNA backbone. There is a need for stricter control of permissible levels of OBMF in food and drug products.
Development and validation of a new spectrophotometric method for the determination of acyclovir
(Faculty of Pharmaceutical Sciences, University of Jos, Jos. Nigeria., 2012) Thomas, O. E.; Adegoke, O. A.
A new spectrophotometric method has been developed for the analysis of acyclovir in bulk and dosage forms. The method is based on the diazo coupling reaction between diazotized acyclovir and p-dimethylaminobenzaldehyde (DMAB). Spot tests and thin layer chromatographic analysis confirmed the formation of a greenish-yellow adduct which was stable in the laboratory environment for more than three hours. Critical factors affecting optimal detector response were identified and optimized. The optimal temperature and coupling reaction time were established at 50oC and 10 min. The azo adduct was determined at 404 nm where neither diazotized acyclovir nor DMAB has any significant absorptivity. Methanol was found as the best diluting solvent after coupling. The assays of acyclovir were linear over the range 1.81-9.06 μg/mL with a correlation coefficient of 0.9998 and limit of detection of 0.024 μg/mL. The method was accurate (error < 3 %) and precise (RSD < 2.7 %) over three days assessment. There was no interference from commonly used excipients. The method was successfully applied to the determination of acyclovir in tablets and creams with similar accuracy to the official USP spectrophotometric method. The method is rapid, simple and cost-effective and could find application in the in-process quality control of acyclovir.
Development of a new visible spectrophotometric method for the analysis of Ganciclovir in bulk sample and dosage form.
(Pharmacotherapy Group, Faculty of Pharmacy, University of Benin, Nigeria, 2015) Thomas, O. E.; Adegoke, O. A.
Purpose: To develop and validate a simple visible spectrophotometric method for the quantitative determination of ganciclovir in bulk sample and dosage form. Method: The method was based on the diazo coupling reaction between diazotized ganciclovir and acidified p-dimethylaminobenzaldehyde. Various analytical parameters for the azo adduct were established. Validation of the new method was carried out using current ICH guidelines with parameters including linearity, repeatability, reproducibility and selectivity determined. The developed method was thereafter applied to determine ganciclovir in a commonly available brand. Results: Coupling reaction generated a yellow-coloured product in an alcohol medium with optimal wavelength at 404 nm. Linear correlation was obtained at concentrations of 10.3 - 25.7 μg/mL. The method was accurate and precise with recovery in the range of 99.37 - 103.15 % while intra- and inter-day precision (% RSD) at three different concentrations was < 2.7 %. The limits of detection and quantification were 0.23 and 0.70 μg/mL, respectively. When applied to the analysis of the dosage form, there was no statistically significant difference between the new method and the official HPLC method. Conclusion: The method is simple, inexpensive, reproducible and fast, and can be employed as a reliable alternative to the official method for the routine analysis of ganciclovir in bulk and dosage forms.
Heavy Metal Contamination of Paediatric Paracetamol and Ascorbic Acid Drug Products in South-West Nigeria.
(West African Postgraduate College of Pharmacists (WAPCP), 2019) Thomas, O. E.; Itopa, M. O.; Adegoke, O. A.
Background: Water is a primary contributor to human populations’ heavy metals exposure and industrial contamination of products. Consequently, paediatric medications because of their high-water constitution can contribute significantly to intake of heavy metals in excess of allowable limits. There is therefore a need for effective preventive and control strategies. Unfortunately, studies investigating heavy metal content in paediatric formulations in Nigeria are scarce and often limited in the range of elements assayed. Objective: To evaluate elemental impurities in the two most frequently administered paediatric medications-paracetamol and ascorbic acid marketed in South-west Nigeria. Methods: Thirteen paediatric syrup brands were used for the study. Sample pretreatment involved dry ashing followed by digestion using concentrated aqua regia (nitric acid:hydrochloric acid, 3:1). Chromium, lead, copper, cadmium, zinc, nickel, cobalt and manganese were assayed with the atomic absorption spectrophotometer with the limit of detection set at 0.001. Results: The most abundant metal ions present in all the formulations were chromium (1.16-1290.2 mg/) and nickel (2.37-1289.0 mg/L). Cadmium was detected at low concentration in only two of the brands while lead was detected in three brands at concentrations ranging from 0.09 - 0.12 mg/L. The calculated expected daily exposures of lead in the three brands were in excess of the permissible daily exposure for oral drug products. Conclusion: Some of the paracetamol and vitamin C syrups sold in the South-West of Nigeria are contaminated with cadmium, nickel and lead.
In vitro cytotoxicity, genotoxicity and apoptoxicity of 8-hydroxy-3,6-disulphonaphthyl azohydroxynaphthalenes using Human Lymphocytes: Experimental and theoretical profiling
(Taylor & Francis, 2023) Thomas, O. E.; Adegoke, O. A.; Mukherjee, A.; Banerjee, R.
Regulatory agencies require demonstration of non-genotoxicity of new chemical entities prior to their use as pharmaceuticals or additives. Consequently, the in vitro cytotoxicity, genotoxicity and apoptoxicity of five novel monoazo colourants (8-hydroxy-3,6-disulphonaphthyl azohydroxynaphthalenes, 3a-e) on human lymphocytes were evaluated using a cell viability assay, alkaline comet assay, DNA diffusion assay, DFT calculations and molecular docking. The test concentrations of the compounds varied from 0 to 3.4 mM. Relative to negative control, the compounds at concentrations up to 0.5mM induced small dose-dependent reduction (< 20%) in viability of lymphocytes. Statistically significant changes (p<0.05) in DNA damage parameters (percent tail DNA, tail extent moment, olive tail moment) were observed at all concentrations of 3a, 3b while 3c-e showed genotoxicity at 2.8, 0.17 and 3.4 mM respectively. Compounds 3a, 3b, 3d induced apoptosis at concentrations below cytotoxic doses while 3c and 3e were non-apoptoxic at all test concentrations. DFT calculations showed the genotoxicity of 3a-e increased with electrophilicity and ionization potentials of the compounds. Molecular docking of 3a-e with apoptosis-associated proteins revealed binding affinity patterns that were consistent with observed experimental apoptoxicity. The structure-genotoxicity relationships of five novel monoazo compounds, which can be employed in the design of safer congeners, have been elucidated.
Interaction of Multiwalled Carbon Nanotube Produces Structural Alteration of DNA
(2016-01) Ghosh, M.; Adegoke, O. A; Jana, A.; Mukherjee, A.
Multiwalled carbon nanotube (MWCNT) has been found to produce structural changes in Calf Thymus-DNA (CT-DNA). The interaction or binding of the multi-walled carbon nanotubes (MWCNT) was investigated in order to discover if it brings about any significant changes of the DNA double helix using CD spectra of the CT-DNA at two concentration levels of MWCNT representing an increasing MWCNT/DNA molar ratio. In addition, spectrophotometric titrations between MWCNT and CT-DNA were carried out in order to utilize spectral changes as a means of detecting specific binding modes of either intercalation or degradation of DNA. Interactions of MWCNT induced significant changes in the CD spectra of the B-form of natural DNA. The intensities of the positive CD band at 280 nm decreased significantly. This decrease was found to be concentration-dependent. Following spectrophotometric titrations; specific subtle conformational changes were observed with a molar ratio combination of 2:1 between MWCNT and CT-DNA and these were characterized by a formation constant of the order of 103 M-1 and a negative Gibbs free energy suggesting that MWCNT avidly binds to DNA. Thermodynamic considerations revealed that electrostatic interactions between the DNA base pairs and the MWCNT are taking place accounting for the negative free energy change, positive enthalpy change with a small entropy change. The results obtained in the study of the binding interactions of MWCNT with DNA confirm that a cytogenetic effect of MWCNT with DNA is a possibility in vivo.
Modelling of 4-Carboxyl-2, 6-dinitrobenzenediazonium ion (CDNBD) hydrolysis through addition of Water and Alkaline Buffer in a strongly acidic medium.
(Springer Science+Business Media, 2015) Idowu, S. O.; Thomas, O. E.; Bioku, O. O.
The transition from aryl diazonium reagent solution to a crystalline form has substantial merits, namely augmented stability and versatility. Absorbance decay data was from photometric titration with hydroxyl ion, supplied incrementally by water and alkaline buffer (pH 12.0), to 4-carboxyl-2,6-dinitrobenzenediazonium ion (CDNBD) and simpler analogs in a strongly acidic medium. The data were fitted to nested models (mono- and bi-exponential decay). Akaike’s Information Criterion was used for statistical model comparison. Preferred model identification shows simpler diazonium analogs are less reactive towards hydroxyl ion when alkaline buffer solution is the diluting medium. In contrast, CDNBD hydrolysis is faster when an alkaline diluting medium is added, owing to profound positive effect of strong electron withdrawing groups on its electrophilic reactivity. Acidic diluting medium was shown, unambiguously, as a critical requirement for maintaining CDNBD, in an acidic solution as the cation species. Key input process variables were reliably predicted, using model parameters like V_(1⁄2) and 〖V^T〗_(1⁄2), thus giving direction for optimal synthesis of crystalline CDNBD.
Molecular docking and ADMET studies of the Interaction of 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalenes with Bovine Serum Albumin
(Faculty of Pharmaceutical Sciences, University of Jos, Nigeria., 2023) Thomas, O.E.
Previous spectrophotometric investigations revealed strong binding affinities between four potential monoazo colourants (code-named AZ-01 to 04) and bovine serum albumin (BSA) which could dictate the tissue distribution and toxicity of the additives. The molecular docking interactions of the dyes with BSA were analyzed using AutoDock vina and PatchDock in order to elucidate the functional groups involved in complex stabilization. Docking conformations confirmed the ligands preferentially inserted into the hydrophobic cavities of BSA site I. Structure-BSA binding relationships revealed the binding of AZ-02 was driven by hydrogen bond donation from its free phydroxynaphthalene substituent to Ser-479 while the predominantly hydrazone form of its positional isomer, AZ-01, increased its lipophilicity and tendency for hydrophobic interactions. The relatively higher C/H ratio of AZ-03 and -04, which contain additional C-7 substituents, was responsible for their stronger binding and the extensive involvement of their aromatic rings in ligand-site I complex stabilization via Pi-Pi T-shaped, Pi-alkyl and alkyl-alkyl interactions. Moreso, AZ-01, -03 and -04 exist predominantly as hydrazone tautomers with an overall positive charge which provided complementary modes for interaction with negatively charged aspartic and glutamic acids. The structure-BSA binding relationships of the molecules, which can be employed in synthesis of safer congeners, have been elucidated.
New spectrophotometric method for the determination of Gabapentin in bulk and dosage forms using p-dimethylaminobenzaldehyde
(Taylor & Francis, 2018) Adegoke, O. A.; Adegbolagun, O. M.; Aiyenale, E.; Thomas, O.E.
A new simple, accurate and economic spectrophotometric method based on azo dye derivatization for the determination of gabapentin (GBP) was developed. Critical factors were optimized. The method was validated and assay of dosage forms was done. Spot tests and TLC confirmed the formation of azo adduct. A 0.3M NaNO2 solution using 2M HCl was used for diazotization. The optimal temperature and time were 30°C and 10 min. Azo adducts were determined at 430 nm. Methanol was found to be the best solvent. Gabapentin coupled at a ratio of 1:1 with DMAB. The assays of GBP were linear over the range 1–6 μg/mL (r = 0.9973) and LOD of 0.8322 μg/mL. The methods were accurate (error < 2%) and precise (RSD < 0.5%). The methods were successfully applied to the assay of GBP in dosage forms and compared favorably with reference method (p > .05). The successful diazotization of gabapentin and the azo adduct formation with DMAB is reported for the first time.
Novel colorimetric sensors for cyanide based on azo-hydrazone tautomeric skeletons
(Elsevier B.V., 2014) Adegoke, O. A.; Adesuji, T. E.; Thomas, O. E.
The monoazo dyes, 4-carboxyl-2, 6-dinitrophenylazohydroxynaphthalenes dyes (AZ-01, AZ-03 and AZ-04), were evaluated as a highly selective colorimetric chemosensor for cyanide ion. The recognition of cyanide ion gave an obvious colour change from light yellow to brownish red and upon dilution with acetone produced a purple to lilac colour. Optimum conditions for the reaction between the azo dyes and cyanide ion were established at 300C for 5 min, and different variables affecting the reaction were carefully studied and optimised. Under the optimum conditions, linear relationships between the CN- concentrations and light absorption were established. Using these azo-hydrazone molecular switch entities, excellent selectivity towards the detection of CN- in aqueous solution over miscellaneous competitive anions was observed. Such selectivity mainly results from the possibility of nucleophilic attack on the azo-hydrazone chemosensors by cyanide anions in aqueous system, which is not afforded by other competing anions. The cyanide chemosensor method described here should have potential application as a new family probes for detecting cyanide in aqueous solution.
Phytosynthesis, Antimicrobial and Catalytic Activities of Silver Nanoparticles derived using Leaf and Stem Extracts of Indigofera macrophylla
(Nigeria Association of Pharmacists in Academia, 2022) Thomas, O. E.; Adegoke, O. A.; Adeniyi, E. M.; Oliver, C. G.
Background: The phytosynthesis of metal nanoparticles is a promising green alternative to traditional chemical approaches. Objective: The aim of this study was to synthesize silver nanoparticles (AgNPs) with antimicrobial and biocatalytic activities using aqueous leaf and stem extracts of Indigofera macrophylla. Methods: Critical reaction variables for the biosynthesis of AgNPs were optimized using UV-vis spectroscopy before the biosynthesised AgNPs were characterized using various spectroscopic and microscopic techniques. The biological activities of the biogenic nanoparticles were then investigated with particular focus on their antimicrobial activity and biocatalytic efficiency in the degradation of methylene blue. Results: The surface plasmon resonance of silver nanoparticles biosynthesized using aqueous extracts of leaf (LEAgNPs) and stem (SE-AgNPs) of I. macrophylla occurred at 430 and 426 nm respectively. Scanning electron microscopy images of the nanoparticles showed highly aggregated polymorphs with mostly spherical shape. The particle sizes of LE-AgNPs and SE-AgNPs as determined by Transmission electron microscopy were 48.61±8.60 and 18.09±4.13 nm respectively with Energy dispersive X-ray analysis confirming characteristic absorption band at 3 KeV. In susceptibility assays, LE-AgNPs showed dose-dependent zones of inhibition against Escherichia coli (18mm), Staphylococcus aureus (18 mm), Pseudomonas aeruginosa (20 mm) while SE-AgNP was only active against Staphylococcus aureus (10 mm). Both LE-AgNPs and SE-AgNPs showed good biocatalytic efficiency in the degradation of methylene blue with rate constants of 0.0204 and 0.0182 min-1 respectively. Conclusion: Silver nanoparticles with antimicrobial and catalytic activities have been biosynthesized using the aqueous extract of Indigofera macrophylla.
Preferential solvation of 4-carboxyl-2, 6-dinitrophenylazohydroxynaphthalenes in mixed hydroxylic solvents
(Nigeria Association of Pharmacists in Academia, 2021) Thomas, O. E.; Adegoke, O. A.; Adenmosun, F. G.; Abiodun, O. J.
Background: The applications of a group of 4-carboxyl-2,6-dintrophenylazohydroxynaphathalenes, AZ-01 to 04, as colourants, chemosensors or synthetic intermediates have been limited by their solubility. Aim: To investigate the effect of solvent mixture composition on the solubility, solution thermodynamics and position of equilibrium processes of the dyes. Method: The UV-visible spectral patterns of the dyes in binary mixtures including Methanol:Water, Ethanol:Water, Methanol:Ethanol, Methanol:Propan-1-ol, Methanol:Propan-2-ol, Propan-1-ol:Water and Propan-2-ol:Water were acquired. The type and quantitative estimation of solute-solvent interactions at play were determined by fitting spectral patterns to solvent parameters using multilinear regression. Results: Preferential solvation was detected by the non-ideality of the plots of E12 as against the mole fractions of cosolvent in all binary mixtures. In pure solvents, the spectral shifts of AZ-01, 03 and 04, which exist predominantly in the hydrazone form, were affected by polarity of solvent milieu while solvent basicity and acidity, in that order, were the significant parameters for AZ-02. In aqueous alcoholic mixtures, solvent polarity was contributory, although to different degrees, to the observed spectral data of the four dyes. However, solvent acidity and basicity were the primary determinants of spectral shifts observed with AZ-04 and AZ-03 respectively. Spectra-structure relationships identified the formation of the charged hydrazone tautomer which requires stabilisation by polar solvent milieu as responsible for the observed trend. In addition, interactions between new aggregated solvent-solvent species and the propionic acid substituent present in AZ-03 contributed to its spectral shifts. Conclusion: The solvatochromic properties of the phenylazonaphthalene series in binary mixtures have been successfully studied.
Preferential Solvation of 4-Carboxyl-2,6-dinitrophenylazohydroxynaphthalenes in Aqueous Dimethylformamide and Dimethylsulfoxide Binary Mixtures by UV-Visible Spectroscopy.
(Springer New York / Springer Science+Business Media., 2019) Thomas, O. E.; Adegoke, O. A.; Adenmosun, F. G.; Abiodun, O. J.
The objective of this study was to evaluate the influence of partly aqueous solvent mixtures on the solubility and azohydrazone equilibrium processes for a group of phenylazohydroxynaphthalenes, AZ-01, AZ-02, AZ-03, and AZ-04, whose applications as potential color additives and chemosensors have been demonstrated in previous studies. The UV-visible spectrum was acquired between 190-900 nm at concentrations of the dyes that precluded molecular aggregation for each dye in aqueous dimethylformamide and dimethylsulfoxide binary mixtures of varying compositions. The plots of E12 against mole fractions of the co-solvent showed deviation from ideality in the behaviors of the four dyes in the aqueous solvent mixtures. The solvation data were largely influenced by the structural chemistry of the dyes. In particular, AZ-01, which contains a free parahydroxyl group that can donate hydrogen to hydrogen bond acceptor solvents showed substantial bathochromic shifts in the aqueous DMF and DMSO mixtures as well as a local accumulation of the organic solvent in its solvation sphere. Conversely, the positional isomer AZ-02 with its ortho hydroxyl group being involved in intramolecular hydrazone rearrangement exhibited dielectric enrichment in both aqueous solvent mixtures. In addition, synergism through formation of the water-DMSO and water-DMF complexes was observed with all the dyes in the solvent mixtures with AZ-01 being solvated by the more polar component of the complex while AZ-02 and AZ-04 were solvated by the less polar solvent mixture component. Thus, the preferential solvation of the phenylazohydroxynaphthalene series from AZ-01 to AZ-04 in the partly aqueous DMSO and DMF solvent mixtures has been successfully studied using UV-visible spectroscopy.
Preferential Solvation of Mordant Black and Solochrome Dark Blue in Mixed Solvents Systems.
(Sami Publishing Company, 2019) Thomas, O. E.; Adegoke, O .A.; Kazeem, A. F.; Ezeuchenne, I. C.
In this study, the preferential solvation of Mordant Black and Solochrome Dark Blue were investigated in mixed solvent systems of aqueous methanol, ethanol, propan-1-ol, propan-2-ol, methanol: ethanol, ethanol:propan-1-ol, methanol:propan-2-ol, ethanol:propan-1-ol, ethanol:propan-2-ol, propan-1-ol:propan-2-ol and carbon tetrachloride: dimethylformamide. Results showed a deviation of solvation data from ideality over the majority of composition ranges in all the solvent mixtures. The type and contribution of specific and non-specific solute-solvent interactions were analyzed in the framework of the linear solvation energy relationships. Statistical analysis of single, dual, and multiparametric equations revealed that in pure solvents, spectral behaviours of MB and SDB were affected by the polarity and basicity of the solvent milieu respectively. However in aqueous alcohols, polarity of the solvent milieu was the most significant determinant of spectral patterns with α and β parameters playing secondary contributory roles in the spectral changes of MB and SDB, respectively. Multiparametric equations generally yielded the best fitted model in mixed alcohol systems with polarity remaining the largest contributor, followed by β and α of the solvent milieu in that order. Spectral-structure relationships identified ion-dipole interactions involving the charged sulphonate and hydrazone moieties as well as protondonor-acceptor interactions of the common labile hydroxyl groups as mechanisms for the observed solvation data.
Spectrophotometric and thermodynamic studies of the charge-transfer complexation of Tranexamic Acid with Chloranilic Acid
(Nigeria Association of Pharmacists in Academia, 2018) Thomas, O. E.; Adedoyin, O.
Background: Tranexamic acid is a synthetic analogue of lysine that is clinically useful as an antifibrinolytic agent. Due to its lack of chromophores and aromaticity, chemical derivatization is necessitated and outcomes are often poor and/or associated with low sensitivity and poor stability. Objective: To develop a colorimetric method for the determination of tranexamic acid (TXA) following the optimization and parameterization of the charge-transfer (CT) complexation of the drug with chloranilic acid (CAA). Method: The method involved the utilization of TXA as n-electron donor and CAA as π-acceptor in methanol to generate a CT complex. Factors contributory to the formation and stabilization of the complex were optimized. The Benesi-Hilderbrand equation was used to estimate the molar absorptivity and formation constant of the CT band before its application to dosage form analysis. Results: The CT band which absorbed maximally at 520 nm was associated with molar absorptivity of 807 Lmol- 1cm-1 and a large formation constant (1.14x104). The calculated physicochemical properties including transition energy (2.303eV), oscillator strength (0.267), transition dipole moment (5.455 Debye), resonance energy (1.159 eV), ionization potential (8.679 eV) and dissociation energy (5.276 eV) as well as the thermodynamic parameters were indicative of a highly stable charge-transfer complex. Under optimal conditions, the assays of the drug were linear over the range 10-100 μg/mL and the method was accurate and reproducible (inter-day relative errors and standard deviations not greater than 2.92% and 3.40% respectively). When applied to dosage forms, there was no statistical difference in the mean recoveries of the new method when compared to reference method. Conclusion: The new method is rapid, accurate and precise. It can serve as alternative to the routine analysis of tranexamic acid in bulk and dosage forms.