The present study was conducted to evaluate the feasibility of apatitic tricalcium phosphate with a Ca/P ratio of 1.50 for the adsorption of phenol and tyrosine from aqueous solutions. The adsorbent was synthesized at room temperature using an aqueous double decomposition method and characterized through physicochemical methods. Batch adsorption studies were conducted as a function of contact time, initial adsorbate concentration, temperature, and pH. The adsorption kinetics of phenol and tyrosine were well fitted to the pseudo-second-order model. The maximum adsorption capacity was found to be 5.56 mg/g for phenol and 9.65 for tyrosine mg/g at 298 K. The adsorption of phenol and tyrosine was well explained using the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevick models. The Langmuir model is the most suitable, with a maximum monolayer adsorption capacity of 7.32 mg/g for phenol and 11.43 mg/g for tyrosine at 298 K. The thermodynamic parameters indicate that the adsorption process is favorable, spontaneous, exothermic, and controlled by physisorption with electrostatic interactions between compounds containing the phenolic group and apatite. The results of this study have demonstrated the potential utility of apatitic tricalcium phosphate, which could be developed into a viable technology for the adsorption of compounds containing the phenolic group from aqueous solutions.

The adsorption properties of hydroxyapatite of low crystallinity towards methionine have been examined. The chemical composition of hydroxyapatite was taken as an experimental variable in order to have a point of view on the parameters of the adsorption process and the mechanisms established between adsorbent-adsorbate. The adsorption kinetics are relatively fast, and the high amounts adsorbed at saturation are obtained for non-stoichiometric hydroxyapatite, containing more HPO4^2- ions and having a high specific surface area. The good agreement of the experimental data with kinetic models confirms that the mechanism can be perfectly described by pseudo-second-order kinetics. Adsorption isotherm models show that Langmuir's model gives a better fit of experimental data compared to that of Freundlich, Temkin and Dubinin-Kaganer-Radushkevich. Fourier transform infrared spectroscopy confirmed the interaction between the -COO^- ions of methionine and the Ca²⁺ ions of hydroxyapatite. The thermodynamic parameters, the isoelectric point of methionine and the point of zero charge of hydroxyapatite with different Ca/P ratios show that the adsorption process is considered spontaneous, exothermic and often controlled by physisorption with interactions electrostatic.

The non-stoichiometric, calcium-deficient hydroxyapatite was prepared through a low-temperature from aqueous solutions method and characterized using Physico-chemical methods. The potential of this hydroxyapatite to adsorb and release insulin from aqueous solutions was evaluated under physiological conditions. The effect of contact time and initial concentration were studied in batch experiments. The adsorption rate reached up to 81±5% in the first half-hour of contact, while the release rate of insulin incubation was about 41 ± 5% after 1 hour. The pseudo-first-order, pseudo-second-order, Elovich equation, Weber and Morris intraparticle diffusion model and Bangham’s pore diffusion model were applied to study the kinetics of the adsorption process. The pseudo-second-order kinetic model provided the best correlation R²(0.998) of the used experimental data compared to the other models. The adsorption of insulin onto hydroxyapatite was correlated well R²(0.998) with the Langmuir model as compared to Freundlich, Temkin and Dubinin–Kaganer–Radushkevich (D-K-R) models, with a maximum adsorption capacity of 24.46 mg/g. The isotherms parameters values of ΔG⁰, b_t and E show that the adsorption process is favorable, spontaneous, exothermic, and controlled by physisorption. The point of zero charge (pHZPC) of hydroxyapatite and the isoelectric point (pI) of insulin indicate that the interaction of insulin molecules with prepared apatite can be well described as an ions exchange reaction.

A series of isoxazole derivatives, 3-aryl-5-[5-(4-nitrophenyl)-2-furyl]-2,3-dihydroisoxazoles (5a-j) were synthesized by cyclocondensation reaction between 1-aryl-3-[5-(4-nitrophenyl)-2-furyl]prop-2-en-1-ones (4a-j) and hydroxylamine hydrochloride in presence of sodium acetate in glacial acetic acid at reflux temperature. Formerly, compounds (4a-j) were synthesized by the condensation of 5-(4-nitrophenyl) furan-2-carbaldehyde (3) with various aromatic ketones by using alkali as catalyst. The structures of the synthesized various isoxazole have been characterized by using elemental analysis, Infrared,¹H-NMR spectroscopy and further supported by Mass spectroscopy. All the products have been screened for their in-vitro biological assay like antibacterial activity towards Gram-positive and Gram-negative bacterial strains and antifungal activity towards Aspergillus niger at a concentration of 40 µg/ml. It was exposed that the compounds 5a, 5c, 5e, 5f, and 5i showed inspiring antibacterial and antifungal activity compared to the used reference standard.