Assessment of halloysite nanotubes as vehicles of isoniazid.

Equilibrium and thermodynamic aspects of the adsorption of isoniazid (INH) onto halloysite nanotubes (HLNTs) and characteristics of the resultant drug/nanocarrier systems are investigated. Equilibrium studies were performed in aqueous medium at different times, temperatures and drug concentrations. The overall adsorption process was explained as the result of two simple processes: adsorption on the activated sites of HLNTs and precipitation of INH on HLNTs surface. Formation of the INH-loaded HLNTs was spontaneous, endothermic and endoentropic, increasing the thermodynamic stability of the system (ΔH=70.40kJ/mol; ΔS=0.2519kJ/molK). Solid state characterization corroborated the effective interaction between the components that was also described by modeling at molecular level by quantum mechanics calculations along with empirical interatomic potentials. Transmission electron microphotographs confirmed the double allocation and homogeneous distribution of INH in the nanohybrids. FTIR spectra revealed the interaction via hydrogen bonds between the inner hydroxyl groups of HLNTs and N in INH molecules. Loading of INH in the nanohybrids was approximately 20% w/w. Effective loading of INH and activation energies of the interactions enable to propose the designed nanohybrids in the development of modified drug delivery systems.

Theoretical study on the influence of the Mg2+ and Al3+ octahedral cations on the vibrational spectra of the hydroxy groups of dioctahedral 2:1 phyllosilicate models.

The effect on the vibrational spectrum of the hydroxy groups in dioctahedral 2:1 phyllosilicates of the isomorphous cation substitution of Mg(2+) by Al(3+) in the octahedral sheet was investigated at the DFT level. Ortho, meta and para Mg(2+) configurational polymorphs were defined. The theoretical vibration frequencies of OH groups depend significantly on the nature of the cations they are joined with. Theoretical values are spread out over narrow ranges: 3,612-3,626 cm(-1) for ν(AlOHMg), 3,604-3,606 cm(-1) for ν(AlOHAl), and 3,657-3,660 cm(-1) for ν(MgOHMg); 803-830 cm(-1) for δ(AlOHMg), 877 cm(-1) for δ(AlOHAl), and 693-711 cm(-1) for δ(MgOHMg), in agreement with known experimental values. From the intensities of the XOHY bands, we observe that the vibrational adsorptivities of the ν(OH) vibrations are not the same for all XOHY groups, and that ν(MgOHMg) absorptivity is much lower than that of ν(AlOHAl). These theoretical results should be taken into account in quantitative analysis of experimental vibrational studies in clay minerals, introducing different molar extinction coefficients in the Lambert-Beer law to determine the relative concentrations of both cationic arrangements.