T. Moyo

Preparation and solid-state characterization of ball milled saquinavir mesylate for solubility enhancement

Saquinavir is an anti-retroviral drug with very low oral bioavailability (e.g. 0.7-4.0%) due to its affinity toward efflux transporters (P-gp) and metabolic enzymes (CYP3A4). The aim of this study was to characterize the effects of high-energy ball milling on saquinavir solid-state characteristics and aqueous solubility for the design of effective buccal drug delivery systems. The solubility of saquinavir mesylate was evaluated in simulated saliva before and after milling for 1, 3, 15, 30, 50, and 60 h. To elucidate changes in crystallinity and long-range structure in the drug, analyses of the milled powders were performed using XRD, ATR-IR, DSC/TGA, BET surface area, EDX and SEM. In addition, the effects of milling time on saquinavir solubility were statistically correlated using repeated measures ANOVA. Results of this study indicate that the milling of saquinavir mesylate produces nanoporous particles with unique surface structures, thermal properties, and increased aqueous solubility. Optimal milling time occurred at 3h and corresponded to a 9-fold solubility enhancement in simulated saliva. Thermal analysis revealed only a slight decrease in melting point (T(m)) from 242 °C to 236 °C after 60 h milling. XRD diffractograms indicate a gradual crystalline-to-amorphous transition with some residual crystallinity remaining after 60 h milling time. Unstable polymorphic structures appeared between 15 and 30 h which were converted to more stable isomorphs at 60 h. Aggregate formation also seems to occur after 15 h but no metal contamination of the drug was observed during the milling process as determined by EDX analysis. In conclusion, high-energy ball milling may be a method of choice for improving the solubility of saquinavir and facilitating novel drug formulations design.

Structural and M?ssbauer studies of Mn0.5Co0.5Fe2O4 ferrites prepared by high energy ball milling and glycolthermal methods

We have investigated the properties of three Mn0.5Co0.5Fe2O4 ferrites synthesized directly from high purity metal oxides (Sample A) and from MnFe2O4 and CoFe2O4 ferrites (Sample B) by mechanical milling and by glycolthermal process (Sample C). XRD results show essentially single phase spinel structure. Sample C is the best sample followed by Sample B based on the presence of minor impurity peaks near 2? ? 38? and 52?. More impurity peaks appear to grow after annealing above 400 ?C. Samples A and B have been found to have similar Fe-57 M?ssbauer spectra before and after annealing at 1050 ?C. The spectrum for each sample changes significantly after annealing. This is attributed to changes of both grain sizes and impurity phases with thermal annealing. At least two sextets and two doublets are used to fit the M?ssbauer spectra.

NiO–ZrO2 nanocomposite modified electrode for the sensitive and selective determination of efavirenz, an anti-HIV drug

The present study reports the synthesis of NiO–ZrO2 nanocomposites followed by their characterization using X-ray powder diffraction, high-resolution scanning electron microscopy, high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. A new chemically modified glassy carbon electrode was fabricated based on the synthesized nanocomposite and used as a highly sensitive electrochemical sensor for the determination of efavirenz, an anti-HIV drug. The modification increased the effective surface area of the sensor ten times in comparison to the bare glassy carbon electrode. Cyclic voltammograms revealed that the modified electrode exhibits excellent electrocatalytic activity towards oxidation of the drug. The current displayed a wide linear response ranging from 0.01 to 10 μM with a detection limit of 1.36 nM. The effect of interferents on the peak current response was studied. The electrode displayed advantages such as simple preparation, appreciable stability, reproducibility and high sensitivity. The feasibility of the proposed method was successfully demonstrated by determining efavirenz in commercial pharmaceutical formulations and human urine samples.

Investigation of magnetic and electrochemical sensing properties of novel Ba1/3Mn1/3Co1/3Fe2O4 nanoparticles

Novel Ba1/3Mn1/3Co1/3Fe2O4 nanoparticles were successfully synthesized using the glycol thermal route. The X-ray diffraction study confirmed a well defined spinel phase structure of the sample. The microstrain was investigated based on the Williamson–Hall plot. Crystallinity, shape and size of the nanoparticles were studied using high resolution transmission electron microscopy and high resolution scanning electron microscopy. Brunauer–Emmet–Teller measurement revealed that the sample has a high surface area of 116 m2 g−1. The Barrett–Joyner–Halenda test showed that the sample is mesoporous. The magnetization was found to increase from 66.5 ± 0.3 emu g−1 at 300 K to 84.4 ± 0.5 emu g−1 at 4 K. Furthermore, the electrochemical sensing properties of Ba1/3Mn1/3Co1/3Fe2O4 nanoparticles were investigated using cyclic voltammetry. A glassy carbon electrode was modified using the synthesized Ba1/3Mn1/3Co1/3Fe2O4 nanoparticles. The modified electrode demonstrated excellent electrocatalytic activity towards didanosine, an anti-HIV drug. A linear response to the drug concentration was obtained in the range from 0.001 to 5.0 μM with a detection limit of 1.0 nM. The electrode was highly stable, reproducible and was successfully used to determine trace amounts of didanosine in human urine samples.

Tetracycline-ferrite nanocomposites formed via high-energy ball milling and the influence of milling conditions

High-energy ball milling was used to mediate the formation of nanocomposites containing tetracycline and magnetic nanoparticles. Tetracycline-HCl was ball milled for 1, 3, 5, 15, and 30 h under argon or air atmosphere with preformed Mg 0.5 Zn 0.5 Fe2O4 nanoferrites prepared by glycolthermal method. The structural, thermal, and magnetic properties of these novel materials and the effect of milling atmosphere on composition, crystallinity and cation distribution were then characterized by ICP-OES, DSC/TGA, XRPD, ATR-IR, UV-Vis and Mössbauer spectroscopy. Tetracycline underwent rapid and consecutive metal coordination events in the milling process to yield complexes characterized by bathochromic shifts in its electronic spectra and suppression of electronic absorbance at 365 nm. Changes in stretching vibrations due to the A-ring carbonyl (1616 cm(-1)), amide II nitrogen (1602 cm(-1)), and CO bond (1039 cm(-1)) indicate Mg-type interactions imposed on the metals. Exothermic oxidation of the drug at 235°C disappeared after 5h milling with the nanoferrites, and the composites formed remained thermostable up to 500°C. Tetracycline-nanoferrites (Tet-NF) are magnetic-ordered materials with a well-defined spinel-type structure. Analysis of the Mössbauer data suggests that the milling time and atmosphere have significant influence on cation distributions in Tet-NF composites.

Effect of chitosan coating on the structural and magnetic properties of MnFe2O4 and Mn0.5Co0.5Fe2O4 nanoparticles

We report the influence of polymer coatings on structural and magnetic properties of MnFe2O4 and Mn0.5Co0.5Fe2O4 nanoferrites synthesized by glycol thermal technique and then coated with chitosan viz. CHI-MnFe2O4 and CHI-Mn0.5Co0.5Fe2O4. The compounds were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), high-resolution scanning electron microscopy (HRSEM), Mossbauer spectroscopy and magnetization measurements. The powder XRD patterns of naked nanoferrites confirmed single-phase spinel cubic structure with an average crystallite size of 13 nm, while the coated samples exhibited an average particle size of 15 nm. We observed a reduction in lattice parameters with coating. HRTEM results correlated well with XRD results. 57Fe Mossbauer spectra showed ordered magnetic spin states in both nanoferrites. This study shows that coatings have significant effects on the structural and magnetic properties of Mn-nanoferrites. Magnetization studies performed at room temperature in fields up to 14 kOe revealed the superparamagnetic nature of both naked and coated nanoparticles with spontaneous magnetizations at room temperature of 49.2 emu/g for MnFe2O4, 23.6 emu/g for coated CHI–MnFe2O4 nanoparticles, 63.2 emu/g for Mn0.5Co0.5Fe2O4 and 33.2 emu/g for coated CHI–Mn0.5Co0.5Fe2O4 nanoparticles. We observed reduction in coercive fields due to coating. Overall, chitosan-coated manganese and manganese-cobalt nanoferrites present as suitable candidates for biomedical applications owing to physicochemical, and magnetic properties exhibited.We report the influence of polymer coatings on structural and magnetic properties of MnFe2O4 and Mn0.5Co0.5Fe2O4 nanoferrites synthesized by glycol thermal technique and then coated with chitosan viz. CHI-MnFe2O4 and CHI-Mn0.5Co0.5Fe2O4. The compounds were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), high-resolution scanning electron microscopy (HRSEM), Mossbauer spectroscopy and magnetization measurements. The powder XRD patterns of naked nanoferrites confirmed single-phase spinel cubic structure with an average crystallite size of 13 nm, while the coated samples exhibited an average particle size of 15 nm. We observed a reduction in lattice parameters with coating. HRTEM results correlated well with XRD results. 57Fe Mossbauer spectra showed ordered magnetic spin states in both nanoferrites. This study shows that coatings have significant effects on the structural and magnetic properties of Mn-nanoferrites. Magnetization studies performed at room te...

Structural, magnetic and magnetocaloric effect studies of Ni42.5(Fe, Co, Ni, Cu)0.5Mn46Sn11 Heusler alloys

We investigated the structural and magnetic properties of Ni42.5(Fe, Co, Ni, Cu)0.5Mn46Sn11 alloys fabricated by arc melting. Substitution of Ni by Fe, Co and Cu causes lattice expansions consistent with increasing atomic sizes. The zero-field cooled and field cooled results show second-order magnetic transition at the high-temperature austenite phase to a first-order magnetic transition in the low-temperature martensite phase. The substitution of Ni by Fe and Co increases the austenite Curie temperature TCA from 282 K to 289 K and 294 K respectively while Cu reduces it to 278 K. The martensitic transition temperature TM increased from 221 K to 241 K for Fe substitution and decreased to 210 K and 209 K for Co and Cu respectively. The coercive field HC increased significantly from 457 Oe for Ni at 100 K to 729 Oe for Co at 80 K. The increase to 763 Oe for Fe and 769 Oe for Cu occurred at the same temperature of 40 K. We attribute such increases to domain wall pinning effects due to the inclusions of Fe, Co and Cu. The HC exhibited an anomalous temperature dependence in all the samples. The exchange bias field HEX also showed a significant enhancement below 40 K from 196 Oe for Ni to 476 Oe, 430 Oe and 434 Oe for Fe, Co, and Cu substitutions respectively. The fits to the temperature dependence of the HC reveal significant changes in the competition between ferromagnetic and antiferromagnetic interactions. The peak magnetic entropy change ΔSMpk has a linear dependence on the magnetic field H2/3. The highest value of 28.8 J kg-1 K−1 for ΔSM is obtained in the first order magnetic transition compared to 3.0 J kg-1 K−1 in the second order transition. We report an effective cooling power of 155 J kg-1 in the second order magnetic transition.We investigated the structural and magnetic properties of Ni42.5(Fe, Co, Ni, Cu)0.5Mn46Sn11 alloys fabricated by arc melting. Substitution of Ni by Fe, Co and Cu causes lattice expansions consistent with increasing atomic sizes. The zero-field cooled and field cooled results show second-order magnetic transition at the high-temperature austenite phase to a first-order magnetic transition in the low-temperature martensite phase. The substitution of Ni by Fe and Co increases the austenite Curie temperature TCA from 282 K to 289 K and 294 K respectively while Cu reduces it to 278 K. The martensitic transition temperature TM increased from 221 K to 241 K for Fe substitution and decreased to 210 K and 209 K for Co and Cu respectively. The coercive field HC increased significantly from 457 Oe for Ni at 100 K to 729 Oe for Co at 80 K. The increase to 763 Oe for Fe and 769 Oe for Cu occurred at the same temperature of 40 K. We attribute such increases to domain wall pinning effects due to the inclusions of Fe, Co...