Using basic parameters to evaluate adsorption potential of alternative materials: example of amoxicillin adsorption by activated carbon produced from termite bio-waste.

The minimum set of parameters that can be used to assess the adsorption capacity of activated carbon (AC) produced from termite bio-waste was determined. Three types of AC were prepared: AC600 at 600 °C, MAC600 at the same temperature and impregnated with FeCl3, and AC800 at 800 °C. The influence of the solution pH on the adsorption, adsorption kinetics, isotherms and thermodynamic parameters was considered to characterize the amoxicillin (AMX) adsorption process. The AC materials had surface areas (m2 g-1) of approximately 248.8 for AC600, 501.6 for AC800 and 269.5 for MAC600, with point of zero charge (pHPZC) values of 8.3, 7.5 and 1.7, respectively. A time period of 30 min was chosen for the adsorption kinetics, which was best represented by the pseudo-first-order model for AC600, the intraparticle diffusion model for AC800 and the pseudo-second-order model for MAC600. Regarding the isotherms, a maximum adsorption of 23.4 mg g-1 was found for AC800. In general, the thermodynamic parameters demonstrated a non-spontaneous process. It seems that the medium conditions, the adsorbate and adsorbent characteristics, and the Gibbs free energy are the most important parameters to be considered in a preliminary assessment of the adsorption efficiency of specific adsorbent/adsorbate pairs.

Spray-dried O-carboxymethyl chitosan as potential hydrophilic matrix tablet for sustained release of drug.

OBJECTIVE: The aim of the present investigation was to evaluate the use of spray-dried O-carboxymethyl chitosan (OCMCS) as potential hydrophilic matrix excipient for sustained release of drug. METHODS: The polymer was synthesized from chitosan, then spray-dried and characterized. Tablets with different OCMCS concentrations (80, 50, 30, 5 and 2% w/w), containing diltiazem (DTZ) as model drug, were prepared for direct compression (DC) and after the wet granulation method (WG). RESULTS: The spray-dried OCMCS powder was spherical, with a smooth surface and an average size of 2.2 µm. The tablets prepared for WG disintegrated in time less than 30 min. The tablets obtained for DC presented high retention of the drug, with zero order or Higuchi release kinetic. There was a direct relationship between the OCMCS concentration and the release ratio, swelling degree and water uptake behavior. DC tablets containing 80% OCMCS presented behavior as an effective swelling-control system. The DC tablets with 5% OCMCS showed a similar release profile at formulations with 30% HPMC. CONCLUSION: Spray-dried OCMCS showed great potential as hydrophilic matrices for drug-sustained release.

Chitosan iron(III) reduces phosphorus levels in alloxan diabetes-induced rats with signs of renal failure development.

This study evaluates the effect of complex cross-linked chitosan iron-(III) (CH-FeCL) polymer as phosphate binder in renal failure induced by alloxan (150 mg/kg, i.p.) in rats. The animals (male and female) were divided into four groups and received the treatment once a day for 15 days: (i) control group, which received a single injection of saline (3 ml/kg, i.p.) and normal diet; (ii) alloxan group, which received only a dose of alloxan and normal diet; (iii) phosphate (PO4) group, which received diet supplemented with phosphate 1.2%; and (iv) CH-FeCL group, which received diet supplemented with phosphate 1.2% + CH-FeCL 0.5% (0.054% Fe elemental). It was observed that the CH-FeCL treatment did not alter body-weight, relative weight of the organs and haematological parameters in the treated and control groups for both sexes. However, a decrease in serum phosphorus level of the CH-FeCL group was observed after 15 days, compared with the phosphate group in both sexes. The serum iron concentration of the CH-FeCL group did not differ from the control group in either sex. CH-FeCL polymer decreases intestinal phosphate absorption in rats with renal failure and is promising for the treatment of phosphate retention in patients with renal failure.

Local atomic structure and magnetic ordering of iron in Fe-chitosan complexes.

The iron crosslinked chitosan (Ch-Fe-CL) and N-carboxylmethyl chitosan (N-CM-Ch-Fe) complexes were studied by complementary techniques: structurally sensitive Mössbauer and X-ray absorption methods, as well as static magnetic measurements. A detailed and consistent description of these complexes including, besides the overall magnetic behavior, the spin ordering and local atomic structure around Fe ions is presented. Fe atoms in the investigated samples are mostly penta-coordinated and appear in a high spin Fe (3+) ionic state. In Ch-Fe-CL, two kinds of Fe near neighbors are equally probable and several Fe atoms are situated in the second coordination sphere. The magnetic interactions between these Fe ions lead to a sperimagnetic-like ordering. In N-CM-Ch-Fe, only one Fe neighborhood was found. Other Fe atoms were identified neither in the first nor in the second coordination sphere, but the third coordination sphere indicates the presence of Fe atoms. The magnetic coupling between these atoms is antiferromagnetic, but the dominant part of Fe in this sample remains in a paramagnetic state.