Effects of anabolic and catabolic nutrients on woody plant encroachment after long-term experimental fertilization in a South African savanna.

The causes of the worldwide problem of encroachment of woody plants into grassy vegetation are elusive. The effects of soil nutrients on competition between herbaceous and woody plants in various landscapes are particularly poorly understood. A long-term experiment of 60 plots in a South African savanna, comprising annual applications of ammonium sulphate (146-1166 kg ha-1 yr-1) and superphosphate (233-466 kg ha-1 yr-1) over three decades, and subsequent passive protection over another three decades, during which indigenous trees encroached on different plots to extremely variable degrees, provided an opportunity to investigate relationships between soil properties and woody encroachment.

Low molecular weight quaternised chitosan (11): in vitro assessment of absorption enhancing properties.

N-Trimethyl chitosan chloride (TMC; high molecular weight) and N-trimethyl chitosan oligosaccharide (TMO; low molecular weight) with different degrees of quaternisation were synthesised and evaluated for their absorption enhancing properties across mucosal epithelia. These quaternised chitosan derivatives (0.0625% w/v-0.

Low molecular weight quaternised chitosan (I): synthesis and characterisation.

For a better understanding of the behaviour of macromolecules in vitro and in vivo, their structural and chemical properties that may be influential as experimental variables need to be characterised. N-Trimethyl chitosan chloride and N-triethyl chitosan chloride have been synthesised from chitosan to increase the solubility range of these polymers. However, little is known about the effect of the degree of quaternisation, molecular weight, viscosity and different substitution groups on the polymer's ability to enhance the transport of large hydrophilic compounds, such as peptide and protein drugs, across intestinal and nasal epithelia and on their toxicity profile.

Evaluation of the mucoadhesive properties of N-trimethyl chitosan chloride.

Previous studies have established that N-trimethyl chitosan chloride (TMC) is a potent absorption enhancer for peptides and large hydrophilic compounds across mucosal surfaces, especially in neutral and basic environments where chitosan is ineffective as an absorption enhancer. The degree of quaternization of TMC plays an important role on its absorption-enhancing properties. Several TMC polymers with different degrees of quaternization were synthesized and the molecular mass of the polymers was determined by SEC/MALLS.