M Vehabovic | PubMed Health

PubMed2000

Amperometric sensor for L-ascorbic acid determination based on MnO2 bulk modified screen printed electrode.

A simple biosensor constructed by bulk-modification of carbon ink with manganese dioxide as a mediator was investigated for its ability to serve as amperometric detector for L-ascorbic acid in hydrodynamic mode. The sensor could be operated at pH 5.0 (0.05 M phosphate buffer) and exhibited excellent reproducibility and stability. Optimization of measurement parameters such as applied working potential and pH value were studied in detail. The screen printed electrode exhibited a linear amperometric increase with the concentration of L-ascorbic acid from 50 mg L(-1) to 250 mg L(-1) and gave a (LOD = 3sigma) detection limit of 0.2 mg L(-1) (1.172 micromol L(-1)). The manganese dioxide modified screen printed electrode shows long term stability.

Ascorbic Acid↗

PubMed1998

Synthesis and evaluation of lysozyme derivatives exhibiting an enhanced antimicrobial action.

In order to generate novel preservatives exhibiting a broad antimicrobial spectrum against Gram-positive as well as Gram-negative bacteria, lysozyme was modified by the covalent attachment of caffeic acid and cinnamic acid, respectively. Linkage of these organic acids to lysozyme was achieved by the constitution of amide bindings between the carboxyl group of ligands and primary amino groups of the enzyme mediated by a carbodiimide. Compared to nonmodified lysozyme, the lytic activity of all resulting conjugates was reduced. In contrast, bacterial growth of Escherichia coli (ATCC 8739) could be strongly inhibited by lysozyme-caffeic acid conjugates and to a lower degree also by lysozyme-cinnamic acid conjugates. The minimal inhibitory concentration against E. coli was 0.05% for the lysozyme derivative of the highest antimicrobial activity. However, the efficacy of lysozyme derivatives against Staphylococcus aureus (ATCC 6538) was slightly reduced. As the antimicrobial spectrum of lysozyme altogether could be substantially widened, these derivatives represent promising candidates as novel preservatives for various pharmaceutical and cosmetic formulations.

Amino Acids↗