Diffusion of (de)acylated antibiotic A40926 in alginate and carrageenan beads with or without cells and/or soybean meal

Effective diffusion coefficients (D-e) of antibiotic A40926 and its deacyla ted derivative were determined in Ca-alginate (2% wt/wt) and kappa -carrage enan (2.6% wt/wt) gel beads with or without immobilized Actinoplanes teicho myceticus cells and/or soybean meal (SBM). The method used was based on tra nsient concentration changes in a well-stirred antibiotic solution in which gel bends, initially free of solute, were suspended. Unsteady-state diffus ion in a sphere was applied and D-e determined from the best fit of experim ental data. A40926 showed markedly different diffusion characteristics than its deacylated derivative. Diffusivity of deacyl-A40926 in alginate or car rageenan gel beads was six to seven times that of A40926. Large differences in partition coefficients (Kp) were also found. In case of beads without a dditions, A40926, in contrast to deacyl-A40926, strongly partitioned to the liquid phase. Introduction of SBM and/or mycelium in the gel beads decreas ed the effective diffusivity of deacyl-A40926, but increased its partitioni ng to the solid phase. Our findings indicate that a relatively moderate str uctural change of a lipoglycopeptide molecule could lead to a major change in its diffusion/partition characteristics. (C) 2001 Elsevier Science Inc. All rights reserved.