Adsorption Behavior of Microbes on a QCM Chip Modified with an Artificial Siderophore–Fe³⁺ Complex

Three hydroxamate-type artificial siderophores with terminal NH(2) groups, tris[2-{3-(N-acyl-N-hydroxamino)propylamido}propyl]aminomethane (1-3, acyl-R group = Me, Et, and Ph, respectively), and their Fe(3+) complexes, 4-6, were prepared. The stability constant (log β) of 4 was estimated to be about 31 by its EDTA titration. The biological activities of 4-6 for Microbacterium flavescens, which is a hydroxamate-type siderophore, auxotrophic gram-positive microbe, clearly indicated that they permeated the cell membrane depending on their terminal bulky acyl-R groups. These artificial siderophore complexes, 4-6, were modified on Au electrode surfaces with the terminal NH(2) group (4-6/Au). The surface modification of 4-6 was confirmed by several electrochemical measurements. The quartz crystal microbalance (QCM) chips were also modified with 4-6. Microbe adsorption measurements using these modified QCM chips for M. flavescens, Pseudomonas putida, and Eschrichia coli were performed. The QCM chips have the ability to adsorb microbes selectively as a result of the differences in the interactions between the structures of Fe(3+)-artificial siderophore complexes and their receptors or binding proteins within the cell membrane.