Handbook of Microbial Iron Chelates (1991)

Gunther Winkelmann

• Publisher: CRC Press
• Year: 2017
• Print ISBN: 9781138559707
• eBook ISBN: 9781351362665
• Topic: Biological Sciences
• Subtopic: Biology
• Index: Biological Sciences

Handbook of Microbial Iron Chelates emphasizes the various microbial compounds and synthetic analogues functioning as siderophores in microbes and as potential drugs in human iron metabolism. There are chapters describing the isolation, chemical characterization, synthesis and physicochemical properties of microbial iron chelates. Other chapters deal with the physiology and genetics of transport and receptors involved in iron uptake. Chemists, biologists, biochemists, pharmacologists, and medical doctors interested in the general aspects of iron metabolism, siderophores, receptors, and iron complex formation should consider this book a rich information source.

AQUEOUS SOLUTION EQUILIBRIUM AND KINETIC STUDIES OF IRON SIDEROPHORE AND MODEL SIDEROPHORE COMPLEXES

Crumbliss Alvin L.

INTRODUCTION

The emphasis in this review is on chemical studies which are relevant to siderophore-mediated iron uptake by microorganisms. Since almost all chelators which have been established to function as siderophores contain either the hydroxamate (I) or catecholate (II) Fe³⁺ binding group, we will focus our attention on solution equilibria, ligand exchange kinetics, and oxidation-reduction reactions of Feaq3+

with siderophores and synthetic chelators which contain the hydroxamate and/or catecholate binding group.

The processes involved in microbial iron assimilation are solubilization, transport to the cell, and deposition at an appropriate site within the cell. The important chemical characteristics of the natural iron chelators which are related to these processes are affinity and selectivity for Fe³⁺, and lability at a specific site (e.g., cell wall or interior). This lability occurs either through ligand exchange, which often involves ternary complex intermediates, and/or a reduced oxidation state for iron (i.e., Fe²⁺).

In this review we first treat solution equilibria and the associated Fe³⁺ formation or stability constants for hydroxamate and catecholate siderophores and their synthetic analogues. Then we will consider the kinetics and mechanism of Feaq3+

chelation and dechelation processes and ligand exchange reactions for these complexes. Finally, we will briefly review the relevant literature dealing with Fe³⁺-siderophore oxidation-reduction reactions. The reader is also referred to other recent related reviews which treat the synthesis, solution chemistry, and biochemistry of this interesting class of compounds.^1-8

IRON-SIDEROPHORE COMPLEX STABILITY IN AQUEOUS SOLUTION

Formation constants can serve to define the stability of an Fe-siderophore complex in solution. In addition, these constants are a measure of the siderophore ligand’s selectivity for Feaq3+

in the presence of competing metal ions and its ability to solubilize Fe and prevent precipitation by hydrolysis. The Feaq3+

stability constant may also be the deciding factor in determining the mechanism for iron release from the siderophore, by influencing the Fe dissociation rate constant and Fe(III/II) reduction potential.

METHODS OF EXPRESSING IRON-SIDEROPHORE COMPLEX STABILITY

Since both the hydroxamate and catecholate groups are bidentate ligands, multiple complexation equilibria must be considered for mono- or bis-hydroxamates or catecholates in order to saturate the Fe³⁺ coordination number of six. These equilibrium steps are usually expressed as follows, where Lⁿ⁻ represents a bidentate ligand and coordinated H₂O has been omitted for clarity. The constants K_n and β_n are defined as stepwise and overall formation or stability constants, respectively. It is usually true that K₁ > K₂ > K₃.

Feaq3++Ln−⇌FeL(3−n)+(3)

K1=[FeL(3−n)+][Feaq3+][Ln−]=β1(4)

FeL(3−n)++Ln−⇌FeL2(3−2n)+(5)

K2=...

Table of contents

• Cover
• Title Page
• Copyright Page
• Table of Contents
• Preface
• The Editor
• Contributor
• Detection, Determination, Isolation, Characterization and Regulation of Microbial Iron Chelates
• Structures, Coordination Chemistry and Functions of Microbial Iron Chelates
• Specificity of Iron Transport in Bacteria and Fungi
• Genetics of Bacterial Iron Transport
• Pyoverdins and Pseudobactins
• Molecular Genetics of Siderophore Biosynthesis In Fluorescent Pseudomonads
• Aqueous Solution Equilibrium and Kinetic Studies of iron Siderophore and Model Siderophore Complexes
• Isolation and Spectroscopic Identification of Fungal Siderophores
• Synthesis of Catecholamide and Hydroxamate Siderophores
• BIOMIMETIC SIDEROPHORES
• Therapeutically Useful Iron Chelators
• Index