Dihydroxamates

Figure 11. Isokinetic relationship for the Lossen rearrangement of dihydroxamic acids (208), in the log kj versus log k, plot, real (full line) and apparent (broken line) relations.

A number of crown and related ligand systems have been synthesized with pendent arms that contain donors other than nitrogen. Potentiometric titration studies of dihydroxamate derivatives... 

Synthetic linear dihydroxamic acids may be considered as models of rhodotorulic acid (3) to investigate steric effects on the formation of mono- or di-iron(III) species (127,128). pH-dependent electrospray ionization-mass spectrometry (ESI-MS) methods show that ferric complexes with dihydroxamates with short linker chains (37 and 38 in Fig. 15) will prefer the dimeric... 

In addition to structure, the dihydroxamate connecting chain length will affect the affinity of linear siderophores and side-rophore mimics for iron(III) (Table IIIA). If the chain connecting the hydroxamates is long, there will be a significant entropic... 

Fig. 15. Linear dihydroxamic acid siderophore mimics with alkyl connecting chains.

The kinetics of iron(III) dissociation from a series of dihydrox-amate siderophores and siderophore mimics, including rhodo-torulic acid (3) and alcalagin, have been investigated (52,127,128, 177,178). ESI-MS studies show that these systems form multiple species as a function of pH and siderophore/iron ratio (128). The lability of these systems and the resultant multiple species leads to several parallel paths to iron(III) dissociation (177). Both the distribution of structures and kinetics of dissociation were shown to be dependent on the length of the spacer chain between the dihydroxamate donor groups (52,127). 

A combination first coordination shell-second coordination shell based recognition BLM transport system was devised, including active transport (200). This is based on a labile dihydroxamic acid system, including alcaligin, and a free lysine hydroxamic acid ligand capable of ternary complex formation to... 

Atkin CL, Neilands JB (1968) Rhodotorulic Acid, a Diketopiperazine Dihydroxamic Acid with Growth-Factor Activity. I. Isolation and Characterization. Biochemistry 7 3734... 

Hou Z, Sunderland CJ, Nishio T, Raymond KN (1996) Preorganization of Ferric Alcaligin, Ee2L3. The Eirst Structure of aEerric Dihydroxamate Siderophore. J Am Chem Soc 118 5148... 

Ledyard KM, Butler A (1997) Structure of Putrebactin, a New Dihydroxamate Siderophore Produced by Shewanella putrefaciens. J Biol Inorg Chem 2 93... 

Nishio T, Tanaka N, Hiratake J, Katsube Y, Ishida Y, Oda J (1988) Isolation and Structure of the Novel Dihydroxamate Siderophore Alcaligin. J Am Chem Soc 110 8733... 

Okujo N, Sakakibara Y, Yoshida T, Yamamoto S. (1994) Structure of Acinetoferrin, a New Citrate-based Dihydroxamate Siderophore from Acinetobacter haemolyticus. BioMetals 7 170... 

The first example of a helical complex with pre-determined chirality was the dinuclear complex [Fe2(rdt)3], where rdtFl2 is the fungal iron chelator rhodotorulic acid, (15), a dihydroxamate siderophore. Several more helical and chiral Fe " " and Fe complexes are documented in the diimine and in the hydroxamate and catechol sections. A doubly looped ( bow tie ) complex has been constructed with the aid of a tris-terimine ligand (Section 5.4.3.5.7). 

A multiple-path mechanism has been elaborated for dissociation of the mono- and binuclear tris(hydroxamato)-iron(III) complexes with dihydroxamate ligands in aqueous solution. " Iron removal by edta from mono-, bi-, and trinuclear complexes with model desferrioxamine-related siderophores containing one, two, or three tris-hydroxamate units generally follows first-order kinetics though biphasic kinetics were reported for iron removal from one of the binuclear complexes. The kinetic results were interpreted in terms of discrete intrastrand ferrioxamine-type structures for the di-iron and tri-iron complexes of (288). " Reactivities for dissociation, by dissociative activation mechanisms, of a selection of bidentate and hexadentate hydroxamates have been compared with those of oxinates and salicylates. ... 

Chromium(III) complexes of a number of polyhydroxamic acids, microbial iron sequestering and transport agents (siderochromes) have been reported.797,798 The kinetic inertness of the chromium(III) complexes allows the facile separation of isomers for the model complex tris(iV-methyl-( - )-methoxyacetylhydroxamato)chromium(III), D-cis, L-cis and the l/d-trans isomers have been separated.798 The chromium complexes of desferrioxamine B (191) have been investigated the possible isomers are illustrated below (192-196). The cis isomer was isolated in relatively pure form.799 Thiohydroxamate800 and dihydroxamate (rhodotorulic acid) complexes have also been studied.801... 

The dihydroxamic acid polymer containing carboxylic acid groups as well as hydroxamic acid groups was used to examine the adsorptivity for uranium in seawater the adsorptivity was 40 pg/g resin in 8 days116). 

Among natural products the two well established members of the dihydroxamic acid class are the mycobactins and mycelianamide. The myco-bactins contain a third pair of atoms capable of coordinating iron and the resulting complex is thought to have biological significance (125). Mycelianamide is a cyclic anhydride of Na-hydroxyamino acids and, as... 

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