Interaction chelating agent-cation

Further evidence of the strength of the chelating agent-cation interaction comes from the H NMR spectra of chelated LiBr systems which have an excess of chelating agent. We have already noted the large up-field shift of the N-CH2- protons of iso-HMTT LiBr in benzene relative to free iso-HMTT (Table II). In several experiments distinct peaks for free and complexed iso-HMTT could be observed. In order to study this system without the interference of the N-CH3 protons, selectively deu-terated iso-HMTT-di8 was used (> 99% N-CD3). Figure 7 shows the... 

We have looked at the chelating agent-cation interaction from the point of view of the chelating agent NMR), the cation (7Li NMR), and the anion (ESR). In each case we have seen clear-cut evidence that a chelated Li+ or Na+ cation is a well defined chemical species. 

We note a very interesting manifestation of the strong chelating agent-cation interaction, i.e. the ESR linewidths observed for Chel Na+C10H8" in the presence of excess Ci0H8. We consider two processes which can broaden the ESR lines, anion-neutral molecule electron transfer... 

We conclude that chelated salts are tight ion pairs in aromatic hydrocarbon solution with an anion-cation interaction which is a sensitive function of the chelating agent-cation interaction. 

Many of the projected and actual uses of macrocyclic compounds depend on their marked ion specificities. Consequently, a knowledge of log K values for the interaction between these compounds and cations becomes of utmost importance in predicting their behavior and determining their uses. Macrocyclic compounds should be ideally suited for applications as complexing agents and ion-chelating resins since ring size, number and... 

Evidence is presented which shows that a chelated cation is a distinct, long-lived chemical species and that different chelated cations may coexist in solution as discrete observable species. Investigation of the anion-cation interaction shows that chelated salts in benzene exist as tight ion pairs down to the limit of spectrometer sensitivity. The effect of chelating agent on ion pair separation is considered. Finally we describe a series of experiments conducted in mixed solvents, the results of which reveal a stereospecific association of aromatic solvent molecules with a chelated lithium salt. 

Absorption of antimicrobial agents such as fluoroquinolones and tetracyclines that can be bound by divalent and trivalent cations potentially could be compromised by administration with EN formulas containing these cations. The fluoroquinolones (e.g., levofloxacin and ciprofloxacin) have been best studied in this regard, and results of studies are not consistent. Mechanisms for an interaction between fluoroquinolones and EN formulas other than chelation by cations have been postulated.40 Some institutions hold tube feedings for 30 to 60 minutes or more before and after enteral dosages of fluoroquinolones. Because ciprofloxacin absorption has been shown to be decreased with jejunal administration, this drug probably should not be given by jejunal tube.41... 

The rational design of chelating agents as antidotes requires a careful consideration of acid-base chemistry. Metal ions are Lewis acids, while the chelating agents or ligands are Lewis bases. The concepts of hardness and softness may be used to describe systematically the interaction between them. A hard metal cation is one that retains its... 

These ligands are frequently used as metal ion traps to bind undesired metal ions, e. g. in formulations of X-ray contrast agents. Chelated cations may associate electrostatically with anionic compounds and with solvent molecules by weak interactions. This results in the formation of an outer coordination sphere. Instead of the term complex the term chelate is very frequently used meaning that the metal ion is covered by the ligand like a claw ( chela word from the Greek for claw). 

The foundation of metal ion and nucleic acid interactions as a chemotherapy originate with the well known work of Rosenberg64 on platinum(II) complexes. Those containing chelating agents could destabilize nucleic acid structures by removing cations which promote the stability of histones. 

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