The Structure of Complexones and Their Complex-Forming Power

Abstract

The availability at the Paul Scherrer Institute (PSI) of a spot-scanning technique with an isocentric beam delivery system (gantry) allows the realization of intensity-modulated proton therapy (IMPT). The development of 3D dosimetry is an important tool for the verification of IMPT therapy plans based on inhomogeneous 3D conformal dose distributions. For that purpose new dosimeters are being developed. The concept is to use a system of many millimetre sized scintillating volumes distributed in a polyethylene block, which are read on a CCD camera over a bundle of optical fibres and which can be irradiated from any direction orthogonal to the fibre axis. The purpose of this work is to investigate the composition of such small sensitive volumes. A mixture of inorganic phosphors and optical cement allows an optimal coupling between the scintillating volume and the optical fibre. Five different inorganic phosphors, available as powder, have been examined by considering their response along the Bragg curve. In particular, two phosphors have shown interesting behaviours: Gd 2 O 2 S:Tb and (Zn, Cd)S:Ag. Both phosphors have a high emission efficiency but contrasting behaviour in the Bragg peak region. The efficiency of Gd 2 O 2 S:Tb decreases with increasing stopping power (quenching of luminescence) while that of (Zn, Cd)S:Ag increases. Because of these contrasting behaviours it is possible to prepare a mixture of the two scintillating powders in a certain ratio in order to modulate the height of the measured Bragg peak relative to the entrance value so that it is in agreement with the ionization chamber measurements. We propose to use a mixture for the sensitive volume consisting of the following weight fractions: 48% Gd 2 O 2 S:Tb, 12% (Zn, Cd)S:Ag and 40% optical cement.

Organophosphorus Complexones

“…Bisdihydroxyphosphinylmethylethylenediaminediacetic acid (BPMEDDA) forms with copper (Π) and the rare-earth elements more stable complexes than does ethylenediaminetetra-acetic acid (EDTA) 124 , 12β , while ethylenediaminetetrakismethylphosphonic acid (EDTMP) 48 » 126 and cyclohex-1,2-ylenediaminetetrakismethylphosphonic acid (CHDATMP) 49 f exhibit weaker complexing powers than do their carboxylic analogues-EDTA and CHDATA. 1 The stability constants of the metal complexes of CHDATMP seem too low, since they have probably been calculated without regard to the hydrogen complexes [see subsection 3, below]. somewhat diminishes the stability of the complexes formed with alkaline-earth and transition metals, only those with the rare-earth elements constituting an exception 126 .…”

“…It has been found 187 that derivatives of 1-amino-l-methylethylphosphonic acid, applied parenterally as the sodium salts, are tolerated in large doses by animals (mice, rats, guinea-pigs, and rabbits). Thus LD m i n of sodium ethylenediaminebisisopropylphosphonate (the corresponding medicinal preparation is "phosphicin") is 6 g kg" 1 for rats and mice. The absence of hypocalcaemia among the animals' symptoms, as a consequence of the low stability constant of the calcium complex, has enabled the sodium salts of these acids to be used even in large doses.…”

A Potentiometric Study of Metal Chelates With Tetraethylenepentaaminehepta-Acetic Acid

“…These early studies included TPHA complexes with alkaline earth divalent metals as well as some transition metals.2'6-8 Further investigations included rare-earth In general, the stability of 1 : 1 metal complexes were highest for DTPA with a small decline for both TTHA and TPHA, respectively. 6 The latest publication of TPHA involved a comparison of various Ga(II1) complexes with ten ligands ranging from acetates to phenolates.' ' Letkeman and Sawyer carried out an NMR study of TPHA" and saw evidence that the last deprotonation step was well above pH = 10, contrary to the Dyatlova results.…”

Metal – Aminopolycarboxylic Acid Complexes. III. Studies of Lead(II) – Tetraethylenepentaamineheptaacetic Acid in Aqueous Solution by Proton Nuclear Magnetic Resonance Spectroscopy

“…The new ligand was first used in the removal of internally deposited radionuclides from rats (6,7). This study as well as a 1965 review paper (8) conclude the complexing ability of TPHA is slightly weaker than that of TTHA, which in turn was less than diethylenetriaminepentaacetic acid (DTPA). Such a trend has been attributed to the increased steric hindrance and inability to use all of the carboxyl groups when forming metal complexes (8).…”

“…The complexes of Mg(II), Ca(II), Sr(II), and Ba(I1) have a metal-ligand ratio of 2:1, while those for Co(II), Ni(II), Cu(II), Zn(II), and Pb(I1) have ratios of 3 :2 (8).…”