EDTA, analogs

Recently new data have become available on the stabilities of metal chelates formed from NTA and EDTA analogs, represented by XVIII, through the publication of equilibrium data on the chelates of two higher members of the series, triethylenetetraminehexaacetic acid (TTHA) and tetraethylenepentamineheptaacetic acid (TPHA) (5, 4)- The stabilities of some representative metal chelates of the series of ligands represented by Formula XVIII are listed in Table VI. 

The EDTA analog, N,N,N ,N -tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), forms stable complexes with lanthanides Ln(TPEN) as shown in the work [111]. The stability constant for Am complex of the similar composition was calculated from potentiometry titration in the work [33]. The [M(TPEN)] complex is the major and the [M(OH)] is the minor components from the... 

Now that we know something about EDTA s chemical properties, we are ready to evaluate its utility as a titrant for the analysis of metal ions. To do so we need to know the shape of a complexometric EDTA titration curve. In Section 9B we saw that an acid-base titration curve shows the change in pH following the addition of titrant. The analogous result for a titration with EDTA shows the change in pM, where M is the metal ion, as a function of the volume of EDTA. In this section we learn how to calculate the titration curve. We then show how to quickly sketch the titration curve using a minimum number of calculations. 

The analogous reaction between anhydrides and alkoxysilanes also produces acyloxysilanes. The direct reaction of acids with chlorosilanes does not cleanly lead to full substitution. Commercial production of methyltriacetoxysilane direcdy from methyltrichlorosilane and acetic acid has been made possible by the addition of small amounts of acetic anhydride or EDTA, or acceptance of dimethyltetraacetoxydisiloxane in the final room temperature vulcanising (RTV) appHcation (41—43). A reaction that leads to the formation of acyloxysilanes is the interaction of acid chlorides with silylamides. 

LCo(H20)6] ion, and bidentate /V-donor ligands such as cn, bipy and phen form octahedral cationic complexes [Co(L-L)3] , which are much more stable to oxidation than is the hexaammine [Co(NH3)6l . Acac yields the orange [Co(acac)2(H20)2] which has the tram octahedral structure and can be dehydrated to [Co(acac)2l which attains octahedral coordination by forming the tetrameric species shown in Fig. 26.3. This is comparable with the trimeric [Ni(acac>2]3 (p. 1157), like which it shows evidence of weak ferromagnetic interactions at very low temperatures. fCo(edta)(H20)] is ostensibly analogous to the 7-coordinate Mn and complexes with the same stoichiometry, but in fact the cobalt is only 6-coordinate, 1 of the oxygen atoms of the cdta being too far away from the cobalt (272 compared to 223 pm for the other edta donor atoms) to be considered as coordinated. 

Effect of Chelate Ring Size on Complex Stability Comparison of Stabilities of Complexes of EDTA (Chelate Ring Size Five Involving the Two Nitrogens) and TMDTA (Analogous Chelate Ring Size Six ) ... 

Na salts of ribonucleotide triphosphates (Roche or Sigma) bovine serum albumin RNase-free, 20 mg/ml (Roche) RNasin ribonuclease inhibitor, 40 U/ml (Promega) both bacteriophage T7 RNA polymerase and RNA Cap structure analog m7G(5/)ppp(5/)G are from BioLabs DNase-RNase-free (Roche) complete EDTA-free proteinase inhibitors cocktail (Roche) pyruvate kinase (PK) (Roche). 

The second-order rate constants for thiocyanate anation vs pH are shown in Fig. 1.13. The full line represents (1.216) with the values shown in scheme (1.217). This profile had been earlier recognized in the ring closure of the three analogous pH-related forms of Co(III)-edta to give Co(edta) in which the edta is completely coordinated.In the Co(lll) case the reactivities of the three forms are much closer. A plot of A [H+] -1-[H+] is a quadratic curve from which / ah2> ah be obtained. 

A number of Co(III) complexes, such as Co(edta) and Co(phen)3, can be resolved into optical isomers and are extremely stable towards racemization. The Co(II) analogs are configurationally labile and resolution has proved impossible. Suggest how with a double mixing apparatus it might be possible to measure half-lives in the 10 -1 s range for the first-order racemization of the Co(Il) complexes. 

These derivatives are soluble in an acetone/water mixture with their p i values similar to that of PIDAA. The phenylene analogs are similar to EDTA except that the two nitrogens are bridged by aromatic rings. These derivatives are soluble in acetone/water. They were characterized by measuring their H- and C-nuclear magnetic resonance (NMR) spectra and Fourier transform infrared (FTTR) spectra. All the PIDAA derivatives showed a peak near 53 ppm for the methylene carbons in carbon NMR spectra. The methylene carbon resonance appears around 44 ppm in the NPG derivative. Thus offers an easier way to characterize these materials. The FTNMR data are listed in Table 1 below. 

Peroxynitrite reacts with the active site of superoxide dismutase (SOD) to form a nitronium-like species (Fig. 37), analogous to the Fe EDTA reactions described earlier. However, copper in the active site of superoxide dismutase was necessary for the formation of the adduct. Removing copper from the active site by reduction with borohydride and dialysis against 50 mM KCN resulted in no adduct being formed, while restoration of copper to the active site gave back full enzyme activity. To account for the essential role of copper in the active site and the subsequent formation of 3-nitrotyrosine located 18-21 A distal from the active site, we proposed that peroxynitrite is attracted by the same electrostatic force field that draws superoxide into the active site (Beckman et al., 1992 Ischiropoulos et al., 1992b). Peroxynitrite appears to bind to copper in the active site to form a transient cuprous adduct as shown. 

Because the drug and the mobilized metals are excreted via the urine, the drug is relatively contraindicated in anuric patients. In such instances, the use of low doses of EDTA in combination with hemodialysis or hemofiltration has been described. Nephrotoxicity from EDTA has been reported, but in most cases can be prevented by maintenance of adequate urine flow, avoidance of excessive doses, and limitation of a treatment course to 5 or fewer consecutive days. EDTA may result in temporary zinc depletion that is of uncertain clinical significance. Analogs of EDTA, the calcium and zinc disodium... 

The cross-redox reaction discussed above and formation of the Vm dimers has also been reported in the case of the edta complexes. Scheme 12 summarizes part of the equilibria proposed to explain potentiometric and spectroscopic data at t = 25 °C and I = 0.20 M in NaC104.336-338 The polarographic behaviour of V111 complexes of edta and analogous ligands has also been studied.339... 

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