EDTA structure

The various producers launching the above-mentioned additives onto the market use trade names that nearly always relate to mixtures of reagents, of which neither the identity nor the concentration is made public because of corporate propriety. A comparative analysis has shown that the various additives contain similar products a minor modification to the structure common to all the stabilisers is the EDTA structure, although the terminal groups on the amine positions can be different11. 

Multidentate ligands can also give rise to optical isomerism in metal complexes. One of the many such cases is that of (+)- and ( )- [Co(EDTA)], structures XXVII and XXVin. 

EDTA (ethylenediarrtinetetraacetic acid), first patented in Germarty in 1935 and in the U.S. in 1946, has long dominated the market for synthetic cheating agents (1). Four carboxylate (RCOO ) and two amine (R2N) Lewis Base groups are fevorably placed within the EDTA structure for occupying up... 

Ethylenediaminetetraacetic acid, or EDTA, is an aminocar-boxylic acid. The structure of EDTA is shown in Eigure 9.25a. 

Structures of (a) EDTA, and (b) a six-coordinate metal-EDTA complex. 

Betyllium, because of its small size, almost invariably has a coordination number of 4. This is important in analytical chemistry since it ensures that edta, which coordinates strongly to Mg, Ca (and Al), does not chelate Be appreciably. BeO has the wurtzite (ZnS, p. 1209) structure whilst the other Be chalcogenides adopt the zinc blende modification. BeF2 has the cristobalite (SiOi, p. 342) structure and has only a vety low electrical conductivity when fused. Be2C and Be2B have extended lattices of the antifluorite type with 4-coordinate Be and 8-coordinate C or B. Be2Si04 has the phenacite structure (p. 347) in which both Be and Si... 

Oxygen chelates such as those of edta and polyphosphates are of importance in analytical chemistry and in removing Ca ions from hard water. There is no unique. sequence of stabilities since these depend sensitively on a variety of factors where geometrical considerations are not important the smaller ions tend to form the stronger complexes but in polydentate macrocycles steric factors can be crucial. Thus dicyclohexyl-18-crown-6 (p. 96) forms much stronger complexes with Sr and Ba than with Ca (or the alkali metals) as shown in Fig. 5.6. Structural data are also available and an example of a solvated 8-coordinate Ca complex [(benzo-l5-crown-5)-Ca(NCS)2-MeOH] is shown in Fig. 5.7. The coordination polyhedron is not regular Ca lies above the mean plane of the 5 ether oxygens... 

Tetrahedral [NHa]", [NH3(0H)]", [NF4]", H3NBF3 and innumerable other coordination complexes of NH3, NR3, en, edta, etc., including Mc3NO and sulfamic acid (H3NSO3). BN (layer structure and Zn blende-type), AIN (wurtzite-type), [PhAlNPh]4 (cubane-type)... 

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. 

Depending upon the structure of the substrates 49, 52, and 56 hexahydropyrido[l,2-n]-[3,l]benzoxazines 50, 54, 2-aminobenzaldehyde 53, 1-substituted piperidones 51, 55, 57, 3,4,5,6-tetrahydropyridinium salt 58, or their mixture was obtained during the oxidation of 1-(2-hydroxymethyl-, 2-formyl- and 2-acetylphenyl)piperazines (49, 52, 56) with Hg(II)-EDTA complex (Schemes 6-8) (79AP219, 98ZN(B)37, 98ZN(B)1369). 

Chemical Name N,N -1,2-Ethanediylbis[N-(carboxymethyl)glycine] -disodium ssit Common Name EDTA disodium Structural Formula NaOOCCH2... 

Structure of the EDTA ion the chelating atoms, six in all, have color screens. 

However, EDTA has the widest general application in analysis because of its powerful complexing action and commercial availability. The spatial structure of its anion, which has six donor atoms, enables it to satisfy the coordination number of six frequently encountered among the metal ions and to form strainless five-membered rings on chelation. The resulting complexes have similar structures but differ from one another in the charge they carry. 

A considerable number of EDTA complexes of ruthenium have been synthesized [130-132] there has been interest in their catalytic potential while several compounds have had their structures determined. Synthetic routes relating to these compounds are shown in Figure 1.50. 

The structure of the aqua complex (Figure 1.51), which is an active intermediate in some catalytic systems, shows the Ru-OH2 distance to be some 0.1 A longer than in the ruthenium(III) hexaqua ion, indicating a possible reason for its lability the water molecule also lies in a fairly exposed position, away from the bulk of the EDTA group. 

Figure 1.51 The structure of [Ru(EDTA-H)(H20)]. (Reproduced with permission from the Indian J. Chem., Sect. A, 1992, 206.)...

The extracellular domain of cadherins consists of a variable number of a repeated sequence of about 110 amino acids. This sequence is termed the cadherin repeat and resembles in overall structure, but not in sequence, the Ig like domains. The cadherin repeat is the characteristic motive common to all members of the cadherin superfamily. Classical and desmosomal cadherins contain five cadherin repeats, but as many as 34 repeats have been found in the FAT cadherin (see below). Cadherins are calcium-dependent cell adhesion molecules, which means that removal of Ca2+, e.g., by chelating agents such as EDTA, leads to loss of cadherin function. The Ca2+-binding pockets are made up of amino acids from two consecutive cadherin repeats, which form a characteristic tertiary structure to coordinate a single Ca2+ion [1]. 

The size of the EDTA ring structure complex (not too big or too small), plus the multiple points of attachment, provides a very stable complex (high stability constant) that overcomes reaction tendencies to reach equilibrium via the lowest possible energy state or maximum state of disorder (entropy). 

Earlandite structure, 6,849 Edge-coalesced icosahedra eleven-coordinate compounds, 1, 99 repulsion energy coefficients, 1,33,34 Edta — see Acetic acid, ethylenediaminetetra-Effective atomic number concept, 1,16 Effective bond length ratios non-bonding electron pairs, 1,37 Effective d-orbital set, 1,222 Egta — see Acetic acid,... 

Numerous positive delayed skin tests in patients with contrast medium-induced non-immediate skin reactions have been reported when the patients were tested with the culprit contrast medium [summarized in 1]. In a large European multicenter study, 37% of patients with non-immediate reactions were positive in delayed IDEs and/or patch tests [13]. The majority of the patients also reacted to the culprit contrast medium and also to other, structurally similar RCM. Notably, in more than 30% of those skin test-positive patients a RCM had been administered for the first time. Thus, there is a lack of a sensitization phase. Again it may be hypothesized that these previously non-exposed patients may have already been sensitized. Different patterns of RCM cross-reactivity indicate that several chemical entities could be involved. No positive skin tests have been obtained with other contrast medium excipients, such as ethylenediaminetetraacetic acid (EDTA), and only rarely patients have been found to react to inorganic iodide. 

A chelating ligand contains two or more donor atoms in a structure that allows the ligand to wrap around the metal. Examples featured in Chapter 18 are the bidentate ligand ethylenediamine (en, chemical formula H2 NCH2 CH2 NH2) and the hexadentate ethylenediaminetetraacetate (EDTA). 

The second example that is used to illustrate the design methodologies is a modification to the EDTA problem as follows. The structure of the flowsheet is exactly the same as the one presented in Section IV. The only change to the problem is the statement that sulfuric acid and formaldehyde should not be allowed to come into contact with each other. 

The formation of colloidal sulfur occurring in the aqueous, either alkaline or acidic, solutions comprises a serious drawback for the deposits quality. Saloniemi et al. [206] attempted to circumvent this problem and to avoid also the use of a lead substrate needed in the case of anodic formation, by devising a cyclic electrochemical technique including alternate cathodic and anodic reactions. Their method was based on fast cycling of the substrate (TO/glass) potential in an alkaline (pH 8.5) solution of sodium sulfide, Pb(II), and EDTA, between two values with a symmetric triangle wave shape. At cathodic potentials, Pb(EDTA)2 reduced to Pb, and at anodic potentials Pb reoxidized and reacted with sulfide instead of EDTA or hydroxide ions. Films electrodeposited in the optimized potential region were stoichiometric and with a random polycrystalline RS structure. The authors noticed that cyclic deposition also occurs from an acidic solution, but the problem of colloidal sulfur formation remains. 

A similar one-step process was employed successfully [66] to prepare well-crystallized CdS thin films of optical quality on Au(lll) from an aqueous solution of CdSOa, EDTA, and Na2S at room temperature. A phase transition from cubic (zinc blende) to hexagonal (wurtzite) CdS structure was observed with decreasing pH below 5, while highly preferential orientation along [11.0] directions for the... 

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