Transition-metal chelators

The ligand pATa values and transition metal chelate stability constants of arylisoxazoles were detected photometrically and the stability of the complexes studied (79JlCi25i). 

Studies in the photoinitiation of polymerization by transition metal chelates probably stem from the original observations of Bamford and Ferrar [33]. These workers have shown that Mn(III) tris-(acety]acetonate) (Mn(a-cac)3) and Mn (III) tris-(l,l,l-trifluoroacetyl acetonate) (Mn(facac)3) can photosensitize the free radical polymerization of MMA and styrene (in bulk and in solution) when irradiated with light of A = 365 at 25°C and also abstract hydrogen atom from hydrocarbon solvents in the absence of monomer. The initiation of polymerization is not dependant on the nature of the monomer and the rate of photodecomposition of Mn(acac)3 exceeds the rate of initiation and the initiation species is the acac radical. The mechanism shown in Scheme (14) is proposed according to the kinetics and spectral observations ... 

Stereoselectivity in the binding of transition metal chelate complexes to nucleic acid constituents bonding and non-bonding effects. L. G. Marzilli and T. J. Kistenmacher, Acc. Chem. Res., 1977, 10,146-152 (29). 

Lewis TA, A Paszczynski, SW Gordon-Wylie, S Jeedigunta, C-H Lee, RL Crawford (2001) Carbon tetrachloride dechlorination by the bacterial transition metal chelator pyridine,2,6-bis(thiocarboxylic acid). Environ Sci Technol 35 552-559. 

Transition-metal Chelators 102 5. Potential Pro-inflammatory Influences ... 

Fig. 2 Depiction of common transition-metal chelates (or transition metal complexes of macrocyclic N4 ligands) reproduced from ref. 9.

The nature of the active site formed during pyrolysis of transition metal chelates has been the focus of much debate in the literature. Researchers from several different groups have reported that the metal center remains intact during the... 

Anthocyanins have the potential to moderate the total oxidative load via three mechanisms. First, they can chelate to copper and iron, thereby decreasing the possibility of hydroxyl radical production from Haber-Weiss reactions. These chelates might also protect other low molecular weight antioxidants (LMWAs), such as ascorbate and a-tocopherol, from autoxidation by transition metals.Anthocyanin-transition metal chelation has been demonstrated in vitro many times,but is unlikely to feature significantly in planta. 

The above-listed examples show that many different immobilization procedures have been applied in fabrication of solid-state devices for ECL based sensing. Due to possible practical application one can expect, however, that this particular aspect of ECL will be object of further intensive studies and obtained results will allow construction of a still-better solid-state ECL detector. Especially promising seems to be the application of transition metal chelates other than mostly used Ru(bipy)32 + that may lead to distinct improvement of this analytical tool. 

A study has been made of the relative efficiencies with which various transition metal chelates quench triplet benzophenone.194 The chelates vary widely in efficiency, and no generalizations can be drawn except that in some cases triplet energy transfer to a coupled metal-ligand triplet energy level probably accounts for at least part of the quenching. Rare earth ions can quench excited triplets by energy transfer, since, as discussed earlier, sensitized fluorescence of the metal ion results. 

An application has been found in which a system that exhibits an upper, or lower, critical consolute point, UCST or LCST, respectively, is utilized. At a temperature above or below this point, the system is one homogeneous liquid phase and below or above it, at suitable compositions, it splits into two immiscible liquids, between which a solute may distribute. Such a system is, for instance, the propylene carbonate - water one at 25°C the aqueous phase contains a mole fraction of 0.036 propylene carbonate and the organic phase a mole fraction of 0.34 of water. The UCST of the system is 73 °C (Murata, Yokoyama and Ikeda 1972), and above this temperature the system coalesces into a single liquid. Temperature cycling can be used in order to affect the distribution of the solutes e.g. alkaline earth metal salts or transition metal chelates with 2-thenoyl trifluoroacetone (Murata, Yokayama and Ikeda 1972). 

Spencer KT, Lindower PD, Buettner GR, Kerber RE, Transition metal chelators reduce directly measured myocardial free radical production during reperfusion, J Cardiovas Pharmacol 1998 32(3) 343-348. 

Keier, N. P., Mamaeva, E. K., Alikina, G. M., Tyuleneva, L. I., Afanaseva, S. M. Catalytic Activity of the Transition Metal Chelate Salts of Quinaldine Dithioamides on Oxidation of Cumene. Kinetika Katal. 6, 849 (1965). 

Potassium hydrotris(l-pyrazolyl)borate is a white crystalline solid. As prepared, m.p. 185-190°C., it is suitable for the synthesis of transition-metal chelates. Its melting point may be raised to 188-189°C. by recrystallization from anisole but this entails large solubility losses. Its infrared spectrum has a sharp BH peak at 2500 cm.-1. This salt is very soluble in water, alcohols, and polar organic solvents. It is stored best as a solid, and its reactions should be carried out on freshly prepared solutions. 

D. A. Owen and M. Frederick Hawthorne Carborane-transition metal chelate complexes... 

Figure 8 Transition metal chelates. (Modified from Reference 3.) (a) Structure of the commercially available ruthenium complex, Ru(bpy)2(phen-5-isothiocyanate)(PFg)2. (b) The resulting absorption and emission profiles of the ruthenium complex.

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