Cadmium Model Complexes

Biomimetic Cd(II) complexes which mimic either structural or functional aspects of their enzymatic counterpart are rare in the literature and mostly based on mimicking mononuclear enzymes like alcohol dehydrogenase and carbonic anhydrase [4, 10-16]. Di- and multinuclear Cd(II) complexes are mostly studied in terms of their NMR-shift, structure and coordination number [3, 4, 17-19]. Of peculiar interest are models that employ the same metals as their enzymatic analog. For GpdQ a comparative study of its Cd(II) derivative and a biomimetic has been reported [2]. The structure of the respective model is depicted in Fig. 5.1 the ligand mimics the N,0 donor atoms of the active site of the enzyme GpdQ (Fig. 5.1, left). 

The two metal ions in MpLs are usually bridged by a hydroxide and have a 4, 5 mixed coordination sphere. The mechanism proposed for dinuclear Zn(ll) MpLs, based on UV-Vis stopped flow measurements, and model complex studies, is shown in Fig. 5.3 [29]. The first step in the catalytic cycle is the binding of the 

A blue anionic intermediate has been observed by UV-Vis spectroscopy when the water levels of the assay were decreased to 20 % [26, 41]. The absorption maximum of the intermediate at 640 nm was similar as found previously in the MPL enzyme from Bacillus fragilis [26, 31, 42]. The blue color was proposed to arise from deprotonation of the amine nitrogen and resulting extended conjugation [26, 31, 42]. The species found in the enzyme catalyzed hydrolysis of nitrocefin 

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Krishnamurti, G. S. R., Megharaj, M., and Naidu, R. 2004. Bioavailability of cadmium-organic complexes to soil alga an exception to the free ion model. J. Agric. Food Chem. 52, 3894-3899. 

Discrepancies between experimentally obtained and theoretically calculated data for cadmium concentration in the strip phase are 10-150 times at feed or strip flow rate variations. These differences between the experimental and simulated data have the following explanation. According to the model, mass transfer of cadmium from the feed through the carrier to the strip solutions is dependent on the diffusion resistances boundary layer resistances on the feed and strip sides, resistances of the free carrier and cadmium-carrier complex through the carrier solution boundary layers, including those in the pores of the membrane, and resistances due to interfacial reactions at the feed- and strip-side interfaces. In the model equations we took into consideration only mass-transfer relations, motivated by internal driving force (forward... 

F. E. Jacobsen, S.M. Cohen, in Using cobalt(II) and cadmium(II) Substituted Model Complexes to Improve zinc(TT)-metalloprotein Inhibitor Design. 229th ACS National Meeting, in San Diego, CA, 2005... 

Vanadium(n) Complexes.—Dehydration of VSO. THjO has been shown to proceed via the formation of VS04,mH20 (where n = 6, 4, or 1) and V(OH)-(SO4), which were characterized by X-ray studies. The polarographic behaviour and the oxidation potential of the V -l,2-cyclohexanediamine-tetra-acetic acid complex, at pH 6—12, have been determined.Formation constants and electronic spectra have been reported for the [Vlphen),] " and [V20(phen)] complexes. The absorption spectrum of V ions doped in cadmium telluride has been presented and interpreted on a crystal-field model. The unpaired spin density in fluorine 2pit-orbitals of [VF ] , arising from covalent transfer and overlap with vanadium orbitals, has been determined by ENDOR spectroscopy and interpreted using a covalent model. " ... 

A structure determination of CdL(H20)5 3H20 (L = guanosine-5 -phosphate) reveals a cadmium ion octahedrally coordinated by live water molecules and the N-7 of the purine ring system (Cd—N = 2.37 A Cd—O = 2.24-2.34 A).568 Similarly, a structure determination of CdL2(H20)4 (L = 8-azahypoxanthinato) reveals octahedral cadmium bonded to N-7 of the purine anions and to four water molecules.569 Theophylline (83) is frequently used as a substitute for guanine (84) in model systems, and the complexes [CdI (RNH2)2(H20)2] (L = 83) have been described.570... 

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