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| Content Provider | Springer Nature Link |
|---|---|
| Author | Vaidyanathan, Mathrubootham Palaniandavar, Mallayan |
| Copyright Year | 2000 |
| Abstract | Galactose oxidase (GOase) is a fungal enzyme which is unusual among metalloenzymes in appearing to catalyse the two electron oxidation of primary alcohols to aldehydes and H$_{2}$O$_{2}$. The crystal structure of the enzyme reveals that the coordination geometry of mononuclear copper(II) ion is square pyramidal, with two histidine imidazoles, a tyrosinate, and either H$_{2}$O (pH 7.0) or acetate (from buffer,pH 4-5) in the equatorial sites and a tyrosinate ligand weakly bound in the axial position. This paper summarizes the results of our studies on the structure, spectral and redox properties of certain novel models for the active site of the inactive form of GOase. The monophenolato Cu(II) complexes of the type [Cu(L1)X][H(L1) = 2-(bis(pyrid-2-ylmethyl)aminomethyl)-4-nitrophenol and X$^{−}$ = Cl$^{−}$ 1, NCS$^{−}$ 2, CH$_{3}$COO$^{−}$ 3, ClO$_{4}$ $^{−}$ 4] reveal a distorted square pyramidal geometry around Cu(II) with an unusual axial coordination of phenolate moiety. The coordination geometry of 3 is reminiscent of the active site of GOase with an axial phenolate and equatorial CH$_{3}$COO$^{−}$ ligands. All the present complexes exhibit several electronic and EPR spectral features which are also similar to the enzyme. Further, to establish the structural and spectroscopic consequences of the coordination of two tyrosinates in GOase enzyme, we studied the monomeric copper(II) complexes containing two phenolates and imidazole/pyridine donors as closer structural models for GOase. N,N-dimethylethylenediamine and N,N’-dimethylethylenediamine have been used as starting materials to obtain a variety of 2,4-disubstituted phenolate ligands. The X-ray crystal structures of the complexes [Cu(L5)(py)], (8) [H$_{2}$(L5) = N,N-dimethyl-N’,N’-bis(2-hydroxy-4-nitrobenzyl) ethylenediamine, py = pyridine] and [Cu(L8)(H$_{2}$O)] (11), [H$_{2}$(L8) = N,N’-dimethyl-N,N’-bis(2-hydroxy-4-nitrobenzyl)ethylenediamine] reveal distorted square pyramidal geometries around Cu(II) with the axial tertiary amine nitrogen and water coordination respectively. Interestingly, for the latter complex there are two different molecules present in the same unit cell containing the methyl groups of the ethylenediamine fragmentcis to each other in one molecule andtrans to each other in the other. The ligand field and EPR spectra of the model complexes reveal square-based geometries even in solution. The electrochemical and chemical means of generating novel radical species of the model complexes, analogous to the active form of the enzyme is presently under investigation. |
| Starting Page | 223 |
| Ending Page | 238 |
| Page Count | 16 |
| File Format | |
| ISSN | 02534134 |
| Journal | Journal of Chemical Sciences |
| Volume Number | 112 |
| Issue Number | 3 |
| e-ISSN | 09737103 |
| Language | English |
| Publisher | Springer India |
| Publisher Date | 2000-01-01 |
| Publisher Institution | Indian Academy of Sciences |
| Publisher Place | New Delhi |
| Access Restriction | One Nation One Subscription (ONOS) |
| Subject Keyword | Cu(II) phenolate complexes X-ray structures electronic spectra electron paramagnetic resonance spectra redox behaviour galactose oxidase Chemistry/Food Science |
| Content Type | Text |
| Resource Type | Article |
| Subject | Chemistry |
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