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Journal of the Chilean Chemical Society

versão On-line ISSN 0717-9707

J. Chil. Chem. Soc. v.49 n.2 Concepción jun. 2004

http://dx.doi.org/10.4067/S0717-97072004000200008 

 

J. Chil. Chem. Soc., 49, N 2 (2004), pags.:147-148

Isolation and characterization of cobalt(III)tris-D-glucosamine

José Parada Aliste*, Guillermo Larrazábal Rojas.

 

Departamento de Química Inorgánica y Analítica, Facultad de Ciencias Químicas y Farmacéutica, Universidad de Chile

Dirección para correspondencia


ABSTRACT

Mixed bis-phenanthroline Co(III) complexes with amino sugars disproportionate over a period of months, giving non-ionic tris-(aminosugar)complexes. The complex with a-D-glucosamine has the L-configuration with facial isomerism on the base of molecular composition and absorption and circular dichroism spectra.


Mixed Co(III) complexes of bis-phenanthroline (phen) and an aminosugar (a-D-glucosamine; a-D-galactosamine or b-D-mannosamine) [1] disproportionate over a period of months into Co(III)(phen)3, Co(II)(H2O)6 and Co(III)(aminosugar)3 [2]. The isolation, characterization and stereochemistry of the D-glucosamine complex, Co(III)(D-glucosamine)3, is described.

The D mixed complex with a-D-glucosamine was left, as an aqueous solution, for 2 months at room temperature, and the tris-D-glucosamine complex was isolated chromatographically on SP-Sephadex C25 by elution with NaCl in a gradient of concentrations, ranging from 0.02 to 0.1 M, and monitoring the optical activity of the fractions. The optically active fractions were concentrated to dryness and extracted with MeOH to remove NaCl. Both the tris-phenanthroline and hexa-aquo complexes are racemic in the conditions of the experiment [3].

Microanalysis for [Co(a-D-glucosamine)3]5H2O gave: Co 8.51 (8.64); C 31.0 % (31.63); N 5.98 % (6.15); H 6.52 % (6.73). Calculated values are inside parenthesis.

The absorption and circular dichroism spectra (Figure and Table) are characteristic of the L-configuration at Co(III) [4] and the structure is shown in the following Scheme for the neutral complex:.

 
Scheme

Generally the absorption and CD bands at ca. 550 nm, due a the 1A1g ®1T1g transition are characteristic of low symmetry octahedral complexes with three bonded nitrogens and three oxygens [5]. In this case there are two CD signals of opposite signs. They can be related with the 1A1 y and 1Ea states of Co(III) under C3 microsymmetry, with facial isomery [5]. The absorption spectrum has a shoulder at ca. 400 nm, corresponding to a 1A1g ®1T2g transition with a positive DC signal, as expected for this type of isomerism (Figure and Table) [4, 5].


 
Fig.: Absorption and circular dichroism spectra in the visible region of the complex L-[Co(D-glucosamine)3]


Table: Values of absorption and circular dichroism for complexes L- [Co(D-glucosamine)3]

  l, nm log e l, nm b De (M-1cm-1)

D-glucosamine 420h 2.47 435 +1.4
  568 2.13 529 -2.0
      622 +1.6

Mixed Co(III) complexes of bis-phenanthroline and aminosugars involve cis-NH2-O- ligands, ie., in the present complexes: equatorial NH2 and axial, a-O- [1,2], as in Scheme.

On the basis of preliminary results, the configuration of the tris-a-D-galactosamine complex is similar to that of the complex with D-glucosamine. Characterization of this last compound will be covered in more detail elsewhere.

 

References

1 A. Blasko, C.A. Bunton, S. Bunel, E. Moraga, C. Ibarra, J. Parada, Bol. Soc. Chil.Quím. 40 (1995) 449.         [ Links ] S. Bunel, C. Ibarra, E. Moraga, J. Parada, A. Blasko, C.A. Bunton, Bol. Soc. Chil. Quím. 42 (1997)109.         [ Links ] S. Bunel, C. Ibarra, E. Moraga, J. Parada, A. Blasko, C. Whiddon, C.A. Bunton, Carbohydr. Res. 312 (1998) 191.         [ Links ]2 J. Parada, Doctoral Thesis in Chemistry, University of Chile, 2003.         [ Links ]

3 C.J. Hawkins, "Absolute Configurations of Metal Complexes", Wiley Interscience, New York (1971).         [ Links ] K. Nakanishi, N. Berova, R.W. Woody, "Circular Dichroism, Principles and Applications", V. C. H. Publishers, New York, (1994).         [ Links ]

4 P.A. Williams, Inorg. Chim. Acta 58 (1982)101.         [ Links ] T.J. Goodwin, P. Williams, R.S. Vagg, Inorg. Chim. Acta 63 (1982) 133.         [ Links ] J.A. Chambers, R.D. Gillard, P.A. Williams, R.S. Vagg, Inorg. Chim. Acta 70 (1983) 167.         [ Links ]

5 V.S. Sastri, C.H. Langford, Can. J. Chem. 47 (1969) 4237.         [ Links ] J. Ferguson, C.J. Hawkins, N.A.P. KaneMaguire, H. Lip, Inorg. Chem. 8 (1969) 771.         [ Links ]

 

Correspondencia a: Casilla 233, Santiago, Chile, e-mail: jparada@ciq.uchile.cl.

 

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