RESEARCH ARTICLE

 

Speciation of Co(II), Ni(II) and Cu(II) complexes with L-glutamic acid in Dioxan-Water mixtures

 

 

S. Raju; K. Bharath Kumar Naik; B. Ananda Kumar; G. Nageswara Rao^*

School of Chemistry, Andhra University, Visakhapatnam-530003, India

 

 

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ABSTRACT

Chemical speciation of Co(II), Ni(II) and Cu(II) complexes of L-glutamic acid in the presence of Dioxan-Water mixtures at an ionic strength of 0.16 mol L^-1 at 303 K was studied pH- metrically. Glu is taken as a model compound for amino acid residues and dioxan is used to mimic the low dielectric constant at the active site cavities in bioactive molecules like enzymes and proteins. The active forms of the ligand were LH₃⁺, LH₂, LH^- and L^2-. The models containing different numbers of species were refined using the computer program, MINIQUAD75. The predominant species detected were ML₂H₂,ML₂H^-,ML₂^2-, MLH⁺ and ML. The best fit chemical models were arrived at based on statistical parameters. The trend in variation of complex stability constants with the medium composition was explained on the basis of changes in the dielectric constant of the solution. Effect of errors in the ingredients on the stability constants was also studied. Chemical speciation is discussed based on the distribution diagrams.

Keywords: Complex equilibria, chemical speciation, L-glutamic acid, essential metals, dioxan

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Full text available only in pdf format.

 

Acknowledgements

The authors (SR, KBK and BAK) thank the University Grants Commission, New Delhi, India, for financial support under the Faculty Development Programme.

 

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Received 20 June 2011
Revised 10 August 2011
Accepted 23 August 2011

 

 

* To whom correspondence should be addressed. E-mail: gollapallinr@yahoo.com