Potentiometric studies on the complexation of copper(II) by phenolic acids as discrete ligand models of humic substances

• Type: Article in International Scientific Journal
• Date: 2005

Authors

Borges, F (Author) FFUP; Guimaraes, C (Author) Other; Lima, JL (Author) FFUP; Pinto, I (Author) Other; Reis, S (Author) FFUP

Journal

Title: Talanta

Vol. 66 No. 3

Pages: 670-673

ISSN: 0039-9140

Publisher: Elsevier

Indexing

ISI Web of Knowledge - 53 Citations

ISI Web of Science

Scopus - 53 Citations

Scientific classification

FOS: Natural sciences > Chemical sciences

CORDIS: Health sciences ; Physical sciences > Chemistry > Applied chemistry

Other information

Authenticus ID: P-000-3RZ

DOI: 10.1016/j.talanta.2004.12.012

Resumo (PT): Studies on the complexation of copper(II) by phenolic acids, as ligand models of humic substances were done by potentiometry. The acids under study were: 3,4-dihydroxyhydrocinnamic acid or hydrocaffeic acid (1), 3,4-dihydroxyphenylacetic acid (2) and 3,4-dihydroxybenzoic acid or protocatechuic acid (3). Acidity constants of the ligands and the formation constants of metal–ligand complexes were evaluated by computer programs. The carboxylic group of the phenolic acids has different pKa1 values, being the dissociation constants intrinsically related with the distance between the function and the aromatic nucleus. The results obtained allow concluding that acidity constants of the catechol moiety of the compounds are similar with pKa2 and pKa3 values between 9.47–9.41 and 11.55–11.70. The complexation properties of the three ligands towards copper(II) ion are quite similar, being the species found not different either in nature or stability. Although the model ligands have some structural differences no significant differences were found in their complexation properties towards copper(II). So, it can be postulated that complexation process is intrinsically related with the presence of a catechol group. <br> <br> Keywords: Phenolic acids; Dissociation constants; Complexation properties; Copper(II); Humic substances <br> <a target="_blank" href="http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6THP-4F8TKKC-2&_user=2460038&_coverDate=04%2F30%2F2005&_rdoc=22&_fmt=high&_orig=browse&_srch=doc-info(%23toc%235288%232005%23999339996%23596297%23FLA%23display%23Volume)&_cdi=5288&_sort=d&_docanchor=&_ct=40&_acct=C000057398&_version=1&_urlVersion=0&_userid=2460038&md5=0077f4ff21a0664606a4ff660a22578c"> Texto integral </a> <br> <br>

Abstract (EN): Studies on the complexation of copper(II) by phenolic acids, as ligand models of humic substances were done by potentiometry. The acids under study were: 3,4-dihydroxyhydrocinnamic acid or hydrocaffeic acid (1), 3,4-dihydroxyphenyl acetic acid (2) and 3,4-dihydroxybenzoic acid or protocatechuic acid (3). Acidity constants of the ligands and the formation constants of metal-ligand complexes were evaluated by computer programs. The carboxylic group of the phenolic acids has different pK(a1) values, being the dissociation constants intrinsically related with the distance between the function and the aromatic nucleus. The results obtained allow concluding that acidity constants of the catechol moiety of the compounds are similar with pK(a2) and pK(a3) values between 9.47-9.41 and 11.55-11.70. The complexation properties of the three ligands towards copper(II) ion are quite similar, being the species found not different either in nature or stability. Although the model ligands have some structural differences no significant differences were found in their complexation properties towards copper(II). So, it can be postulated that complexation process is intrinsically related with the presence of a catechol group.

Language: English

Type (Professor's evaluation): Scientific