ScienceAsia 29 (2003): 045-049 |doi: 10.2306/scienceasia1513-1874.2003.29.045

Determination of Acidity and Basicity Constants of Polyaspartic Acids by Potentiometric Titrations

Vithaya Ruangpornvisuti^* and Boosayarat Tomapatanaget

ABSTRACT: The acidity and basicity constants of asp-asp-asp, asp-asp-asp-asp, asp-asp-asp-asp-asp and asp-asp-asp-asp-asp-asp polypeptides were determined in 0.1 M potassium nitrate at 25 ^oC by potentiometric titrations. Logarithm of the basicity constants of the asp-asp-asp, asp-asp-asp-asp, asp-asp-asp-asp-asp and asp-asp-asp-asp-asp-asp are 8.34, 8.50, 8.56 and 8.99 respectively. The number of the acidity constants of the polyaspartic acids is equivalent to the number of carboxylic acids in their molecules. The pH at the isoelectric points of the asp-asp-asp, asp-asp-asp-asp, asp-asp-asp-asp-asp and asp-asp-asp-asp-asp-asp in aqueous solution, evaluated from their corresponding acidity constants and the titration data are 3.1, 2.8, 2.7 and 2.4, respectively.

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Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand.

* Corresponding author, Email: vithaya.r@chula.ac.th

Received 6 Dec 2001, Accepted 1 Jut 2002