Determination of the pKa of glucuronic acid and the carboxy groups of heparin by 13C-nuclear-magnetic-resonance spectroscopy

Abstract

As part of our continuing studies on heparin, the present paper uses 13C-n.m.r. spectroscopy to examine the acidity of heparin's uronic acid carboxylate groups. Heparin contains three different uronic acids. In porcine mucosal heparin these account for approx. 91, 7 and 2 mol% of the total uronic acid residues. These are alpha-L-idopyranosyluronic acid 2-sulphate, beta-D-glucopyranosyluronic acid and alpha-L-idopyranosyluronic acid. The pKa values of their carboxylate groups were determined as 3.13 (using heparin), 2.79 (using heparin) and 3.0 (predicted by using model compounds) respectively. 18C-n.m.r. spectroscopy, performed at various pH values, provided a convenient method of simultaneously determining the pKa of multiple carboxylate groups, of similar acidity, within heparin D-Glucopyranosyluronic acid and heparin-derived di-, tetra- and hexa-saccharides were used as model compounds to determine pKa values of the different carboxy groups. The results suggested that molecular size had an effect on pKa. Unambiguous assignment of carboxy carbon resonances were accomplished through the use of two-dimensional n.m.r. spectroscopy. Finally, application of this method to the simplest model compound, D-glucopyranosyluronic acid, permitted the determination of the pKa of both its alpha- and beta-anomers.

Quality control of chondroitin sulphate used in dietary supplements

“…Time (s) COND UV ______ the molecular size affects pK (Wang et al 1991). For example, the pK of unsaturated disaccharide was 3.35 while for unsaturated hexasaccharide it was 2.24.…”

“…Disaccharide unit of CS contains one carboxylic group (pK a ~ 3.3) (Tommeraas & Wahlund 2009;Wang et al 1991) and one (or more) O-sulphate group (pK a ~ -1). CS is a strong poly-acid negatively charged even at low pH (< 3).…”

Molecular structure of basic oligomeric building units of heparan-sulfate glycosaminoglycans

“…5). As it is apparent from experimental and calculated pK a values of sulfate and carboxyl acidic groups of essential structural units of heparin, both the sulfate and carboxyl groups are at physiological pH = 7.3 fully ionized [16,53]. Sodium salts of heparin and its derivatives, as salts of weak acids, are almost completely ionized in solution.…”

Influence of Natural Polysaccharides on the Redox Processes of CuTsPc Thin Films and Dopamine Sensing

“…After purification, 0.25 mL of ethanol was added to 5.0 g of gum, which was immediately dissolved in 100 mL of Milli-Q water under stirring for 24 h, followed by filtration. The final aqueous solution had a concentration of 50 mg/mL and pH 6.5, as the pKa of glucuronic acid is 2.93 [33], the pH was adjusted with 0.1 M HCl. All the reagents were purchased from VETEC (Brazil) and were of analytical grade.…”

“…The Dopamine Sensing LbL films deposited in the sequences (1) and (2) on ITO with an active area of 0.4 cm 2 (geometric area) were employed as working electrodes. Experiments were carried out using a solution of H 2 SO 4 (0.05 mol/L) at 22 °C (Under the conditions used for pH, temperature and time, this electrolyte is not able to force an acid hydrolysis of polysaccharides into soluble sugars, this gums are stable in these conditions [33]). Also the experiments were carried under an oxygen atmosphere, there is not effect of the oxygen on voltammetric response of the modified electrode (Eº (oxigen) = 1.229 V) [34].…”