Synthesis and acidity constants of 13CO2H-labelled dicarboxylic acids. pKas from 13C-NMR

Add time:07/30/2019    Source:sciencedirect.com

Simple dicarboxylic acids: adipic (1), succinic (2) and malonic (3); more complex linear tetrapyrroles with two propionic acid groups: mesobiliverdin-XIIIα (4) and mesobilirubin-XIIIα (5), and a rubin analog with a gem-dimethyl at C10 (6) were prepared with 99% 13C-enrichment in their CO2H groups. Their pKa values were determined from titration curves in water and in H2O-(CD3)2SO solutions: plots of carboxyl carbon 13C-NMR chemical shifts with varying pH. Titration curves of diacids 1–3 with known pKa's in H2O served as calibration standards for determination of pKas of tetrapyrrole diacids 4–6: pKa1 = 3.9, pKa2 = 5.3 for 4; pKa1 = 4.2, pKa2 = 4.9 for 5, and pKa1 = 4.7, pKa2 = 5.7 for 6 in H2O.

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