Sequestration of biogenic amines by alginic and fulvic acids.

The interaction of natural (alginic and fulvic acids) and synthetic (polyacrylic acid 2.0 kDa) polyelectrolytes with some protonated polyamines [diamines: ethylendiamine, 1,4-diaminobutane (or putrescine), 1,5-diaminopentane (or cadaverine); triamines: N-(3-aminopropyl)-1,4- diaminobutane (or spermidine), diethylenetriamine; tetramine: N,N′-bis(3-aminopropyl)-1,4-diaminobutane (or spermine); pentamine: tetraethylene-pentamine; hexamine: pentaethylenehexamine] was studied at T=25°C by potentiometry and calorimetry. Measurements were performed without supporting electrolyte, in order to avoid interference, and results were reported at I=0 mol L− 1. For all the systems, the formation of (am)L2Hi species was found (am=amine; L=polyelectrolyte; i=1…4, depending on the amine considered). The stability of polyanion–polyammonium cation complexes is always significant, and for high-charged polycations, we observe a stability comparable to that of strong metal complexes. For example, by considering the formation reaction (am)Hi+2L=(am)L2Hi we found log Ki=6.0, 6.5 and 10.8 for i=1, 2 and 3, respectively, in the system alginate–spermidine. Low and positive formation ΔH° values indicate that the main contribution to the stability is entropic in nature. The sequestering ability of polyelectrolytes toward amines was modelled by a sigmoid Boltzman type equation. Some empirical relationships between stability, charges and ΔG° and TΔS° are reported. Mean values per salt bridge of formation thermodynamic parameters (ΔX°n) are ΔG°n=−5.8±0.4, ΔH°n=0.7±0.5 and TΔS°n=6.5±0.5kJmol− 1 for all the systems studied in this work.