TY - JOUR

T1 - On the Binding Mechanisms of Calcium Ions to Polycarboxylates

T2 - Effects of Molecular Weight, Side Chain, and Backbone Chemistry

AU - Gindele, Maxim B.

AU - Malaszuk, Krzysztof K.

AU - Peter, Christine

AU - Gebauer, Denis

N1 - Funding Information: DG was a Research Fellow of the Zukunftskolleg of the University of Konstanz and partly supported by SFB 1214 (German Research Foundation, DFG) during this work. We thank Tobias Lemke for valuable discussions during the project. We thank Michael Voggel for his help with ITC experiments. We thank Teodora Ilić for help with titration experiments and Eduard Wiedenbeck for help with the evaluation of ITC experiments in ITCsy. We thank Cristina Ruiz-Agudo for ideas regarding polymer purification and Stephan Siroky for help with NMR experiments.

PY - 2022/11/29

Y1 - 2022/11/29

N2 - We experimentally determined the characteristics and Langmuir parameters of the binding of calcium ions to different polycarboxylates. By using potentiometric titrations and isothermal titration calorimetry, the effects of side chain chemistry, pH value, and chain length were systematically investigated using the linear polymers poly(aspartic acid), poly(glutamic acid), and poly(acrylic acid). We demonstrate that for polymers with high polymerization degrees, the binding process is governed by higher-order effects, such as the change of apparent pKaof carboxyl groups, and contributions arising from the whole polymer chain while the chemistry of the monomer unit constituting the polymer plays a subordinate role. In addition, primary binding sites need to be present in the polymer, thus rendering the abundance and sequential arrangement of protonated and deprotonated groups important. The detection of higher-order effects contradicts the assumptions posed by the Langmuir model of noninteracting binding sites and puts a question mark on whether ion binding to polycarboxylates can be described using solely a Langmuir binding model. No single uniform mechanism fits all investigated systems, and the whole polymer chain, including terminal groups, needs to be considered for the interpretation of binding data. Therefore, one needs to be careful when explaining ion binding to polymers solely based on studies on monomers or oligomers.

AB - We experimentally determined the characteristics and Langmuir parameters of the binding of calcium ions to different polycarboxylates. By using potentiometric titrations and isothermal titration calorimetry, the effects of side chain chemistry, pH value, and chain length were systematically investigated using the linear polymers poly(aspartic acid), poly(glutamic acid), and poly(acrylic acid). We demonstrate that for polymers with high polymerization degrees, the binding process is governed by higher-order effects, such as the change of apparent pKaof carboxyl groups, and contributions arising from the whole polymer chain while the chemistry of the monomer unit constituting the polymer plays a subordinate role. In addition, primary binding sites need to be present in the polymer, thus rendering the abundance and sequential arrangement of protonated and deprotonated groups important. The detection of higher-order effects contradicts the assumptions posed by the Langmuir model of noninteracting binding sites and puts a question mark on whether ion binding to polycarboxylates can be described using solely a Langmuir binding model. No single uniform mechanism fits all investigated systems, and the whole polymer chain, including terminal groups, needs to be considered for the interpretation of binding data. Therefore, one needs to be careful when explaining ion binding to polymers solely based on studies on monomers or oligomers.

UR - http://www.scopus.com/inward/record.url?scp=85142001899&partnerID=8YFLogxK

U2 - 10.1021/acs.langmuir.2c01662

DO - 10.1021/acs.langmuir.2c01662

M3 - Article

C2 - 36367750

AN - SCOPUS:85142001899

VL - 38

SP - 14409

EP - 14421

JO - LANGMUIR

JF - LANGMUIR

SN - 0743-7463

IS - 47

ER -