TY - JOUR
T1 - Opening the Egg Box: NMR spectroscopic analysis of the interactions between s-block cations and kelp monosaccharides
AU - Rowbotham, Jack
AU - Dyer, Philip W.
AU - Greenwell, H. Christopher
N1 - Funding Information:
The staff of the Durham University NMR service, Drs Alan Kenwright and Juan Aguilar, are thanked for their assistance in the running of experiments for this work. Funding: This work was supported by the Centre for Process Innovation (CPI), Durham University, and the Engineering and Physical Sciences Research Council (EPSRC).
Publisher Copyright:
© The Royal Society of Chemistry.
PY - 2021/9/6
Y1 - 2021/9/6
N2 - The best-known theory accounting for metal-alginate complexation is the so-called "Egg Box"model. In order to gain greater insight into the metal-saccharide interactions that underpin this model, the coordination chemistry of the corresponding monomeric units of alginate, l-guluronate (GulA) and d-mannuronate (ManA) have been studied herein. GulA and ManA were exposed to solutions of different s-block cations and then analysed by 1H and 13C NMR spectroscopy. It was found that the α/β ratio of the pyranose anomeric equilibria of GulA showed large pertubations from the starting value (α/β = 0.21 ± 0.01) upon contact with 1.0 M Ca2+, Sr2+, and Ba2+ (α/β = 1.50 ± 0.03, 1.20 ± 0.02, and 0.58 ± 0.02, respectively) at pD 7.9, but remained almost constant in the presence of Na+, K+, and Mg2+ (α/β = 0.24 ± 0.01, 0.19 ± 0.01, and 0.26 ± 0.01, respectively). By comparison, no significant changes were observed in the α/β ratios of ManA and related mono-uronates d-glucuronate (GlcA) and d-galacturonate (GalA) in the presence of all of the metal ions surveyed. Analysis of the 1H and 13C coordination chemical shift patterns indicate that the affinity of α-GulA for larger divalent cations is a consequence of the unique ax-eq-ax arrangement of hydroxyl groups found for this uronate anomer.
AB - The best-known theory accounting for metal-alginate complexation is the so-called "Egg Box"model. In order to gain greater insight into the metal-saccharide interactions that underpin this model, the coordination chemistry of the corresponding monomeric units of alginate, l-guluronate (GulA) and d-mannuronate (ManA) have been studied herein. GulA and ManA were exposed to solutions of different s-block cations and then analysed by 1H and 13C NMR spectroscopy. It was found that the α/β ratio of the pyranose anomeric equilibria of GulA showed large pertubations from the starting value (α/β = 0.21 ± 0.01) upon contact with 1.0 M Ca2+, Sr2+, and Ba2+ (α/β = 1.50 ± 0.03, 1.20 ± 0.02, and 0.58 ± 0.02, respectively) at pD 7.9, but remained almost constant in the presence of Na+, K+, and Mg2+ (α/β = 0.24 ± 0.01, 0.19 ± 0.01, and 0.26 ± 0.01, respectively). By comparison, no significant changes were observed in the α/β ratios of ManA and related mono-uronates d-glucuronate (GlcA) and d-galacturonate (GalA) in the presence of all of the metal ions surveyed. Analysis of the 1H and 13C coordination chemical shift patterns indicate that the affinity of α-GulA for larger divalent cations is a consequence of the unique ax-eq-ax arrangement of hydroxyl groups found for this uronate anomer.
UR - http://dx.doi.org/10.1039/d0dt04375c
U2 - 10.1039/d0dt04375c
DO - 10.1039/d0dt04375c
M3 - Article
SN - 1477-9226
VL - 50
SP - 13246
EP - 13255
JO - Dalton Transactions
JF - Dalton Transactions
IS - 38
ER -