Time-domain NMR relaxometry as an alternative method for analysis of chitosan-paramagnetic ion interactions in solution

Abstract

Chitosan (CHI)-paramagnetic ion interactions in aqueous solution as affected by pH were studied using time-domain NMR (TD-NMR) relaxometry. Longitudinal (T) and transverse (T) relaxation times of CHI solutions with Fe, Cu, and Mn were measured using a single-shot pulse sequence named CP-CWFP. The results indicate that CHI interacted with Fe ions or iron oxide nanoparticles, maintaining the metal ion in solution at pH ranging from 3 to 5. Above this pH, CHI coagulated and removed Fe ions or nanoparticles, resulting in a clear supernatant. CHI probably interacted with Cu ions at pH 6.2 through the deprotonated CHI-NH groups maintaining the relaxation effect in alkaline solution, whereas Mn did not interact with CHI strongly enough to produce a complex of high stability. The proposed method can also be further exploited in the study of interactions paramagnetic ions with others CHI and CHI derivatives as well as of other water-soluble polysaccharides.

Time Domain NMR in Polymer Science: From the Laboratory to the Industry

“…Interaction is apparent for Fe 3+ , Cu 2+ , and Mn 2+ , with the formation of a stable complex with Cu 2+ , as hypothesized analyzing the results of Figure 17a. Analysis of supernatant after centrifugation showed the good capability of CHI in removing metal ions from solution, evidenced by the different behavior between the supernatant of the CHI-solutions and free ions solutions (Figure 17b) [102]. CWFP sequence as function of pH in aqueous solutions.…”

“…Relaxation profiles of T1 (full squares) and T2 (empty circles) against pH for Cu 2+ -CHI solutions (a) and the supernatant after centrifugation of the aqueous solution (b). Solid lines are the sigmoidal fittings for the experimental data of the Cu 2+ -CHI solutions, while dotted lines are the fittings for free Cu 2+ ions in solution (Reprinted with permission from reference[102]. Copyright 2017 Elsevier).…”

Strong and Ultratough Ionogel Enabled by Ingenious Combined Ionic Liquids Induced Microphase Separation

“…IL‐3 exhibited the earliest peak, demonstrating the strongest interaction between IL and polymers. [ 38 ] The DFT calculation was used to verify the above experimental results. The largest solvent accessible area of IL‐1 system indicated that the polymers moved more freely in ILs, while the smallest solvent accessible area of IL‐4 system demonstrated that the polymers were more agglomerated in ILs (Figures S12 and S13, Supporting Information), [ 39 ] which was consistent with the results of time‐domain NMR.…”

Alginate-Based Carriers Loaded with Mulberry (Morus alba L.) Leaf Extract: A Promising Strategy for Prolonging 1-Deoxynojirimicyn (DNJ) Systemic Activity for the Nutraceutical Management of Hyperglycemic Conditions

“…A second pulse is then applied, which effectively locks the magnetization vector into the transverse plane (xy). During the spin-locking pulse, the magnetization vector decays to its equilibrium value, with a time constant equal to T 1 ρ. T 1 ρ is known to be more sensitive than T 1 to slow molecular fluctuations, typical of in vivo processes such as chemical exchanges with macromolecules [ 48 , 49 , 50 ]. To assess whether a sort of interaction existed, the T 1 ρ values of DNJ were measured in the absence and presence of ALG in a molar ratio of 50:1.…”