Abstract
We demonstrate how different anions from across the Hofmeister series can influence the behavior of enzyme-mediated dynamic combinatorial libraries of cyclodextrins (CDs). Using cyclodextrin glucanotransferase to catalyze reversible transglycosylation, dynamic mixtures of interconverting cyclodextrins can be formed wherein the relative concentrations of α-CD, β-CD and γ-CD is determined by their intrinsic stabilities and any stabilizing influences of added template (guest) molecules. Here, we find that addition of high concentrations of kosmotropic anions can be used to enhance the effects of added hydrophobic templates, while chaotropic anions can themselves act as templates, causing predictable and significant changes in the cyclodextrin composition due to weak, but specific, binding interactions with α-CD.
Highlights
Since the groundbreaking work of Franz Hofmeister more than a century ago into how salts affect the solubility of proteins (Hofmeister, 1888), countless studies have repeatedly revealed the Hofmeister series of anions: F−, SO42−, AcO−, Cl−, Br−, NO3−, ClO3−, I−, ClO4−, and SCN−
We have previously described how dynamic combinatorial libraries (DCLs) of interconverting cyclodextrins can be generated by employing an enzyme that enables reversible transglycosylation (Larsen and Beeren, 2019, Larsen and Beeren, 2020, Larsen and Beeren, 2021)
To explore the influence of anions on Cyclodextrin glucanotransferase (CGTase)-mediated DCLs of cyclodextrins, we examined a series of DCLs prepared in the presence of different sodium salts at concentrations up to 4 M
Summary
Since the groundbreaking work of Franz Hofmeister more than a century ago into how salts affect the solubility of proteins (Hofmeister, 1888), countless studies have repeatedly revealed the Hofmeister series of anions: F−, SO42−, AcO−, Cl−, Br−, NO3−, ClO3−, I−, ClO4−, and SCN− Kosmotropes, such as F− and SO42−, generally decrease the solubility of proteins and other solutes (salting out), and while the rules governing these phenomena are not fully understood, these ions are said to enhance the hydrophobic effect (Gibb, 2011). While investigating different reaction conditions, it was found that CGTase could tolerate very high concentrations of NaNO3 (up to 7.5 M) but that the presence of NaNO3 altered the distribution of cyclodextrins in the DCL that was formed. The binding constants used were obtained from a study carried out by Tokunaga and coworkers, where the authors used 1H-NMR spectroscopy to determine binding constants between inorganic anions and cyclodextrins (Matsui et al, 1997)
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