Chaotropic and Kosmotropic Anions Regulate the Outcome of Enzyme-Mediated Dynamic Combinatorial Libraries of Cyclodextrins in Two Different Ways

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.

Opposite Regulatory Effects of Immobilized Cations on the Folding Vs. Assembly of Melittin

Ions are crucial in modulating the protein structure. For the free ions in bulk solution, ammonium is kosmotropic (structure forming) and guanidinium is chaotropic (structure breaking) to the protein structure within the Hofmeister series. However, the effect of immobilized ions on a protein surface is less explored. Herein, we explored the influence of two immobilized cations (ammonium in the side chain of lysine and guanidinium in the side chain of arginine) on the folding and assembly of melittin. Melittin adopts an α-helix structure and is driven by hydrophobic interactions to associate into a helical bundle. To test the influence of immobilized cations on the peptide structure, we designed the homozygous mutants exclusively containing ammonium (melittin-K) or guanidinium (melittin-R) and compared the differences of melittin-K vs. melittin-R in their folding, assembly, and molecular functions. The side chains of lysine and arginine differ in their influences on the folding and assembly of melittin. Specifically, the side chain of R increases the α-helical propensity of melittin relative to that of K, following an inverse Hofmeister series. In contrast, the side chain of K favors the assembly of melittin relative to the side chain of R in line with a direct Hofmeister series. The opposite regulatory effects of immobilized cations on the folding and assembly of melittin highlight the complexity of the noncovalent interactions that govern protein intermolecular architecture.

Tripodal, Squaramide-Based Ion Pair Receptor for Effective Extraction of Sulfate Salt

Combining three features—the high affinity of squaramides toward anions, cooperation in ion pair binding and preorganization of the binding domains in the tripodal platform—led to the effective receptor 2. The lack of at least one of these key elements in the structures of reference receptors 3 and 4 caused a lower affinity towards ion pairs. Receptor 2 was found to form an intramolecular network in wet chloroform, which changed into inorganic–organic associates after contact with ions and allowed salts to be extracted from an aqueous to an organic phase. The disparity in the binding mode of 2 with sulfates and with other monovalent anions led to the selective extraction of extremely hydrated sulfate anions in the presence of more lipophilic salts, thus overcoming the Hofmeister series.

The many-body expansion for aqueous systems revisited: III. Hofmeister ion–water interactions

We report a Many Body Energy (MBE) analysis of aqueous ionic clusters containing kosmotropic and chaotropic anions and cations at the two opposite ends of the Hofmeister series to quantify how these ions alter the interaction between the water molecules in their immediate surroundings.

The Electrostatic Origins of Specific Ion Effects: Quantifying the Hofmeister Series for Anions

Life as we know it is dependent upon water, or more specifically salty water, for without dissolved ions the interactions between biological molecules are insufficiently complex to support life. This...