Effects of Solvent Properties on the Anion Binding of Neutral Water-Soluble Bis(cyclopeptides) in Water and Aqueous Solvent Mixtures

Abstract

In this study, the anion-binding bis(cyclopeptide) 2 is introduced, which dissolves freely in water, affording up to 10 mM concentrations, thanks to triethylene glycol-derived substituents in the cyclopeptide subunits and the linker connecting them. Binding studies provided evidence that the anion affinity previously demonstrated for less-soluble analogs of this compound is retained under highly competitive aqueous conditions. The highest affinity in water was observed for iodide, closely followed by sulfate anions, whereas binding of soft and weakly coordinating anions could not be observed. The anion selectivity of 2 thus differs from that of other recently described receptors, which also do not require electrostatic or coordinative interactions for anion binding in water but typically fail to bind strongly coordinating sulfate anions. The ability of 2 to overcome sulfate hydration is attributed to the special mode of binding, combining direct N–H···A – interactions with the release of water molecules from the receptor cavity. The characterization of the anion binding of 2 and a related bis(cyclopeptide) in a variety of different solvents and aqueous solvent mixtures furthermore allowed the correlation of the binding properties with solvent parameters. These analyses provided qualitative and even quantitative insights into the solvent properties and solvation phenomena that mainly affect anion complexation.

The Chaotropic Effect as an Assembly Motif in Chemistry

“…Understanding the driving forces between ions and concave binding sites is therefore of prime importance for the supramolecular design of synthetic receptors with defined affinity and selectivity.A ccordingly,t he unexpectedly high binding affinities of superchaotropic anions and the chaotropic effect as ag eneric driving force have recently found their entry into the important area of anion recognition. [44,65,117,[131][132][133][134][135][136][137][138][139][140][141][142][143] In follow-up studies with inclusion complexes,the affinity of dodecaborate clusters to cyclodextrins (CDs) has been extended to the larger CD homologues (Figure 3) [23] as well as other borate clusters, [14,144] both in solution and in the gas phase. [14,23,24] Theb inding propensity of borate clusters has also been demonstrated for calixarenes [21] and at etrathiafulvalene host [24] as an alternative macrocyclic host (Figure 3).…”

Anion Recognition in Water, Including Sulfate, by a Bicyclam Bimetallic Receptor: A Process Governed by the Enthalpy/Entropy Compensatory Relationship

“…Theset wo features suggest that the enthalpy change associated with the metal-anion interaction (DH8 MÀX )p lays ap rominent role, with respectt ot he hydration term DH8 hydr-X À .T his may be because each pseudohalide anion offers two distinct donor atoms for coordination; thus allowing the formationo f more intense coordinative interactions and reinforcing DH8 MÀX . [28]). [28]).…”

“…[28]). [28] Figure 7. a) Enthalpy/entropy compensationdiagramfor anion complexation by [Cu II 2 (bicyclam)] 4 + (coloured symbols) and corresponding regression line (dashed);b)the same diagram as that in a), with added symbols (grey triangles), which refer to halidea nd sulfate complexationbyb is-cyclopeptide 3.…”

“…In particular,as olution of the sodium salt of the envisaged anion was added stepwise to as olution of [Cu II 2 (bicyclam)](ClO 4 ) 4 placed in the sample cell. [28] Potentiometrict itrations Potentiometric titrations were performed at 25 8Cb yu sing ac arbonate-free solution of NaOH as at itrant, under an itrogen atmosphere. [38] Blank titrations were performed and subtracted from the corresponding titrations to remove the effect of dilution.…”

Synthesis, Secondary Structure, and Anion Binding of Acyclic Carbohydrate‐Derived Oligo(amide‐triazole)s

“…[11] The groups of Flood, [12,13] Craig, [14] Hecht, [15] Beer, [16] Schubert, [17] and Kubik [18][19][20][21] have significantly contributed to the study of 1,2,3-triazoles as anion receptors. [11] The groups of Flood, [12,13] Craig, [14] Hecht, [15] Beer, [16] Schubert, [17] and Kubik [18][19][20][21] have significantly contributed to the study of 1,2,3-triazoles as anion receptors.…”