Impact of the Syn/Anti Relative Configuration of Cryptophane-222 on the Binding Affinity of Cesium and Thallium

Abstract

We report in this article the synthesis, the X-ray crystal structure of compound syn-2, and its binding properties with cesium and thallium in aqueous solution under basic conditions. Compound syn-2 is the diastereomeric compound of anti-1 that shows very high affinity for cesium and thallium in aqueous solution under the same conditions. Despite the close structural similarities that exist between the syn-2 and anti-1 compounds, they show large discrepancy in their ability to bind cesium and thallium cations in the same conditions. Indeed, the syn-2 derivative has a lower affinity for these two cationic species and the binding constants are several orders of magnitude lower than those found for its congener. The large differences in affinity observed with these two compounds can be explained by the relative position of the six hydroxyl groups to each other.

Synthesis of Cryptophanes: Recent Advances

“…In another study by Brotin et al the syn-isomer 48 underwent hydrogenolysis in 83 % yield and 53 was used to study the binding properties with Cs + and Tl + ions (Scheme 7b). [54] Berthault et al transformed the syn-isomer 48 in to a watersoluble hexacarboxylic acid substituted cryptophane 54 in a stepwise manner, using methyl bromoacetate. [55] The syn-54 displays a high binding constant towards Xe.…”

“…In another study by Brotin et al . the syn ‐isomer 48 underwent hydrogenolysis in 83 % yield and 53 was used to study the binding properties with Cs + and Tl + ions (Scheme 7b) [54] . Berthault et al .…”

Chiroptical Properties of a Cryptophane Soluble at Neutral pH

“…Our previous work revealed that the presence of hydroxyl functions was mandatory to sequester these two species, and that complexation efficiency increased with the number of hydroxyl functions [6c–e] . Moreover, increasing the size of the cavity decreased the complexation efficiency [6a,c] . Thus, the anti ‐cryptophane 1 ( D 3 ‐symmetry) decorated with six hydroxyl functions shows higher binding constants in basic solutions whereas the anti ‐cryptophane 2 ( C 3 ‐symmetry) decorated with six OCH 2 COOH groups was unable to bind cesium in the same conditions (Figure S17 in Ref.…”

Understanding the surrounding effects on Raman optical activity signatures of a chiral cage system: Cryptophane-PP-111

“…Their ability to encapsulate a large range of atoms and molecules, neutral or charged, aroused people interest and contributed significantly to the development of these host cage-systems. They are able to encapsulate neutral guests, such as CH 2 Cl 2 /CHCl 3 [11] or methyloxirane [12][13][14], and charged species, such as Cs + /Tl + [15][16][17][18][19], in organic solutions as in aqueous ones. In addition, xenon is another guest of high interest that can enter the cavity of small cryptophanes.…”