[3.2.1] and [4.1.1] isomers of Lehn's [2.2.2] Cryptand: Prediction of ion selectivity by quantum chemical calculations XV**

Preparation of Macrobicyclic Cryptands for Radiometal Complexation: Preparation of Macropa-Based Cryptands for Efficient Complexation of Radiometals

Macrobicyclic cryptands and especially derivatives with functionalized side arms (picolinate, pyrimidine carboxylate, and bipyridine carboxylate) are able to complex metal ions effectively. In this regard, four new functionalized cryptands were prepared in a convenient two-step synthesis procedure starting from basic compound 4,10,16,22,27-pentaoxa-1,7,13,19-tetraazabicyclo[11.11.5]nonacosane and fully characterized. Their complexation behavior was tested via 1H NMR titration with Ba2+, Sc3+, La3+, Lu3+, In3+, and Pb2+ pointing out log K values between 1.4 and 4.0. Radiolabeling with selected cations of radiopharmaceutical relevance (131Ba, 225Ac, and 133La) was performed.

Cryptate binding energies towards high throughput chelator design: metadynamics ensembles with cluster-continuum solvation

A tiered forcefield/semiempirical/meta-GGA pipeline together with a thermodynamic scheme designed with error cancellation in mind was developed to calculate binding energies of [2.2.2] cryptate complexes of mono- and divalent cations. Stable complexes of Na, K, Rb, Ca, Zn and Pb were generated, revealing consistent cation-N lengths but highly variable cation-O lengths and an amine stacking mechanism potentially augmenting the cation size selectivity. Metadynamics, used for searching the high-dimensional potential energy surface, together with a cluster-continuum model for affordable - yet accurate - solvation modeling, enabled the discovery of more stable geometries than those previously reported. Similar solvation energy curve shapes for lone vs. coordinated ions enabled rapid solvation convergence via the cancellation of errors stemming from finite cluster sizes. An R2 of 0.850 vs. experimental aqueous binding energies was obtained, validating this scheme as the backbone of a high-throughput workflow for chelator design.

Superalkali Coated Rydberg Molecules

A series of complexes of Na, K, NH4, and H3O with [bpy.bpy.bpy]cryptand, [2.2.2]cryptand, and spherical cryptand were investigated via DFT and ab initio methods. We found that by coating Rydberg molecules with the "organic skin" one could further decrease their ionization potential energy, reaching the values of ∼1.5 eV and a new low record of 1.3 eV. The neutral cryptand complexes in this sense possess a weakly bounded electron and may be considered as very strong reducing agents. Moreover, the presence of an organic cage increases the thermodynamic stability of Rydberg molecules making them stable toward the proton detachment.