1H NMR Study of a Chiral Argentivorous Molecule/Ag+ Complex: Assignment of Proton Signals of Four Aromatic Rings with Slightly Different Environments

Bis-Argentivorous Molecules Bridged by Phenyl and 4,4'-Biphenyl Groups: Structural and Dynamic Behavior of Silver Complexes

Bis-argentivorous molecules (L^a and L^b), which have phenyl and 4,4'-biphenyl groups as linkers, have been prepared. The structures of Ag⁺ complexes with the new ligands (L^a and L^b) were investigated in solution and the solid state. The CSI-MS and ¹H NMR titration of L^a and L^b with Ag⁺ show 1:1 and 1:2 complexes depending on the [Ag⁺]:[L] ratios. In the solid-state structures, single crystals of L^a and L^b with 2 equiv of Ag⁺ were prepared. X-ray crystallography of the silver(I) complexes with L^a and L^b showed that an intramolecular racemic structure (Δ(δδδδ)Λ(λλλλ) form) and a racemic mixture of Δ(δδδδ)Δ(δδδδ) and Λ(λλλλ)Λ(λλλλ) forms were formed, respectively. The dynamic ¹H NMR studies suggest the following: (i) the activation entropies (ΔS^⧧) of the side arm rotations in the Ag⁺ complex with L^a were all negative, indicating restricted rotation of the side arms due to their shortness, and (ii) the ΔS^⧧ values of the Ag⁺ complexes with L^b were negative only when the side arms of both cyclens rotated simultaneously, and the ΔS^⧧ values for the 1:1 and 1:2 complexes were positive when one cyclen side arm was rotated. These values of ΔS^⧧ indicate that the biphenyl side arms between the two cyclens are not long enough to rotate the ring freely.

Structural dynamism of chiral sodium peraza-macrocycle complexes derived from cyclic peptoids

A variety of cyclen and hexacyclen derivatives decorated with (S)-1-phenylethyl side chains or (S)-pyrrolidine units have been prepared via a reductive approach from the corresponding cyclic peptoids containing N-(S)-(1-phenylethyl)glycine and l-proline residues. Spectroscopic and DFT studies on their Na+ complexes show that point chirality and ring size play a crucial role in controlling the structural dynamism of 1,2-diaminoethylene units and pendant arms. The detection of highly symmetric C4- and C3-symmetric metalated species demonstrates that a full understanding of the relationship between the structure and conformational properties of peraza-macrocyclic metal complexes is possible.

Argentivorous Molecules with Oxyethylene Chains in Side-Arms: Silver Ion-Induced Selectivity Changes toward Alkali Metal Ions

Argentivorous molecules with mono, di, tri, tetra, and penta-oxyethylene chains in aromatic side-arms were prepared (L1-L5). Titration experiments using proton nuclear magnetic resonance and cold electrospray ionization (cold-spray ionization, CSI) mass spectrometry showed that silver ions were trapped in the cyclen moiety and the arranged oxyethylene chains of the side-arms when two equivalents of silver ions were added. The silver complexes formed by adding one equivalent of silver ion to L2-L5 bind alkali metal ions using the oxyethylene chains; alkali metal ion-induced CSI mass spectral changes of L2-L5 were measured in the absence and presence of silver ions to compare the binding properties of the ligand for Li⁺, Na⁺, and K⁺ ions. As a result, the intensity ratios of [L + H + M]²⁺/[L + H]⁺ in L1-L3 were almost zero or very low. L4 and L5, which have tetra(oxyethylene) and penta(oxyethylene) chains, respectively, bind a larger size of alkali metal ions. On the other hand, in the presence of silver ions, the ratio for [L + Ag + M]²⁺/[L + H]⁺ (M = Li, Na, K) in L2-L5 was increased. The highest [L + Ag + M]²⁺/[L + H]⁺ ratios for K⁺ were observed in L4 and L5, while selectivity for Na⁺ was observed in the case of L2 and L3. These results indicate that the increased binding ability and selectivity by L2-L5 are due to the arrangement of oxyethylene chains by the conformational change of the aromatic side-arms. The Ag⁺-induced carbon-13 nuclear magnetic resonance spectral changes suggested that the second and third oxyethylene units, close to the benzene, are involved in the coordination of the second metal ion.