Evaluating the Effects of Metal Adduction and Charge Isomerism on Ion-Mobility Measurements using m-Xylene Macrocycles as Models.

Gas-phase ion-mobility spectrometry provides a unique platform to study the effect of mobile charge(s) or charge location on collisional cross section and ion separation. Here, we evaluate the effects of cation/anion adduction in a series of xylene and pyridyl macrocycles that contain ureas and thioureas. We explore how zinc binding led to unexpected deprotonation of the thiourea macrocyclic host in positive polarity ionization and subsequently how charge isomerism due to cation (zinc metal) and anion (chloride counterion) adduction or proton competition among acceptors can affect the measured collisional cross sections in helium and nitrogen buffer gases. Our approach uses synthetic chemistry to design macrocycle targets and a combination of ion-mobility spectrometry mass spectrometry experiments and quantum mechanics calculations to characterize their structural properties. We demonstrate that charge isomerism significantly improves ion-mobility resolution and allows for determination of the metal binding mechanism in metal-inclusion macrocyclic complexes. Additionally, charge isomers can be populated in molecules where individual protons are shared between acceptors. In these cases, interactions via drift gas collisions magnify the conformational differences. Finally, for the macrocyclic systems we report here, charge isomers are observed in both helium and nitrogen drift gases with similar resolution. The separation factor does not simply increase with increasing drift gas polarizability. Our study sheds light on important properties of charge isomerism and offers strategies to take advantage of this phenomenon in analytical separations.

Temperature-induced pseudopolymorphism of molecular salts from a pyridyl bis-urea macrocycle and naphthalene-1,5-disulfonic acid.

Molecular salts, often observed as cocrystals, play an important role in the fields of pharmaceutics and materials science, where salt formation is used to tune the properties of active pharmaceutical ingredients (APIs) and improve the stability of solid-state materials. Salt formation via a proton-transfer reaction typically alters hydrogen-bonding motifs and influences supramolecular assembly patterns. We report here the molecular salts formed by the pyridyl bis-urea macrocycle 3,5,13,15,21,22-hexaazatricyclo[15.3.1.17,11]docosa-1(21),7(22),8,10,17,19-hexaene-4,14-dione, (1), and naphthalene-1,5-disulfonic acid (H2NDS) as two salt cocrystal solvates, namely 4,14-dioxo-3,5,13,15,21,22-hexaazatricyclo[15.3.1.17,11]docosa-1(21),7(22),8,10,17,19-hexaene-21,22-diium naphthalene-1,5-disulfonate dimethyl sulfoxide disolvate, C16H20N6O22+·C10H6O6S22-·2C2H6OS, (2), and the corresponding monosolvate, C16H20N6O22+·C10H6O6S22-·C2H6OS, (3). This follows the ΔpKa rule such that there is a proton transfer from H2NDS to (1), forming the reported molecular salts through hydrogen bonding. Prior to salt formation, (1) is relatively planar and assembles into columnar structures. The salt cocrystal solvates were obtained upon slow cooling of dimethyl sulfoxide-acetonitrile solutions of the molecular components from two temperatures (363 and 393 K). The proton transfer to (1) significantly alters the conformation of the macrocycle, changing the formerly planar macrocycle into a step-shaped conformation with trans-cis urea groups in (2) or into a bowl-shape conformation with trans-trans urea groups in (3).

Structural, electrochemical and photophysical properties of an exocyclic di-ruthenium complex and its application as a photosensitizer.

The reaction of cis-bis(2,2'-bipyridine)dichlororuthenium(ii) hydrate with a conformationally mobile bipyridyl macrocycle afforded [(bpy)2Ru(µ-L)Ru(bpy)2]Cl4·6H2O, a bridged di-Ru complex. Single crystal X-ray diffraction showed the macrocyclic ligand adopting a bowl-like structure with the exo-coordinated Ru(ii) centers separated by 7.29 Å. Photophysical characterization showed that the complex absorbs in the visible region (λmax = 451 nm) with an emission maximum at 610 nm (τ = 706 ns, ΦPL = 0.021). Electrochemical studies indicate the di-Ru complex undergoes three one-electron reversible reductions and a reversible one-electron oxidation process. This electrochemical reversibility is a key characteristic for its use as an electron transfer agents. The complex was evaluated as a photocatalyst for the electronically mismatched Diels-Alder reaction of isoprene and trans-anethole using visible light. It afforded the expected product in good conversion (69%) and selectivity (dr > 10 : 1) at low loadings (0.5-5.0 mol%) and the sensitizer/catalyst was readily recycled. These results suggest that the bipyridyl macrocycle could be widely applied as a bridging ligand for the generation of chromophore-catalyst assemblies.