Novel hydrogen- and halogen-bonding anion receptors based on 3-iodopyridinium units

Abstract

Novel tripodal 3-iodopyridinium-based receptors were investigated through (i) UV-vis and NMR titrations with anions in solution, (ii) theoretical calculations, and (iii) X-ray diffraction studies. Their anion binding properties were compared to those of the monobranched model and/or non-halogenated model systems. Investigations in acetonitrile pointed out that the iodine atom in the meta position to pyridinium enhances anion affinity. According to computational studies, this effect seemed to depend on the electron-withdrawing nature of the iodine-substituents. Notably, 1 : 1 adducts were observed to form in solution with all the investigated anions. The strong de-shielding effect observed on the receptors' protons upon anion binding indicated their participation in hydrogen-bonds with the coordinated anion. This result was supported by theoretical calculations and, in the solid state, by X-ray diffraction studies on the complexes with nitrate and bromide. In the crystalline state, the pyridinium arms of the tripodal receptor assume a "2-up, 1-down" conformation. Both nitrate and bromide anions are included in the receptor's cavity, forming two hydrogen-bonding interactions with the protons of the "2-up" arms, and one halogen-bonding interaction with the C-I group of a second molecular cation. The combination of hydrogen and halogen bonds leads to supramolecular chains in the crystals

Halogen Bonding in Solution: Anion Recognition, Templated Self‐Assembly, and Organocatalysis

“…[32] Thea ffinity for ac ertain binding partner can be significantly increased by switching from bidentate complexation modes to multiple interaction points adjusted in ac oncerted manner.A lthough the design and synthesis of multidentate XB donors is rather challenging due to the strict linearity of the interaction, it also offers the advantage of creating more rigid and ordered structures with an improved selectivity. [25,26] This general design strategy was successfully used in different studies by implementing pyridinium (3), [33] imidazolium (4, 5), [34,35] or triazolium (6) [35] moieties to build at ridentate bowl-shaped cavity.T hese structures enabled anion binding in stable 1:1( 3, 5,a nd 6)o r1:3 (4)c omplexes through charge-assisted HB/XB interactions ( Figure 3).…”

Relationships between hydrogen bonds and halogen bonds in biological systems

“…Interest in halogen bonds (XBs) has seen a revival in the past couple of decades, as the potential to exploit their unique properties has become better recognized (Erdé lyi, 2012;Gilday et al, 2015;Cavallo et al, 2016). XBs are widely applied to the chemical engineering of crystals and supramolecular assemblies (Metrangolo & Resnati, 2001;Metrangolo et al, 2005), including designing liquid crystals (Nguyen et al, 2004;Bruce, 2008;Chen et al, 2014;Fernandez-Palacio et al, 2016), and organometallic frameworks (Maharramov et al, 2016), stabilizing volatile liquids (Aakerö y et al, 2015), synthesizing organic catalysts (Coulembier et al, 2010;Jungbauer & Huber, 2015;Matsuzawa et al, 2016), designing anion receptors (Sarwar, Dragisic, Sagoo et al, 2010;Kilah et al, 2011;Tepper et al, 2015;Amendola et al, 2016;Wageling et al, 2016;Mullaney et al, 2016;Hoque & Das, 2016), and in host-guest assemblies (Dumele et al, 2015;Noa et al, 2015Noa et al, , 2016Gonzá lez et al, 2016;Puttreddy et al, 2016). In biology (Auffinger et al, 2004;Scholfield et al, 2013), XBs are seen to direct DNA macromolecular conformations (Voth, Hays & Ho, 2007), to increase the affinity of agonists (Rohde et al, 2012) and antagonists to protein targets (Lam et al, 2009;Lu, Shi et al, 2009;Hardegger et al, 2011;Scholfield et al, 2013;Xu et al, 2014;…”

Halogenbrücken in Lösung: Anionenerkennung, Templat‐gestützte Selbstorganisation und Organokatalyse

“…Diese Strategie wurde beispielsweise in verschiedenen aktuellen Studien eingesetzt, in denen Pyridinium‐ ( 3 ), Imidazolium‐ ( 4 , 5 ) oder Triazoliumeinheiten ( 6 ) zum Aufbau dreizähniger Kavitäten verwendet wurden (Abbildung ). Diese Strukturen ermöglichten dabei durch ladungsassistierte HB/XB‐Wechselwirkungen eine Anionenkoordination in stabilen 1:1‐ ( 3 , 5 und 6 ) oder 1:3‐Komplexen ( 4 ).…”

“… Dreizähnige XB/HB‐Donorsysteme auf Basis von Pyridinium‐, Imidazolium‐ oder Triazoliumeinheiten. 3 : K a ‐Werte erhalten durch UV/Vis‐Titration in CH 3 CN bei 298 K; 4 : K a ‐Werte erhalten durch ITC‐Titration in CH 3 C bei 298 K, β a (1:3‐Komplex); 5 , 6 : K a ‐Werte erhalten durch 1 H‐NMR‐Titration in [D 6 ]DMSO bei 298 K …”