ABSTRACT
Proving the structures of charged metallacages obtained by metal ion coordination-driven solution self-assembly is challenging, and the common use of routine NMR spectroscopy and mass spectrometry is unreliable. Carefully determined diffusion coefficients from diffusion-ordered proton magnetic resonance (DOSY NMR) for six cages of widely differing sizes lead us to propose a structural reassignment of two molecular cages from a previously favored trimer to a pentamer or hexamer, and another from a trimer to a much higher oligomer, possibly an intriguing tetradecamer. In the former case, strong support for the reassignment to a larger cage is provided by an observation of a slow reversible transformation of the initially formed cage into a smaller but spectrally very similar one upon dilution. In the latter case, freeze-fracture transmission electron micrographs demonstrate that at least some of the solutions are colloidal, and high-resolution electron transmission and atomic force microscopy images are compatible with a tetradecamer but not a trimer. Comparison of solute partial molar volumes deduced from measurement of solution density with volumes anticipated from molecular models argues strongly against the presence of large voids (solvent vapor bubbles) in cages dissolved in nitromethane. The presence of bubbles was previously proposed in an attempt to account for the bilinear nature of the Eyring plot of the rate constant for pyridine ligand edge exchange reaction in one of the cages and for the unusual activation parameters in the high-temperature regime. An alternative interpretation is proposed now.
ABSTRACT
Supramolecular self-assembly using weak interactions under quasi-equilibrium conditions has provided easy access to very complex but often quite fragile molecules. We now show how a labile structure obtained from reversible transition-metal-directed self-assembly of rods and connectors serves as a template that can be converted into a sturdy structure of identical topology and similar geometry. The process consists of Cu(I)-catalyzed replacement of all rods or connectors terminated with pyridines for analogues terminated with ethynyls, converting dative NâPt(+) bonds into covalent C-Pt bonds. The procedure combines the facility and high yield of reversible self-assembly with the robustness of covalent synthesis.
Subject(s)
Copper/chemistry , Pyridines/chemistry , Spectrometry, Mass, Electrospray IonizationABSTRACT
The combination of hydrophobic effects and ionic pairing within a triphenylene-based receptor were exploited for the binding of biological phenylethylamines, serotonin and D-glucosamine in phosphate buffered water.
Subject(s)
Chrysenes/chemistry , Glucosamine/chemistry , Phenethylamines/chemistry , Phosphates/chemistry , Serotonin/chemistry , Ions/chemistry , Models, Molecular , Molecular Structure , Water/chemistryABSTRACT
Several dynamic hexaimine cryptophanes, that are built up from two triformylcyclotribenzylene cavitands and three diamino linkers and spontaneously assemble in water in the presence of a suitable templating guest, are reported. X-ray structure, kinetics and thermodynamics of assembly and molecular recognition properties are discussed.
Subject(s)
Polycyclic Compounds/chemistry , Water/chemistry , Models, Molecular , Molecular Conformation , StereoisomerismABSTRACT
A fluorescent cyclotriveratrylene 1 was synthesized and characterized in methanol and water. Soluble in pure water and physiological media, compound 1 has binding properties towards acetylcholine. This detection is direct, contrary to most fluorescent systems which rely upon a competition principle between the guest and a fluorophore.
Subject(s)
Acetylcholine/chemistry , Fluorescence , Polycyclic Compounds/chemistry , Polycyclic Compounds/chemical synthesis , Water/chemistry , Methanol/chemistry , Models, Chemical , Molecular ConformationABSTRACT
Synthesis and binding properties of a new hydrosoluble triphenylene 1b are reported. Selective recognition of acetylcholine (ACh) against other aliphatic ammoniums is achieved by this flat receptor, which also forms complexes with epibatidine and nicotine. Ionic pairing and hydrophobic effects between host 1b and ACh are studied by infrared spectroscopy.
Subject(s)
Acetylcholine/chemistry , Bridged Bicyclo Compounds, Heterocyclic/chemistry , Nicotine/chemistry , Pyridines/chemistry , Water/chemistry , Ammonia/chemistry , Binding Sites , Cholinergic Agents/chemistry , Magnetic Resonance Spectroscopy , Molecular Structure , Solubility , ThermodynamicsABSTRACT
Designed as a multivalent hydrogen bond acceptor, new receptors, Discopus 1a,b, were built from a triphenylene core surrounded by six (diaryl)phosphinate groups. An efficient synthesis was developed to prepare these elaborated structures in a high overall yield. The X-ray structure of receptor 1b showed strong cooperative hydrogen bonds with two water molecules and intermolecular CH-pi contacts. In chloroform, Discopus 1a,b displayed recognition properties toward dihydroxybenzenes, selectively forming complexes with catechol derivatives 4a-c in a 1:2 (host:guest) stoichiometry. According to NMR and microcalorimetry titrations, association constants were found in the 30-2837 M(-1) range, which were larger than those reported for curvated catechol receptors (14-120 M(-1)). Interestingly, Discopus present two distinct catechol binding sites. Weak hydrogen bonding between host phosphinates and guest hydroxyl groups was shown by infrared spectroscopy and (31)P NMR. Molecular dynamics simulations and recognition experiments suggested that a stronger hydrogen bond assisted by a pi-interaction between the Discopus core and one catechol molecule could exist within the 1:2 complex.
