Inclusion and Charge Transfer Interaction of a Multi-Redox Active 1,3,5-Triazine Derivative by Cucurbit[7,8]urils.

The redox active 1,3,5-triazine derivative (MPT) was used as a guest to study host-guest, charge transfer interaction with CB[7,8] in water. The multi-redox active MPT undergoes four chemically and electrochemically reversible one electron redox states in organic media, but in water, the fourth redox state shows an unstable nature. As a guest, the host-guest interaction of MPT was studied with two macrocyclic cucurbit[7,8]uril (CB[7,8]) hosts in water; resulting supramolecular complexes were characterized by NMR, ESI-MS, UV-vis, ITC, and cyclic voltammetric studies.

Interaction of Phenyl-Substituted Diazaperylenium with Cucurbit[n]uril: Complex versus Supramolecular Polymer.

A phenyl-substituted diazaperylenediium dication (DAP) was synthesized that shows concentration-dependent aggregation in water. The host-guest complexation of DAP was studied with the macrocyclic host cucurbit[n]uril (n = 7, 8) in water. With CB[7], it forms a 1:2 complex by placing two aryl substituents inside the CB[7]; whereas, with CB[8], a supramolecular polymer is formed. The resulting complex and supramolecular polymer have been characterized by ITC (isothermal titration calorimetry), ESI-MS (electrospray ionization mass spectrometry), 1H NMR (proton nuclear magnetic resonance), 2D NOESY (two-dimensional nuclear Overhauser enhancement spectroscopy), and DOSY (diffusion-ordered spectroscopy) spectra.

A structural analog of ralfuranones and flavipesins promotes biofilm formation by Vibrio cholerae.

Phosphoenolpyruvate-carbohydrate phosphotransferase system (PTS) is a highly conserved, multistep chemical process which uses phosphate transfer to regulate the intake and use of sugars and other carbohydrates by bacteria. In addition to controlling sugar uptake, the PTS regulates several bacterial cellular functions such as chemotaxis, glycogen metabolism, catabolite repression and biofilm formation. Previous studies have shown that the phosphoenolpyruvate (PEP) to pyruvate ratio is a critical determinant of PTS functions. This study shows that 2-oxo-4-phenyl-2,5-dihydro-3-furancarbonitrile (MW01), a compound with structural similarity to known natural products, induces Vibrio cholerae to grow preferentially in the biofilm mode in a mechanism that involves interaction with pyruvate. Spectrophotometric assays were used to monitor bacterial growth kinetics in microtiter plates and quantitatively evaluate biofilm formation in borosilicate glass tubes. Evidence of MW01 and pyruvate interactions was determined by nuclear magnetic resonance spectroscopy. Given the established connection between PTS activity and biofilm formation, this study also highlights the potential impact that small-molecule modulators of the PTS may have in the development of innovative approaches to manage desired and undesired microbial cultures in clinical, industrial and environmental settings.

Synthesis and Catalytic Reactivity of a Dicopper(II) µ-η(2):η(2)-Peroxo Species Supported by 1,4,7-Tri-tert-butyl-1,4,7-triazacyclononane.

O2-derived Cu(n)O2 adducts are attractive targets for aerobic oxidation catalysis because of their remarkable reactivity, but oxidation of the supporting ligand limits catalytic turnover. We report that (t)Bu3tacn (1,4,7-tri-tert-butyl-1,4,7-triazacyclononane) supports a dicopper(II) µ-η(2):η(2)-peroxo species with the highest solution stability outside of an enzyme. Decomposition of this species proceeds without oxidation of the (t)Bu3tacn ligand. Additive-free catalytic aerobic oxidation reactions at or above room temperature are described, highlighting the potential of oxidatively robust ligands in aerobic copper catalysis.

An investigation of the electron density of a Jahn-Teller-distorted Cr(II) cation: the crystal structure and charge density of hexakis(acetonitrile-κN)chromium(II) bis(tetraphenylborate) acetonitrile disolvate.

In the crystal structure of the title homoleptic Cr(II) complex, [Cr(CH3CN)6](C24H20B)2·CH3CN, the [Cr(CH3CN)6](2+) cation is a high-spin d(4) complex with strong static, rather than dynamic, Jahn-Teller distortion. The electron density of the cation was determined by single-crystal X-ray refinements using aspherical structure factors from wavefunction calculations. The detailed picture of the electronic density allowed us to assess the extent and directionality of the Jahn-Teller distortion of the Cr(II) cation away from idealized octahedral symmetry. The topological analysis of the aspherical d-electron density about the Cr(II) cation showed that there are significant valence charge concentrations along the axial Cr-N axes. Likewise, there were significant valence charge depletions about the Cr(II) cation along the equatorial Cr-N bonds. These charge concentrations are in accordance with a Jahn-Teller-distorted six-coordinate complex.

1,4,7-Triazacyclononane ligands bearing tertiary alkyl nitrogen substituents.

The first synthesis of 1,4,7-tri-tert-butyl-1,4,7-triazacyclononane ((t)Bu3tacn) and its adamantyl analog Ad3tacn are described. Cr(II), Mn(II), Fe(II), Co(II), Ni(II), and Cu(I) compounds of (t)Bu3tacn are reported: the steric properties of this ligand enforce four-coordinate geometries except in the case of five-coordinate Cr(II), enabling design of pseudotetrahedral compounds bearing this tridentate redox-inert ancillary ligand.

Breaking aggregation and driving the keto-to-gem-diol equilibrium of the N,N'-dimethyl-2,6-diaza-9,10-anthraquinonediium dication to the keto form by intercalation in cucurbit[7]uril.

(1)H NMR, ESI-MS, and DFT calculations with the M062X/6-31G* method show that, in water, the bistetrafluoroborate salt of N,N'-dimethyl-2,6-diaza-9,10-anthraquinonediium dication (DAAQ·2BF4(-)) exists in equilibrium with both its gem-diol and several aggregates (from dimers to at least octamers). With high concentrations of HCl (e.g., 1.2-1.5 M), all aggregates break up and the keto-to-gem-diol equilibrium is shifted quantitatively toward the quinone form. The same effect is observed with 1.5 mol equiv of cucurbit[7]uril, CB[7], with which all equilibria are shifted toward the quinone form, which undergoes slow exchange with the CB[7] cavity as both the free and the CB[7]-intercalated quinone (DAAQ@CB[7]) are observed simultaneously by (1)H NMR. The affinity of DAAQ for the CB[7] cavity (Keq = 4 × 10(6) M(-1)) is in the range found for tricyclic dyes (0.4-5.4 × 10(6) M(-1)), and among the highest observed to date. A computational comparative study of the corresponding CB[7] complex of the N,N'-dimethyl-4,4'-bipyridinium dication (N,N'-dimethyl viologen, MeV) suggests that the higher binding constant for intercalation of DAAQ may be partially attributed to a lesser distortion of CB[7] (required to maximize favorable nonbonding interactions) as a result of the flat geometry of DAAQ.

Orientation of pyrylium guests in cucurbituril hosts.

According to recent reports, supramolecular complexes of the pyrylium cation with cucurbit[x]urils (CB[x], x = 7, 8) show promising photoluminescence suitable for electroluminescent devices. In turn, photoluminescence seems to be related to the stereochemistry of the complexes; however, that has been controversial. Here, we report that in H(2)O, 2,6-disubsituted-4-phenyl pyryliums (Pylm) form dimers quantitatively (equilibrium constants >10(4) M(-1)), but they enter as such only in the larger CB[8]. In terms of orientation, (1)H NMR shows that Me-Pylm, Ph-Pylm, and t-Bu-Pylm insert their 4-phenyl groups in either the CB[7] or CB[8] cavity. The orientation of iPr-Pylm in the iPr-Pylm@CB[7] complex is similar. Experimental conclusions are supported by DFT calculations using the M062X functional and the 6-31G(d) basis set. In the case of (iPr-Pylm)(2)@CB[8], (1)H NMR of both the guest and the host indicates that both guests might enter CB[8] from the same side with their iPr groups in the cavity, but DFT calculations leave room for ambiguity. In addition to the size and hydrophobicity of the 2,6-substituents of the guests, as well as the size and flexibility of the hosts, theory reveals the importance of explicit solvation (H(2)O) and finite temperature effects (particularly for (1)H NMR shielding calculations) in the determination of the stereochemistry of those complexes.

Simultaneous electron transfer from free and intercalated 4-benzoylpyridinium cations in cucurbit[7]uril.

N-Substituted 4-benzoylpyridinium monocations form stable host-guest complexes with cucurbit[7]uril (CB[7]) in DMSO (K(eq) approximately 0.6-1.9 x 10(3) M(-1)). Observation of simultaneous reversible and quasi-reversible e-transfer processes from the free and intercalated quests, respectively, is attributed to the pre-e-transfer host-guest equilibrium. The standard rate constant for Me-BP@CB[7] (k(s) = 1.0 x 10(-4) cm.s(-1)) reflects e-transfer across 5.7 A, corresponding to the distance of the intercalated guest from the outmost perimeter of CB[7] (5.3 A).

Control of the ketone to gem-diol equilibrium by host-guest interactions.

In water, N-methyl-4-(p-substituted benzoyl)pyridinium cations, BP-X, exist in equilibrium with their hydrated forms (gem-diols), whose concentrations depend on the para substituent (-X). In the presence of cucurbit[7]uril (CB[7]), the benzoyl group shows a preference for the CB[7] cavity, and the ketone to gem-diol equilibrium is shifted toward the keto form, meaning that the stabilization realized through hydrophobic interactions of the benzoyl group in the CB[7] cavity exceeds the hydrogen-bonding stabilization of the gem-diols in the aqueous environment.