Crystallographic and Computational Studies of Non-Covalent Interactions of Molecular Clips with a Series of Small Solvent Molecules

Molecular clips hold the potential of self-association and the ability to form host–guest complexes. Here we describe the synthesis of a 1,2-dimethoxyphenyl terminated glycoluril molecular clip (2) that binds with smaller solvent molecules by π?H–C and C=O?H–O non-covalent interactions. We obtained single crystals of 2 and 2 + CH₂Cl₂, CH₃OH, CH₃CN, and DMF solvents complexed within the clip. These solvents always form two π?H–C interactions between the aromatic rings in the clip, and CH₃OH formed an additional C=O?H–O hydrogen bond with the glycoluril carbonyl group. Based on single crystal data we found that π?H–C interactions of 2 + CH₂Cl₂ are stronger than 2 + CH₃CN and 2?+?DMF, due to the presence of stronger electron withdrawing groups in CH₂Cl₂, which lead to a decrease in dihedral angle of two glycoluril aromatic planes. We also investigated the non-covalent interaction energies of these solvent molecules with 2 using computational methods.

Graphical Abstract

Several solvent adducts of a glycoluril derivative have been isolated and characterized by single crystal X-ray diffraction, revealing two common pi?H–C non-covalent bonds within the molecular clip.

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Large Deviations, Dynamics and Phase Transitions in Large Stochastic and Disordered Neural Networks

Neuronal networks are characterized by highly heterogeneous connectivity, and this disorder was recently related experimentally to qualitative properties of the network. The motivation of this paper is to mathematically analyze the role of these disordered connectivities on the large-scale properties of neuronal networks. To this end, we analyze here large-scale limit behaviors of neural networks including, for biological relevance, multiple populations, random connectivities and interaction delays. Due to the randomness of the connectivity, usual mean-field methods (e.g. coupling) cannot be applied, but, similarly to studies developed for spin glasses, we will show that the sequences of empirical measures satisfy a large deviation principle, and converge towards a self-consistent non-Markovian process. From a mathematical viewpoint, the proof differs from previous works in that we are working in infinite-dimensional spaces (interaction delays) and consider multiple cell types. The limit obtained formally characterizes the macroscopic behavior of the network. We propose a dynamical systems approach in order to address the qualitative nature of the solutions of these very complex equations, and apply this methodology to three instances in order to show how non-centered coefficients, interaction delays and multiple populations networks are affected by disorder levels. We identify a number of phase transitions in such systems upon changes in delays, connectivity patterns and dispersion, and particularly focus on the emergence of non-equilibrium states involving synchronized oscillations.     

Hydrazine-mediated cyclization of Ugi products to synthesize novel 3-hydroxypyrazoles

This report discloses a novel concise synthesis of a series of 3-hydroxypyrazoles 5 via a tandem Ugi/debenzylation /hydrazine-mediated cyclization sequence. Herein, n-butyl isocyanide 4b was utilized as an alternative to classical convertible isocyanides enabling high yielding hydrazine-mediated cyclization. Taken together, a novel class of 3-hydroxypyrazoles 5a-5i was synthesized with potential to be of interest in future library enrichment strategies.     

Low molecular weight organogelators derived from threefold symmetric tricarbamates

A group of new low molecular weight organogelators based on threefold symmetric tricarbamate were synthesized and characterized. The tricarbamates with long alkyl chains were able to gelate a wide range of polar and nonpolar organic solvents such as acetonitrile and cyclohexane, generally at concentrations lower than 20 g/L. The best organogel formation was obtained using a threefold symmetric tricarbamate in n-dodecane, in which a sufficiently transparent gel was formed at the critical gelation concentration 1 g/L. Intermolecular hydrogen bonding by the tricarbamate in a nonpolar solvent benzene-d₆ was indicated by ¹H NMR spectra. Its maximum UV absorption was 11 nm higher in chloroform than in n-dodecane, and this red shift indicated increased conjugation between the benzene core and the carbamate substituents, which confirmed a change in its conformation from nonpolar to polar solvent. The self-assembling behavior of the tricarbamate in dilute solutions was investigated by TEM. Fiber-like networks were observed in a large range of solution concentrations.     

Hydrogen bonding in brucinium dihydrogen citrate trihydrate at 130 K

The structure of brucinium dihydrogen citrate trihydrate (systematic name: 2,3‐dimeth­oxy‐10‐oxostrychnidinium dihydrogen citrate trihydrate), C₂₃H₂₇N₂O₄⁺·C₆H₇O₇⁻·3H₂O, has been determined at 130 K. The crystallographic asymmetric unit comprises two brucinium cations, two dihydrogen citrate anions and six water mol­ecules of solvation. The two citrate anions, which are conformationally dissimilar, associate through extensive hydrogen‐bonding inter­actions with the common undulating brucinium cation layer substructures and the water mol­ecules, forming a three‐dimensional framework polymer.     

Synthesis of triazole analogues of the nanaomycin antibiotics using ‘click chemistry’

A series of triazole analogues of the nanaomycin family of antibiotics have been prepared using a ‘click’ dipolar cycloaddition of a naphthalene azide to various alkynes, followed by oxidation to the desired pyranonaphthoquinones.