Exploiting the CH-π interactions in supramolecular hydrogels of aromatic carbohydrate amphiphiles

A novel class of supramolecular hydrogels derived from amino sugars is reported, where the self-assembly of aromatic carbohydrate amphiphiles is driven by CH-π interactions, rather than π–π stacking and H-bonding associated with gelators based on aromatic peptide amphiphiles. Spectroscopic data is provided as evidence for this mode of self-assembly and in silico studies revealed that a combination of CH-π and T-stacking of the fluorenyl groups contribute to the formation of the aggregated structures

Exploiting the phase of NMR signals to carry useful information. Application to the measurement of chemical shifts in aliased 2D spectra

Taking advantage of the phase of nuclear magnetic resonance (NMR) signals to encode NMR information is not easy because of their low precision and their sensitivity to nearby signals. We nevertheless demonstrated that the phase in indirect dimension of 1H–13C heteronuclear single quantum coherence (HSQC) signals could provide carbon chemical shifts at low, but sufficient precision to resolve the ambiguities of the chemical shifts in aliased spectra. This approach, we called phase-encoding of the aliasing order Na (PHANA), only requires inserting a constant delay during the t1 evolution time to obtain spectra where signals with mixed phases can be decoded at the processing to reconstruct full spectra with a 15-fold increase in resolutio

Analysis of the Phases of Signals in Two-Dimensional NMR

Some two-dimensional experiments suffer from ‘phase problems’, meaning that instead of resulting with spectra with absorptive signals, they have a dispersive component causing extensive line broadening and baseline distortions. We shall illustrate how a spectral decomposition determining the phases of the peaks together with the other lineshape parameters makes it possible to reconstruct synthetic spectra containing signals with corrected phases. When applied to the two-pulse COSY spectra, this type of analysis allows one to discriminate the diagonal and the cross peaks according to their phases and reconstruct separate synthetic spectra with pure absorption lineshapes. Similarly, J-resolved spectra producing phase-twisted signals can be analyzed and have their phases corrected. This method can also exploit spectra generated by NMR pulse sequences encoding an NMR parameter as a controlled phase distortion in F1 dimension. In the case of chemical shift encoding, the extracted information were used to resolve the ambiguities caused by spectral aliasing. Finally it can be used to identify and eliminate signal artifacts when their phase properties differ from those of normal signals

Exploring the Role of Solvent on Carbohydrate-Aryl Interactions by Diffusion NMR-Based Studies

Carbohydrate-protein interactions play an important role in many molecular recognition processes. An exquisite combination of multiple factors favors the interaction of the receptor with one specific type of sugar, whereas others are excluded. Stacking CH-aromatic interactions within the binding site provide a relevant contribution to the stabilization of the resulting sugar-protein complex. Being experimentally difficult to detect and analyze, the key CH-pi interaction features have been very often dissected using a variety of techniques and simple model systems. In the present work, diffusion NMR spectroscopy has been employed to separate the components of sugar mixtures in different solvents on the basis of their differential ability to interact through CH-pi interactions with one particular aromatic cosolute in solution. The experimental data show that the properties of the solvent did also influence the diffusion behavior of the sugars present in the mixture, inhibiting or improving their separation. Overall, the results showed that, for the considered monosaccharide derivatives, their diffusion coefficient values and, consequently, their apparent molecular sizes and/or shapes depend on the balance between solute/cosolute as well as solute/solvent interactions. Thus, in certain media and in the presence of the aromatic cosolute, the studied saccharides that are more suited to display CH-pi interactions exhibited a lower diffusion coefficient than the noncomplexing sugars in the mixture. However, when dissolved in another medium, the interaction with the solvent strongly competes with that of the aromatic cosolute