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

Polar interactions with branching xyloses and CH-π interactions define carbohydrate binding module recognition of xyloglucan

Engineering of novel carbohydrate-binding proteins that can be utilized in various biochemical and biotechnical applications would benefit from a deeper understanding of the biochemical interactions that determine protein-carbohydrate specificity. In an effort to understand further the basis for specificity we present the crystal structure of the multi-specific carbohydrate-binding module (CBM) X-2 L110F bound to a branched oligomer of xyloglucan (XXXG). X-2 L110F is an engineered CBM that can recognize xyloglucan, xylans and β-glucans. The structural observations of the present study compared with previously reported structures of X-2 L110F in complex with linear oligomers, show that the π-surface of a phenylalanine, F110, allows for interactions with hydrogen atoms on both linear (xylopentaose and cellopentaose) and branched ligands (XXXG). Furthermore, X-2 L110F is shown to have a relatively flexible binding cleft, as illustrated in binding to XXXG. This branched ligand requires a set of reorientations of protein side chains Q72, N31, and R142, although these residues have previously been determined as important for binding to xylose oligomers by mediating polar contacts. The loss of these polar contacts is compensated for in binding to XXXG by polar interactions mediated by other protein residues, T74, R115, and Y149, which interact mainly with the branching xyloses of the xyloglucan oligomer. Taken together, the present study illustrates in structural detail how CH-π interactions can influence binding specificity and that flexibility is a key feature for the multi-specificity displayed by X-2 L110F, allowing for the accommodation of branched ligands