Gelation process followed by NMR

Journal cover: Organic & Biomolecular ChemistryLow-molecular-weight gelators consisting of hybrid cyclobutane-based peptides
by Sergi Celis, Pau Nolis, Ona Illa, Vicenç Branchadell, Rosa M. Ortuño, Organic & Biomolecular Chemistry 2013, 11, 2839 DOI: 10.1039/c3ob27347d

Some hybrid tetrapeptides consisting of (1R,2S)-2-aminocyclobutane-1-carboxylic acid and glycine, β-alanine, or γ-aminobutyric acid (GABA) joined in alternation, compounds 1–3, respectively, have been investigated to gain information on the non-covalent interactions responsible for their self-assembly to form ordered aggregates, as well as on parameters such as their morphology and size. All three peptides formed nice gels in many organic solvents and significant difference in their behaviour was not observed. Scanning electron microscopy (SEM) and circular dichroism (CD) pointed out that peptide 1, which contains the shortest C2 linear residue, presented the most defined fibril network and afforded nanoscale helical aggregates. Tetrapeptide 3, with C4 linear residues in its structure, also showed bundles of fibres whereas a homogeneous spherulitic network was observed for tetrapeptide 2, with a C3 spacer between cyclobutane residues. Computational calculations for 1 allowed us to model the self-assembly of the molecules and suggested a head-to-head arrangement to give helical structures corresponding to hydrogen-bonded single chains. These features were corroborated by a high-resolution NMR spectroscopy study of the dynamics of the gelation process in toluene-d8 which evidenced that molecules self-assemble to afford ordered aggregates with a supramolecular chirality.

Gelation process monitored by variable-temperature 1H NMR spectroscopy experiments in 30 mM solutions of 1 in toluene-d8. A 400 MHz Bruker Avance III spectrometer equipped with a cooling unit BCU-Xtreme was used. (a) NH region from 5.6 ppm to 7.3 ppm. (b) Aliphatic region from 2.8 ppm to 5.2 ppm.

Graphical abstract: Low-molecular-weight gelators consisting of hybrid cyclobutane-based peptides

CLIP-HSQMBC: Very easy, direct and accurate measurement of nJ(CH) in organic molecules and natural products

CLIP-HSQMBC: Easy measurement of small proton-carbon coupling constants in organic molecules, by Josep Saurí, Teodor Parella and Juan F. Espinosa; Org. Biomol. Chem. (2013). DOI:10.1039/C3OB40675J

A user-friendly 2D NMR approach denoted as CLIP-HSQMBC is proposed for the very easy, direct and accurate measurement of long-range proton-carbon coupling constants in organic molecules and natural products. The J value can be extracted directly from the analysis of resolved in-phase 1H multiplets that show an additional splitting arising from the proton-carbon coupling. In cases of unresolved peaks, a simple fitting analysis using the internal satellite lines as reference is performed. Addition of a spin-lock period results in a CLIP-HSQMBC-TOCSY experiment that is suitable for the measurement of very small coupling values or to observe correlations from overlapped resonances.

Graphical Abstract   Pulse Program Code for Bruker:

NMR confirms cysteine labelling with SFB in peptides

issue 1 - RSC Advances_2012.indd“Efficient cysteine labelling of peptides with N-succinimidyl 4-[18F]fluorobenzoate: stability study and in vivo biodistribution in rats by positron emission tomography ( PET)” by Santiago Rojas, Pau Nolis, Juan D. Gispert, Jan Spengler, Fernando Albericio, José R. Herance, Sergio Abad.  RSC Advances. 2013. DOI: 10.1039/C3RA40754C

A rapid and high-yielding cysteine labelling of peptides has been observed with the specific labelling agent for amines, N-succinimidyl 4-[18F]fluorobenzoate ([18F]SFB). Interestingly, NMR demonstrates that conjugation of the 4-fluorobenzoyl (FB) moiety is selectively achieved through a cysteine (Cys) thiol of the peptides with high yield (>80%) in short time (<5 min), while for a Cys amino acid derivative, a slow process has been observed. The large reactivity of these peptides for the conjugation reaction is rationalised on the basis of electrostatic interactions between the sulfhydril and the guanidinium groups of the amino acid side chains. Moreover, the stability of these novel conjugates and the biodistribution of the radiolabelled dodecapeptide by positron emission tomography (PET) in rats has been examined.

rat

J-selHSQMBC: Simultaneous measurement of J(HH) and two different nJ(CH) using IPAP, J-resolved and E.COSY principles

cover_MRC“Simultaneous measurement of J(HH) and two different nJ(CH) coupling constants from a single multiply-edited 2D cross-peak”, by Josep Saurí and Teodor ParellaMagn. Reson. Chem. 201351, 397-402. DOI: 10.1002/mrc.3960

Three different J-editing methods (IPAP, E.COSY and J-resolved) are implemented in a single NMR experiment to provide spin-state-edited 2D cross-peaks from which simultaneous measurement of different homonuclear and heteronuclear coupling constants can be performed. A new J-selHSQMBC-IPAP experiment is proposed for the independent measurement of two different nJ(CH) coupling constants along the F2 and F1 dimensions of the same 2D cross-peak. In addition, the E.COSY pattern provides additional information about the magnitude and relative sign between J(HH) and nJ(CH) coupling constants.

Graphical abstract

Pulse Program Code for Bruker: J-selHSQMBC

Metabolic responses of Quercus ilex seedlings to wounding analysed with nuclear magnetic resonance profiling

Plant Biology“Metabolomic responses of Quercus ilex seedlings to wounding simulating herbivory” By Jordi Sardans, Albert Gargallo-Garriga, Míriam Pérez-Trujillo, Teodor Parella, Roger Seco, Iolanda Filella, Josep  Peñuelas. Plant biology. April 2013. DOI: 10.1111/plb.12032.

Plants defense themselves against herbivory at several levels. One of these levels is the synthesis of inducible chemical defenses. By using NMR metabolomic technique we studied the metabolic changes of plant leaves after a wounding treatment simulating herbivore attack in the Mediterranean sclerophyllous tree Quercus ilex. Continue reading

New biweekly seminars

stlenc-headsFew weeks ago I proposed my research colleagues at the NMR Service to have regular seminars about our research activities.

The proposal was enthusiastically welcomed and after some discussion we agreed on having a 20-minutes seminar every two weeks at 10am on Thursdays, and that PhD students would be giving talks more frequently than senior staff.

Continue reading

Conformational Bias of Several Types of γ-Peptides

EurJoc“The Role of the Chiral cis-1,3-Disubstituted 2,2-Dimethylcyclobutane Motif in the Conformational Bias of Several Types of γ-Peptides”  by Jordi Aguilera, Juan A. Cobos, Raquel Gutiérrez-Abad, Carles Acosta, Pau Nolis, Ona Illa, Rosa M. Ortuño. Eur.  J. Org. Chem. 2013 (early view). DOI: 10.1002/ejoc.201300066

Three series of new γ-peptides have been synthesized by starting from conveniently protected cis-3-amino-2,2-dimethylcyclobutane-1-carboxylic acid derivatives. The first series is constructed with only one enantiomer of this γ-amino acid, whereas in the second one both enantiomeric cyclobutane residues are joined in alternating fashion. Continue reading

8th Workshop on Magnetic Resonance Spectroscopy and Imaging (MRI/MRS) Applied to Laboratory Animals

Dates:  10th to 13th June 2013

Organized by the SeRMN of the Autonomous University of Barcelona (UAB).

LimbAngio_3DTOFThis workshop combines a comprehensive series of lectures on the technology of Magnetic resonance spectroscopy and imaging (MRS/MRI) with hands-on laboratory sessions to provide practical demonstrations of key concepts and procedures for preclinical studies.

Whether you are considering MRI as a research tool in your lab or just would like to learn more about MRI, this workshop addresses practical aspects of experimental MRI with laboratory animals and provide valuable hands-on experience on a 7 Tesla Bruker BioSpec spectrometer.

Number of participants will be limited to 4.

For the registration, please fill the Registration Form and email it to silvia.lope@uab.es (registration deadline ends May 27st)

See Workshop Brochure for more information or contact Dra. Silvia Lope.