Cyclobutane scaffold in bolaamphiphiles : Effect of diastereoisomerism and regiochemistry on their surface activity aggregate structure

Cationic bolaamphiphiles have been synthesized starting from meso cis- or chiral trans-1,2-difunctionalized cyclobutane derivatives. They include cis/trans pairs of diastereoisomers, of N- or C-centered bisamides. The goal of this work was to investigate the influence of stereochemistry and regiochemistry on their abilities as surfactants and self-assembly. Very large differences in surface coverage (2-fold), critical micellar concentration (cmc, up to 2 orders of magnitude), and aggregate structure (from lamellae to fibers) for the four molecules are remarkable due to regio- and stereochemistry differences. Computational calculations were carried out to rationalize the experimental findings and a new methodology has been developed to calculate the structure of these bolaamphiphiles at the surface. Although the four surfactants adopt a wicket-like conformation, for N-centered trans, the distance between polar heads is much larger than that for the other three molecules, as suggested by calculations. We have shown that the interplay between the regiochemistry and stereoisomerism, enhanced by rigidity of the cyclobutane ring, affects different physicochemical properties quite differently. That is, the cmc value is mainly governed by stereochemistry, with regiochemistry only modulating this value. On the other hand, regiochemistry definitely governs the morphology of the supramolecular aggregates (i.e., long fibers versus plates or spherical assemblies), with stereochemistry finely modulating their structural parameters. All these results must help in the rational design of new bolaamphiphiles with predictable properties and useful potential applications

Anàlisi de molècules molt eficients per millorar la síntesis orgànica

Mitjançant tècniques experimentals i informàtiques, els autors d'aquest treball van analitzar l'eficiència d'alguns grups de molècules, derivades de compostos de pirazol, usades com a precatalitzadors en els processos de síntesis orgàniques realitzats amb la reacció de Heck.A través de técnicas experimentales e informáticas, los autores de este trabajo analizaron la efectividad de algunos grupos de moléculas, derivados de compuestos de pirazol, usadas como precatalizadores en los procesos de síntesis orgánica realizados mediante la Reacción de Heck.Based on a combined experimental and computacional study, authors of this work analized the effectiveness of some groups of molecules derivated from pirazol, used as precatalists in organic synthesis developed by Heck reactions

Càlculs mecano-quàntics per entendre la síntesi peptídica

Investigadors del Departament de Química de la UAB han publicat un treball de recerca que permet conèixer millor com funciona el mecanisme de síntesi dels pèptids en els ribosomes. Per a aquesta recerca els científics de la UAB han utilitzant càlculs mecano-quàntics i un model del ribosoma que ha permès arribar a resultats que aporten noves idees sobre com funciona la formació dels pèptids i que, a la vegada, concorden amb els darrers resultats experimentals obtinguts.Investigadores del Departamento de Química de la UAB han publicado un trabajo de investigación que permite conocer mejor cómo funciona el mecanismo de síntesis de los péptidos en los ribosomas. Para esta investigación los científicos de la UAB han utilizando cálculos mecano- cuánticos y un modelo del ribosoma que ha permitido alcanzar resultados que aportan nuevas ideas sobre cómo funciona la formación de los péptidos y que, a la vez, concuerdan con los últimos resultados experimentales obtenidos

Foldamers of β-peptides : conformational preference of peptides formed by rigid building blocks : The first MI-IR spectra of a triamide nanosystem

To determine local chirality driven conformational preferences of small aminocyclobutane-1-carboxylic acid derivatives, X-(ACBA) n -Y, their matrix-isolation IR spectra were recorded and analyzed. For the very first time model systems of this kind were deposited in a frozen (~10 K) noble gas matrix to reduce line width and thus, the recorded sharp vibrational lines were analyzed in details. For cis-(S,R)-1 monomer two “zigzag” conformers composed of either a six or an eight-membered H-bonded pseudo ring was identified. For trans-(S,S)-2 stereoisomer a zigzag of an eight-membered pseudo ring and a helical building unit were determined. Both findings are fully consistent with our computational results, even though the relative conformational ratios were found to vary with respect to measurements. For the dimers (S,R,S,S)-3 and (S,S,S,R)-4 as many as four different cis,trans and three different trans,cis conformers were localized in their matrix-isolation IR (MI-IR) spectra. These foldamers not only agree with the previous computational and NMR results, but also unambiguously show for the first time the presence of a structure made of a cis,trans conformer which links a “zigzag” and a helical foldamer via a bifurcated H-bond. The present work underlines the importance of MI-IR spectroscopy, applied for the first time for triamides to analyze the conformational pool of small biomolecules. We have shown that the local chirality of a β-amino acid can fully control its backbone folding preferences. Unlike proteogenic α-peptides, β- and especially (ACBA) n type oligopeptides could thus be used to rationally design and influence foldamer’s structural preferences

Electron hole formation in acidic zeolite catalysts

The formation of an electron hole on an AlO4H center of the H-ZSM-5 zeolite has been studied by a hybrid quantum mechanics/shell-model ion-pair potential approach. The Becke-3-Lee-Yang-Parr (B3LYP) and Becke-Half&Half-Lee-Yang-Parr (BHLYP) hybrid density functionals yield electron holes of different nature, a delocalized hole for B3LYP and a hole localized on one oxygen atom for BHLYP. Comparison with coupled cluster calculations including single and double substitutions and with perturbative treatment of triple substitutions CCSD(T) and with experimental data for similar systems indicate that the localized description obtained with BHLYP is more accurate. Generation of the electron hole produces a substantial geometry relaxation, in particular an elongation of the Al-O distance to the oxygen atom with the unpaired electron. The zeolite framework stabilizes the positive charge by long-range effects. Our best estimates for the vertical and adiabatic ionization energies are 9.6–10.1 and 8.4–8.9 eV, respectively. Calculations for silicalite, the all-silica form of ZSM-5, also yield a localized electron hole, but the energy cost of the process is larger by 0.6–0.7 eV. The deprotonation energy of H-ZSM-5 is found to decrease from 12.86 to 11.40 eV upon electron hole formationPeer Reviewe