Química Orgánica
http://hdl.handle.net/10347/2927
2024-03-19T09:11:38Zβ-Peptides incorporating polyhydroxylated cyclohexane β-amino acid: synthesis and conformational study
http://hdl.handle.net/10347/33219
β-Peptides incorporating polyhydroxylated cyclohexane β-amino acid: synthesis and conformational study
Reza Ramos, David; Balo Becerra, Rosalino; Otero, José M.; Fletcher, Ai M.; García Fandiño, Rebeca; Sánchez-Pedregal, Víctor M.; Davies, Stephen G.; Estévez Cabanas, Ramón José; Estévez Cabanas, Juan Carlos
We describe the synthesis of trihydroxylated cyclohexane β-amino acids from (−)-shikimic acid, in their cis and trans configuration, and the incorporation of the trans isomer into a trans-2-aminocyclohexanecarboxylic acid peptide chain. Subsequently, the hydroxyl groups were partially or totally deprotected. The structural study of the new peptides by FTIR, CD, solution NMR and DFT calculations revealed that they all fold into a 14-helix secondary structure, similarly to the homooligomer of trans-2-aminocyclohexanecarboxylic acid. This means that the high degree of substitution of the cyclohexane ring of the new residue is compatible with the adoption of a stable helical secondary structure and opens opportunities for the design of more elaborate peptidic foldamers with oriented polar substituents at selected positions of the cycloalkane residues.
2023-01-01T00:00:00ZIntroducing Design Strategies to Preserve N‐Heterocycles Throughout the On‐Surface Synthesis of Graphene Nanostructures
http://hdl.handle.net/10347/33146
Introducing Design Strategies to Preserve N‐Heterocycles Throughout the On‐Surface Synthesis of Graphene Nanostructures
Tenorio, María; Moreno, César; Vilas Varela, Manuel; Castro Esteban, Jesús; Febrer, Pol; Pruneda, Miguel; Peña Gil, Diego; Mugarza, Aitor
Despite the impressive advances in the synthesis of atomically precise graphene nanostructures witnessed during the last decade, advancing in compositional complexity faces major challenges. The concept of introducing the desired functional groups or dopants in the molecular precursor often fails due to their lack of stability during the reaction path. Here, a study on the stability of different pyridine and pyrimidine moieties during the on-surface synthesis of graphene nanoribbons on Au(111) is presented. Combining bond-resolved scanning tunneling microscopy with X-ray photoelectron spectroscopy, the thermal evolution of the nitrogen dopants throughout the whole reaction sequence is tracked. A comparative experimental and ab initio electronic characterization confirms the presence of dopants in the final structures, revealing also that the pyridinic nitrogen leads to a significant band downshift. The results demonstrate that, by using synthetic strategies to lower the reaction temperatures, one can preserve specific N-heterocycles throughout all the reaction steps of the synthesis of graphene nanoribbons and beyond the interibbon coupling reaction that leads to nanoporous graphene
2023-01-01T00:00:00ZP/M Macromolecular Switch Based on Conformational Control Exerted by an Achiral Side Chain within an Axially Chiral Locked Pendant
http://hdl.handle.net/10347/33032
P/M Macromolecular Switch Based on Conformational Control Exerted by an Achiral Side Chain within an Axially Chiral Locked Pendant
Lago Silva, María; Cid, María Magdalena; Quiñoá Cabana, Emilio; Freire Iribarne, Félix Manuel
Molecular switches, supramolecular chemistry, and polymers can be combined to create stimuli-responsive multichiral materials. Therefore, by acting on the extended/bent conformational composition of an achiral arm, it is possible to create a macromolecular gear, where different supramolecular interactions can be activated/deactivated to control the helical sense of a polymer containing up to five different chiral axial motifs. For this, a chiral allene with a flexible achiral arm was introduced as a pendant in poly(phenylacetylene). Through flexible arm control between extended and bent conformations, it is possible to selectively induce either a P or M helical sense in the polymer, while the relative spatial distribution of the substituents in the allene remains unaltered in two perpendicular planes (configurationally locked). These results show that complex dynamic multichiral materials can be obtained by the polymerization of appropriate monomers that combine chirality, switching properties, and the ability to generate chiral supramolecular assemblies.
2023-01-01T00:00:00ZMicellization of dodecyldimethyl-N-2-phenoxyethylammonium bromide (domiphen) in aqueous solution. Comparison with other alkyl ammonium surfactants
http://hdl.handle.net/10347/33006
Micellization of dodecyldimethyl-N-2-phenoxyethylammonium bromide (domiphen) in aqueous solution. Comparison with other alkyl ammonium surfactants
Vázquez-Gómez, Silvia; Vázquez Tato, María del Pilar; Seijas Vázquez, Julio Antonio; Meijide, Francisco; Vázquez Tato, José; Fraga López, Francisco José
Dodecyldimethyl-N-2-phenoxyethylammonium bromide (domiphen) is a quaternary ammonium salt which has been used in oral hygiene long time ago. The published studies on its characterization as surfactant evidence several contradictory results. In this paper, measurements of surface tension, conductimetry, fluorescence and mainly isotermal titration calorimetry (ITC) have been performed at different temperatures. The enthalpy of demicellization varies linearly with temperature in the interval 15–45 °C, from which a value of 704 ± 39 J mol−1K−1 in water has been determined for the change of heat capacity. The obtained results are compared with published values for alkyltrimethylammonium bromides with different alkyl chain lengths (CnTAB). For instance, its critical micelle concentration, cmc, is almost ten times lower than that of C12TAB. The substitution of one methyl group by the phenoxyethyl has a strong influence on the behavior of domiphen making it equivalent to a CnTAB surfactant with n = 15–19 methylene groups, the number depending on the studied property. From ITC an average aggregation number of 45 ± 3 is obtained in good agreement with the one from fluorescence quenching of pyrene equal to 44.5–47.6. From the analysis of specific conductivity, the fraction of bound counterions to micelles was obtained, the values linearly decreasing with temperature. Below cmc domiphen behaves as a strong 1:1 electrolyte without association of monomers. Other themodynamic parameters have also been obtained. The fjord and reef hydration models are used to propose a structure for domiphen micelles.
2023-01-01T00:00:00Z