Melittin-solid phospholipid mixed films trigger amyloid-like nano-fibril arrangements at air-water interface.

We used the Langmuir monolayers technique to study the surface properties of melittin toxin mixed with either liquid-condensed DSPC or liquid-expanded POPC phospholipids. Pure melittin peptide forms stable insoluble monolayers at the air-water interface without interacting with Thioflavin T (Th-T), a sensitive probe to detect protein amyloid formation. When melittin peptide is mixed with DSPC lipid at 50 % of peptide area proportion at the surface, we observed the formation of fibril-like structures detected by Brewster angle microscopy (BAM), but they were not observable with POPC. The nano-structures in the melittin-DSPC mixtures became Th-T positive labeling when the arrangement was observed with fluorescence microscopy. In this condition, Th-T undergoes an unexpected shift in the typical emission wavelength of this amyloid marker when a 2D fluorescence analysis is conducted. Even when reflectivity analysis of BAM imaging evidenced that these structures would correspond to the DSPC lipid component of the mixture, the interpretation of ATR-FTIR and Th-T data suggested that both components were involved in a new lipid-peptide rearrangement. These nano-fibril arrangements were also evidenced by scanning electron and atomic force microscopy when the films were transferred to a mica support. The fibril formation was not detected when melittin was mixed with the liquid-expanded POPC lipid. We postulated that DSPC lipids can dynamically trigger the process of amyloid-like nano-arrangement formation at the interface. This process is favored by the relative peptide content, the quality of the interfacial environment, and the physical state of the lipid at the surface.

Stitching together a nm thick peptide-based semiconductor sheet using UV light.

Langmuir monolayer allows for a two-dimensional nano-scale organization of amphiphilic molecules. We have adapted this technique to measure lateral and transverse conductivity in confined peptide nanosheets for the first time. We reported that two retro-isomers amphipathic peptides form stable monolayers showing a semiconductor-like behavior. Both peptides exhibit the same hydrophobicity and surface stability. They differ in the lateral conductivity and current-voltage due to the asymmetric peptide bond backbone orientation at the interface. Both peptides contain several tyrosines allowing the lateral crosslinking in neighboring molecules induced by UVB. UVB-light induces changes in the lateral conductivity and current-voltage behavior as well as monolayer heterogeneity monitored by Brewster Angle Microscopy. The semiconductor properties depend on the peptide bond backbone orientation and tyrosine crosslinking. Our results indicate that one may design extended nano-sheets with particular electric properties, reminiscent of semiconductors. We propose to exploit such properties for biosensing and neural interfaces.

Aß-Amyloid Fibrils Are Self-Triggered by the Interfacial Lipid Environment and Low Peptide Content.

We studied the surface properties of Aß(1-40) amyloid peptides mixed with 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) (liquid state) or 1,2-disteraoyl-phosphatidylcholine (DSPC) (solid state) phospholipids by using nanostructured lipid/peptide films (Langmuir monolayers). Pure Aß(1-40) amyloid peptides form insoluble monolayers without forming fibril-like structures. In a lipid environment [phospholipid/Aß(1-40) peptide mixtures], we observed that both miscibility and stability of the films depend on the peptide content. At low Aß(1-40) amyloid peptide proportion (from 2.5 to 10% of peptide area proportion), we observed the formation of a fibril-like structure when mixed only with POPC lipids. The stability acquired by these mixed films is within 20-35 mN·m-1 compatible with the equivalent surface pressure postulated for natural biomembranes. Fibrils are clearly evidenced directly from the monolayers by using Brewster angle microscopy. The so-called nanostructured fibrils are thioflavin T positive when observed by fluorescence microscopy. The amyloid fibril network at the surface was also evidenced by atomic force microscopy when the films are transferred onto a mica support. Aß(1-40) amyloid mixed with the solid DSPC lipid showed an immiscible behavior in all peptide proportions without fibril formation. We postulated that the amyloid fibrillogenesis at the membrane can be dynamically nano-self-triggered at the surface by the quality of the interfacial environment, that is, the physical state of the water-lipid interface and the relative content of amyloid protein present at the interface.

Introducción a la resonancia magnética nuclear biomédica

Presentación. Prefacio. Principios básicos de la resonancia magnética nuclear. Relajación: T1 tiempo de relajación espín-retítulo. Relajación: T1, tiempo de relajación espín-espín. Espectroscopia de RMN de alta resolución. Formación de imágenes. Conceptos avanzados. Seguridad de pacientes y personal. Componentes de la imagen por RMN. Densidad de protones T1 y T2 imágenes por computador. La importancia del movimiento del agua en la RMN biomédica. Contraste y relación contraste-ruido en la formación de imágenes por resonancia magnética. El flujo en la formación de imágenes por resonancia nuclear. Aplicaciones en la biomedicina. Formación de imágenes del cerebro por resonancia magnética. Formación de imágenes de la espina dorsal por resonancia magnética. Formación de imágenes cardiovasculares: introducción. Formación de imágenes cardiovasculares utilizando resonancia magnética en el hombre. Formación de imágenes del abdomen por resonancia magnética. Formación de imágenes en el cáncer por resonancia magnética. Formación de imágenes en el cáncer por resonancia magnética. Introducción a los principios e instrumentación de la resonancia magnética metabólica

Introducción a la resonancia magnética nuclear biomédica

Presentación. Prefacio. Principios básicos de la resonancia magnética nuclear. Relajación: T1 tiempo de relajación espín-retítulo. Relajación: T1, tiempo de relajación espín-espín. Espectroscopia de RMN de alta resolución. Formación de imágenes. Conceptos avanzados. Seguridad de pacientes y personal. Componentes de la imagen por RMN. Densidad de protones T1 y T2 imágenes por computador. La importancia del movimiento del agua en la RMN biomédica. Contraste y relación contraste-ruido en la formación de imágenes por resonancia magnética. El flujo en la formación de imágenes por resonancia nuclear. Aplicaciones en la biomedicina. Formación de imágenes del cerebro por resonancia magnética. Formación de imágenes de la espina dorsal por resonancia magnética. Formación de imágenes cardiovasculares: introducción. Formación de imágenes cardiovasculares utilizando resonancia magnética en el hombre. Formación de imágenes del abdomen por resonancia magnética. Formación de imágenes en el cáncer por resonancia magnética. Formación de imágenes en el cáncer por resonancia magnética. Introducción a los principios e instrumentación de la resonancia magnética metabólica

Magnetic resonance imaging: avantages of the multiple spin echo approach

In nuclear magnetic resonance imaging (MRI) the spin echo sequence with multiple echoes provides most of the information necessary to receive both best contrast and best spatial resolution. The principles and advantages of this imaging method are explained in this paper