Verónica I. Dodero

Stereoselective hydrostannation of substituted alkynes with trineophyltin hydride

Hydrostannation of mono- and disubstituted alkynes with trineophyltin hydride (1) leads to vinylstannanes in good to excellent yields, the configuration of the products depending on the reaction conditions. Thus, whereas hydrostannation under radical conditions leads stereoselectively to only one of the two possible products corresponding to an anti addition in 60–99% yield, the additions catalyzed by bis(triphenylphosphine)palladium dichloride gave mixtures of the syn adducts (60–79% yield). Full 1H-, 13C-, and 119Sn-NMR as well as mass spectra data of the organotin adducts are given.

Circular dichroism and electron microscopy studies in vitro of 33-mer gliadin peptide revealed secondary structure transition and supramolecular organization.

Gliadin, a protein present in wheat, rye, and barley, undergoes incomplete enzymatic degradation during digestion, producing an immunogenic 33-mer peptide, LQLQPF(PQPQLPY)3 PQPQPF. The special features of 33-mer that provoke a break in its tolerance leading to gliadin sensitivity and celiac disease remains elusive. Herein, it is reported that 33-mer gliadin peptide was not only able to fold into polyproline II secondary structure but also depending on concentration resulted in conformational transition and self-assembly under aqueous condition, pH 7.0. A 33-mer dimer is presented as one initial possible step in the self-assembling process obtained by partial electrostatics charge distribution calculation and molecular dynamics. In addition, electron microscopy experiments revealed supramolecular organization of 33-mer into colloidal nanospheres. In the presence of 1 mM sodium citrate, 1 mM sodium borate, 1 mM sodium phosphate buffer, 15 mM NaCl, the nanospheres were stabilized, whereas in water, a linear organization and formation of fibrils were observed. It is hypothesized that the self-assembling process could be the result of the combination of hydrophobic effect, intramolecular hydrogen bonding, and electrostatic complementarity due to 33-mers high content of proline and glutamine amino acids and its calculated nonionic amphiphilic character. Although, performed in vitro, these experiments have revealed new features of the 33-mer gliadin peptide that could represent an important and unprecedented event in the early stage of 33-mer interaction with the gut mucosa prior to onset of inflammation. Moreover, these findings may open new perspectives for the understanding and treatment of gliadin intolerance disorders.

Rheological properties of ovalbumin hydrogels as affected by surfactants addition

The gel properties of ovalbumin mixtures with three different surfactants (sodium perfluorooctanoate, sodium octanoate and sodium dodecanoate) have been studied by rheological techniques. The gel elasticities were determined as a function of surfactant concentration and surfactant type. The fractal dimension of the formed structures was evaluated from plots of storage modulus against surfactant concentration. The role of electrostatic, hydrophobic and disulfide SS interactions in these systems has been demonstrated to be the predominant. The viscosity of these structures tends to increase with surfactant concentration, except for the fluorinated one. Unfolded ovalbumin molecules tend to form fibrillar structures that tend to increase with surfactant concentration, except for the fluorinated one. This fact has been related to the particular nature of this molecule.

Self-organization of gliadin in aqueous media under physiological digestive pHs

Here we showed that gliadin, a complex protein system related to celiac disease and other human diseases, is spontaneously self-organized in a very dilute solution at pH 3.0 and 7.0 in water under low ionic strength (10mM NaCl). The spontaneous self-organization at pH 3.0 increases the apparent solubility due to the formation of finite sized aggregates, such as those formed in the micellization of amphiphilic molecules. Switching the pH from 3.0 to 7.0 lead to a phase separation, however part of the nano-particles are stable remaining disperse in water after centrifugation. Also, beside the pH change led to changes in protein composition and concentration, we determined that the secondary structure of both system is the same. Moreover, Tyrs are slightly more buried and Trps are slightly more exposed to water at pH 7.0 than those at pH 3.0. Electron microscopy techniques showed that both gliadin systems are composed of nanostructures and in the case of pH 7.0 amorphous microaggregates were found, too. Only nanostructures at pH 3.0 showed a micromolar binding affinity to Nile red probe, suggesting the presence of accessible hydrophobic patches which are not more accessible at pH 7.0. All our results suggest that gliadin is able to self-organized at pH 3.0 forming protein micelles type nanostructures (ζ=+13, 42 ± 1.55 mV), meanwhile at 7.0 the decrease of superficial charge to ζ of +4, 78 ± 0.48 mV led to the formation of stable colloidal nanoparticles, unable to interact with Nile red probe. Our findings may open new perspectives for the understanding of gliadin ability to avoid proteolysis, to reach and cross the intestinal lumen and to trigger different immunological disorders.

Development of a Nonionic Azobenzene Amphiphile for Remote Photocontrol of a Model Biomembrane

We report the synthesis and characterization of a simple nonionic azoamphiphile, C12OazoE3OH, which behaves as an optically controlled molecule alone and in a biomembrane environment. First, Langmuir monolayer and Brewster angle microscopy (BAM) experiments showed that pure C12OazoE3OH enriched in the (E) isomer was able to form solidlike mesophase even at low surface pressure associated with supramolecular organization of the azobenzene derivative at the interface. On the other hand, pure C12OazoE3OH enriched in the (Z) isomer formed a less solidlike monolayer due to the bent geometry around the azobenzene moiety. Second, C12OazoE3OH is well-mixed in a biological membrane model, Lipoid s75 (up to 20%mol), and photoisomerization among the lipids proceeded smoothly depending on light conditions. It is proposed that the cross-sectional area of the hydroxyl triethylenglycol head of C12OazoE3OH inhibits azobenzenes H-aggregation in the model membrane; thus, the tails conformation change due to photoisomerization is transferred efficiently to the lipid membrane. We showed that the lipid membrane effectively senses the azobenzene geometrical change photomodulating some properties, like compressibility modulus, transition temperature, and morphology. In addition, photomodulation proceeds with a color change from yellow to orange, providing the possibility to externally monitor the system. Finally, Gibbs monolayers showed that C12OazoE3OH is able to penetrate the highly packing biomembrane model; thus, C12OazoE3OH might be used as photoswitchable molecular probe in real systems.

Translational Chemistry Meets Gluten-Related Disorders

Abstract Gluten‐related disorders are a complex group of diseases that involve the activation of the immune system triggered by the ingestion of gluten. Among these, celiac disease, with a prevalence of 1 %, is the most investigated, but recently, a new pathology, named nonceliac gluten sensitivity, was reported with a general prevalence of 7 %. Finally, there other less‐prevalent gluten‐related diseases such as wheat allergy, gluten ataxia, and dermatitis herpetiformis (with an overall prevalence of less than 0.1 %). As mentioned, the common molecular trigger is gluten, a complex mixture of storage proteins present in wheat, barley, and a variety of oats that are not fully degraded by humans. The most‐studied protein related to disease is gliadin, present in wheat, which possesses in its sequence many pathological fragments. Despite a lot of effort to treat these disorders, the only effective method is a long‐life gluten‐free diet. This Review summarizes the actual knowledge of gluten‐related disorders from a translational chemistry point of view. We discuss what is currently known from the literature about the interaction of gluten with the gut and the critical host responses it evokes and, finally, connect them to our current and novel molecular understanding of the supramolecular organization of gliadin and the 33‐mer gliadin peptide fragment under physiological conditions.

Large Supramolecular Structures of 33-mer Gliadin Peptide Activate Toll-like Receptors in Macrophages

Gliadin, an immunogenic protein present in wheat, is not fully degraded by humans and after the normal gastric and pancreatic digestion, the immunodominant 33-mer gliadin peptide remains unprocessed. The 33-mer gliadin peptide is found in human faeces and urine, proving not only its proteolytic resistance in vivo but more importantly its transport through the entire human body. Here, we demonstrate that 33-mer supramolecular structures larger than 220 nm induce the overexpression of nuclear factor kappa B (NF-κB) via a specific Toll-like Receptor (TLR) 2 and (TLR) 4 dependent pathway and the secretion of pro-inflammatory cytokines such as IP-10/CXCL10 and TNF-α. Using helium ion microscopy, we elucidated the initial stages of oligomerisation of 33-mer gliadin peptide, showing that rod-like oligomers are nucleation sites for protofilament formation. The relevance of the 33-mer supramolecular structures in the early stages of the disease is paving new perspectives in the understanding of gluten-related disorders.

Insights into gliadin supramolecular organization at digestive pH 3.0

Alpha-gliadin is a highly immunogenic protein from wheat, which is associated with many human diseases, like celiac disease and non-celiac gluten sensitivity. Because of that, gliadin solution is subject to intense biomedical research. However, the physicochemical nature of the employed gliadin solution at physiological pH is not understood. Herein, we present a supramolecular evaluation of the alpha-gliadin protein in water at pH 3.0 by dynamic light scattering (DLS), cryo-transmission electron microscopy (cryo-TEM) and small-angle-.X-ray scattering (SAXS). We report that at 0.5 wt% concentration (0.1 mg/ml), gliadin is already a colloidal polydisperse system with an average hydrodynamic radius of 30 ± 10 nm. By cryo-TEM, we detected mainly large clusters. However, it was possible to visualise for the first time prolate oligomers of around 68 nm and 103 nm, minor and major axis, respectively. SAXS experiments support the existence of prolate/rod-like structures. At 1.5 wt% concentration gliadin dimers, small oligomers and large clusters coexist. The radius of gyration (Rg1) of gliadin dimer is 5.72 ± 0.23 nm with a dimer cross-section (Rc) of 1.63 nm, and an average length of around 19 nm, this suggests that gliadin dimers are formed longitudinally. Finally, our alpha-gliadin 3D model, obtained by ab initio prediction and analysed by molecular dynamics (MD), predicts that two surfaces prone to aggregation are exposed to the solvent, at the C-terminus. We hypothesise that this region may be involved in the dimerisation process of alpha-gliadin.

Stereoselective Synthesis of 8-Trialkylstannylmenthols

Trialkyltin menthones of type 2 are obtained selectively by 1,4-addition of trialkylstannyl lithium to (-)-pulegone. Reduction of 2 with borane in THF using as catalyst the reagent prepared from borane and (S)-valinol gave a mixture of the corresponding trialkyltin alcohols 3 (Me: 84%; n-Bu: 90,6%) and 4 (Me: 16% and n-Bu: 9,4%).

Synthesis of Ethylenic and Acetylenic Triorganotins with Bulky Organic Ligands

The syntheses of trineophyl- (1a) and tri-(-)-menthylstannyl phenylacetylene (1b) as well as that of (E)-1-trineophylestannyl-2-phenylethene (2) and (E)-1-trineophylstannyl-1,2-diphenylethene (3) are described. The hydrostannation of 1a with an excess of trimethyltin hydride led to 1,1,1-tris(trimethyltin)-2-phenylethane (4) and/or 1,1-bis(trimethyltin)-2-phenylethene (5) depending on the reaction conditions.