Liquid crystalline order in mucus

Mucus plays an exceptionally wide range of important biological roles. It operates as a protective, exchange, and transport medium in the digestive, respiratory, and reproductive systems of humans and other vertebrates. Mucus is a polymer hydrogel. It is secreted as discrete packages (secretory granules) by specialized secretory cells. Mucus hydrogel is stored in a condensed state inside the secretory granules. Depending upon the architecture of their constituent macromolecules and on the composition of the solvent, polymer gels can form liquid crystalline microstructures, with orientational order being exhibited over optically resolvable distances. Individual mucin molecules consist of alternating rigid segments (heavily glycosylated; hydrophilic) and flexible segments (nonglycosylated; hydrophobic). Polymer molecules consisting of rigid units linked by flexible spacers are frequently associated with liquid crystalline behavior, which again raises the possibility that mucus could form anisotropic fluid phases. Suggestions that mucins may be self-associating in dilute solution have previously been challenged on the basis of sedimentation-equilibrium studies performed on mucus in which potential sites of association were competitively blocked with inhibitors. However, the formation of stable liquid crystalline phases does not depend on the existence of inter- or intramolecular associations; these phases can form on the basis of steric considerations alone.     

A library approach to the generation of bisubstrate analogue sulfotransferase inhibitors

[reaction: see text]. A library of potential bisubstrate analogue inhibitors (1) targeting sulfotransferase enzymes was generated by the chemoselective ligation of the PAPS mimic 2 with a panel of 447 aldehydes. Preliminary screening has identified compounds that inhibit estrogen sulfotransferase (EST), an enzyme relevant to breast cancer.     

GFP immunogold staining, from light to electron microscopy, in mammalian cells

GFP has emerged as an important reporter for monitoring gene expression, protein localization, cell transformation and cell lineage. The development of GFP as a marker in many different biological systems has emphasized the need to image GFP at high resolution. GFP immunogold labeling with colloidal gold particles becomes essential for electron microscopy (EM) ultrastructural detection. Because of the small size, colloidal gold particles require silver enhancement, a procedure to increase the size of the particle as well as gold toning to stabilize the silver layer. GFP preembedding immunogold staining enables high quality cellular-ultrastructural EM analysis mainly for two reasons, on one hand it allows adequate fixation for EM analysis maintaining GFP antigenicity, on the other hand it also enables the epoxy resins inclusion after immunogold staining. Both of them help to preserve better the ultrastructure. However GFP immunogold staining presents some drawbacks, such as the progressive decrease in immunogold labeling with tissue depth. Special attention must be taken when using GFP-tagged protein, since the fusion could interfere with their localization and function. In this review we provide a detailed protocol of the GFP immunogold staining, their main applications for EM and possible troubles.     

Complex absorbing potentials for stark resonances

In this work, we study the problem in calculation of Stark resonances by using complex absorbing potentials (CAPs), and its solutions. The motivation of using CAPs for calculating Stark resonances stems from the fact that CAPs can be easily inserted to a large variety of available codes for calculating the electronic structure of molecules and atoms. Our conclusion is that the appropriate CAPs for studying ac/dc Stark resonances are those that are associated with smooth-exterior-scaling (SES) transformations, which rotate the spatial contour of integration into the complex plane. The performance of SES-CAPs vs standard commonly used CAPs in different types of basis sets is investigated.     

Chiral Triazolium Salts and Ionic Liquids: From the Molecular Design Vectors to Their Physical Properties through Specific Supramolecular Interactions

An exhaustive experimental study based on X‐ray diffraction analysis, NMR, FTIR‐ATR (attenuated total reflection), and Raman spectroscopy as well as theoretical calculations is reported in order to understand how the non‐covalent intermolecular contacts are fundamental to explain structure–property relationships and allowing us to correlate a basic macroscopic property (i.e., the melting point, T_m) with the structural variables of a family of enantiopure 1,4‐dialkyl‐1,2,4‐triazolium salts. The effect of different structural vectors such as the ring size, the spatial disposition of the substituent, the substitution on the oxygen atom, the nature of the anion, or the N4 alkylation of the triazole on the intermolecular interactions of these chiral salts of a well‐defined 3D structure is reported. The non‐covalent intermolecular contacts mainly implicating the triazolium H3 proton are fundamental to explain structure–property relationships and, therefore, the physical properties of these new chiral salts, rather than simple anion–cation interactions. Overall, our findings highlight the importance of the specific supramolecular interactions for the understanding of the physical properties of triazolium salts and ionic liquids.     

Dynamics of a ring of three coupled relaxation oscillators

The dynamics of a ring of three identical relaxation oscillators is shown to exhibit a variety of periodic motions, including clockwise and counter-clockwise wave-like modes, and a synchronous mode in which all three oscillators are in phase. The model involves individual oscillators which exhibit sudden jumps, modeling the relaxation oscillations of van der Pol oscillators. Methods include (i) numerical integration, (ii) a semi-analytical method involving solving transcendental equations numerically, and (iii) perturbation methods. A variety of bifurcations of the periodic motions are identified. This work is motivated by application to the design of a decision-making machine which can sort initial conditions according to their steady state.     

Modeling Ca-Polyanion Crosslinking in Secretory Networks. Assessment of Charge Density and Bond Affinity in Polyanionic Secretory Networks

Materials released by secretory cells are stored inside intracellular membrane-bound vesicles. These moieties are not freely diffusible in the vesicle but remain immobilized in a Ca²⁺-crosslinked condensed-phase polyanionic polymer matrix. During exocytosis a Na⁺/Ca²⁺ ion exchange process triggers a volume phase transition resulting in massive swelling and release of the materials to the extracellular space. Here we formulate a simple model to assess Ca²⁺-ion binding from the swelling kinetics of polymer networks. We found the diffusivity of the networks (D) exhibits a power-law dependency on the Ca²⁺ concentration where D ∝ [Ca²⁺]^−2/3. The model yields an estimate of charge density and ionic affinity of the polymer chains. Studies of post-exocytic swelling kinetics in airway mucin granules, mast cell granules and granules from the microalga (Phaeocystis globosa) were used to validate predictions from our model. These results suggest that independent of the cell type, from animal to plant cells, a single polyelectrolyte interaction mechanism appear to be responsible for product release in exocytosis.     

[C^N]-Alkenyl Gold(III) Complexes by Proximal Ring-Opening of (2-Pyridyl)alkylidenecyclopropanes: Mechanistic Insights

Pyridine-substituted alkylidenecyclopropanes (Py-ACPs) react with gold(III) salts under mild reaction conditions through an unprecedented, proximal ring-opening pathway, to generate highly appealing, catalytically active pyridine alkenyl [C^N]-gold(III) species. Mechanistic studies reveal that the activation of the C−C bond of the ACP takes place through an unusual concerted, σ-bond metathesis type-process.     

Synthesis and characterization of the conductivity and polarization processes in supported ionic liquid-like phases (SILLPs)

Different crosslinked polystyrene resins containing ionic liquid fragments covalently attached (supported ionic liquid-like phases: SILLPs) have been prepared and their conductivity has been studied by means of dielectric impedance spectroscopy. The main structural parameters considered in this study have been the presence of C2H bonds in the imidazolium subunits and the nature (level of hydrophobicity) of the N-substituents (methyl vs. butyl). The results obtained show that the presence of C2H fragments can have an influence on intrinsic conductivity. In the same way the role of the hydrophobicity of the N-substituents seems to play only a minor role. The main structural component associated with conductivity is the nature of the counteranion. The bulkiest, less coordinating anions, in particular the NTf₂^? anion, seem to be associated with the highest conductivities, with the values obtained being two orders of magnitude higher than those calculated for the same systems containing the Cl^? anions for each of the temperatures under study. The results obtained rule out the participation of some given conduction mechanisms such as the involvement of carbene formation. Instead, the formation of ion-pairs of higher or lower association (strong/weak ion pairs) could be responsible for the observed behavior.