Bioconjugating Thiols to Poly(acrylamide) Gels for Cell Culture Using Methylsulfonyl Co‐monomers

Poly(acrylamide) P(AAm) gels have become relevant model substrates to study cell response to the mechanical and biochemical properties of the cellular microenvironment. However, current bioconjugation strategies to functionalize P(AAm) gels, mainly using photoinduced arylazide coupling, show poor specificity and hinder conclusive studies of material properties and cellular responses. We describe methylsulfonyl‐containing P(AAm) hydrogels for cell culture. These gels allow easy, specific and functional covalent coupling of thiol containing bioligands in tunable concentrations under physiological conditions, while retaining the same swelling, porosity, cytocompatibility, and low protein adsorption of P(AAm) gels. These materials allow quantitative and standardized studies of cell‐materials interactions with P(AAm) gels.     

A non-standard statistical approach to the silo discharge

We present molecular dynamics simulations of the beginning of a silo discharge by gravity. The evolution of the velocity profile and the probability density functions for the displacements of the grains are obtained. These PDFs reveal non-gaussian statistics and superdiffusive behavior similar to that observed in some experiments. We propose an analytical expression for the PDFs and an explanation for its dynamical origin in connection with the ideas of the “spot" model and non-extensive thermodynamics.     

Effect of shear on vesicle and lamellar phases of DDAB/lecithin ternary systems

The influence of shear flow on bilayer structures (vesicle and planar lamellar phases, L(α)), formed in DDAB/lecithin ternary systems, is studied by means of conventional rheology, Rheo NMR, and optical microscopy. The vesicles in the diluted (Lam(1)) phase are polydisperse multilamellae which turn into smaller monodisperse vesicles under shear. The concentrated (Lam(2)) phase is formed by non-oriented lamellae that do not surprisingly exhibit any pronounced shear-induced alignment prior to the transition into giant multilamellar vesicles. The biphasic region (Lam(1)+Lam(2)) shows a mosaic texture with a powder pattern indicating the prevalence of lamellae that transform into onions under shear.     

Fluorescence detection by intensity changes for high-performance thin-layer chromatography separation of lipids using automated multiple development

Changes in emission of berberine cation, induced by non-covalent interactions with lipids on silica gel plates, can be used for detecting and quantifying lipids using fluorescence scanning densitometry in HPTLC analysis. This procedure, referred to as fluorescence detection by intensity changes (FDIC) has been used here in combination with automated multiple development (HPTLC/AMD), a gradient-based separation HPTLC technique, for separating, detecting and quantifying lipids from different families. Three different HPTLC/AMD gradient schemes have been developed for separating: neutral lipid families and steryl glycosides; different sphingolipids; and sphingosine-sphinganine mixtures. Fluorescent molar responses of studied lipids, and differences in response among different lipid families have been rationalized in the light of a previously proposed model of FDIC response, which is based on ion-induced dipole interactions between the fluorophore and the analyte. Likewise, computational calculations using molecular mechanics have also been a complementary useful tool to explain high FDIC responses of cholesteryl and steryl-derivatives, and moderate responses of sphingolipids. An explanation for the high FDIC response of cholesterol, whose limit of detection (LOD) is 5 ng, has been proposed. Advantages and limitations of FDIC application have also been discussed.     

Synthesis of the gymnodimine tetrahydrofuran core through a Ueno-Stork radical cyclization

A straightforward access to the C10-C20 skeleton of gymnodimine, incorporating a tetrahydrofuran fragment, is described. The elaboration of the THF moiety is based on a stereocontrolled Ueno-Stork cyclization. A Lewis-acid mediated allylation of the resulting acetal at C13 and a Horner-Wadsworth-Emmons olefination on the ketone at C17 complete the synthesis.     

Intercalation studies of zinc hydroxide chloride: Ammonia and amino acids

Zinc hydroxide chloride (ZHC) is a layered hydroxide salt with formula Zn₅(OH)₈Cl₂·2H₂O. It was tested as intercalation matrix for the first time and results were compared with intercalation products of the well-known zinc hydroxide nitrate and a Zn/Al layered double hydroxide. Ammonia was intercalated into ZHC, while no significant intercalation occurred in ZHN. Aspartic acid intercalation was only achieved by co-precipitation at pH=10 with ZHC and pH=8 with zinc hydroxide nitrate. Higher pH resistance in ZHC favored total deprotonation of both carboxylic groups of the Asp molecule. ZHC conferred more thermal protection against Asp combustion presenting exothermic peaks even at 452 °C while the exothermic event in ZHN was 366 °C and in the LDH at 276 °C.     

Light-activated gating and permselectivity in interfacial architectures combining "caged" polymer brushes and mesoporous thin films

We demonstrate that "caged" macromolecular building blocks can endow mesoporous thin films with light responsiveness and lead to the creation of functional hybrid ensembles with phototriggered permselective properties.     

Quantum-critical theory of the spin-fermion model and its application to cuprates: Normal state analysis

We present the full analysis of the normal state properties of the spin-fermion model near the antiferromagnetic instability in two dimensions. The model describes low-energy fermions interacting with their own collective spin fluctuations, which soften at the antiferromagnetic transition. We argue that in 2D, the system has two typical energies—an effective spin-fermion interaction g¯ and an energy ω_sf below which the system behaves as a Fermi liquid. The ratio of the two determines the dimensionless coupling constant for spin-fermion interaction λ² ∝ g¯/ω_sf. We show that λ scales with the spin correlation length and diverges at criticality. This divergence implies that the conventional perturbative expansion breaks down. We develop a novel approach to the problem—the expansion in either the inverse number of hot spots in the Brillouin zone, or the inverse number of fermionic flavours—which allows us to explicitly account for all terms which diverge as powers of λ, and treat the remaining, O(log λ) terms in the RG formalism. We apply this technique to study the properties of the spin-fermion model in various frequency and temperature regimes. We present the results for the fermionic spectral function, spin susceptibility, optical conductivity and other observables. We compare our results in detail with the normal state data for the cuprates, and argue that the spin-fermion model is capable of explaining the anomalous normal state properties of the high T _c materials. We also show that the conventional {⁴ theory of the quantum-critical behaviour is inapplicable in 2D due to the singularity of the {⁴ vertex.     

A new class of non-linear monotone Hermite interpolants

Monotonicity-preserving approximation methods are used in numerous applications. These methods are expected to reconstruct a function from a discrete set of data preserving Monotonicity properties (i.e., the reconstructed function has to be monotone wherever the discrete data are). Most Monotonicity-preserving methods sacrifice accuracy in order to obtain Monotonicity. In this work we propose and analyze a Monotonicity-preserving Hermite interpolant that does not fully sacrifice accuracy. A key ingredient in the proposed technique is the approximation of derivatives using ENO (Essentially Non Oscillatory) and WENO (Weighted Essentially Non Oscillatory) interpolatory techniques. Then, an appropriate filtering process ensures the preservation of Monotonicity while maintaining, at the same time, the order of accuracy as high as possible. We perform several numerical experiments which confirm the properties of the proposed algorithms and compare them to other standard interpolatory approximation techniques.