A Synthetic Cation-Transporting Calix[4]arene Derivative Active in Phospholipid Bilayers

One order of magnitude: The transport of Na⁺ and K⁺ ions through a phospholipid bilayer occurs with much higher conductance levels with 1 and 2 than with typical Na⁺-transporting proteins or gramicidin. However, the cations do not appear to pass through the calix[4]arene ring, which has a rigid 1,3-alternate conformation. diazacrown=10-benyzl-1,10-diaza[18]crown-6 group.     

Computing the nearest diagonally dominant matrix

We solve the problem of minimizing the distance from a given matrix to the set of symmetric and diagonally dominant matrices. First, we characterize the projection onto the cone of diagonally dominant matrices with positive diagonal, and then we apply Dykstra's alternating projection algorithm on this cone and on the subspace of symmetric matrices to obtain the solution. We discuss implementation details and present encouraging preliminary numerical results. Copyright © 1999 John Wiley & Sons, Ltd.     

h-MoO3 phase transformation by four thermal analysis techniques

Journal of Thermal Analysis and Calorimetry - Molybdenum trioxide (MoO3) has been studied by four thermal analysis techniques. The as-synthesized material has hexagonal structure (h-MoO3). The...     

Computational and Experimental Study of Turbo-Organomagnesium Amide Reagents: Cubane Aggregates as Reactive Intermediates in Pummerer Coupling

The dynamic equilibria of organomagnesium reagents are known to be very complex, and the relative reactivity of their components is poorly understood. Herein, a combination of DFT calculations and kinetic experiments is employed to investigate the detailed reaction mechanism of the Pummerer coupling between sulfoxides and turbo-organomagnesium amides. Among the various aggregates studied, unprecedented heterometallic open cubane structures are demonstrated to yield favorable barriers through a concerted anion-anion coupling/ S−O cleavage step. Beyond a structural curiosity, these results introduce open cubane organometallics as key reactive intermediates in turbo-organomagnesium amide mixtures.     

Weakly reversible CF-decompositions of chemical kinetic systems

Journal of Mathematical Chemistry - This paper studies chemical kinetic systems which decompose into weakly reversible complex factorizable (CF) systems. Among power law kinetic systems, CF systems...     

Impact of a Water-Soluble Gallic Acid-Based Dendrimer on the Color-Stabilizing Mechanisms of Anthocyanins

The interaction of two anthocyanins with a water-soluble polyanionic dendrimer was studied through UV/Vis, stopped-flow, and NMR spectroscopy. Cyanidin-3-glucoside (cy3glc) revealed a stronger interaction than malvidin-3-glucoside (mv3glc) at pH 1 according to their apparent association constants. A higher color increased was also obtained for cy3glc at pH 3.5 as a result of this stronger interaction. A high-frequency chemical shift of the cy3glc aromatic protons suggest the formation of ionic pairs. The interaction parameters (K≈700 m ⁻¹, n≈295) indicated the binding of approximately two anthocyanin molecules by each sulfate group. The equilibrium and rate constants of cy3glc in the presence of dendrimer showed an increased stability of the flavylium cation and a higher protection of this species from hydration (pK′_a and pK_h increased almost one pH unit). The tuning and color stabilization of anthocyanins by using this dendrimer allow novel applications as colorimetric sensors for food packaging.     

Characterization of O/W emulsions of carotenes in blackberry juice performed by ultrasound and high-pressure homogenization

Carotene compounds are a group of natural pigments with potential applications in the food industry for their antioxidant activity, but due to their physicochemical instability and incompatibility with many food matrices, different technologies have been employed, such as emulsification, to improve stability and compatibility. Therefore, the physicochemical stability and antioxidant activity of carotene oil-in-water (O/W) emulsions were studied, using carotene compounds extracted from carrot as the oil phase and blackberry juice as the continuous phase. The effect of different factors on the stability of the emulsion – the relative concentration of the dispersed phase, the hydrophilic-lipophilic balance (HLB), the surfactant concentration, and the emulsification method – was assessed using surface response analysis. The emulsion with the best properties was obtained in the phase ratio 2:8 (v/v) with 6% surfactant and an HLB of 16.7. The ultrasound method produced emulsions with higher antioxidant stability and lower carotene degradation rates than those prepared by high pressure, when compared after 60 days of storage at 25°C. This study allowed the development of a stable emulsion with antioxidants in each of the phases of the emulsion that could be incorporated into several types of food products to produce functional foods.     

Photoswitchable architecture transformation of a DNA-hybrid assembly at the microscopic and macroscopic scale

Molecular recognition-driven self-assembly employing single-stranded DNA (ssDNA) as a template is a promising approach to access complex architectures from simple building blocks. Oligonucleotide-based nanotechnology and soft-materials benefit from the high information storage density, self-correction, and memory function of DNA. Here we control these beneficial properties with light in a photoresponsive biohybrid hydrogel, adding an extra level of function to the system. An ssDNA template was combined with a complementary photo-responsive unit to reversibly switch between various functional states of the supramolecular assembly using a combination of light and heat. We studied the structural response of the hydrogel at both the microscopic and macroscopic scale using a combination of UV-vis absorption and CD spectroscopy, as well as fluorescence, transmission electron, and atomic force microscopy. The hydrogels grown from these supramolecular self-assembly systems show remarkable shape-memory properties and imprinting shape-behavior while the macroscopic shape of the materials obtained can be further manipulated by irradiation.

Molecular recognition-driven self-assembly employing single-stranded DNA (ssDNA) as a template is a promising approach to access complex architectures from simple building blocks.