Encapsulation of yeast cells in colloidosomes

Polymeric colloidosomes encapsulating viable Baker's yeast cells were prepared. To make the capsules, an aqueous suspension of 153 nm poly(methyl methacrylate-co-butyl acrylate) latex particles plus yeast cells is emulsified in a continuous phase of sunflower oil. By adding a small amount of ethanol to the oil phase, the latex particles at the surface of the emulsion droplets aggregate, forming the colloidosome shells. The microcapsules have been examined using optical, confocal, and scanning electron microscopies. The viability of the yeast cells was tested using fluorescent molecular probes. The encapsulated Baker's yeast cells were able to metabolize glucose from solution, although at a slower rate compared to nonencapsulated yeast. This demonstrates diffusion limitation through the colloidosome shell. The diffusive resistance could be increased by manufacturing colloidosomes with a double latex shell.     

Finite-depth and intrinsic losses in vertically etched two-dimensional photonic crystals

We address the issue of out-of-plane losses in two-dimensional (2D) photonic crystals (PC) etched through a GaAs monomode waveguide clad with standard GaAlAs alloys. We correlate experimental transmission of PCs with two kinds of loss simulation results. The first kind is 2D and introduces an ad hoc imaginary index in the air holes to account for the losses [see (Benisty et al. Appl. Phys. Lett. 76, 532, 2000)]. The second kind is a novel exact three-dimensional calculation inspired by grating-Fourier analysis that provides quantitatively unprecedented agreement with experimental measurements taking into account hole depth as a limiting parameter. We conclude that, in revision to the conclusions of the above reference, the experimental losses are not the intrinsic ones, being larger by a factor of 5 to 10 due to insufficient hole depth. The transition occurs at a critical etch depth shown to be here around 700 nm. We thus predict, for holes deeper than 700 nm, much improved crystals with very low transmission losses and microresonators with ultra-high quality factors.     

High-pressure dissociation of silver mercury iodide, Ag2HgI4

High-pressure X-ray diffraction has been used to probe the behavior of the superionic conductor silver mercury iodide (Ag₂HgI₄) at pressures up to 5 GPa and at temperatures from 295 to 370 K. Significant changes in the diffraction spectra, indicative of structural transitions, are observed around 0.7 and 1.3 GPa across the range of temperatures studied. The change at 0.7 GPa is shown to correspond to the dissociation of silver mercury iodide into silver iodide and mercury iodide, i.e., Ag₂HgI₄→2AgI+HgI₂. The second transition, at 1.3 GPa, is due to a structural phase transition within HgI₂. Rietveld analysis of the diffraction data is used to confirm and refine all the known crystal structures.     

The role of new eudesmane-type sesquiterpenoid and known eudesmane derivatives from the red alga Laurencia obtusa as potential antifungal–antitumour agents

A new eudesmane sesquiterpenoid, eudesma-4(15),7-diene-5,11-diol (1) along with the known trinor-sesquiterene, teuhetenone (2), and a seco-eudesmane sesquiterpene, chabrolidione B (3), have been isolated from the Red Sea red alga Laurencia obtusa. The chemical structures were elucidated on the basis of extensive spectroscopic analysis. The antifungal and cytotoxic activities of the isolated metabolites were tested against several fungi, yeast and human mammary carcinoma cell line (MCF-7). Compounds 1 and 3 showed a much better activity [minimum inhibitory concentration (MIC): 2.9 μM] than that of amphotericin B (MIC: 4.6 μM). Interestingly, compound 2, the least active antifungal compound, retained the high anticancer activity against MCF-7 (22 μM) in comparison with cisplatin (59 μM), which was determined by employing lactate dehydrogenase assay. Compounds 1–3 are recorded here for the first time from algal flora. The chemotaxonomic importance of the isolated metabolites was discussed.     

Argentophilicity-dependent colossal thermal expansion in extended prussian blue analogues

The thermal expansion behavior of isostructural variants of the colossal thermal expansion material Ag3[CoIII(CN)6] has been investigated using variable temperature X-ray and neutron powder diffraction. It was found that substitution at the octahedral transition metal site did not strongly affect the thermal expansion behavior, giving Ag3[FeIII(CN)6] as a new colossal thermal expansion material. Substitution at the Ag site (by D) was shown to reduce the thermal expansion coefficients by an order of magnitude. It was proposed that this correlation between the presence of argentophilic interactions and extreme thermal expansion behavior may explain a variety of thermal effects in flexible framework materials containing metallophilic interactions.     

Principles of melting in hybrid organic–inorganic perovskite and polymorphic ABX3 structures

Four novel dicyanamide-containing hybrid organic–inorganic ABX₃ structures are reported, and the thermal behaviour of a series of nine perovskite and non-perovskite [AB(N(CN)₂)₃] (A = (C₃H₇)₄N, (C₄H₉)₄N, (C₅H₁₁)₄N; B = Co, Fe, Mn) is analyzed. Structure–property relationships are investigated by varying both A-site organic and B-site transition metal cations. In particular, increasing the size of the A-site cation from (C₃H₇)₄N → (C₄H₉)₄N → (C₅H₁₁)₄N was observed to result in a decrease in T_m through an increase in ΔS_f. Consistent trends in T_m with metal replacement are observed with each A-site cation, with Co < Fe < Mn. The majority of the melts formed were found to recrystallise partially upon cooling, though glasses could be formed through a small degree of organic linker decomposition. Total scattering methods are used to provide a greater understanding of the melting mechanism.

Increasing the size of the A-site cation from (C₃H₇)₄N → (C₄H₉)₄N → (C₅H₁₁)₄N in hybrid organic–inorganic ABX₃ structures was observed to result in a decrease in T_m, through an increase in ΔS_f.     

Self-Immolative Activation of β-Galactosidase-Responsive Probes for In Vivo MR Imaging in Mouse Models

Our lab has developed a new series of self-immolative MR agents for the rapid detection of enzyme activity in mouse models expressing β-galactosidase (β-gal). We investigated two molecular architectures to create agents that detect β-gal activity by modulating the coordination of water to Gd^III. The first is an intermolecular approach, wherein we designed several structural isomers to maximize coordination of endogenous carbonate ions. The second involves an intramolecular mechanism for q modulation. We incorporated a pendant coordinating carboxylate ligand with a 2, 4, 6, or 8 carbon linker to saturate ligand coordination to the Gd^III ion. This renders the agent ineffective. We show that one agent in particular (6-C pendant carboxylate) is an extremely effective MR reporter for the detection of enzyme activity in a mouse model expressing β-gal.     

Neo-debromoaplysiatoxin C,with new structural rearrangement,derived from debromoaplysiatoxin

Abstract

Neo-debromoaplysiatoxin C (1), a new member of the aplysiatoxin family, was isolated from the marine cyanobacterium Lyngbya sp. The structure of 1 was elucidated based on spectroscopic data, and its stereochemistry was determined from NOESY spectrum and biosynthetic considerations. This new compound presents an intriguing 10-membered lactone ring skeleton derived from debromoaplysiatoxin by structural rearrangement, which is the first example in the aplysiatoxin family. Its biological properties were evaluated for cytotoxicity, PKCδ activation and inhibitory effects on potassium channel.