Liposome-templated supramolecular assembly of responsive alginate nanogels

Nanosized gel particles (nanogels) are of interest for a variety of applications, including drug delivery and single-molecule encapsulation. Here, we employ the cores of nanoscale liposomes as reaction vessels to template the assembly of calcium alginate nanogels. For our experiments, a liposome formulation with a high bilayer melting temperature (Tm) is selected, and sodium alginate is encapsulated in the liposomal core. The liposomes are then placed in an aqueous buffer containing calcium chloride, and the temperature is raised up to Tm. This allows permeation of Ca2+ ions through the bilayer and into the core, whereupon these ions gel the encapsulated alginate. Subsequently, the lipid bilayer covering the gelled core is removed by the addition of a detergent. The resulting alginate nanogels have a size distribution consistent with that of the template liposomes (ca. 120-200 nm), as confirmed by transmission electron microscopy and light scattering. Nanogels of different average sizes can be synthesized by varying the template dimensions, and the gel size can be further tuned after synthesis by the addition of monovalent salt to the solution.     

Reconstruction of the time-dependent wave function exclusively from position data

A method is presented that reconstructs the amplitude and phase of an unknown time-dependent pure-state wave function entirely from experimental position data. No assumptions about the wave function are needed. At a series of times, a large collection of position data is taken, but no measurements of momentum or energy are necessary. The momenta, however, are required for the reconstruction of the wave function and are supplied by analysis of the position data via quantum particle trajectories. Simulations of the method are provided for helium atoms in single and double slit experiments.     

Vectorial phase retrieval for linear characterization of attosecond pulses

The waveforms of attosecond pulses produced by high-harmonic generation carry information on the electronic structure and dynamics in atomic and molecular systems. Current methods for the temporal characterization of such pulses have limited sensitivity and impose significant experimental complexity. We propose a new linear and all-optical method inspired by widely used multidimensional phase retrieval algorithms. Our new scheme is based on the spectral measurement of two attosecond sources and their interference. As an example, we focus on the case of spectral polarization measurements of attosecond pulses, relying on their most fundamental property-being well confined in time. We demonstrate this method numerically by reconstructing the temporal profiles of attosecond pulses generated from aligned CO(2) molecules.     

Accurate mass measurement by matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry. I. Measurement of positive radical ions using porphyrin standard reference materials

A method for the accurate mass measurement of positive radical ions by matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry (MALDI‐TOFMS) is described. Initial use of a conjugated oligomeric calibration material was rejected in favour of a series of meso‐tetraalkyl/tetraalkylaryl‐functionalised porphyrins, from which the two calibrants required for a particular accurate mass measurement were chosen. While all measurements of monoisotopic species were within ±5 ppm, and the method was rigorously validated using chemometrics, mean values of five measurements were used for extra confidence in the generation of potential elemental formulae. Potential difficulties encountered when measuring compounds containing multi‐isotopic elements are discussed, where the monoisotopic peak is no longer the lowest mass peak, and a simple mass‐correction solution can be applied. The method requires no significant expertise to implement, but care and attention is required to obtain valid measurements. The method is operationally simple and will prove useful to the analytical chemistry community. Copyright © 2010 John Wiley & Sons, Ltd.     

Photosensitive gelatin

Employing photodestructible surfactants in gelatin-based aqueous gels presents novel possibilities for controlling colloidal and aggregation properties of surfactant gelatin complexes. Light-triggered breakdown of the gelatin-bound photosurfactant aggregates causes dramatic changes in viscosity and aggregation.     

Investigation into accurate mass capability of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, with respect to radical ion species

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) has been shown to be an effective technique for the characterization of organometallic, coordination, and highly conjugated compounds. The preferred matrix is 2-[(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-enylidene]malononitrile (DCTB), with radical ions observed. However, MALDI-TOFMS is generally not favored for accurate mass measurement. A specific method had to be developed for such compounds to assure the quality of our accurate mass results. Therefore, in this preliminary study, two methods of data acquisition, and both even-electron (EE+) ion and odd-electron (OE+.) radical ion mass calibration standards, have been investigated to establish the basic measurement technique. The benefit of this technique is demonstrated for a copper compound for which ions were observed by MALDI, but not by electrospray (ESI) or liquid secondary ion mass spectrometry (LSIMS); a mean mass accuracy error of -1.2 ppm was obtained.     

Bounds on the connected domination number of a graph

A subset S$S$ of vertices in a graph G=(V,E)$G=(V,E)$ is a connected dominating set of G$G$ if every vertex of V?S$V?S$ is adjacent to a vertex in S$S$ and the subgraph induced by S$S$ is connected. The minimum cardinality of a connected dominating set of G$G$ is the connected domination number _γc(G)${\gamma }_c\left(G\right)$. The girth g(G)$g\left(G\right)$ is the length of a shortest cycle in G$G$. We show that if G$G$ is a connected graph that contains at least one cycle, then _γc(G)≥g(G)−2${\gamma }_c\left(G\right)\ge g\left(G\right)-2$, and we characterize the graphs obtaining equality in this bound. We also establish various upper bounds on the connected domination number of a graph, as well as Nordhaus–Gaddum type results.     

Oxa-enediynes: probing the electronic and stereoelectronic contributions to the Bergman cycloaromatization

Efficient routes to three classes of 10-membered oxa-enediynes are presented. The electronic and stereoelectronic contributions to half-lives are supported by density functional theory calculations. One member of this class cyclizes to give an isochroman which binds to and degrades the aryl hydrocarbon receptor (AhR).