Optical excitation and decay dynamics of ytterbium atoms embedded in a solid neon matrix

Neutral ytterbium atoms embedded in solid neon qualitatively retain the structure of free atoms. Despite the atom-solid interaction, the 6s6p 3P(0) level is found to remain metastable with its lifetimes determined to be in the range of ten to hundreds of seconds. The atomic population can be almost completely transferred between the ground level and the metastable level via optical excitation and spontaneous decay. The dynamics of this process is examined and is used to explicitly demonstrate that the transition broadening mechanism is homogeneous.     

Influence of preparation conditions on the depth-dependent composition of AuPd nanoparticles grown on planar oxide surfaces

The high resolution depth profiling capabilities of medium energy ion scattering are employed to determine the depth dependent composition of Au/Pd nanoparticles grown on thin silica films on Si(100) as functions of Au/Pd composition, total metal loading and annealing temperature. We show that, despite the fact that Au is deposited prior to Pd, the surface of the particles is generally enriched in Au compared to the bulk composition. The extent of this Au enrichment decreases with annealing temperature. In addition, we examine the influence of the adsorption of acetic acid on the surface composition of Au/Pd particles grown on thin alumina films on NiAl(110). We find that acetic acid causes limited segregation of Pd to the bimetallic surface of relatively Au-rich particles.     

Structure‐based redesign of proteins for minimal T‐cell epitope content

The protein universe displays a wealth of therapeutically relevant activities, but T‐cell driven immune responses to non‐“self” biological agents present a major impediment to harnessing the full diversity of these molecular functions. Mutagenic T‐cell epitope deletion seeks to mitigate the immune response, but can typically address only a small number of epitopes. Here, we pursue a “bottom‐up” approach that redesigns an entire protein to remain native‐like but contain few if any immunogenic epitopes. We do so by extending the Rosetta flexible‐backbone protein design software with an epitope scoring mechanism and appropriate constraints. The method is benchmarked with a diverse panel of proteins and applied to three targets of therapeutic interest. We show that the deimmunized designs indeed have minimal predicted epitope content and are native‐like in terms of various quality measures, and moreover that they display levels of native sequence recovery comparable to those of non‐deimmunized designs. © 2013 Wiley Periodicals, Inc.     

Orientational ordering in nematic liquid crystals 1CB-d11 dissolved in 5CB-d6

The ²H-N.M.R. spectra of mixtures of the non-mesogenic compound 4-cyano-4′-methylbiphenyl (1CB) and the nematic liquid crystal 4-cyano-4′-n-pentylbiphenyl (5CB) are measured as a function of concentration and temperature. Concentrations of up to 25 mol% 1CB have no effect on the N.M.R. spectrum and therefore on the orientational order of 5CB at a given reduced temperature. The order matrix of the 1CB is calculated from the measured quadrupole couplings. The results are analysed in terms of a model for orientational order that includes two anisotropic terms: (a) interaction between the molecular quadrupole moment and the mean electric field gradient of the medium, and (b) short range repulsive interactions. An estimate of the molecular quadrupole moment tensor of 1CB is obtained from the analysis.     

Piezoelectricity of phospholipids: a possible mechanism for mechanoreception and magnetoreception in biology

We show that phospholipids, which are the main constituents of cell membranes, are piezoelectric. This was done by periodically shearing and compressing films of hydrated l‐α‐phosphatidylcholine, inducing a tilt of the molecules with respect to the bilayer’s normal, which produced an electric current perpendicular to the tilt plane, corresponding to a polarisation of about 300 nC cm^?2 at 5° of tilt. We also measured electric currents induced by an alternating magnetic field of less than 100 G in hydrated phospholipids doped with 0.5 wt% of ferrofluid of magnetite (Fe₃O₄) nanoparticles. A discussion of possible implications of these effects on biophysical processes is also provided.     

Synthesis and Some Properties of Some Sulfonium Polyelectrolytes: Polymers and Copolymers Derived from Methylthioethyl Acrylate

Methylthioethyl acrylate, prepared by ester exchange from methylthioethanol and methyl acrylate, behaves in copolymerization like a typical acrylate ester such as butyl acrylate. This monomer can be alkylated to yield corresponding sulfonium monomers. With dimethyl sulfate, (2-acryloxyethyl) dimenthylsulfonium methyl sulfate is obtained. This latter monomer has a predictable lower relative copolymerization rate with alkyl acrylates than methylthioethyl acrylate. Water-soluble sulfonium polymers are polymeric cations and can act effectively as flocculants.     

Recent Advances in Free-Radical Ring-Opening Polymerization

Although cyclic ketene acetals, such as 2-methylene-1, 3-dioxepane, undergo quantitative free-radical ring-opening polymerization, their reactivity in copolymerization is rather low. In order to find a series of monomers that have high reactivities in copolymerization and still undergo free radical ring-opening polymerization, a series of cyclic acrylates was synthesized and polymerized. For example, β-bromolactic acid condensed with benzaldehyde to give a cyclic acetal lactone which on treatment with base gave the cyclic acrylate. Free-radical solution polymerization at 140°C of the cyclic acrylate, which produced a benzyl radical upon ring opening, gave quantitative ring opening. However, in bulk at 120°C, only 20% of the rings were opened during poiymerization. The resulting polymers containing the pyruvate ester units were shown to be highly biodegradable with microorganisms. Vesicles containing these cyclic acrylates on the end of one of the hydrophobic chains of the lipidlike molecules were shown to undergo free-radical ring-opening polymerization to give polymerized vesicles which were biodegradable. In order to discover groups other than carbonyl groups and strained rings that would promote free-radical ring-opening polymerization, a series of spiromethylenecyclohexadienes were prepared and polymerized. Thus, 3-methylenespiro [5,5] undeca-1,4-diene in bulk at 130°C gave a polymer in which 79% of the rings had opened and in solution at 130°C gave a polymer in which nearly all of the rings had opened. A benzo derivative, 3-methylene-8,9-benzo [5,5] undeca-1,4,8-triene, gave a polymer that is essentially an alternating copolymer of p-xylylene and o-xylylene and has a very high thermal decomposition temperature. A tricyclic dispirocyclohexadiene derivative was shown to undergo double free-radical ring-opening polymerization to give a polymer with expansion in volume containing a p-phenylene group in the backbone.     

The Heusler phases LiRh2Si and LiRh2Ge: Synthesis, structure and properties

The isostructural Heusler phases LiRh₂Si and LiRh₂Ge have been synthesized from the elements and an excess of lithium at 1000 °C. Both materials adopt the CuMn₂Al crystal structure, space group Fm−3m (No. 225) with the room temperature lattice parameter a=5.747(1) Å [Vol=189.866(1) Å³] and a=5.847(1) Å [Vol=199.88(6) Å³] for LiRh₂Si and LiRh₂Ge, respectively. X-ray analyses suggest mixed site occupancy of the form Li_1−xRh₂Si_1+x (x<0.4), but not for LiRh₂Ge. Both materials are diamagnetic, χ_mol(LiRh₂Si)=−6×10⁻⁵ cm³(mole)⁻¹ and χ_mol(LiRh₂Ge)=−10×10⁻⁵ cm³(mole)⁻¹ and metallic with room temperature resistivities of approximately 19 and 32 μΩ cm, respectively. These properties are consistent with the calculated electronic structure.     

Pure insulin nanoparticle agglomerates for pulmonary delivery

Diabetes is a set of diseases characterized by defects in insulin utilization, either through autoimmune destruction of insulin-producing cells (Type I) or insulin resistance (Type II). Treatment options can include regular injections of insulin, which can be painful and inconvenient, often leading to low patient compliance. To overcome this problem, novel formulations of insulin are being investigated, such as inhaled aerosols. Sufficient deposition of powder in the peripheral lung to maximize systemic absorption requires precise control over particle size and density, with particles between 1 and 5 microm in aerodynamic diameter being within the respirable range. Insulin nanoparticles were produced by titrating insulin dissolved at low pH up to the pI of the native protein, and were then further processed into microparticles using solvent displacement. Particle size, crystallinity, dissolution properties, structural stability, and bulk powder density were characterized. We have demonstrated that pure drug insulin microparticles can be produced from nanosuspensions with minimal processing steps without excipients, and with suitable properties for deposition in the peripheral lung.