Topological Order in an Antiferomagnetic Tetratic

We study lattice melting in two dimensional antiferromagnets. We argue that, for strong enough magnetic interactions, single lattice dislocations are prohibitive due to magnetic frustration. This leads to a melting scenario in which a tetratic phase, composed of free dislocation pairs and bound disclinations, separates the solid from the liquid phases. We demonstrate this phase numerically in a system of hard spheres confined between parallel plates, where spins are represented by the the heights of the spheres. We find that, in the tetratic phase, the spins are as antiferromagnetically ordered as allowed by their spatial configuration

Self-assembly of a modified amyloid peptide fragment: pH-responsiveness and nematic phase formation

The self-assembly of peptide YYKLVFFC based on a fragment of the amyloid beta (A) peptide, A beta 16-20, KLVFF has been studied in aqueous solution. The peptide is designed with multiple functional residues to examine the interplay between aromatic interactions and charge on the self-assembly, as well as specific transformations such as the pH-induced phenol-phenolate transition of the tyrosine residue. Circular dichroism (CD) and Fourier-transform infrared (FTIR) spectroscopies are used to investigate the conditions for beta-sheet self-assembly and the role of aromatic interactions in the CD spectrum as a function of pH and concentration. The formation of well-defined fibrils at pH 4.7 is confirmed by cryo-TEM (transmission electron microscope) and negative stain TEM. The morphology changes at higher pH, and aggregates of short twisted fibrils are observed at pH 11. Polarized optical microscopy shows birefringence at a low concentration (1 wt.-%) of YYKLVFFC in aqueous solution, and small-angle X-ray scattering was used to probe nematic phase formation in more detail. A pH-induced transition from nematic to isotropic phases is observed on increasing pH that appears to be correlated to a reduction in aggregate anisotropy upon increasing pH

Poly(glycoamidoamine) brush nanomaterials for systemic siRNA delivery in vivo

Delivery is the key challenge for siRNA based therapeutics. Here, we report the development of new poly(glycoamidoamine) brush nanomaterials for efficient siRNA delivery. GluN4C10 polymer brush nanoparticles, a lead material, demonstrated significantly improved delivery efficiency for siRNA against factor VII (FVII) in mice compared to poly(glycoamidoamine) brush nanomaterials reported previously.National Institutes of Health (U.S.) (Grant R01-EB000244–27)National Institutes of Health (U.S.) (Grant 5-R01-CA132091–04)National Institutes of Health (U.S.) (Grant R01-DE016516–03

Passivation, phase, and morphology control of CdS nanocrystals using fluorinated aromatic amines

Nanocrystals are widely explored for a range of medical, imaging, sensing, and energy conversion applications. CdS nanocrystals have been reported as excellent photocatalysts, with thin film CdS also highly important in photovoltaic devices. To maximise catalytic activity of nanocrystals, control over phase, facet, and morphology are vital. Here, CdS nanocrystals were synthesised by the solvothermal decomposition of a Cd xanthate single source precursor. To attempt to control CdS nanocrystal surfaces and morphology, the solvent used in the nanocrystal synthesis was altered from pure trioctylphosphine oxide (TOPO) to a mixed TOPO:fluorinated aromatic amine (either 3-fluorobenzyl amine (3-FlBzAm) or 3-fluoroaniline (3-FlAn)), which also provides a sensitive NMR-active probe moiety (mono-fluorinated capping ligands on the CdS nanocrystal surface). Powder X-ray diffraction found that the CdS nanocrystals synthesised from TOPO:3-FlAn solvent mixtures were predominantly cubic whilst the TOPO:3-FlBzAm synthesised nanocrystals were predominantly hexagonal. Raman spectroscopy identified hexagonal CdS in all samples, indicating a likely mixture of phases in at least some of the synthesised systems. Solid-state NMR of 113Cd, 19F, 13C, and 1H was employed to investigate the local Cd environments, surface ligands, and ligand interactions. This showed there was a mixture of CdS phases present in all samples and that surfaces were capped with TOPO:fluorinated aromatic amine mixtures, but also that there was a stronger binding affinity of 3-FlBzAm compared with 3-FlAn on the CdS surface. This work highlights that fluorinated aromatic amines can be used to passivate NC surfaces and also control NC properties through their influence during NC growth

Poly(glycoamidoamine) Brushes Formulated Nanomaterials for Systemic siRNA and mRNA Delivery in Vivo

Safe and effective delivery is required for siRNA and mRNA-based therapeutics to reach their potential. Here, we report on the development of poly(glycoamidoamine) brush nanoparticles as delivery vehicles for siRNA and mRNA. These polymers were capable of significant delivery of siRNA against FVII and mRNA-encoding erythropoietin (EPO) in mice. Importantly, these nanoparticles were well-tolerated at their effective dose based on analysis of tissue histology, systemic cytokine levels, and liver enzyme chemistry. The polymer brush nanoparticles reported here are promising for therapeutic applications.MIT-Harvard Center of Cancer Nanotechnology Excellence (Grant U54-CA151884)National Heart, Lung, and Blood Institute (Contract HHSN268201000045C)Shire PharmaceuticalsAlnylam Pharmaceuticals (Firm)National Institutes of Health (U.S.) (Grants R01-EB000244-27, 5- R01-CA132091-04, and R01-DE016516-03)National Institute for Biomedical Imaging and Bioengineering (U.S.) (Postdoctoral Fellowship 1F32EB017625