Borotropic shifting of the hydrotris[3-(2-furyl)pyrazol-1-yl]borate ligand in high-coordinate lanthanide complexes

The coordination of hydrotris[3-(2-furyl)pyrazol-1-yl]borate (Tp2-Fu, C21H16BN6O3) to lanthanide(III) ions is achieved for the first time with the complex [Ln(Tp2-Fu)2](BPh4)·xCH2Cl2 (1-Ln has Ln = Ce and x = 2; 1-Dy has Ln = Dy and x = 1). This was accomplished via both hydrous (Ln = Ce) and anhydrous methods (Ln = Dy). When isolating the dysprosium analogue, the filtrate produced a second crop of crystals which were revealed to be the 1,2-borotropic-shifted product [Dy(κ4-Tp2-Fu)(κ5-Tp2-Fu*)](BPh4) (2) {Tp2-Fu* = hydrobis[3-(2-furyl)pyrazol-1-yl][5-(2-furyl)pyrazol-1-yl]borate}. We conclude that the presence of a strong Lewis acid and a sterically crowded coordination environment are contributing factors for the 1,2-borotropic shifting of scorpionate ligands in conjunction with the size of the conical angle with the scorpionate ligand.

Non-equilibrium Virus Particle Dynamics: Microsecond MD Simulations of the Complete Flock House Virus Capsid Under Different Conditions

Flock House virus (FHV) is an animal virus and considered a model system for non-enveloped viruses. It has a small, icosahedral capsid (T=3) and a bipartite positive-sense RNA genome. We present an extensive study of the FHV capsid dynamics from all-atom molecular dynamics simulations of the complete capsid. The simulations explore different biologically relevant conditions (neutral/low pH, with/without RNA in the capsid) using the CHARMM force field. The results show that low pH destabilizes the capsid, causing radial expansion, and RNA stabilizes the capsid. The finding of low pH destabilization is biologically relevant because the capsid is exposed to low pH in the endosome, where conformational changes occur leading to genome release. We also observe structural changes at the fivefold and twofold symmetry axes that likely relate to the externalization of membrane active γ peptides through the fivefold vertex and extrusion of RNA at the twofold axis. Simulations using the Amber force field at neutral pH are also performed and display similar characteristics to the CHARMM simulations.

Genetic Modifications of Icosahedral Plant Virus-based Nanoparticles for Vaccine and Immunotherapy Applications

Vaccine development is one of the greatest achievements of modern medicine. Vaccines made of live-attenuated pathogens can revert to virulent live strains, which causes safety concerns. On the other hand, the use of purified antigenic components as subunit vaccines is safer, but less effective, as these components induce lower levels of protective immunity. Multiple copy presentation of an antigenic determinant in a well-ordered and well-defined orientation on a nanosized particle can mimic the natural host-pathogen surface interaction to provide antigen stability and immunogenicity similar to that of conventional vaccines with improved safety. The icosahedral symmetry of plant viral capsid based nanoparticles is highly ordered and their multivalent structured protein nanostructures facilitate genetic modifications that result in the display of heterologous epitopes or antigens attached to coat proteins. These recombinant plant virus-based nanoparticles (PVNs) provide platforms for the induction of humoral and cellular immune responses to genetically fused antigens from pathogenic viruses, bacteria, tumors, and toxins in man and animals. Here, we comprehensively review the developments of several recombinant PVNs as prophylactic and/or therapeutic vaccines for the prevention or treatment of several microbial diseases, pathologies, and toxin poisoning.

Turning the Halide Switch in the Synthesis of Au-Pd Alloy and Core-Shell Nanoicosahedra with Terraced Shells: Performance in Electrochemical and Plasmon-Enhanced Catalysis

Au-Pd nanocrystals are an intriguing system to study the integrated functions of localized surface plasmon resonance (LSPR) and heterogeneous catalysis. Gold is both durable and can harness incident light energy to enhance the catalytic activity of another metal, such as Pd, via the SPR effect in bimetallic nanocrystals. Despite the superior catalytic performance of icosahedral (IH) nanocrystals compared to alternate morphologies, the controlled synthesis of alloy and core-shell IH is still greatly challenged by the disparate reduction rates of metal precursors and lack of continuous epigrowth on multiply twinned boundaries of such surfaces. Herein, we demonstrate a one-step strategy for the controlled growth of monodisperse Au-Pd alloy and core-shell IH with terraced shells by turning an ionic switch between [Br(-)]/[Cl(-)] in the coreduction process. The core-shell IH nanocrystals contain AuPd alloy cores and ultrathin Pd shells (<2 nm). They not only display more than double the activity of the commercial Pd catalysts in ethanol electrooxidation attributed to monatomic step terraces but also show SPR-enhanced conversion of 4-nitrophenol. This strategy holds promise toward the development of alternate bimetallic IH nanocrystals for electrochemical and plasmon-enhanced catalysis.

The Structural Biology of Hepatitis B Virus: Form and Function

Hepatitis B virus is one of the smallest human pathogens, encoded by a 3,200-bp genome with only four open reading frames. Yet the virus shows a remarkable diversity in structural features, often with the same proteins adopting several conformations. In part, this is the parsimony of viruses, where a minimal number of proteins perform a wide variety of functions. However, a more important theme is that weak interactions between components as well as components with multiple conformations that have similar stabilities lead to a highly dynamic system. In hepatitis B virus, this is manifested as a virion where the envelope proteins have multiple structures, the envelope-capsid interaction is irregular, and the capsid is a dynamic compartment that actively participates in metabolism of the encapsidated genome and carries regulated signals for intracellular trafficking.

Virus Structure and Classification

Viruses have several common characteristics: they are small, have DNA or RNA genomes, and are obligate intracellular parasites. The virus capsid functions to protect the nucleic acid from the environment, and some viruses surround their capsid with a membrane envelope. Most viruses have icosahedral or helical capsid structure, although a few have complex virion architecture. An icosahedron is a geometric shape with 20 sides, each composed of an equilateral triangle, and icosahedral viruses increase the number of structural units in each face to expand capsid size. The classification of viruses is very useful, and the International Committee on Taxonomy of Viruses is the official body that classifies viruses into order, family, genus, and species taxa. There are currently seven orders of viruses.

The crystallographic structure of Panicum Mosaic Virus (PMV)

The structure of Panicum Mosaic Virus (PMV) was determined by X-ray diffraction analysis to 2.9Å resolution. The crystals were of pseudo symmetry F23; the true crystallographic unit cell was of space group P2(1) with a=411.7Å, b=403.9Å and c=412.5Å, with β=89.7°. The asymmetric unit was two entire T=3 virus particles, or 360 protein subunits. The structure was solved by conventional molecular replacement from two distant homologues, Cocksfoot Mottle Virus (CfMV) and Tobacco Necrosis Virus (TNV), of ∼20% sequence identity followed by phase extension. The model was initially refined with exact icosahedral constraints and then with icosahedral restraints. The virus has Ca(++) ions octahedrally coordinated by six aspartic acid residues on quasi threefold axes, which is completely different than for either CfMV or TNV. Amino terminal residues 1-53, 1-49 and 1-21 of the A, B and C subunits, respectively, and the four C-terminal residues (239-242) are not visible in electron density maps. The additional ordered residues of the C chain form a prominent "arm" that intertwines with symmetry equivalent "arms" at icosahedral threefold axes, as was seen in both CfMV and TNV. A 17 nucleotide hairpin segment of genomic RNA is icosahedrally ordered and bound at 60 equivalent sites at quasi twofold A-B subunit interfaces at the interior surface of the capsid. This segment of RNA may serve as a conformational switch for coat protein subunits, as has been proposed for similar RNA segments in other viruses.

Rearrangements in icosahedral boranes and carboranes revisited

The structure, stability, and intermolecular rearrangements between ortho-, meta-, and para-C2B10H12 and were investigated using the hybrid density functional B3LYP/6-31G(d) for vibrational frequencies, as well as B3LYP/6-311+G(2d,p) for single-point electronic energies. The general trends in free energies of rearrangement between ortho-C2B10H12 to meta-C2B10H12 and meta-C2B10H12 to para-C2B10H12 presented here are consistent with experimental reaction temperatures. In addition, the majority of the rearrangements can be viewed in terms of concerted diamond-square-diamond steps and triangular face rotations.