Amphiphilic Hybrid Nano Building Blocks with Surfactant-Mimicking Structures.

We report the preparation and self-assembly of amphiphilic hybrid nano building blocks (NBBs) with surfactant-mimicking structures. These NBBs, composed of hydrophilic silica-like heads tethered with well-defined one or two hydrophobic polystyrene (PS) tails, were prepared by efficient intramolecular cross-linking via silane chemistry. Using a series of "AB" diblock copolymers (BCPs) and "ABA" tri-BCPs of PS and poly(tert-butyl acrylate-co-3-(trimethoxysilyl)propyl methacrylate) (P(tBA-co-TMSPMA)), the intramolecular self-folding of P(tBA-co-TMSPMA) blocks and the deprotection of tert-butyl groups were demonstrated to be an efficient method to prepare amphiphilic NBBs with a hydrophilic silica head tethered by one or two PS tails. The formation of NBBs was carefully studied by gel permeation chromatography, nuclear magnetic resonance spectroscopy, and transmission electron microscopy. The self-assembly of these amphiphilic NBBs was further investigated by fixing the molecular weight of PS tails and varying the size of hydrophilic heads. The intramolecular cross-linking of hydrophilic heads that shifted the hydrophilic/hydrophobic balance of polymers resulted in morphological transitions from bilayered vesicles to spherical micelles. Spherical micelles prepared from NBBs with large hydrophilic heads were found to have surface protrusions that differed from the self-assembly of linear BCPs. We also observed that the chain conformation of PS tails was critical for the self-assembly of NBBs, where the bitailed NBBs with highly stretched PS tails favored bilayered vesicle structures.

pH-programmable self-assembly of plasmonic nanoparticles: hydrophobic interaction versus electrostatic repulsion.

We report a general strategy to conceptualize a new design for the pH-programmable self-assembly of plasmonic gold nanoparticles (AuNPs) tethered by random copolymers of poly(styrene-co-acrylic acid) (P(St-co-AA)). It is based on using pH as an external stimulus to reversibly change the surface charge of polymer tethers and to control the delicate balance of interparticle attractive and repulsive interactions. By incorporating -COOH moieties locally within PSt hydrophobic segments, the change in the ionization degree of -COOH moieties can dramatically disrupt the hydrophobic attraction within a close distance. pH acts as a key parameter to control the deprotonation of -COOH moieties and "programs" the assembled nanostructures of plasmonic nanoparticles in a stepwise manner. At a higher solution pH where -COOH groups of polymer tethers became highly deprotonated, electrostatic repulsion dominated the self-assembly and favored the formation of end-to-end, anisotropic assemblies, e.g. 1-D single-line chains. At a lower pH, the less deprotonated -COOH groups led to the decrease of electrostatic repulsion and the side-to-side aggregates, e.g. clusters and multi-line chains of AuNPs, became favorable. The pH-programmable self-assembly allowed us to engineer a "manual" program for a sequential self-assembly by changing the pH of the solution. We demonstrated that the two-step pH-programmable assembly could generate more sophisticated "multi-block" chains using two differently sized AuNPs. Our strategy offers a general means for the programmable design of plasmonic nanoparticles into the specific pre-ordained nanostructures that are potentially useful for the precise control over their plasmon coupling.

Molecular identification key of the family Streptococcaceae.

The gene order conservation (GOC) between the species of family Streptococcaceae was analysed. The rate of GOC in the strains belonging to the same species is 70% or more. When we compared different species belonging to the same genus, the rate of GOC was 30-47% while it was below 20% when the species were from different genera. A molecular identification key was established for identifying those genera and species within the family Streptococcaceae which have an already known full genome sequence (24 Streptococcus and 2 Lactococcus species). Identical genome parts of the species belonging to the same genus were used for determination of genera. These are the sections surrounding the replication origin dnaA, the sequence from gene phaB to the gene accA, and the sequence of alr acpS secA. Sections around the genes pepX, leuS and rplM were used for identifying the species. The gene order analysis and data in molecular identification key showed that S. uberis and S. parauberis also belong to the same species, and our suggestion for their new names is S. uberis subsp. uberis and S uberis subsp. parauberis. Based on this data, a new definition of bacterial species is proposed: two isolates belong to the same species if the order of the genes in their genomes is almost identical.