The wide diversity of room-temperature ionic liquids (ILs) presents opportunities for studying, and controlling, polymer phase behavior. We have examined the phase behavior of poly(N-isopropyl acrylamide) (PNIPAM) in imidazolium ILs and their mixtures with water. We find there is a strong influence of the IL anion; specifically, the tetrafluoroborate anion yields a complex phase diagram with both LCST and UCST-type regimes. PNIPAM is generally miscible at intermediate IL-water compositions, although this range depends on the polymer molecular weight. Solvatochromatic characterization of both neat and mixed solvents reveals a key role for the interplay between PNIPAM-IL hydrogen-bonding and ion-pairing within the IL. These results demonstrate that appropriate selection of ILs should allow for increased control over polymer phase behavior.

[DO NOT ALTER/DELETE THIS TEXT] 5Controlling interactions between building blocks, in either guided or selfassemblies, is becoming increasingly important for creation of functional materials. We have focused our attention on the well-known model assembly, the filamentous bacteriophage, where our strategy is to selectively alter surface features by focusing on spatially distinct capsid 10 proteins. Towards introducing stimulus-responsive behavior in these flexible, rod-like particles, we have introduced elastin-like polypeptide (ELP) motifs of isoleucine and tyrosine "guest" residues by recombinant DNA methods. Our hypothesis is that modification of the major coat capsid protein would be greatly amplified by the 2700 copies per particle. 15Characterization of ELP-phage particles was carried out by microbiological assays, zeta potential, dynamic light scattering, and calorimetry. Bacteria producing ELP-phage particles grow more slowly and surprisingly, ELPmodified phages display a significant reduction in viral infectivity. For the lengths of ELP inserts studied, modified phages do not aggregate from 20 solution as monitored by DLS. However, the hydrodynamic size of the phages depends on the details of the ELP motif.Zeta potential measurements reveal the particles are electrostatically stabilized, and this contributes in part to the energetic barrier against aggregation. Preliminary calorimetric data indicate subtle thermal transitions in the range 35-40 o C, 25 suggesting that the ELP motif may collapse without triggering macroscopic aggregation. The results are consistent with the classical picture of critical solution phenomena at low concentrations, where to drive phase separation, solvent quality must be increasingly poor. Apart from being model systems to study basic questions of self-assembly, extending the these modular 30 systems is likely to result in improved understanding and control over selfassembly in various applications.

The ability of both viruses and DNA to self-assemble in solution has continues to enable numerous applications at the nanoscale. Here we review the relevant interactions dictating the assembly of these structures, as well as discussing how they can be exploited experimentally. Because self-assembly is a process, we discuss various strategies for achieving spatial and temporal control. Finally, we highlight a few examples of recent advances that exploit the features of these nanostructures.

There were no significant differences in catheter integrity between SLC or CBT catheters exposed to a 70% EL for 26 weeks. Given its low cost, potential to avoid antibiotic resistance and structural integrity after 6 months of high-dose ethanol, ELs should be studied prospectively against antibiotic locks to assess the efficacy and safety in hemodialysis patients.

While elastin-like polypeptides and peptides (ELPs) have been used for various stimulus-responsive applications, details of their switching remain unclear. We therefore constructed a novel series of filamentous phage particles displaying a high surface density of short ELPs. The surface display of ELPs did not disrupt either particle shape or dimensions, and the resulting ELP-phage particles were colloidally stable over several weeks. However, in spite of a saturating surface density, macroscopic aggregation of ELP-phages cannot be triggered in water. To investigate the underlying mechanisms we examined conformational changes in the secondary structure of the phage proteins by circular dichroism and tryptophan fluorescence, which indicate partial protein unfolding in ELP-phage particles. To gain further insight into the ELP itself, analogous "free" ELP peptides were synthesized and characterized. Circular dichroism of these peptides shows the onset of β-type conformations with increasing temperature, consistent with the accepted view of the microscopic transition that underlies the inverse phase behavior of ELPs. Increased guest residue hydrophobicity was found to depress the microscopic transition temperature of the peptides, also consistent with a previously proposed intramolecular hydrogen-bonding mechanism. Importantly, our results indicate that although the nanoscale presentation state can suppress macroscopic aggregation of ELPs, microscopic transitions of the ELP can still occur. Given the growing use of ELPs within supra-molecular scaffolds, such effects are important design considerations for future applications.

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