Materials Inspired by Nature

Larken E. Euliss

Materials Inspired By Nature:

The Synthesis and Cooperative Assembly of Novel Inorganic Materials

Utilizing Block Copolypeptides

1. Design of Block Copolypeptides to Direct the Formation of Calcium Carbonate Microspheres. ;

The highly-tailored properties of biominerals and bio-composites reflect a strong level of control over the size, morphology, and orientation of crystalline constituents. In large part, this control is exerted by specialized proteins that interact with inorganic building blocks in a structure-directing fashion. Utilizing these ideas, the crystallization of calcium carbonate into microspheres (Figure 1) has been accomplished using rationally-designed, block co-polypeptides as structure-directing agents. The poly-peptides utilized in this application include the doubly-hydrophilic polymer poly{N-2[2-(2-methoxyethoxy)-ethoxy]acetyl-L-lysine}100-b-poly(L-aspartate sodium salt)30 and the amphiphilic block copolypeptides poly{b-poly(L-aspartate sodium salt100-b-poly(L-phenylalanine-L-leucine)random30 and poly{ b-poly(L-glutamate sodium salt100-b-poly(L-phenylalanine-L-leucine)random30.

2. Cooperative Assembly of Magnetic Nanoparticles and Polypeptides in Aqueous Media

In collaboration with Dr. Christopher B. Murray’s group at the IBM T.J. Watson Research Center, we have demonstrated that highly crystalline, monodisperse maghemite (g-Fe2O3) nanoparticles, synthesized in organic solvents, can be stabilized at neutral pH and transferred into an aqueous medium using an ammonium salt. The nanoparticles remain monodisperse (confirmed by TEM and XRD) as well as superparamagnetic (determined by SQUID magnetometry). When this aqueous maghemite dispersion is combined with the block copolypeptide poly(EG2-lys)100-b-poly(asp)30, the nanoparticles assemble into uniform clusters composed of approximately 20 nanoparticles. The resulting water- soluble block copolypeptide–nanoparticle composite structure is illustrated in Figure 2. Alternatively, block copolypeptides functionalized with folate ligands (for cell-targeting applications) or various organic dyes (for imaging applications) can be used to assemble the nanoparticles. Furthermore, an outer silica shell can be assembled around the magnetic nanoparticles by adding silica nanoparticles. The resulting iron oxide/silica composite microshells range in size ranges from 1 to 5 mm in diameter.