Venkatesh Rao

Biomimetic synthesis of superparamagnetic iron oxide particles in proteins

Matrix-mediated in situ synthesis of monodispersed magnetite and maghemite nanoparticles (2-16 nm) was carried out using the cavities present in gels of globular proteins such as egg white and bovine serum albumin. Under stringent conditions, spatial-charge-distribution-assisted molecular recognition of proteins for inorganic ions led to the site- and polymorph-specific synthesis of superparamagnetic iron oxide particles. A transformation from magnetite to maghemite as a nucleating phase could be observed by partially denaturing the egg white protein, signifying the delicate role of quaternary structure of proteins under different reaction conditions, in determining the size and shape of the polymorph.

Synthesis of Nanosized Copper Powder by an Aqueous Route

Nanostructured, crystalline copper powder was produced at ambient temperature by aqueous reduction of a copper salt by sodium borohydride. Conditions were optimized to produce boron-free copper powder with an average particle diameter of 200 nm, surface area of 5.48 m * m/g, and oxygent content of 0.155%. The effects of different experimental conditions on average particle size of the powder were also studied. The sintering phenomenon exhibited by produced copper particles at 100°C may be attributed to the low oxygen content of the powder along with other size variation-dependent factors.

Polymer-Mediated Synthesis of Fine-Sized Cobalt Particles

A novel method to synthesize monodisperse, fine-sized cobalt particles (average particle size 200 nm) by a polymer matrix (not commonly known for chemical chelation)-mediated sodium borohydride reduction of cobalt chloride has been demonstrated and discussed. As against the conventional concept of using a supramolecule as a growth Poisson during the crystallization of inorganic salt from solution, the present procedure adopts the path very similar to biomineralization. The polymer matrix chelates the cobalt ions by a combined process of physical entrapment and chemical chelation. The process leads to a controlled nucleation and ordered growth of cobalt salt in polymer matrix. Orderly grown cobalt salt on reduction yields monodisperse cobalt particles having uniform size and morphology.

Patterning of copper particles on polymeric surface

In situ synthesis of fine copper particles (> 200 nm) has been carried out using borohydride reduction in preorganized gel of poly(vinyl alcohol). The copper ions were chelated by polymer matrix at room temperature thorough physical entrapment along with a weak chemical complexation. The process is akin to biomimetic route and demonstrates a high order of control over nucleation, growth, and morphologies as well as orientation of the end product. The organized arrays of copper sulfate precipitate and copper particles replicate the conformation of organic matrix and form patterned structures similar to one observed in stationary chemical waves.