I. Self-Assembly of Novel Helical Polypeptides

 

Motivated by these reasons, we have focused on the principles governing self-assembly in rod-like polymer systems and investigated the interplay between solvent polarity, time of assembly, and length of a novel sulfide modified rod-like material.  We have built on these principles by self-assembling a hinged, photo-responsive PBLG material (PAzP) for use in engineering interfacial and optical properties.  In recent  work we have explored the  synthesis of PAzP and the impact of the hinged structure on physical properties such as dipole moment, relaxation time, and isomerization kinetics.

II. Engineering Nanoscale Constructs of Metallic Nanoparticles and Stimuli-Sensitive, Rod-Like Polymers

Responsive nanoscale constructs of metallic nanoparticles and synthetic biopolymers are of great interest in the area of nanobiotechnology.  The synergism between biological characteristics such as recognition and conformational change and the unique optical and electronic properties of nanomaterials can lead to novel applications such as sensors, photonic materials, and biomolecular electronics.  Our goal is to use extrinsic, triggered responses in the organic biopolymer to manipulate the nanoparticles and utilize their unique functional properties. 

In this context, we have demonstrated reversible aggregation of gold nanoparticles that are modified by self-assembly of a simple homopolypeptide, namely, disulfide modified poly(L-glutamic acid) that is prepared by polymerization of the N-Carboxy Anyhydride (NCA).  The SSPLGA spontaneously modifies the gold nanoparticle surface via chemisorption of the disulfide headgroup.  Cycling the pH changes the aggregation state of the gold colloids in solution from dispersed to aggregated (color transition from pink to blue).

 

In ongoing work we are focusing on directing self-assembly of anisotropic metallic nanoparticles such as gold nanorods.  These unique materials have interesting optical properties such as strong transverse and  longitudinal resonances in the visible and near IR spectrum.  As a result,  gold nanorods are extremely relevant to sensors, biomedicine, diagnotics, and nano-electronics.

 

· J. Y. Shim. and V. K. Gupta, “Reversible Aggregation of Gold Nanoparticles Induced by pH Dependent Conformational Transitions of a Self-Assembled Polypeptide”, Journal of Colloid and Interface Science (In Press).

 

 

New advances in engineering of interfaces using self-assembled monolayers (SAMs) have increasingly focused on molecules that are complex in structure, function, and design. 

Self-assembly of a-helical polypeptides such as poly-g-benzyl-L-glutamate (PBLG) is one example where a new structural motif has been explored.  Their assembly at interfaces is relevant to piezoelectric devices, optical data storage, biomimetics, and non-linear optics. 

 

 

 

 

 

 

 

· Alveda J. Williams and Vinay K. Gupta, "Structure and Formation of Self-Assembled Monolayers of Helical Poly(g-benzyl L-glutamate) by Surface Plasmon Resonance and Infrared Spectroscopy", Thin Solid Films, 423(1/2), 228-234 (2003).

· Alveda J. Williams and Vinay K. Gupta, "Role of Photochromic Initiator in the Synthesis and Physical Properties of Hinged, Photoresponsive Polypeptides”, J. Polymer Science: Part B Physics, 39, 2759 - 2773 (2001).

· Alveda J. Williams and Vinay K. Gupta, "Self-Assembly of a Rod-like Polypeptide on Solid Surfaces: Role of Solvent, Molecular Weight, and Time of Assembly”, J. Physical Chemistry B, 105, 5223-5230 (2001).