Preparation of CdS nanoparticles within an ordered polypeptide matrix

Abstract

CdS nanoparticles have been synthesized within an ordered polypeptide matrix of Poly-L-glutamic acid (PGA). PGA forms a lyotropic liquid crystalline phase which can be mechanically sheared to prepare macroscopically oriented films of closepacked, parallel, helical polypeptides. Cadmium was introduced into the polypeptide by neutralizing the acid groups on exposing PGA films to an aqueous solution of Cd(OH) 2 for different times, and subsequent reaction with H 2S causes CdS nanoparticles to form in this uniaxial matrix. Absorption spectroscopy and polarizing optical and infrared spectroscopy were used to determine PGA conformation and alignment. Absorption spectroscopy and TEM were used to determine the sizes of the CdS particles. Sizes ranged from 27 Å to 46 Å and were inversely dependent upon the length of the Cd(OH) 2 exposure period. However, no evidence for CdS nanoparticle shape anisotropy or orientation was detected in materials synthesized in the aligned polypeptide host matrix.