Temperature-dependent structural change of D-penicillamine-capped chiral gold nanoparticles investigated by infrared spectroscopy

The structure and stability of D-penicillamine-capped gold nanoparticles (D-Pen Au NPs) were studied using spectroscopic tools. The synthesis of D-Pen Au NPs was examined using high-resolution transmission electron microscopy (HR-TEM), UV-vis absorption spectroscopy, and circular dichroism (CD). Temperature-dependent reversible structural changes of D-Pen Au NPs were observed using infrared spectroscopic tools. The three thiol, carboxyl, and amino binding groups of D-Pen were presumed to interact with Au NP surfaces on the basis of the infrared spectral features, a-Pen appeared to form quite a stable structure and desorb at a high temperature above 453 K on Au NPs. Our deconvolution analysis indicated the nu(s)(COO-) and nu(as)(COO-) carboxylate bands at similar to 1392 and similar to 1560 cm(-1) appeared to be weakened, whereas the amino band at similar to 1595 cm(-1) remained strong in increasing the temperature from 293 to 373K. On the other hand, the intensities of the zwitter ionic bands at similar to 999, similar to 1117, and similar to 1631 cm(-1) for NH3+ appeared to decrease presumably due to the deprotonation process at 373 K. Our infrared spectroscopic study suggests that the deprotonated amino groups bind stronger, whereas the intra-carboxylate bonds become weaker as the temperature increase. Such structural changes of D-Pen Au NPs appeared to be reversible between 293 and 373 K. (C) 2012 Elsevier B.V. All rights reserved.