Graduate student Praneeth Nimmala will present his dissertation research “Gold nanomolecules: Developing synthetic protocols, Characterization and investigating the ligand effects on structure and properties” to the department.
Gold nanoparticles are chemical entities in the size range 1 to 100 nm. They have been known to exist since ancient times in the fields of jewelry as they produce vibrant, size dependent, colors upon interaction with light. Gold is a preferred choice of metal for the synthesis of nanoparticles mainly due to its inertness to atmospheric conditions and most chemicals. Gold thiolate nanomolecules, which is the primary focus of this dissertation research, are chemical molecules with a fixed number of gold atoms and organo-thiolate ligands. They are of the form Aux(SR)y and possess molecule-like properties as a result of distinctive quantum confinement effects occurring at the nanoscale size. The optical and electronic properties of these molecules change as a function of “x” and “y”. The stability of these nanomolecules can be attributed due in part to their symmetrical geometry as evidenced by the X-ray crystallography and theoretical calculations. Recent research in the field has focused on exploiting the size-dependent properties of gold nanomolecules in applications like nano-electronics, biological sensing and catalysis. But much of the hindrance to these advances come from the lack of established protocols to synthesize monodisperse nanomolecules in high yields. In my talk, the following topics related to the synthesis of gold nanomolecules are covered 1) One-phase synthesis protocol for synthesis of gold-thiolate nanomolecules wherein the gold salt and the capping ligands are essentially dissolved in a single solvent system. This protocols is peculiar in that it yields sizes like Au67 and Au~103-105 which are otherwise not observed. 50+ mg of the pure Au67 was isolated for the first time1 using the above designed protocols. The high yields of the product has enabled its complete characterization using mass spectrometry, optical spectroscopy, NMR, powder-XRD and electrochemistry. 2) The isolation and purification nanomolecules using size exclusion chromatography (SEC) which proved to be highly reproducible and less laborious. 3) Protocols of “etching” and “core size conversion” as a way to minimize the polydispersity of nanomolecules.2 These protocols can be used to exclusively synthesize highly stable Au38 and Au40 sizes. 4) The role of capping ligands in determining size, geometry and properties of nanomolecules; a factor which typically overlooked in this field was investigated.3,4
(1) Nimmala, P. R.; Yoon, B.; Whetten, R. L.; Landman, U.; Dass, A. The Journal of Physical Chemistry A 2013, 117, 504.
(2) Nimmala, P. R.; Jupally, V. R.; Dass, A. Langmuir 2014, 30, 2490.
(3) Nimmala, P. R.; Dass, A. Journal of the American Chemical Society 2011, 133, 9175.
(4) Nimmala, P. R.; Knoppe, S.; Jupally, V. R.; Delcamp, J. H.; Aikens, C. M.; Dass, A. The Journal of Physical Chemistry B 2014, 118, 14157.