NMR Determine Chirality Gold Nanoparticles

NMR to Determine Chirality of Gold Nanoparticles

2:36 AM, 12th December 2011
NMR to Determine Chirality of Gold Nanoparticles
Chiral nanoparticles


PITTSBURGH, US: Roberto R. Gil, Research Scientist and Director, NMR Facility Department of Chemistry and Rongchao Jin, assistant Professor, Department of Chemistry, Carnegie Mellon University have successfully used NMR to analyze the structure of infinitesimal gold nanoparticles, which could advance the development and use of the tiny particles in drug development.

Their approach offers a significant advantage over routine methods for analyzing gold nanoparticles because it can determine whether the nanoparticles exhibit chirality (right-handed and left-handed configuration).

Drugs with only one of the configurations are effective in the body. In some cases, the other isomer may even be harmful. Thalidomide, which consisted of two isomers, one of which helped pregnant women control nausea while the other caused damage to the developing fetus. In an effort to create safe & effective drugs, drug manufacturers are looking for ways to produce substances with only one isomer.

Huifeng Qian, student, Carnegie Mellon University created a gold nanoparticle that has the potential to catalyze chemical reactions that will produce one isomer rather than the other.

"Growing a pure crystal from nanoparticles is very challenging, and you may not even be able to get a crystal at all," said Jin. "In the nanoparticle community, the crystal structures of only three nanoparticles have been reported."

In Jin's case, X-ray crystallography revealed that the gold nanoparticle is chiral. Chemists typically probe the internal chiral structure of gold nanoparticles using a technique called circular dichoism spectroscopy. When pure chiral molecules are exposed to circularly polarized light, each isomer absorbs the light differently, resulting in a unique and of opposite sign spectrum for each isomer. The process of creating the gold nanoparticles often results in a 50/50 mix of each isomer, known as racemates.

"Because the spectrum is of opposite sign for each isomer, they cancel each other out and the net optical response is zero. This makes circular dichoism (CD) spectroscopy useless," said Gil.

Since Jin couldn't use CD spectroscopy, Gil used NMR to help Jin distinguish between his gold nanoparticles' isomers.

NMR spectroscopy takes advantage of the physical phenomenon wherein some nuclei wobble and spin like tops, emitting and absorbing a radio frequency signal in a magnetic field. By observing the behavior of these spinning nuclei, scientists can piece together the chemical structure of the compound.

Gil and Jin compared the NMR signal from the hydrogen atoms in a non-chiral gold nanoparticle with the NMR signal from the hydrogen atoms in chiral gold nanoparticle. The non-chiral nanoparticle's NMR spectrum did not reveal any differences, but the chiral nanoparticle's NMR spectrum revealed two different hydrogen signals, providing a efficient way of telling whether the particle is chiral or not or racemates.

"NMR is an alternative and very efficient method for providing useful information about how the atoms in nanoparticles form the molecular structure. Because NMR can determine chirality in some cases, it can readily be used to determine the purity of a nanoparticle mixture," said Jin.


© Carnegie Mellon University News 




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