Chiral supramolecular nanoparticles: The study of chiral surface modification of silver nanoparticles by cysteine and its derivatives

• Cysteine, penicillamine, α-methylcystein immobilization on nanoparticles was proved.
• Different nanoparticles have similar optical activity in the presence of cysteine.
• Chiral ECD bands are provided only in the presence of cysteine.
• Adsorbed cysteine derivatives molecules are lesser than cysteine molecules.
• 3D supramolecular structure of adsorbed molecules is needed to origin of ECD signal.

Many studies dealing with modified nanoparticles are based on the assumption that organic molecules form single-layer structure on their surface. In this work, we suggest a novel approach to study the important phenomenon of supramolecular chirality at metal nanoparticle surfaces. Self-assembly layers of several ligands, namely l-cysteine, l-penicillamine and α-methyl-l-cysteine, on different silver nanoparticles were studied by means of absorption and electronic circular dichroism spectroscopy in UV–vis range and surface enhanced Raman scattering spectroscopy. The amount of ligands bonded to the surface of nanoparticles was quantified by absorption spectroscopy. Quantification was performed indirectly by measuring concentration of free ligands in solution after incubation with absorption labels 4-toluenesulfonyl chloride or 1-fluoro-2,4-dinitrobenzene. Data were obtained for ligands at concentration levels from 10−6 to 10−3 mol L−1. The results showed the significantly lower adsorbed molecules of methyl derivatives of cysteine than for cysteine themselves. This fact could explain the unexpected behavior of silver nanoparticles that provide ECD bands in the presence of cysteine and not in the presence of its derivatives.

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