Chiral Graphene Quantum Dots

Abstract

Chiral nanostructures from metals and semiconductors attract wide interest as components for polarization-enabled optoelectronic devices. Similarly to other fields of nanotechnology, graphene-based materials can greatly enrich physical and chemical phenomena associated with optical and electronic properties of chiral nanostructures and facilitate their applications in biology as well as other areas. Here, we report that covalent attachment of l/d-cysteine moieties to the edges of graphene quantum dots (GQDs) leads to their helical buckling due to chiral interactions at the "crowded" edges. Circular dichroism (CD) spectra of the GQDs revealed bands at ca. 210-220 and 250-265 nm that changed their signs for different chirality of the cysteine edge ligands. The high-energy chiroptical peaks at 210-220 nm correspond to the hybridized molecular orbitals involving the chiral center of amino acids and atoms of graphene edges. Diverse experimental and modeling data, including density functional theory calculations of CD spectra with probabilistic distribution of GQD isomers, indicate that the band at 250-265 nm originates from the three-dimensional twisting of the graphene sheet and can be attributed to the chiral excitonic transitions. The positive and negative low-energy CD bands correspond to the left and right helicity of GQDs, respectively. Exposure of liver HepG2 cells to L/D-GQDs reveals their general biocompatibility and a noticeable difference in the toxicity of the stereoisomers. Molecular dynamics simulations demonstrated that d-GQDs have a stronger tendency to accumulate within the cellular membrane than L-GQDs. Emergence of nanoscale chirality in GQDs decorated with biomolecules is expected to be a general stereochemical phenomenon for flexible sheets of nanomaterials.

Plasmonic Chiral Nanostructures: Chiroptical Effects and Applications

“…[148] As for the efficiency problem, a recent report pointed out that chiral graphene quantum dots were promising for drug delivery to achieve more efficient and selective phototherapies. [149] In the future study, advanced characterization methods are needed for deeper nature. The nearfield imaging of chiral optical density of state (ODOS) can act as a promising tool.…”

Controlled Covalent Functionalization of Thermally Reduced Graphene Oxide To Generate Defined Bifunctional 2D Nanomaterials

“…This clearly indicates a quantitative substitution of the first and second chlorine atoms of TRGO‐Trz 1 by controlled post‐modification (Supporting Information, page S32 and Figure S13). Since they are enantiomers, substitution of the first chlorine atom of the dichlorotriazine groups by l ‐Cys should produce chiral 2D nanomaterials 27. Meanwhile, substitution of the second chlorine atom would racemize the system.…”

Synthesis, Optical, and Magnetic Properties of Graphene Quantum Dots and Iron Oxide Nanocomposites

“…Under these optimized conditions, we obtained a high yield of 1-2 nm GQDs product. e given conditions are also suitable for engineering the GQDs-Fe 3 Samples were characterized with a high-resolution transmission electron microscope (HRTEM) (JEOL JEM-2200FS TEM operated at 200 kV). e UV-visible spectra were recorded on a Varian Cary 1E UV spectrophotometer.…”

“…Zero-dimensional, graphene quantum dots (GQDs) [1,2] have shown exceptional physical and chemical properties [3] including, among others, photoluminescence, chemical stability, and pronounced quantum confinement effect making them attractive for novel optoelectronic and energyrelated applications [4]. In addition, due to low toxicity [5], GQDs have significant potential to be used in the field of biophysics and medical sciences as active and passive agents, where they have shown great promise in future therapies for photodynamic treatment of cancerous tumors, imaging, and drug delivery applications [6].…”