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Papers by Amrita Chakraborty
Accounts of Chemical Research, 2018
Supramolecular chemistry is a major area of chemistry that utilizes weaker non-covalent interacti... more Supramolecular chemistry is a major area of chemistry that utilizes weaker non-covalent interactions between molecules, including hydrogen bonding, van der Waals, electrostatic, π•••π, and C−H•••π interactions. Such forces have been the basis of several molecular self-assemblies and host−guest complexes in organic, inorganic, and biological systems. Atomically precise nanoclusters (NCs) are materials of growing interest that display interesting structure−property correlations. The evolving science of such systems reaffirms their molecular behavior. This gives a possibility of exploring their supramolecular chemistry, leading to assemblies with similar or dissimilar cluster molecules. Such assemblies with compositional, structural, and conformational precision may ultimately result in cluster-assembled hybrid materials. In this Account, we present recent advancements on different possibilities of supramolecular interactions in atomically precise cluster systems that can occur at different length scales. We first present a brief discussion of the aspicule model of clusters, considering Au 25 (SR) 18 as an example, that can explain various aspects of its atomic precision and distinguish the similar or dissimilar interacting sites in their structures. The supramolecular interaction of 4-tert-butylbenzyl mercaptan (BBSH)-protected [Au 25 (SBB) 18 ] − NCs with cyclodextrins (CD) to form Au 25 SBB 18 ∩CD n (n = 1−4) and that of [Ag 29 (BDT) 12 ] 3− with fullerenes to form [Ag 29 (BDT) 12 (C 60) n ] 3− (n = 1−9) (BDT = 1,3-benzenedithiolate) are discussed subsequently. The formation of these adducts was studied by electrospray ionization mass spectrometry (ESI MS), optical absorption and NMR spectroscopy. In the subsequent sections, we discuss how variation in intercluster interactions can lead to polymorphic crystals, which are observable in single-crystal X-ray diffraction. Taking [Ag 29 (BDT) 12 (TPP) 4 ] 3− (TPP = triphenylphosphine) clusters as an example, we discuss how the different patterns of C−H•••π and π•••π interactions between the secondary ligands can alter the packing of the NCs into cubic and trigonal lattices. Finally, we discuss how the supramolecular interactions of atomically precise clusters can result in their hybrid assemblies with plasmonic nanostructures. The interaction of p-mercaptobenzoic acid (p-MBA)-protected Ag 44 (p-MBA) 30 NCs with tellurium nanowires (Te NWs) can form crossed-bilayer precision assemblies with a woven-fabric-like structure with an angle of 81°between the layers. Similar crossed-bilayer assemblies show an angle of 77°when Au 102 (p-MBA) 44 clusters are used to form the structure. Such assemblies were studied by transmission electron microscopy (TEM). Precision in these hybrid assemblies of Te NWs was highly controlled by the geometry of the ligands on the NC surface. Moreover, we also present how Ag 44 (p-MBA) 30 clusters can encapsulate gold nanorods to form cage-like nanostructures. Such studies involved TEM, scanning transmission electron microscopy (STEM), and three-dimensional tomographic reconstructions of the nanostructures. The hydrogen bonding interactions of the −COOH groups of the p-MBA ligands were the major driving force in both of these cases. An important aspect that is central to the advancement of the area is the close interplay of molecular tools such as MS with structural tools such as TEM along with detailed computational modeling. We finally conclude this Account with a future perspective on the supramolecular chemistry of clusters. Advancements in this field will help in developing new materials with potential optical, electrical, and mechanical properties.
The Journal of Physical Chemistry C, 2021
Directing the assembly of plasmonic nanoparticles into chiral superstructures has diverse applica... more Directing the assembly of plasmonic nanoparticles into chiral superstructures has diverse applications including, chiroptical sensing, nonlinear optics, and biomedicine. Though soft template-mediated assemblies of both spherical and nonspherical gold nanoparticles have made significant progress, most approaches require sophisticated chemical synthesis or advanced methodologies. Besides, reports of structurally precise chiral plasmonic assemblies beyond nanoscale are limited. Here, we propose an efficient yet simple strategy to grow such precision assemblies up to mesoscale, which is beneficial for a broader community. Briefly, cationic gold nanorods (AuNRs) are allowed to systematically assemble along atomically precise, chiral, rodlike tobacco mosaic virus (TMV) particles via electrostatic attraction under ambient condition. This leads to spontaneous formation of helical hybrid microwires with high structural precision, as evidenced by cryogenic transmission electron microscopy and tomography. Resulting composite superstructures show a strong circular dichroism response at the plasmon wavelength of the AuNRs, which is supported by simulations using discrete dipole approximation. Further, chirality of the system is investigated at a single-microwire level using polarized dark-field scattering microscopy. An alternative chiral template, negatively charged colloidal cellulose nanocrystals, also arrange AuNRs into similar chiral microstructures. Thus, our report proposes a generic methodology to obtain chiral plasmonic response at the NIR region using inexpensive templates that will encourage the exploration of a wider range of nanoscale templates for creating hybrid mesostructures with emerging optoelectronic properties.
Angewandte Chemie (International ed. in English), 2018
We present the self-assembled structures of atomically precise, ligand-protected noble metal nano... more We present the self-assembled structures of atomically precise, ligand-protected noble metal nanoclusters leading to encapsulation of plasmonic gold nanorods (GNRs). Unlike highly sophisticated DNA nanotechnology, our approach demonstrates a strategically simple hydrogen bonding-directed self-assembly of nanoclusters leading to octahedral nanocrystals encapsulating GNRs. Specifically, we use the p-mercaptobenzoic acid (pMBA) protected atomically precise nanocluster, Na4[Ag44(pMBA)30] and pMBA functionalized GNRs. High resolution transmission and scanning transmission electron tomographic reconstructions suggest that the geometry of the GNR surface is responsible for directing the assembly of silver nanoclusters via H-bonding leading to octahedral symmetry. Further, use of water dispersible gold nanoclusters, Au~250(pMBA)n and Au102(pMBA)44 also formed layered shells encapsulating GNRs. Such cluster assemblies on colloidal particles present a new category of precision hybrids with di...
Accounts of Chemical Research, 2018
Supramolecular chemistry is a major area of chemistry that utilizes weaker non-covalent interacti... more Supramolecular chemistry is a major area of chemistry that utilizes weaker non-covalent interactions between molecules, including hydrogen bonding, van der Waals, electrostatic, π•••π, and C−H•••π interactions. Such forces have been the basis of several molecular self-assemblies and host−guest complexes in organic, inorganic, and biological systems. Atomically precise nanoclusters (NCs) are materials of growing interest that display interesting structure−property correlations. The evolving science of such systems reaffirms their molecular behavior. This gives a possibility of exploring their supramolecular chemistry, leading to assemblies with similar or dissimilar cluster molecules. Such assemblies with compositional, structural, and conformational precision may ultimately result in cluster-assembled hybrid materials. In this Account, we present recent advancements on different possibilities of supramolecular interactions in atomically precise cluster systems that can occur at different length scales. We first present a brief discussion of the aspicule model of clusters, considering Au 25 (SR) 18 as an example, that can explain various aspects of its atomic precision and distinguish the similar or dissimilar interacting sites in their structures. The supramolecular interaction of 4-tert-butylbenzyl mercaptan (BBSH)-protected [Au 25 (SBB) 18 ] − NCs with cyclodextrins (CD) to form Au 25 SBB 18 ∩CD n (n = 1−4) and that of [Ag 29 (BDT) 12 ] 3− with fullerenes to form [Ag 29 (BDT) 12 (C 60) n ] 3− (n = 1−9) (BDT = 1,3-benzenedithiolate) are discussed subsequently. The formation of these adducts was studied by electrospray ionization mass spectrometry (ESI MS), optical absorption and NMR spectroscopy. In the subsequent sections, we discuss how variation in intercluster interactions can lead to polymorphic crystals, which are observable in single-crystal X-ray diffraction. Taking [Ag 29 (BDT) 12 (TPP) 4 ] 3− (TPP = triphenylphosphine) clusters as an example, we discuss how the different patterns of C−H•••π and π•••π interactions between the secondary ligands can alter the packing of the NCs into cubic and trigonal lattices. Finally, we discuss how the supramolecular interactions of atomically precise clusters can result in their hybrid assemblies with plasmonic nanostructures. The interaction of p-mercaptobenzoic acid (p-MBA)-protected Ag 44 (p-MBA) 30 NCs with tellurium nanowires (Te NWs) can form crossed-bilayer precision assemblies with a woven-fabric-like structure with an angle of 81°between the layers. Similar crossed-bilayer assemblies show an angle of 77°when Au 102 (p-MBA) 44 clusters are used to form the structure. Such assemblies were studied by transmission electron microscopy (TEM). Precision in these hybrid assemblies of Te NWs was highly controlled by the geometry of the ligands on the NC surface. Moreover, we also present how Ag 44 (p-MBA) 30 clusters can encapsulate gold nanorods to form cage-like nanostructures. Such studies involved TEM, scanning transmission electron microscopy (STEM), and three-dimensional tomographic reconstructions of the nanostructures. The hydrogen bonding interactions of the −COOH groups of the p-MBA ligands were the major driving force in both of these cases. An important aspect that is central to the advancement of the area is the close interplay of molecular tools such as MS with structural tools such as TEM along with detailed computational modeling. We finally conclude this Account with a future perspective on the supramolecular chemistry of clusters. Advancements in this field will help in developing new materials with potential optical, electrical, and mechanical properties.
The Journal of Physical Chemistry C, 2021
Directing the assembly of plasmonic nanoparticles into chiral superstructures has diverse applica... more Directing the assembly of plasmonic nanoparticles into chiral superstructures has diverse applications including, chiroptical sensing, nonlinear optics, and biomedicine. Though soft template-mediated assemblies of both spherical and nonspherical gold nanoparticles have made significant progress, most approaches require sophisticated chemical synthesis or advanced methodologies. Besides, reports of structurally precise chiral plasmonic assemblies beyond nanoscale are limited. Here, we propose an efficient yet simple strategy to grow such precision assemblies up to mesoscale, which is beneficial for a broader community. Briefly, cationic gold nanorods (AuNRs) are allowed to systematically assemble along atomically precise, chiral, rodlike tobacco mosaic virus (TMV) particles via electrostatic attraction under ambient condition. This leads to spontaneous formation of helical hybrid microwires with high structural precision, as evidenced by cryogenic transmission electron microscopy and tomography. Resulting composite superstructures show a strong circular dichroism response at the plasmon wavelength of the AuNRs, which is supported by simulations using discrete dipole approximation. Further, chirality of the system is investigated at a single-microwire level using polarized dark-field scattering microscopy. An alternative chiral template, negatively charged colloidal cellulose nanocrystals, also arrange AuNRs into similar chiral microstructures. Thus, our report proposes a generic methodology to obtain chiral plasmonic response at the NIR region using inexpensive templates that will encourage the exploration of a wider range of nanoscale templates for creating hybrid mesostructures with emerging optoelectronic properties.
Angewandte Chemie (International ed. in English), 2018
We present the self-assembled structures of atomically precise, ligand-protected noble metal nano... more We present the self-assembled structures of atomically precise, ligand-protected noble metal nanoclusters leading to encapsulation of plasmonic gold nanorods (GNRs). Unlike highly sophisticated DNA nanotechnology, our approach demonstrates a strategically simple hydrogen bonding-directed self-assembly of nanoclusters leading to octahedral nanocrystals encapsulating GNRs. Specifically, we use the p-mercaptobenzoic acid (pMBA) protected atomically precise nanocluster, Na4[Ag44(pMBA)30] and pMBA functionalized GNRs. High resolution transmission and scanning transmission electron tomographic reconstructions suggest that the geometry of the GNR surface is responsible for directing the assembly of silver nanoclusters via H-bonding leading to octahedral symmetry. Further, use of water dispersible gold nanoclusters, Au~250(pMBA)n and Au102(pMBA)44 also formed layered shells encapsulating GNRs. Such cluster assemblies on colloidal particles present a new category of precision hybrids with di...