skip to main content

Attention:

The NSF Public Access Repository (PAR) system and access will be unavailable from 11:00 PM ET on Thursday, February 13 until 2:00 AM ET on Friday, February 14 due to maintenance. We apologize for the inconvenience.


This content will become publicly available on September 5, 2025

Title: Discovery of Isomerization Intermediates in CdS Magic-Size Clusters
Isomerization, the process by which a molecule is coherently transformed into another molecule with the same molecular formula but a different atomic structure, is an important and well-known phenomenon of organic chemistry, but has only recently been observed for inorganic nanoclusters. Previously, CdS nanoclusters were found to isomerize between two end point structures rapidly and reversibly (the α-phase and β-phase), mediated by hydroxyl groups on the surface. This observation raised many significant structural and pathway questions. One critical question is why no intermediate states were observed during the isomerization; it is not obvious why an atomic cluster should only have two stable end points rather than multiple intermediate arrangements. In this study, we report that the use of amide functional groups can stabilize intermediate phases during the transformation of CdS magic-size clusters between the α-phase and the β-phase. When treated with amides in organic solvents, the amides not only facilitate the α-phase to β-phase isomerization but also exhibit three distinct excitonic features, which we call the β340-phase, β350-phase, and β367-phase. Based on pair distribution function analysis, these intermediates strongly resemble the β-phase structure but deviate greatly from the α-phase structure. All phases (β340-phase, β350-phase, and β367-phase) have nearly identical structures to the β-phase, with the β340-phase having the largest deviation. Despite these intermediates having similar atomic structures, they have up to a 583 meV difference in band gap compared to the β-phase. Kinetic studies show that the isomers and intermediates follow a traditional progression in the thermodynamic stability of β340-phase/β350-phase < α-phase < β367-phase < β-phase. The solvent identity and polarity play a crucial role in kinetically arresting these intermediates. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy studies paired with simple density functional theory calculations reveal that the likely mechanism is due to the multifunctional nature of the amides that form an amphoteric surface binding bond motif, which promotes a change in the carboxylic acid binding mode. This change from chelating binding modes to bridging binding modes initiates the isomerization. We propose that the carbonyl group is responsible for the direct interaction with the surface, acting as an L-type ligand which then pulls electron density away from the electron-poor nitrogen site, enabling them to interact with the carboxylate ligands and initiate the change in the binding mode. The isomerization of CdS nanoclusters continues to be a topic of interest, giving insight into fundamental nanoscale chemistry and physics.  more » « less
Award ID(s):
2003586 2120947 2344586 1719875
PAR ID:
10541551
Author(s) / Creator(s):
; ;
Publisher / Repository:
American Chemical Society
Date Published:
Journal Name:
ACS Nano
ISSN:
1936-0851
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. NMR-assisted crystallography—the integrated application of solid-state NMR, X-ray crystallography, and first-principles computational chemistry—holds significant promise for mechanistic enzymology: by providing atomic-resolution characterization of stable intermediates in enzyme active sites, including hydrogen atom locations and tautomeric equilibria, NMR crystallography offers insight into both structure and chemical dynamics. Here, this integrated approach is used to characterize the tryptophan synthase α-aminoacrylate intermediate, a defining species for pyridoxal-5′-phosphate–dependent enzymes that catalyze β-elimination and replacement reactions. For this intermediate, NMR-assisted crystallography is able to identify the protonation states of the ionizable sites on the cofactor, substrate, and catalytic side chains as well as the location and orientation of crystallographic waters within the active site. Most notable is the water molecule immediately adjacent to the substrate β-carbon, which serves as a hydrogen bond donor to the ε-amino group of the acid–base catalytic residue βLys87. From this analysis, a detailed three-dimensional picture of structure and reactivity emerges, highlighting the fate of the L-serine hydroxyl leaving group and the reaction pathway back to the preceding transition state. Reaction of the α-aminoacrylate intermediate with benzimidazole, an isostere of the natural substrate indole, shows benzimidazole bound in the active site and poised for, but unable to initiate, the subsequent bond formation step. When modeled into the benzimidazole position, indole is positioned with C3 in contact with the α-aminoacrylate C β and aligned for nucleophilic attack. Here, the chemically detailed, three-dimensional structure from NMR-assisted crystallography is key to understanding why benzimidazole does not react, while indole does. 
    more » « less
  2. Recently, 2D tellurene (Te) structures have been experimentally synthesized. These structures possess high carrier mobility and stability which make them ideal candidates for applications in electronics, optoelectronics and energy devices. We performed density functional theory (DFT) and molecular dynamics (MD) simulations to investigate the stability and electronic structure of 2D α- and β-Te sheets, and hydrogen, oxygen, and fluorine functionalized counterparts, including spin–orbit coupling effects. Our calculations show that bare α and β-Te sheets are stable with band gaps of 0.44 eV and 1.02 eV respectively. When functionalized, α and β monolayers exhibit metallic properties, except for hydrogenated β-Te, which exhibits semiconducting properties with a band gap of 1.37 eV. We see that H, O and F destabilize the structure of α-Te. We also find that F and H cause β-Te layers to separate into functionalized atomic chains and O causes β-Te to transform into a Te 3 O 2 -like structure. We also studied single atom and molecule binding on the Te surface, the effects of adatom coverage, and the effects of functionalized Te on a GaSe substrate. Our results indicate that tellurene monolayers and functionalized counterparts are not only suitable for future optoelectronic devices, but can be used as metallic contacts in nanoscale junctions. 
    more » « less
  3. β-titanium (β-Ti) alloys are useful in diverse industries because their mechanical properties can be tuned by transforming the metastable β phase into other metastable and stable phases. Relationships between lattice parameter and β-Ti alloy concentrations have been explored, but the lattice parameter evolution during β-phase transformations is not well understood. In this work, the β-Ti alloys, Ti-11Cr, Ti-11Cr-0.85Fe, Ti-11Cr-5.3Al, and Ti-11Cr-0.85Fe-5.3Al (all in at.%), underwent a 400 °C aging treatment for up to 12 h to induce the β-to-ω and β-to-α phase transformations. Phase identification and lattice parameters were measured in situ using high-temperature X-ray diffraction. Phase compositions were measured ex situ using atom probe tomography. During the phase transformations, Cr and Fe diffused from the ω and α phases into the β matrix, and the β-phase lattice parameter exhibited a corresponding decrease. The decrease in β-phase lattice parameter affected the α- and ω-phase lattice parameters. The α phase in the Fe-free alloys exhibited α-phase c/a ratios close to those of pure Ti. A larger β-phase composition change in Ti-11Cr resulted in larger ω-phase lattice parameter changes than in Ti-11Cr-0.85Fe. This work illuminates the complex relationship between diffusion, composition, and structure for these diffusive/displacive transformations.

     
    more » « less
  4. null (Ed.)
    Ultrasmall metal nanoparticles (below 2.2 nm core diameter) start to show discrete electronic energy levels due to strong quantum confinement effects and thus behave much like molecules. The size and structure dependent quantization induces a plethora of new phenomena, including multi-band optical absorption, enhanced luminescence, single-electron magnetism, and catalytic reactivity. The exploration of such new properties is largely built on the success in unveiling the crystallographic structures of atomically precise nanoclusters (typically protected by ligands, formulated as M n L m q , where M = metal, L = Ligand, and q = charge). Correlation between the atomic structures of nanoclusters and their properties has further enabled atomic-precision engineering toward materials design. In this frontier article, we illustrate several aspects of the precise engineering of gold nanoclusters, such as the single-atom size augmenting, single-atom dislodging and doping, precise surface modification, and single-electron control for magnetism. Such precise engineering involves the nanocluster's geometric structure, surface chemistry, and electronic properties, and future endeavors will lead to new materials design rules for structure–function correlations and largely boost the applications of metal nanoclusters in optics, catalysis, magnetism, and other fields. Following the illustrations of atomic-precision engineering, we have also put forth some perspectives. We hope this frontier article will stimulate research interest in atomic-level engineering of nanoclusters. 
    more » « less
  5. Cation exchange is a versatile post-synthetic method to explore a wide range of nanoparticle compositions, phases, and morphologies. Recently, several studies have expanded the scope of cation exchange to magic-size clusters (MSCs). Mechanistic studies indicated that MSC cation exchange undergoes a two-stage reaction pathway instead of the continuous diffusion-controlled mechanism found in nanoparticle cation exchange reactions. The cation exchange intermediate, however, has not been well-identified despite it being the key to understanding the reaction mechanism. Only indirect evidence, such as exciton peak shifts and powder x-ray diffraction, has been used to indicate the formation of the cation exchange intermediate. In this paper, we investigate the unusual nature of cation exchange in nanoclusters using our previously reported CdS MSC. High-resolution mass spectra reveal two cation exchanged reaction intermediates [Ag2Cd32S33(L) and AgCd33S33(L), L: oleic acid] as well as the fully exchanged Ag2S cluster. Crystal and electronic structure characterizations also confirm the two-stage reaction mechanism. Additionally, we investigate the Cu/CdS MSC cation exchange reaction and find a similar two-stage reaction mechanism. Our study shows that the formation of dilutely exchanged intermediate clusters can be generally found in the first stage of the MSC cation exchange reaction. By exchanging different cations, these intermediate clusters can access varying properties compared to their unexchanged counterparts. 
    more » « less