Ana de Bettencourt-Dias

The study of the coordination structure in lanthanide-ligand complexes is important to gain insight into the selectivity of ligands for specific lanthanide ions. We recently designed lanthanide binding cyclic peptides (LBCPs), which display selectivity toward the middle lanthanides. In this study, we report micromolar affinity in a Eu-LBCP complex and resolve the structure of the europium complexes with two LBCPs by comparing experimental extended X-ray absorption fine structure (EXAFS) spectra to ensemble-average spectra derived from molecular dynamics (MD) simulation, as well as to spectra from a fitting model. Our results show agreement between the computationally derived and experimentally measured EXAFS spectra, which supports the predicted Eu coordination structure in LBCP complexes, as well as the utility of combining molecular simulation and EXAFS to study the structure of lanthanide-ligand complexes in solution.

We isolated Eu2O3 nanoparticles, capped with the sensitizers dipicolinic acid (DPA) and kynurenic acid (KA) and a combination of the two, as imaging agents for biological tissues. The latter system, EuPEGKADPA, combined the advantages of the individual sensitizers and exhibited the longest emission lifetime of 1.244 ms and a quantum yield of 1.7% in Tris-buffer. In the presence of tissue lysate, this system displayed an emission intensity ∼60% higher than that of tissue autofluorescence. With time-gating, an almost 800-fold increase in the signal-to-noise ratio was observed. Eu(III) emission was observed with EuPEGKADPA in dried tissue samples mounted with DPX, ProLong Diamond, and Permount. In the DPX-mounted tissue, EuPEGKADPA demonstrated a 15-fold improvement in detection limit on a concentration basis for the nanoparticles when compared to rhodamine B. The long-lived lifetime, high signal-to-noise ratio, and improved detection limit of the systems studied here validate further studying of ligand-sensitized Eu(III) nanoparticles for bioimaging applications.

New water-soluble imidazolium-based and benzenetriol-based ligands and their 3:2 ligand-to-lanthanide sandwich-type complexes, [Ln₂(L₁)₃H₂O], [Ln₂(L₂)₃H₂O], and [Ln₂(L₃)₃H₂O] (Ln = Er(III), Gd(III), and Lu(III)), were isolated. Upon 980 nm excitation, the Er(III) complexes exhibited metal-centered up-conversion emission in the solid state and in aqueous solution. When incubated in HeLa cells, the complexes appear to localize in the mitochondria, and red and green Er(III)-centered up-conversion emission was observed.

Understanding how outer-sphere interactions influence the inner-sphere structure of lanthanide complexes in solution is crucial for advancing applications in separations, materials, and nuclear chemistry. Here, we investigate the solution-phase coordination environment of Nd(NO₃)₃ in acetonitrile encapsulated by the dipicolylamine-functionalized triazine ligand dpat. Extended X-ray absorption fine structure (EXAFS) spectroscopy at the Nd L₃-edge was used to probe the solution structures, while ab initio molecular dynamics (AIMD) simulations provided atomistic models of the ion coordination environment. The supramolecular encapsulation complex [Nd(NO₃)₆(H₃dpat)₂]³⁺, previously identified in the solid state, is shown to persist in an acetonitrile solution without substantial changes to its structure or first coordination shell. Theoretical EXAFS spectra derived from the AIMD simulations reproduce the experimental features, confirming that dpat encapsulation stabilizes the high-nitrate coordination environment in solution. These findings underscore the role of weakly coordinating molecules (nitrate, acetonitrile, and dpat) in shaping the structure of solvated lanthanide complexes.

Electron-withdrawing groups in the ortho -position of the terpyridine ligand modulate the structure and photoluminescence characteristics of Eu( iii ) and Tb( iii ) complexes.

Lanthanide ions are difficult to separate from one another due to their similar chemical properties. The discovery of lanthanide-binding peptides and proteins in nature has led to an increased interest in the possibility of utilizing the strong binding of peptides to lanthanide ions for their separations; as such, there has been an effort to identify or design peptides with improved lanthanide binding and selectivity toward particular lanthanide ions. In this study, we designed and characterized lanthanide-binding cyclic peptides (LBCPs) with molecular dynamics simulations, electronic structure calculations, and emission spectroscopy. Luminescent decay measurements were done to determine the number of water molecules coordinated to the Eu³⁺ ion in Eu-LBCP complexes and compare to the predicted number of water molecules by computation to assess the lanthanide-binding affinity of LBCPs. Measured stability constants show binding of the LBCPs to the Eu³⁺ ion with stronger than micromolar affinity. We were able to identify multiple peptides that selectively bind to middle lanthanides. We describe the structural basis of the lanthanide-binding selectivity trend with strongest binding to the middle lanthanides, followed by the heavier lanthanides, and finally to the lighter ions.

We report on the synthesis of two novel nanographenes, syn- and anti-dinaphthopentacene. This small variation in structure leads to stark differences in structural and photophysical properties as well as OLED device efficiency.

The role of intramolecular vibrational energy redistribution is critical when considering the thermal properties of coordination complexes. The interactions and redistribution of vibrational energy can be uncovered through the use of two-dimensional infrared (2D IR) spectroscopy by observing the cross-peaks between different vibrational signatures. In this study, the energetic landscape consisting of the vibrations of [6,2':6',2″-terpyridine]-2-carbaldehyde (terpyCHO) is studied directly in the region between 1400 and 1740 cm^-1. Information on the anharmonic coupling between different groups of vibrations estimates the delocalization in the detected normal modes. The delocalization of the aldehyde stretch is directly comparable to that calculated from density functional theory (DFT) calculations and local mode analysis via the LModeA program, a freeware that can characterize the normal modes in terms of a nonredundant set of local modes. Tracking of the relative cross-peak intensities as a function of the waiting time reveals a complex network of energy exchange pathways responsible for energy dissipation and vibrational dephasing. These dynamics reveal the aldehyde to be an efficient inlet and outlet of vibrational energy flow and the C-H bends as energetic dumps with the pyridine ring stretches acting as bridging modes between them. Finally, signatures of vibrational coherences are observed in the diagonal peak dynamics of the 2D IR data, further revealing a network of couplings to lower energy modes that mediate this energy exchange. These findings provide new insights into the energetic landscape of organic molecules potentially useful as ligands in single molecule magnets.

Ensemble-average sampling of structures from ab initio molecular dynamics (AIMD) simulations can be used to predict theoretical extended X-ray absorption fine structure (EXAFS) signals that closely match experimental spectra. However, AIMD simulations are time-consuming and resource-intensive, particularly for solvated lanthanide ions, which often form multiple nonrigid geometries with high coordination numbers. To accelerate the characterization of lanthanide structures in solution, we employed the Northwest Potential Energy Surface Search Engine (NWPEsSe), an adaptive-learning global optimization algorithm, to efficiently screen first-shell structures. As case studies, we examine two systems: Eu(NO3)3 dissolved in acetonitrile with a terpyridine ligand (terpyNO2), and Nd(NO3)3 dissolved in acetonitrile. The theoretical spectra for structures identified by NWPEsSe were compared to both experimental and AIMD-derived EXAFS spectra. The NWPEsSe algorithm successfully identified the proper solvation structure for both Eu(NO3)3(terpyNO2) and Nd(NO3)(acetonitrile)3, with the calculated EXAFS signals closely matching the experimental spectra for the Eu-ligand complex and showing good similarity for the Nd salt; the better agreement with the ligand-containing structure is attributed to a less dynamic coordination environment due to the rigid ligand. The key advantage of the global optimization algorithm lies in its ability to sample the coordination environment across the potential energy surface and reduce the time required to identify structures from generally a month to within a week. Additionally, this approach is versatile and can be adapted to characterize main-group metal complexes.

Ensemble-average sampling of structures sampled from ab initio molecular dynamics (AIMD) simulations can be used to predict theoretical extended X-ray absorption fine structure (EXAFS) signals that closely match experimental spectra. However, AIMD simulations are time-consuming and resource-intensive, particularly for solvated lanthanide ions, which often form multiple non-rigid geometries with high coordination numbers. To accelerate the characterization of lanthanide structures in solution, we employed the Northwest Potential Energy Surface Search Engine (NWPEsSe), an adaptive-learning global optimization algorithm, to efficiently screen first-shell structures. As case studies, we examine two systems: Eu(NO3)3 dissolved in acetonitrile with a terpyridine ligand (terpyNO2), and Nd(NO3)3 dissolved in acetonitrile. The theoretical spectra for structures identified by NWPEsSe were compared to both experimental and AIMD-derived EXAFS spectra. The NWPEsSe algorithm successfully identified the proper solvation structure for both Eu(NO3)3(terpyNO2) and Nd(NO3)(acetonitrile)3, with the calculated EXAFS signals closely matching the experimental spectra for the Eu-ligand complex and showing good similarity for the Nd salt; the better agreement with the ligand-containing structure is attributed to a less dynamic coordination environment due to the rigid ligand. The key advantage of the global optimization algorithm lies in its ability to sample the coordination environment across the potential energy surface. The structure identification process can be done with a variety of methods and generally has reduced the time required from a month to within a week.