skip to main content

Title: Synergistic regulation of nonbinary molecular switches by protonation and light

We report a molecular switching ensemble whose states may be regulated in synergistic fashion by both protonation and photoirradiation. This allows hierarchical control in both a kinetic and thermodynamic sense. These pseudorotaxane-based molecular devices exploit the so-called Texas-sized molecular box (cyclo[2]-(2,6-di(1H-imidazol-1-yl)pyridine)[2](1,4-dimethylenebenzene); 14+, studied as its tetrakis-PF6salt) as the wheel component. Anions of azobenzene-4,4′-dicarboxylic acid (2H+•2) or 4,4′-stilbenedicarboxylic acid (2H+•3) serve as the threading rod elements. The various forms of 2 and 3 (neutral, monoprotonated, and diprotonated) interact differently with 14+, as do the photoinducedcisortransforms of these classic photoactive guests. The net result is a multimodal molecular switch that can be regulated in synergistic fashion through protonation/deprotonation and photoirradiation. The degree of guest protonation is the dominating control factor, with light acting as a secondary regulatory stimulus. The present dual input strategy provides a complement to more traditional orthogonal stimulus-based approaches to molecular switching and allows for the creation of nonbinary stimulus-responsive functional materials.

; ; ; ; ;
Publication Date:
Journal Name:
Proceedings of the National Academy of Sciences
Page Range or eLocation-ID:
Article No. e2112973118
Proceedings of the National Academy of Sciences
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Conical intersections between electronic states often dictate the chemistry of photoexcited molecules. Recently developed sources of ultrashort extreme ultraviolet (XUV) pulses tuned to element-specific transitions in molecules allow for the unambiguous detection of electronic state-switching at a conical intersection. Here, the fragmentation of photoexcitediso-propyl iodide andtert-butyl iodide molecules (i-C3H7I andt-C4H9I) through a conical intersection between3Q0/1Q1spin–orbit states is revealed by ultrafast XUV transient absorption measuring iodine 4dcore-to-valence transitions. The electronic state-sensitivity of the technique allows for a complete mapping of molecular dissociation from photoexcitation to photoproducts. In both molecules, the sub-100 fs transfer of a photoexcited wave packet from the3Q0state into the1Q1state at the conical intersection is captured. The results show how differences in the electronic state-switching of the wave packet ini-C3H7I andt-C4H9I directly lead to differences in the photoproduct branching ratio of the two systems.

  2. Abstract

    We compare embedded young massive star clusters (YMCs) to (sub-)millimeter line observations tracing the excitation and dissociation of molecular gas in the starburst ring of NGC 1365. This galaxy hosts one of the strongest nuclear starbursts and richest populations of YMCs within 20 Mpc. Here we combine near-/mid-IR PHANGS–JWST imaging with new Atacama Large Millimeter/submillimeter Array multi-JCO (1–0, 2–1 and 4–3) and [Ci] (1–0) mapping, which we use to trace CO excitation viaR42=ICO(4−3)/ICO(2−1)andR21=ICO(2−1)/ICO(1−0)and dissociation viaRCICO=I[CI](1−0)/ICO(2−1)at 330 pc resolution. We find that the gas flowing into the starburst ring from northeast to southwest appears strongly affected by stellar feedback, showing decreased excitation (lowerR42) and increased signatures of dissociation (higherRCICO) in the downstream regions. There, radiative-transfer modeling suggests that the molecular gas density decreases and temperature and [CI/CO] abundance ratio increase. We compareR42andRCICOwith local conditions across the regions and find that both correlate with near-IR 2μm emission tracing the YMCs and with both polycyclic aromatic hydrocarbon (11.3μm) and dust continuum (21μm) emission. In general,RCICOexhibits ∼0.1 dex tighter correlations thanR42, suggestingCito be a more sensitive tracer of changing physical conditions in the NGC 1365 starburst than CO (4–3). Our results are consistent with a scenario where gas flows into the two armmore »regions along the bar, becomes condensed/shocked, forms YMCs, and then these YMCs heat and dissociate the gas.

    « less
  3. Abstract

    Feedback from massive stars plays an important role in the formation of star clusters. Whether a very massive star is born early or late in the cluster formation timeline has profound implications for the star cluster formation and assembly processes. We carry out a controlled experiment to characterize the effects of early-forming massive stars on star cluster formation. We use the star formation software suiteTorch, combining self-gravitating magnetohydrodynamics, ray-tracing radiative transfer,N-body dynamics, and stellar feedback, to model four initially identical 104Mgiant molecular clouds with a Gaussian density profile peaking at 521.5 cm−3. Using theTorchsoftware suite through theAMUSEframework, we modify three of the models, to ensure that the first star that forms is very massive (50, 70, and 100M). Early-forming massive stars disrupt the natal gas structure, resulting in fast evacuation of the gas from the star-forming region. The star formation rate is suppressed, reducing the total mass of the stars formed. Our fiducial control model, without an early massive star, has a larger star formation rate and total efficiency by up to a factor of 3, and a higher average star formation efficiency per freefall time by up to a factor of 7. Early-forming massive stars promote the buildupmore »of spatially separate and gravitationally unbound subclusters, while the control model forms a single massive cluster.

    « less
  4. Increases in CO2concentration in plant leaves due to respiration in the dark and the continuing atmospheric [CO2] rise cause closing of stomatal pores, thus affecting plant–water relations globally. However, the underlying CO2/bicarbonate (CO2/HCO3) sensing mechanisms remain unknown. [CO2] elevation in leaves triggers stomatal closure by anion efflux mediated via the SLAC1 anion channel localized in the plasma membrane of guard cells. Previous reconstitution analysis has suggested that intracellular bicarbonate ions might directly up-regulate SLAC1 channel activity. However, whether such a CO2/HCO3regulation of SLAC1 is relevant for CO2control of stomatal movements in planta remains unknown. Here, we computationally probe for candidate bicarbonate-interacting sites within the SLAC1 anion channel via long-timescale Gaussian accelerated molecular dynamics (GaMD) simulations. Mutations of two putative bicarbonate-interacting residues, R256 and R321, impaired the enhancement of the SLAC1 anion channel activity by CO2/HCO3inXenopusoocytes. Mutations of the neighboring charged amino acid K255 and residue R432 and the predicted gate residue F450 did not affect HCO3regulation of SLAC1. Notably, gas-exchange experiments withslac1-transformed plants expressing mutated SLAC1 proteins revealed that the SLAC1 residue R256 is required for CO2regulation of stomatal movements in planta, but not for abscisic acid (ABA)-induced stomatal closing. Patch clamp analyses of guard cells show that activation ofmore »S-type anion channels by CO2/HCO3, but not by ABA, was impaired, indicating the relevance of R256 for CO2signal transduction. Together, these analyses suggest that the SLAC1 anion channel is one of the physiologically relevant CO2/HCO3sensors in guard cells.

    « less
  5. Abstract

    Kohn-Sham density functional theory (DFT) is a standard tool in most branches of chemistry, but accuracies for many molecules are limited to 2-3 kcal ⋅ mol−1with presently-available functionals. Ab initio methods, such as coupled-cluster, routinely produce much higher accuracy, but computational costs limit their application to small molecules. In this paper, we leverage machine learning to calculate coupled-cluster energies from DFT densities, reaching quantum chemical accuracy (errors below 1 kcal ⋅ mol−1) on test data. Moreover, density-basedΔ-learning (learning only the correction to a standard DFT calculation, termedΔ-DFT ) significantly reduces the amount of training data required, particularly when molecular symmetries are included. The robustness ofΔ-DFT  is highlighted by correcting “on the fly” DFT-based molecular dynamics (MD) simulations of resorcinol (C6H4(OH)2) to obtain MD trajectories with coupled-cluster accuracy. We conclude, therefore, thatΔ-DFT  facilitates running gas-phase MD simulations with quantum chemical accuracy, even for strained geometries and conformer changes where standard DFT fails.