Selectivity in tip-induced skeletal editing via heteroatom substitution

summary

The gist

Skeletal editing enables precise structural modifications of molecules at late stages of a synthetic sequence, with applications in drug discovery and materials science.

In short

Researchers used tip-induced reactions on dinaphtho[1,8-bc:1',8'-ef]thiepine (DNT) adsorbed on NaCl to perform single-molecule skeletal editing. They found that sulfur deletion was the predominant reaction, yielding perylene. This demonstrates that choosing the heteroatom significantly controls which atom is removed during these precise structural modifications.

Key concepts

Skeletal Editing: This involves making precise changes to a molecule's structure by adding, removing, or exchanging individual atoms at late stages of synthesis. It aims to create specific molecules without needing to synthesize the entire structure from scratch, which is useful for drug discovery.
Tip-Induced Chemistry: This technique uses the sharp tip of a microscope (STM/AFM) to deliver precise energy or chemical reactions directly onto single molecules adsorbed on a surface. This allows chemists to perform chemistry on a single molecule rather than in bulk solution, enabling single-molecule control over reactions.
Heteroatom Selection: This refers to the strategic choice of which atom within a molecule (like sulfur or oxygen) is targeted for deletion during skeletal editing. The study showed that selecting sulfur leads to atom deletion, while oxygen leads to different outcomes like ring contraction.
DFT Calculations: Density Functional Theory calculations are used as a theoretical tool to predict reaction pathways and energy barriers between different chemical possibilities (like deleting sulfur versus oxygen). These calculations confirmed why sulfur deletion is favored in DNT over oxygen deletion.

Terminology used across episodes

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This episode discusses

Selectivity in tip-induced skeletal editing via heteroatom substitution · Paper Radio

The paper

Selectivity in tip-induced skeletal editing via heteroatom substitution · Read on arXiv

Department of Physics and Astronomy, Chalmers University of Technology · Competence Centre for Catalysis, Chalmers University of Technology · Center for Research in Biological Chemistry and Molecular Materials, and Department of Organic Chemistry, University of Santiago de Compostela · IBM Research Europe – Zurich · Oportunius, Galician Innovation Agency

Skeletal editing enables precise structural modifications of molecules at late stages of a synthetic sequence, with applications in drug discovery and materials science. We recently demonstrated skeletal editing on the single-molecule scale. Voltage pulses applied by the tip of a scanning probe microscope to an oxygen-containing seven-membered heterocycle led to both oxygen deletion and ring-contraction rearrangement reactions. An open question is whether selective skeletal editing of a heterocyclic core can be achieved by an appropriate choice of the heteroatom. Here, we show that tip-induced reactions of an analogous sulfur-containing seven-membered ring results in sulfur deletion in virtually all cases. Our results demonstrate that the combination of tip-induced chemistry and heteroatom selection in the molecular design is a powerful strategy for single-molecule skeletal editing, with the potential to enable diverse structural transformations of heterocyclic frameworks.

DOI: 10.1021/jacs.6c12567

Transcript

Introduction to the show: ident: Quantum Radio. Generated commentary on the latest quantum physics and condensed matter papers.

Kai: Today's paper: "Selectivity in tip-induced skeletal editing via heteroatom substitution".

Mira: Skeletal editing enables precise structural modifications of molecules at late stages of a synthetic sequence, with applications in drug discovery and materials science.

Kai: First, who's behind it and why it matters.

Paper summary: Kai: To summarize this paper, "Selectivity in tip-induced skeletal editing via heteroatom substitution," the main idea is that you can perform precise structural modifications to molecules at a late stage of synthesis by using a scanning probe tip. They claim that the key to controlling *which* atom gets edited lies in choosing the right heteroatom within the molecular skeleton.

Mira: The paper explores skeletal editing, which involves inserting, deleting, or exchanging individual atoms in a molecule's structure. What they specifically investigate is whether this can be done reliably at the single-molecule level through tip-induced chemistry. They focus on dinaphtho

eighteen-bc:one',eight'-ef: oxepine (DNO) and its sulfur analog, DNT, to test this concept <ref:2606.22677#pg1,dinaphtho 1,8-bc:1',8'-ef oxepine (DNO>.

Lev: From a researcher's viewpoint, the significance lies in overcoming the limitations of solution-phase chemistry when it comes to achieving highly specific molecular modifications. If you can target an individual molecule with a tip and control the outcome atom by atom, that capability becomes incredibly valuable for designing complex functional units.

Kai: Exactly. The paper shows that by comparing DNT and DNO, they found a strong preference for sulfur deletion when using this method on a specific surface setup involving bilayer NaCl films. This isn't just about making a product; it’s about demonstrating control over the reaction pathway based on the chemical makeup of the molecule itself.

Mira: The paper claims that tip-induced reactions of DNT predominantly lead to sulfur deletion, accounting for ninety-four percent of successful reactions, which is a high degree of selectivity compared to other possible outcomes like ring-contraction rearrangement <ref:2606.22677#pg0>. This selectivity is theoretically supported by DFT calculations showing lower activation barriers for the sulfur elimination pathway.

Lev: If the DFT data holds up under experimental conditions, it suggests that this method offers a predictable mechanism for structural manipulation, which would be a huge plus when trying to scale up any molecular assembly process, even if only for small units initially.

Kai: So, essentially, they’re proving that combining tip-induced chemistry with careful heteroatom selection gives us a tool capable of achieving single-molecule skeletal editing with atomistic precision. This moves the field forward by showing a new way to access elusive molecular structures directly.

Mira: It matters because it shows how fundamental structural decisions—like which atom is removed—can be dictated by the system's inherent chemistry, rather than just brute-force reaction conditions in solution chemistry. It provides a blueprint for designing targeted molecular transformations.

Conclusion: Kai: Reflecting on "Selectivity in tip-induced skeletal editing via heteroatom substitution," it really comes down to this: they’ve established a powerful method for making specific atomic deletions on molecules at the single-molecule scale by cleverly choosing the heteroatom involved. The authors, including Mishra, Svensson, Malave, Albrecht, VilasVarela, Grönbeck, Gross and Peña—they’ve mapped out how to use tip chemistry to achieve this level of atomistic control.

Mira: Their implication is that we can design molecular scaffolds with pre-determined structural features by controlling the reaction based on the heteroatom's nature. This means we are no longer limited to synthesizing molecules through sequential chemical steps where you hope for a certain outcome; instead, we dictate the structure during the reaction itself.

Lev: For error correction researchers like myself, this is intriguing because it suggests a pathway to creating molecular components with highly tailored electronic properties from scratch, which could be useful in designing next-generation quantum systems that need extremely specific structural configurations.

Kai: Right. It’s about realizing that we can use the probe to guide the chemistry toward a very specific structural change, rather than just observing what happens in a bulk solution. This capability speaks to accessing molecular complexity with unprecedented control over structure and composition.

Mira: The core implication is shifting the focus from synthesizing molecules entirely through chemical reactions to selectively modifying existing molecular frameworks using localized, controlled probes like this tip-induced chemistry. This opens up new avenues for targeted material design and drug discovery applications where precise structural changes are needed.

Lev: If we can reliably execute these kinds of atom-specific manipulations, it means we might be able to engineer molecular architectures with properties that are optimized for specific physical tasks, which is exactly what we need when designing functional components for hardware.

Kai: So the takeaway from this paper is that this work validates a method where the combination of tip-induced chemistry and heteroatom selection allows for selective and atomically precise skeletal editing of carbon frameworks. It’s a demonstration of powerful control over molecular structure at the single-molecule level.

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