Helvetica Chimica Acta

Rybakova, Olga; Reisinger, Josef; Rieser, Philipp; Geyer, Philipp; Gerlich, Stefan; Arndt, Markus; Kumar, Amal; Häussinger, Daniel; Mayor, Marcel; Köhler, Valentin

doi: 10.1002/hlca.202500022pmid: N/A

Optical control of molecular beams is intriguing as it promises to become a new tool for mass spectrometry and quantum interferometry, where a single or two photons deterministically remove a tailored tag from a larger molecular structure, e. g., a polypeptide. This cleavage process can change the charge state of the macromolecule, provide reporting signals for both fragments by mass spectrometry and it can selectively remove the fragments from a molecular beam by the momentum recoil generated in the dissociation process. Here, we explore a series of porphyrin derivatives as candidates for photocleavage in the gas phase. They share a large, conjugated core which promises a high absorption cross section for visible light. We present the individualization and beam formation of candidate molecules and study their photo‐dissociation under tunable, visible radiation. We observe a significant wavelength shift and broadening in the photocleavage cross section for molecules in the gas phase compared to those in solution and we find that a single photon can suffice to trigger the cleavage process.

Qu, Di; Wang, Minglei; Bezinge, Léonard; Hensky, Celine; Longo, Filippo; Masucci, Claudia; Suloska, Mirushe; Wang, Jing; Bleiner, Davide

doi: 10.1002/hlca.202400100pmid: N/A

Extreme ultraviolet (XUV) radiation is highly efficient for functionalization of solid materials by means of pronounced radical formation. To prevent collective effects, and study single photon effects, a low‐fluence XUV source with 200 μJ/cm2 was used to irradiate polymers such as poly‐methyl methacrylate (PMMA) and poly‐tetrafluoroethylene (PTFE). The unexposed and XUV‐exposed sample domains were analyzed with time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS), Fourier transform infrared spectroscopy (FT‐IR), and X‐ray photoelectron spectroscopy (XPS). The findings show that XUV photons drive photochemical modification of the surface, fragmentation, and ionization of the desorbed products. Besides a theoretical analysis, the XUV‐induced surface modification of PTFE is discussed a new application for surface functionalization.

Yamashita, Yasuhiro; Hisada, Tomoya; Sato, Yuki; Kobayashi, Shū

doi: 10.1002/hlca.202400207pmid: N/A

The role of Mg(SPh)2 on photocatalytic alkylation of an active methylene with a nonactivated alkene was investigated. Kinetic studies indicate that one‐electron oxidation of a Mg enolate is the rate‐determining step. ESR experiments suggest an interaction between Lewis acidic metals and a radical anion species of 4CzIPN. These results suggest that the higher Lewis acidity of Mg(SPh)2 stabilizes the 4CzIPN radical anion species to enhance its relative abundance and might influence both the one‐electron oxidation step and the radical addition step in the catalytic cycle, leading to enhanced reaction efficiency.

Rodiño, Ricardo; Mascareñas, Jose L.; López, Fernando

doi: 10.1002/hlca.202500011pmid: N/A

Carbonyl‐tethered alkylidenecyclopropanes can react with aryl isocyanates in presence of Pd(0)‐phosphoramidite catalysts to give seven‐membered heterobicyclic products in a formal [3+2+2] cycloaddition process. The reaction involves the formation of a palladium π‐allyl complex intermediate (A), which behaves as a formal 1,5‐dipole, and can be trapped by externally added isocyanates. This report also includes preliminary assays of asymmetric variants, as well as DFT computational studies that shed some light on the nature of the catalytic cycle.

Gorbachev, Vladimir; Tetering, Lara; Martens, Jonathan; Oomens, Jos; Berden, Giel; Tsybizova, Alexandra; Chen, Peter

doi: 10.1002/hlca.202400205pmid: N/A

Protonation and tautomerization significantly impact the conformational landscape and non‐covalent interactions in bis(oxazoline) (BOX) ligands, which are crucial for their applications in catalysis. These interactions influence properties such as binding affinity and catalytic efficiency. While tautomerization has been reported for neutral BOX ligands, its role in protonated forms remains less understood. Here we report the structural and spectroscopic characterization of (S,S−Ph‐BOX)H+ and its tautomerization‐resistant derivative (S,S−Ph‐diMeBOX)H+. We show through IRMPD spectroscopy and TIMS experiments, combined with DFT calculations that (S,S−Ph‐BOX)H+ is present in its tautomeric form, while a broader conformational landscape is observed for (S,S−Ph‐diMeBOX)H+, in which an N−H⋅⋅⋅N proton‐shared conformer is identified. These findings provide a deeper understanding of the relationship between tautomerization and non‐covalent interactions in protonated BOX ligands, offering insights for the design of catalytic systems.

Kumar, Ravi; Luber, Sandra

doi: 10.1002/hlca.202400130pmid: N/A

We present electric dipole polarizability calculations employing atomic‐orbitals based linear response theory within the Kohn‐Sham Density Functional Theory (KS‐DFT) framework, considering both non‐periodic and periodic boundary conditions. We adopt the optimization scheme introduced by T. Helgaker et al. in Chemical Physics Letters 327, 397 (2000) for the single‐electron atomic‐orbitals density matrix. We conduct a comparative analysis between the static polarizability computed using atomic orbitals‐based and previously implemented molecular orbitals‐based methods. In our calculations involving periodic boundary conditions, we implement polarizability calculation using velocity representation of the electric dipole operator in atomic orbitals‐based algorithm, subsequently comparing the results with those computed using the Berry‐phase formulation and velocity representation in molecular orbitals‐based algorithm. We investigate 10 small and medium‐sized molecules in the gas phase, analyze liquid‐phase systems with up to 256 water molecules, and the solid‐state structures of anatase TiO2 and bulk WO3. All polarizability results obtained from the AO‐based solver exhibit good agreement with MO‐based results. From our example calculations, we find that the AO‐based solver exhibits better computational scaling and less memory demand than the MO‐based solvers, which makes it better suited for very large systems.

Greis, Kim; Busse, Linus F.; Benzenberg, Lukas R.; Wu, Ri; Zenobi, Renato

doi: 10.1002/hlca.202500043pmid: N/A

Native mass spectrometry ionizes biomolecules from aqueous buffered solutions using electrospray ionization. Collisions and lasers are often used to study the structures of such native biomolecular ions. While structural changes upon collisions have been studied in more detail, interactions with photons mostly comprise fragmentation. It remains unclear to what degree biomolecular ions undergo unfolding until cleavage. Here, gas‐phase Förster resonance energy transfer (FRET) is used to study fluorescence lifetimes of a 32‐residue α‐helical peptide to monitor peptide unfolding. Increases in lifetime of up to 1.2 ns per charge are observed for different charge states, showing that a low charge is necessary for peptides to retain a compact structure. Increases in lifetime by up to 0.5 ns are observed upon collisional and laser‐based activation and show that the peptide is partially unfolding upon activation. The results contribute to understanding the unfolding dynamics of biomolecules upon activation in mass spectrometry experiments.

doi: 10.1002/hlca.202570501pmid: N/A

Flaget, Arthur; Cesa, Orlando; Mazet, Clément

doi: 10.1002/hlca.202500009pmid: N/A

We report two catalytic enantioselective borylation/oxidation sequences that streamline access to either enantioenriched 1,2‐ or 1,3‐diols starting from O‐benzyl‐protected allylic alcohols as a single precursor. The approach takes advantage of the complementary regioselectivity of the Cu‐catalyzed protoboration and the Cu‐catalyzed hydroboration of disubstituted alkenes, which effectively install a borane function and a hydrogen atom on opposite C(sp2) carbon atoms of a carbon–carbon double bond. The two methods feature broad substrate scope and are amenable to large scale without measurable loss of the catalytic efficiency. Both protocols display high levels of regioselectivity and enantioselectivity.

Birkbeck, Anthony A.; Chapuis, Christian; Schalk, Michel

doi: 10.1002/hlca.202500010pmid: N/A

The rich chemistry of East Indian Sandalwood oil has fascinated chemists for over a century. Whilst the synthesis on industrial scale of the principal odour vector (−)‐(Z)‐β‐Santalol 2, has resisted all attempts to date, many synthetic fragrant sandalwood ingredients have been discovered and manufactured on industrial scale. This precious wood is still listed as endangered and appears on the CITES red list, despite an increased number of plantations being developed. This review will focus on the interesting chemistry of Santalum album (Linn.) essential oil and the subsequent efforts by researchers to find a viable substitute for this highly appreciated oil both by investigating novel structures and using biotech approaches. The emphasis will be on the approaches to these highly appreciated odorants made from renewable resources that are currently manufactured on multi‐MT scale. Lesser emphasis will be placed on close structural analogues that have not been commercially successful.