London dispersion, which constitutes the attractive part of the famous van der Waals potential, has long been underappreciated in molecular chemistry as an important element of structural stability, ...and thus affects chemical reactivity and catalysis. This negligence is due to the common notion that dispersion is weak, which is only true for one pair of interacting atoms. For increasingly larger structures, the overall dispersion contribution grows rapidly and can amount to tens of kcal mol−1. This Review collects and emphasizes the importance of inter‐ and intramolecular dispersion for molecules consisting mostly of first row atoms. The synergy of experiment and theory has now reached a stage where dispersion effects can be examined in fine detail. This forces us to reconsider our perception of steric hindrance and stereoelectronic effects. The quantitation of dispersion energy donors will improve our ability to design sophisticated molecular structures and much better catalysts.
Center of attraction: Dispersion attraction makes all the difference in the stability of molecular structures, reactivity, and the design of catalysts. Although small for one pair of interactions, dispersion grows rapidly as the molecular size increases.
Peroxy radical hydrogen‐shifts are pivotal elementary reaction steps in the oxidation of small hydrocarbons in autoignition and the lower atmosphere. Although these reactions are typically associated ...with a substantial barrier, we demonstrate that the 1,5H‐shift in the peroxy species derived from the 2‐hydroxyphenyl radical 1 is so facile that it even proceeds rapidly in an argon matrix at 35 K through a proton‐coupled electron transfer mechanism. Hydrogen‐bound complexes of o‐benzoquinone are identified as the main reaction products by infrared spectroscopy although their formation through O−O bond scission is hampered by a barrier of 11.9 kcal mol−1 at the ROCCSD(T)/cc‐pVTZ/UB3LYP/6–311G(d,p) level of theory.
Addition of O2 to the 2‐hydroxyphenyl radical at cryogenic temperatures does not stop at the peroxy radical, but leads to a facile hydrogen‐shift through a proton‐coupled electron transfer mechanism and O−O bond breaking instead.
Matrix isolation studies in solid argon and neon at 4.2 K reveal that iodoacetic acid initially only exists as its ground state (c,x) conformer with an almost perpendicular I–C–CO dihedral angle, ...but UV irradiation in the 240–255 nm range leads to population of the 0.8 kcal mol–1 less stable (c,c) isomer. The latter structure exhibits a close 3.23 Å contact of the iodine and carbonyl oxygen atoms decidedly below the sum of their van der Waals radii (3.50 Å). Increasing the matrix temperature by only a few Kelvin triggers the thermal back reaction of (c,c) to (c,x) and leads to an estimated upper limit of 0.38 kcal mol–1 for the associated torsional barrier. While wave function methods including completely uncorrelated Hartree–Fock theory have no problem to identify (c,c) as a proper minimum, many popular density functionals fail to describe the C–C torsional potential in cis-iodoacetic acid qualitatively correct. We assessed the performance of 12 density functionals of different levels of sophistication, namely, the BLYP, PBE, TPSS, B3LYP, BHandHLYP, PBE0, M06-2X, CAM-B3LYP, ωB97X-D3, B2-PLYP, B2GP-PLYP, and DSD-PBEP86 methods, against accurate extrapolated CCSD(T)/CBS(T–Q)//MP2/def2-TZVPP energies and found that almost all of them yield acceptable relative energies. Still, even some of the best performers fail to find a reasonably deep minimum in the region of the (c,c) conformer, and addition of the empirical D3-dispersion correction does not remedy the qualitative shortcoming. Instead, inclusion of a sufficient amount of (long-range) exact exchange and likely a proper treatment of medium-range correlation effects all along the torsional coordinate play an important role in the proper description of the sub-van der Waals iodine–oxygen contact. More modern, recommended functionals do not suffer from the described shortcoming.
The OH+ cation is a well‐known diatomic for which the triplet (3Σ−) ground state is 50.5 kcal mol−1 more stable than its corresponding singlet (1Δ) excited state. However, the singlet forms a strong ...donor–acceptor bond to argon with a bond energy of 66.4 kcal mol−1 at the CCSDT(Q)/CBS level, making the singlet ArOH+ cation 3.9 kcal mol−1 more stable than the lowest energy triplet complex. Both singlet and triplet isomers of this molecular ion were prepared in a cold molecular beam using different ion sources. Infrared photodissociation spectroscopy in combination with messenger atom tagging shows that the two spin isomers exhibit completely different spectral signatures. The ground state of ArOH+ is the predicted singlet with a covalent Ar−O bond.
Singlet and triplet ArOH+ cations were both generated in a cold molecular beam experiment and their infrared spectra were measured. The singlet displays a strong donor–acceptor‐type chemical bond, making this species the global minimum of this molecular system at the highest levels of theory.
The immunopeptidomic landscape of ovarian carcinomas Schuster, Heiko; Peper, Janet K.; Bösmüller, Hans-Christian ...
Proceedings of the National Academy of Sciences,
11/2017, Volume:
114, Issue:
46
Journal Article
Peer reviewed
Open access
Immunotherapies, particularly checkpoint inhibitors, have set off a revolution in cancer therapy by releasing the power of the immune system. However, only little is known about the antigens that are ...essentially presented on cancer cells, capable of exposing them to immune cells. Large-scale HLA ligandome analysis has enabled us to exhaustively characterize the immunopeptidomic landscape of epithelial ovarian cancers (EOCs). Additional comparative profiling with the immunopeptidome of a variety of benign sources has unveiled a multitude of ovarian cancer antigens (MUC16, MSLN, LGALS1, IDO1, KLK10) to be presented by HLA class I and class II molecules exclusively on ovarian cancer cells. Most strikingly, ligands derived from mucin 16 and mesothelin, a molecular axis of prognostic importance in EOC, are prominent in a majority of patients. Differential gene-expression analysis has allowed us to confirm the relevance of these targets for EOC and further provided important insights into the relationship between gene transcript levels and HLA ligand presentation.
The protonated formaldehyde dimer (H2CO)2H+ was generated in an electrical discharge and supersonic expansion of argon saturated with formalin solution vapor. Its infrared spectrum was measured in ...the region from 900 to 4000 cm–1 employing infrared laser photodissociation and messenger atom tagging. Comparison of the experiment to quantum chemical computations at the CCSD(T)/cc-pVQZ//MP2/cc-pVTZ level reveals that the experimentally observed structure is the head-to-tail dimer and not the more stable proton-bound dimer. This is consistent with the usually observed C–O bond formation upon formaldehyde oligomerization under acidic conditions in solution and resembles the structure of the neutral (H2CO)2 dimer in the gas phase. There is no evidence for the formation of other isomers, most notably protonated glycolaldehyde, that could result from covalent bond formation. These findings may be relevant to a proposed carbohydrate formation mechanism in the interstellar medium starting from protonated formaldehyde dimer.
The response of pristine, nitrogen and boron doped carbon nanotube (CNT) sensors to NO2, CO, C2H4 and H2O at ppm concentrations was investigated at both room temperature and 150°C. N-doped CNTs show ...the best sensitivity to nitrogen dioxide and carbon monoxide, while B-doped CNTs show the best sensitivity to ethylene. All tubes (including undoped) show strong humidity response. Sensing mechanisms are determined via comparison with density functional calculations of gas molecule absorption onto representative defect structures in N and B-doped graphene. N-CNTs show decreased sensitivity with temperature, and detection appears to occur via gas physisorption. B-CNTs appear to react chemically with many of the absorbed species as shown by their poor baseline recovery and increasing sensitivity with temperature. This limits their cyclability. Overall gas sensitivity is as good or better than post-growth functionalised nanotubes, and used in combination, CNTs, N-CNTs and B-CNTs appear highly promising candidates for cheap, low power, room temperature gas sensing applications.
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