Sniffing out camphor: the fine balance between hydrogen bonding and London dispersion in the chirality recognition with α-fenchol.

Binary complexes between the chiral monoterpenoids camphor and α-fenchol were explored with vibrational and rotational jet spectroscopy as well as density functional theory in order to explore how chirality can influence the binding preferences in gas-phase complexes. The global minimum structures of the two diastereomers were assigned. It is found that chirality recognition leads to different compromises in the fine balance between intermolecular interactions. While one isomer features a stronger hydrogen bond, the other one is more tightly arranged and stabilized by larger London dispersion interactions. These new spectroscopic results help understand the influence of chirality in molecular aggregation and unveil the kind of interactions involved between a chiral alcohol and a chiral ketone with large dispersion contributions.

Von Hippel-Lindau Disease: A Rare Radiological Case Report of a Symptomatic Patient and His Asymptomatic Genetic Counterpart.

Von Hippel-Lindau (VHL) disease is an inherited syndrome manifested as a benign and malignant tumor. It is an autosomal dominant syndrome diagnosed approximately in 1 in 36,000 people. We report a case where male siblings presented with the involvement of bilateral kidneys and the multi-cystic lesion on the pancreas in both. Reverse transcription polymerase chain reaction (RT-PCR) was conducted to detect the VHL gene, which turned out to be a significant finding in our study. The rare involvement of both pancreas and kidneys was noted in the siblings with VHL in the present study. In patients with VHL-associated tumour presentations, the most frequent detection of pathogenic variants in the VHL gene is the result of directed genetic testing or inherited cancer gene panels. The presence of renal and pancreatic involvement is rare but a significant finding present within the family member who needs to be screened.

Benchmarking a new segmented K-band chirped-pulse microwave spectrometer and its application to the conformationally rich amino alcohol isoleucinol.

Isoleucinol, a potential precursor to the essential α-amino acid isoleucine, has been studied using microwave spectroscopy from 2-26 GHz. The measurements between 18-26 GHz were performed with a newly developed segmented chirped-pulse Fourier transform microwave spectrometer, which has reduced the cost of the instrument by half compared to a single pulse excitation and direct detection chirped-pulse microwave spectrometer in the same frequency range. The performance of the instrument has been demonstrated and found to be comparable to the previous design. For isoleucinol, the flexibility of the sec-butyl side chain (R = -CH(CH3)CH2CH3) can result in more than 200 different conformers from its five dihedral angles, and experimentally, seven conformers have been assigned. A fit including the hyperfine splitting due to nitrogen nuclear quadrupole coupling for the rotational transitions is reported for all conformers, along with the experimental structures of the three lowest energy conformers. The observed conformers have intramolecular NH-O hydrogen bond interactions, similar to the second energetically favorable conformer of the analogous amino acid, isoleucine. A complete linelist has been provided to facilitate a search for isoleucinol in the interstellar medium.

The first microsolvation step for furans: New experiments and benchmarking strategies.

The site-specific first microsolvation step of furan and some of its derivatives with methanol is explored to benchmark the ability of quantum-chemical methods to describe the structure, energetics, and vibrational spectrum at low temperature. Infrared and microwave spectra in supersonic jet expansions are used to quantify the docking preference and some relevant quantum states of the model complexes. Microwave spectroscopy strictly rules out in-plane docking of methanol as opposed to the top coordination of the aromatic ring. Contrasting comparison strategies, which emphasize either the experimental or the theoretical input, are explored. Within the harmonic approximation, only a few composite computational approaches are able to achieve a satisfactory performance. Deuteration experiments suggest that the harmonic treatment itself is largely justified for the zero-point energy, likely and by design due to the systematic cancellation of important anharmonic contributions between the docking variants. Therefore, discrepancies between experiment and theory for the isomer abundance are tentatively assigned to electronic structure deficiencies, but uncertainties remain on the nuclear dynamics side. Attempts to include anharmonic contributions indicate that for systems of this size, a uniform treatment of anharmonicity with systematically improved performance is not yet in sight.

Rotational Signatures of Dispersive Stacking in the Formation of Aromatic Dimers.

The aggregation of aromatic species is dictated by inter- and intramolecular forces. Not only is characterizing these forces in aromatic growth important for understanding grain formation in the interstellar medium, but it is also imperative to comprehend biological functions. We report a combined rotational spectroscopic and quantum-chemical study on three homo-dimers, comprising of diphenyl ether, dibenzofuran, and fluorene, to analyze the influence of structural flexibility and the presence of heteroatoms on dimer formation. The structural information obtained shows clear similarities between the dimers, despite their qualitatively different molecular interactions. All dimers are dominated by dispersion interactions, but the dibenzofuran dimer is also influenced by repulsion between the free electron pairs of the oxygen atoms and the π-clouds. This study lays the groundwork for understanding the first steps of molecular aggregation in systems with aromatic residues.

The phenyl vinyl ether-methanol complex: a model system for quantum chemistry benchmarking.

The structure of the isolated aggregate of phenyl vinyl ether and methanol is studied by combining a multi-spectroscopic approach and quantum-chemical calculations in order to investigate the delicate interplay of noncovalent interactions. The complementary results of vibrational and rotational spectroscopy applied in molecular beam experiments reveal the preference of a hydrogen bond of the methanol towards the ether oxygen (OH∙∙∙O) over the π-docking motifs via the phenyl and vinyl moieties, with an additional less populated OH∙∙∙P(phenyl)-bound isomer detected only by microwave spectroscopy. The correct prediction of the energetic order of the isomers using quantum-chemical calculations turns out to be challenging and succeeds with a sophisticated local coupled cluster method. The latter also yields a quantification as well as a visualization of London dispersion, which prove to be valuable tools for understanding the role of dispersion on the docking preferences. Beyond the structural analysis of the electronic ground state (S0), the electronically excited (S1) state is analyzed, in which a destabilization of the OH∙∙∙O structure compared to the S0 state is observed experimentally and theoretically.

The Effect of Dispersion on the Structure of Diphenyl Ether Aggregates.

Dispersion interactions can play an important role in understanding unusual binding behaviors. This is illustrated by a systematic study of the structural preferences of diphenyl ether (DPE)-alcohol aggregates, for which OH⋅⋅⋅O-bound or OH⋅⋅⋅π-bound isomers can be formed. The investigation was performed through a multi-spectroscopic approach including IR/UV and microwave methods, combined with a detailed theoretical analysis. The resulting solvent-size-dependent trend for the structural preference turns out to be counter-intuitive: the hydrogen-bonded OH⋅⋅⋅O structures become more stable for larger alcohols, which are expected to be stronger dispersion energy donors and thus should prefer an OH⋅⋅⋅π arrangement. Dispersion interactions in combination with the twisting of the ether upon solvent aggregation are key for understanding this preference.

Multi-spectroscopic and theoretical analyses on the diphenyl ether-tert-butyl alcohol complex in the electronic ground and electronically excited state.

Aromatic ethers such as diphenyl ether (DPE) represent molecules with different docking sites for alcohols leading to competing OH-O and OH-π interactions. In a multi-spectroscopic approach in combination with quantum chemical calculations the complex of DPE with tert-butyl alcohol (t-BuOH) is investigated in the electronic ground state (S0) and the electronically excited state (S1). FTIR, microwave as well as mass- and isomer-selective IR/R2PI spectra are recorded, revealing co-existing OH-O and OH-π isomers in the S0 state. Surprisingly, they are predicted to be of almost equal stability in contrast to the previously investigated DPE-MeOH complex, where the OH-π structure is preferred by both theory and experiment. The tert-butyl group in t-BuOH allows for a simultaneous optimization of hydrogen-bonding and dispersion interactions, which provides a sensitive meeting point between theory and experiment. In the electronically excited state of DPE-t-BuOH, vibrational spectra could be recorded separately for both isomers using UV/IR/UV spectroscopy. In the S1 state the same structural binding motifs are obtained as in the S0 state with the OH-O bond being weakened for the OH-O arrangement and the OH-π interaction being strengthened in the case of the OH-π isomer compared to the S0 state.