Herein we present the results of a blind challenge to quantum chemical methods in the calculation of dimerization preferences in the low temperature gas phase. The target of study was the first step of the microsolvation of furan, 2-methylfuran and 2,5-dimethylfuran with methanol. The dimers were investigated through IR spectroscopy of a supersonic jet expansion. From the measured bands, it was possible to identify a persistent hydrogen bonding OH–O motif in the predominant species. From the presence of another band, which can be attributed to an OH-π interaction, we were able to assert that the energy gap between the two types of dimers should be less than or close to 1 kJ/mol across the series. These values served as a first evaluation ruler for the 12 entries featured in the challenge. A tentative stricter evaluation of the challenge results is also carried out, combining theoretical and experimental results in order to define a smaller error bar. The process was carried out in a double-blind fashion, with both theory and experimental groups unaware of the results on the other side, with the exception of the 2,5-dimethylfuran system which was featured in an earlier publication.

This paper was selected as Featured ARTICLES YOU MAY BE INTERESTED INProbabilistic performance estimators for computational chemistry methods: Systematic improvement probability and ranking probability matrix. I. Theory

The microwave spectrum of o-methyl anisole (2-methoxytoluene), CH OC H CH has been measured by using a pulsed molecular jet Fourier transform microwave spectrometer operating in the frequency range 2-26.5 GHz. Conformational analysis using quantum chemical calculations at the MP2/6-311++G(d,p) level of theory yields only one stable conformer with a C structure, which was assigned in the experimental spectrum. A-E splittings due to the internal rotation of the ring methyl group could be resolved and the barrier to internal rotation was determined to be 444.05(41) cm . The experimentally deduced molecular parameters such as rotational and centrifugal distortion constants as well as the torsional barrier of the ring methyl group are in agreement with the calculated values.

The Fourier transform microwave (FTMW) spectrum of allyl acetate (CH 3 -COO-CH 2 -CH=CH 2 ) has been measured under molecular beam conditions. By comparing the experimental data with quantum chemical calculations we identified one conformer of C 1 symmetry, in which the ethylene group is bent by an angle of approximately 129° against the plane of the C-COO-C backbone. Large A-E splittings (in some cases up to 1 GHz) of all lines due to internal rotation of the acetate methyl group were found. Analyzing the spectrum with the program BELGI-C 1 yielded a torsional barrier of only 98.58(15) cm -1 .

A hint of cassis: By a combination of microwave spectroscopy and quantum chemistry, the gas‐phase structures of the Cassyrane stereoisomers and its dihydro derivatives have been determined, and correlated with their olfactory properties. Superposition analyses of the structures (see picture; black Cassyrane, silver Oxane, red O, yellow S) reveal the importance of the 5S configuration on the cassis odor, with the 2S,5R isomers being the most intense.

Many proteins have the potential to aggregate into amyloid fibrils, protein polymers associated with a wide range of human disorders such as Alzheimer's and Parkinson's disease. The thermodynamic stability of amyloid fibrils, in contrast to that of folded proteins, is not well understood: the balance between entropic and enthalpic terms, including the chain entropy and the hydrophobic effect, are poorly characterised. Using a combination of theory, in vitro experiments, simulations of a coarse-grained protein model and meta-data analysis, we delineate the enthalpic and entropic contributions that dominate amyloid fibril elongation. Our prediction of a characteristic temperature-dependent enthalpic signature is confirmed by the performed calorimetric experiments and a meta-analysis over published data. From these results we are able to define the necessary conditions to observe cold denaturation of amyloid fibrils. Overall, we show that amyloid fibril elongation is associated with a negative heat capacity, the magnitude of which correlates closely with the hydrophobic surface area that is buried upon fibril formation, highlighting the importance of hydrophobicity for fibril stability.

We perform here enhanced sampling simulations of N-terminally acetylated human α-synuclein, an intrinsically disordered protein involved in Parkinson's disease. The calculations, consistent with experiments, suggest that the post-translational modification leads to the formation of a transient amphipathic α-helix. The latter, absent in the non-physiological form, alters protein dynamics at the N-terminal and intramolecular interactions.

The microwave spectrum of linalool, an acyclic monoterpene, was recorded for the first time in the range from 9 to 16 GHz. The only conformer observed under molecular beam conditions was assigned. Fitting the rotational spectrum with two different programs treating internal rotation yielded the rotational constants A = 1.64674020(46) GHz, B = 0.68219862(16) GHz, C = 0.61875100(20) GHz, and the centrifugal distortion constants. The standard deviation of the fit was close to experimental accuracy. A-E splittings due to the internal rotation of one methyl group could be resolved and the internal rotation barrier was determined to be 400.20(64) cm(-1). The results from microwave spectroscopy were used to validate the molecular geometry obtained from quantum chemical calculations.