On the structural intricacies of a metabolic precursor: Direct spectroscopic detection of water-induced conformational reshaping of mevalonolactone

Weakly Bound Complexes of γ-Butyrolactone with Water as Observed in Matrix Isolation FTIR and Theoretical Calculations

A computational and spectroscopic analysis of weakly bound complexes of 1:1 γ-butyrolactone with water has been completed. In this work, multiple density-functional theories and perturbation theory were used to explore the energy-landscape of the complex. Four unique structures were identified in this analysis. One structure was characterized by the formation of a water to carbonyl hydrogen bond and the other three were formed from water to ester hydrogen bonds. The carbonyl-bound conformation was found to be the global minimum across a comprehensive panel of calculations. A wave function analysis demonstrated that the structures were additionally stabilized by weak van der Waals interactions. FTIR spectroscopy of matrix-isolated samples indicated the presence of at least two of the calculated geometries. The structures were identified to be a carbonyl-bound and at least one ester-bound structure. The transitions identified for the carbonyl-bound complex were noted to be significantly more intense than those of the ester bound, indicating greater prevalence in the matrix.

Modifying conformational distribution of chiral tetrahydro-2-furoic acid through its interaction with water: a rotational spectroscopic and theoretical investigation

Rotational spectrum of a binary complex formed between tetrahydro-2-furoic acid (THFA) and water was measured using a chirped pulse Fourier transform microwave spectrometer. A comprehensive theoretical conformational search procedure was carried out using CREST, a conformational searching tool, and DFT calculations to aid the spectral assignment and interpretation. The final conformer ensemble is classified into two structural groups: Type 1 conformers showing a classic carboxylic acid monohydrate structure with two strong hydrogen-bonds formed between the COOH group of cis-THFA and water, and the much less stable Type 2 conformers with trans-THFA and weaker intermolecular interactions with water. The 'cis-' and 'trans-' labels refer to the configurations where the carboxylic C[double bond, length as m-dash]O and OH functional groups are on the same or opposite side, respectively. Only the two most stable Type 2 conformers containing trans-THFA I and II were observed experimentally in a neon jet expansion with an abundance ratio of 1 : 1. This relative abundance observation differs greatly from that of the THFA monomer, i.e. with trans-THFA I : trans-THFA II : cis-THFA III of 10 : 1 : 1 in a neon jet expansion, reported previously. The observation indicates a kinetically controlled formation process of different types of the monohydrates in a jet expansion, whereas a thermodynamically controlled process dominates within each type of structures. The relative stability of the THFA ring conformations is altered by interaction with water, showing a noticeable water induced conformational preference.

Laboratory blueprints for interstellar searches of aromatic chiral molecules: rotational signatures of styrene oxide

The tracking of symmetry-breaking events in space is a long-lasting goal of astrochemists, aiming at an understanding of homochiral Earth chemistry. One current effort at this frontier aims at the detection of small chiral molecules in the interstellar medium. For that, high-resolution laboratory spectroscopy data is required, providing blueprints for the search and assignment of these molecules using radioastronomy. Here, we used chirped-pulse Fourier transform microwave and millimeter-wave spectroscopy and frequency modulation absorption spectroscopy to record and assign the rotational spectrum of the chiral aromatic molecule styrene oxide, C6H5C2H3O, a relevant candidate for future radioastronomy searches. Using experimental data from the 2-12, 75-110, 170-220, and 260-330 GHz regions, we performed a global spectral analysis, which was complemented by quantum chemistry calculations. A global fit of the ground state rotational spectrum was obtained, including rotational transitions from all four frequency regions. Primary rotational constants as well as quartic and sextic centrifugal distortion constants were determined. We also investigated vibrationally excited states of styrene oxide, and for the three lowest energy vibrational states, we determined rotational constants including centrifugal distortion corrections up to the sextic order. In addition, spectroscopic parameters for the singly-substituted 13C and 18O isotopologues were retrieved from the spectrum in natural abundance and used to determine the effective ground state structure of styrene oxide in the gas phase. The spectroscopic parameters and line lists of rotational transitions obtained here will assist future astrochemical studies of this class of chiral organic molecules.

Rotational spectra and theoretical study of tetramers and trimers of 2-fluoroethanol: dramatic intermolecular compensation for intramolecular instability

Cooperativity and chirality dominate in stabilizing the 2-fluoroethanol tetramer, thanks to a fully bifurcated C–H⋯F H-bond network.