Aspartame and Its Microhydrated Aggregates Revealed by Laser Spectroscopy: Water-Sweetener Interactions in the Gas Phase.

The popular sweetener, aspartame, is an agonist of the tongue's sweet taste receptor. How water molecules affect its conformation or which aspartame atoms are more prone to interact with solvent are helpful questions to understand its activity in different environments. Here, the combination of IR-UV spectroscopic techniques with computational simulations has been successfully applied to characterize aspartame·water0-2 clusters, showing that the addition of water molecules simplifies the conformational panorama of aspartame, favoring the formation of folded structures by interaction with the polar part of the molecule.

Competition between O-H and S-H Intermolecular Interactions in Conformationally Complex Systems: The 2-Phenylethanethiol and 2-Phenylethanol Dimers.

Noncovalent interactions involving sulfur centers play a relevant role in biological and chemical environments. Yet, detailed molecular descriptions are scarce and limited to very simple model systems. Here we explore the formation of the elusive S-H···S hydrogen bond and the competition between S-H···O and O-H···S interactions in pure and mixed dimers of the conformationally flexible molecules 2-phenylethanethiol (PET) and 2-phenylethanol (PEAL), using the isolated and size-controlled environment of a jet expansion. The structure of both PET-PET and PET-PEAL dimers was unraveled through a comprehensive methodology that combined rotationally resolved microwave spectroscopy, mass-resolved isomer-specific infrared laser spectroscopy, and quantum chemical calculations. This synergic experimental-computational approach offered unique insights into the potential energy surface, conformational equilibria, molecular structure, and intermolecular interactions of the dimers. The results show a preferential order for establishing hydrogen bonds following the sequence S-H···S < S-H···O ≲ O-H···S < O-H···O, despite the hydrogen bond only accounting for a fraction of the total interaction energy.

Exploring the interaction sites in glucose and galactose using phenol as a probe.

Sugars, together with amino acids and nucleobases, are the fundamental building blocks of a cell. They are involved in many fundamental processes and they especially play relevant roles as part of the immune system. The latter is connected to their ability to establish a collection of intermolecular interactions, depending on the position of their hydroxyl groups. Here we explore how the position of the OH in C4, the anomeric conformation and the nature substituent affect the interaction with phenol, which serves as a probe of the preferred site for the interaction. Using mass-resolved excitation spectroscopy and density functional calculations, we unravel the structure of the dimers and compare their conformation with those found for similar systems. The main conclusion is that the hydroxymethyl group has a very strong influence, guiding the whole aggregation process and that the position of the substituent in C4 has a stronger influence on the final structure of the dimer than the anomeric conformation.

Aggregation of nucleobases and metabolites: Adenine-theobromine trimers.

The selection of cytosine, guanine, thymine, and adenine as components of the information biopolymers was a complex process influenced by several factors. Among them, the intermolecular interactions may have played a determinant role. Thus, a deep understanding of the intermolecular interactions between nucleobases and other prebiotic molecules may help understand the first instants of chemical evolution. Following this hypothesis, we present here a combined spectroscopic and computational study of theobromine2-adenine and thebromine-adenine2 trimers. While adenine is a nucleobase, theobromine was probably part of the prebiotic chemistry. The trimers were formed in jets and probed by a combination of UV and IR spectroscopic techniques. The spectra were interpreted in light of the predictions obtained using density-functional methods. The results suggest the existence of a subtle balance between formation of hydrogen bonds and π-π interactions. Thus, while theobromine2-adenine tends to form complex in stacked structures, theobromine-adenine2 prefers formation of planar structures, maximizing the interaction by hydrogen bonds. The small energy difference between planar and stacked structures highlights the importance of accurately modeling the dispersion forces in the functionals to produce reliable predictions.