Evolution of Solute–Water Interactions in the Benzaldehyde-(H₂O)_1–6 Clusters by Rotational Spectroscopy

Abstract

The investigation on the preferred arrangement and intermolecular interactions of gas phase solute−water clusters gives insights into the intermolecular potentials that govern the structure and dynamics of the aqueous solutions. Here, we report the investigation of hydrated coordination networks of benzaldehyde-(water) n (n = 1−6) clusters in a pulsed supersonic expansion using broadband rotational spectroscopy. Benzaldehyde (PhCHO) is the simplest aromatic aldehyde that involves both hydrophilic (CHO) and hydrophobic (phenyl ring) functional groups, which can mimic molecules of biological significance. For the n = 1−3 clusters, the water molecules are connected around the hydrophilic CHO moiety of benzaldehyde through a strong CO•••HO hydrogen bond and weak CH•••OH hydrogen bond(s). For the larger clusters, the spectra are consistent with the structures in which the water clusters are coordinated on the surface of PhCHO with both the hydrophilic CHO and hydrophobic phenyl ring groups being involved in the bonding interactions. The presence of benzaldehyde does not strongly interfere with the cyclic water tetramer and pentamer, which retain the same structure as in the pure water cluster. The book isomer instead of cage or prism isomers of the water hexamer is incorporated into the microsolvated cluster. The PhCHO molecule deviates from the planar structure upon sequential addition of water molecules. The PhCHO−(H 2 O) 1−6 clusters may serve as a simple model system in understanding the solute−water interactions of biologically relevant molecules in an aqueous environment.

Spectroscopic identification of the ammonia–mercapto radical complex

“…5 As the most common type of noncovalent interactions, hydrogen bonding interactions have attracted numerous experimental and theoretical studies. 2,6 Particularly, water-containing complexes have dominated the hydrogen bonding systems due to the ubiquity of water molecules in the universe. Up to now, a large number of water complexes have been characterized by combining spectroscopic techniques with quantum chemical calculations.…”

Interplay of Hydrogen, Pnicogen, and Chalcogen Bonding in X(H2O)n=1–5 (X = NO, NO+, and NO–) Complexes: Energetics Insights via a Molecular Tailoring Approach

“…In order to answer these questions and to identify and quantify the individual noncovalent interactions in X­(H 2 O) n =1–5 clusters, we have used combined MESP and MTA-based analyses. We believe that this work is highly relevant since the solute-water clusters in the gas phase provide a fundamental model for studying the features of various intermolecular interactions of bulk-water systems . Herein, a stepwise escalation of water cluster size (up to 5 water molecules, i.e., n = 1–5) is followed to model and bridge the gap between the effect of microsolvation and bulk solvation of solute-water clusters …”

Rotational Spectroscopy Probes Lone Pair···π-Hole Interactions in Hexafluorobenzene-Tertiary Alkylamines Complexes

“…Noncovalent interactions (NCIs) are ubiquitous in nature, governing the molecular structures and thus biochemical functionalities and reactivities, such as maintaining the three-dimensional structures of biomolecules and leading molecular recognitions by the delicate balance between different NCIs on top of the covalently bound structural backbone. − Great effort has been devoted to the characterization of NCIs and the understanding of their nature. − NCIs are relatively weak compared to covalent bonds, and accurate characterization of the structure and interaction energy of NCIs experimentally is often facing significant challenges. − Molecular rotational spectroscopy offers a way to study NCIs on model systems under well-defined jet expansion conditions. ,, Rotational spectroscopy is directly related to the principal moments of inertia of the molecule including their centrifugal distortion and, therefore, is suited for analysis of geometric structures of weakly bound molecular complexes. − Recent rotational spectroscopic investigations have unveiled the nature of tetrel, pnictogen, chalcogen, halogen, CH···π, OH···π CC , and π-stacking noncovalent interactions.…”

“…The rotational spectra of C 6 F 6 –NC 7 H 13 and C 6 F 6 –N­(CH 3 ) 3 in the 6–18 GHz frequency range are measured using the coaxially oriented beam resonator arrangement (COBRA) Fourier Transform Microwave (FTMW) spectrometer at the University of Bologna. − A hyperfine structure is observed for both species, as exemplified by the transitions shown in Figure a,b, respectively. The spectrum of C 6 F 6 –NC 7 H 13 is further measured in the low-frequency range by the newly built chirped pulse FTMW Spectrometer (CP-FTMW) at Fudan University, which covers the range from 2 to 8 GHz in a single signal collection event. ,, The broadband spectra of C 6 F 6 –N­(CH 3 ) 3 in the frequency range of 6–12.5 GHz is measured using a CP-FTMW with a new solid-state amplifier. The experimental details can be found in the Supporting Information.…”

“…The spectrum of C 6 F 6 − NC 7 H 13 is further measured in the low-frequency range by the newly built chirped pulse FTMW Spectrometer (CP-FTMW) at Fudan University, which covers the range from 2 to 8 GHz in a single signal collection event. 11,48,49 The broadband spectra of C 6 F 6 −N(CH 3 ) 3 in the frequency range of 6−12.5 GHz is measured using a CP-FTMW with a new solid-state amplifier. The experimental details can be found in the Supporting Information.…”