![]() The non-covalent interactions (NCI) and the atoms-in-molecules (AIM) analysis indicate that water rotation has little effect on the interactions between water and pyruvic acid molecules, and ring structures are formed where two hydrogen bonds connect the water and acid molecules. Strong hydrogen bonds are formed between pyruvic acid and water molecules where water acts as a hydrogen bond donor and acceptor. , where the rotational spectrum measurements confirm that the structure of pyruvic acid isomers is planar and the monohydrated clusters of PA. The importance of intermolecular hydrogen bonds in the effective molecular recognition of pyruvic acid-water mixtures has been highlighted by Schnitzler et al. demonstrate that PA prefers to stay as a monomer in nonpolar solvents, such as carbon tetrachloride, due to its ability to form intramolecular hydrogen bonds, and when it comes to the water atmosphere, hydrogen bonds C=O⋅⋅⋅H-O and O-H⋅⋅⋅O-H are established between pyruvic acid and water molecules. Ĭonsiderable effort has been devoted to the investigation of the structure and photochemistry of PA in an aqueous solution. The intramolecular hydrogen bond energy, E intra-HB which is classically defined as the energy difference between the closed and open conformations of a PA molecule, is theoretically estimated to be about 8.80 kJ/mol, where a zero point in the energy scale is fixed. This conformer has additional stabilization due to the intramolecular hydrogen bond between the acid hydrogen and the α-carbonyl. The most stable conformer is generally a labeled trans–cis eclipsed form (Tce isomer) and has a planar structure. The PA molecule displays conformational complications in the gas and solution phases due to the possibility of intramolecular rotation around the C–C and C–O bonds. The PA monomer has been the subject of many computational and experimental studies. It is also confirmed that the muscular contraction under physical efforts is associated with the level of both pyruvic and lactic acids. This organic substance is widely distributed in nature as a metabolic intermediate and supplies energy to living cells through the Krebs cycle when oxygen is present (aerobic respiration), and when oxygen is lacking, it ferments to produce lactic acid. Pyruvic acid (CH3COCOOH, PA) is one of the important chemical components that exist in atmospheric aerosols, fog, and clouds. In large clusters, classical O–H⋅⋅⋅O hydrogen bonds still exist between water molecules, and a cage-like structure is built around some parts of the central molecule of pyruvic acid. Atoms in molecules analysis shows that pyruvic acid can form a ring structure with water, and the molecular structures are stabilized by both strong O–H⋅⋅⋅O and C–H⋅⋅⋅O hydrogen bonds. Appropriate topological and geometrical parameters are considered primary indicators of H-bond strength. Among several optimized molecular clusters, we present here the most stable molecular arrangements obtained when one, two, three, and four water molecules are hydrogen-bonded to a central pyruvic acid molecule. The molecular geometries of the possible conformations of pyruvic acid–water complexes (PA-(H 2O) n = 1–4) have been fully optimized at DFT/B3LYP/6-311G++ (d, p) levels of calculation. 2Laboratory of Quantum and Statistical Physics, Department of Physics, Faculty of Sciences, University of Monastir, Monastir, Tunisia.1Physics and Chemistry of Materials Laboratory, Department of Physics, Faculty of Sciences, University of Monastir, Monastir, Tunisia.Ferid Hammami 1* † and Noureddine Issaoui 2 †
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