title: Understanding the Aldo-Enediolate Tautomerism of Glycolaldehyde in Basic Aqueous Solutions.
abstract: The biochemically important interconversion process between aldoses and ketoses is assumed to take place via 1,2-enediol or 1,2-enediolate intermediates, but such intermediates have never been isolated. The current work was undertaken in an attempt to detect the presence of the 1,2-enediol structure of glycolaldehyde in alkaline medium, actually a 1,2-enediolate, and to try to clarify the scarce data existing about both the formation of deprotonated enediol and the aldo-enediolate equilibrium. The Raman spectra of neutral and basic solutions were recorded as a function of time for eleven days. Several bands associated with the presence of the enediolate were observed in alkaline medium. Glycolaldehyde exists as three different structures in aqueous solution at neutral pH, that is, hydrated aldehydes, aldehydes and dimers, with a respective ratio of approximately 4:0.25:1. Additionally, the formation of Z-enediolate forms takes place at basic pH, together with an increase in the concentration of aldehyde species, such as 2-oxoethan-1-olate, and a decrease in the concentrations of the hydrated aldehyde and dimeric forms. The theoretical ratio of ≈1.5:1 for aldehyde:Z-enediolate reproduces the experimental Raman spectrum in basic medium, with an additional contribution of the previously mentioned ratio between the hydrated aldehyde and dimeric forms. Finally, Raman spectroscopy allowed us to monitor the enolization of this carbohydrate model and conclude that aldo-enediol tautomerism-formally aldo-enediolate-happens when a suitable amount of basic species is added.
authors.affiliation: Instituto de Química Médica (IQM), Consejo Superior de Investigaciones Científicas (CSIC), Juan de la Cierva, 3, E-28006, Madrid (Spain).
authors.forename: Luis Miguel
authors.initials: LM
authors.lastname: Azofra
authors.affiliation: Departamento de Química Física y Analítica, Universidad de Jaén, Campus Las Lagunillas, E-23071, Jaén (Spain).
authors.forename: María Mar
authors.initials: MM
authors.lastname: Quesada-Moreno
authors.affiliation: Instituto de Química Médica (IQM), Consejo Superior de Investigaciones Científicas (CSIC), Juan de la Cierva, 3, E-28006, Madrid (Spain). ibon@iqm.csic.es.
authors.forename: Ibon
authors.initials: I
authors.lastname: Alkorta
authors.affiliation: Departamento de Química Física y Analítica, Universidad de Jaén, Campus Las Lagunillas, E-23071, Jaén (Spain).|Current address: Departamento de Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Sevilla (Spain).
authors.forename: Juan Ramón
authors.initials: JR
authors.lastname: Avilés-Moreno
authors.affiliation: Instituto de Química Médica (IQM), Consejo Superior de Investigaciones Científicas (CSIC), Juan de la Cierva, 3, E-28006, Madrid (Spain).
authors.forename: José
authors.initials: J
authors.lastname: Elguero
authors.affiliation: Departamento de Química Física y Analítica, Universidad de Jaén, Campus Las Lagunillas, E-23071, Jaén (Spain). jjlopez@ujaen.es.
authors.forename: Juan Jesús
authors.initials: JJ
authors.lastname: López-González
mesh_terms: D000079:Acetaldehyde / Q000031:analogs & derivatives* / Q000737:chemistry; D011789:Quantum Theory; D012996:Solutions; D013059:Spectrum Analysis, Raman; D014867:Water / Q000737:chemistry
chemical_list: D012996:Solutions; D014867:Water; D000079:Acetaldehyde; C010972:glycolaldehyde
keywords: Raman spectroscopy; hydrogen bonds; quantum chemical calculations; solvents; tautomerism