Computed Mass-Fragmentation Energy Profiles of Some Acetalized Monosaccharides for Identification in Mass Spectrometry

Abstract

Our study found that quantum calculations can differentiate fragmentation energies into isomeric structures with asymmetric carbon atoms, such as those of acetalized monosaccharides. It was justified by the good results that have been published in recent years on the discrimination of structural isomers and diastereomers by correlating the calculated mass energy fragmentation profiles with their mass spectra. Based on the quantitative structure–fragmentation relationship (QSFR), this technique compares the intensities of primary ions from the experimental spectrum using the mass energy profiles calculated for the candidate structures. Maximum fit is obtained for the true structure. For a preliminary assessment of the accuracy of the identification of some di-O-isopropylidene monosaccharide diastereomers, we used fragmentation enthalpies (ΔfH) and Gibbs energies (ΔfG) as the energetic descriptors of fragmentation. Four quantum chemical methods were used: RM1, PM7, DFT ΔfH and DFT ΔfG. The mass energy database shows that the differences between the profiles of the isomeric candidate structures could be large enough to be distinguished from each other. This database allows the optimization of energy descriptors and quantum computing methods that can ensure the correct identification of these isomers.

Mass–Energy Profiles Obtained by Quantum Chemical Computing Applied in Mass Spectrometry: A Case Study with Identification of a Group of Acetalized Monosaccharide Isomers

“…where ∆ f H (I i + ) is the formation enthalpy of the resulted fragmentation ion, Σ∆ f H (F i ) is the sum of the formation enthalpies of accompanying fragments, and ∆ f H (M) is the molecular enthalpy of candidate structure. The meanings are similar for ∆ f G [11] For ease of reference, they were also assigned the following acronyms: DAG (diacetone-D-glucose) (1), DAM (diacetone-D-mannose) (2), DAGal (diacetone-D-galactose) (3), DAF (diacetone-D-fructose) (4), and DAS (diacetone-L-sorbose) (5). Through the perspective of the "Lock and Key" concept, the calculated profiles represent the keys.…”

“…Any other QC method can be used to generate these descriptors because the mining algorithm removes any energy profile that does not provide the maximum docking score. The mass-energy profiles calculated in a previous paper with HyperChem 8.0.10, MOPAC2012, and Gaussian 09 software were used (Tables A1-A4) [11][12][13][14]. They correspond to structures 1-5 from Figure 1.…”

“…If primary ions with the same m/z originate from different molecular structures, they will need different energies for their formation. QC methods were even able to highlight energetic differences, indeed minor, between the mass-energy profiles of some acetalized diastereomers of monosaccharides [11]. For ease of reference, they were also assigned the following acronyms: DAG (diacetone-D-glucose) (1), DAM (diacetone-D-mannose) (2), DAGal (diacetone-D-galactose) (3), DAF (diacetone-D-fructose) (4), and DAS (diacetone-L-sorbose) (5).…”

“…The QSFR technique presented here uses the well-known correlation between enthalpies and Gibbs energies, along with ionic currents (IC), as a tool for mining chemical structures from many calculated mass-energy profiles for the possible structures of the analyte. In the analytical context mentioned above, our study has the following main objectives: (i) the extension of the QSFR analytical technique based on mass-energy profiles to structural isomers and acetalized diastereomers of some monosaccharides; (ii) the simulation of structural analysis for five such isomers using the mining of experimental profiles obtained by mass spectrometry, in the set of quantum chemical (QC)-calculated mass-energy profiles for the candidate structures; (iii) the establishment of the analytical conditions that lead to the best matching scores between the experimental and calculated profiles, such that they indicate the true structures; (iv) the detailed presentation of the chemical structure mining algorithm and the relationship for the calculation of the profile matching score, in order to disseminate this QSFR technique; (v) the validation of QC-calculated mass-energy profiles for such isomers, located in a database obtained in a previous work [11]. The main novelty of the work is that the mining of isomeric structures is conducted in parallel in two databases with mass-energy profiles, by calculating the matching score.…”

“…The main novelty of the work is that the mining of isomeric structures is conducted in parallel in two databases with mass-energy profiles, by calculating the matching score. One of the databases was quantum chemically calculated in a previous study [11]. The other was obtained in the present paper from the mass spectrometry analysis of the five isomeric chemical standards.…”