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| - Synergy of Intramolecular Hydrogen-Bonding Network inmyo-Inositol 2-Monophosphate: Theoretical Investigationsinto the Electronic Structure, Proton Transfer, and pKa
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| - This work demonstrates the pivotal role that an intramolecular hydrogen-bonding network (intra-HBN) plays in the determination of the conformation of myo-inositol 2-monophosphate (Ins(2)P1), a memberof the inositol phosphate family of compounds, which are important participants in the role that phosphatesplay in biological and environmental chemistry. For biologically significant compounds that contain phosphateand hydroxyl groups, Ins(2)P1 is a model system for studying both the primary forces that determine theirconformations and their chemical properties from the effect of phosphate group addition. We performedab initio calculations to determine the intra-HBN within important thermally accessible conformations forneutral Ins(2)P1 and its anions, Ins(2)P11- and Ins(2)P12-. The results show that the global minima prefer1a/5e structures where the phosphate group is in the axial position with all −OH groups in the equatorialpositions. The calculations of transition state structures for ring inversion at each ionization state predictan activation energy of 18.16 kcal/mol for the neutral species in water, while the activation energy is lowerfor the charged compounds, 15.62 kcal/mol for Ins(2)P11- and 12.48 kcal/mol for Ins(2)P12-. The pKa valuesof Ins(2)P1 were calculated by modeling the solvent as a polarizable continuum medium (PCM) and asexplicit solvent molecules. These values are in good agreement with experimental data. A novel four-center pattern of hydrogen bonding was found to stabilize the system. The intramolecular proton transferacross a low barrier hydrogen bond between the charged phosphate and hydroxyl groups was found tooccur under standard conditions with an activation energy that is less than 0.5 kcal/mol.
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