Effect of mono- and di-hydration on the stability and tautomerisms of different tautomers of creatinine: A thermodynamic and mechanistic study

Looking for the Elusive Imine Tautomer of Creatinine: Different States of Aggregation Studied by Quantum Chemistry and Molecular Spectroscopy

“…In Figure 2, together with the possible tautomers and isomers of creatinine, the relative energies are also reported. These confirm that, as previously suggested, [27][28][29] enolic forms are significantly less stable than their ketonic counterparts. Therefore, their contribution is surely negligible in all aggregation states and will not be considered in the following.…”

“…Adducts incorporating only the two "bridge" molecules were already analyzed in ref. [29], and provided a reasonable model. However, we preferred to investigate in detail a 5 W model in which two further water molecules interact with the lone-pairs of the carbonyl oxygen, and the fifth molecule forms a hydrogen bond with the outer hydrogen atom of the amine or imine group.…”

“…Indeed, a few theoretical investigations have been carried out, which cannot, however, be considered at the state of the art according to current standards [7] because they are based on semiempirical models, [25,26] second-order Møller-Plesset perturbation theory (MP2), or density functional theory (DFT), employing in the latter two cases rather small basis sets. [27,28,29] All these works suggest that, in the gas phase, the imine tautomer (I, see Figure 1) is slightly more stable than the amine form (A, obtained by the migration of H10 from N3 to N6; see Figure 1 for labelling). On the other hand, NMR and Raman studies suggest that only the amine form is present or, at least, strongly favoured in polar solvents.…”

“…Enolic tautomers are also possible, which can be obtained either from the migration of H10 from N3 to O8 (Hy) or the migration of H11 (or H12) from C5 to O8, in this latter case starting either from imine (IH) or amine (AH) tautomers. [29] Furthermore, E and Z isomers are possible for the imine moiety (labeled EI and ZI, respectively). We are thus left with the eight structures shown in Figure 2.…”

Dual-triggered nanoaggregates of cucurbit[7]uril and gold nanoparticles for multi-spectroscopic quantification of creatinine in urinalysis

“…The most stable form of CRN under standard conditions is (amino tautomer, 2-amino-1-methyl-2-imidazoline-4-one). 41 The pK a of the conjugated acid of CRN [CRN-H] + is 9.2, 42 implying that CRN exists in the protonated form in water and in synthetic urine (SU) where the pH is between 5 and 7.…”