tautomer 2-iminothiazoline-4-carboxylic acid (ITCA), protein adducts,
Only its Enol
tautomer qualifies it to be a UVA filter with a [lambda]max of 357nm.
The minimized internal energies (total energy and binding energy) beside the formation energy (Tables 1 and 2) of 21
tautomers suggest their high stability which outweigh their production from the coupling reaction and indicate that the most stable
tautomer is 21A.
Dziembowska et al., "Keto-enol tautomerism of two structurally related Schiff bases: Direct and indirect way of creation of the excited keto
tautomer," Chemical Physics Letters, vol.
As a [beta]-diketone, curcumin also exists as a keto-enol
tautomer that chelates transition metal ions with high affinity.
Principle: Creatinine in alkaline medium reacts with picric acid to form a red
tautomer of creatinine picrate, the intensity of which is measured by colorimeter at 520nm.
In deuterated acetone, regioisomer 14aS is mainly present as the thioxo
tautomer II whose proton signals are downfield shifted with respect to
tautomer I in nice keeping with the observations reported in literature for thiopurine derivatives [28].
Therefore, we considered the additional two models of the dissociated (Figure 3(b), Scheme 2) and
tautomer (Figure 3(c), Scheme 2) states and calculated the frequencies of these two models which are shown in Tables 3 and 4.
[sup.1]H-NMR Spectra: In the [sup.1]H-NMR spectra of triazolothiadiazines (III), the characteristic downfield signal at [delta] 8.70 ppm attributed to the -N=C-SH (-NH-C=S of the
tautomer) in compound II is present, as is a sharp signal at [delta] 7.32 ppm attributable to the N-N[H.sub.2] group in the parent triazole [14].