Synthesis, NMR and computational studies on tautomerism of dichloroacetate of hydroxyanthraquinone

Study of Tetrahydroxylated Anthraquinones—Potential Tool to Assess Degradation of Anthocyanins Rich Food

“…computational study) strongly supporting its involvement in the processes observed in our study [35,36]. Interestingly, as mentioned above, the ratio of native and oxidized forms differs among studied anthraquinones.…”

“…In fact, trace amounts of these tautomers are also observed in the reconstructed chromatogram of the ATCS standard (with RT range of roughly 7.0-8.6 min). Tautomerization has been already described to occur at hydroxy-substituted anthraquinones (using synthesis, NMR, and computational study) strongly supporting its involvement in the processes observed in our study [35,36].…”

“…Note that the MS/MS spectrum of this isomer does not contain the signal of the oxidized form (m/z 269, Figure 5E) and corresponds well with the MS/MS spectrum of THAQ2 (Figure 3D). As already mentioned above, the mutual conversions of isomers of various hydroxylated anthraquinones were described to readily occur [35,36]. A high similarity of already discussed analytical data (i.e., both agreement in mass and fragmentation and virtual absence of the oxidized form in the related spectra of THAQ2 and THAQ3) and the described tautomerization strongly evidences the structural analogy and similarity of THAQ2 and THAQ3.…”

Stressing the differences in alizarin and purpurin dyes through UV-visible light absorption and 1 H-NMR spectroscopies

“…From the 1 H-NMR perspective, 3 main types of protons exist in HAQ, depending on the nuclei to which they are bound: (i) sp 2 carbon participating to an extended conjugated π electronic system, (ii) hydroxy oxygen atoms involved in intra-molecular hydrogen bonds and (iii) hydroxy oxygen atoms involved in intermolecular hydrogen bonds with the HAQ surroundings. It must be immediately noted that HAQ molecules feature acidic protons and tautomer forms, possibly complicating their chemical spaces, which in turn complicates the analysis and the interpretation of HAQ 1 H-NMR spectra 9,10 . From previous works in which experimental and theoretical NMR spectra of HAQ systems are confronted, it turns out that Density Functional Theory (DFT) is most of the time accurate enough for reaching a 5 to 10% error with respect to the experimental chemical shifts of protons bound to sp 2 carbon atoms.…”

Stressing the differences in alizarin and purpurin dyes through UV-visible light absorption and 1 H-NMR spectroscopies

“…From the 1 H-NMR perspective, 3 main types of protons exist in HAQ, depending on the nuclei to which they are bound: (i) sp 2 carbon participating in an extended conjugated π electronic system, (ii) hydroxy oxygen atoms involved in intra-molecular hydrogen bonds and (iii) hydroxy oxygen atoms involved in intermolecular hydrogen bonds with the HAQ surroundings. It must be immediately noted that HAQ molecules feature acidic protons and tautomer forms, possibly complicating their chemical spaces, which in turn complicates the analysis and the interpretation of HAQ 1 H-NMR spectra 18,19 . From previous works in which experimental and theoretical NMR spectra of HAQ systems are confronted, it turns out that Density Functional Theory (DFT) is most of the time accurate enough for reaching a 5 to 10% error with respect to the experimental chemical shifts of protons bound to sp 2 carbon atoms.…”