A theoretical study of the intramolecular proton transfer and calculation of the nucleus independent chemical shift in juglone and some of its derivatives

Two-dimensional quantitative structure-activity relationship study of 1,4-naphthoquinone derivatives tested against HL-60 human promyelocytic leukaemia cells

A series of 50 derivatives of 1,4-naphthoquinone tested against human HL-60 leukaemic cells showed activity at a wide range of concentrations. A multivariate quantitative structure-activity relationship (QSAR) study of 45 compounds was performed through principal component analysis (PCA) and partial least squares (PLS) regression. A good PLS regression model was obtained with two factors describing 60.1% of the total variance, and the selected descriptors were partial atomic charge at carbons 1 and 10 (C1 and C10) and total dipole moment (DIP). The calibration model exhibited the determination coefficient r² = 0.78 and the standard error of calibration = 0.29. For external validation, r² and the standard error of prediction were 0.74 and 0.32, respectively. DIP and C1 were the main descriptors for PCA, as well as for PLS, such that the pIC₅₀ value increases when C1 increases and DIP diminishes. The selected descriptors are in accordance with the literature, once C10 and C1 are bound or close to the quinone oxygens involved in the production of radical anions (O₂-∙). From the QSAR analysis, the structures of two new naphthoquinones were proposed and their estimated IC₅₀ values were 1.42 and 1.13 μmol L^-1.

Electron attachment to some naphthoquinone derivatives: long-lived molecular anion formation

RATIONALE

Electron Affinity (EA) is one of the fundamental properties of a molecule. EA values can be measured with various experimental methods, although their availability is still relatively limited. We make an attempt to use Dissociative Electron Attachment Spectroscopy (DEAS) data for evaluation of the EAs of twelve naphthoquinone (NQ) derivatives.

METHODS

Naphthoquinone (NQ) and eleven of its hydroxyl derivatives were investigated by means of DEAS. A combined investigation of NQ and juglone by means of the Electron Transmission Spectroscopy (ETS) and DEAS techniques, with the support of density functional theory (DFT) calculations, allowed us to elucidate the empty-level structures of NQ and its hydroxyl derivatives.

RESULTS

All molecules under investigation form extremely long-lived molecular anions associated with three resonant states (except for NQ, where only two long-lived resonances were observed). The hydroxyl substituents of NQ cause an increase in EA and number of internal degrees of freedom (N), and, as a result, an increase in the mean electron autodetachment lifetimes of the molecular negative ions (NIs). Evaluation of the EAs from the measured lifetimes of the molecular NIs through a simple Arrhenius approximation gives results in reasonable agreement with those obtained with DFT calculations.

CONCLUSIONS

NI lifetime measurements by means of a modified DEAS instrumentation can provide quantitative data of EA. A simple Arrhenius approximation seems to be adequate to describe the process of electron detachment from molecular anions.