Electrochemical oxidation of tamoxifen revisited

Tamoxifen is a selective estrogen receptor modulator that is used as an adjuvant and/or chemotherapeutic agent for the treatment of all stages of hormone-dependent breast cancer. Currently there is a deep interest in the study of tamoxifen biotransformation and identification of metabolites since they can significantly contribute to the overall pharmacological or adverse effects of the drug. Accordingly, the study of the electrochemical behavior of tamoxifen in aqueous solution is reported. To clarify the occurring oxidative process and to assess the influence of the functional groups on the oxidation mechanism, the voltammetric assessment was extended to the study of tamoxifen’s analogues (E)-tamoxifen and dihydrotamoxifen, and to its main phase I oxidative metabolite, N-desmethyl tamoxifen. The data found shows that the oxidative processes occurring in tamoxifen are essentially related with the two chemical moieties present in the molecule: the substituted aromatic nucleus and the tertiary amine group. Moreover, the results obtained suggest that the ethylenic linkage is not critical for tamoxifen’s oxidation although it could play an important role in the course of the oxidation process. These results could contribute to highlight some remaining questions regarding tamoxifen’s metabolic behavior and to the development of new analytical strategies, based on electrochemical approaches

Effect of the Exchange-Correlation Potential on the Transferability of Bronsted-Evans-Polanyi Relationships in Heterogeneous Catalysis

As more and more accurate density functional methods emerge, the transferability of Bronsted-Evans-Polanyi (BEP) relationships obtained with previous models is an open question. In this work, BEP relationships derived from different density functional theory based calculations are analyzed to answer this question. In particular, BEP relationships linking the activation energy of O-H bond breaking reactions taking place on metallic surfaces with the adsorption energy of the reaction products are chosen as a case study. These relationships are obtained with the widely used Perdew-Wang (PW91) generalized gradient approximation (GGA) exchange-correlation functional and with the more accurate meta-GGA Tao-Perdew Staroverov-Scuseria (TPSS) one. We provide compelling evidence that BEP relationships derived from PW91 and TPSS functionals are essentially coincidental. This finding validates previously published BEP relationships and indicates that the reaction activation energy barrier can be obtained by the determination of the energy reaction descriptor value at the less computationally demanding GGA level; an important aspect to consider in future studies aimed at the computational design of catalysts :with improved characteristics

Effect of van der Waals interactions in the DFT description of self-assembled monolayers of thiols on gold

The structure and energetic properties of self-assembled monolayers (SAMs) of alkanethiol derivatives (simple alkanethiols, mercaptoalkanoic acids and aminoalkanethiols with different chain length) adsorbed on the metallic Au(111) surface are investigated through periodic DFT calculations. To sort out the effect of van der Waals (vdW) interactions on the DFT calculations, the results of the standard GGA-PBE functional are compared with those obtained with approaches including the vdW interactions such as those incorporating the Grimme's (GGA-PBE-D2) and the Tkatchenko-Scheffler's (GGA-PBE-TS) schemes, as well as with the optB86b-vdW density functional. The most significant difference between the two sets of results appears for the adsorption energies per thiol molecules: The standard functional predicts energy values 30-40 % lower than those obtained when the van der Waals interactions are taken into account. This is certainly due to a better description of the lateral interactions between the chains of the thiols when including the van der Waals effects. Differences are also found between the adsorption energies predicted by density functionals taking into account the vdW corrections, with values increasing in the order GGA-PBE-D2 < GGA-PBE-TS < optB86b-vdW. Furthermore, the functionals considering dispersion interactions favor much more tilted orientations of the SAMs over the surface with respect to those found using the standard GGA functional (the SAMs' tilt angles increase from 17 degrees-24 degrees to 37 degrees-46 degrees), being the former in closer agreement with available experimental data. In contrast, the SAMs' precession angle and monolayer thickness are less affected by the type of DFT exchange-correlation functional employed. In the case of low surface coverage, the chains of the thiols adopt more tilted configurations and tend to lay side-down onto the surface