Henar Martínez-García

NMR assignment in regioisomeric hydroquinones

A set of regioisomeric pairs of tricyclic hydroquinones, analogues of antitumor 9,10‐dihydroxy‐4,4‐dimethyl‐5,8‐dihydroanthracen‐1(4H)‐one (1) and other derivatives, were synthesized and their regiochemistry and NMR spectra assigned by using 1H‐detected one‐bond (CH) HMQC and long‐range CH HMBC, in good agreement with theoretical O3LYP/Alhrichs‐pVTZ calculations. The 5‐hydroxymethyl derivatives (11, 15, 19) showed a 3JH, H coupling constant of methylene protons evidencing the presence of a seven‐membered intramolecular hydrogen bonded ring, not observed for the 8‐hydroxymethyl isomers. Copyright

Structural Consequences of the N7 and C8 Translocation on the Metal Binding Behavior of Adenine

7-Deaza-8-aza-adenine, namely 4-aminopyrazolo[3,4-d]pyrimidine (H4app), is a bioisoster of adenine (Hade) resulting from the translocation of N7 and C8 atoms on the purine moiety. With the aim of studying the influence of this translocation on the metal binding abilities of H4app, we have prepared and structurally characterized two ternary copper(II) complexes having H4app and one N-benzyl-iminodiacetate chelator (MEBIDA or FBIDA, with a methyl or fluoro group in para- of the benzyl aromatic ring): [Cu(2)(MEBIDA)(2)(μ(2)-N1,N8-H4app)(H(2)O)(2)]·4H(2)O (1) and [Cu(4)(FBIDA)(4)(μ(2)-N8,N9-H4app)(2)(H(2)O)]·3.5H(2)O (2). Furthermore, thermal, spectral, and magnetic properties have been also investigated. In 1, H(N9)4app is disordered over two equally pondered positions and the μ(2)-N1,N8 coordination mode is assisted by N6-H···O and N9-H···O intramolecular interactions, respectively. The acyclic nonlinear molecular topology of 2 is strongly influenced by two intramolecular H-bonding interactions (O-H···O-carboxylate) involving the apical aqua ligand of a terminal Cu(II) atom. Thus, both compounds have in common the Cu-N8 bond. In order to better understand our limited structural information, DFT calculations for the individual tautomers of H4app as well as mononuclear Cu(II) model systems have been carried out. According to previous results, we conclude that H(N9)4app is the most stable tautomer followed by H(N8)4app. When N9 and N8 are metalated, then the tautomer H(N1)4app can come into play as observed in compound 2. Likewise, the findings concerning compound 1 suggest that the formation of a Cu-N1 bond in H4app results was favored compared to neutral adenine, for which only one case has been reported with such coordination despite the large variety of related Cu(II)-Hade described in the literature.

N-O and P-O bond nature in hypervalent compounds. Is Bader analysis basis set and geometry independent?

The Atoms in Molecules Theory description for the X-O (X=N,P) bonds in hypervalent molecules has been tested at various levels and basis sets. Calculations in H3PO, F3PO, H3NO, F3NO molecules have been carried out at the HF, B3LYP and MP2(full) levels using the 3–21G, 3–21G*, 6–31G, 6–31G*, 6–311G, 6–311+G* and 6–311+G(3d,2p) basis sets, showing that polarization functions are essential for an adequate geometrical description of hypervalent molecules, especially when second row atoms are present. The dependence of the numerical parameters at the different bond critical points and the Bader charges on X and O atoms have been studied by the aforementioned methods. The AIM analysis is independent from the chosen level or basissets, when polarization functions are present. The geometry dependence of the X-O Bader analysis has also been tested by performing calculations for H3PO by varying P-O bond lengths. This analysis has been proven as invariable for medium bond lengths variations. The results are also compared with the H3P⋯O van der Waals complex.