The suitability of a hybrid density functional to qualitatively reproduce geometric and energetic details of parallel pi-stacked aromatic complexes is presented. The hybrid functional includes an ad hoc mixture of half the exact (HF) exchange with half of the uniform electron gas exchange, plus Lee, Yang, and Parr's expression for correlation energy. This functional, in combination with polarized, diffuse basis sets, gives a binding energy for the parallel-displaced benzene dimer in good agreement with the best available high-level calculations reported in the literature, and qualitatively reproduces the local MP2 potential energy surface of the parallel-displaced benzene dimer. This method was further critically compared to high-level calculations recently reported in the literature for a range of pi-stacked complexes, including monosubstituted benzene-benzene dimers, along with DNA and RNA bases, and generally agrees with MP2 and/or CCSD(T) results to within +/-2 kJ mol(-1). We also show that the resulting BH&H binding energy is closely related to the electron density in the intermolecular region. The net result is that the BH&H functional, presumably due to fortuitous cancellation of errors, provides a pragmatic, computationally efficient quantum mechanical tool for the study of large pi-stacked systems such as DNA.

Extensive quantum chemical DFT calculations were performed on the high-resolution (1.9 Å) crystal structure of photosystem II in order to determine the protonation pattern and the oxidation states of the oxygen-evolving Mn cluster. First, our data suggest that the experimental structure is not in the S(1)-state. Second, a rather complete set of possible protonation patterns is studied, resulting in very few alternative protonation patterns whose relevance is discussed. Finally, we show that the experimental structure is a mixture of states containing highly reduced forms, with the largest contribution (almost 60%) from the S(-3)-state, Mn(II,II,III,III).

Over the past 10 years, anion-p interaction has been recognized as an important weak force that may occur between anionic systems and electron-deficient aromatics. Lately, this supramolecular contact has experienced a rapidly growing interest, as reflected by numerous recent literature reports. The present paper highlights the tremendous progress achieved in the field by emphasizing three important studies involving anion-p interactions published in 2010. In addition, a pioneering search of the Protein Data Bank (PDB) reveals short anion-p contacts in some protein structures.

Density functional calculations on a range of hydrogen bonded clusters of cisplatin are reported. A systematic search of 1:1 cisplatin:water complexes reveals only three stable minima, which contain a number of common, recurring interactions, such as an N-H...O-H...Cl bridging mode. Expanding these clusters by adding water molecules leads to a model of the first solvation shell of cisplatin, which contains the above motifs along with several strong water-water interactions. The strengths of such interactions are rationalized on the basis of electrostatic potentials, and quantified by use of Atoms in Molecules properties. This analysis also allows us to estimate cisplatin's position on Abraham's hydrogen bond acidity and basicity scales, indicating that cisplatin is a strong donor and acceptor of hydrogen bonds due to the dominance of hard, electrostatic interactions. The effects of this explicit solvation on the barrier to hydrolysis, and hence activation, of cisplatin are explored, indicating a slightly higher barrier than in the gas phase, leading to better agreement with experiment than either gas phase or continuum solvation calculations.

Copper-1,10-phenanthroline (phen) complexes Cu(phen)(2)(), Cu(2-Clip-phen), and Cu(3-Clip-phen) (Clip = a serinol bridge between the phen parts) are typically employed as DNA-cleaving agents and are now becoming increasingly important for building multifunctional drugs with improved cytotoxic properties. For instance, Cu(3-Clip-phen) has been combined with distamycin-like minor-groove binders and cisplatin-derivatives, leading to promising results. Density Functional Theory (DFT) and docking calculations as well as molecular dynamics (MD) simulations were performed to describe the mode of binding to DNA of these complexes. Our data suggest the minor-groove binding to be more probable than (partial) intercalation and major-groove binding. In addition, it was found that a combination of factors including planarity, van der Waals interactions with DNA, and structural complementarities may be the key for the cleavage efficiency of these copper complexes.