A comprehensive analysis of crystal packing and energetic features of the selected uracil derivatives (i.e., 1-methyluracil, 1,5dimethyluracil, 5-fluorouracil, 2-thiouracil, 4-thiouracil, 2,4-dithiouracil, and 6-methyl-2-thiouracil) is reported. High-quality X-ray diffraction data sets of the studied compounds were subjected to the TAAM procedure (Transferable Aspherical Atom Model based on the Hansen−Coppens formalism), which gave results comparable both with the optimized and neutron-diffraction-derived geometries. Crystal packing motifs were investigated with the aid of Hirshfeld surface fingerprint plots. Most of the structures form hydrogen-bonded layers kept together by π-stacking interactions. The only exception is 2,4-dithiouracil, which exhibits a rather complex 3D network based on N−H•••S and C−H•••S contacts. The TAAM procedure allows also for a quite reliable reconstruction of the electron density distribution in a crystal structure. It was therefore possible to rationalize the existence of some F•••F interactions in 5-fluorouracil on the basis of the derived deformation density map. Additional insight into the nature of crystal architectures was obtained through theoretical computations, concerning cohesive energy, dimer interaction energy, and molecule deformation energy evaluation. The balance between molecular layer stabilization and their mutual interactions is essential for crystal growth, and thus it is reflected in crystal morphology and quality. Cohesive energy ranges from −100 kJ•mol −1 for 2,4-thiouracil to about −140 kJ•mol −1 for uracil and 5-fluorouracil, and there is no significant correlation with the melting point temperature observed. Hydrogen-bonded layers are more strongly stabilized one with another, when methyl substituents or sulfur atoms are present. Remarkable differences between 2-thio and 4-thio derivatives were found and supported by the corresponding values of aromaticitity indices. Furthermore, the energy calculations revealed the particular importance of properly determined positions of hydrogen atoms.

The theoretical databank of aspherical pseudoatoms (UBDB) was recently extended with over 100 new atom types present in RNA, DNA and in some other molecules of great importance in biology and pharmacy. The atom-type definitions were modified and new atom keys added to provide a more precise description of the atomic charge-density distribution. X-H bond lengths were updated according to recent neutron diffraction studies and implemented in the LSDB program as well as used for modelling the appropriate atom types. The UBDB2011 databank was extensively tested. Electrostatic interaction energies calculated on the basis of the databank of aspherical atom models were compared with the corresponding results obtained directly from wavefunctions at the same level of theory (SPDFG/B3LYP/6-31G** and SPDFG/B3LYP/aug-cc-pVDZ). Various small complexes were analysed to cover most of the different interaction types, i.e. adenine-thymine and guanine-cytosine with hydrogen bonding, guanine-adenine with stacking contacts, and a group of neutral and charged species of nucleic acid bases interacting with amino acid side chains. The energy trends are well preserved (R(2) > 0.9); however the energy values differ between the two methods by about 4 kcal mol(-1) (1 kcal mol(-1) = 4.184 kJ mol(-1)) on average. What is noticeable is that the replacement of one basis set by another in a purely quantum chemical approach leads to the same electrostatic energy difference, i.e. of about 4 kcal mol(-1) in magnitude. The present work opens up the possibility of applying the UBDB2011 for macromolecules that contain DNA/RNA fragments. This study shows that on the basis of the UBDB2011 databank electrostatic interaction energies can be estimated and structure refinements carried out. However, some method limitations are apparent.

Three naphthalene-based analogues (4 a-c) of the Hoveyda-Grubbs metathesis catalyst exhibited immense differences in reactivity. Systematic structural and spectroscopic studies revealed that the ruthenafurane ring present in all 2-isopropoxyarylidene chelates possesses some aromatic character, which inhibits catalyst activity. This aromatic stabilization within the chelate ring may be controlled by variation of the polycyclic core topology as was demonstrated for tetraline and phenanthrene derivatives (4 d, e). General conclusions about a new mode of ligand-structure tuning in catalytic systems are presented.

We find that crystallographically resolved Ti17O24(OPr(i))20 nanoparticles, functionalized by covalent attachment of 4-nitrophenyl-acetylacetonate or coumarin 343 adsorbates, exhibit hole injection into surface states when photoexcited with visible light (λ = 400-680 nm). Our findings are supported by photoelectrochemical measurements, EPR spectroscopy, and quantum dynamics simulations of interfacial charge transfer. The underlying mechanism is consistent with measurements of photocathodic currents generated with visible light for thin layers of functionalized polyoxotitanate nanocrystals deposited on FTO working electrodes. The reported experimental and theoretical analysis demonstrates for the first time the feasibility of p-type sensitization of TiO2 solely based on covalent binding of organic adsorbates.