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Semiempirical quantum chemistry methods have been used mainly to treat organic and biological compounds with hundreds of atoms and problems involving larger systems. However, their use in the description of solids is still quite restricted. Our aim was to show that semiempirical methods can be used to study MOF (Metal−Organic Framework) systems. The present study analyzed the predictive power of AM1, PM3, PM6, and PM7 methods with respect to the calculation of up to 72 crystal structures of MOFs, and evaluated how the use of the algorithm MOZYME impacted the predictions. Our results showed that PM6 and PM7 methods yielded an accurate description of the geometric arrangement of these MOFs, also observing that MOZYME does not compromise the accuracy of these methods and, for larger systems (above 700 atoms), the computation time is reduced to about 50%. Supported by these results, we chose to evaluate whether the semiempirical methods can be applied to investigate gas adsorption, using a system theoretically and experimentally well investigated: Mg-MOF-74/CO 2 . PM6 obtained a description for the geometry of host−guest interaction and adsorption enthalpy in agreement with traditional DFT, while PM7 is in agreement with experimental results and DFT estimates with the use of dispersion corrections.

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Drug delivery systems are a viable resource to be used in medical treatments that tend to be very aggressive to patients, increasing the bioavailability.

Coumarins are natural and synthetic active ingredients widely applied in diverse types of medicinal treatments, such as cancer, inflammation, infection, and enzyme inhibition (monoamine oxidase B). Dihydrocoumarin compounds are of great interest in organic chemistry due to their structural versatilities and, as part of our investigations concerning the structural characterization of small molecules, this work focuses on crystal structure and spectroscopic characterization of the synthesized and crystallized compound 4-(4-methoxyphenyl)-3,4-dihydro-chromen-2-one (CHO). Additionally, a theoretical calculation was performed using density functional theory to analyze the sites where nucleophilic or electrophilic attack took place and to examine the molecular electrostatic potential surface. Throughout all of these calculations, both density functional theory and Car-Parrinello molecular dynamics were performed by fully optimized geometry. The spectroscopic analysis indicated the presence of aromatic carbons and hydrogen atoms, and also the carbonyl and methoxy groups that were confirmed by the crystallographic structure. The CHO compound has a non-classical intermolecular interaction of type C-H⋅⋅⋅O that drives the molecular arrangement and the crystal packing. Moreover, the main absorbent groups were characterized throughout calculated harmonic vibrational frequencies. Also, natural bond orbital analysis successfully locates the molecular orbital with π-bonding symmetry and the molecular orbital with π* antibonding symmetry. Finally, the gap between highest occupied and lowest unoccupied molecular orbitals implies in a high kinetic stability and low chemical reactivity of title molecule.

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Density functional theory (DFT) calculations have been performed to develop a systematic structural analysis of Au 13 L 8 3+ , where L = SCH 3 , SeCH 3 , SCH 2 OCH 3 and S(CH 2) 2 NH 2 , in order to examine the influence of different ligands. Binding energy calculations indicate that the gold core is more stabilized by the ligand in the following sequence S(CH 2) 2 NH 2 > SCH 2 OCH 3 > SeCH 3 > SCH 3. Natural bond orbital (NBO) analysis describes the interaction between the gold and the ligands, showing that the strongest electron donation occurs from a lone pair orbital on the sulfur and selenium atoms to the antibonding acceptor σ * (Au−S) and σ * (Au−Se) orbitals, respectively. The NBO analysis allowed to understand the origin of enhanced stability of the [Au 13 (S(CH 2) 2 NH 2) 8 ] 3+. Time-dependent DFT (TDDFT) calculations have been performed to simulate the optical absorption spectra of Au 13 L 8 3+ in gas phase and under the effect of solvents with different polarities. The absorption spectrum of [Au 13 (S(CH 2) 2 NH 2) 8 ] 3+ shows a spectral profile that differs considerably from the others in gas phase and which is strongly affected by the solvent.