No abstract

The generalization of the PICVib approach [M. V. P. dos Santos et al., J. Comput. Chem., 2013, 34, 611] for calculating infrared intensities is shown to be successful and to preserve all interesting features of the procedure such as easiness of implementation and parallelization, flexibility, treatment of large systems and at high theoretical levels. It was tested and validated for very diverse molecular systems: XH3 (D3h), YH4 (D4h), conformers of RDX, S(N)2 and E2 reaction product complexes, the [W(dppe)2(NNC5H10)] complex, carbon nanotubes, and hydrogen-bonded complexes (H2O···HOH, MeHO···HOH, MeOH···OH2, MeOH···OHMe) including the guanine-cytosine pair. The PICVib shows an excellent overall performance for calculating infrared intensities of localized normal modes and even mixed vibrations, whereas care must be taken for vibrations involving intermolecular interactions. DFT functionals are still the best combination with high level ab initio methods such as CCSD and CCSD(T).

The adsorption and release of two drugs 5FU (5fluorouracil) and CAF (caffeine) into and from the ZIF-8 framework were simulated by the Gibbs-ensemble Monte Carlo approach employing two models for representing the sorbent: one without surface (ZIF-8P) and another with surface (ZIF-8S). The inner pores of ZIF-8S were inaccessible to the drugs, but accessible to the solvents (methanol or water). The ZIF-8P model is not recommended to describe the actual sorption processes because it lacks surface and solvent effects, which are reflected in the poor quantitative agreement with experimental results. The ZIF-8S model yielded results for the sorption of CAF in very close agreement with the experimental loading from methanol solution and release of the drug into water. For 5FU, the computer simulations provided qualitative agreements, which suggests that the sorbent−5FU interaction potentials should be improved. The excellent performance of the ZIF-8S model is due to its adequate description of the surface and by exposing adsorption sites such as undercoordinated zinc ions to interactions with large molecules. This was achieved by applying periodic conditions to a ZIF-8 nanocrystal, instead of an elementary cell, which is easy to generalize and used to describe several surface defects. Furthermore, the combination of this ZIF-8S model with the Monte Carlo method provides a very simple and efficient approach to simulate the inaccessibility of the ZIF-8 inner porosity to large molecules. Namely, any trial moves that inserted the drug within the pore were disregarded. This is a quite simple and general approach that can be promptly applied to a large number of MOF sorbents and of drugs that cannot access the inner pores.