Aniele Z. Tier

Preparation of TiO2 Nanoparticles Coated with Ionic Liquids: A Supramolecular Approach

Coated TiO2 nanoparticles by dicationic imidazolium-based ionic liquids (ILs) were prepared and studied by differential scanning calorimetry (DSC), dynamic light scattering (DLS), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), and scanning electron microscopy (SEM). Three ILs with different hydrophobicity degrees and structural characteristics were used (IL-1, IL-2, and IL-3). The interaction between IL molecules and the TiO2 surface was analyzed in both solid state and in solution. The physical and chemical properties of coated nanoparticles (TiO2 + IL-1, TiO2 + IL-2, and TiO2 + IL-3) were compared to pure materials (TiO2, IL-1, IL-2, and IL-3) in order to evaluate the interaction between both components. Thermal behavior, diffraction pattern, and morphologic characteristics were evaluated in the solid state. It was observed that all mixtures (TiO2 + IL) showed different behavior from that detected for pure substances, which is an evidence of film formation. DLS experiments were conducted to determine film thickness on the TiO2 surface comparing the size (hydrodynamic radius, Rh) of pure TiO2 with coated nanoparticles (TiO2 + IL). Results showed the thickness of the film increased with hydrophobicity of the IL compound. TEM images support this observation. Finally, X-ray diffraction patterns showed that, in coated samples, no structural changes in TiO2 diffraction peaks were observed, which is related to the maintenance of the crystalline structure. On the contrary, ILs showed different diffraction patterns, which confirms the hypothesis of interactions happening between IL and the TiO2 nanoparticles surface.

Energetic and topological insights into the supramolecular structure of dicationic ionic liquids

The crystal structures of dicationic ILs [DBMIM][2BF4] (1) and [DBMIM][2Br]·[2H2O] (2) were investigated in order to explore the intermolecular interactions in these compounds. An energetic and topological approach for characterization of supramolecular clusters in organic crystals was used. The study of the crystals was done by considering the stabilization energy and topological properties such as contact surfaces and energy content between cations and neighboring anions (supramolecular clusters). The study showed that: 1 is auto-organized into layers (one-dimensional structure) by an anion–cation interaction (weak electrostatic and ionic), and the three-dimensional supramolecular structure of 2 is constructed through simultaneous interactions between cations, anions, and water molecules. This network results in interaction chains in two different directions. Additionally, the supramolecular cluster approach allowed evaluation of the participation of the topological component during the formation of the crystals of 1 and 2. Among the different types of interactions proposed, the most predominant was the one classified as type III, which has small and medium energy values, and a medium-sized contact surface. The thermal and morphological properties were also studied to further characterize these materials and to better understand the resulting structure–property relationships.

Proposal for crystallization of 3-amino-4-halo-5-methylisoxazoles: an energetic and topological approach

The supramolecular structure of 3-amino-4-halo-5-methylisoxazoles (halo = Cl, Br, and I) was investigated in order to suggest a route for crystallization of small molecules. The hierarchy of intermolecular interactions during the growth of the crystal was established by X-ray diffraction, 1H NMR titration, QTAIM analysis and quantum mechanical calculations. The relationship between QTAIM and energetic data was the fundamental innovation in this work. It allowed partitioning of the dimer interaction energy between interacting atoms. The partitioning shows the cooperation of the intermolecular interactions in the stabilization of the dimers and led to observation of the energetic consequences that small changes in the molecular structure of each compound may have on the crystal packing. The proposed route for the crystallization of the supramolecular cluster was based on the energetic hierarchy, in which the hydrogen bond is the strongest interaction and the first to form, and the π-interactions are weaker than the hydrogen bond and cannot compete with it. However, the π-interactions are responsible for the growth of the crystal, connecting the rising layers of the hydrogen bond dimers. The other interaction formed, the halogen bond, is too weak to compete with the other two interactions, but it is fundamental for linking the layer that leads to the final three-dimensional arrangement. Finally, a new way of understanding the crystallization process and the design of new materials is presented.

Energetic and topological approach for characterization of supramolecular clusters in organic crystals

In this work, an approach is proposed for understanding the crystal arrangements of organic compounds. The crystals are studied taking into account the stabilization energy and the topological properties like contact surfaces of a molecule (M1) due to the presence of neighboring Mn (cluster). The molecular system models chosen were five heterocycles and one β-enaminone. The cluster of compounds had a Molecular Coordination Number (MCN) of 14, except for one compound that had an MCN of 16. Our study showed that intermolecular interactions can be divided into four main types: type I, with large energy values and a small contact surface; type II, involving a large value for both the energy and the contact surface; type III, with small and medium energy values, and a medium-sized contact surface; and type IV, with small energy values and a relatively large contact surface. Additionally, from this approach we show that only from the supramolecular cluster is it possible to observe the participation of the topological component during the formation of the crystal. This is demonstrated by the fact that the fragility of the electrostatic interaction between M1 and one Mn in the same plane is compensated by a strong interaction of M1 with a molecule in another plane.

Thermodynamic, energetic, and topological properties of crystal packing of pyrazolo[1,5-a]pyrimidines governed by weak electrostatic intermolecular interactions

A series of pyrazolo[1,5-a]pyrimidines was used as a molecular model in order to understand the crystal packing of compounds with weak electrostatic intermolecular interactions. Additionally, the relationship between the energetic content of intermolecular interactions, the contact surfaces of molecules, and the thermodynamic properties of the crystal was established. The approach, which is based on a supramolecular cluster, shows that for compounds with weak electrostatic intermolecular interactions, the energetic content of the interactions is associated with a large contact surface. The crystal packing of the studied compounds is mainly governed by interactions that involve high interaction energy over a large contact surface. These results show that π⋯π interaction may be as responsible as other strong interactions for driving the crystal packing of compounds with weak electrostatic intermolecular interactions. Furthermore, the correlation between sublimation enthalpy and cluster energy showed that the theoretical calculation of cluster energy provided the real energetic content of crystal lattice energy and confirmed that the first coordination sphere (the supramolecular cluster) is the smallest portion of the crystal that represents all the information necessary for understanding the intermolecular interactions over the entire crystal.

Polymorphism in an 18-membered macrocycle: an energetic and topological approach to understand the supramolecular structure

The synthesis, crystallization, and theoretical calculations (energetic dimers and QTAIM analyses) of three polymorphs of 3,12-dihydrotetrabenzo[d,h,m,q]-[1–3, 10–12]hexaazacyclooctadeca-1,10-dien-5,14-diyne are reported. The supramolecular cluster approach is proposed for understanding the formation and stabilization of crystal arrangements of the polymorphs. The results show that the π⋯π-interactions were responsible for the crystal packing of the three polymorphs and that they are in a determined energetic region. The energetic difference between the more stable and less stable polymorphs is around 8 kcal mol−1, indicating that if, probably other polymorphs will be formed, all of them will be in the same energetic region. The results confirmed that the first molecular coordination sphere (supramolecular cluster) is the smallest portion of the crystal that represents all necessary energy information for understanding the intermolecular interactions in the entire crystal.

Pharmaceutical Salts: Solids to Liquids by Using Ionic Liquid Design

Ionic liquids (ILs) have attracted increasing interest lately in several areas such as chemistry, physics, engineering, material science, molecular biochemistry, energy and fuels, among others. Scientific literature has been daily invaded by papers that show a variety of new ionic liquids and new applications. Furthermore, the range of ILs used has been broadened, and there has been a significant increase in the scope of both physical and chemical IL properties [1, 2]. ILs are defined as liquid organic salts composed entirely of ions, and a melting point criterion has been proposed to distinguish between molten salts and ionic liquids (mp< 100 °C) [3].

Novel ibuprofenate- and docusate-based ionic liquids: emergence of antimicrobial activity

Six new ionic-liquid-based active pharmaceutical ingredients (IL-APIs) were prepared and their molecular structures characterized. Solubility and thermal properties was determined and compared with the salt precursors. Antifungal and antibacterial activities were also investigated. Some of the IL-APIs demonstrated limited water solubility and high thermal stability when compared with the salt precursor. The most interesting observation was that the combination of two pharmacologically active ingredients in an IL-API results in antifungal activity that was not present in the precursors. The antibacterial activities were very promising considering that one of them was active against Staphylococcus, which is a bacterium resistant to penicillin and methicillin. The study of the pharmacological properties of synthesized IL-APIs is essential for evaluating how a drug may interfere with the pharmacological properties of another drug, thus furnishing knowledge about the advantages or disadvantages related to the association of APIs.