Filipe C. D. A. Lima

Industrial Scale Isolation, Structural and Spectroscopic Characterization of Epiisopiloturine from Pilocarpus microphyllus Stapf Leaves: A Promising Alkaloid against Schistosomiasis.

This paper presents an industrial scale process for extraction, purification, and isolation of epiisopiloturine (EPI) (2(3H)-Furanone,dihydro-3-(hydroxyphenylmethyl)-4-[(1-methyl-1H-imidazol-4-yl)methyl]-, [3S-[3a(R*),4b]]), which is an alkaloid from jaborandi leaves (Pilocarpus microphyllus Stapf). Additionally for the first time a set of structural and spectroscopic techniques were used to characterize this alkaloid. EPI has shown schistomicidal activity against adults and young forms, as well as the reduction of the egg laying adult worms and low toxicity to mammalian cells (in vitro). At first, the extraction of EPI was done with toluene and methylene chloride to obtain a solution that was alkalinized with ammonium carbonate. The remaining solution was treated in sequence by acidification, filtration and alkalinization. These industrial procedures are necessary in order to remove impurities and subsequent application of the high performance liquid chromatography (HPLC). The HPLC was employed also to remove other alkaloids, to obtain EPI purity higher than 98%. The viability of the method was confirmed through HPLC and electrospray mass spectrometry, that yielded a pseudo molecular ion of m/z equal to 287.1 Da. EPI structure was characterized by single crystal X-ray diffraction (XRD), 1H and 13C nuclear magnetic resonance (NMR) in deuterated methanol/chloroform solution, vibrational spectroscopy and mass coupled thermal analyses. EPI molecule presents a parallel alignment of the benzene and the methyl imidazol ring separated by an interplanar spacing of 3.758 Å indicating a π-π bond interaction. The imidazole alkaloid melts at 225°C and decomposes above 230°C under air. EPI structure was used in theoretical Density Functional Theory calculations, considering the single crystal XRD data in order to simulate the NMR, infrared and Raman spectra of the molecule, and performs the signals attribution.

LAPONITE®-pilocarpine hybrid material: experimental and theoretical evaluation of pilocarpine conformation

The intercalation of protonated pilocarpine (Pilo+) into model LAPONITE® (Lap) is here investigated in order to address its conformational properties upon entrapment. Pilo is an alkaloid available as a drug for the treatment of glaucoma and xerostomia, and clays are potential candidates for drug delivery. Therefore, the physico-chemical characterization of the Pilo-Lap material is here studied through chemical elementary analysis, X-ray diffraction, mass spectrometry coupled to thermogravimetric analysis (TGA-MS), solid state 13C nuclear magnetic resonance (NMR) and Raman spectroscopy. The experimental spectroscopic data are confronted with performed calculations which confirmed the presence of pilocarpine, while the XRD data also show the immobilization of Pilo+ into the clay. TGA-MS analyses indicated a significant modification in the thermal decomposition profile of the organic species after intercalation. A DTG peak associated with the release of carbon dioxide and water molecules is observed at 315 °C for PiloHCl and at 378 °C for Pilo-Lap. Supported by the theoretical calculations, the experimental XRD, vibrational and NMR spectra suggest that pilocarpine may undergo geometrical changes upon the intercalation process. A characteristic fingerprint was observed as a vibrational change in the band at 768 cm−1 for PiloHCl (assigned mainly to the lactone ring breathing vibrational mode) and a band at 782 cm−1 for Pilo-Lap (assigned mainly to the imidazole ring bending in the plane) in the Raman spectra.

Structural and spectroscopic characterization of epiisopiloturine-metal complexes, and anthelmintic activity vs. S-mansoni

Abstract Epiisopiloturine (EPI), extracted from leaves of Pilocarpus microphyllus, a plant originally from the Amazon and Savanna regions in Brazil, was described as a potential drug against Schistosomiasis, a neglected severe disease. Herein, EPI was complexed with copper(II) or zinc(II) salts and the isolated species, [Cu(epi)4](ClO4)2 (1) and [Zn(epi)2Cl2] (2), were structurally and spectroscopically characterized. By using X-ray diffraction, the crystal structures of both metal complexes were determined, indicating a square pyramidal geometry for copper for 1 and a tetrahedral environment around zinc for 2. EPR spectra of 1 show a typical tetragonal environment around the central metal ion with some tetrahedral distortion, both in the solid state and in frozen acetonitrile solution, in accordance with crystallographic data. For 2, NMR spectra have bands consistent with a tetrahedral species in solid state or in DMSO-d6 solution. These spectroscopic characterization data were further supported by Density Functional Theory calculations, showing that these metal complexes are also stable in solution. Those metal complexes were tested against adult worms of Schistosoma mansoni, in comparison to the free alkaloid as anthelmintic agent. Coordination with copper(II) improved the alkaloid schistosomicidal properties, while binding to zinc(II) decreased its activity.

Adsorption of asphaltenes on the calcite (10.4) surface by first-principles calculations

Asphaltenes play a key role in oil production and its exploration from natural reservoirs. In carbonate reservoirs, the calcite (10.4) surface retains asphaltenes. However, its aggregate structure and deposition process are not fully understood. Using first-principles calculations based on density-functional theory (DFT) with van der Waals (vdW) dispersion, we studied the adsorption of asphaltene, resin and resin–asphaltene dimer molecular models on the CaCO3 surface in the presence of a dielectric water–toluene environment. These large molecules impose a challenging description at the electronic level. Our calculations indicate that there is a minor steric hindrance in the effective interaction of the aromatic region of asphaltene on the calcite surface. However, aliphatic chains with sulphide groups can play a significant role on the adsorption process and its availability to receive electronic charge density from the surface. Accordingly, the preferential LUMO localized in the aromatic region of asphaltene may also allow the adsorption on the calcite surface and π–π stacking interactions. Initially, the resin molecule tends to be trapped during dimer formation with the asphaltene, whereas a significant intramolecular charge rearrangement due to the heteroatoms is necessary to increase the π–π stacking interactions. For the dimer, the adsorbed form of asphaltene favors more available electronic states to increase the likelihood of nanoaggregation. Therefore, changes in the continuum dielectric constant only had a minor effect on the calculated adsorption energies. Experimental work related to the oil–water interface in the presence of toluene show similar behavior during asphaltene adsorption. Our studies indicate that nanoaggregates are grown through resin and the calcite (10.4) surface selectively adsorbs the less polar asphaltenes from oil.

Metal coordination study at Ag and Cd sites in crown thioether complexes through DFT calculations and hyperfine parameters

Structural and electronic properties of [C12H24S6X], [C13H26S6OX], and [C14H28S6OX] (X: Ag+, Cd2+) crown thioether complexes were investigated within the framework of the density functional theory (DFT) using the projector augmented wave (PAW) method. The theoretical results were compared with time-differential perturbed γ–γ angular correlations (TDPAC) experiments reported in the literature using the 111Ag→111Cd probe. In the case of X=Ag+, a refinement of the structure was performed and the predicted equilibrium structures compared with available X-ray diffraction experimental data. Structural distortions induced by replacing Ag+ with Cd2+ were investigated as well as the electric-field gradient (EFG) tensor at the Cd2+ sites. Our results suggest that the EFG at Cd2+ sites corresponds to the Ag+ coordination sphere structure, i.e., before the structural relaxations of the molecule with X=Cd2+ are completed. The results are discussed in terms of the characteristics of the TDPAC 111Ag→111Cd probe and the time window of the measurement, and provide an interesting tool with which to probe molecular relaxations.