Gold complexes with benzimidazole derivatives: synthesis, characterization and biological studies.

Synthesis, characterization, DFT studies and biological assays of new gold(I) and gold(III) complexes of benzimidazole are reported. Molecular and structural characterizations of the compounds were based on elemental (C, H and N) and thermal (TG-DTA) analyses, and FT-IR and UV-Visible spectroscopic measurements. The structures of complexes were proposed based DFT calculations. The benzimidazole compounds (Lig1 and Lig2) and the gold complexes were tested against three Leishmania species related to cutaneous manifestations of leishmaniasis. The free benzimidazole compounds showed no leishmanicidal activity. On the other hand, the gold(I and III) complexes have shown to possess significant activity against Leishmania in both stages of parasite, and the gold(III) complex with Lig2 exhibited expressive leishmanicidal activity with IC50 values below 5.7 µM. Also, the gold complexes showed high leishmania selectivity. The gold(I) complex with Lig1, for example, is almost 50 times more toxic for the parasite than for macrophages. Besides the leishmanicidal activity, all complexes exhibited toxic effect against SK-Mel 103 and Balb/c 3T3, cancer cells.

The photophysical, photobiological, and DNA/HSA-binding properties of corroles containing carbazole and phenothiazine moieties.

This study characterized four corrole derivatives, namely Cbz-Cor, MetCbz-Cor, PTz-Cor, and PTzEt-Cor, examining their photophysical, electrochemical, photobiological, and biomolecule-binding properties. Experimental photophysical data of absorption and emission elements correlated with a theoretical analysis obtained through time-dependent density functional theory (TD-DFT). As for the photophysical properties, we observed lower fluorescence quantum yields and discernible differences between the excited and ground states, as indicated by Stokes shift values. Natural Transition Orbit (NTO) plots presented high occupied molecular orbital - low unoccupied molecular orbital (HOMO-LUMO) densities around the tetrapyrrolic macrocycle in all examples. Our findings demonstrate that corroles maintain stability in solution and offer photostability (<20 %), predominantly in DMSO(5 %)/Tris-HCl (pH 7.4) buffer solution. Furthermore, the singlet oxygen (1O2) quantum yield and log POW values underscore their potential application in photoinactivation approaches, as these corroles serve as effective ROS generators with more lipophilic features. We also evaluated their biomolecular binding capacity towards salmon sperm DNA and human serum albumin using spectroscopic techniques and molecular docking analysis for sustenance. Concerning biomolecule interaction profiles, the corrole derivatives showed a propensity for interacting in the minor grooves of the double helix DNA due to secondary forces, which were more pronounced in site III of the human serum protein.

Interaction studies of oxindole-derivatives with ß-amyloid peptides inhibiting its aggregation induced by metal ions.

Some hydrazones and Schiff bases derived from isatin, an endogenous oxindole formed in the metabolism of tryptophan, were obtained to investigate their effects on in vitro aggregation of ß-amyloid peptides (Aß), macromolecules implicated in Alzheimer's disease. Some hydrazone ligands, prepared by condensation reactions of isatin with hydrazine derivatives, showed a large affinity binding to the synthetic peptides Aß, particularly to Aß1-16. Measurements by NMR spectroscopy indicated that those interactions occur mainly at the metal binding site of the peptide, involving His6, His13, and His14 residues, and that hydrazone E-diastereoisomer interacts preferentially with the amyloid peptides. Experimental results were consistent with simulations using a docking approach, where it is demonstrated that the amino acid residues Glu3, His6, His13, and His14 are those that mostly interact with the ligands. Further, these oxindole-derived ligands can efficiently chelate copper(II) and zinc(II) ions, forming moderate stable [ML] 1:1 species. The corresponding formation constants were determined by UV/Vis spectroscopy, by titrations of the ligands with increasing amounts of metal salts, and the obtained log K values were in the range 2.74 to 5.11. Both properties, good affinity for amyloid peptides, and reasonably good capacity of chelating biometal ions, like copper and zinc, can explain the efficient inhibition of Aß fragments aggregation, as shown by experiments carried out with the oxindole derivatives in the presence of metal ions.

Tracking chemical interactions of folic acid on gold surface by SERS spectroscopy.

Surface-enhanced Raman scattering (SERS) spectroscopy was used in the investigation of the adsorption of folic acid (FA) on the surface of gold nanoparticles (AuNPs) in the absence and presence of surface modifiers hydrochloride acid (HCl) and 1-mercaptoethanol (ME). The proposal for the chemical interactions of FA with the metallic surface was based on vibrational assignment supported by Density Functional Theory (DFT) calculations. In the absence of surface modifiers, FA interacts with the gold surface through the pteridine moiety in a tilted geometry. In the presence of ME, the molecule of FA is anchored through hydrogen bonds with the surface modifier. The presence of HCl induced ion-pair interactions involving chloride ions, adsorbed on gold surfaces, and both the nitrogen N1 of the pteridine ring and the γ-carboxylic acid of the glutamic acid moiety. In this condition, keto-enol equilibrium can be evidenced by a remarkable enhancement of marker bands in the SERS spectra.

Insights of adsorption mechanisms of Trp-peptides on plasmonic surfaces by SERS.

The adsorptions of tryptophan (Trp) on silver or gold surfaces were investigated by surface-enhanced Raman scattering (SERS) measurements. In addition, peptides with Trp in different chain positions were studied and the adsorption sites were determined based on marker bands. The indole ring was the main group responsible for the interactions with gold nanoparticles (AuNPs). In the presence of HCl, the SERS spectra suggested that the anchoring of such peptides on AuNPs was reinforced by ionic pair interactions between protonated amine and chloride ions. The adsorptions of Trp and its derivatives on silver nanoparticles (AgNPs) show some variability in the spectral patterns, even though the enhanced carboxilate and amino features were ever ascribed as preferable adsorption site. Based on DFT calculations the vibrational assignment allows the reinterpretation of previous published works. The investigations showed that both the high affinity of indole moiety for the AuNP surfaces make these substrates adequate for studying the adsorption of peptides containing Trp and the proposed SERS assignments could be helpful for further studies of more complex structures.

Synthesis, spectroscopic and computational characterization of the tautomerism of pyrazoline derivatives from chalcones.

In the present study a series of novel pyrazolines derivatives has been synthesized, and their structures assigned on the basis of FT-Raman, (1)H and (13)C NMR spectral data and computational DFT calculations. A joint computational study using B3LYP/6-311G(2d,2p) density functional theory and FT-Raman investigation on the tautomerism of 3-(4-substituted-phenyl)-4,5-dihydro-5-(4-substituted-phenyl)pyrazole-1-carbothioamide and 3-(4-substituted-phenyl)-4,5-dihydro-5-(4-substituted-phenyl)pyrazole-1-carboxamide are presented. The structures were characterized as a minimum in the potential energy surface using DFT. The calculated Raman and NMR spectra were of such remarkable agreement to the experimental results that the equilibrium between tautomeric forms has been discussed in detail. Our study suggests the existence of tautomers, the carboxamide/carbothioamide group may tautomerize, in the solid state or in solution. Thermodynamic data calculated suggests that the R(CS)NH2 and R(CO)NH2 species are more stable than the R(CNH)SH and R(CNH)OH species. Additionally, results found for the (1)H NMR shifting, pointed out to which structure is present.

Structural and vibrational study of 8-hydroxyquinoline-2-carboxaldehyde isonicotinoyl hydrazone--a potential metal-protein attenuating compound (MPAC) for the treatment of Alzheimer's disease.

A comprehensive structural and vibrational study of the potential metal-protein attenuating compound 8-hydroxyquinoline-2-carboxaldehyde isonicotinoyl hydrazone is reported. X-ray diffraction data, as well as FT-IR and Raman frequencies, were compared with the respective theoretical values obtained from DFT calculations. Theory agrees well with experiment. In this context, an attempt of total assignment concerning the FT-IR and Raman spectra of the title compound was performed, shedding new light on previous partial assignments published elsewhere.