Publications

Abstract Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) has been used for the structural characterization of peptides and their interactions with membranes. Antimicrobial peptides (AMPs) are part of our immune system and widely studied in recent years. Many linear AMPs have been studied, but their cyclization was shown to enhance the peptide's activity. We have used cyclic peptides (CPs) of an even number of alternating D- and L-alpha-amino acids, an emerging class of potential AMPs. These CPs can adopt a flat-ring shape that can stack into an antiparallel structure, forming intermolecular hydrogen bonds between different units, creating a tubular beta-sheet structure - self-assembled cyclic peptide nanotubes (SCPNs). To get the structural information on peptides in solution and/or in contact with membranes, Amide I and II absorptions are used as they can adopt frequency and shape band characteristics that are influenced by the strength of existing hydrogen bonds between the amide CO and NH involved in secondary structures such as helix, beta-sheet or aperiodic structures. The combination of polarized lens with ATR-FTIR provides an important tool to study the orientation of peptides when interacting with lipid membranes as the information can be derived on the position relative to the membrane normal. This work shows how ATR-FTIR used together with polarized light was successfully used to characterize structurally two CPs (RSKSWPgKQ and RSKSWX(C10)KQ) in solution and upon interaction with negatively charged membranes of DMPG, assessing the formation and orientation of tubular structures (SCPNs) that were shown to be enhanced by the presence of the lipid membrane.

Abstract The synthesis of protic ionic liquids based in carboxylate anions, too often admitted as being straightforward, is actually challenging and must be carefully addressed. This review discusses the importance of oligomeric anions, in particular those based on carboxylates, in the behavior and nature of protic ionic liquids. There is strong evidence in the literature that the synthesis, and subsequent purification, of protic ionic liquids involving carboxylic acids, leads to structures in the liquid phase with an acid:base proportion different from the expected 1:1 stoichiometry. The formation of the oligomeric anions, mostly dependent on the proton transfer from the Bronsted acid to the Bronsted base, may lead to a higher ionicity that suggests the formation of true ionic liquids. It is here stressed the relevance of deepening the understanding of the interactions between the species and the speciation of the liquid phase, combining experimental and theoretical approaches to establish foundations for insightful advances in the area.

Abstract A small-scale ITC benchmarking study was performed involving 9 biophysics laboratories/facilities, to evaluate inter-laboratory and intra-laboratory basal levels of uncertainty. Our prime goal was to assess a number of important factors that can influence both the data gathered by this technique and the thermodynamic parameter values derived therefrom. In its first part, the study involved 5 laboratories and 13 different instruments, working with centrally prepared samples and the same experimental protocol. The second part involved 4 additional laboratories and 6 more instruments, where the users prepared their own samples according to provided instructions and did the experiments following the same protocol as in the first part. The study design comprised: (1) selecting a minimal set of laboratories; (2) providing very stable samples; (3) providing samples not requiring preparation or manipulation; and (4) providing a well-defined and detailed experimental protocol. Thus, we were able to assess: (i) the variability due to instrument and data analysis performed by each user on centrally prepared samples; (ii) the comparability of data retrieved when using 4 different software packages to analyze the same data, besides the data analysis carried out by the different users on their own experimental results; and (iii) the variability due to local sample preparation (second part of the study). Individual values, as well as averages and standard deviations for the binding parameters for EDTA-cation interaction, were used as metrics for comparing the equilibrium association constant (logK), enthalpy of interaction (Delta H), and the so-called "stoichiometry" (n), a concentration-correction factor.

Abstract Chagas disease is the most widespread contagious tropical disease in Latin America, being an important public health problem. Treatments against this disease are still very ineffective, presenting several side effects. Therefore, the search for alternative therapeutic solutions is urgent. In the present work, we evaluate the trypanocidal activity and the mechanism of action of a select series of synthetic 4-acyloxy-3-nitrocoumarins. All the coumarin derivatives showed moderate trypanocidal activity in trypomastigotes, along with low cytotoxicity. In addition, compound 1 decreased the number of infected Vero cells in an intracellular T. cruzi model. Electron spin resonance and electrochemical studies showed the formation of nitro radical anions. The Fukui index provided additional information to elucidate the proposed reduction mechanism. Furthermore, in vitro radical formation studies demonstrated the potential of these compounds to achieve higher concentrations of intracellular free radicals, proposing oxidative stress as a possible trypanocidal mechanism. Furthermore, no correlation was observed between the diffusion of these compounds, which shows that lipophilicity is not a predominant factor for activity. Elsevier Ltd. All rights reserved. (C) 2020 The Author(s). Published by Elsevier B.V. on behalf of King Saud University.

Abstract High performance liquid chromatography coupled with ultra-violet, diode array detection (HPLC-UV-DAD), was used to study the degradation reactions of ultraviolet (UV) filter hexyl 244-(diethylamino)-2-hydroxybenzoyl]- benzoate (DHHB). Degradation by-products were detected and identified by means of liquid chromatography coupled with diode array detection and mass spectrometry (LC-DAD-MS). Environmentally-relevant characteristics, such as water pH, chlorine levels, water temperature and dissolved organic matter (DOM) concentration, were modulated and studied in order to determine their influence on the degradation reactions. Results show that DHHB degrades quite rapidly in typical drinking water disinfection conditions, displaying a kinetic rate constant of k(obs) = 0.0060 + 0.0002 s(-1) and a half-life period of merely t(1/)(2) = 116 +/- 4 s. As far as the non-volatile disinfection by-products (DBPs) are concerned, only the mono and dichlorinated forms of DHHB were detected in the degradation reactions. Regarding influential variables on DHHB degradation, the presence or absence of DOM in solution did not alter the trends that were found (degradation of DHHB is more significant at lower pH values and higher levels of active chlorine in solution). Chlorinated DBPs have also been found to predominate under higher pH values and lower levels of chlorine, whereas they were found to be unstable and further degradable, quite likely into smaller and more volatile compounds, when in lower pH and higher chlorine concentrations. As for the photo-degradation studies, DHHB was found to be extremely photo-stable, with only about 15% degradation rate detected during artificial irradiation periods of 6 h.

Abstract The emergence of a large number of new psychoactive substance (NPS) on the global drug market poses a significant risk to public health and a challenge to drug control systems. Over the last decades, electrochemical sensing of illicit drugs has experienced a very significant growth, since these techniques can provide fast, portable, sensitive and low-cost detection alternatives for the analysis of drugs, metabolites and/or transformation products in different matrices. To understand and clarify the oxidative mechanism of piperazine designer drugs, the voltammetric profile of psychoactive piperazine derivatives 1-phenylpiperazine (PhPIP), 3-chlorophenylpiperazine (mCPP), 3-trifluoromethylphenylpiperazine (TFMPP), 4-fluorophenylpiperazine (pFPP) and benzylpiperazine (BZP) has been investigated at a glassy carbon electrode. The data found showed the crucial role of the aromatic amine, present in PhPIP, mCPP, pFPP and TFMPP molecular' structures, on the oxidative profiles. The voltammetric behavior of BZP is quite different from those found for the other piperazines under study due to the nature of the amine group present in BZP molecular' structure, benzylic instead of an aromatic amine. This work can be a helpful contribution to the ability to predict and identify metabolites and the development of new analytical approaches that can allow the rapid and specific quantitative detection of psychoactive piperazine derivatives.

Abstract The human normal breast cell line MCF-10A is being widely used as a model in toxicity studies due to its structural similarity to the normal human mammary epithelium. Over the years, application of carbon dots (C-dots) in biomedicine has been increasing due to their photoluminescence properties, biocompatibility, biosafety and possible applications in bioimaging and as drug carriers. In this work we prepared three different C-dots from the same set of carbon and nitrogen precursors (citric acid and urea, respectively) via three distinct bottom-up synthetic routes and their safety was tested against the normal breast cell line MCF-10A. The characterization results demonstrated a similar size range and composition for all the C-dots. The MCF-10A cells were treated with different concentrations of C-dots for 24, 48 and 72 h to evaluate the cell viability over time. For the 24 h incubation, there were no significant decreases in the viability of the MCF-10A cells. For the 48 h treatment, there was a significant decrease in the viability of the cells treated with calcination-based C-dots, but without significant cellular viability changes for microwave and hydrothermal-based C-dots. For 72 h, cells treated with hydrothermal-based C-dots have the most promising viability profile. Also, compared with paclitaxel, these C-dots have a safety profile very close to that of an antineoplastic in non-tumor cells. Our results suggest that these new C-dots have potential as imaging candidates or biosensing tools as well as drug carriers, and further investigation in animal models is needed for future application in medicine.

Abstract In-vitro imaging by swept-source optical coherence tomography (OCT) represents a class of advanced tomography that provides comprehensive and accurate clinical diagnostics. Here colloidal NaGdF4:Er3+/Yb3+ particles having an average size of 32 nm were successfully synthesized by a facial thermal decomposition method and then used as a contrast agent in OCT imaging. Prepared phosphor has shown bright green upconversion emission under 976 nm diode laser. The phosphor particles had increased the scattering of OCT scanning radiation, and thus higher image contrast was observed. The results indicate that upconversion phosphors may work as suitable contrast agents for OCT imaging.

Abstract Research on mitochondria-targeted active molecules became a hot topic in the past decade. Development of mitochondria permeability transition pore (mPTP)-targeting agents with clinical applications is needed not only because of the importance of the target in several diseases but also due to the fact that the current developed molecules have shown poor clinical success. In fact, only a reduced percentage reach mitochondria, effectively preventing pathological mPTP opening. The mitochondrial-targeting strategies should be a promising solution to increase the selectivity of compounds to the mPTP, reducing also their potential side effects. Chemical conjugation of bioactive molecules with a lipophilic cation such as the triphenylphosphonium (TPP+) has been established as a robust strategy to specifically target mitochondria. Phytochemicals such as hydroxybenzoic acids are normal constituents of the human diet. These molecules display beneficial healthy effects, ranging from antioxidant action through diverse mechanisms to modulation of mitochondrial-related apoptotic system, although their therapeutic application is limited due to pharmacokinetic drawbacks. Accordingly, the development of a new antioxidant based on the dietary benzoic acid—gallic acid—is described as well as the demonstration of its mitochondriotropic characteristics. © 2021, Springer Science+Business Media, LLC, part of Springer Nature.