Juan Oyarzo

In searching for new therapeutic agents for treating American trypanosomiasis and Human African trypanosomiasis, four nitroheterocyclic acylhydrazones of general formulae [R¹‐CH=N‐NH‐C(O)‐(5‐C₄H₂X)] (where R¹ = ferrocenyl or cyrhetrenyl, and X = O or S) have been synthesized and characterized by spectroscopic techniques. Comparative studies of their stability by ¹H‐NMR and UV–Vis experiments were reported. Single‐crystal X‐ray diffraction confirmed the molecular structures of NF‐1 and NT‐2. Their X‐ray crystal structures reveal that both adopt an E‐configuration on the C=N moiety. Regarding the ‐NH‐C(O)‐ bond, the structure of NF‐1 confirmed a trans conformation, while NT‐2 exhibited a cis‐amide conformation. The cyclic voltammetry and electron spin resonance (ESR) experiments were conducted to study the electrochemical behavior of N‐acylhydrazones. The antiparasitic activities of compounds against Trypanosoma cruzi (epimastigotes) and Trypanosoma brucei (trypomastigotes) revealed that cyrhetrenyl complexes were more effective than their ferrocenyl analogs. The cyrhetrenyl derivative NT‐2 (EC₅₀ = 2.25 μM) showed activity against T. brucei comparable to the standard drug nifurtimox (Nfx, EC₅₀ = 3.56 μM). The ferrocenyl compound NT‐1 (>200 μM) was at least two times less cytotoxic than the Nfx (88.7 μM) against the L₆ rat skeletal myoblast cell line and exhibited a selectivity like Nfx toward T. brucei. Density functional theory (DFT) calculations were utilized as an approximation to explain the impact of organometallic and heterocyclic rings on antiparasitic activities. This study supported the experimental results, confirming that the cyrhetrenyl fragment in N‐acylhydrazone derivatives plays a significant role in the antitrypanosomal activity, which can be attributed to an increase in positive charge on the metal.

Current selective modification methods, coupled with functionalization through organic or inorganic molecules, are crucial for designing and constructing custom-made molecular materials that act as electroactive interfaces. A versatile method for derivatizing surfaces is through an aryl diazonium salt reduction reaction (DSRR). A prominent feature of this strategy is that it can be carried out on various materials. Using the DSRR, we modified gold surface electrodes with 4-aminebenzene from 4-nitrobenzenediazonium tetrafluoroborate (NBTF), regulating the deposited mass of the aryl film to achieve covering control on the electrode surface. We got different degrees of covering: monolayer, intermediate, and multilayer. Afterwards, the ArNO₂ end groups were electrochemically reduced to ArNH₂ and functionalized with Fe(II)-Phthalocyanine to study the catalytic performance for the oxygen reduction reaction (ORR). The thickness of the electrode covering determines its response in front of ORR. Interestingly, the experimental results showed that an intermediate covering film presents a better electrocatalytic response for ORR, driving the reaction by a four-electron pathway.

The understanding of the mean free path (MFP) distribution of the energy carriers in materials (e.g., electrons, phonons, magnons, etc.) provides a key physical insight into their transport properties. In this context, MFP spectroscopy has become an important tool to describe the contribution of carriers with different MFP to the total transport phenomenon. In this work, we revise the MFP reconstruction technique and present a study on the impact of the regularization parameter on the MFP distribution of the energy carriers. By using the L-curve criterion, we calculate the optimal mathematical value of the regularization parameter. The effect of the change from the optimal value in the MFP distribution is analyzed in three case studies of heat transport by phonons. These results demonstrate that the choice of the regularization parameter has a large impact on the physical information obtained from the reconstructed accumulation function, and thus cannot be chosen arbitrarily. The approach can be applied to various transport phenomena at the nanoscale involving carriers of different physical nature and behavior.

The syntheses, characterization, X-ray crystal structures, electrochemical properties and anticancer and antichagasic activities of the first examples of 2-substituted 2,4-dihydro-1H-3,1-benzoxazines with half-sandwich organometallic arrays, [M(η⁵-C₅H₄)(CO)₃] (M = Re or Mn), at position-2 are described. Experimental and computational studies based on DFT calculations on the open forms [Schiff bases of general formulae R-CHN-C₆H₄-2-CH₂OH] (5), with R = ferrocenyl (a), phenyl (b), cyrhetrenyl (c) or cymantrenyl (d), and their tautomeric forms (2-substituted 2,4-dihydro-1H-3,1 benzoxazines) have allowed us to establish the influence of substituents a–d and solvents on: (a) the extent of tautomeric equilibria (5a–5d) ↔ (6a–6d) and (b) their electrochemical properties and the electronic distribution on the open and closed forms. Despite the formal similarity between 6c and 6d, their anticancer and antiparasitic activities are markedly different. Compound 6d is inactive in the HCT116, MDA-MB231 and MCF7 cancer cell lines, but 6c shows moderate activity in the latter cell line, while the Mn(I) complex (6d) is a more potent anti-Trypanosoma cruzi agent than its Re(I) analogue (6c).

The synthesis and characterization of two novel and isomeric hybrid ferrocenyl/cyrhetrenyl aldimines [(η⁵-C₅H₅)Fe{(η⁵-C₅H₄)-CHN-(η⁵-C₅H₄)}Re(CO)₃] (1) and [(η⁵-C₅H₅)Fe{(η⁵-C₅H₄)-NCH-(η⁵-C₅H₄)}Re(CO)₃] (2) are reported. Their X-ray crystal structures reveal that both adopt the E form. However, molecules of 1 and 2 differ in the relative arrangement of the “Fe(η⁵-C₅H₅)” and “Re(CO)₃” units (anti in 1 and syn in 2). This affects the type of intermolecular interactions, the assembly of the molecules and therefore their crystal architecture. Comparative studies of their electrochemical, spectroscopic and photo-physical properties have allowed us to clarify the effect produced by the location of the organometallic arrays (ferrocenyl or cyrhetrenyl) on electronic delocalization, the proclivity of the metals to undergo oxidation and their emissive properties. Theoretical studies based on Density Functional Theory (DFT) calculations on the two compounds have also been carried out in order to rationalize the experimental results and to assign the bands detected in their electronic spectra. The cytotoxic activities of compounds 1 and 2 against human adenocarcinoma cell lines [breast (MCF7 and MDA-MB-231) and colon (HCT-116)] reveal that imine 2 has a greater inhibitory growth effect than 1 and it is ca. 1.8 times more potent than cisplatin in the triple negative MDA-MB 231 and in the cisplatin resistant HCT-116 cell lines. A comparative study of their effect on the normal and non-tumour human skin fibroblast BJ cell lines is also reported.