Examinando por Autor "Günther, Germán"
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Ítem Flavonoids in microheterogeneous media, relationship between their relative location and their reactivity towards singlet oxygen(Public Library of Science, 2015-06) Günther, Germán; Berrîos, Eduardo; Pizarro, Nancy; Valdés, Karina; Montero, Guillermo; Arriagada, Francisco; Morales, JavierIn this work, the relationship between the molecular structure of three flavonoids (kaempferol, quercetin and morin), their relative location in microheterogeneous media (liposomes and erythrocyte membranes) and their reactivity against singlet oxygen was studied. The changes observed in membrane fluidity induced by the presence of these flavonoids and the influence of their lipophilicity/hydrophilicity on the antioxidant activity in lipid membranes were evaluated by means of fluorescent probes such as Laurdan and diphenylhexatriene (DPH). The small differences observed for the value of generalized polarization of Laurdan (GP) curves in function of the concentration of flavonoids, indicate that these three compounds promote similar alterations in liposomes and erythrocyte membranes. In addition, these compounds do not produce changes in fluorescence anisotropy of DPH, discarding their location in deeper regions of the lipid bilayer. The determined chemical reactivity sequence is similar in all the studied media (kaempferol < quercetin < morin). Morin is approximately 10 times more reactive than quercetin and 20 to 30 times greater than kaempferol, depending on the medium. Copyright: © 2015 Günther et al.Ítem Photochemistry of P,N-bidentate rhenium(i) tricarbonyl complexes: Reactive species generation and potential application for antibacterial photodynamic therapy(Royal Society of Chemistry, 2021-09) Acosta, Alison; Antipán, Javier; Fernández, Mariano; Prado, Gaspar; Sandoval-Altamirano, Catalina; Günther, Germán; Gutiérrez-Urrutia, Izabook; Poblete-Castro, Ignacio; Vega, Andrés; Pizarro, NancyIn this work, we describe the photoisomerization of facial rhenium(i) tricarbonyl complexes bearing P,N-bidentate pyridyl/phosphine ligands with different chelating rings and anions: RePNBr, RePNTfO, and RePNNBr, which are triggered under irradiation at 365 nm in solutions. The apparent photodegradation rate constants (kapp) depend on the coordinating ability of the solvent, being lowest in acetonitrile. The kapp value increases as the temperature rises, suggesting a reactive IL excited state thermally populated from the MLCT excited state involved. Using the Eyring equation, positive activation enthalpies (ΔH≠) accompanied by high negative values for the activation entropy (ΔS≠) were obtained. These results suggest whatever the P,N-ligand or anion, the reaction proceeds through a strongly solvated or a compact transition state, which is compatible with an associative mechanism for the photoisomerization. A 100-fold decrease in the log10 CFU value is observed for E. coli and S. aureus in irradiated solutions of the compounds, which follows the same tendency as their singlet oxygen generation quantum yield: RePNBr > RePNTfO > RePNNBr, while no antibacterial activity is observed in the darkness. This result indicates that the generation of singlet oxygen plays a key role in the antibacterial capacity of these complexes. © The Royal Society of Chemistry.Ítem Photodegradation of nimodipine and felodipine in microheterogeneous systems(Sociedad Chilena de Química, 2012) Brito, Julio; Pozo, Andrés; García, Cristóbal; Núñez-Vergara, Luis J.; Morales, Javier; Günther, Germán; Pizarro, NancyThe photochemical behavior of nimodipine (NIMO) and felodipine (FELO), photolabile drugs widely used as antihypertensive calcium channel blockers, is studied in constrained media. Specifically, we are interested in the kinetic analysis of 4-aryl-1,4-dihydropyridine photodegradation processes when they are incorporated in biological-mimicking systems like micelles or liposomes. In order to establish if the nature of the head of surfactant (ionic or nonionic) could be important modulating the photo-reactivity of these drugs, we studied the photodegradation of NIMO and FELO incorporated in micelles formed with sodium dodecyl sulfate (SDS, anionic), dodecyl-pyridinium chloride (DPC, cationic) and mono lauryl sucrose ester (MLS, nonionic) as surfactants. Additionally, the results of the photodegradation of these compounds in liposomes were also included. The results clearly indicate that both dihydropyridines studied, NIMO and FELO, are located near to the interface, but the surface charge of micelles does not affect neither, the photodegradation rate constant nor the photodegradation products profile. The absence of singlet oxygen generation in micellar media is consistent with the proposition of these 4-aryl-1,4-dihidropyridines located near to the interface of the micelle, where a polar environment is sensed. In addition, the ethanol preferential location on membranes and dihydropyridine enhanced photodegradation by alcohol presence are interesting results to consider in future research.Ítem The binuclear dual emitter [Br(CO)3Re(P⋯N)(N⋯P)Re(CO)3Br] (P⋯N): 3-chloro-6-(4-diphenylphosphinyl)butoxypyridazine, a new bridging: P, N -bidentate ligand resulting from the ring opening of tetrahydrofuran(Royal Society of Chemistry, 2017) Saldías, Marianela; Manzur, Jorge; Palacios, Rodrigo E.; Gómez, María L.; Fuente, Julio De La; Günther, Germán; Pizarro, Nancy; Vega, AndrésLithium diphenylphosphide unexpectedly provokes the ring-opening of tetrahydrofuran (THF) and by reaction with 3,6-dichloropyridazine leads to the formation of the ligand 3-chloro-6-(4-diphenylphosphinyl)butoxypyridazine (P⋯N), which was isolated. The reaction of this ligand with the (Re(CO)3(THF)Br)2 dimer yields the novel complex [Br(CO)3Re(μ-3-chloro-6-(4-diphenylphosphinyl)butoxypyridazine)2Re(CO)3Br] (BrRe(P⋯N)(N⋯P)ReBr), which was crystallized in the form of a chloroform solvate, (C46H40Br2Cl2N4O8P2Re2)·(CHCl3). The monoclinic crystal (P21/n) displays a bimetallic cage structure with a symmetry inversion centre in the middle of the rhenium to rhenium line. The molecule shows two oxidation signals occurring at +1.50 V and +1.76 V which were assigned to the ReI/ReII and ReII/ReIII metal-centered couples, respectively, while signals observed at -1.38 V and -1.68 V were assigned to ligand centered reductions. Experimental and DFT/TDDFT results indicate that the UV-Vis absorption maximum of BrRe(P⋯N)(N⋯P)ReBr occurring near 380 nm displays a metal to ligand charge transfer (MLCT) character, which is consistent with CV results. Upon excitation at this wavelength, a weak emission (Φem < 1 × 10-3) is observed around 580 nm (in dichloromethane) which decays with two distinct lifetimes τ1 and τ2 of 24 and 4.7 ns, respectively. The prevalence of non-radiative deactivation pathways is consistent with efficient internal conversion induced by the high conformational flexibility of the P⋯N ligand's long carbon chain. Measurements in a frozen solvent at 77 K, where vibrational deactivation is hindered, show intense emission associated with the 3MLCT state. These results demonstrate that BrRe(P⋯N)(N⋯P)ReBr preserves the dual emitting nature previously reported for the mononuclear complex RePNBr, with emission associated with and states. © 2017 The Royal Society of Chemistry.