Artículos (Química Física)

URI permanente para esta colecciónhttps://hdl.handle.net/11441/10914

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Thermodynamics of Solids Including Anharmonicity through Quasiparticle Theory
(Nature, 2024) Blancas, Ernesto J.; Lobato, Álvaro; Izquierdo Ruiz, Fernando; Márquez Cruz, Antonio Marcial; Recio, J. Manuel; Nath, Pinku; Plata Ramos, José Javier; Otero de la Roza, Alberto; Universidad de Sevilla. Departamento de Química Física; Ministerio de Ciencia, Innovación y Universidades (MICIU). España; Principado de Asturias; Red Española de Supercomputación (RES)
The quasiharmonic approximation (QHA) in combination with density-functional theory is the main computational method used to calculate thermodynamic properties under arbitrary temperature and pressure conditions. QHA can predict thermodynamic phase diagrams, elastic properties and temperature- and pressure-dependent equilibrium geometries, all of which are important in various fields of knowledge. The main drawbacks of QHA are that it makes spurious predictions for the volume and other properties in the high temperature limit due to its approximate treatment of anharmonicity, and that it is unable to model dynamically stabilized structures. In this work, we propose an extension to QHA that fixes these problems. Our approach is based on four ingredients: (i) the calculation of the n-th order force constants using randomly displaced configurations and regularized regression, (ii) the calculation of temperature-dependent effective harmonic frequencies ω(V, T) within the self-consistent harmonic approximation (SCHA), (iii) Allen’s quasiparticle (QP) theory, which allows the calculation of the anharmonic entropy from the effective frequencies, and (iv) a simple Debye-like numerical model that enables the calculation of all other thermodynamic properties from the QP entropies. The proposed method is conceptually simple, with a computational complexity similar to QHA but requiring more supercell calculations. It allows incorporating anharmonic effects to any order. The predictions of the new method coincide with QHA in the low-temperature limit and eliminate the QHA blowout at high temperature, recovering the experimentally observed behavior of all thermodynamic properties tested. The performance of the new method is demonstrated by calculating the thermodynamic properties of geologically relevant minerals MgO and CaO. In addition, using cubic SrTiO3 as an example, we show that, unlike QHA, our method can also predict thermodynamic properties of dynamically stabilized phases. We expect this new method to be an important tool in geochemistry and materials discovery.
Enhancing the Thermoelectric Figure of Merit of BiN Via Polymorphism, Pressure, and Nanostructuring
(Royal Society of Chemistry, 2024) Rodríguez Remesal, Elena; Posligua Hernández, Víctor Hugo; Mahíllo Paniagua, M.; Glazyrin, K.; Fernández Sanz, Javier; Márquez Cruz, Antonio Marcial; Plata Ramos, José Javier; Universidad de Sevilla. Departamento de Química Física; Ministerio de Ciencia e Innovación (MICIN). España; Red Española de Supercomputación (RES)
Materials discovery extends beyond the synthesis of new compounds. Detailed characterization is essential to understand the potential applications of novel materials. However, experimental characterization can be challenging due to the vast chemical and physical spaces, as well as the specific conditions required for certain techniques. Computational high-throughput methods can overcome these challenges. In this work, the transport and thermoelectric properties of the recently synthesized bulk BiN are explored, including the effects of temperature, pressure, carrier concentration, polymorphism and polycrystalline grain size. We find that the band structure is strongly dependent on pressure and the polymorph studied. Both polymorphs exhibit low thermal conductivity at 0 GPa, which rapidly increases when pressure is applied. Electronic transport properties can be finely tuned based on the effects of pressure and polymorph type on the band gap, carrier mobilities, and presence of secondary pockets. The thermoelectric figure of merit can reach values around 0.85 for both p- and n-type BiN if the power factor and lattice thermal conductivity are optimized at 600 K, making this material competitive with other well-known thermoelectric families, such as Bi2Te3 or PbX, in the low-to-medium temperature range.
Challenges Reconciling Theory and Experiments in the Prediction of Lattice Thermal Conductivity: The Case of Cu-Based Sulvanites
(American Chemical Society, 2024) Caro Campos, I.; González Barrios, M. M.; Dura, O. J.; Fransson, E.; Plata Ramos, José Javier; Ávila, D.; Fernández Sanz, Javier; Prado Gonjal, J.; Márquez Cruz, Antonio Marcial; Universidad de Sevilla. Departamento de Química Física; Ministerio de Ciencia, Innovación y Universidades (MICIU). España; Comunidad Autónoma de Madrid; Red Española de Supercomputación (RES)
The exploration of large chemical spaces in search of new thermoelectric materials requires the integration of experiments, theory, simulations, and data science. The development of high-throughput strategies that combine DFT calculations with machine learning has emerged as a powerful approach to discovering new materials. However, experimental validation is crucial to confirm the accuracy of these workflows. This validation becomes especially important in understanding the transport properties that govern the thermoelectric performance of materials since they are highly influenced by synthetic, processing, and operating conditions. In this work, we explore the thermal conductivity of Cu-based sulvanites by using a combination of theoretical and experimental methods. Previous discrepancies and significant variations in reported data for Cu3VS4 and Cu3VSe4 are explained using the Boltzmann Transport Equation for phonons and by synthesizing well-characterized defect-free samples. The use of machine learning approaches for extracting high-order force constants opens doors to charting the lattice thermal conductivity across the entire Cu-based sulvanite family─finding not only materials with κl values below 2 W m-1 K-1 at moderate temperatures but also rationalizing their thermal transport properties based on chemical composition.
Selective Design of MOF-derived Electrocatalytic Interphases by Potential-driven Surface Reconstruction
(Elsevier, 2025) Hernández Salvador, Sergio; Márquez Escudero, Inmaculada; Gutiérrez Tarriño, Silvia; Calvente Pacheco, Juan José; Río Rodríguez, José Luis del; Oña Burgos, Pascual; Andreu Fondacabe, Rafael Jesús; Olloqui Sariego, José Luis; Universidad de Sevilla. Departamento de Química Física; Ministerio de Ciencia, Innovación y Universidades (MICIU). España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Junta de Andalucía; Ministerio de Ciencia e Innovación (MICIN). España; Generalitat Valenciana; Universitat Politècnica de València (UPV)
Metal-organic frameworks (MOFs) can be used as precursors for the directed synthesis of derived materials with enhanced performance for electrocatalysis. Herein, we report on an in-situ electrochemical strategy for the selective synthesis of hybrid electrocatalysts using a cobalt MOF (2D-CoMOF) as a precursor for constructing electrochemical sensors to monitor the glucose oxidation reaction (GOR). By using in-situ Raman spectroelectrochemistry, it is demonstrated that a precise control of the applied potential during amperometric treatment of 2D-CoMOF can promote the generation of derived heterostructures in which the original MOF coexists with metal oxides and/or oxyhydroxides (MOF-MOx) with different compositions. The so-prepared electrodes exhibit high electroactive surface areas, a high number of electrocatalytically active cobalt sites and an efficient charge transport across the catalytic film. Moreover, their composition-dependent electrocatalytic performance for the glucose oxidation reaction is examined, establishing a relationship between the applied potential, the macroscopic chemical composition of the heterostructure and the electrocatalytic performance for glucose sensing. In particular, the hybrid phases consisting of Co-MOF/Co3O4/CoOOH display superior electrocatalytic sensing performance with a wide linear concentration range and high sensitivity. The present work emphasizes the significance that the precise control of the applied potential has on the electrochemically-assisted MOF transformation for developing highly efficient MOF-derived electrocatalysts.
Influence of carbon nanotubes on the antimicrobial character of the β-lactam antibiotics Cefepime and Meropenem
(Elsevier, 2025-05) Bernal Pérez, Eva; Mata Hijosa, Laura; López-Cornejo, María del Pilar; Moyá Morán, María Luisa; Madinabeitia, Nuria; Merino Bohórquez, Vicente; López-López, Manuel; Lebrón Romero, José Antonio; Universidad de Sevilla. Departamento de Química Física; Universidad de Sevilla. Departamento de Farmacología
The overuse of antibiotics over decades has led to a multi-resistance of bacteria that today poses a serious threat to human health. β-lactam antibiotics are one of the most prescribed drugs against bacterial infectious diseases, which has conducted to increased resistance. The short half-life of these drugs results in low bioavailability, which limits their clinical use and requires continuous administration by infusion. Encapsulation of these antibiotics in nanocarriers would improve their biopharmaceutical properties by protecting them. With this in mind, single- and multi-walled carbon nanotubes (SWCNTs and MWCNTs, respectively) were used here as nanocarriers for the antibiotics Meropenem and Cefepime. The adsorption process of these antibiotics in the carbon nanotubes (CNTs) was optimized to obtain a high encapsulation efficiency. The complexes CNT/drug prepared were characterized by dynamic light scattering and spectroscopic measurements. The growth of Escherichia coli and Staphylococcus aureus bacteria was analyzed in the presence of the CNT/drug complexes to evaluate the pharmacological properties of the encapsulated antibiotics. Results showed lower minimum inhibitory concentration (MIC) values of the CNT/drug complexes compared to free drugs. This indicates the preservation of the pharmacological properties of the encapsulated antibiotics. In addition, the stability of the encapsulated antibiotics was observed to last at least 24 h, which was a great improvement compared to the free drugs.
Impact of Frozen Storage on Sensory, Physicochemical, and Volatile Compounds Parameters of Different Extra Virgin Olive Oils
(Multidisciplinary Digital Publishing Institute (MDPI), 2024-11-24) Díaz Montaña, Enrique Jacobo; Barbero López, María; Aparicio Ruiz, Ramón; García González, Diego Luis; Morales Millán, María Teresa; Universidad de Sevilla. Departamento de Química Física; Universidad de Sevilla. Departamento de Química Analítica; Ministerio de Ciencia, Innovación y Universidades (MICIU). España
Storage is important for virgin olive oil, a product obtained only during the harvest period, which requires a year-round storage until its best-before date. Low temperatures slow undesirable reactions, though this method is not widely applied. The objective of this paper is to assess the impact of frozen storage on the volatile composition and sensory properties of virgin olive oils. The quality parameters, volatile composition, and sensory profiles were analyzed for samples stored under different conditions (time 0, sixth month supermarket and frozen storage, and long-term-frozen). The physicochemical parameters of the samples stored under supermarket conditions showed significant differences (p < 0.05), with the frozen-storage sample after three months of storage. Additionally, the samples stored under supermarket conditions showed higher volatile concentrations than frozen ones, with increased concentrations of aldehydes and acids producing sensory defects. Thirty-two samples, considered as the long-term-frozen, were divided into three groups depending on the frozen-storage time (1, 6 or 10 years). These long-term-frozen storage samples confirmed the suitability of the proposed oxidation markers (pentanal, hexanal, heptanal, nonanal, acetic, propanoic, butanoic, and hexanoic acids) for differentiating storage conditions and times. This work highlights the oxidation process under different storage conditions and suggests oxidation markers.
Cooperative interaction between metallosurfactants, derived from the [Ru(2,2 '-bpy)(3)](2+) complex, and DNA
(Elsevier, 2015) Lebrón Romero, José Antonio; Ostos Marcos, Francisco José; Moyá Morán, María Luisa; López López, M.; Carrasco Carrasco, Carlos Jesús; López-Cornejo, María del Pilar; Universidad de Sevilla. Departamento de Química Física; Universidad de Sevilla. Departamento de Química Inorgánica; Junta de Andalucía; European Union (UE)
With the idea of improving and advancing the design and preparation of new reagents based on cationic surfactants for gene therapy, two luminescent metallosurfactants derived from the [Ru(2,2′-bpy)3]2+ complex were synthesized. Their interaction with DNA and the effect they exert on the conformation of the polynucleotide were studied by using different techniques. The equilibrium binding constants, Kb, of the two surfactants to DNA were obtained at different molar ratios X = [surfactant]/[DNA]. The observed sigmoidal dependence of Kb on X confirms the cooperative character of the binding. After the addition of a determined surfactant concentration, the condensation of the polymer was observed. The amount of surfactant needed to produce this conformational change is lower for the double stranded surfactant than for the single chain surfactant due to a stronger hydrophobic interaction. The addition of α-cyclodextrin molecules to the metallosurfactant/DNA solutions results in polynucleotide decompaction, which confirms the importance of the hydrophobic interactions in the condensation of the polynucleotide. Results also show the importance of choosing both a proper system to study and the most seeming measuring technique to use. It is demonstrated that, in some cases, the use of several techniques is desirable to obtain reliable and accurate results.
Structural, Optical and Magnetic Properties of a New Metal-organic CoII-based Complex
(Royal Society of Chemistry, 2024) Jabeur, W.; Korb, M.; Hamdi, M.; Holub, M.; Princík, D.; Zelenák, V.; Sánchez Coronilla, Antonio; Shalash, M.; Cizmár, E.; Naïli, H.; Universidad de Sevilla. Departamento de Química Física; Northern Border University (NBU). Arabia Saudí; Slovak Research and Development Agency; Junta de Andalucía; Ministerio de Ciencia, Innovación y Universidades (MICIU). España
A mononuclear cobalt(ii) complex [C5H8N3]2[CoCl4(C5H7N3)2] (I) was synthesized and structurally characterized. Single crystal X-ray diffraction analysis indicates that monometallic Co(ii) ions acted as coordination nodes in a distorted octahedral geometry, giving rise to a supramolecular architecture. The latter is made up of a ½ unit form composed of an anionic element [Co0.5Cl2(C5H7N3)]− and one 2-amino-4-methylpyrimidinium cation [C5H8N3]+. The crystalline arrangement of this compound adopts the sandwich form where inorganic parts are sandwiched between the organic sheets following the [100] direction. More information regarding the structure hierarchy has been supplied based on Hirshfeld surface analysis; the X⋯H (X = N, Cl) interactions play a crucial role in stabilizing the self-assembly process of I, complemented by the intervention of π⋯π electrostatic interaction created between organic entities. Thermal analyses were carried out to study the thermal behavior process. Static magnetic measurements and ab initio calculations of compound I revealed the easy-axis anisotropy character of the central Co(ii) ion. Two-channel field-induced slow-magnetic relaxation was observed; the high-frequency channel is characterized by underbarrier relaxation with Ueff = 16.5 cm−1, and the low-frequency channel involves a direct relaxation process affected by the phonon-bottleneck effect.
Magnetic Dimeric Metal-porphyrin Rings Mechanically Bonded Around Carbon Nanotubes: the Role of Nanotube Defects Modulating Magnetic Properties
(Royal Society of Chemistry, 2024) Sánchez de Armas, María Rocío; Montenegro-Pohlhammer, Nicolás; Pérez, E. M.; Burzuri, E.; Jiménez Calzado, Carmen; Universidad de Sevilla. Departamento de Química Física; Ministerio de Ciencia e Innovación (MICIN). España; Gobierno de España; Ministerio de Ciencia, Innovación y Universidades (MICIU). España
Carbon nanotubes constitute an excellent option to connect molecular nanomagnets (MNMs) to solid-state devices, allowing the electrical control of the molecule spin state. The main challenge in this area is to obtain stable nanohybrid structures that preserve the magnetic properties and functionality of the molecule. One of the strategies developed to build these structures combining MNMs and carbon nanotubes involves the encapsulation of the nanotube within magnetic organic macrocycle(s), leading to magnetic mechanically interlocked derivatives of carbon nanotubes (mMINTs). Recently, mMINTs with dimeric metal-porphyrin rings containing Cu2+ or Co2+ attached to carbon nanotubes have been synthesized. Different structural and spectroscopic techniques confirm that the metal centers in both mMINTs preserve the coordination sphere and structure of the free macrocycles, with only small deviations from the square planar geometry. However, different magnetic behaviors are observed depending on the metal. The Cu derivative has well-preserved spin geometry, with quantum coherence times on the microsecond scale, as in the free molecule (τ = 25 μs). In contrast, the continuous-wave electron paramagnetic resonance (EPR) spectrum measured on the Co derivative does not show any clear contribution from Co, although EXAFS unambiguously shows the presence of Co2+. In order to understand this different magnetic behavior, we studied mMINTs by means of periodic DFT calculations. The analysis of the optimized geometries, the spin density of the free macrocycles and the mMINTs, the adsorption energies, the extension of the charge transfer between the macrocycle and the nanotube and the density of states reveals a stronger macrocycle-nanotube interaction for the Co-mMINT. Our results point to carbon vacancies in the nanotubes as responsible for the different macrocycle-nanotube interaction and the observed loss of the Co2+ EPR signal in the Co-mMINT.
Guest-dependent Spin Transitions in Hofmann-like FeII SCO Metal-organic Frameworks: Hints from Quantum Chemistry Calculations
(Royal Society of Chemistry, 2024) Arias Olivares, Nelson David; Sánchez de Armas, María Rocío; Jiménez Calzado, Carmen; Universidad de Sevilla. Departamento de Química Física; Ministerio de Ciencia e Innovación (MICIN). España; Junta de Andalucía
The family of 3D Hofmann-like FeII coordination polymers with the formula [Fe(bpd)[MII(CN)4]]·2G, M = Pt, Pd, and Ni is known for having a large capacity to host guest molecules (G) such as nitrobenzene or naphthalene. The presence of the guest molecules modulates the spin-crossover properties. In fact, these clathrates present a large hysteresis loop, in one single step or two well separated steps depending on the guest. In this work, we analyse by means of state-of-the-art DFT-based calculations the main effects governing the occurrence of the multistep spin transition, and the differences due to the nature of the divalent M metal and the encapsulated guest molecules. The study determines the relative stability of the mixed-spin state, the amplitude and nature of the host–guest and guest–guest intermolecular interactions, and the key role played by the C[triple bond, length as m-dash]N stretching modes of the M-cyanide units. Our results provide hints on the distinct roles of each of these factors and how they promote or prevent a direct transition from the high-spin state to the low-spin state.
Preparation and characterization of metallomicelles of Ru(II). Cytotoxic activity and use as vector
(Elsevier, 2019-03-19) Lebrón Romero, José Antonio; Ostos Marcos, Francisco José; López López, M.; Moyá Morán, María Luisa; Kardell, O; Sánchez, A; Carrasco Carrasco, Carlos Jesús; García Calderón, Margarita; Valle Rosado, Iván; López-Cornejo, María del Pilar; Universidad de Sevilla. Departamento de Química Física; Junta de Andalucía; Universidad de Sevilla; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER)
The use of nanovectors in several medicinal treatments has reached a great importance in the last decade. Some drugs need to be protected to increase their lifetimes in the blood flow, to avoid degradation, to be delivered into target cells or to decrease their side effects. The goal of this work was to design and prepare nanovectors formed by novel surfactants derived from the [Ru(bpy)3]2+ complex. These amphiphilic molecules are assembled to form metallomicelles which can act as pharmaceutical agents and, at the same time, as nanovectors for several drugs. TEM images showed a structural transition from spherical to elongated micelles when the surfactant concentration increased. Fluorescence microscopy confirmed the internalization of these metallomicelles into diverse cell lines and cytotoxicity assays demonstrated specificity for some human cancer cells. The encapsulation of various antibiotics was carried out as well as a thorough study about the DNA condensation by the metallomicelles. To the best of our knowledge, applications of these metallomicelles have not been shown in the literature yet.
Novel theoretical studies based on CIELab and deconvolution methods to characterize AuNPs aggregation processes
(Elsevier, 2024-12) Hernández, Haimar; López Pérez, Germán; Grueso Molina, Elia María; Giráldez Pérez, Rosa María; Hidalgo Toledo, José; Prado Gotor, Rafael; Universidad de Sevilla. Departamento de Química Física; Junta de Andalucía; Universidad de Sevilla
The study of the interaction of spherical gold nanoparticles when they undergo aggregation phenomena due to the presence of a ligand in solution is presented, based on both colorimetric parameters (using CIELab space) and traditional deconvolution analysis. The feasibility of using CIELab space for this purpose can be an important method to simplify the required instrumentation (colorimeter versus UV spectrophotometer) as well as being less time consuming compared with the traditional computational analysis. For these reasons, in this work we present the first experimental approach of the proposed methodology for its application in this field of research. The synthetized AuNPs employed in this work have been previously characterized by means of the maxima of their LSPR bands, zeta potential and electron microscopy images. The aggregation of spherical AuNPs (with a diameter of 12 nm) by an inert electrolyte (NaCl) is investigated in a first step with successfully results, allowing to obtain the characteristic CIELab parameters (a*, b* and L*). At a later stage, the color changes induced in the optical properties of the solution due to the interaction of AuNPs (with increasing diameters of 12, 25 and 33 nm) with an amino acid such as lysine at neutral pH, have been also described using the CIELab spatial framework. The obtained a*, b* and L* parameters of the CIELab space allow to characterize satisfactorily the color change from red to blue which describes the aggregation phenomena, relying on deconvolution analysis of the LSPR bands. The results obtained support the validity of the CIELab space as a valid tool for the investigation of the aggre gation process of colloidal solutions. It will allow simplifying the whole process using simpler and cheaper instrumentation as well as a decrease in the required analysis time.
Self-aggregation in Aqueous Solution of Amphiphilic Cationic Calix[4]arenes. Potential Use as Vectors and Nanocarriers
(Elsevier, 2020) Ostos Marcos, Francisco José; Lebrón Romero, José Antonio; López-Cornejo, María del Pilar; López López, Manuel; García Calderón, Margarita; García Calderón, Clara Beatriz; Valle Rosado, Iván; Kalchenko, Vitaly I.; Rodik, Roman V.; Moyá Morán, María Luisa; Universidad de Sevilla. Departamento de Química Física; Universidad de Sevilla. Departamento de Bioquímica Vegetal y Biología Molecular; Junta de Andalucía; Universidad de Sevilla; Ministerio de Ciencia, Innovación y Universidades (MICINN). España; European Union (UE)
The self-aggregation of four amphiphilic cationic calix[4]arenes, CALIX, in aqueous solutions was investigated in this work. The nature of the polar group present at the upper rim as well as the length of the hydrophobic tails attached to the lower rim was varied. All the calixarenes present two critical aggregation concentrations, CAC1 and CAC2. For [CALIX] < CAC1 only micelles are present, within the range CAC1 < [CALIX] < CAC2 micelles as well as vesicles are observed, and for [CALIX] > CAC2 micelles and a wide distribution of vesicles were found. Cell viability experiments show that calixarene micelles and several of the calixarene vesicles investigated could be used as biocompatible nanocarriers. On this basis, the study of the interactions between the cationic calixarene aggregates (micelles and vesicles) and calf thymus DNA, ctDNA, were done and the results indicated that most of them strongly interact with the polynucleotide, inverting its charge. Micelles totally compact the ctDNA, while vesicles only partially cause conformational changes in the nucleic acid. Therefore, the CALIX micelles show potential as vectors in gene therapy. The encapsulation of the antineoplastic drug doxorubicin into the calixarene aggregates was also investigated. A high encapsulation efficiency was found for micelles and, specially, for vesicles. However, DOX-loaded calixarene vesicles present low stability at 37 °C, which is a serious restriction in their use as nanocarriers for this drug. The release of DOX from the calixarene micelles shows that they could lengthen the half-life of free doxorubicin in the body and, as a result, lower amounts of drug could be used in the cancer treatments diminishing the important side effects of DOX.
The Role of Pristine Carbon Nanotubes as Nanocarriers of 7,8-dihydroxyflavone
(Editions de Sante, 2024) Espíndola, Cecilia; Gómez Méndez, Ana; Moyá Morán, María Luisa; López Vallejo, Fabián; Bernal Pérez, Eva; Lebrón Romero, José Antonio; Martín, Victoria I.; Ostos Marcos, Francisco José; López-Cornejo, María del Pilar; López López, Manuel; Universidad de Sevilla. Departamento de Química Física; Universidad de Sevilla. Departamento de Bioquímica Médica y Biología Molecular e Inmunología; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER)
Flavonoids are secondary plant metabolites with a wide range of pharmacological effects. Among others, their antioxidant, anti-inflammatory and vasoprotective actions are noteworthy. However, the low bioavailability of flavonoids limits their direct clinical use. Nanoencapsulation of flavonoids is an effective tool to improve their biopharmaceutical characteristics, as the drug is protected inside the nanocarrier and specifically released into the therapeutic target. Bearing this in mind, pristine single- and multi-walled carbon nanotubes have been studied in this work as nanocarriers of 7,8-dihydroxyflavone, 7,8-DHF. Flavone encapsulation is optimized according to the influence of pH, the type of CNTs and their concentration on the association process. The equilibrium binding constants of 7,8-DHF to the CNTs are determined by measuring the variation observed in the flavone absorbance when the concentration of carbon nanotubes increases. CNTs/flavone complexes are characterized by particle size distribution and Z-potential measurements, as well as Transmission Electron Microscopy. The antioxidant capacity of free 7,8-DHF and the CNTs/7,8-DHF complexes are estimated by using the DPPH⋅, 2,2-diphenyl-1-picrylhydrazyl radical scavenging method. The results show that the encapsulation of the flavone in the CNTs results in a preservation of its pharmacological properties and provides stability to the encapsulated drug.
Synergistic Antifungal Activity against Candida Albicans between Voriconazole and Cyclosporine a Loaded in Polymeric Nanoparticles
(Elsevier, 2024) Martín, Victoria I.; Ruiz de la Haba, Rafael; López-Cornejo, María del Pilar; López López, M.; Lebrón Romero, José Antonio; Bernal Pérez, Eva; Baeza, N.; Ruiz, S.; Ostos Marcos, Francisco José; Merino Bohórquez, Vicente; Moyá Morán, María Luisa; Universidad de Sevilla. Departamento de Química Física; Universidad de Sevilla. Departamento de Microbiología y Parasitología; Universidad de Sevilla; Junta de Andalucía
The goal of this work is to investigate if the synergistic antifungal activity between cyclosporine A, CsA, and voriconazole, VRZ, increases when both drugs are encapsulated in a nanocarrier as compared when they are free. The preparation and characterization of blank and VRZ and CsA loaded polymeric based PLGA nanoparticles (PLGA, PLGA-PEG, and PLGA+PEG) was a necessary previous step. Using the more suitable NPs, those of PLGA, the antifungal susceptibility tests performed with VRZ-loaded PLGA NPs, show no significant increase of the antifungal activity in comparison to that of free VRZ. However, the synergistic behavior found for the (VRZ+CsA)-loaded PLGA NPs was fourfold stronger than that observed for the two free drugs together. On the other hand, the investigation into the suppression of C. albicans biofilm formation showed that blank PLGA NPs inhibit the biofilm formation at high NPs concentrations. However, a minor effect or even a slight biofilm increase formation was observed at low and moderate NPs concentrations. Therefore, the enhancement of the biofilm inhibition found for the three tested treatments (CsA alone, VRZ alone, and VRZ+CsA) when comparing free and encapsulated drugs, within the therapeutic window, can be attributed to the drug encapsulation approach. Indeed, polymeric PLGA NPs loaded with CsA, VRZ, or VRZ+CsA are more effective at inhibiting the C. albicans biofilm growth than their free counterparts.
Influence of the degree of oligomerization of surfactants on the DNA/surfactant interaction
(Elsevier, 2019-10) López, Alberto; López-Cornejo, María del Pilar; López-López, Manuel; Lebrón Romero, José Antonio; Ostos Marcos, Francisco José; Pérez Alfonso, David; Moyá Morán, María Luisa; Universidad de Sevilla. Departamento de Química Física; Junta de Andalucía; Universidad de Sevilla
The interaction between calf thymus DNA, ctDNA, and a series of oligomeric surfactants derived from N-benzyl-N,N-dimethyl-N-(1-dodecyl)ammonium chloride is investigated. The influence of the surfactants' degree of oligomerization (2, 3 and 4) on the ctDNA/surfactant interaction is studied, as well as the effect of the structure of the spacer group linking the individual surfactant fragments. In particular, the effect of the distance between the positive charges and the hydrophobic chains within the oligomers on these interactions was examined, by using the three positional isomers (i.e., ortho−, meta−, and para−) with the rigid xylidene moiety as spacer. Results show that the dimeric ("gemini") surfactants are much more efficient in the inversion of the nucleic acid charge than the single-chained (monomeric) surfactant. Whereas the ortho − isomer causes a partial condensation, the meta − and para − isomers can completely condense ctDNA. The meta − and para − isomers of the trimeric surfactants can also completely condense the polynucleotide. In contrast, the tetrameric surfactant investigated does not change the morphology of the nucleic acid from an elongated coil into a compacted form, in spite of effectively inverting the nucleic acid's charge in their complex. Accordingly, the capacity for ctDNA compaction of oligomeric surfactants is not simply correlated to their degree of oligomerization, but depends on a complex balance of the number and relative distance of cationic charges and/or hydrophobic tails in the surfactants for effectively interacting with the nucleic acid to form the appropriate complex. This information will help to design more effective cationic surfactants as non-viral vectors for gene therapy.
Electrochecmical Impedance Spectroscopy analysis of an adsorption process with a coupled preceding chemical step
(ELSEVIER, 2017-02-24) Prieto Dapena, Francisco; Álvarez Malmagro, Julia; Rueda Rueda, Manuela; Universidad de Sevilla. Departamento de Química Física; Universidad de Sevilla. FQM202: Electroquímica de Biointerfases
The impedance equations for the case of an adsorption process including a preceding homogeneous chemical step have been derived and compared to the corresponding equations for the case of a pure adsorption process. They involve behaviours with the frequency that differ from those of the impedance equations for a pure adsorption process. However, two limiting cases have been deduced in which the frequency behaviour of the impedance cannot be distinguished from the case of an adsorption process without any chemical step: the high frequency and the low frequency limits that hold for low and high values of the rate constant of the chemical reaction, respectively. The analysis as a function of the frequency is discussed on the basis of the complex frequency-normalized admittance plots and also based on the frequency dependence of the real and imaginary frequency-normalized admittance components. The influence of the values of the equilibrium and the rate constants of the chemical step is discussed for different adsorption kinetic regimes. In this way the conditions for detecting the chemical step are delimited and suitable analysis are proposed to obtain the adsorption parameters and the characteristic constants of the chemical step. The analysis is applied as an example, to the impedance of adenine adsorption on Au(111) electrodes from acidic solutions at a representative electrode potential. It is proved that the low frequency limit applies and the equilibrium constant for the chemical step is obtained.
Electrochecmical Impedance Spectroscopy Analysis of an Adsorption Process with a Coupled Preceding Chemical Step
(Elsevier, 2017) Prieto Dapena, Francisco; Rueda Rueda, Manuela; Álvarez Malmagro, Julia; Universidad de Sevilla. Departamento de Química Física; Ministerio de Economía y Competitividad (MINECO). España; Junta de Andalucía
The impedance equations for the case of an adsorption process including a preceding homogeneous chemical step have been derived and compared to the corresponding equations for the case of a pure adsorption process. They involve behaviours with the frequency that differ from those of the impedance equations for a pure adsorption process. However, two limiting cases have been deduced in which the frequency behaviour of the impedance cannot be distinguished from the case of an adsorption process without any chemical step: the high frequency and the low frequency limits that hold for low and high values of the rate constant of the chemical reaction, respectively. The analysis as a function of the frequency is discussed on the basis of the complex frequency-normalized admittance plots and also based on the frequency dependence of the real and imaginary frequency-normalized admittance components. The influence of the values of the equilibrium and the rate constants of the chemical step is discussed for different adsorption kinetic regimes. In this way the conditions for detecting the chemical step are delimited and suitable analysis are proposed to obtain the adsorption parameters and the characteristic constants of the chemical step. The analysis is applied as an example, to the impedance of adenine adsorption on Au(111) electrodes from acidic solutions at a representative electrode potential. It is proved that the low frequency limit applies and the equilibrium constant for the chemical step is obtained.
Importance of hydrophobic interactions in the single-chained cationic surfactant-DNA complexation
(Elsevier, 2018-07-01) López-López, Manuel; López-Cornejo, María del Pilar; Martín, Victoria I.; Ostos Marcos, Francisco José; Checa Rodríguez, Cintia; Prados Carvajal, Rosario; Lebrón Romero, José Antonio; Huertas Sánchez, Pablo; Moyá Morán, María Luisa; Universidad de Sevilla. Departamento de Química Física; Universidad de Sevilla. Departamento de Biología Celular; Universidad de Sevilla. Departamento de Genética; Junta de Andalucía; Universidad de Sevilla; Ministerio de Economía y Competitividad (MINECO). España
The goal of this work was to understand the key factors determining the DNA compacting capacity of single-chained cationic surfactants. Fluorescence, zeta potential, circular dichroism, gel electrophoresis and AFM measurements were carried out in order to study the condensation of the nucleic acid resulting from the formation of the surfactant-DNA complexes. The apparent equilibrium binding constant of the surfactants to the nucleic acid, Kapp, estimated from the experimental results obtained in the ethidium bromide competitive binding experiments, can be considered directly related to the ability of a given surfactant as a DNA compacting agent. The plot of ln(Kapp) vs. ln(cmc), cmc being the critical micelle concentration, for all the bromide and chloride surfactants studied, was found to be a reasonably good linear correlation. This result shows that hydrophobic interactions mainly control the surfactant DNA compaction efficiency
Mechanism of Dinitrogen Photoactivation by P2PPhFe Complexes: Thermodynamic and Kinetic Computational Studies
(American Chemical Society, 2024-10-23) Prada, C.; Dzib, E.; Núñez-Zarur, F.; Salvador, P.; Merino, G.; Jiménez Calzado, Carmen; Zapata-Rivera, J.; Universidad de Sevilla. Departamento de Química Física; European Union; Ministerio de Ciencia, Innovación y Universidades (MICINN). España
The P2PPhFe(N2)(H)2 catalyst showed a significant ammonia yield under light irradiation. However, under thermal conditions, the hydrogen evolution reaction (HER) is favored over the nitrogen reduction reaction (N2RR), making P2PPhFe(N2)(H)2 an ideal system for studying the competition between both reactions. In this study, we used a series of computational tools to elucidate the photochemical reaction mechanism for the N2RR and thermal pathways leading to the HER with this catalyst. We calculated the energy profile for each transformation and estimated the rate constants for each step. Our results, which are consistent with experimental observations, indicate that photoinduced H2 elimination from P2PPhFe(N2)(H)2 promotes the formation of P2PPhFe(N2)2, which is on-path for N2RR. However, this elimination process is kinetically hindered due to high-energy barriers. Furthermore, our calculations reveal enhanced dinitrogen activation upon the conversion of P2PPhFe(N2)(H)2 to P2PPhFe(N2)2.

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