Search results for "Fisicoquímica"
showing 10 items of 18 documents
Halide-Mediated Modification of Magnetism and Electronic Structure of α-Co(II) Hydroxides: Synthesis, Characterization, and DFT+U Simulations.
2019
The present study introduces a comprehensive exploration in terms of physicochemical characterization and calculations based on density functional theory with Hubbard's correction (DFT+U) of the whole family of α-Co(II) hydroxyhalide (F, Cl, Br, I). These samples were synthesized at room temperature by employing a one-pot approach based on the epoxide route. A thorough characterization (powder X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis/mass spectroscopy, and magnetic and conductivity measurements) corroborated by simulation is presented that analyzes the structural, magnetic, and electronic aspects. Beyond the inherent tendency of intercalated anions to …
Vibronic Model for Intercommunication of Localized Spins via Itinerant Electron
2019
In this article, we propose a vibronic pseudo Jahn–Teller model for partially delocalized mixed-valence molecules aimed to describe the magnetic coupling between the localized spins mediated by the delocalized electron. The simplest partially delocalized system that retains the main studied features is assumed to consist of a one-electron mixed-valence dimer, which is connected to the two terminal magnetic ions. The model involves the following key interactions: electron transfer in the spin-delocalized subsystem of a mixed-valence molecule, which is mimicked by a dimeric unit, coupling of the itinerant electrons with the molecular vibrations, and isotropic magnetic exchange between the loc…
Plant-wide modelling in wastewater treatment: showcasing experiences using the Biological Nutrient Removal Model
2020
Abstract Plant-wide modelling can be considered an appropriate approach to represent the current complexity in water resource recovery facilities, reproducing all known phenomena in the different process units. Nonetheless, novel processes and new treatment schemes are still being developed and need to be fully incorporated in these models. This work presents a short chronological overview of some of the most relevant plant-wide models for wastewater treatment, as well as the authors' experience in plant-wide modelling using the general model BNRM (Biological Nutrient Removal Model), illustrating the key role of general models (also known as supermodels) in the field of wastewater treatment…
Linking Electrostatic Effects and Protein Motions in Enzymatic Catalysis. A Theoretical Analysis of Catechol O-Methyltransferase
2014
The role of protein motions in enzymatic catalysis is the subject of a hot scientific debate. We here propose the use of an explicit solvent coordinate to analyze the impact of environmental motions during the reaction process. The example analyzed here is the reaction catalyzed by catechol O-methyltransferase, a methyl transfer reaction from S-adenosylmethionine (SAM) to the nucleophilic oxygen atom of catecholate. This reaction proceeds from a charged reactant to a neutral product, and then a large electrostatic coupling with the environment could be expected. By means of a two-dimensional free energy surface, we show that a large fraction of the environmental motions needed to attain the…
Molecular excited state calculations with adaptive wavefunctions on a quantum eigensolver emulation: reducing circuit depth and separating spin states
2021
Ab initio electronic excited state calculations are necessary for the quantitative study of photochemical reactions, but their accurate computation on classical computers is plagued by prohibitive resource scaling. The Variational Quantum Deflation (VQD) is an extension of the quantum-classical Variational Quantum Eigensolver (VQE) algorithm for calculating electronic excited state energies, and has the potential to address some of these scaling challenges using quantum computers. However, quantum computers available in the near term can only support a limited number of quantum circuit operations, so reducing the quantum computational cost in VQD methods is critical to their realisation. In…
Combined Theoretical and Experimental Study of the Photophysics of Asulam
2013
The photophysics of the neutral molecular form of the herbicide asulam has been described in a joint experimental and theoretical, at the CASPT2 level, study. The unique π → π* aromatic electronic transition (f, ca. 0.5) shows a weak red-shift as the polarity of the solvent is increased, whereas the fluorescence band undergoes larger red-shifts. Solvatochromic data point to higher dipole moment in the excited state than in the ground state (μ(g)μ(e)). The observed increase in pKa in the excited state (pKa* - pKa, ca. 3) is consistent with the results of the Kamlet-Abboud-Taft and Catalán et al. multiparametric approaches. Fluorescence quantum yield varies with the solvent, higher in water (…
How important is roaming in the photodegradation of nitrobenzene?
2020
At low excitation energies nitrobenzene photoreleases NO with low translational and rotational energy, while at higher excitation energies NO is photoreleased with both low and high translational and rotational energy. The fast products are formed through a singlet-triplet crossing (STC) region featuring an oxaziridine ring, while a ground state roaming mechanism was suggested to produce the slow molecules. Computing translational and rotational energies performing CASSCF classical dynamics, we here prove how the same oxaziridine STC can account for both fast and slow photoproducts, depending on the region of the seam through which the ground state is populated. A roaming-type STC/CI has al…
Sensing of the Molecular Spin in Spin-Crossover Nanoparticles with Micromechanical Resonators
2019
In the past years, the use of highly sensitive silicon microelectromechanical cantilevers has been proposed as a tool to characterize the spin-crossover phenomenon by employing fast optical readout of the motion. In this work, Fe II -based spin-crossover nanoparticles of the well-known [Fe(Htrz) 2 (trz)](BF 4 ) complex wrapped with thin silica shells of different sizes will be studied by means of silicon microresonators. The silica shell will enhance its chemical stability, whereas the low thickness will allow a proper mechanical coupling between the cantilever and the spin-crossover core. To maximize the sensing of the spin-crossover phenomena, different cantilever geometries and flexural…
Incorporation of potassium halides in the mechanosynthesis of inorganic perovskites: feasibility and limitations of ion-replacement and trap passivat…
2018
Potassium halides (KX; X = I, Br, or Cl) were incorporated as partial replacements of CsBr in the mechanosynthesis of CsPbBr3. This led to partial substitution of both monovalent ions forming mixed Cs1−xKxPbBr3−yXy perovskites. Longer photoluminescence lifetimes were also observed, possibly linked to the formation of a non-perovskite KPb2X5 passivating layer.
Photoinduced Formation Mechanism of the Thymine−Thymine (6−4) Adduct
2013
The photoinduced mechanism leading to the formation of the thymine-thymine (6-4) photolesion has been studied by using the CASPT2//CASSCF approach over a dinucleotide model in vacuo. Following light absorption, localization of the excitation on a single thymine leads to fast singlet-triplet crossing that populates the triplet (3)(nπ*) state of thymine. This state, displaying an elongated C(4)═O bond, triggers (6-4) dimer formation by reaction with the C(5)═C(6) double bond of the adjacent thymine, followed by a second intersystem crossing, which acts as a gate between the excited state of the reactant and the ground state of the photoproduct. The requirement of localized excitation on just …