Quantum chemistry of the excited state: recent trends in methods developments and applications

Advances (2016–2017) in Quantum Chemistry of the Excited State (QCEX) are presented in this book chapter focusing firstly on developments of methodology and excited-state reaction-path computational strategies and secondly on the applications of QCEX to study light–matter interaction in distinct fields of biology, (nano)-technology, medicine and the environment. We highlight in this contribution developments of static and dynamic electron-correlation methods and methodological approaches to determine dynamical properties, recent examples of the roles of conical intersections, novel DNA spectroscopy and photochemistry findings, photo-sensitisation mechanisms in biological structures and the current knowledge on chemi-excitation mechanisms that give rise to light emission (in the chemiluminescence and bioluminescence phenomena)

Photochemistry of oxidized Hg(I) and Hg(II) species suggests missing mercury oxidation in the troposphere

Mercury (Hg), a global contaminant, is emitted mainly in its elemental form Hg0 to the atmosphere where it is oxidized to reactive HgII compounds, which efficiently deposit to surface ecosystems. Therefore, the chemical cycling between the elemental and oxidized Hg forms in the atmosphere determines the scale and geographical pattern of global Hg deposition. Recent advances in the photochemistry of gas-phase oxidized HgI and HgII species postulate their photodissociation back to Hg0 as a crucial step in the atmospheric Hg redox cycle. However, the significance of these photodissociation mechanisms on atmospheric Hg chemistry, lifetime, and surface deposition remains uncertain. Here we implement a comprehensive and quantitative mechanism of the photochemical and thermal atmospheric reactions between Hg0, HgI, and HgII species in a global model and evaluate the results against atmospheric Hg observations. We find that the photochemistry of HgI and HgII leads to insufficient Hg oxidation globally. The combined efficient photoreduction of HgI and HgII to Hg0 competes with thermal oxidation of Hg0, resulting in a large model overestimation of 99% of measured Hg0 and underestimation of 51% of oxidized Hg and ∼66% of HgII wet deposition. This in turn leads to a significant increase in the calculated global atmospheric Hg lifetime of 20 mo, which is unrealistically longer than the 3–6-mo range based on observed atmospheric Hg variability. These results show that the HgI and HgII photoreduction processes largely offset the efficiency of bromine-initiated Hg0 oxidation and reveal missing Hg oxidation processes in the troposphere

Genomic transformation and social organization during the Copper Age-Bronze Age transition in southern Iberia

The emerging Bronze Age (BA) of southeastern Iberia saw marked social changes. Late Copper Age (CA) settlements were abandoned in favor of hilltop sites, and collective graves were largely replaced by single or double burials with often distinctive grave goods indirectly reflecting a hierarchical social organization, as exemplified by the BA El Argar group. We explored this transition from a genomic viewpoint by tripling the amount of data available for this period. Concomitant with the rise of El Argar starting ~2200 cal BCE, we observe a complete turnover of Y-chromosome lineages along with the arrival of steppe-related ancestry. This pattern is consistent with a founder effect in male lineages, supported by our finding that males shared more relatives at sites than females. However, simple two-source models do not find support in some El Argar groups, suggesting additional genetic contributions from the Mediterranean that could predate the BA

The OpenMolcas Web: A Community-Driven Approach to Advancing Computational Chemistry

The developments of the open-source OpenMolcas chemistry software environment since spring 2020 are described, with a focus on novel functionalities accessible in the stable branch of the package or via interfaces with other packages. These developments span a wide range of topics in computational chemistry and are presented in thematic sections: electronic structure theory, electronic spectroscopy simulations, analytic gradients and molecular structure optimizations, ab initio molecular dynamics, and other new features. This report offers an overview of the chemical phenomena and processes OpenMolcas can address, while showing that OpenMolcas is an attractive platform for state-of-the-art atomistic computer simulations

On the chemiluminescence emission of luminol: Protic and aprotic solvents and encapsulation to improve the properties in aqueous solution

Luminol is a popular molecule that is currently gaining further interest due to its potential role for non-invasive cancer treatments. Design of more efficient derivatives in this context would benefit from a clear knowledge on the origin of the distinct intensity and spectroscopic properties in protic and aprotic solvents observed experimentally, which are still not rationalized. By efficiently combining molecular dynamics, quantum methodologies based on density functional theory and multiconfigurational quantum chemistry and hybrid approaches, and developing herein a computational approach for accurately determining "molar negative extinction (or gain) coefficients of emission", we firstly demonstrate that the amino and imino forms of the 3-Aminophthalate dianion are responsible for the chemiluminescence in protic and aprotic medium, respectively. Secondly, we show that the coupling between the adjacent amino and carboxylate groups of luminol existing in aprotic solvents must be kept in aqueous solution to increase the chemiexcitation and emission intensity. Thirdly, modifications of luminol are proposed and simulated showing improved performances as compared to the parent molecule (stronger emission electronic transition and longer emission wavelengths) under the physiological conditions of relevance in biological and medical applications.This work was supported by the Spanish “Ministerio de Ciencia e Innovación (MICINN)” (Project Ref. CTQ2017-87054-C2-2-P), a 2019 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation. The Foundation takes no responsibility for the opinions, statements, and contents of this project, which are entirely the responsibility of its authors. A. B.-S. thanks the Andalusian local government for project RNM1897. D. R.-S. is grateful to the Spanish MICINN for the “Ramón y Cajal” grant (Ref. RYC-2015-19234). A. G. is thankful to the Universitat de València for his “Atracció de Talent 2018” postdoctoral grant and also to the Spanish MICINN for the “Juan de la Cierva” grant (Ref. IJC2018-035123-I)

Ab initio quantum-chemical computations of the absorption cross sections of HgX2 and HgXY (X, y = Cl, Br, and I): Molecules of interest in the Earth's atmosphere

13 pags., 4 figs., 2 tabs.The electronic-structure properties of the low-lying electronic states and the absorption cross sections (σ(E)) of mercury halides HgCl, HgBr, HgI, HgBrCl, HgClI, and HgBrI have been determined within the UV-vis spectrum range (170 nm ≤ λ ≤ 600 nm) by means of the DKH3-MS-CASPT2/SO-RASSI quantum-chemical methodology (with the ANO-RCC basis set) and a semi-classical computational strategy based on nuclear sampling for simulating the band shapes. Computed band energies show a good agreement with the available experimental data for HgX with errors around 0.1-0.2 eV; theoretical and σ(E) are within the same order of magnitude. For the mixed HgXY compounds, the present computed data allow us to interpret previously proposed absorption bands estimated from the spectra of the parent molecules HgX and HgY, measured in methanol solution. The analyses performed on the excited-state electronic structure and its changes around the Franck-Condon region provide a rationale on the singlet-triplet mixing of the absorption bands and the heavy-atom effect of the Hg compounds. Furthermore, the present benchmark of HgX and HgXY absorption σ values together with the previous benchmark of the electronic-structure properties of HgBr [see S. P. Sitkiewicz, et al., J. Chem. Phys., 2016, 145, 244304] has been helpful to set up a methodological and computational protocol which shall be used for predicting the atmospheric absorption and photolysis properties of several Hg compounds present in the atmospheric cycle of Hg.S. P. S. acknowledges the Basque Government for funding through a predoctoral fellowship (PRE 2017 1 0403). D. R.-S. is thankful to the Spanish MINECO/FEDER for financial support through project CTQ2017-87054-C2-2-P and the Ramon y Cajal fellowship with Ref. RYC-2015-19234

Photochromic System among Boron Hydrides: The Hawthorne Rearrangement

Photoswitchable molecules have attracted wide interest for many applications in chemistry, physics, and materials science. In this work, we revisit the reversible photochemical and thermal rearrangements of the two BH isomers reported by Hawthorne and Pilling in 1966, whose mechanism had not been understood so far. We investigate the rearrangements by means of a joint experimental and computational study with the outcome that BH represents the first boron-based photochromic system ever reported. Both photochemical and thermal isomerizations occur through the same intermediate and involve a diamond-square-diamond (DSD) mechanism. Given the absence within boron chemistry of named chemical reactions as opposed to organic chemistry, we propose to label the BH photo- A nd thermal isomerization processes as the Hawthorne rearrangement