Alcohol Self-Aggregation: the Preferred Configurations of the Ethanol Trimer.

An atomic-level knowledge of the aggregation of archetypal molecular systems is essential to accurately model supramolecular structures and the transition from gas to liquid phase. The structures and forces involved in ethanol aggregation have been investigated using microwave spectroscopy and extensive quantum chemical calculations. Four isomers of the ethanol trimer have been observed and identified based on comparisons between experimental and predicted spectroscopic parameters, and considering collisional relaxation in the supersonic expansion.

[Intentional search and reclassification of maternal deaths: quality information and its analysis to reduce maternal mortalityBusca intencional e reclassificação de mortes maternas: informação de qualidade e sua análise para reduzir a mortalidade materna].

Objective: To describe the methodology of the intentional search and reclassification of maternal deaths (BIRMM, acronym in Spanish), which allows the identification and correction of misclassification and underreporting of maternal deaths.

Methods: The BIRMM methodology, initially developed in Mexico in 2003 and disseminated in other Latin American countries since 2012, was used. BIRMM consists of four key components: i) reclassification of confirmed maternal deaths; ii) identification and investigation of suspected cases of maternal death; iii) cross-referencing with other information sources; and iv) publication of results and statistical analysis.

Hydride and halide abstraction reactions behind the enhanced basicity of Be and Mg clusters with nitrogen bases.

In this study, we investigate the protonation effects on the structure, relative stability and basicity of complexes formed by the interaction of monomers and dimers of BeX and MgX (X = H, F) with NH, CHNH, HCN, and NCH bases. Calculations were performed using the M06-2X/aug-cc-pVTZ formalism, along with QTAIM, ELF and NCI methods for electron density analysis and MBIE and LMO-EDA energy decomposition analyses for interaction enthalpies. The protonation of the MH- and MH-Base complexes occurs at the negatively charged hydrogen atoms of the MH and MH moieties through typical hydride abstraction reactions, while protonation at the N atom of the base is systematically less exothermic.

Characterization of 1,1- and 1,2-ethenedithiol, elusive compounds of potential astrochemical interest.

Context: 1,1- and 1,2-ethenedithiol are elusive systems that could potentially exist in interstellar space, similar to analogous diols. In this paper, we investigate the structure, stability, and bonding characteristics of these compounds as well as the ions produced by protonation, deprotonation, or simple ionization processes. 1,2-ethenedithiol has two isomers, Z and E, with the most stable conformer being syn-anti for the Z isomer and anti-anti for the E isomer.

Discovering trends in the Lewis acidity of beryllium and magnesium hydrides and fluorides with increasing clusters size.

We have reported in the last years the strong effect that Be- and Mg-containing Lewis acids have on the intrinsic properties of typical bases, which become acids upon complexation. In an effort to investigate these changes when the Be and Mg derivatives form clusters of increasing size, we have examined the behavior of the (MX) (M = Be, Mg; X = H, F; n = 1, 2, 3) clusters when they interact with ammonia, methanimine, hydrogen cyanide and pyridine, and with their corresponding deprotonated forms. The complexes obtained at the M06-2X/aug-cc-pVTZ level were analyzed using the MBIE energy decomposition formalism, in parallel with QTAIM, ELF, NCIPLOT and AdNDP analyses of their electron density.

A Holistic View of the Interactions between Electron-Deficient Systems: Clustering of Beryllium and Magnesium Hydrides and Halides.

In the search for common bonding patterns in pure and mixed clusters of beryllium and magnesium derivatives, the most stable dimers and trimers involving BeX and MgX (X = H, F, Cl) have been studied in the gas phase using B3LYP and M06-2X DFT methods and the G4 ab initio composite procedure. To obtain some insight into their structure, stability, and bonding characteristics, we have used two different energy decomposition formalisms, namely MBIE and LMO-EDA, in parallel with the analysis of the electron density with the help of QTAIM, ELF, NCIPLOT, and AdNDP approaches. Some interesting differences are already observed in the dimers, where the stability sequence observed for the hydrides differs entirely from that of the fluorides and chlorides.

Ionization, intrinsic basicity, and intrinsic acidity of unsaturated diols of astrochemical interest: 1,1- and 1,2-ethenediol: A theoretical survey.

The structure, stability, and bonding characteristics of 1,1- and 1,2-ethenediol, their radical cations, and their protonated and deprotonated species were investigated using high-level ab initio G4 calculations. The electron density of all the neutral and charged systems investigated was analyzed using the QTAIM, ELF, and NBO approaches. The vertical ionization potential (IP) of the five stable tautomers of 1,2-ethenediol and the two stable tautomers of 1,1-ethenediol go from 11.

Dispersion, Rehybridization, and Pentacoordination: Keys to Understand Clustering of Boron and Aluminum Hydrides and Halides.

The structure, stability, and bonding characteristics of dimers and trimers involving BX and AlX (X = H, F, Cl) in the gas phase, many of them explored for the first time, were investigated using different DFT (B3LYP, B3LYP/D3BJ, and M06-2X) and ab initio (MP2 and G4) methods together with different energy decomposition formalisms, namely, many-body interaction-energy and localized molecular orbital energy decomposition analysis. The electron density of the clusters investigated was analyzed with QTAIM, electron localization function, NCIPLOT, and adaptive natural density partitioning approaches. Our results for triel hydride dimers and AlX (X = F, Cl) clusters are in good agreement with previous studies in the literature, but in contrast with the general accepted idea that BF and BCl do not exist, we have found that they are predicted to be weakly bound systems if dispersion interactions are conveniently accounted for in the theoretical schemes used.

20 Years of ICF-International Classification of Functioning, Disability and Health: Uses and Applications around the World.

The International Classification of Functioning Disability and Health (ICF) was approved in 2001 and, since then, several studies reported the increased interest about its use in different sectors. A recent overview that summarizes its applications is lacking. This study aims to provide an updated overview about 20 years of ICF application through an international online questionnaire, developed by the byline authors, and sent to each World Health Organization Collaborating Centers of the Family of International Classifications (WHO-FIC CCs).

Open questions on toxic heavy metals Cd, Hg and Pb binding small components of DNA and nucleobases. Are there any predictable trends?

In this perspective article, we provide a bibliographic compilation of experimental and theoretical work on Cd, Hg, and Pb, and analyze in detail the bonding of M and CHM (M = Zn, Cd, Hg, Pb) with urea and thiourea as suitable models for larger biochemical bases. Through the use of DFT calculations, we have found that although in principle binding energies decrease according to ionic size (Zn > Cd > Pb), Hg largely breaks the trend. Through the use of EDA (Energy Decomposition Analysis) it is possible to explain this behavior, which is essentially due to the strong contribution of polarization to the binding.

Disrupting bonding in azoles through beryllium bonds: Unexpected coordination patterns and acidity enhancement.

Although triazoles and tetrazole are amphoteric and may behave as weak acids, the latter property can be hugely enhanced by beryllium bonds. To explain this phenomenon, the structure and bonding characteristics of the complexes between triazoles and tetrazoles with one and two molecules of BeF have been investigated through the use of high-level G4 ab initio calculations. The formation of the complexes between the N basic sites of the azoles and the Be center of the BeF molecule and the (BeF) dimer leads to a significant bonding perturbation of both interacting subunits.

Dismantlement of ammonia upon interaction with Be (n ≤ 10) clusters.

The interaction of ammonia with Be (n < 1-10) clusters has been investigated by density functional theory and ab initio calculations. The main conclusion is that, regardless of the size of the Be cluster, neither the structure of ammonia nor that of the Be clusters are preserved due to a systematic dissociation of its NH bonds and a spontaneous H-shift toward the available Be atoms. This H migration not only leads to rather stable BeH bonds, but dramatically enhances the strength of the BeN bonds as well.

Enthalpies of Adduct Formation between Boron Trifluoride and Selected Organic Bases in Solution: Toward an Accurate Theoretical Entry to Lewis Basicity.

The Lewis basicity of selected organic bases, modeled by the enthalpies of adduct formation between gaseous BF and bases in dichloromethane (DCM) solution, is critically examined. Although experimental enthalpies for a large number of molecules have been reported in the literature, it may be desirable to estimate missing or uncertain data for important Lewis bases. We decided to use high-level ab initio procedures, combined with a polarized continuum solvation model, in which the solvated species were the clusters formed by specific hydrogen bonding of DCM with the Lewis base and the Lewis base/BF adduct.

Perturbating Intramolecular Hydrogen Bonds through Substituent Effects or Non-Covalent Interactions.

An analysis of the effects induced by F, Cl, and Br-substituents at the α-position of both, the hydroxyl or the amino group for a series of amino-alcohols, HOCH(CH)CHNH ( = 0-5) on the strength and characteristics of their OH···N or NH···O intramolecular hydrogen bonds (IMHBs) was carried out through the use of high-level G4 ab initio calculations. For the parent unsubstituted amino-alcohols, it is found that the strength of the OH···N IMHB goes through a maximum for = 2, as revealed by the use of appropriate isodesmic reactions, natural bond orbital (NBO) analysis and atoms in molecules (AIM), and non-covalent interaction (NCI) procedures. The corresponding infrared (IR) spectra also reflect the same trends.

Large Stabilization Effects by Intramolecular Beryllium Bonds in -Benzene Derivatives.

Intramolecular interactions are shown to be key for favoring a given structure in systems with a variety of conformers. In -substituted benzene derivatives including a beryllium moiety, beryllium bonds provide very large stabilizations with respect to non-bound conformers and enthalpy differences above one hundred kJ·mol are found in the most favorable cases, especially if the newly formed rings are five or six-membered heterocycles. These values are in general significantly larger than hydrogen bonds in 1,2-dihidroxybenzene.

Spontaneous bond dissociation cascades induced by Be clusters (n = 2,4).

High-level single and multireference ab initio calculations show that the Be cluster behaves as a very efficient Lewis acid when interacting with conventional Lewis bases such as ammonia, water or hydrogen fluoride, to the point that the corresponding acid-base interaction triggers a sequential dissociation of all the bonds of the Lewis base. Notably, this behavior is already found for the simplest beryllium cluster, the Be dimer. However, whereas for Be the first dissociation process involves a low activation barrier which is above the reactants, for Be all the bond dissociation processes involve barriers below the entrance channel leading to a cascade of successive exothermic processes, which end up spontaneously in a global minimum in which the bonding patterns of both the base and the Lewis acid are completely destroyed.

The Importance of Strain (Preorganization) in Beryllium Bonds.

In order to explore the angular strain role on the ability of Be to form strong beryllium bonds, a theoretical study of the complexes of four beryllium derivatives of -carboranes with eight molecules (CO, N, NCH, CNH, OH, SH, NH, and PH) acting as Lewis bases has been carried out at the G4 computational level. The results for these complexes, which contain besides Be other electron-deficient elements, such as B, have been compared with the analogous ones formed by three beryllium salts (BeCl, COBe and SOBe) with the same set of Lewis bases. The results show the presence of large and positive values of the electrostatic potential associated to the beryllium atoms in the isolated four beryllium derivatives of -carboranes, evidencing an intrinsically strong acidic nature.

Looking for the Azeotrope: A Computational Study of (Ethanol)-Water, (Methanol)-Water, (Ethanol), and (Methanol) Heptamers.

Considering that a molecular-level understanding of the azeotropic ethanol-water system can contribute to the search of new methodologies and/or modifications of industrial separation methods, this study tries to provide some clues to understand why azeotropes should be expected for ethanol, but not for methanol. Our exploration of the potential energy surface of (ethanol)-water heteroheptamers, carried out at the B3LYP-D3/6-311++G(d,p) level, shows these heteroclusters to exhibit a cyclic structure where the cooperativity effects between the OH···O HBs is a fundamental ingredient. An analysis of this cooperativity clearly indicates that ethanol-water systems will exhibit a similarly high stability as the heterocluster size approaches the azeotrope.

From Very Strong to Inexistent Be-Be Bonds in the Interactions of Be with π-Systems.

Isolated Be is a typical example of a weakly bound system, but interaction with other systems may give rise to surprising bonding features. The interactions between Be and a set of selected neutral C H (n=2-8) π-systems have been analyzed through the use of G4 and G4MP2 ab initio methods, along with multireference CASPT2//CASPT2 calculations. Our results systematically show that the C H -Be -C H clusters formed are always very stable.

Mutual Influence of Pnicogen Bonds and Beryllium Bonds: Energies and Structures in the Spotlight.

Pnicogen bonds, which are weak noncovalent interactions (NCIs), can be significantly modified by the presence of beryllium bonds, one of the strongest NCIs known. We demonstrate the importance of this influence by studying ternary complexes in which both NCIs are present, that is, the ternary complexes formed by a nitrogen base (NH, NHCH, and NCH), a phosphine (fluorophosphane, PHF) and a beryllium derivative (BeH, BeF, BeCl, BeCO, and BeSO). Energies, structures, and nature of the chemical bonding in these complexes are studied by means of computational methods.

Are Anions of Cyclobutane Beryllium Derivatives Stabilized through Four-Center One-Electron Bonds?

High-level G4 ab initio calculations allowed us to show that CH(BeX) (X = H, Cl) derivatives behave as rather efficient electron capturers due to their ability to trap the extra electron through the formation of a four-membered beryllium ring. This finding is in agreement with previous work showing the ability of highly electron-deficient atoms, such as beryllium, to lead to multicenter one-electron bonds. In our particular case, the formation of the four-center bond is characterized, in very good harmony, by different topological methods such as quantum theory of atoms in molecules (QTAIM), the electron localization function (ELF), and the noncovalent interactions (NCI) approach and is accompanied by large electron affinity values, around 300 kJ·mol, in the gas phase.

Relativistic Effects on NMR Parameters of Halogen-Bonded Complexes.

Relativistic effects are found to be important for the estimation of NMR parameters in halogen-bonded complexes, mainly when they involve the heavier elements, iodine and astatine. A detailed study of 60 binary complexes formed between dihalogen molecules (XY with X, Y = F, Cl, Br, I and At) and four Lewis bases (NH, HO, PH and SH) was carried out at the MP2/aug-cc-pVTZ/aug-cc-pVTZ-PP computational level to show the extent of these effects. The NMR parameters (shielding and nuclear quadrupolar coupling constants) were computed using the relativistic Hamiltonian ZORA and compared to the values obtained with a non-relativistic Hamiltonian.

On the Lewis Basicity of Phosphoramides: A Critical Examination of Their Donor Number through Comparison of Enthalpies of Adduct Formation with SbCl and BF.

The Lewis basicity of a series of phosphoryl compounds was examined using DFT and ab initio methods, including solvation effects. The enthalpies of adduct formation with two archetypal Lewis acids, antimony pentachloride and boron trifluoride, used to define the donor number DN and the BF affinity (BF A) respectively, were examined. The BF adducts allow the use of the high-accuracy G4 approach, whereas for SbCl adducts, three different DFT formalisms, including empirical dispersion corrections, were used because the G4 formalism is not available for third-row elements.

Weak Interactions Get Strong: Synergy between Tetrel and Alkaline-Earth Bonds.

Weak and strong noncovalent interactions such as tetrel bonds and alkaline-earth bonds, respectively, cooperate and get reinforced when acting together in ternary complexes of general formula RN··· SiHF···MY, where MY is a Be or Mg derivative and RN is a N-containing Lewis base with different hybridization patterns. Cooperativity has been studied in the optimized MP2/aug'-cc-pVTZ ternary complexes by looking at changes on geometries, binding energies, Si NMR chemical shifts, and topological features according to the atoms in molecules theoretical framework. Our study shows that cooperativity in terms of energy is in general significant: more than 40 kJ/mol, and up to 83.