Noble gas (or aerogen) bond (NgB) can be outlined as the attractive interaction between an electron-rich atom or group of atoms and any element of Group-18 acting as an electron acceptor. The IUPAC ...already recommended systematic nomenclature for the interactions of groups 17 and 16 (halogen and chalcogen bonds, respectively). Investigations dealing with noncovalent interactions involving main group elements (acting as Lewis acids) have rapidly grown in recent years. They are becoming acting players in essential fields such as crystal engineering, supramolecular chemistry, and catalysis. For obvious reasons, the works devoted to the study of noncovalent Ng-bonding interactions are significantly less abundant than halogen, chalcogen, pnictogen, and tetrel bonding. Nevertheless, in this short review, relevant theoretical and experimental investigations on noncovalent interactions involving Xenon are emphasized. Several theoretical works have described the physical nature of NgB and their interplay with other noncovalent interactions, which are discussed herein. Moreover, exploring the Cambridge Structural Database (CSD) and Inorganic Crystal Structure Database (ICSD), it is demonstrated that NgB interactions are crucial in governing the X-ray packing of xenon derivatives. Concretely, special attention is given to xenon fluorides and xenon oxides, since they exhibit a strong tendency to establish NgBs.
In this review, several examples of the application of pnictogen (Pn) (group 15) and chalcogen (Ch) bonding (group 16) interactions in organocatalytic processes are gathered, backed up with Molecular ...Electrostatic Potential surfaces of model systems. Despite the fact that the use of catalysts based on pnictogen and chalcogen bonding interactions is taking its first steps, it should be considered and used by the scientific community as a novel, promising tool in the field of organocatalysis.
The σ- and π-hole interactions are used to define attractive forces involving elements of groups 12–18 of the periodic table acting as Lewis acids and any electron rich site (Lewis base, anion, and ...π-system). When the electrophilic atom belongs to group 14, the resulting interaction is termed a tetrel bond. In the first part of this feature paper, tetrel bonds formed in crystalline solids involving sp3-hybridized carbon atom are described and discussed by using selected structures retrieved from the Cambridge Structural Database. The interaction is characterized by a strong directionality (close to linearity) due to the small size of the σ-hole in the C-atom opposite the covalently bonded electron withdrawing group. The second part describes the utilization of two allotropic forms of carbon (C60 and carbon nanotubes) as supramolecular catalysts based on anion–π interactions (π-hole tetrel bonding). This part emphasizes that the π-hole, which is considerably more accessible by nucleophiles than the σ-hole, can be conveniently used in supramolecular catalysis.
The w(hole) picture: A tetrel bond is a directional noncovalent interaction between a covalently bonded atom of Group IV and a negative site, for example, the lone pair of a Lewis base or an anion. ...It involves a region of positive electrostatic potential (σ hole), and energetically, they are comparable to hydrogen bonds and other σ‐hole‐based interactions.
•Some regions of the world have higher infection rates from SARS-CoV-2 and with a higher mortality.•These regions have high concentration of air pollutants, especially PM 2.5 and NO2.•Chronic ...exposure, especially to PM 2.5, correlates with alveolar ACE-2 receptor overexpression leading to more severe COVID-19 infection.•High ambient NO2 may be responsible for the extensive lung injury in COVID-19 pneumonia associated with a worse outcome.
In areas of SARS-CoV-2 outbreak worldwide mean air pollutants concentrations vastly exceed the maximum limits. Chronic exposure to air pollutants have been associated with lung ACE-2 over-expression which is known to be the main receptor for SARS-CoV-2. The aim of this study was to analyse the relationship between air pollutants concentration (PM 2.5 and NO2) and COVID-19 outbreak, in terms of transmission, number of patients, severity of presentation and number of deaths.
COVID-19 cases, ICU admissions and mortality rate were correlated with severity of air pollution in the Italian regions.
The highest number of COVID-19 cases were recorded in the most polluted regions with patients presenting with more severe forms of the disease requiring ICU admission. In these regions, mortality was two-fold higher than the other regions.
From the data available we propose a “double-hit hypothesis”: chronic exposure to PM 2.5 causes alveolar ACE-2 receptor overexpression. This may increase viral load in patients exposed to pollutants in turn depleting ACE-2 receptors and impairing host defences. High atmospheric NO2 may provide a second hit causing a severe form of SARS-CoV-2 in ACE-2 depleted lungs resulting in a worse outcome.
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In this review, we provide a consistent description of noncovalent interactions, covering most groups of the Periodic Table. Different types of bonds are discussed using their trivial names. ...Moreover, the new name “Spodium bonds” is proposed for group 12 since noncovalent interactions involving this group of elements as electron acceptors have not yet been named. Excluding hydrogen bonds, the following noncovalent interactions will be discussed: alkali, alkaline earth, regium, spodium, triel, tetrel, pnictogen, chalcogen, halogen, and aerogen, which almost covers the Periodic Table entirely. Other interactions, such as orthogonal interactions and π-π stacking, will also be considered. Research and applications of σ-hole and π-hole interactions involving the p-block element is growing exponentially. The important applications include supramolecular chemistry, crystal engineering, catalysis, enzymatic chemistry molecular machines, membrane ion transport, etc. Despite the fact that this review is not intended to be comprehensive, a number of representative works for each type of interaction is provided. The possibility of modeling the dissociation energies of the complexes using different models (HSAB, ECW, Alkorta-Legon) was analyzed. Finally, the extension of Cahn-Ingold-Prelog priority rules to noncovalent is proposed.
Elements from groups 14–18 and periods 3–6 commonly behave as Lewis acids, which are involved in directional noncovalent interactions (NCI) with electron-rich species (lone pair donors), π systems ...(aromatic rings, triple and double bonds) as well as nonnucleophilic anions (BF4−, PF6−, ClO4−, etc.). Moreover, elements of groups 15 to 17 are also able to act as Lewis bases (from one to three available lone pairs, respectively), thus presenting a dual character. These emerging NCIs where the main group element behaves as Lewis base, belong to the σ–hole family of interactions. Particularly (i) tetrel bonding for elements belonging to group 14, (ii) pnictogen bonding for group 15, (iii) chalcogen bonding for group 16, (iv) halogen bonding for group 17, and (v) noble gas bondings for group 18. In general, σ–hole interactions exhibit different features when moving along the same group (offering larger and more positive σ–holes) or the same row (presenting a different number of available σ–holes and directionality) of the periodic table. This is illustrated in this review by using several examples retrieved from the Cambridge Structural Database (CSD), especially focused on σ–hole interactions, complemented with molecular electrostatic potential surfaces of model systems.
In this study the ability of metal coordinated Chalcogen (Ch) atoms to undergo Chalcogen bonding (ChB) interactions has been evaluated at the PBE0-D3/def2-TZVP level of theory. An initial CSD ...(Cambridge Structural Database) inspection revealed the presence of square planar Pd/Pt coordination complexes where divalent Ch atoms (Se/Te) were used as ligands. Interestingly, the coordination to the metal center enhanced the σ-hole donor ability of the Ch atom, which participates in ChBs with neighboring units present in the X-ray crystal structure, therefore dictating the solid state architecture. The X-ray analyses were complemented with a computational study (PBE0-D3/def2-TZVP level of theory), which shed light into the strength and directionality of the ChBs studied herein. Owing to the new possibilities that metal coordination offers to enhance or modulate the σ-hole donor ability of Chs, we believe that the findings presented herein are of remarkable importance for supramolecular chemists as well as for those scientists working in the field of solid state chemistry.
Herein, we describe the fascinating architectures of POMs-based hybrid compounds constructed using metal ions and different kinds of polyoxometalates. Complementing, the important role of POMs, the ...choice of adequate ligands is fundamental to modulate the properties of inorganic–organic hybrids as highlighted in this review.
•Influence of the topological diversity and flexibility of ligands upon the topology of hybrids inorganic–organic based polyoxometalates.•Entangled structures and other structures within hybrids inorganic–organic based polyoxometalates.•Influence of the negative charge of polyoxometalates upon their supramolecular assemblies in the solid state.
Currently, the design and assembly of hybrid inorganic–organic compounds has become an area of rapid growth due to their structural diversities as molecular building blocks. Polyoxometalates (POMs) as a subset of metal oxides, that represent a tremendous range of inorganic clusters with unique physical and chemical performances, possess intriguing structures and abundant potential applications. In the self-assembling process of POM-based architectures, in addition to the important role of POMs, the choice of adequate ligands is significant to modulate the properties of inorganic–organic hybrids. Moreover, flexible N-donor ligands, including imidazole, triazole, tetrazole, and pyridyl derivatives with strong coordination capacity have been used for construction of POM-based compounds with attractive topologies and different dimensionality. Thus, this review puts into perspective latest research on this topic focusing to the construction of hybrid inorganic–organic materials based on flexible ligands. Remarkably, they provide to POM-based systems the flexibility and conformational freedom necessary to satisfy the coordination environment of the metal centers creating fascinating structural topologies, such as entangled and other structures with various architectures. In addition, this review also describes recent work devoted to analyze how the negative charge of POMs influences the supramolecular assembly of hybrid inorganic–organic compounds.
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