[NH4+][BxH3x+1-] (x = 1-5): Role of Polynuclear Superhalogens in High-Capacity Hydrogen Storage.

Superhalogen anions are characterized by a higher vertical detachment energy (VDE) than those of halides. Ammonium borohydride, [NH4+][BH4-], is a potential candidate for high-capacity hydrogen storage but is not practically used due to its instability against dissociation to ammonia borane. Interestingly, BH4- is a superhalogen anion, and therefore, we use polynuclear BxH3x+1- superhalogen anions and study [NH4+][BxH3x+1-] complexes for x = 2-5 using density functional theory. The gravimetric hydrogen density of these complexes is smaller than that of [NH4+][BH4-] only slightly. We calculate the dehydrogenation energy and the Gibbs free energy of [NH4+][BxH3x+1-] complexes through ammonia borane. We notice that these complexes are more stable than [NH4+][BH4-], whose stability increases with an increase in x. The enhanced stability of [NH4+][BxH3x+1-] complexes appears as a consequence of the increase in the VDE of polynuclear BxH3x+1- superhalogen anions. We believe that these findings might attract experimentalists to synthesize these complexes.

Docking and MM study of non-structural protein (NS5) of Japanese Encephalitis Virus (JEV) with some derivatives of adenosyl.

Introduction: The flavivirus NS5, a non-structural protein of Japanese Encephalitis Virus (JEV), a serious deadly human pathogen responsible for epidemics in South East Asia, consists of N-terminal methyl transferase (MTase) domain and RNA-dependent RNA polymerase (RdRp) is known for unique viral genome replication and cap formation activity. S-adenosyl executes a crucial function in these viral activities. S-adenosyl derivatives are chosen as potential binders with the MTase domain of NS5 based on MM and docking studies. Methods: MM GBSA (Generalized Born Surface Area) simulation were performed to evaluate the binding energy, following the 100 nanosecond (ns) production MD simulation in the periodic boundary condition (PBC) for the selected docked ligands with NS5. Quasi-harmonic entropy of the ligands was also calculated with semi-empirical calculations at the PM3/PM6 level supporting docking and MM-GBSA results. Results and discussion: The residue-wise decomposition energy reveals that the key hydrophobic residues Gly 81, Phe 133, and Ile 147 in the RdRp-MTase interface, indicate the biological relevance. These residues act as the key residue stabilizer, binding vigorously with S-Adenosyl derivatives in the vicinity of the interface between the MTase domain and RdRp. This paves the way for the other potential drug as an inhibitor for the enzymatic activity of the NS5.

Boronyl-Based Polycyclic Superhalogens.

Superhalogenity refers to the tendency of radicals to have higher electron affinity (EA) than halogens or anions to possess higher vertical detachment energy (VDE) than do halides (3.64 eV). In Srivastava, A. K. J. Phys. Chem. A 2023, 127, 4867-4872, we demonstrated a simple strategy in which some polycyclic hydrocarbons (PHs) can be turned into polycyclic superhalogens (PSs) by substituting CN groups in the place of hydrogens. We also notice that the superhalogenity of cyanide-based PSs is related to their aromaticity. Boronyl (BO) is an isoelectronic and inorganic analog of the cyano (CN) group. Therefore, we consider the substitution of BO in PHs and compare them with CN-based PSs using the density functional theory. In the case of C5H5-, we notice that the B3LYP and CCSD(T) calculated VDEs of resulting C5H5-n(BO)n- anions increase with the increase in the number of BO substituents (n) such that they become superhalogens for n ≥ 3 like C5H5-n(CN)n- anions. However, their aromaticity does not correspond to the superhalogenity, unlike C5H5-n(CN)n-. Similarly, all BO-substituted PHs possess structures similar to their CN analogs. Although their aromaticity is reduced compared to CN-based anions, the VDE of all these BO-based polycyclic anions and the EA of their radicals exceed 5 eV than those of the corresponding CN-based PSs. Therefore, this study proposes a new class of boronyl-based polycyclic superhalogens. These superhalogen anions might attract synthetic chemists and experimentalists for further explorations.

Recent progress on the design and applications of superhalogens.

The research on superhalogens has successfully completed four decades. After their prediction in 1981 and experimental verification in 1999, such species have attracted attention due to their unusual structures and intriguing applications. Superhalogens are species whose electron affinity exceeds that of halogen or whose anions possess a larger vertical detachment energy than that of halides. Initially, these species were designed using s and p block atoms having a central electropositive atom as the core with excess electronegative atoms as ligands such as F, Cl, O etc. The last decade has witnessed enormous progress in the field of superhalogens. The transition metal atoms have played the role of the central core and a variety of new ligands have been explored. Further, new classes of superhalogens such as polynuclear superhalogens, magnetic superhalogens, aromatic superhalogens, etc. have been reported. The first application of superhalogens as strong oxidizers appeared much before their conceptualization. In the last decade, however, their applications have spanned a variety of fields such as energy storage, superacids, organic superconductors, ionic liquids, liquid crystals, etc. This makes research in the field of superhalogens truly interdisciplinary. This article is intended to highlight the progress on the design and applications of superhalogens in the last decade.

A Simple Strategy to Design Polycyclic Superhalogens.

Polycyclic hydrocarbon (PH) radicals and anions such as C9H7-, C11H7-, C13H9-, and C15H9- generally possess low electron affinity (EA) and vertical detachment energy (VDE), respectively, due to their aromaticity and, consequently, enhanced stability. In this work, we propose a simple strategy to design polycyclic superhalogens (PSs) by replacing all hydrogens by cyano (CN) groups. Superhalogens can be defined as the radicals having higher EA than halogens or anions having higher VDE than halides (3.64 eV). Our density functional calculations suggest that the EA (VDE) of PS radicals (anions) exceeds 5 eV. All these PS anions are aromatic, except C11(CN)7-, which is anti-aromatic. The superhalogen property of these PSs can be attributed to the EA of CN ligands, leading to the delocalization of extra electronic charge significantly as explained using prototype C5H5-x(CN)x systems. We also notice that the 'superhalogenity' (superhalogen behavior) of C5H5-x(CN)x- is directly related to their aromaticity. We have also shown that the substitution of CN is energetically favorable, which confirms their experimental viability. Our findings should motivate experimentalists to synthesize these superhalogens for further exploration and future applications.

M(BO)k+1- Anions: Novel Superhalogens Based on Boronyl Ligands.

Superhalogens have been a subject of continuous attraction in the last four decades due to their unusual structures and interesting applications. In the quest for new superhalogens based on boronyl (BO) ligands, we investigate M(BO)k+1- anions using a high-level ab initio CCSD(T) and B3LYP density functional method for M = Li, Na, K, Be, Mg, Ca, B, and Al. Their structures are linear for M = Li, Na, K; trigonal planar for M = Be, Mg, Ca; and tetrahedral for M = B, Al. These anions are energetically and thermodynamically stable against various fragmentations. Their superhalogen property has been established due to their higher vertical detachment energy (VDE) than halogen, being in the range 4.44-7.81 eV. For a given k, the stability and VDE of M(BO)k+1- anions decrease with an increase in the size of M, which is due to the decrease in charge delocalization on BO moieties. There exists a linear correlation between frontier orbitals energy gap and VDE with coefficient R2 = 0.93888. It was also noticed that the BO ligand, due to the lower dimerization energy, can be preferably used as an inorganic analogue of CN. However, the structural relaxation in BO-based neutral species significantly affect the VDE and, hence, their superhalogen nature. We believe that these findings should be interesting for researchers working in superatomic chemistry as well as in boron chemistry.

Superhalogens as Building Blocks of Ionic Liquids.

Ionic liquids (ILs) are composed of large asymmetric organic cations with a wide range of anions. The simple anions, e.g., halogen, result in less stable ILs, and therefore, ILs generally consist of complex anions such as BF4 and PF6. These anions coincidently belong to a special class known as superhalogen. This prompted us to enquire whether the concept of superhalogen can be exploited to design new ILs. We study the complexes of 1-butyl-3-methylimidazolium (BMIM) cation and typical superhalogen (X) anions such as LiF2, BeF3, BO2, NO3, BF4, and PF6 including Cl using density functional theory and the quantum theory of atoms in molecule. Our ωB97XD/6-311++G(d,p) calculations suggest that the BMIM-X complexes are stable in which the charge transfer of 0.90-0.97 e takes place from BMIM to X. The charge-transferred tends to delocalize as the size of X increases. These complexes are stabilized by several ionic and/or covalent intramolecular interactions (H-bonds). The BMIM-X complexes prefer to dissociate into ionic fragments (BMIM+ + X-) than neutral fragments (BMIM + X). The dissociation energy and energy gap of BMIM-X complexes are closely related to the electron affinity of superhalogens (X). These findings not only reveal the superhalogens as building blocks of ILs but also suggest the design of highly stable ILs by employing the superhalogens with higher electron affinities.

Lithiated Graphene Quantum Dot and its Nonlinear Optical Properties Modulated by a Single Alkali Atom: A Theoretical Perspective.

The functional modification in graphene leads to novel characteristics. We study a lithiated graphene quantum dot (LiG) and adsorption of a single alkali atom (M = Li, Na, and K) on its surface using the B3LYP-D3 method. The structures of M@LiG attain the lowest energy with M adsorbed on the terminal ring of LiG. The isomers of M@LiG are stable against dissociation into M and LiG. The frontier orbital energy gap of M@LiG is significantly reduced to 0.41-0.58 eV as compared to that of LiG (2.16 eV). There is a strong charge transfer of 0.91-0.96|e| from M to LiG in all M@LiG systems, which is slightly reduced in the lowest-energy Na@LiG structure. The CAM-B3LYP results suggest a significant increase in the dipole moment and mean polarizabilities of M@LiG due to the charge transfer and smaller energy gaps, respectively. The first static hyperpolarizability (ß0) value of the lowest-energy M@LiG structures becomes as large as 11.5 × 105 a.u. for M = K. Our time-dependent density functional theory (TDDFT) calculations suggest that the enormously high value of ß0 results due to lower transition energy and higher transition dipole moment for the crucial electronic transition.

External electric field modulated second-order nonlinear optical response and visible transparency in hexalithiobenzene.

External electric fields (EEFs) offer a unique opportunity to tune certain activity of molecules by orienting the alignment of the electric field along the specific axis. The second-order NLO response of hexalithiobenzene (C6Li6) is very poor due to its first mean hyperpolarizability of 0.5 a.u. Therefore, we have analyzed the effect of EEFs on the structural, electronic properties, and NLO response of C6Li6 using a density functional approach. We notice that the structure of the C6Li6 molecule remains planar, with the slight change in C-C and C-Li bond lengths, but their stability is increased under the effect of EEFs. By applying EEFs, the conductivity or reactivity of C6Li6 is increased as their HOMO-LUMO energy gap is decreased. Furthermore, C6Li6 attains a finite dipole moment in the presence of EEF, which increases linearly as the EEF increases. More interestingly, the first static hyperpolarizability of C6Li6 is significantly enhanced, becoming as high as 3.4 × 104 a.u. for EEF = 50 × 10-4 a.u. This suggests the EEF as an effective way to enhance the second-order NLO responses, leading to the design of potential NLO materials. Nevertheless, the visible transparency of C6Li6 with and without EEF may suggest its possible applications in optical devices.

DFT and QTAIM studies on the reduction of carbon monoxide by superalkalis.

Carbon monoxide (CO) is a toxic gas molecule with no positive electron affinity, which makes it difficult to reduce it into CO¯. In this work, we perform density functional theory (DFT) and quantum theory of atoms in molecule (QTAIM) based studies on the interaction of CO molecule with superalkali (SA) clusters. Our findings suggest that this interaction results in SA(CO) complexes, which are stabilized by purely ionic as well as partially covalent bonds although their binding energy decreases with the increase in the size of SA clusters. In these ionic complexes, the electron is transferred from the SA cluster to the CO molecule. This suggests the single-electron reduction of the CO molecule by interacting with superalkalis. This work may offer some novel insights into the detection and reduction of stable CO molecule and related systems.

OxH2x+1+ clusters: A new series of non-metallic superalkali cations by trapping H3O+ into water.

The term 'superalkali' refers to the clusters with lower ionization energy than alkali atoms. Typical superalkali cations include a central electronegative core with excess metal ligands, OLi3+, for instance, which mimic the properties of alkali metal ions. We report a new series of non-metallic superalkali cations, OxH2x+1+ (x = 1-5) using ab initio MP2/6-311++G(d,p) level. These cations are designed by successive hydration of the hydronium cation (OH3+), which can be expressed in the form of OH3+ … (x-1)H2O complexes. These OxH2x+1+ clusters possess a number of electrostatic as well as partially covalent H-bonds, with the interaction energy in the range 5.2-29.3 kcal/mol as revealed by quantum theory of atoms in molecules analyses. These cations are found to be stable against deprotonation as well as dehydration pathways, and their stability increases with the increase in x. Interestingly, the vertical electron affinities (EAv) of OxH2x+1+ clusters decreases rapidly from 5.16 eV for x = 1 to 2.67 eV for x = 5, which suggest their superalkali nature. It is also possible to continue this series of non-metallic superalkali cations for x > 5 with even lower EAv, down to an approximated limit of 1.85 eV, which is obtained for OH3+ trapped into water cavity implicitly using polarizable continuum model. The findings of this study will establish the OxH2x+1+ clusters as a new series of superalkali cations, which can be exploited for their interesting applications.

Hydrogenated superalkalis and their possible applications.

Superalkali species possess lower ionization energy than alkali metals, which allow them to form a variety of unusual compounds with interesting properties. Herein, we report the structures and properties of hydrogenated superalkalis (SAHs) such as FLi2H, OLi3H, and NLi4H using ab initio MP2/6-311++G(d,p) level of theory. All SAH species are found to be thermodynamically stable, which can be considered as a salt between SA cation and H‾ anion. The gas phase basicity and nonlinear optical properties (NLO) of SAH have been explored. The larger proton affinity of NLi4H isomers 1187-1226 kJ mol(-1) and significant mean hyperpolarizability 1.5 × 10(3)-3.7 × 10(3) a.u. suggest their strong basic nature and enhanced NLO properties, respectively. We have also demonstrated some possible applications of hydrogenated superalkalis, as reducing agent as well as building block of supersalts. Graphical abstract The gas phase basicity and nonlinear optical properties of hydogenated superalkalis increase with the increase in the size of superalkalis, FLi2 < OLi3 < NLi4.

Nonlinear optical behavior of Li n F (n = 2-5) superalkali clusters.

Hyperlithiated clusters are known for their unusual bonding characteristics and lower ionization potentials. This study reports nonlinear optical (NLO) properties of a series of hyperlithiated clusters, Li n F (n = 2-5) for the first time. The structures of small Li n F (n = 2-5) clusters, obtained using second order Møller-Plesset perturbative method, are found to be stable against eliminations of F, F‾, and LiF. These Li n F species are stabilized by both ionic as well as covalent interactions. Our study shows that Li n F species can be thought of as superalkali-halogen (Li n - F) clusters but belong to the class of superalkalies themselves. These clusters may also possess alkalide and/or electride characteristics due to excess electrons. The dipole moment, mean polarizability, and hyperpolarizability suggest their significant NLO responses which are explained using the highest occupied molecular orbital surfaces and TD-DFT analysis. The exceptionally large hyperpolarizability of Li2F (~10(5) a.u.) and its electride characteristics are particularly highlighted. This study may guide the researchers in the design of novel materials with significant NLO responses useful for electro-optical applications. Graphical Abstract Li2F superalkali resemble an electride in which the excess electron is pushed out by Li2 (+) moiety, leading to its high hyperpolarizability of order of 10(5) a.u.

Structures, stability, and electronic properties of novel superalkali-halogen clusters.

We have computationally designed some novel clusters by interaction of superalkali (SA) species (FLi2, OLi3, NLi4) with halogen (X = F, Cl) atoms. The ground state electronic structures of these superalkali-halogen (SA-X) clusters are identified and their stabilities are analyzed. The electronic properties of SA-X clusters are also discussed. Like alkali halides, these clusters can also be regarded as SA(+)X(-) species. We have noticed, however, that these clusters prefer to dissociate into ionic fragments, in contrast to alkali halides. The mean polarizabilities of SA-X clusters are much larger than alkali halides, reaching to 136.28 a.u. for NLi4-Cl, which further doubles in the case of its dimer, i.e., (NLi4-Cl)2. We believe that these SA-X clusters can be used as building blocks of novel materials, analogous to traditional alkali halides.

Vibrational spectra, HOMO, LUMO, MESP surfaces and reactivity descriptors of amylamine and its isomers: A DFT study.

Amylamine constitutes an important class of organic compounds which exists in a variety of ammonia derivatives. In present study, a comparative analysis of amylamine and its two potential isomers, iso-amylamine and tert-amylamine, has been performed using density functional theory with B3LYP method and 6-311G(d,p) as the basis set. The equilibrium structures of amylamine as well as its iso and tert forms have been obtained. The vibrational spectroscopic analysis has been carried out for the three molecules and complete assignments to all possible modes have been offered. The HOMO, LUMO and MESP surfaces are analyzed to discuss the chemical reactivity patterns in the molecules. A number of reactivity parameters have been calculated to further explain their chemical reactivity. The thermodynamic and nonlinear optical parameters are also calculated and discussed.

FT-IR spectroscopy, intra-molecular C-H⋯O interactions, HOMO, LUMO, MESP analysis and biological activity of two natural products, triclisine and rufescine: DFT and QTAIM approaches.

The present study deals with two natural products, triclisine and rufescine which are extracted from the Amazonian wines but ubiquitous in nature. The quantum chemical density functional method at B3PW91/6-311+G(d,p) level is used to obtain the equilibrium geometries of these molecules. The quantum theory of atoms-in-molecule approach is employed to study various intra-molecular C-H⋯O interactions within these molecules. We have also performed vibrational analyses of triclisine and rufescine at their equilibrium geometries and presented the complete assignments of the significant vibrational modes. The calculated vibrational frequencies are shown to be in perfect agreement with the experimentally observed FTIR spectra of molecules under study. In addition, the electronic properties of these molecules are also discussed with the help of HOMO-LUMO and MESP surfaces and a number of electronic as well as thermodynamic parameters are calculated which are closely related to their chemical reactivity and reaction paths. The biological activities of both molecules have also been predicted which highlight their pharmacological importance.