Large Interaction Energy Research Articles

Intermolecular interactions between metallylenes and carbonyl chalcogenides: Chalcogen bond and tetrel bond

The intermolecular interactions between the singlet metallylenes XH2 (X = Si, Ge, Sn, Pb) and carbonyl chalcogenides OCY (Y = S, Se, Te) have been studied by the high-level quantum chemical calculations. The chalcogen-bonded and tetrel-bonded complexes can be formed between XH2 and OCY due to their ambiphilic character. The structure and binding strength of the complexes have been explored on the basis of the MEP surfaces of the monomers, and geometrical parameters and interaction energies of the complexes. The nature of the complexes has been investigated by the NBO, AIM and SAPT analysis. The tetrel-bonded complexes exhibit a much stronger binding strength with larger interaction energies and shorter binding distances compared to the chalcogen-bonded complexes. The interaction energies of the complexes become larger with the increase of the Y atomic number, but become smaller with the increase of the X atomic number. NBO analysis reveals that the dominant orbital interactions in the chalcogen-bonded and tetrel-bonded complexes are LP(X) → σ*(C-Y) and LP(Y) → LP*(X), respectively. AIM analysis suggests that the chalcogen-bonded complexes are the purely noncovalent, but the tetrel-bonded complexes have partial covalent character. SAPT analysis indicates that the contribution of the energy component decreases in the order of Eele > Edisp > Eind for most chalcogen-bonded complexes, and this order is Eele > Eind > Edisp for most tetrel-bonded complexes.

The crystal structures and Hirshfeld surface analysis of three new bromo-substituted 3-methyl-1-(phenylsulfonyl)-1H-indole derivatives

Three new 1H-indole derivatives, namely, 2-(bromomethyl)-3-methyl-1-(phenylsulfonyl)-1H-indole, C16H14BrNO2S, (I), 2-[(E)-2-(2-bromo-5-methoxyphenyl)ethenyl]-3-methyl-1-(phenylsulfonyl)-1H-indole, C24H20BrNO3S, (II), and 2-[(E)-2-(2-bromophenyl)ethenyl]-3-methyl-1-(phenylsulfonyl)-1H-indole, C23H18BrNO2S, (III), exhibit nearly orthogonal orientations of their indole ring systems and sulfonyl-bound phenyl rings. Such conformations are favourable for intermolecular bonding involving sets of slipped π–π interactions between the indole systems and mutual C—H...π hydrogen bonds, with the generation of two-dimensional monoperiodic patterns. The latter are found in all three structures, in the form of supramolecular columns with every pair of successive molecules related by inversion. The crystal packing of the compounds is additionally stabilized by weaker slipped π–π interactions between the outer phenyl rings (in II and III) and by weak C—H...O, C—H...Br and C—H...π hydrogen bonds. The structural significance of the different kinds of interactions agree with the results of a Hirshfeld surface analysis and the calculated interaction energies. In particular, the largest interaction energies (up to −60.8 kJ mol−1) are associated with pairing of antiparallel indole systems, while the energetics of weak hydrogen bonds and phenyl π–π interactions are comparable and account for 13–34 kJ mol−1.

The single metal atom (Ni, Pd, Pt) anchored on defective hexagonal boron nitride for oxidative desulfurization.

Single-atom catalysts (SACs) have attracted great attention for various chemical reactions because of their strong activity, high metal utilization ratio, and low cost. Here, by using the density functional theory (DFT) method, the stability of a single VIII-group metal atom (M = Ni, Pd, Pt) anchored on the defective hexagonal boron nitride (h-BN) sheet and its possible application in oxidative desulfurization (ODS) are investigated. Calculations show that the stability of the single M atom embedded in the h-BN surface with B and N vacancies is strikingly enhanced compared to that on the perfect h-BN surface. The catalytic activities of the defective h-BN-supported single metal atom are further studied by the activation of molecular oxygen and subsequent oxidation of dibenzothiophene (DBT). O2 is activated to the super-oxo state with large interaction energies on three M/VN surfaces. However, among the three M/VB surfaces, only Pt/VB performs efficient activation of O2. The oxidation of DBT proceeds in two steps; the rate-determining step is the initial step, in which activated O2 oxidizes DBT to produce sulfoxide. By comparing the energy barrier in the first reaction step, both Ni/VN and Pt/VB are revealed as promising candidates for the ODS reaction.

What are the minimal folding seeds in proteins? Experimental and theoretical assessment of secondary structure propensities of small peptide fragments.

Certain peptide sequences, some of them as short as amino acid triplets, are significantly overpopulated in specific secondary structure motifs in folded protein structures. For example, 74% of the EAM triplet is found in α-helices, and only 3% occurs in the extended parts of proteins (typically β-sheets). In contrast, other triplets (such as VIV and IYI) appear almost exclusively in extended parts (79% and 69%, respectively). In order to determine whether such preferences are structurally encoded in a particular peptide fragment or appear only at the level of a complex protein structure, NMR, VCD, and ECD experiments were carried out on selected tripeptides: EAM (denoted as pro-'α-helical' in proteins), KAM(α), ALA(α), DIC(α), EKF(α), IYI(pro-β-sheet or more generally, pro-extended), and VIV(β), and the reference α-helical CATWEAMEKCK undecapeptide. The experimental data were in very good agreement with extensive quantum mechanical conformational sampling. Altogether, we clearly showed that the pro-helical vs. pro-extended propensities start to emerge already at the level of tripeptides and can be fully developed at longer sequences. We postulate that certain short peptide sequences can be considered minimal "folding seeds". Admittedly, the inherent secondary structure propensity can be overruled by the large intramolecular interaction energies within the folded and compact protein structures. Still, the correlation of experimental and computational data presented herein suggests that the secondary structure propensity should be considered as one of the key factors that may lead to understanding the underlying physico-chemical principles of protein structure and folding from the first principles.

Molecular dynamics study on effect of wettability on boiling heat transfer of thin liquid films

How surface wettability affects boiling heat transfer of thin liquid film on a nanoscale remains a challenging research topic. In this work, the effects of wettability on the nanoscale boiling heat transfer for a thin liquid film on hydrophilic surface and hydrophobic surface are investigated by molecular dynamics simulation. Results demonstrate that the hydrophilic surface has better heat transfer performance than the hydrophobic surface. It has a shorter boiling onset time, higher temperature, heat flux, interfacial thermal conductance, and weakened interfacial thermal resistance. The hydrophilic surface throughout has higher critical heat flux than the hydrophobic surface in both macro-system and nanoscale system. Besides, a two-dimensional surface potential energy is proposed to reveal the mechanism of wettability affecting the boiling heat transfer. The absolute value of potential energy in one regular unit of hydrophilicity (–0.34 eV) is much higher than that of hydrophobicity (–0.09 eV). That is the crucial reason why the heat transfer enhancement via improving surface wettability should be primarily the powerful surface potential energy. In addition, the interaction energy is calculated to further address the nucleation mechanism and heat transfer performance for liquid film on different wettability surfaces. The interaction energy values are ordered as <i>I</i><sub>phi</sub> (1.57 eV/nm<sup>2</sup>) > <i>I</i><sub>water</sub> (0.48 eV/nm<sup>2</sup>) > <i>I</i><sub>pho</sub> (0.26 eV/nm<sup>2</sup>), indicating that the better heat transfer performance of hydrophilic surface is because of the large interaction energy at the solid/liquid interface. Besides, the bubble nucleation on a hydrophilic surface needs absorbing more energy and occurs inside the thin liquid film, while it needs absorbing less energy and triggering off at the solid/liquid interface with hydrophobicity. Those uncover the principal mechanisms of how wettability influences the bubble nucleation and boiling heat transfer performance on a nanoscale.

A therapeutic epitopes-based vaccine engineering against Salmonella enterica XDR strains for typhoid fever: a Pan-vaccinomics approach

A prevalent food-borne pathogen, Salmonella enterica serotypes Typhi, is responsible for gastrointestinal and systemic infections globally. Salmonella vaccines are the most effective, however, producing a broad-spectrum vaccine remains challenging due to Salmonella’s many serotypes. Efforts are urgently required to develop a novel vaccine candidate that can tackle all S. Typhi strains because of their high resistance to multiple kinds of antibiotics (particularly the XDR H58 strain). In this work, we used a computational pangenome-based vaccine design technique on all available (n = 119) S. Typhi reference genomes and identified one TonB-dependent siderophore receptor (WP_001034967.1) as highly conserved and prospective vaccine candidates from the predicted core genome (n = 3,351). The applied pan-proteomics and Immunoinformatic approaches help in the identification of four epitopes that may trigger adequate host body immune responses. Furthermore, the proposed vaccine ensemble demonstrates a stable binding conformation with the examined immunological receptor (HLAs and TRL2/4) and has large interaction energy determined via molecular docking and molecular dynamics simulation techniques. Eventually, an expression vector for the Escherichia. coli K12 strain was constructed from the vaccine sequence. Additional analysis revealed that the vaccine may help to elicit strong immune responses for typhoid infections, however, experimental analysis is required to verify the vaccine’s effectiveness based on these results. Moreover, the applied computer-assisted vaccine design may considerably decrease vaccine development costs and speed up the process. The study’s findings are intriguing, but they must be evaluated in the experimental labs to confirm the developed vaccine’s biological efficiency against XDR S. Typhi. Communicated by Ramaswamy H. Sarma

π-Hole Triel Bonds between TrPhX2 (Tr = B, Al, Ga; X = F, Cl, Br, CH3, OH) and (BH)2(NHC)2 (NHC = Nitrogen-Heterocyclic Carbene)

The π-hole triel bond formed by (BH)2(NHC)2 (NHC denotes nitrogen-heterocyclic carbene) and TrPhX2 (Tr = B, Al, and Ga; X = F, Cl, Br, CH3, and OH) was investigated computationally, with the B=B bond in (BH)2(NHC)2 being the electron donor. A large interaction energy ensures that the complex is quite stable. When the substituent X in the electron acceptor is fixed, the magnitude of the interaction energy varies with the identity of the Tr atom. When Tr is Al or Ga, the interaction energy is stronger than when it is B. With an increase in the electron-withdrawing ability of the substituents, the interaction energy shows distinct changes. When Tr is B or Al, the interaction energy varies as TrPhBr2 > TrPhCl2 > TrPhF2, which is different from the order of their positive electrostatic potentials. When Tr = Ga, the interaction energy hardly changes with an increase in the electronegativity of the halogen atoms. For CH3 and OH substitution, larger interaction energies were obtained, with the interaction energy for the OH substituent being the largest. The main interactions in these systems are a triel bond and an X· ·H hydrogen bond. When the substituents are fixed, the interaction energy of the triel bond increases in the order AlPhX2 < GaPhX2 < BPhX2, which is different from the order of the positive electrostatic potentials on the Tr atom in TrPhX2. When X is a halogen atom, the interaction energy of the triel bond decreases in the order Br > Cl > F, which is opposite to the trend for the positive electrostatic potentials on Tr in TrPhX2. In most complexes, the interaction energy for the hydrogen bond is less than that for the triel bond; there is no hydrogen bond in the methyl-substituted complex. In general, the interaction energy of the hydrogen bonds increases with an increase in the electronegativity of the halogen atoms.

Single-Point Extrapolation to the Complete Basis Set Limit through Deep Learning.

Machine learning (ML) offers an attractive method for making predictions about molecular systems while circumventing the need to run expensive electronic structure calculations. Once trained on ab initio data, the promise of ML is to deliver accurate predictions of molecular properties that were previously computationally infeasible. In this work, we develop and train a graph neural network model to correct the basis set incompleteness error (BSIE) between a small and large basis set at the RHF and B3LYP levels of theory. Our results show that, when compared to fitting to the total potential, an ML model fitted to correct the BSIE is better at generalizing to systems not seen during training. We test this ability by training on single molecules while evaluating on molecular complexes. We also show that ensemble models yield better behaved potentials in situations where the training data is insufficient. However, even when only fitting to the BSIE, acceptable performance is only achieved when the training data sufficiently resemble the systems one wants to make predictions on. The test error of the final model trained to predict the difference between the cc-pVDZ and cc-pV5Z potential is 0.184 kcal/mol for the B3LYP density functional, and the ensemble model accurately reproduces the large basis set interaction energy curves on the S66x8 dataset.

Simulating the Detection of Dioxin-like Pollutants with 2D Surface-Enhanced Raman Spectroscopy Using h-BNC Substrates

The ability of 2D hybrid structures formed by boron, nitrogen and carbon atoms (h-BNCs) to act as potential substrates for the surface-enhanced Raman spectroscopy (SERS) detection of dioxin-like pollutants is theoretically analyzed. The strong confinement and high tunability of the electromagnetic response of the carbon nanostructures embedded within the h-BNC sheets point out that these hybrid structures could be promising for applications in optical spectroscopies, such as SERS. In this work, two model dioxin-like pollutants, TCDD and TCDF, and a model h-BNC surface composed of a carbon nanodisk of ninety-six atoms surrounded by a string of borazine rings, BNC96, are used to simulate the adsorption complexes and the static and pre-resonance Raman spectra of the adsorbed molecules. A high affinity of BNC96 for these pollutants is reflected by the large interaction energies obtained for the most stable stacking complexes, with dispersion being the most important contribution to their stability. The strong vibrational coupling of some active modes of TCDF and, specially, of TCDD causes the static Raman spectra to show a ”pure” chemical enhancement of one order of magnitude. On the other hand, due to the strong electromagnetic response of BNC96, confined within the carbon nanodisk, the pre-resonance Raman spectra obtained for TCDD and TCDF display large enhancement factors of 108 and 107, respectively. Promisingly, laser excitation wavelengths commonly used in SERS experiments also induce significant Raman enhancements of around 104 for the TCDD and TCDF signals. Both the strong confinement of the electromagnetic response within the carbon domains and the high modulation of the resonance wavelengths in the visible and/or UV region in h-BNCs should lead to a higher sensitivity than that of graphene and white graphene parent structures, thus overcoming one of the main disadvantages of using 2D substrates for SERS applications.

Intramolecular interaction between sidechains in intact Trp-cage miniprotein(TC5b)

Intramolecular interaction energies of sidechains in the intact TC5b are individually computed using density fitted 2nd order Moller-Plesset perturbation theory with aug-cc-pVTZ basis set. Large intramolecular interaction energies are observed in between residue lysine(8), aspartate(9), and arginine(16). Strong attractive interaction is also observed between terminal residues. In general, the interaction energies between sidechains without the influence of solvent molecules are relatively small if the pair does not have charges. The sum of 2-body interactions between sidechains in residues1-10 and residues 11–20 are found to be attractive, consistent with the fact TC5b is known to fold at physiological pH. This is largely due to attractive interactions between the charged residues arginine(16) and aspartate(9).

Molecular Understanding of Adhesion of Epoxy Resin to Graphene and Graphene Oxide Surfaces in Terms of Orbital Interactions

The adhesion mechanism of epoxy resin (ER) cured material consisting of diglycidyl ether of bisphenol A (DGEBA) and 4,4'-diaminodiphenyl sulfone (DDS) to pristine graphene and graphene oxide (GO) surfaces is investigated on the basis of first-principles density functional theory (DFT) with dispersion correction. Graphene is often used as a reinforcing filler incorporated into ER polymer matrices. The adhesion strength is significantly improved by using GO obtained by the oxidation of graphene. The interfacial interactions at the ER/graphene and ER/GO interfaces were analyzed to clarify the origin of this adhesion. The contribution of dispersion interaction to the adhesive stress at the two interfaces is almost identical. In contrast, the DFT energy contribution is found to be more significant at the ER/GO interface. Crystal orbital Hamiltonian population (COHP) analysis suggests the existence of hydrogen bonding (H-bonding) between the hydroxyl, epoxide, amine, and sulfonyl groups of the ER cured with DDS and the hydroxyl groups of the GO surface, in addition to the OH-π interaction between the benzene rings of ER and the hydroxyl groups of the GO surface. The H-bond has a large orbital interaction energy, which is found to contribute significantly to the adhesive strength at the ER/GO interface. The overall interaction at the ER/graphene is much weaker due to antibonding type interactions just below the Fermi level. This finding indicates that only dispersion interaction is significant when ER is adsorbed on the graphene surface.

Intermolecular interactions of cytosine DNA nucleoside base with Gallic acid and its Methylgallate and Ethylgallate derivatives

Abstract3,4,5‐trihydroxybenzlic acid (gallic acid) and its derivatives exist mostly as secondary metabolites of the phenol family found in plants. Herein, the interaction of gallic acid (GA), methylgallic acid (MGA), ethylgallic acid (EGA) with cytosine (the most reactive part of DNA) has been studied in detail using first principle density functional theory (DFT). Several interaction configurations between the gallic acid and selected derivatives have been investigated using DFT at the M06‐2X/6‐31+G(d,p) theoretical method, topological analysis based on quantum theory of atoms‐in‐molecule (QTAIM), and the noncovalent interaction (NCI) which aid in the understanding of interactions between studied compounds. The results obtained from the interaction energy and energy decomposition analysis (EDA) show that methylgallate (GA) has the largest interaction energy with cytosine, along with the strongest H‐bond interaction and is best suited for drug design due to its lowest value of stabilization energy at the interaction site 1.Similarly, weak interactions were observed between EGA and cytosine of DNA between −0.02 to 0.01 a.u with a sparing trace of H bond with the aid of non‐covalent interaction (NCI). The reactivity of the studied compound depicts GA to be the most reactive. Although gallic acid competes favorably, this study, however, revealed the great potential of its derivatives: EGA and MGA having great potential for drug design. Their applications are vast and mostly hinged on antioxidant properties, especially in the pharmaceutical industry and, hence, form the basis of an effective class of phytomedicines.

Mechanistic Insights of TiO2 Nanoparticles with Different Surface Charges on Aβ42 Peptide Early Aggregation: An In Vitro and In Silico Study.

Humans may intendedly or unintendedly be exposed to nanomaterials through food, water, and air. Upon exposure, nanomaterials can pierce the bloodstream and translocate to secondary organs, including the brain, which warrants increased concern for the potential health impacts of nanomaterials. Due to their large surface area and interaction energy, nanomaterials can adsorb surrounding proteins. The misfolding and self-aggregation of amyloid-β (Aβ) have been considered significant factors in the pathogenesis of Alzheimer's disease. We thus hypothesize that brain-targeted nanomaterials may modulate Aβ aggregation and cause related neurotoxicity. Here, we showed that TiO2 nanoparticles (NPs) and their aminated analogue (TiO2-NH2 NPs) adsorb the Aβ42 peptide and accelerate its early oligomerization. Molecular dynamics simulation indicated that the adsorption onto TiO2 NPs and TiO2-NH2 NPs surfaces can stabilize the β-sheet-rich conformations formed by the Aβ42 peptide. The binding sites between TiO2-NH2 NPs and the Aβ42 oligomer surface were mainly concentrated in the hydrophobic core region, and the β-sheet conformation spontaneously formed by Aβ42 oligomers can be better stabilized through a hydrogen bond, electrostatic attraction, and hydrophobic interaction. This study will further help in the understanding of nanomaterial-related neurotoxicities and the regulation of their applications.

Eutectic Mixture Formation and Relaxation Dynamics of Coamorphous Mixtures of Two Benzodiazepine Drugs

The formation of coamorphous mixtures of pharmaceuticals is an interesting strategy to improve the solubility and bioavailability of drugs, while at the same time enhancing the kinetic stability of the resulting binary glass and allowing the simultaneous administration of two active principles. In this contribution, we describe kinetically stable amorphous binary mixtures of two commercial active pharmaceutical ingredients, diazepam and nordazepam, of which the latter, besides being administered as a drug on its own, is also the main active metabolite of the other in the human body. We report the eutectic equilibrium-phase diagram of the binary mixture, which is found to be characterized by an experimental eutectic composition of 0.18 molar fraction of nordazepam, with a eutectic melting point of Te = 395.4 ± 1.2 K. The two compounds are barely miscible in the crystalline phase. The mechanically obtained mixtures were melted and supercooled to study the glass-transition and molecular-relaxation dynamics of amorphous mixtures at the corresponding concentration. The glass-transition temperature was always higher than room temperature and varied linearly with composition. The Te was lower than the onset of thermal decomposition of either compound (pure nordazepam decomposes upon melting and pure diazepam well above its melting point), thus implying that the eutectic liquid and glass can be obtained without any degradation of the drugs. The eutectic glass was kinetically stable against crystallization for at least a few months. The relaxation processes of the amorphous mixtures were studied by dielectric spectroscopy, which provided evidence for a single structural (α) relaxation, a single Johari-Goldstein (β) relaxation, and a ring-inversion conformational relaxation of the diazepinic ring, occurring on the same timescale in both drugs. We further characterized both the binary mixtures and pure compounds by FTIR spectroscopy and first-principles density functional theory (DFT) simulations to analyze intermolecular interactions. The DFT calculations confirm the presence of strong attractive forces within the heteromolecular dimer, leading to large dimer interaction energies of the order of -0.1 eV.

Energetic and atomic structural analyses of the screw dislocation absorption at tilt grain boundaries in BCC-Fe.

The dislocation-grain boundary (GB) interaction plays an important role in GB-related plasticity. Therefore, an atomistic investigation of the interaction provides a deeper understanding of the strength and fracture of polycrystalline metals. In this study, we investigated the absorption of a screw dislocation with a Burgers vector perpendicular to the GB normal and the corresponding symmetric tilt grain boundaries (STGBs) in BCC-Fe based on molecular static simulations focusing on the STGB-dislocation interaction energy and atomistic structural changes at GB. The STGB-screw dislocation interaction depends on the energetical stability of the STGB against the GB shift along the Burgers vector direction. When the interaction exhibited a large attractive interaction energy, the dislocation dissociation and the GB shift along the Burgers vector direction occurred simultaneously. The interaction energy reveals that the interaction depends on the energetical stability of the STGB in terms of the GB shift in addition to the geometrical descriptor of the GB type, such as the Σ value. The same behavior was also obtained in the reaction when the second dislocation was introduced. We also discuss the screw dislocation absorption and rearrangement of the GB atomistic structure in STGB from an energetic viewpoint.

Tetrel Bonding in Anion Recognition: A First Principles Investigation

Twenty-five molecule-anion complex systems [I4Tt···X-] (Tt = C, Si, Ge, Sn and Pb; X = F, Cl, Br, I and At) were examined using density functional theory (ωB97X-D) and ab initio (MP2 and CCSD) methods to demonstrate the ability of the tetrel atoms in molecular entities, I4Tt, to recognize the halide anions when in close proximity. The tetrel bond strength for the [I4C···X-] series and [I4Tt···X-] (Tt = Si, Sn; X = I, At), was weak-to-moderate, whereas that in the remaining 16 complexes was dative tetrel bond type with very large interaction energies and short Tt···X close contact distances. The basis set superposition error corrected interaction energies calculated with the highest-level theory applied, [CCSD(T)/def2-TZVPPD], ranged from -3.0 to -112.2 kcal mol-1. The significant variation in interaction energies was realized as a result of different levels of tetrel bonding environment between the interacting partners at the equilibrium geometries of the complex systems. Although the ωB97X-D computed intermolecular geometries and interaction energies of a majority of the [I4Tt···X-] complexes were close to those predicted by the highest level of theory, the MP2 results were shown to be misleading for some of these systems. To provide insight into the nature of the intermolecular chemical bonding environment in the 25 molecule-anion complexes investigated, we discussed the charge-density-based topological and isosurface features that emanated from the application of the quantum theory of atoms in molecules and independent gradient model approaches, respectively.

Methoxyl-substituted phosphine ligand properties and a case study of formation adducts to indium(III) bromide by DFT calculations

Six bulky triphenylphosphine ligands containing substituted methoxyl groups (tris(2,4,6-trimethoxyphenyl)phosphine (TMP), tris(2,6-dimethoxyphenyl)phosphine (TDP), tris(o-methoxyphenyl)phosphine (o-Anis3P), tris(p-methoxyphenyl)phosphine (p-Anis3P), tris(m-methoxyphenyl)phosphine (m-Anis3P) and triphenylphosphine (PPh3)) were studied by DFT (density functional theory) calculations and experimental solution/solid-state 31P NMR spectroscopy. The basicity and binding ability of these substituted ligands, proven by comparison of structural data with DFT-predicted data, are in the order TMP > TDP > o-Anis3P > p-Anis3P > m-Anis3P > PPh3. Molecular structures for InBr3 with bulky ligands (TMP, TDP, o-Anis3P, p-Anis3P, m-Anis3P and PPh3) were calculated using DFT. P-In bond distances generated from these six optimized molecular structures and the calculated intramolecular interaction energies are in agreement with the ligand properties, with strong donation ability for those with the short bond distance; the In-P bond distance from shortest to longest follows a similar trend as predicted by DFT calculations. DFT calculations for these adducts show that methoxyl substitution to triphenylphosphine (PPh3) ligands contributed to its electron donor ability resulting in lower P-In bond distances with relatively large bond interaction energies.

Catalytic Effect of Ferrocenyl Energetic Catalysts for N-Guanylurea Dinitramide (GUDN or FOX-12) Decomposition.

Four N,N-dimethylaminomethylferrocene polynitrogen catalysts were applied to the thermal decomposition of FOX-12, and their catalytic effect on FOX-12 was investigated by TG-DSC. The kinetic parameters and kinetic model of the mixed system were revealed by the Kissinger method, Freidman method, and combined kinetic analysis. The results showed that MAFcTAZ is the catalyst with the strongest effect on FOX-12, the decomposition peak temperature of FOX-12 is reduced, and the decomposition weight loss is higher than those for other catalysts, which prove that the decomposition of FOX-12 is more thorough under the catalysis of MAFcTAZ. The introduction of the four catalysts reduced the thermal decomposition peak temperature of FOX-12. MAFcTAZ was the most active catalyst for the decomposition of FOX-12, and the maximum heat release of catalyzing the decomposition of FOX-12 can reach 1236.76 J·g–1. The activation energy (Ea) of FOX-12 decomposition decreased from 217.91 to 128.19, 137.85, 157.65, and 151.91 kJ·mol–1 under the effect of MAFcNO3, MAFcPA, MAFcNTO, and MAFcTAZ. The Freidman analysis illustrated that MAFcTAZ reduced the activation energy during the entire decomposition process of FOX-12. The physical model of the decomposition reaction of FOX-12 transformed from the random nucleation and two-dimensional growth of nuclei model (A2) to the random scission model (L2) in the presence of MAFcNO3 and two-dimensional diffusion (D2) under the effect of MAFcPA, MAFcNTO, and MAFcTAZ. By analyzing the molecular structures, MAFcTAZ has a higher iron content and nitrogen content, which are the essence of its excellent catalytic performance. From the perspective of interaction energy, the strong catalytic effect of MAFcTAZ is attributed to its large interaction energy with FOX-12 by energy decomposition analysis.

Influence of the anion base X (X=F−, Cl−, Br−, NO3− and SO42−) on the formation of Chalcogen bonds in Chalcogenodiazoles [formula omitted] (Ch=S, Se and Te)

In recent years, due to the high directionality and adjustable strength, chalcogen bonds have attracted extensive attention from both crystal engineering and theoretical perspectives. A search of the Cambridge Structural Database (CSD) has revealed a large number of crystal structures containing chalcogen group elements and anions. On this basis, some typical structures containing chalcogen group elements C4N4Ch (Ch=S, Se and Te) and anions X (X=F−,Cl−,Br−,NO3− and SO42−) were chosen to form the Ch⋯X chalcogen bond. The properties of these chalcogen bonds are analyzed in detail, including bond lengths, interaction energies, charge transfer, electron densities and energy decomposition analyses. The results show that these studied Ch⋯X chalcogen bonds dominated by electrostatic interactions have large interaction energy, reaching a maximum of 97.41 kcal/mol in the case of C4N4Te⋯SO42− complex. Interestingly, the double chalcogen bond is found in these studied C4N4Ch⋯X complexes.

Insight into Spodium-π Bonding Characteristics of the MX2⋯π (M = Zn, Cd and Hg; X = Cl, Br and I) Complexes-A Theoretical Study.

The spodium–π bonding between MX2 (M = Zn, Cd, and Hg; X = Cl, Br, and I) acting as a Lewis acid, and C2H2/C2H4 acting as a Lewis base was studied by ab initio calculations. Two types of structures of cross (T) and parallel (P) forms are obtained. For the T form, the X–M–X axis adopts a cross configuration with the molecular axis of C≡C or C=C, but both of them are parallel in the P form. NCI, AIM, and electron density shifts analyses further, indicating that the spodium–π bonding exists in the binary complexes. Spodium–π bonding exhibits a partially covalent nature characterized with a negative energy density and large interaction energy. With the increase of electronegativity of the substituents on the Lewis acid or its decrease in the Lewis base, the interaction energies increase and vice versa. The spodium–π interaction is dominated by electrostatic interaction in most complexes, whereas dispersion and electrostatic energies are responsible for the stability of the MX2⋯C2F2 complexes. The spodium–π bonding further complements the concept of the spodium bond and provides a wider range of research on the adjustment of the strength of spodium bond.