Ultrahigh Heat/Fire-Resistant, Mechanically Robust, and Closed-Loop Chemical Recyclable Polycarbonate Enabled by Facile Bond Dissociation Energy Modulation.

Plastics serve as an essential foundation in contemporary society. Nevertheless, meeting the rigorous performance demands in advanced applications and addressing their end-of-life disposal are two critical challenges that persist. Here, an innovative and facile method is introduced for the design and scalable production of polycarbonate, a key engineering plastic, simultaneously achieving high performance and closed-loop chemical recyclability. The bisphenol framework of polycarbonate is strategically adjusted from the low-bond-dissociation-energy bisphenol A to high-bond-dissociation-energy 4,4'-dihydroxydiphenyl, in combination with the incorporation of polysiloxane segments. As expected, the enhanced bond dissociation energy endows the polycarbonate with an extremely high glow-wire flammability index surpassing 1025 °C, a 0.8 mm UL-94 V-0 rating, a high LOI value of 39.2%, and more than 50% reduction of heat and smoke release. Furthermore, the π-π stacking interactions within biphenyl structures resulted in a significant enhancement of mechanical strength by as more as 37.7%, and also played a positive role in achieving a lower dielectric constant. Significantly, the copolymer exhibited outstanding closed-loop chemical recyclability, allowing for facile depolymerization into bisphenol monomers and the repolymerized copolymer retains its high heat and fire resistance. This work provides a novel insight in the design of high-performance and closed-loop chemical recyclable polymeric materials.

Superior Heavy Metal Ion Adsorption Capacity in Aqueous Solution by High-Density Thiol-Functionalized Reduced Graphene Oxides.

The preparation of mercapto-reduced graphene oxides (m-RGOs) via a solvothermal reaction using P4S10 as a thionating agent has demonstrated their potential as an absorbent for scavenging heavy metal ions, particularly Pb2+, from aqueous solutions due to the presence of thiol (-SH) functional groups on their surface. The structural and elemental analysis of m-RGOs was conducted using a range of techniques, including X-ray diffraction (XRD), Raman spectroscopy, optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy equipped with energy-dispersive spectroscopy (STEM-EDS), and X-ray photoelectron spectroscopy (XPS). At pH 7 and 25 °C, the maximum adsorption capacity of Pb2+ ions on the surface of m-RGOs was determined to be approximately 858 mg/g. The heavy metal-S binding energies were used to determine the percent removal of the tested heavy metal ions, with Pb2+ exhibiting the highest percentage removal, followed by Hg2+ and Cd2+ ions having the lowest percent removal, and the binding energies observed were Pb-S at 346 kJ/mol, Hg-S at 217 kJ/mol, and Cd-S at 208 kJ/mol. The time-dependent removal study of Pb2+ ions also yielded promising results, with almost 98% of Pb2+ ions being removed within 30 min at pH 7 and 25 °C using a 1 ppm Pb2+ solution as the test solution. The findings of this study clearly demonstrate the potential and efficiency of thiol-functionalized carbonaceous material for the removal of environmentally harmful Pb2+ from groundwater.

Estimation of the reducing power and electrochemical behavior of few flavonoids and polyhydroxybenzophenones substantiated by bond dissociation energy: a comparative analysis.

Oxidative stress that damages cellular components affects various organs including the brain. It is thus believed to play an active role in neurodegenerative diseases, wherein the intrinsic antioxidant enzymes metabolize toxic intermediates. For therapeutic purpose, instead of antioxidant enzymes, small organic compounds as antioxidants may be more effective. Here, reducing power and electrochemical behavior of some flavanols, flavanonols, flavones, flavonols and O-methylated flavonols have been estimated and confirmed by the calculated bond dissociation energy. Compared to other classes, flavonols exhibited increased reducing power that decreased with methylation of the oxygen atom in the B-ring. Gossypetin emerged as the most effective of these flavonols. Generally, compounds with two hydroxyl groups in two consecutive positions of the phenyl ring and an enolic group in the C-ring with more preference for the hydroxyl group in the ortho position with respect to each other in the catechol moiety showed major activity. 5 position of the A-ring showed the least effect on the activity. The present understanding therefore may be applied for identifying compounds to be used as scaffold for designing potent antioxidants.

In Silico simulation of Cytochrome P450-Mediated metabolism of aromatic amines: A case study of N-Hydroxylation.

Aromatic amines, the widely used raw materials in industry, cause long-term exposure to human bodies. They can be metabolized by cytochrome P450 enzymes to form active electrophilic compounds, which will potentially react with nucleophilic DNA to exert carcinogenesis. The short lifetime and versatility of the oxidant (a high-valent iron (IV)-oxo species, compound I) of P450 enzymes prompts us to use theoretical methods to investigate the metabolism of aromatic amines. In this work, the density functional theory (DFT) has been employed to simulate the hydroxylation metabolism through H-abstraction and to calculate the activation energy of this reaction for 28 aromatic amines. The results indicate that the steric effects, inductive effects and conjugative effects greatly contribute to the metabolism activity of the chemicals. The further correlation reveals that the dissociation energy of -NH2 (BDEN-H) can successfully predict the time-consuming calculated activation energy (R2 for aromatic and heteroaromatic amines are 0.93 and 0.86, respectively), so BDEN-H can be taken as a key parameter to characterize the relative stability of aromatic amines in P450 enzymes and further to quickly assess their potential toxicity. The validation results prove such relationship has good statistical performance (qcv2 for aromatic and heteroaromatic amines are 0.95 and 0.90, respectively) and can be used to other aromatic amines in the application domain, greatly reducing computational cost and providing useful support for experimental research.

Methyl Substitution Destabilizes Alkyl Radicals.

We have quantum chemically investigated how methyl substituents affect the stability of alkyl radicals Mem H3-m C⋅ and the corresponding Mem H3-m C-X bonds (X = H, CH3 , OH; m = 0 - 3) using density functional theory at M06-2X/TZ2P. The state-of-the-art in physical organic chemistry is that alkyl radicals are stabilized upon an increase in their degree of substitution from methyl

Surprising Homolytic Gas Phase Co-C Bond Dissociation Energies of Organometallic Aryl-Cobinamides Reveal Notable Non-Bonded Intramolecular Interactions.

Aryl-cobalamins are a new class of organometallic structural mimics of vitamin B12 designed as potential 'antivitamins B12 '. Here, the first cationic aryl-cobinamides are described, which were synthesized using the newly developed diaryl-iodonium method. The aryl-cobinamides were obtained as pairs of organometallic coordination isomers, the stereo-structure of which was unambiguously assigned based on homo- and heteronuclear NMR spectra. The availability of isomers with axial attachment of the aryl group, either at the 'beta' or at the 'alpha' face of the cobalt-center allowed for an unprecedented comparison of the organometallic reactivity of such pairs. The homolytic gas-phase bond dissociation energies (BDEs) of the coordination-isomeric phenyl- and 4-ethylphenyl-cobinamides were determined by ESI-MS threshold CID experiments, furnishing (Co-C sp 2 )-BDEs of 38.4 and 40.6 kcal mol-1 , respectively, for the two ß-isomers, and the larger BDEs of 46.6 and 43.8 kcal mol-1 for the corresponding α-isomers. Surprisingly, the observed (Co-C sp 2 )-BDEs of the Coß -aryl-cobinamides were smaller than the (Co-C sp 3 )-BDE of Coß -methyl-cobinamide. DFT studies and the magnitudes of the experimental (Co-C sp 2 )-BDEs revealed relevant contributions of non-bonded interactions in aryl-cobinamides, notably steric strain between the aryl and the cobalt-corrin moieties and non-bonded interactions with and among the peripheral sidechains.

Hexaphenylditetrels - When Longer Bonds Provide Higher Stability.

We present a computational analysis of hexaphenylethane derivatives with heavier tetrels comprising the central bond. In stark contrast to parent hexaphenylethane, the heavier tetrel derivatives can readily be prepared. In order to determine the origin of their apparent thermodynamic stability against dissociation as compared to the carbon case, we employed local energy decomposition analysis (LED) and symmetry-adapted perturbation theory (SAPT) at the DLPNO-CCSD(T)/def2-TZVP and sSAPT0/def2-TZVP levels of theory. We identified London dispersion (LD) interactions as the decisive factor for the molecular stability of heavier tetrel derivatives. This stability is made possible owing to the longer (than C-C) central bonds that move the phenyl groups out of the heavily repulsive regime so they can optimally benefit from LD interactions.

Benchmark Experimental Gas-Phase Intermolecular Dissociation Energies by the SEP-R2PI Method.

The gas-phase ground-state dissociation energy D0(S0) of an isolated and cold bimolecular complex is a fundamental measure of the intermolecular interaction strength between its constituents. Accurate D0 values are important for the understanding of intermolecular bonding, for benchmarking high-level theoretical calculations, and for the parameterization of dispersion-corrected density functionals or force-field models that are used in fields ranging from crystallography to biochemistry. We review experimental measurements of the gas-phase D0(S0) and D0(S1) values of 55 different M⋅S complexes, where M is a (hetero)aromatic molecule and S is a closed-shell solvent atom or molecule. The experiments employ the triply resonant SEP-R2PI laser method, which involves M-centered (S0 → S1) electronic excitation, followed by S1 → S0 stimulated emission spanning a range of S0 state vibrational levels. At sufficiently high vibrational energy, vibrational predissociation of the M⋅S complex occurs. A total of 49 dissociation energies were bracketed to within ≤1.0 kJ/mol, providing a large experimental database of accurate noncovalent interactions.

Antiradical Properties of trans-2-(4-substituted-styryl)-thiophene.

2-substituted thiophene compounds with electron donating and electron withdrawing p-phenyl substitution were synthesized and studied their radical scavenging properties using DPPH assay and DFT method. It is shown that p-hydroxy and p-amino phenyl substituted compound exhibit radical scavenging activity. From DFT and radical scavenging studies, a correlation between IC50 with the bond dissociation enthalpy, proton affinity, ground state dipole moment and optical band gap of compound is found. Compounds 1-3 with electron withdrawing substituent (NO2, CN, Cl) do not show any radical scavenging properties, whereas compounds 6-7 with electron donating substituent (OH, NH2) show antiradical properties. Further, the antiradical activity is reduced drastically by replacing the -OH and -NH2 with methoxy and -N-alkylating group respectively in 6 and 7. The compound with p-hydroxy phenyl substitution, exhibits stronger antiradical activity as compared to the p-amino phenyl substitution due to smaller O-H bond dissociation energy as compared to the N-H bond. From DPPH and DFT studies, it is suggested that the radical scavenging activity in 2-substituted thiophene is occurred through proton transfer mechanism. The other possible SET, SPLET mechanisms are also corroborated. Graphical Abstract Antiradical properties of trans-2-(4-substituted-styryl)-thiophene Anamika Gusain, Naresh Kumar, Jagdeep Kumar, Gunjan Pandey, Prasanta Kumar Hota.

DFT Investigation of Hydrogen Atom Abstraction from NHC-Boranes by Methyl, Ethyl and Cyanomethyl Radicals-Composition and Correlation Analysis of Kinetic Barriers.

Understanding the hydrogen atom abstraction (HAA) reactions of N-heterocyclic carbene (NHC)-boranes is essential for extending the practical applications of boron chemistry. In this study, density functional theory (DFT) computations were performed for the HAA reactions of a series of NHC-boranes attacked by •CH2CN, Me• and Et• radicals. Using the computed data, we investigated the correlations of the activation and free energy barriers with their components, including the intrinsic barrier, the thermal contribution of the thermodynamic reaction energy to the kinetic barriers, the activation Gibbs free energy correction and the activation zero-point vibrational energy correction. Furthermore, to describe the dependence of the activation and free energy barriers on the thermodynamic reaction energy or reaction Gibbs free energy, we used a three-variable linear model, which was demonstrated to be more precise than the two-variable Evans-Polanyi linear free energy model and more succinct than the three-variable Marcus-theory-based nonlinear HAA model. The present work provides not only a more thorough understanding of the compositions of the barriers to the HAA reactions of NHC-boranes and the HAA reactivities of the substrates but also fresh insights into the suitability of various models for describing the relationships between the kinetic and thermodynamic physical quantities.

An ONIOM investigation of the effect of conformation on bond dissociation energies in peptides.

In the present study, we use the ONIOM strategy of Morokuma and coworkers to examine the various CH bond dissociation energies (BDEs) of a small peptide (2ONW) and compare these with values obtained for its component individual amino acid residues. To evaluate suitable methods for ONIOM-based geometry optimizations, we test an "internal consistency" approach against full B3-LYP//B3-LYP results, and find B3-LYP/6-31G(d):AM1 to be appropriate. We find that the BDEs at the α-carbon in 2ONW are generally larger than the corresponding values for the individual residues on their own. This is attributed to the constraints of the peptide backbone leading to conformations that are not ideal for captodative stabilization of the resulting α-radicals. At the more flexible ß- and γ-positions, the differences between the BDEs in 2ONW and the individual residues are smaller. Overall, the α-BDEs are smaller than the ß- and γ-BDEs in most cases. Thus, to rationalize the inertness of peptide backbones with respect to α-hydrogen abstraction that is frequently found experimentally, it is necessary to consider alternative protection mechanisms such as the polar effect. © 2018 Wiley Periodicals, Inc.

Mild and Practical Dirhodium(II)/NHPI-Mediated Allylic and Benzylic Oxidations with Air as the Oxidant.

Aerobic allylic and benzylic oxidations catalyzed by dirhodium(II) complexes with N-hydroxyphthalimide (NHPI) are described. The open flask reaction occurs at mild temperature, using air as the oxidant. Mechanistic studies suggest that dirhodium(II) complexes axially coordinate with NHPI to activate the O-H bond in NHPI and decrease the bond-dissociation energy (BDE).

High-Resolution Infrared Synchrotron Investigation of (HCN)2 and a Semi-Experimental Determination of the Dissociation Energy D0.

The high-resolution infrared absorption spectrum of the donor bending fundamental band ν 61 of the homodimer (HCN)2 has been collected by long-path static gas-phase Fourier transform spectroscopy at 207 K employing the highly brilliant 2.75 GeV electron storage ring source at Synchrotron SOLEIL. The rovibrational structure of the ν 61 transition has the typical appearance of a perpendicular type band associated with a Σ-Π transition for a linear polyatomic molecule. The total number of 100 assigned transitions are fitted employing a standard semi-rigid linear molecule Hamiltonian, providing the band origin ν0 of 779.05182(50) cm-1 together with spectroscopic parameters for the degenerate excited state. This band origin, blue-shifted by 67.15 cm-1 relative to the HCN monomer, provides the final significant contribution to the change of intra-molecular vibrational zero-point energy upon HCN dimerization. The combination with the vibrational zero-point energy contribution determined recently for the class of large-amplitude inter-molecular fundamental transitions then enables a complete determination of the total change of vibrational zero-point energy of 3.35±0.30 kJ mol-1 . The new spectroscopic findings together with previously reported benchmark CCSDT(Q)/CBS electronic energies [Hoobler et al. ChemPhysChem. 19, 3257-3265 (2018)] provide the best semi-experimental estimate of 16.48±0.30 kJ mol-1 for the dissociation energy D0 of this prototypical homodimer.

Ab Initio energetics of SiO bond cleavage.

A multilevel approach that combines high-level ab initio quantum chemical methods applied to a molecular model of a single, strain-free SiOSi bridge has been used to derive accurate energetics for SiO bond cleavage. The calculated SiO bond dissociation energy and the activation energy for water-assisted SiO bond cleavage of 624 and 163 kJ mol-1 , respectively, are in excellent agreement with values derived recently from experimental data. In addition, the activation energy for H2 O-assisted SiO bond cleavage is found virtually independent of the amount of water molecules in the vicinity of the reaction site. The estimated reaction energy for this process including zero-point vibrational contribution is in the range of -5 to 19 kJ mol-1 . © 2017 Wiley Periodicals, Inc.

Coordination of N2 and Other Small Molecules to the Phosphorus Centre of RPW(CO)5 : A Theoretical Study on the Janus Facets of the Stabilization/Activation Problem.

Bonding of neutral terminal phosphinidene tungsten(0) complexes stabilized by ligands bound to phosphorus (ligand-to-P) have been studied using a large testbed of predominantly N-ligands. Most complexes (1 a-r,v-z and 2 l) exhibit a pyramidal P centre with a formal single ligand-to-P bond order. Three ligand-to-P complexes (1 s-u) exhibit planar sp2 -hybridization of P and P,N bonds featuring double bond character. All derivatives with C-ligands (1 v,x-z) exhibit a ligand-to-P bond strength intermediate between the P-N single and double bonded species. Remarkably, dinuclear complexes containing CN- (1 p,w), N3- (1 r) and N2 (1-3 t) as bridging ligands between two phosphorus centres show intertwined terminal W(CO)5 fragments. In particular, the case of N2 bridging ligand (1-3 t) represents a noteworthy example of activation, displaying a weakened N,N bond and two sets of very strong P,N double bonds, the latter resembling the activation-picture of dinitrogen by transition metal complexes. Bond dissociation energies (BDEs) of ligand-to-P bonds do not show any correlation with a range of bond strength descriptors, but display some meaningful, roughly linear variation with the ligand softness. Based on Haaland's definition of dative bonding, a reasonable linear correlation of BDE with dativity (d1 ) and the dative covalence energy (DCE1 ) was found. A moderate correlation was also obtained with the vertical ionization potential of the ligand (I(L)) as well as with the ligands HOMO energy.

[Density functional theory investigation on antioxidant activity of five flavonoids from Hebei Xiangju].

Five main flavonoids of Hebei Xiangju were studied using the Density Functional Theory (DFT) B3LYP method with 6-311 G (d) basis set．Their activities were analyzed based on molecular structure,bond dissociation energy (BDE),natural orbital charge distribution (NBO),bond order and the energy gap between HOMO and LUMO. The results showed that the existing of intra molecular hydrogen bond in B ring can improve the antioxidant activity of the flavonoids, at the same time, the hydroxyl groups on the glycosides do not have the activity of eliminating free radicals, but decrease the total molecular antioxidant activity. As a result, the antioxidant ability order of the five flavonoids compounds is luteolin< luteolin-7-O-glucoside< apigenin < acacetin < acacetin-7-O-glucose, which is agreement with the experimental conclusion reported in literature. The results showed that the DFT method can provide theoretical guidance for the selection of natural flavonoid antioxidants.

The Quadruple Bonding in C2 Reproduces the Properties of the Molecule.

Ever since Lewis depicted the triple bond for acetylene, triple bonding has been considered as the highest limit of multiple bonding for main elements. Here we show that C2 is bonded by a quadruple bond that can be distinctly characterized by valence-bond (VB) calculations. We demonstrate that the quadruply-bonded structure determines the key observables of the molecule, and accounts by itself for about 90% of the molecule's bond dissociation energy, and for its bond lengths and its force constant. The quadruply-bonded structure is made of two strong π bonds, one strong σ bond and a weaker fourth σ-type bond, the bond strength of which is estimated as 17-21 kcal mol(-1). Alternative VB structures with double bonds; either two π bonds or one π bond and one σ bond lie at 129.5 and 106.1 kcal mol(-1), respectively, above the quadruply-bonded structure, and they collapse to the latter structure given freedom to improve their double bonding by dative σ bonding. The usefulness of the quadruply-bonded model is underscored by "predicting" the properties of the (3)Σ+u state. C2's very high reactivity is rooted in its fourth weak bond. Thus, carbon and first-row main elements are open to quadruple bonding!

[Density functional theory investigation on antioxidation activity of four flavonoids from Rhododendri Daurici Folium].

Four main flavonoids of the Chinese medicine Rhododendri Daurici Folium were studied using the density functional theory (DFT) B3LYP method with 6-311 + + G (d, p) basis set．Their activities were analyzed based on molecular structure, bond dissociation energy (BDE) and the energy gap between HOMO and LUMO. As a result, the antioxidant ability order of the four flavonoids compounds is farrerol

A coupled-cluster study on the noble gas binding ability of metal cyanides versus metal halides (metal = Cu, Ag, Au).

A coupled-cluster study is carried out to investigate the efficacy of metal(I) cyanide (MCN; M = Cu, Ag, Au) compounds to bind with noble gas (Ng) atoms. The M-Ng bond dissociation energy, enthalpy change, and Gibbs free energy change for the dissociation processes producing Ng and MCN are computed to assess the stability of NgMCN compounds. The Ng binding ability of MCN is then compared with the experimentally detected NgMX (X = F, Cl, Br) compounds. While CuCN and AgCN have larger Ng binding ability than those of MCl and MBr (M = Cu, Ag), AuCN shows larger efficacy toward bond formation with Ng than that of AuBr. Natural bond orbital analysis, energy decomposition analysis in conjunction with the natural orbital for chemical valence theory, and the topological analysis of the electron density are performed to understand the nature of interaction occurring in between Ng and MCN. The Ng-M bonds in NgMCN are found comprise an almost equal contribution from covalent and electrostatic types of interactions. The different electron density descriptors also reveal the partial covalent character in the concerned bonds.

Relativistic state-specific multireference perturbation theory incorporating improved virtual orbitals: Application to the ground state single-bond dissociation.

Using four-component (4c) relativistic spinors, we present a computationally economical relativistic ab initio method for molecular systems employing our recently proposed second-order state-specific multireference perturbation theory (SSMRPT) incorporating the improved virtual orbital-complete active space configuration interaction (IVO-CASCI) reference wavefunction. The resulting method, 4c-IVO-SSMRPT [calculate one state at a time] is tested in pilot calculations on the homonuclear dimers including Li(2), Na(2), K(2), Rb(2), F(2), Cl(2), and Br(2) through the computations of the ground state potential energy curves (PECs). As SSMRPT curbs intruder effects, 4c-IVO-SSMRPT is numerically stable. To our knowledge, the SSMRPT in the 4c relativistic framework has not been explored in the past. Selective spectroscopic constants that are closely related to the correct shape and accuracy of the energy surfaces have been extracted from the computed PECs. For the halogen molecules, a relativistic destabilization of the bond has been found. Relativistic and electron correlation effects need to be incorporated to get reliable estimates. Our results are in good accordance with reference theoretical and experimental data which manifests the computational accuracy and efficiency of the new 4c-IVO-SSMRPT method. The method opens for an improved description of MR systems containing heavy elements. The inexpensiveness of IVO-CASCI makes 4c-IVO-SSMRPT method promising for studies on large systems of heavy elements.