Low Bond Dissociation Energy Research Articles

Novel silylphenol antioxidants by density functional theory

AbstractWe have scrutinized five novel silylphenol antioxidants, including 2‐silylphenol (1), 4‐silylphenol (2), 2,6‐disilylphenol (3), 2,4‐disilylphenol (4), and 2,4,6‐trisilylphenol (5), at M06/6–311++G** level of theory. To evaluate the antioxidant efficiency, the electronic effects on O─H bond dissociation energy (BDE) and vertical ionization potential (IPv) of 1–5 are investigated, which are mainly governed by electronic effects. The conductor‐like polarized continuum model (CPCM) is applied to measure the antioxidant capacity in the solution phase. The results show that antioxidants with the lowest BDE and IPv values can efficiently act via hydrogen atom transfer (HAT) and single electron transfer (SET) mechanisms, respectively. The stability of resulting radicals is measured by nucleus independent chemical shift (NICS) index, natural bond orbital (NBO) analysis, and nucleophilicity (N) index. The BDE shows lower values in the gas phase with respect to water, while water exhibits lower IPv values than gas. Structure 5 turns out as the most efficient antioxidant. The overall order of antioxidant efficiency in both gas and water phases is 5 > 2 > 3 > 4 > 1.

Efficient C-H Amination Catalysis Using Nickel-Dipyrrin Complexes.

A dipyrrin-supported nickel catalyst (AdFL)Ni(py) (AdFL: 1,9-di(1-adamantyl)-5-perfluorophenyldipyrrin; py: pyridine) displays productive intramolecular C-H bond amination to afford N-heterocyclic products using aliphatic azide substrates. The catalytic amination conditions are mild, requiring 0.1-2 mol% catalyst loading and operational at room temperature. The scope of C-H bond substrates was explored and benzylic, tertiary, secondary, and primary C-H bonds are successfully aminated. The amination chemoselectivity was examined using substrates featuring multiple activatable C-H bonds. Uniformly, the catalyst showcases high chemoselectivity favoring C-H bonds with lower bond dissociation energy as well as a wide range of functional group tolerance (e.g., ethers, halides, thioetheres, esters, etc.). Sequential cyclization of substrates with ester groups could be achieved, providing facile preparation of an indolizidine framework commonly found in a variety of alkaloids. The amination cyclization reaction mechanism was examined employing nuclear magnetic resonance (NMR) spectroscopy to determine the reaction kinetic profile. A large, primary intermolecular kinetic isotope effect (KIE = 31.9 ± 1.0) suggests H-atom abstraction (HAA) is the rate-determining step, indicative of H-atom tunneling being operative. The reaction rate has first order dependence in the catalyst and zeroth order in substrate, consistent with the resting state of the catalyst as the corresponding nickel iminyl radical. The presence of the nickel iminyl was determined by multinuclear NMR spectroscopy observed during catalysis. The activation parameters (ΔH‡ = 13.4 ± 0.5 kcal/mol; ΔS‡= -24.3 ± 1.7 cal/mol·K) were measured using Eyring analysis, implying a highly ordered transition state during the HAA step. The proposed mechanism of rapid iminyl formation, rate-determining HAA, and subsequent radical recombination was corroborated by intramolecular isotope labeling experiments and theoretical calculations.

A DFT study of cis-[Ru(NO)(NO2)bpy(dye)2]n+ complexes as NO donors

The synthesis and characterization of a new complex, cis-[Ru(NO)(NO2)bpy(AO)2](PF6)2, was reported, and the release of NO from ruthenium-nitrosyl complexes with dye ligands was investigated using DFT and TDDFT methods. The complexes are cis-[Ru(NO)(NO2)bpy(dye)]n+, where the dye is either proflavine (1), acridine orange (2), neutral red (3), resorufin (4), thionol (5), or methylene violet (Bernthsen) (6). The optimized structures are in agreement with the experimental data of analogue complex from the literature. Simulated UV–Visible spectrum of complex 2 showed good agreement with the experimental results. The calculated electron affinities (EA) indicated that the N-coordinated complexes 1–3 should be more easily reduced and that this reduction weakens the Ru–NO bond, thus facilitating the NO release. Reduced complexes (Ru-NO0) presented lower bond dissociation energies (BDE) than the complexes (Ru-NO+). Complexes 1–3 showed the lowest BDE. This suggests a lower energy cost to release NO, and therefore, the N-coordinated complexes are the most promising NO donors among the investigated complexes.

The hydrogen transfer reaction between the substance of triplet state thioxanthone and alkane with sp3 hybridization hydrogen.

The activation or functionalization of the saturated C-H is an extremely active field at present. We have explored the triplet state thioxanthone in reactivity of the hydrogen transfer reaction between donors and acceptors. In our works, two donors with quasi-inert sp3 C-H of skipped diene (3,6-nonadiene) and cyclic acetals (benzodioxole) reacted with type II photoinitiators (triplet state of thioxanthone series, TXs) as acceptors are investigated. The excited energies of TXs were obtained by time-dependent density functional theory (TD-DFT). TXs show obvious photosensibility based on their low reorganization energies (< 60kcalmol-1). The isoentropy reactions had linear geometries of transition state (TS). The distortion/interaction model was used to probe the existence of interaction between acceptors and donors in saddle point. The distortion energy and activation barrier of benzodioxole are much higher than those of the corresponding 3,6-nonadiene. The lower bond dissociation energy noticeably affect the transition state. The reaction of triplet state of TXs with skipped dienes were found to have an anomalous low tunneling factors by using Wigner correction and early transition state by using the bond-energy-bond-order method. The triplet state of TXs photoinitiator can induced the hydrogen abstraction from saturated cyclic acetals and the skipped alkadienes. The hydrogen abstraction experiment are confirmed by UV and real-time FTIR.

Investigation into the reaction mechanism underlying the atmospheric low-temperature plasma-induced oxidation of cellulose

Atmospheric low-temperature plasma has been widely applied in surface modification of lignocellulose for manufacturing lightweight, strong composites. This study is aimed at elaborating the structural changes of cellulose after plasma treatment and further understanding the mechanism underlying plasma-induced oxidation of cellulose. Experiments suggested that atmospheric low-temperature plasma exhibits strong capacity to cleave covalent bonds, leading to oxidation and degradation of cellulose. Theoretical analysis revealed that cleavage of C4O covalent bond is the first-step reaction during plasma-induced oxidation due to its low bond dissociation energy (229.2 kJ mol−1). Subsequent pyranose ring-breaking reaction dominates dynamically and thermodynamically. Obtained outcomes are vital for fundamentally understanding the plasma-lignocellulose interaction. On that basis, plasma treatment for activation and oxidation of lignocellulose can be optimized and designed for improved efficiency. Wettability of lignocellulose can be thus improved in a short time, providing an opportunity to manufacture lignocellulose-based composites with enhanced efficiency and mechanical properties in future.

Highly efficient and irreversible removal of cadmium through the formation of a solid solution

Sulfur-containing materials are very attractive for the efficient decontamination of some heavy metals. However, the effective and irreversible removal of Cd2+, coupled with a high uptake efficiency, remains a great challenge due to the relatively low bond dissociation energy of CdS. Herein, we propose a new strategy to overcome this challenge, by the incorporation of Cd2+ into a stable ZnxCd1-xS solid solution, rather than into CdS. This can be realised through the adsorption of Cd2+ by ZnS nanoparticles, which have exhibited a Cd2+ uptake capacity of approximate 400 mg g−1. Through this adsorption mechanism, the Cd2+ concentration in a contaminated solution could effectively be reduced from 50 ppb to <3 ppb, a WHO limit acceptable for drinking water. In addition, ZnS continued to exhibit this noteworthy uptake capacity even in the presence of Cu2+, Pb2+, and Hg2+. ZnS displayed high chemical stability. Particles aged in air for 3 months still retained a> 80% uptake capacity for Cd2+, compared with only 9% uptake capacity for similarly-aged FeS particles. This work reveals a new mechanism for Cd2+ removal with ZnS and establishes a valuable starting point for further studies into the formation of solid solutions for hazardous heavy metal removal applications.

Characteristics of Oxide TFT Using Carbon-Doped Ιn2O3 Thin Film Fabricated by Low-Temperature ALD Using Ethylcyclopentadienyl Indium (Ιn-EtCp) and H2O & O3

Introduction In2O3-based metal oxide semiconductors have been widely investigated as active channel materials for oxide thin film transistors (TFTs) in flexible devices. The bond dissociation energy (BDE) between metal and oxygen element in the In2O3-based metal oxide has been recently focused because a low BDE easily occurs excess oxygen vacancy (Vo) and results in metal like conductor. In-Ti-O, In-Si-O, and In-Si-C-O have been studied in attempts to suppress Vo by a high BDE such as Ti-O (667 kJmol-1), Si-O (779 kJmol-1), and C-O (1076 kJmol-1) [1, 2]. In2O3 is an especially promising material because of a simple binary metal oxide and a high carrier mobility (~ 65 cm2V-1s-1). PET film was generally employed as substrate for flexible devices and limited to a fabrication process temperature below 200 °C. Considering to this process temperature, atomic layer deposition (ALD) technique is essentially suitable to produce the In2O3 films, and many In compounds such as InCl3, TMIn, In(tmhd)3, InCp, and InEtCp have been employed as precursors [3]. As-grown In2O3 film generally exhibited metal-like conductor because of excess Vo into the In2O3 film [4]. To compensate Vo sites in as-grown In2O3 film, the post-metal deposition annealing (PMA) process in air, O2, and O3 was employed during final process of TFT fabrication. However, the PMA was generally carried out at a high temperature above 300 °C [4]. In this paper, we studied growth of In2O3 films as a function of InEtCp and H2O/O3 doses using ALD at 150 °C with InEtCp precursor and H2O/O3 gas. We also demonstrate transistor performance of carbon-doped In2O3 (In-O-C) TFT with SiO2/Al2O3 dielectric after PMA at 150 °C in O3 gas. Experiment The In2O3 films were typically deposited on Si/SiO2 substrates by ALD at 150 °C using InEtCp and H2O/O3. The thickness of the In2O3 films as a function of InEtCp and H2O/O3 doses were measured using a spectroscopic ellipsometer. The chemical bonding state, carbon content and O/In ratio of the In2O3 films were also analyzed by XPS. Back-gate-type In-O-C TFTs were fabricated as follows: Firstly, a 5-nm-thick Al2O3 films deposited on p++Si/SiO2 (250 nm) by ALD using trimethylaluminium precursor and O3 gas. Next, a 5-nm-thick In-O-C channel layer was deposited on the Al2O3 films by the same ALD condition at 150 °C, and subsequently patterned by lithographic process. Ti/Au source and drain electrodes were deposited. Finally, PMA was performed at 150 °C in O3 for 0-150 min. Results and Discussion At first the In2O3 film thickness as a function of H2O/O3 dose per pulse was measured while the InEtCp dose was 2.8×10-5 mol by ALD at 150 °C. The thickness of the In2O3 film was saturated when H2O/O3 was 0.9×10-4/2.9×10-3 mol (an inset graph of Fig. 1). According to this ALD condition, the film thickness as a function of number of ALD cycle was examined and the estimated growth per cycle (GPC) was 0.11 nm/cycle as shown in Fig. 1. The In2O3 films had a carbon content and O/In ratio were about 1.7 at.% and 1.2/1 (InO1.16C0.04), respectively, by XPS (not shown). The electrical properties of InO1.16C0.04 TFT changed dramatically from metal like conductor to semiconductor for PMA time between 0 and 90 min. Threshold voltage (V th) shifted from 4.1 to 4.3 V as PMA time increases from 90 to 150 min. Figure 2 shows the I d-V d characteristics of InO1.16C0.04 TFTs (L/W = 50/5 μm) after PMA for 150 min. The I d was linearly increased at low V d, indicating that ohmic contacts were consistently formed between the InO1.16C0.04 films and the source-drain electrodes. I d also shows saturation at a high V d, which indicates that the electron transport in the channel is well controlled by the V g. The TFT exhibited superior transistor performance such as relatively small S.S. of 0.37 V/decade, a small V th shift of +0.3 V, and a large μ FE of 20.4 cm2/Vs. This is due to the suppression of excess Vo in InO1.16C0.04 channel layer. Conclusions We studied characteristics of as-grown In2O3 films and its InO1.16C0.04 TFT. The excellent characteristics of InO1.16C0.04 TFT, which was fabricated even in a low temperature fabrication process at 150 °C, could be obtained due to the carbon doping into In2O3 film and relatively strong oxidation strength of O3 during PMA.

Gold-Catalyzed C-H Functionalization with Aryl Germanes.

The development of orthogonal Csp2–Csp2 coupling regimes to the omnipresent Pd-catalysis class would enable an additional dimension of modularity in the construction of densely functionalized biaryl motifs. In this context, the identification of potent functional groups for selective transformations is in high demand. Although organogermanium compounds are generally believed to be of low reactivity in homogenous catalysis, this report discloses the highly efficient and orthogonal reactivity of aryl germanes with arenes under gold catalysis. The method is characterized by mildness, the employment of an air- and moisture-stable gold catalyst, and robustness. Our mechanistic studies show that aryl germanes are highly reactive with Au(I) and Au(III). Our computational data suggest that the origin of this reactivity primarily lies in the relatively low bond dissociation energy and as such low distortion energy to reach the key bond activating transition state.

Bismuth Compounds in Radical Catalysis: Transition Metal Bismuthanes Facilitate Thermally Induced Cycloisomerizations.

The controlled radical chemistry of bismuth compounds is still in its infancy. Further developments are fueled by the properties of these complexes (e.g., low toxicity, high functional group tolerance, low homolytic bond dissociation energies, and reversible homolytic bond dissociations), which are highly attractive for applications in synthetic chemistry. Here we report the first catalytic application of transition metal bismuthanes (i.e. compounds with a Bi-TM bond; TM=transition metal). Using the catalyzed radical cyclo-isomerization of δ-iodo-olefins as a model reaction, characteristics complementary or superior to known B, Mn, Cu, Zn, Sn, and alkali metal reagents are demonstrated (including a different crucial intermediate), establishing transition metal bismuthanes as a new class of (pre-)catalysts for controlled radical reactions.

Fast pyrolysis of guaiacol to simple phenols: Experiments, theory and kinetic model

This study is focused on both experimental and theoretical analysis of fast pyrolysis of guaiacol, a major pyrolysate and a model monomeric compound of lignin. Fast pyrolysis experiments were performed in an analytical pyrolyzer coupled with gas chromatograph/mass spectrometer in the temperature range of 450–650 °C. Thermodynamics and kinetics of 19 elementary reactions of 17 species were investigated using quantum chemical density functional theory calculations. Reaction pathways for the formation of four major phenols, viz. phenol, catechol, o-hydroxybenzaldehyde and o-cresol, were proposed. The homolytic cleavage of OCH3 bond, with low bond dissociation energy of 57.7 kcal/mol, is shown to be the primary reaction for the generation of free radicals. The generation of o-hydroxyphenyl radical is found to be vital for the formation of phenol and cresol, while o-hydroxybenzyloxy radical is the key intermediate for the formation of o-hydroxybenzaldehyde. Multiple pathways for the formation of catechol were evaluated. A kinetic model was developed using the elementary reactions and their Arrhenius rate parameters. The concentration of the major products at different temperatures obtained from the model reasonably matched the trends in product yields from the experiments.

Photoredox-Mediated Generation of gem-Difunctionalized Ketones: Synthesis of α,α-Aminothioketones.

A photoredox-mediated gem-difunctionalization of alkynes leading to the synthesis of α,α-aminothio-substituted carbonyl compounds is reported. The work presents concomitant introduction of α-C-N and C-S bonds as a key enabling advance. Furthermore, the low bond dissociation energy of the C-S bond compared to that of C-N or C-C bonds has been exploited for selective functionalization using different nucleophiles to build diverse α,α-disubstituted carbonyl scaffolds. Mild reaction conditions, broad substrate scope, and good yields are some of the added advantages of this reaction.

Antioxidant Motifs in Flavonoids: O-H versus C-H Bond Dissociation.

Flavonoids provide potential health benefits due to their antioxidant properties. The antioxidant activity of natural flavonoids is primarily exerted by phenolic hydroxyl groups; however, C–H bonds also contribute to these properties. In this study, the contributions of phenolic groups and C–H bonds to the antioxidant properties of 13 flavonoids were investigated by using the (RO)B3LYP/6-311++G(2df,2p)//B3LYP/6-311G(d,p) model chemistry in the gas phase and water and ethanol solvents. It was found that the C–H bonds have lower bond dissociation energies than O–H bonds in the 4-carbonyl and/or 3-hydroxyl group containing flavonoids and hence define antioxidant activity. The HOO· radical scavenging of the selected flavonoids is also investigated in detail through the potential energy surface, natural bond orbitals, and kinetic calculations. It was found that the favored radical scavenging mechanism of the flavonoids is hydrogen atom transfer, with the gas phase rate constants in the range of 7.23 × 103–2.07 × 109 L·mol–1·s–1. The results suggest that the flavonoids, isomelacacidin, isoteracacidin, melacacidin, and teracacidin, have antioxidant properties as high as typical phenolic compounds such as quercetin, trans-resveratrol, trolox, and ascorbic acid.

Modular and Processable Fluoropolymers Prepared via a Safe, Mild, Iodo-Ene Polymerization.

Fluoropolymers have infiltrated society as coatings and insulators. However, low processability, few opportunities for polymer functionalization, and explosive monomers hampering academic investigation of these materials have precluded the extension of the unique properties of perfluorocarbons to the cutting edge of material science. Here, we present semifluorinated iodo–ene polymers as a scaffold to overcome fluoropolymer limitations. A sodium dithionate initiated polymerization of perfluorodiiodides and dienes allows for high-molecular-weight polymers (>100 kDa) to be prepared in the presence of oxygen and water with up to 59 wt % fluorine content. These conditions are sufficiently mild to enable the polymerization of functional dienes, leading to biodegradable fluoropolymers. The iodo–ene polymerization results in the addition of polarizable iodine atoms, which improve polymer processability; yet, these atoms can be removed after processing for enhanced stability. Displacement of the iodine atoms with thiols or azides facilitates covalent surface modification and cross-linking. Finally, the low bond dissociation energy of the C–I bond allows allyl group addition as well as photo-cross-linking. Collectively, the simple synthesis and modular nature of the semifluorinated iodo–ene polymers will enable the convergence of perfluorocarbons and advanced materials.

Ultralow-intensity NIR light triggered on-demand drug release by employing highly emissive UCNP and photocleavable linker with low bond dissociation energy.

Background: The design of novel nanoparticles with higher therapeutic efficacy and lower side effects, is still difficult but encouraging in cancer therapy. Specifically, for upconversion nanoparticles (UCNP)-based drug release, a high intensity of NIR light (1.4~5.0 W/cm2) above the maximum permissible exposure (0.33 W/cm2 for 980 nm) is commonly used and severely limits its practical application.Methods: The highly emissive UCNP is first synthesized and then coated with mesoporous silica (MS) shell (UCMS). Next, the surface of UCMS is modified with the thioether (-S-BP) linker, leading to UCMS-S-BP nanoparticles. Finally, after the drug doxorubicin (Dox) is loaded into the pore channels of UCMS, the pore openings are blocked by the β-cyclodextrin (β-CD) gatekeeper through the association with the -S-BP linker (UCMS(Dox)-S-BP@β-CD).Results: Upon 980 nm NIR light irradiation with an ultralow intensity of 0.30 W/cm2, it is found that the loaded Dox can be released through the cleavage of thioether linkers triggering dissociation of β-CD gatekeepers. The in vitro results exhibited significantly therapeutic efficacy with 85.2% of HeLa cells killed in this study.Conclusions: An ultralow-intensity NIR light triggered on-demand drug release system has been developed by employing highly emissive UCNP and photocleavable linker with low bond dissociation energy to avoid the potential photodamage on healthy neighbor cells.

Defluorination of Per- and Polyfluoroalkyl Substances (PFASs) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management.

This study investigates critical structure-reactivity relationships within 34 representative per- and polyfluoroalkyl substances (PFASs) undergoing defluorination with UV-generated hydrated electrons. While C nF2 n+1-COO- with variable fluoroalkyl chain lengths ( n = 2 to 10) exhibited a similar rate and extent of parent compound decay and defluorination, the reactions of telomeric C nF2 n+1-CH2CH2-COO- and C nF2 n+1-SO3- showed an apparent dependence on the length of the fluoroalkyl chain. Cross comparison of experimental results, including different rates of decay and defluorination of specific PFAS categories, the incomplete defluorination from most PFAS structures, and the surprising 100% defluorination from CF3COO-, leads to the elucidation of new mechanistic insights into PFAS degradation. Theoretical calculations on the C-F bond dissociation energies (BDEs) of all PFAS structures reveal strong relationships among (i) the rate and extent of decay and defluorination, (ii) head functional groups, (iii) fluoroalkyl chain length, and (iv) the position and number of C-F bonds with low BDEs. These relationships are further supported by the spontaneous cleavage of specific bonds during calculated geometry optimization of PFAS structures bearing one extra electron, and by the product analyses with high-resolution mass spectrometry. Multiple reaction pathways, including H/F exchange, dissociation of terminal functional groups, and decarboxylation-triggered HF elimination and hydrolysis, result in the formation of variable defluorination products. The selectivity and ease of C-F bond cleavage highly depends on molecular structures. These findings provide critical information for developing PFAS treatment processes and technologies to destruct a wide scope of PFAS pollutants and for designing fluorochemical formulations to avoid releasing recalcitrant PFASs into the environment.

ANTIOXIDANT POTENTIAL OF FIVE COMPOUNDS EXTRACT FROM THE MARINE FUNGUS ASPERGILLUS FLOCCULOSUS BY DFT METHOD: HAT AND SET MECHANISM.

Antioxidant potential of five compounds include ochraceopone F (1), aspertetranone D (2), cycloechinulin (3), wasabidienone E (4) and mactanamide (5) in the extracts from marine fungus Aspergillus flocculosus in Nha Trang was investigated by computational chemistry methods. All calculations were performed at the theoretical level M05-2X/6-311++G(d, p)//M05-2X/6-31+G(d) in the gas phase. The physicochemical properties such as bond dissociation energies (BDE), ionization energies (IE), electron affinity (EA) characterizing HAT (Hydrogen atom transfer) and SET (Single electronic transfer) antioxidant mechanisms were calculated.As a result, the H-atom donating ability of the studies compounds increases in the descending order of BDE value (1) &gt; (2) &gt; (3) &gt; (4) » (5). Wherein the compounds (4) and (5) represent as the most potential antioxidant with the lowest BDE in the gas phase being 74.9 and 75.1 kcal/ mol. Moreover, the electronic donating ability of the compounds increases as function of the descending order of IE value (2) &gt; (1) &gt; (5) &gt; (3) &gt; (4). And the electron accepting abitlity decreases in decreasing EA value (4) &gt; (3) &gt; (2) &gt; (5) &gt; (1). Compound (4) (wasabidienone E) has the smallest IE value of 6.56 eV and has the largest EA value of 2.33 eV.

Evaluation of Polar Effects in Hydrogen Atom Transfer Reactions from Activated Phenols.

Evaluation of polar effects in hydrogen atom transfer (HAT) processes is made difficult by the fact that in most cases substrates characterized by lower bond dissociation energies (BDEs), activated from an enthalpic point of view, are also more activated by polar effects. In search of an exception to this general rule, we found that the introduction of a methoxy substituent in the 3-position of 2,6-dimethylphenol results in a small increase in the O-H BDE and a decrease of the ionization potential of the phenol. These findings suggest that the enthalpic effect associated with the addition of the m-methoxy group to 2,6-dimethylphenol will decrease reaction rates, while the polar effects will increase reaction rates. Our model analysis of polar effects has been experimentally validated by comparing the reactivity of 2,6-dimethylphenol with that of 2,6-dimethyl-3-methoxyphenol in HAT promoted by a series of radicals (cumyloxyl, galvinoxyl, 2,2-diphenylpycrylhydrazyl, phthalimide- N-oxyl, and benzotriazole- N-oxyl radicals). In line with our predictions, the ratio of HAT rate constants ( kH mOMe/ kHH) is larger in cases where there is a greater contribution of polar effects in the HAT reaction, i.e., in HAT promoted by N-oxyl radicals containing electron-withdrawing groups or when more polar solvents are employed.

Theoretical Studies on the Electronic Structure Parameters and Reactive Activity of Neu5Gc and Neu5Ac under Food Processing Solvent Environment.

The animal product hazard factor N-glycolylneuraminic (Neu5Gc) and brain nutrient substance N-acetylneuraminic acid (Neu5Ac) were studied at the M062X/6-311 + G(d,p) geometry optimization level. We considered the electronic structure parameters with different solvents: (benzene ε = 2.27, acetic acid ε = 6.25, ethanol ε = 24.85, lactic acid ε = 22.00, formic acid ε = 51.1, water ε = 78.35). The maximum molecular surface electrostatic potentials, which were 62.77 for Neu5Gc and 60.90 kcal/mol for Neu5Ac, are both located on the carboxyl group hydrogen. The orbital analysis showed that the amide group and carboxyl group confer the sites with susceptibility to nucleophilic and electrophilic attack, respectively. The solvent effect showed that polar solvents, such as formic acid and water, can enhance the two molecules’ nucleophilic activity. To better understand the roles of the hydroxyl group in the two molecules, the independent gradient model theory confirmed the four intramolecular hydrogen bonds of Neu5Gc at gas phase, whereas Neu5Ac only has two. The lowest bond dissociation energy in solvent occurs at O7-H, which is 104.03 kcal/mol in water for Neu5Gc and 104.57 kcal/mol in lactic acid for Neu5Ac. The lowest proton affinity value for Neu5Gc (20.34 kcal/mol) and Neu5Ac (20.76 kcal/mol) was both occur at the carboxyl group O6-H under ethanol. The antioxidant mechanisms of the two sialic acid are prone to sequential proton-loss electron transfer under polar or non-polar solvents.

Carbon‐centered radical initiators for polymerization of unsaturated monomers: Modeling and reactivity studies

A series of sterically encumbered diphenylethane molecules was examined to understand their fundamental ability to undergo homolytic bond cleavage and initiate radical polymerization of unsaturated monomers. The structures computed by density functional theory (DFT) showed a relationship between increasing C‐C bond length of the ground state molecule and reduced bond dissociation energy (BDE). The computed activation barriers associated with radical addition to acrylate were relatively low indicating that once radicals were formed, initiation of polymerization would be facile. Good correlations between computed BDE and experimentally‐determined onset temperatures for acrylate polymerization were found. The Molecule (13) with the lowest BDE (33.8 kcal/mol) determined in this work had an onset temperature of 85 °C. Ethylene polymerization failed to show a similar trend as molecules possessing the weakest C‐C bonds did not effectively initiate ethylene polymerization. Theoretical calculations demonstrated a trend in which the molecules with the lowest BDEs had the highest barriers for addition of ethylene. These barriers were significantly higher than standard peroxide initiation or chain propagation. Upon ramping the temperature, it is postulated that molecules with low BDE values form radicals but do not have sufficient energy to add to ethylene before succumbing to detrimental side‐reactions. POLYM. ENG. SCI., 59:E52–E58, 2019. © 2018 Society of Plastics Engineers

Reductive Defluorination of Branched Per- and Polyfluoroalkyl Substances with Cobalt Complex Catalysts

This study investigates structure–reactivity relationships within branched per- and polyfluoroalkyl substances (PFASs) undergoing cobalt-catalyzed reductive defluorination reactions. Experimental results and theoretical calculations reveal correlations among the extent of PFAS defluorination, the local C–F bonding environment, and calculated bond dissociation energies (BDEs). In general, BDEs increase in the following order: tertiary C–F bonds < secondary C–F bonds < primary C–F bonds. A tertiary C–F bond adjacent to three fluorinated carbons (or two fluorinated carbons and one carboxyl group) has a relatively low BDE that permits an initial defluorination to occur. Both a biogenic cobalt–corrin complex (B12) and an artificial cobalt–porphyrin complex (Co-PP) are found to catalytically defluorinate multiple C–F bonds in selected PFASs. In general, Co-PP exhibits an initial rate of defluorination that is higher than that of B12. Neither complex induced significant defluorination in linear perfluorooctanoic...