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The effect of octahedral cage-structured polyhedral oligomeric silsesquioxane (POSS) on the cathode catalyst layer (CCL) for polymer electrolyte membrane fuel cells (PEMFCs) is investigated via molecular dynamics simulations. A model of CCL is constructed consisting of Pt/C substrate/ionomer–POSS/water–gas. The pair correlation function analysis shows that the dense cover of ionomer chains on the Pt surface and the interaction between sulfonate groups and water molecules are weakened by POSS. At high hydration, the effective water content in the ionomer–POSS phase is drastically reduced with increasing POSS content. Interestingly, at low hydration, the effective water content is slightly improved as the POSS content increases. This water retention effect is probably due to the trapping of water molecules in the POSS cage. The diffusion coefficients of O2 and H3O+ are effectively increased. The method of inserting nanocages into ionomer can avoid the formation of a high-density ionomer film at the Pt/ionomer interface. Moreover, POSS-modified CCLs possess a self-balance of water content, thus achieving enhanced multicomponent transport involving proton, water, and oxygen transfer. It provides a strategy for designing high-performance PEMFC, particularly for fuel cell vehicles due to the self-balance property under changing humidity. [ABSTRACT FROM AUTHOR]

Research has been conducted on conjugate anions. The equilibrium acidities and oxidation potentials of these anions in dimethyl sulfoxide have been investigated and the details are reported.

Research was conducted to examine the role of adjacent onium cations and remote substituents on the H-A+ bond equilibrium acidities in dimethyl sulfoxide solution. The study is an extension of previous investigation on ylide thermodynamic stability scale and its implication for the importance of resonance effect on ylide stabilities. Results suggest that part of the stabilization in the phosphonium and sulfonium ylide cases arises from the backbonding stabilization involving the o* and/or 3d orbital participation.

Research was conducted to determine the influence of enolization enthalpies at 0 and 298 K for nine aliphatic carbonyl and nine aliphatic thiocarbonyl compounds using ab initio complete basis set fourth-order model calculations. Results reveal lower enolization enthalpies for the thiocarbonyl compounds because of higher thioenol tautomer concentrations compared to the corresponding carbonyl compounds. On the other hand, the enolization enthalpies for the cycloketones and thiocycloketones relied upon the size of the cyclic ring.

Free energy data for C-H heterolysis to carbenium ion and hydride in solution was obtained for a series of compounds using a new thermodynamic cycle based on gas-phase C-H bond dissociation enthalpy (BDE). The BDE of the H-R bond in the gas phase was used to calculate the Gibbs free energy for the homolytic cleavage of the bond in solution. Dimethyl sulfoxide and MeCN data for hydride transfer was also compared.

Research was conducted to evaluate the radical substituent effects of fluorine and trifluoromethyl groups from the computed C-H homolytic bond dissociation enthalpies of 30 fluorinated compounds. Results showed a strengthening of the sp(super 3) C-H bond with the introduction of three alpha-fluorine substituents. However, the entry of one or two substituents resulted in the weakening of C-H bond strength due to resonance delocalization.

An investigation of the bond dissociation enthalpies (BDEs) of the C-H bonds adjacent to various radical centers derived from 11 saturated hydrocarbons revealed that these were 33.5 +/- 3 kcal/mol at 298 K. While the BDEs of the C-H bonds beside nine allylic and benzylic radical centers were found to be 48 +/- 3 kcal/mol at 298 K, those adjacent to the benzylic PhCH2CH2* radical was only 29.7 and 30.5 kcal/mol at 0 and 298 K, respectively. Those of vinylic C-H bonds near four vinylic and three allylic radical centers were found to be 35.5 +/- 3.5 kcal/mol and 56.5 +/- 3 kcal/mol both at 298 K, respectively.

The electron transfer reaction mechanism for the ozonations of ammonia, amines, annilines, and p-phenylenediamines was investigated through analysis of oxidation potentials using conventional cyclic voltammetry. Results have shown that the ozonation rate constants for aromatic compounds were relatively smaller than for olefinic compounds due to the larger activation energies required for catalysis of the aromatic ring. The destruction of the aromatic ring was required to generate the radical cations.

The impact of alpha-triphenylphosphonium substituents on equilibrium acidities and homolytic bond dissociation enthalpies is studied in six P-(para-substituted benzyl)triphenylphosphonium cations and analogous cations. The alpha-triphenylphosphonium groups on the acidic C-H bonds has an acidifying effect of ca 25pKHA units or 34 kcal/mol. Incorporation of 4-nitro, 4-bromo, 4-cyano electron-withdrawing groups into the para position of the benzyl ring in p-GC6H4CH2PPh3+ cations enhances the equilibrium acidity as opposed to the addition of 4-ethoxy electron-donating group.

The general rule that the decrease in ground state energies in weak acids tends to increase the BDEs of acidic H-A bonds, and vica versa, is seen by testing the effect of the structural changes on the BDEs of the N-H bonds in DMSO. The association of progressive decreases in ground state energies in the relation ketone > ester > amide may be the cause for the BDEs' increase.

Incorporation of Me3Si group or Ph3Si group into the 9-position of fluorene and into the methyl group of PhSO2CH3 increases the acidity of these substrates. Stabilization of anions due to polarizability effects of these silyl groups and relief of steric strains upon deprotonation to form the carbanions account for the increase in acidity. Introduction of Me3Si, Et3Si or Ph3Si groups into the 9-position of fluorene or incorporation of alpha-Me3Si group into the methyl group of PhSO2CH3 leads to small increase in bond dissociation energy, indicating that these groups exert little destabilizing effects on adjacent radicals. Acidity is significantly increased by the incorporation of two Me3Si groups.

Analyses of homolytic bond dissociation enthalpies (BDEs) of O-H bonds in phenols and S-H bonds in thiophenols show that M- and P-electron withdrawing substituents decrease the ground-state energies, which increases BDEs in the order S-H < N-H < O-H. Paradonor groups stabilize the radicals to decrease BDEs of the acidic H-A bonds. Oxidation potentials of various O-, M- and P-substituted thiophenols exhibit a linear relationship with their pKHA.+ values.

A combination of the equilibrium acidities of weak acids with the oxidation potential of the acid and those of the corresponding A(super -) anions, A(super -) radicals, and HA(super +) radical cations enables the estimation of the acidities of HA(super 2+)-type dications. The instability of the radical cation prevents the measurements of the oxidation potential by cyclic voltammetry. The oxidation potentials of three acids are measured and examined.

Homolytic bond dissociation enthalpies of HA(super .+) radical cations are slightly lower than those of the parent HA nitrogen or oxygen acids when the atom A is oxygen or nitrogen. When the atom A is carbon the values are 30 to 50 kcal lower than those of their parents. The variation is due to the lower stabilities of the cation products in the N-H or O-H acids. Hypovalency in nitrogen cations and oxygen cations is increased by the greater nuclear charges.

Homolytic bond dissociation energy estimates for acidic C-H bonds in weak acid families facilitate an analysis of their polarizability effects. The 9-alkylfluorene family reveals a decrease in acidity due to steric hindrance. The R group in RCH2, R, RS, RSO2, RO and R2N have progressively increasing anion stabilizing polarizabilities that induce the acidity decreases.

Equilibrium acidity studies of P-substituted triphenyl-phosphonium cations reveal that their acidifying effects on adjacent C-H bonds average approximately 29 kilocalories per mole (kcal per mole). This is about 6 Kcal per mole greater than the corresponding value for alpha-pyridinium groups. Field and polarizability effects cause the increased acidity value in triphenylphosphonium cations.

Estimates of bond dissociation energies (BDEs) of acidic H-A bonds in HA+ radical cations and in HA- radical anions in DMSO solution reveal that the DMSO solution cleavage path d competes with the radical anion's acid H-A bond cleavage by path c. Path d represents HA-radical anion-based acidic H-A bond cleavage through hydride ion loss and A radical. The BDEs are calculated using a thermodynamic cycle-based equation.

The effects of the alpha-Me3N+ andalpha-PyN+ groups on equilibrium acidities were determined, specifically their effects on carbon-acid substrates such as acetone, diethyl malonate, fluorene, 2-(phenyl-sulfonyl)fluorene, toluene, p-(phenylsulfonyl)toluene and others. Thetrimethylammonium and pyridinium groups had acidifying effects on the adjacent C-H bonds associated with coulombic stabilization of the negative charge by positive charges on the nitrogen atom. Pyridinium groups had opposite effects on adjacent radicals because they caused destabilization.

Bond dissociation energies of the acidic C-H bonds in 13 alpha-substituted 9-mehtylanthracenes and 11 10-substituted methylanthracenes. This included equilibium acidity (pKHA), reduction potential Ere(HA), oxidation potential Eox(HA), and oxidation potential of conjugate anions Eox(A-) in dimethyl sulfoxide solution. Equilibrium acidities were linearly correlated with Hammettsigma negative constants. Combinations of equilibrium acidities were used to determine homolytic bond dissociation energies.

An approach for the estimation of homolytic bond dissociation energies of the benzylic C-H bonds in radical anions and radical cations is developed. The method is employed for radical anions derived from 19 fluorines, 15 triphenylmethanes, p-nitrotoluene, diphenylmethane, bis(4-nitrophenyl)methane and three xanthenes. The bond dissociation energy values for the C-H bonds in the various radical anion and cation derivatives are provided.

A comparative study reveals the higher equilibrium of C-H bond acidities of three cyclic carboxylic esters having alkoxycarbonyl group locked in an E conformation than those of their acyclic analogues. N-H acidity of acyclic carbamates having alkoxycarbonyl group locked in an E conformation is higher than that of acyclic analogous. However, the structural changes exhibit no influence on the bond dissociation energies of the acidic C-H or N-H bonds in the esters or carbamates.

The acidifying effects of an alpha-triphenylphosphonium family are found to be around 9-20 pK units stronger than related alpha-trimethylammonium on adjacent C-H bonds. The effects of alpha-triphenylarsoinium groups on the equilibrium acidity and the bond dissociation enthalpies (BDEs) of adjacent acidic C-H bonds have been studied. Acidifying effects were found to be 13-20 pK units and were due to the combined Coulombic and polarizable interaction on the ylide anions. The BDEs show that alpha-triphenylarsonium addition decreases adjacent radical stabilities by 2-5 kcal/mol.

The use of a dual palladium/organic photoredox catalytic system enables the directed arylation of arenes with aryldiazonium salts with a broad substrate scope at room temperature under mild reaction conditions. This study thus serves as not only an alternative route for the biaryl motifs but also a new example for the application of an organic photoredox catalyst. [ABSTRACT FROM AUTHOR]

A photoredox catalytic method has been developed for the direct C2 alkylation of pyridine N-oxides. This reaction is compatible with a range of synthetically relevant functional groups for providing efficient synthesis of a variety of C2-alkylated pyridine N-oxides under mild conditions. Mechanistic studies are consistent with the generation of a radical intermediate along the reaction pathway. [ABSTRACT FROM AUTHOR]

Alpha-sulfonium groups are radical stabilizing rather than radical destabilizing, as gleaned from theoretical calculations in an examination of the radical substituent effects of the alpha-sulfonium groups. Results showed that the radical-stabilizing effects of the alpha-dialkylsulfonium groups are smaller and with larger steric hindrance than those for the alpha-RS groups. They were also found to be associated with the free lone pair electrons of the sulfur atom in the sulfonium groups. The latter were found to be able to form a two-center three-electron bond with the unpaired electron of the radical.

Examines the radical substituent effects of fluorine and trifluoromethyl groups, from the calculated C-H bond dissociation enthalpies (BDE) of various model compounds. Importance of structure and reactivity in physical organic chemistry; Use of the ab initio complete basic set model calculations; Methodology, results and discussion on the study.

Reports on the equilibrium acidities and homolytic bond dissociation energies of the acidic carbon-hydrogen bonds in p-substituted triphenylphosphonium cations. Oxidation potential of the conjugate bases in dimethyl sulfoxide solution; Acidifying effects of the alpha-triphenylphosphonium groups.

Presents an equation based on a thermodynamic cycle used for estimating the bond dissociation energies for the cleavage of the acidic hydrogen-A bonds in radical anions. Values for 2- and 9-substituted fluorenes and 10-substituted 9-methylanthracenes; Link between the chemical path and substituents used.

Presents kinetic and mechanistic studies of the nonchain radical nucleophilic substitution reactions. Activation energies and entropies for the single electron transfer (k1) and for the p-nitrochlorobenzene radian anion dissociation.

Features the estimation of the homolytic bond dissociation energies (BDE) for the nitrogen-hydrogen bonds in 21 anilines. Hammett-type correlations for anilines and phenols; Substituent effects on the BDEs; Equilibrium acidities and BDEs; Reaction schemes; Structures and properties.

Compares the pKHA and Eox(A-) (RSE) values of alpha-substituted derivatives of acetone and acetophenone with those of the parents. Alpha-phenyl effects; Alpha-alkyl effects; Alpah-heteroatom effects; Effects of two donors or two acceptors; Alpha-pyridinium and alpha-trimethylammonium effects; Reaction schemes; Detail of experimental procedure.

Discusses the stereoelectronic effects of divalent sulfur functions on radical stabilities. Presentation of homolytic bond dissociation energies (BDE) of carbon-hydrogen bonds adjacent to one and two sulfur atoms; Effects of the presence of two donor MeS groups in the acetophenone; Effects of acyclic and cyclic divalent sulfur functions on acidities and BDEs in acetophenones.

Metal-organic frameworks (MOFs) with high porosity could act as an ideal substitute for supercapacitors, but their poor electrical conductivities limit their electrochemical performances. In order to overcome this problem, conductive polypyrrole (PPy) has been introduced and a novel nanocomposite resulting from polyoxometalate (POM)-based MOFs (NENU-5) and PPy has been reported. It comprises the merits of POMs, MOFs, and PPy. Finally, the highly conductive PPy covering the surfaces of NENU-5 nanocrystallines can effectively improve the electron/ion transfer among NENU-5 nanocrystallines. The optimized NENU-5/PPy nanocomposite (the volume of Py is 0.15 mL) exhibits high specific capacitance (5147 mF·cm -2 ), larger than that of pristine NENU-5 (432 mF·cm -2 ). Furthermore, a symmetric supercapacitor device based on a NENU-5/PPy-0.15 nanocomposite possesses an excellent areal capacitance of 1879 mF·cm -2 , which is far above other MOF-based supercapacitors.

A nanocomposite polyoxomolybdate (PMo 12 )-polypyrrole (PPy)/reduced graphene oxide (RGO) is fabricated by using a simple one-pot hydrothermal method as an electrode material for lithium-ion batteries. This facile strategy skillfully ensures that individual polyoxometalate (POM) molecules are uniformly immobilized on the RGO surfaces because of the wrapping of polypyrrole (PPy), which avoids the desorption and dissolution of POMs during cycling. The unique architecture endows the PMo 12 -PPy/RGO with the lithium storage behavior of a hybrid battery-supercapacitor electrode: the nanocomposite with a lithium storage capacity delivers up to 1000 mAh g -1 at 100 mA g -1 after 50 cycles. Moreover, it still demonstrates an outstanding rate capability and a long cycle life (372.4 mAh g -1 at 2 A g -1 after 400 cycles). The reversible capacity of this nanocomposite has surpassed most pristine POMs and POMs-based electrode materials reported to date., Competing Interests: The authors declare no competing financial interest.