Dissociative electron capture of halocarbon caused by the internal electron transfer from water trimer anion

Dissociative electron capture dynamics of halocarbon absorbed on water cluster anion, caused by internal electron transfer from the water trimer anion to the halocarbon, have been investigated by means of the direct density functional theory (DFT)-molecular dynamics (MD) method. The CF(2)Cl(2) molecule and a water trimer anion e(-)(H(2)O)(3) were used as a halocarbon and a trapped electron, respectively. First, the structure of trapped electron state, expressed by e(-)(H(2)O)(3)-CF(2)Cl(2), was fully optimized. The excess electron was trapped by a dipole moment of water trimer. Next, initial geometries were randomly generated around the equilibrium point of the trapped electron state, and then trajectories were run. The direct DFT-MD calculations showed that the spin density distribution of excess electron is gradually changed from the water cluster (trapped electron state) to CF(2)Cl(2) as a function of time. Immediately, the Cl(-) ion was dissociated from CF(2)Cl(2)(-) adsorbed on the water cluster. The reaction was schematically expressed by e(-)(H(2)O)(3)-CF(2)Cl(2)-->[(H(2)O)(3)-->-CF(2)CL(2)](-) --> (H(2O)(3) + CF(2)CL + CI(-) (I) where [(H(2)O)(3)-CF(2)Cl(2)](-) indicates a transient intermediate state in which the excess electron is widely distributed on both the water cluster and CF(2)Cl(2). The mechanism of the electron capture of halocarbon from the trapped electron in water ice was discussed on the basis of the theoretical results. Also, the dynamics feature was compared with those of the direct electron capture reactions of CF(2)Cl(2) and CF(2)Cl(2)-(H(2)O)(3), i.e. e(-) + CF(2)Cl(2), and e(-) + CF(2)Cl(2)-(H(2)O)(3), investigated in our previous paper [Tachikawa and Abe, J. Chem. Phys., 2007, 126, 194310].     

Supramolecular carbon nanotube-fullerene donor-acceptor hybrids for photoinduced electron transfer

Photoinduced electron transfer in a self-assembled single-wall carbon nanotube (SWNT)-fullerene(C60) hybrid with SWNT acting as an electron donor and fullerene as an electron acceptor has been successfully demonstrated. Toward this, first, SWNTs were noncovalently functionalized using alkyl ammonium functionalized pyrene (Pyr-NH3+) to form SWNT/Pyr-NH3+ hybrids. The alkyl ammonium entity of SWNT/Pyr-NH3+ hybrids was further utilized to complex with benzo-18-crown-6 functionalized fullerene, crown-C60, via ammonium-crown ether interactions to yield SWNT/Pyr-NH3+/crown-C60 nanohybrids. The nanohybrids were isolated and characterized by TEM, UV-visible-near IR, and electrochemical methods. Free-energy calculations suggested possibility of electron transfer from the carbon nanotube to the singlet excited fullerene in the SWNT/Pyr-NH3+/crown-C60 nanohybrids. Accordingly, steady-state and time-resolved fluorescence studies revealed efficient quenching of the singlet excited-state of C60 in the nanohybrids. Further studies involving nanosecond transient absorption studies confirmed electron transfer to be the quenching mechanism, in which the electron-transfer product, fullerene anion radical, was possible to spectrally characterize. The rates of charge separation, kCS, and charge recombination, kCR, were found to be 3.46 x 10(9) and 1.04 x 10(7) s-1, respectively. The calculated lifetime of the radical ion-pair was found to be over 100 ns, suggesting charge stabilization in the novel supramolecular nanohybrids. The present nanohybrids were further utilized to reduce hexyl-viologen dication (HV2+) and a sacrificial electron donor, 1-benzyl-1,4-dihydronicotinamide, in an electron-pooling experiment, offering additional proof for the occurrence of photoinduced charge-separation and potential utilization of these materials in light-energy harvesting applications.     

The N-bromosuccinimide-succinimide anion complex,an intermediate in the electron transfer mediated reduction of N-bromosuccinimide by succinimide anion

Complexes between N-bromosuccinimides and succinimide anions are shown to be intermediates in the reduction of N-bromosuccinimides, and a method for their synthesis as tetra-n-butylammonium salts is described.     

Radical anion chain process initiated by a dissociative electron transfer to a monocyclic endoperoxide

Electron transfer to 3,3,6,6-tetraphenyl-1,2-dioxane results in the cleavage of the oxygen-oxygen bond, generating a distonic radical anion intermediate whose fragmentation initiates an unprecedented radical anion chain process in competition with a second electron transfer.     

Effect of anion ligation on electron transfer of double-linked zinc porphyrin-fullerene dyad

The interaction between metalloporphyrins and their axial ligands plays an important role in the electron transfer (ET) processes in which the excited porphyrin participates. An efficient photoinduced ET reaction of a double-linked zinc(II) porphyrin-fullerene dyad was demonstrated in ionic environment. The chloride ion of tetrabutylammonium chloride (TBACl) electrolyte solution ligates the zinc porphyrin moiety in the dyad which results in a red shift of the absorption bands and lowers the energy of the charge-separated state by about 0.26 eV as compared to the nonligated dyad. Excitation of the porphyrin chromophore results in ET from porphyrin to fullerene in a moderately polar solvent, anisole. In nonionic and nonligating ionic environments, the ET reaction occurs through an intermediate state, an intramolecular exciplex, which has emission in the near-infrared region of the spectrum. This emission is not observed directly for the dyad in TBACl/anisole solution, but evidence of the exciplex intermediate was seen in the time-resolved measurements. The lower energy of the charge-separated state in the ligated environment explains the different ET reaction rates determined in the spectroscopic studies: the charge recombination process of the ligated dyad is about 5 times faster than that of the nonligated one.     

Amino acid based chiral N-amidothioureas. Acetate anion binding induced chirality transfer

N-Amidothioureas generated from amine-dimethylated natural L-phenylalanine and its D-enantiomer bearing a chiral carbon that is by 2 atoms or 3 chemical bonds away from the anion binding site establish chiral communication upon acetate anion binding to the thiourea moiety.     

Supramolecular binding thermodynamics by dispersion-corrected density functional theory

The equilibrium association free enthalpies ΔG(a) for typical supramolecular complexes in solution are calculated by ab initio quantum chemical methods. Ten neutral and three positively charged complexes with experimental ΔG(a) values in the range 0 to -21?kcal?mol(-1) (on average -6?kcal?mol(-1) ) are investigated. The theoretical approach employs a (nondynamic) single-structure model, but computes the various energy terms accurately without any special empirical adjustments. Dispersion corrected density functional theory (DFT-D3) with extended basis sets (triple-ζ and quadruple-ζ quality) is used to determine structures and gas-phase interaction energies (ΔE), the COSMO-RS continuum solvation model (based on DFT data) provides solvation free enthalpies and the remaining ro-vibrational enthalpic/entropic contributions are obtained from harmonic frequency calculations. Low-lying vibrational modes are treated by a free-rotor approximation. The accurate account of London dispersion interactions is mandatory with contributions in the range -5 to -60?kcal?mol(-1) (up to 200?% of ΔE). Inclusion of three-body dispersion effects improves the results considerably. A semilocal (TPSS) and a hybrid density functional (PW6B95) have been tested. Although the ΔG(a) values result as a sum of individually large terms with opposite sign (ΔE vs. solvation and entropy change), the approach provides unprecedented accuracy for ΔG(a) values with errors of only 2?kcal?mol(-1) on average. Relative affinities for different guests inside the same host are always obtained correctly. The procedure is suggested as a predictive tool in supramolecular chemistry and can be applied routinely to semirigid systems with 300-400 atoms. The various contributions to binding and enthalpy-entropy compensations are discussed.     

Ab initio study of long-range electron transfer between biphenyl anion radical and naphthalene

After the separation of the donor, the aeceptor, and the σ-type bridge from the π-σ-π system, the geometries of biphenyl, biphenyl anion radical, naphthalene, and naphthalene anion radical are optimized, and then the reorganization energy for the intermolecular electron transfer (ET) at the levels of HF/4-31G and HF/DZP is calculated. The ET matrix elements of the self-exchange reactions of the π-σ-π systems have been calculated by means of both the direct calculation based on the variational principle, and the transition energy between the molecular orbitals at the linear coordinate R=0.5. For the cross reactions, the ET matrix element and the geometry of the transition state are determined by searching the minimum energy splitting △_(min) along the reaction coordinate. In the evaluation of the solvent reorganization energy of the ET in solution, the Marcus' two-sphere model has been invoked. A few of ET rate constants for the intramolecular ET reactions for the π-σ-π systems, which contain     

Ab initio study of long-range electron transfer between biphenyl anion radical and naphthalene

After the separation of the donor, the acceptor, and the σ-type bridge from the π-σ-π system, the geometries of biphenyl, biphenyl anion radical, naphthalene, and naphthalene anion radical are optimized, and then the reorganization energy for the intermolecular electron transfer (ET) at the levels of HF/4-31G and HF/DZP is calculated. The ET matrix elements of the self-exchange reactions of theπ-σ-π systems have been calculated by means of both the direct calculation based on the variational principle, and the transition energy between the molecular orbitals at the linear coordinateR = 0.5. For the cross reactions, the ET matrix element and the geometry of the transition state are determined by searching the minimum energy splitting Δ_min along the reaction coordinate. In the evaluation of the solvent reorganization energy of the ET in solution, the Marcus’ two- sphere model has been invoked. A few of ET rate constants for the intramolecular ET reactions for the π-σ-π systems, which contain the biphenylyl as the donor and both biphenylyl and naphthyl as the acceptor, have been obtained. Project supported by the National Natural Science Foundation of China (Grant Nos. 29706104 and 29573112), the State Key Laboratory of Theoretical and Computational Chemistry of Jilin University.     

Simulation of ultrafast non-exponential fluorescence decay induced by electron transfer in FMN binding protein

The ultrafast non-exponential fluorescence decay of FMN binding protein (FBP) was analyzed with three electron transfer (ET) theories, Marcus theory, Bixon and Jortner theory and Kakitani and Mataga theory. Center to center distances between electron acceptor, the excited isoalloxazine, and donors, Trp-32, Tyr-35 and Trp-106, in FBP were determined by molecular dynamic simulation. Electron transfer parameters containing in these theories were determined so as to fit the calculated decay with the observed decay, according to a non-linear least squares method. Introduction of electrostatic energies between isoalloxazine anion and other ionic groups and between the donor cations and other ionic groups in the protein into any ET theories improved the fitting. The non-exponential behavior in the fluorescence decay is considered to be ascribed to a fluctuation of the protein structure with long period.     

Complementary anion binding by bidentate boron-containing Lewis acids

Anion binding by the pyroborates (catB)₂O (1, cat = O₂C₆H₄-1,2) and (S,S-Ph₂C₂H₂O₂B)₂O (2) has been investigated by spectroscopic, structural and titration methods. 1 has been shown to act as a bifunctional Lewis acid, exemplified by the complementary (1:1) binding of bidentate bases such as acetate and dihydrogen phosphate. The former complex has been characterized in the solid state by X-ray diffraction and a binding constant of 1500 ± 550 M⁻¹ determined in chloroform solution. The reaction of 2 with acetate, by contrast, leads to breakdown of the Lewis acid chelate and to the formation of the homochiral borate anion [(S,S-Ph₂C₂H₂O₂)₂B]⁻ in good yield (84% based on the chiral component).     

Multiple anion binding by a zinc-containing tetratopic cyclen-resorcinarene

The synthesis and binding properties of a new tetratopic anion receptor are reported. The resorcinarene ligand bearing four cyclen moieties is able to bind four Zn²⁺ ions and subsequently bind anions. NMR titrations show proton shifts during the binding of the first one or two anions. Isothermal titration calorimetry (ITC) titrations show that two or more anions bind to one tetramer. The tetratopic receptor in methanol has high affinity for dihydrogen phosphate, acetate, and halide ions and weak affinity for nitrate and perchlorate.     

阴离子相转移催化的Friedel-Crafts烷基化反应

提出三种阴离子表面活性剂十二烷基苯磺酸钠、十二烷基磺酸钠、十二烷基硫酸钠作为阴离子相转移催化剂特性。研究了它们在Friedel-Crafts反应中的催化性能,结果表明它们都有良好的催化特性合成了七个化合物, 其中五个为未见文献报导的新化合物, 它们是二苯甲基萘酚和二苯甲基酚类化合物。     

Overwhelming decomposition of 4-bromo-4''''-cyanomethylbiphenylyl radical anion without electron transfer to 4,4''''-dibromobiphenyl

Dibromobiphenyl reacted with cynomethyl anion in ammonia under irradiation to form nucleophilic bis-substituted product in high yield without substantial monosubstituted product. Quantum yields for the formations of bis- and monosubstituted products were found to be 85.6 and 2.3×10-6 respectively, while the corresponding pseudo-first-order rates were 6.9×10-3 and 5.2×10-10 mol.L-1.S-1. Block up the possible electron transfer of 4-brome-4'-cyanomethylbiphenylyl radical anion to 4-cyanometbyl-biphenylyl radical and bromine ion.     

Supramolecular semiconductor receptor assemblies: Improved electron transfer at TiO2-β-cyclodextrin colloid interfaces

Semiconductor TiO₂-colloids are stabilized by ß-cyclodextrin (ß-CD). Photoinduced electron transfer at the semiconductor (S.C.) solution interface is controlled in the S.C.-receptor assembly TiO₂-β-CD. Trapping of TiO₂-ß-CD photoexcited conduction-band electrons by N,N’-dioctyl-4,4’-bipyridinium, C₈V²⁺, is 4.4 fold more effective than by N,N’-dimethyl-4,4’-bipyridinium. The kinetics of C₈V²⁺ reduction, inhibition experiments and laser flash photolysis studies reveal that the effective trapping of conduction-band electrons by C₈V²⁺ originates from its association to the ß-CD receptor. Electron transfer from dye, proflavine, Pfl, to the S.C., is similarly controlled by the S.C.-receptor assembly. In the presence of the Pt modified semiconductor-receptor colloid, Pt-TiO₂-ß-CD, effective photoinduced H₂-evolution occurs using Pfl as photosensitizer. Inhibition experiments and flow-dialysis measurements indicate that the effective H₂-evolution originates from the association of Pfl to the ß-CD receptor sites.     

Enhanced electron transfer by dendritic architecture: energy transfer and electron transfer in snowflake-shaped Zn porphyrin dendrimers

[structure: see text] Photoinduced electron transfer was observed for the snowflake-shaped dendrimer with the Zn porphyrin core and anthraquinonyl terminals. Comparison of the electron-transfer efficiency of the dendrimer with the linear analogues indicates the advantage of the dendritic structure for the electron-transfer process.