Syntheses and crystal structures of lithium derivatives of diphosphanes R2P–P(SiMe3)Li · 3L, R = Ph, Pr and Pr2N, L = THF or DME

The reactions of R₂P–P(SiMe₃)₂ (R = Ph, ⁱPr and ⁱPr₂N) with BuLi in THF or DME solution lead to ion-contacted lithium derivatives R₂P–P(SiMe₃)Li · 3THF (R = ⁱPr, ⁱPr₂N) with tetrahedrally surrounded Li atoms and to the solvent-separated ionic [Li · 3DME]⁺[Ph₂P–PSiMe₃]⁻ with an octahedrally surrounded Li atom as confirmed by X-ray crystal structure analysis. The reaction of BuLi with Ph₂P–P(SiMe₃)₂ is accompanied with a significant side-reaction leading to Ph₂P–PPh₂ and to LiP(SiMe₃)₂.     

Synthesis and catalytic activity of neutral salicylaldiminato nickel(II) complexes bearing a single N-heterocyclic carbene ligand

Neutral salicylaldiminato Ni(II) complexes bearing a single N-heterocyclic carbene (NHC) ligand [3,5-^tBu₂-2-(O)C₆H₂CHNAr]Ni(C{RNCHCHNⁱPr})Ph [Ar = 2,6-ⁱPr₂C₆H₃, R = Bn (1); Ar = 2,6-ⁱPr₂C₆H₃, R = ⁱPr (2)], have been synthesized via a one-pot procedure in high yield. The X-ray structure analysis reveals that both of 1 and 2 adopt distorted square-planar coordination geometry and NHC carbon (C_carbene) is trans to the ketimine nitrogen. Preliminary study indicates that complex 1 is inert toward the insertion of ethylene, however, it can catalyze the dimerization of ethylene in the presence of modified methylaluminoxane (MMAO) with a moderate activity of 3.05 × 10⁴ g(mol Ni)⁻¹ h ⁻¹ atm⁻¹ in a highly selective fashion.     

PHOTO-INDUCED ELECTRON TRANSFER FROM TRANSITION METAL CATIONS TO EXCITED STATES OF THE 10-METHYLACRIDINIUM ION

Abstract— Photo-induced electron transfer from cuprous ion to electronically excited 10-methyiacridinium tetrafluoroborate in acetonitrile-water solutions is described. The final photoproducts are Cu²⁺ (aq) and 10,10'-dimethyl-9,9'-biacridane. The proposed mechanism, based on microsecond flash excitation and fluorimetry experiments, is one-electron transfer from Cu⁺ to the 10-methylacridinium ion triplet state (and possibly the singlet state), followed by dimerization of the neutral acridinyl radical. Because the high energy photoproducts revert slowly to reactants, the system may have potential for storage and controlled recovery of light energy.     

Solid-state static Cu and P CP/MAS NMR, and liquid-state EXAFS studies on copper(I) O,O′-dialkyldithiophosphate cluster compounds: Formation of the copper(I) O,O′-di-iso-amyldithiophosphate cluster compound on the surface of synthetic chalcocite

Polycrystalline octa-nuclear copper(I) O,O′-di-i-propyl- and O,O′-di-i-amyldithiophosphate cluster compounds, {Cu₈[S₂P(OR)₂]₆(μ₈-S)} where R = ⁱPr and ⁱAm, were synthesized and characterized by ³¹P CP/MAS NMR at 8.46 T and static ⁶⁵Cu NMR at multiple magnetic field strengths (7.05, 9.4 and 14.1 T). The symmetries of the electronic environments around the P sites were estimated from the ³¹P chemical shift anisotropy (CSA) parameters, δ_aniso and η. Analyses of the ⁶⁵Cu chemical shift and quadrupolar splitting parameters for these compounds are presented with the data being compared to those for the analogous octa-nuclear cluster compounds with R = ⁿBu and ⁱBu. The ⁶⁵Cu transverse relaxation for the copper sites in {Cu₈[S₂P(OⁱPr)₂]₆(μ₈-S)} and {Cu₈[S₂P(OⁱAm)₂]₆(μ₈-S)} was found to be very different, with a relaxation time, T₂, of 590 μs (Gaussian) and 90 μs (exponential), respectively. The structures of {Cu₄[S₂P(OⁱPr)₂]₄} and {Cu₈[S₂P(OⁱPr)₂]₆(μ₈-S)} cluster compounds in the liquid- and the solid-state were studied by Cu K-edge EXAFS. The disulfide, [S₂P(OⁱAm)₂]₂, was obtained and characterized by ³¹P{¹H} NMR. The interactions of the disulfide and of the potassium O,O′-di-i-amyldithiophosphate salt with the surfaces of synthetic chalcocite (Cu₂S) were probed using solid-state ³¹P NMR spectroscopy and only the presence of copper(I) dithiophosphate species with the {Cu₈[S₂P(OⁱAm)₂]₆(μ₈-S)} structure was observed.     

Alkoxy derivatives of trithiazyltrichloride

Reaction of trithiazyltrichloride, (NSCl)₃, with NaOR in ROH (R = Me, Et, ⁱPr, ⁿPr, ^nBu, ^tBu, pentyl, amyl, cyclohexyl, benzyl) gives (NSOR)₃. The compounds have been characterized by IR and mass spectroscopy and in the case of R = methyl, (2a) and benzyl, (2e) by X-ray crystallography. In the structures of both (2a) and (2e) the S₃N₃ ring adopts a flattened chair cyclohexane con7mation with the substituents being axial.     

Photocatalytic oxygenation of anthracenes and olefins with dioxygen via selective radical coupling using 9-mesityl-10-methylacridinium ion as an effective electron-transfer photocatalyst

Visible light irradiation of the absorption band of 9-mesityl-10-methylacridinium ion (Acr+-Mes) in an O2-saturated acetonitrile (MeCN) solution containing 9,10-dimethylanthracene results in formation of oxygenation product, i.e., dimethylepidioxyanthracene (Me2An-O2). Anthracene and 9-methylanthracene also undergo photocatalytic oxygenation with Acr+-Mes to afford the corresponding epidioxyanthracenes under the photoirradiation. In the case of anthracene, the further photoirradiation results in formation of anthraquinone as the final six-electron oxidation product, via 10-hydroxyanthrone, accompanied by generation of H2O2. When anthracene is replaced by olefins (tetraphenylethylene and tetramethylethylene), the photocatalytic oxygenation of olefins affords the corresponding dioxetane, in which the O-O bond is cleaved to yield the corresponding ketones. The photocatalytic oxygenation of anthracenes and olefins is initiated by photoexcitation of Acr+-Mes, which results in formation of the electron-transfer state: Acr*-Mes*+, followed by electron transfer from anthracenes and olefins to the Mes*+ moiety together with electron transfer from the Acr* moiety to O2. The resulting anthracene and olefin radical cations undergo the radical coupling reactions with O2*- to produce the epidioxyanthracene (An-O2) and dioxetane, respectively.     

First principles study of the structure, electronic state and stability of AlnPm cations

Structural and electronic properties of semiconductor binary microclusters Al_nP_m⁺ cations have been investigated using the B3LYP–DFT method in the ranges of n=1,2 and m=1–7. Full structural optimization, adiabatic ionization potentials calculation and frequency analysis are performed with the basis of 6-311G(d). The charge-induced structural changes in these cations have been discussed. The strong P–P bond is also favored over Al–P bonds in the Al_nP_m⁺ cations in comparison with corresponding neutral cluster. With P_m forming the base, adding Al atom(s) in different positions would find the stable structures of Al_nP_m⁺ cations quickly and correctly. Both AlP₄⁺ and AlP₆⁺ are predicted to be species with high stabilities and possible to be produced experimentally.     

Electron transfer in DNA from guanine and 8-oxoguanine to a radical cation of the carbohydrate backbone

Photolysis of a 4'-pivaloyl-substituted nucleotide in single- and double-stranded DNA (1) generated an enol ether radical cation 4 that was reduced to enol ether 17 by electron transfer from the nearest guanoside (G). Variation of the nucleotide sequence demonstrated a strong distance dependence of this electron-transfer rate with beta = 1.0 +/- 0.1 A(-1). When 8-oxoguanosine (G(oxo)) was used as the electron donor, the rate of the electron transfer increased by a factor of 4 but the distance dependence of the transfer remained unchanged within experimental error. In single strands, the number of intervening A, T, and C nucleotides had a much smaller effect; the rate remained nearly constant for two, three, or four intervening nucleotides. This is explained by the flexibility of the single-stranded oligonucleotides.     

A Fourier-transform ion-cyclotron-resonance study of the reactions of polycyclic aromatic hydrocarbon cations with molecules of interstellar interest

The reactivity of naphthalene and pyrene radical cations and their derivatives (C₁₀H_n⁺, n=6,7,8,9), C₁₆H_n (n=9,10,11) has been studied with molecules of interstellar interest in an ion cyclotron resonance apparatus. The radical cations C₁₀H₈⁺ and C₁₆H₁₀⁺ are unreactive with H₂,CO,H₂O and NH₃. Adduct formation is the only channel for almost all reactions of C₁₀H₇⁺ with these molecules. The implications of these results for the stability of polycyclic aromatic hydrocarbon (PAH) cations in the interstellar medium are briefly discussed. Exploratory studies of the ion chemistry of a larger PAH, coronene, have also been done.     

Distinguishing conventional and distonic radical cations by using dimethyl diselenide

Dimethyl diselenide is demonstrated to be among the most powerful reagents used to identify distonic radical cations. Most such ions readily abstract CH₃Se^. from dimethyl diselenide. The reaction is faster and more exclusive than CH₃S^. abstraction from dimethyl disulfide, a reaction used successfully in the past to identify numerous distonic ions. Very acidic distonic ions, such as HC⁺(OH)OCH^.₂, do not undergo CH₃Se^. abstraction, but instead protonate dimethyl diselenide. In sharp contrast to the reactivity of distonic ions, most conventional radical cations were found either to react by exclusive electron transfer or to be unreactive toward dimethyl diselenide. Hence, this reagent allows distinction of distonic and conventional isomers, which was demonstrated directly by examining two such isomer pairs. To be able to predict whether electron transfer is exothermic (and hence likely to occur), the ionization energy of dimethyl diselenide was determined by bracketing experiments. The low value obtained (7.9 ± 0.1 eV) indicates that dimethyl diselenide will react with many conventional carbon-, sulfur-, and oxygen-containing radical cations by electron transfer. Nitrogen-containing conventional radical cations were found either to react with dimethyl diselenide by electron transfer or to be unreactive.     

Density functional studies of the reactivity in the C–F bond activation of fluoromethane by bare lanthanum monocation

The potential energy surface and reaction mechanism corresponding to the reaction of lanthanum monocation with fluoromethane, which represents a prototype of the activation of C–F bond in fluorohydrocarbons by bare lanthanide cations, have been investigated for the first time by using density functional theory. A direct fluorine abstraction mechanism was revealed, namely after coordination of CH₃F to La⁺, electron transfer from La⁺ to the fluorine takes place, which favours the homolytic cleavage of the C–F bond to form LaF⁺ species and methyl radical. The related thermochemistry data involved in reaction of La⁺+CH₃F were determined, which can act as a guide for further experimental researches. The electron-transfer reactivity of the reaction was analyzed by using a state correlation diagram, in which a strongly avoided crossing behaviour on the transition state region was shown. The calculated state split energy between the ground and excited state on the transition state is 18.01 kcal mol⁻¹. The reaction of La⁺ with CH₃F was concluded to process in the adiabatic potential surface. The present results support the reaction mechanism inferred early from experimental data.     

Direct dynamics study of <Emphasis Type="Italic">N</Emphasis>-protonated diglycine surface-induced dissociation. Influence of collision energy

A quantum mechanical and molecular mechanical (QM + MM) direct dynamics classical trajectory simulation is used to study energy transfer and fragmentation in the surface-induced dissociation (SID) of N-protonated diglycine, (gly)₂H⁺. The peptide ion collides with the hydrogenated diamond {111} surface. The Austin Model 1 (AM1) semiempirical electronic structure theory is used for the (gly)₂H⁺ intramolecular potential and molecular mechanical functions are used for the diamond surface potential and peptide/surface intermolecular potential. The simulations are performed at collision energies E_i of 30, 50, 70, and 100 eV and collision angle of 0° (perpendicular to the surface). The percent energy transfer to the peptide ion is nearly independent of E_i, while energy transfer to the surface increases with increase in E_i. A smaller percent of the energy remains in peptide translation as E_i is increased. These trends in energy transfer are consistent with previous trajectory simulations of SID. At each E_i the most likely initial pathway leading to fragmentation is rupture of the ⁺H₃NCH₂---CONHCH₂COOH bond. Fragmentation occurs by two general mechanisms. One is the traditional Rice-Ramsperger-Kassel-Marcus (RRKM) model in which the peptide ion is activated by its collision with the surface, “bounces off”, and then dissociates after undergoing intramolecular vibrational energy redistribution (IVR). The other mechanism is shattering in which the ion fragments as it collides with the surface. Shattering is the origin of the large increase in number of product channels with increase in E_i, i.e., 6 at 30 eV, but 59 at 100 eV. Shattering becomes the dominant dissociation mechanism at high E_i.     

生物醌分子伏安响应的多电子转移辨析

电化学反应中,一个基元电子转移反应仅对应一个电子交换,实际上多电子转移反应也涉及对应数目的单电子转移步骤,分离、辨析每个电子基元反应的氧化还原峰电位十分重要. 本文以辅酶Q₀（CoQ₀）、亚甲基桥连双辅酶Q₀（Bis-CoQ₀）为模型,采用循环伏安和方波伏安技术研究其电化学特性,提出了一种应用于多电子转移体系、分析单个电子转移电位的方法. 实验表明,CoQ₀经历两步单电子还原反应;Bis-CoQ₀中两个醌单元发生强电子相互作用,电极过程为4电子多步转移. 对于表观上的4电子“三步”转移反应,拟用Lorentzian-Gaussian分峰拟合CoQ₀和Bis-CoQ₀体系方波伏安响应曲线,分别获取每个电子转移步骤的电位,进一步证明Bis-CoQ₀经历四分步单电子转移反应,为热力学研究提供更多信息.     

Triplet state mechanism for electron transfer oxidation of DNA

The interaction of anthraquinone-2-sulfonate with nucleotides and DNA in acetonitrile and acetonitrile water solvent mixture have been studied using KrF laser photolysis aimed at elucidation of the reaction mechanism. Laser spectroscopy directly demonstrates that the initial species from interaction of anthraquinone-2-sulfonate with nucleotides are radical cations of nucleotides and radical anion of anthraquinone-2-sulfonate. In addition, formation of ion pair from interaction of any of nucleotides with anthraquinone-2-sulfonate is synchronous with decay of triplet anthraquinone-2-sulfonate, which has provided dynamic evidence for initiation of electron transfer from DNA bases to triplet anthraquinone-2-sulfonate. Moreover, direct observation of stabilized DNA guanyl radical cation from interaction of anthraquinone-2-sulfonate with DNA has provided initial evidence for selective cleavage of DNA at guanine moiety. The solvent-separated ion pairs in acetonitrile have evidently dissociated into free ions, thereby enabling independent study of the behavior of guanyl radical cations and radical anion of anthraquinone-2-sulfonate.     

Global minima of (C60)nCa, (C60)nF and (C60)nI clusters

Likely candidates for the lowest potential energy minima of (C₆₀)_nCa²⁺, (C₆₀)_nF⁻ and (C₆₀)_nI⁻ clusters are located using basin-hopping global optimisation. In each case, the potential energy surface is constructed using the Girifalco form for the C₆₀ intermolecular interaction, an averaged Lennard–Jones C₆₀–ion interaction, and a polarisation potential, which depends on the first few non-vanishing C₆₀ multipole polarisabilities. We find that the ions generally occupy the interstitial sites of a (C₆₀)_n cluster, the coordination shell being tetrahedral for Ca²⁺ and F⁻. The I⁻ ion has an octahedral coordination shell in the global minimum for (C₆₀)₆I⁻, however for 12  n  8 the preferred coordination geometry is trigonal prismatic.     

Intramolecular hydrogen atom transfer in hydrogen-deficient polypeptide radical cations

Irradiation of protonated polypeptides NH₂–RH⁺–COOH by >10 eV electrons leads to further ionization and fast intramolecular charge transfer to the free N-terminus. The resulting species may undergo further hydrogen atom rearrangement to form distonic ions N⁺H₃–RH⁺–COO√. Such transfer is exothermic but can involve an appreciable barrier, e.g., 2.3±0.5 eV for MH^2+√ ions of the peptide ACTH 1–10. Radical polypeptide dications can, therefore, be viewed as hydrogen atom wires. Subsequent capture of low energy electrons results in fragmentation. The pattern of this electronic excitation dissociation (EED) is consistent with hydrogen transfer prior to electron capture.     

Binding energies and electronic structures of Cu(OH2)n and Cu(NH3)n (n=1–4): anomaly of the two ligand Cu complexes

Ab initio calculations up to MP4(SDTQ) level and density functional theory have been used to estimate binding energies and electronic structures of Cu⁺(L)_n (L=OH₂, NH₃, n=1–4) complexes using TZP basis set types. The computed binding energies agree well with experimental values. General trends in structures and energetics are recorded for both Cu⁺(OH₂)_n and Cu⁺(NH₃)_n systems. The first two ligands are more strongly bound to Cu⁺ than the third and fourth molecules. The 4s–3dσ hybridization and electrostatic interactions are the main factors behind the higher binding energies for the first two ligands. Analysis of HOMO mixed orbitals in the copper ion as well as in complexes indicates shrinking of the orbital lobes directed to the ligand with shrinking more effective in the two ligand system. The lower binding energies for the third and fourth ligands were attributed to the attenuation of sdσ hybridization and decreasing of Cu–L attraction at long separation which is necessary to relieve Cu–L and L–L exchange repulsions. NBO analysis and charge-model calculations support the presence of sdσ hybridization and electron transfer to the copper ion in case of the first two ligands.     

Density functional and multiphoton ionization studies of N,N-dimethylformamide–(methanol)n clusters

The multiphoton ionization of the hydrogen-bonded clusters N,N-dimethylformamide–(methanol)_n (DMF–(CH₃OH)_n) was studied using a time-of-flight mass spectrometer at the wavelengths of 355 and 532 nm. At both wavelengths, a series of protonated DMF–(CH₃OH)_nH⁺ ions was obtained. The clusters were also investigated by density functional theory B3LYP method in conjunction with basis sets 6-31+G(d,p) and 6-311+G(2d,p). Equilibrium geometries of both neutral and ionic DMF–CH₃OH clusters, and dissociation channels and dissociation energies of the ionic clusters are presented. The results show that when DMF–CH₃OH is vertically ionized and dissociated, DMFH⁺ and CH₃O are the dominant products via proton transfer reaction. A high energy barrier makes another channel corresponding to the production of DMFH⁺ and CH₂OH disfavored. In the DMF–(CH₃OH)H⁺ ion, the proton prefers to link with the O atom of DMF molecule. Variation of atomic charges during proton transfer in hydrogen bond of the protonated cluster DMF–(CH₃OH)H⁺ ion is also discussed.     

Ab initio and post-ab initio quantum chemical study of the heme spin states in electron transfer reactions

Quantum-chemical calculations of neutral and charged ironporphyrin (FeP, FeP⁺¹ and FeP⁻) systems were performed using B3LYP and MP2 methods. It was shown that all ground states of FeP (S = 1), FeP⁺¹ (S = 3/2) and FeP⁻ (S = 1/2) systems have C_2v symmetry. During the first step of electron transfer process an electron goes to β-LUMO − 1 Fe d_yz-orbital of FeP⁺¹. The second electron goes to β-LUMO of FeP which is attributed to π-system of porphyrin ring. The 3s- and 3p-orbitals do not play a significant role in the electron transfer process. The ability of FeP⁻¹ system to form π-dative chemical bond is low. The formation of π–π-complexes is preferable.     

Charge separation in a ruthenium-quencher conjugate bound to DNA

A novel tris heteroleptic dipyridophenazine complex of ruthenium(II), [{Ru(phen)(dppz)(bpy'-his)}{Ru(NH3)5}]5+, containing a covalently tethered ruthenium pentammine quencher coordinated through a bridging histidine has been synthesized and characterized spectroscopically and biochemically in a DNA environment and in organic solvent. Steady-state and time-resolved luminescence measurements indicate that the tethered Ru complex is quenched relative to the parent complexes [Ru(phen)(dppz)(bpy')]2+ and [Ru(phen)(dppz)(bpy'-his)]2+ in DNA and acetonitrile, consistent with intramolecular photoinduced electron transfer. Intercalated into guanine-containing DNA, [{Ru(phen)(dppz)(bpy'-his)}{Ru(NH3)5}]5+, upon excitation and intramolecular quenching, is capable of injecting charge into the duplex based upon the EPR detection of guanine radicals. DNA-mediated charge transport is also indicated using a kinetically fast cyclopropylamine-substituted base as an electron hole trap. Guanine damage is not observed, however, in measurements using the guanine radical as the kinetically slower hole trap, indicating that back electron-transfer reactions are competitive with guanine oxidation. Moreover, transient absorption measurements reveal a novel photophysical reaction pathway for [{Ru(phen)(dppz)(bpy'-his)}{Ru(NH3)5}]5+ in the presence of DNA that is competitive with the intramolecular flash-quench process. These results illustrate the remarkably rich redox chemistry that can occur within a bimolecular ruthenium complex intercalated in duplex DNA.