Etude vibrationnelle des composes (C4H4P)Mn(CO)3 et [C4H2(CH3)2P]Mn(CO)3 et calcul du champ de force du cycle C4H4P complexe

The Raman and infrared spectra (4000200 cm^?1) of (C₄H₄P)Mn(CO)₃ and (C₄D₄P)Mn(CO)₃, and of [C₄H₂(CH₃)₂P]Mn(CO)₃ and [C₄D₂(CH₃)₂P]Mn(CO)₃ in the liquid and solid states (10–400 K) have been investigated. A complete vibrational assignment is proposed and valence force fields of the (C₅H₅) and (C₄H₄P) cycles are compared. From these results, it is clearly shown that the (C₄H₄P) rings are more electrophilic and weaker π-electron donors than (C₅H₅) rings, this is in agreement with their chemical behavior.     

Transmission of fast H3+ molecules through thin carbon foils

Observed for the first time is the transmission of H₃⁺ molecules (2.4 MeV) through carbon foils (2–7 μg/cm²). The thickness dependence of the yield follows a single decreasing exponential function with a unity coefficient which is expected for H₃⁺ transmitted with their original electrons.     

Another experimental evidence for coherent electronic excitation of channeled He+ ions

The coherent excitation of He⁺ ions passing along the [110] axis of a thin gold crystal has been studied. Excitation occurs for several resonant energies, from 250 to 350 keV, which could be related to the Fourier frequency spectrum of the Coulomb perturbation.     

Positive Jonsson Theories

This paper is a general introduction to Positive Logic, where only what we call h-inductive sentences are under consideration, allowing the extension to homomorphisms of model-theoric notions which are classically associated to embeddings; in particular, the existentially closed models, that were primitively defined by Abraham Robinson, become here positively closed models. It accounts for recent results in this domain, and is oriented towards the positivisation of Jonsson theories.     

The neuroblast and angioblast chemotaxic factor SDF-1 (CXCL12) expression is briefly up regulated by reactive astrocytes in brain following neonatal hypoxic-ischemic injury

Background  

Stromal cell-derived factor 1 (SDF-1 or CXCL12) is chemotaxic for CXCR4 expressing bone marrow-derived cells. It functions in brain embryonic development and in response to ischemic injury in helping guide neuroblast migration and vasculogenesis. In experimental adult stroke models SDF-1 is expressed perivascularly in the injured region up to 30 days after the injury, suggesting it could be a therapeutic target for tissue repair strategies. We hypothesized that SDF-1 would be expressed in similar temporal and spatial patterns following hypoxic-ischemic (HI) injury in neonatal brain.     

Meta and para effects in the ultrafast excited-state dynamics of the green fluorescent protein chromophores

Femtosecond transient absorption and fluorescence upconversion experiments have been performed to investigate the photoinduced dynamics of the meta isomer of the green fluorescent protein chromophore, m-HBDI, and its O-methylated derivative, m-MeOBDI, in various solvent mixtures at neutral, acidic, and basic pH. The para isomer, p-HBDI, and its O- and N-methylated derivatives, p-MeOBDI and p-HBDIMe(+), were also studied for comparison. In all cases, fast quenching of the excited S1 state by internal conversion (IC) to the ground state was observed. In the para compounds, IC, presumably promoted by the internal twisting, arises in <1 ps. A similar process takes place in the meta compounds in nonaqueous solvents but with notably slower kinetics. In aqueous solutions, the meta compounds undergo ultrafast intermolecular excited-state proton transfer that competes with isomerization.     

Photochromism of photoenolizable ketones in quinoline and 1,8-naphthyridine series studied by time-resolved absorption spectroscopy

For the two photochromic molecules, 3-benzoyl-2-benzyl-1-methyl-1H-quinolin-4-one (QC1) and 3-benzoyl-1,2-dibenzyl-1H-1,8-naphthyridin-4-one (QC18a) as well as the nonphotochromic 3-benzoyl-1-benzyl-2-methyl-1H-1,8-naphthyridin-4-one (QC18b), the full photochemical mechanism, which is based on the photoenolization process, has been elucidated using stationary and time-resolved spectroscopy techniques. After photoexcitation, the S1(n,pi*)-T1(n,pi*) ISC process involving the exocyclic carbonyl chromophore is demonstrated to occur. Subsequently, gamma-hydrogen transfer proceeds very rapidly to give rise to the triplet photoenol with a probable 1,4-biradical structure. For all three molecules, the biradical is clearly detected and proved quantitatively to be the direct precursor of the colored form (photochromic compounds) or ground state starting material (nonphotochromic compound). Solvent effects for the three molecules studied may suggest the existence of intramolecular hydrogen bonding in both biradical and colored form species. Structural effects on the gamma-hydrogen transfer rate and biradical decay are related to the photochromic performances.     

New heteroleptic bis-phenanthroline copper(I) complexes with dipyridophenazine or imidazole fused phenanthroline ligands: spectral, electrochemical, and quantum chemical studies

Two new sterically challenged diimine ligands L(1) (2,9-dimesityl-2-(4'-bromophenyl)imidazo[4,5-f][1,10]phenanthroline) and L(2) (3,6-di-n-butyl-11-bromodipyrido[3,2-a:2',3'-c]phenazine) have been synthesized with the aim to build original heteroleptic copper(I) complexes, following the HETPHEN concept developed by Schmittel and co-workers. The structure of L(1) is based on a phen-imidazole molecular core, derivatized by two highly bulky mesityl groups in positions 2 and 9 of the phenanthroline cavity, preventing the formation of a homoleptic species, while L(2) is a dppz derivative, bearing n-butyl chains in α positions of the chelating nitrogen atoms. The unambiguous formation of six novel heteroleptic copper(I) complexes based on L(1), L(2), and complementary matching ligands (2,9-R(2)-1,10-phenanthroline, with R = H, methyl, n-butyl or mesityl) has been evidenced, and the resulting compounds were fully characterized. The electronic absorption spectra of all complexes fits well with DFT calculations allowing the assignment of the main transitions. The characteristics of the emissive excited state were investigated in different solvents using time-resolved single photon counting and transient absorption spectroscopy. The complexes with ligand L(2), bearing a characteristic dppz moiety, exhibit a very low energy excited-state which mainly leads to fast nonradiative relaxation, whereas the emission lifetime is higher for those containing the bulky ligand L(1). For example, a luminescence quantum yield of about 3 × 10(-4) is obtained with a decay time of about 50 ns for C2 ([Cu(I)(nBu-phen)(L(1))](+)) with a weak influence of strong coordinating solvent on the luminescence properties. Overall, the spectral features are those expected for a highly constrained coordination cage. Yet, the complexes are stable in solution, partly due to the beneficial π stacking between mesityl groups and vicinal phenanthroline aromatic rings, as evidenced by the X-ray structure of complex C3 ([Cu(I)(Mes-phen)(L(2))](+)). Electrochemistry of the copper(I) complexes revealed reversible anodic behavior, corresponding to a copper(I) to copper(II) transition. The half wave potentials increase with the steric bulk at the level of the copper(I) ion, reaching a value as high as 1 V vs SCE, with the assistance of ligand induced electronic effects. L(1) and L(2) are further end-capped by a bromo functionality. A Suzuki cross-coupling reaction was directly performed on the complexes, in spite of the handicapping lability of copper(I)-phenanthroline complexes.     

Spontaneous ionization of N-alkylphenothiazine molecules adsorbed in channel-type zeolites: effects of alkyl chain length and confinement on electron transfer

The mere mixing of N-alkylphenothiazines with three channel-type acid zeolites with various structures (ferrierite, H-MFI, and mordenite) induces the spontaneous ionization of the heterocyclic molecule in high yield upon adsorption. The diffuse reflectance UV-visible absorption and Raman scattering spectra show that the accessibility of the highly polarizing acid sites is not indispensable to induce the spontaneous ionization process. Due to their particularly low ionization potential values (6.7 eV), the adsorption of the molecules on the external surface or in the inner volume is the key parameter to generate the radical cation. However, the ionization yield and charge stabilization are intimately correlated to the possibility of the zeolites accommodating molecules inside their channels. Moreover, the higher electrostatic field gradient induced by high confinement is required to favor the second ionization and dication formation. The alkyl chain length plays a decisive role by either slowing down the diffusion process or blocking the molecule at the pore entry. Therefore, the efficiency of the ionization process that depends on the number of adsorbed molecules decreases significantly from phenothiazine to the N-alkylphenothiazines. The spectral data demonstrate that deformation of the alkyl group is necessary to allow the diffusion of the molecules into the channels.     

Nanosecond probing of the early nucleation steps of silver atoms in colloidal zeolite by pulse radiolysis and flash photolysis techniques

The process of formation and the subsequent aggregation of silver atoms (Ag⁰) in nanosized zeolite beta (BEA) are studied by transient absorption spectroscopy. The zeolite nanocrystals are stabilized in aqueous colloidal suspensions with a narrow particle size distribution in the range 30–60 nm. The reduction of silver cations is initiated either by pulse radiolysis of the aqueous suspension or by photoinduced electron transfer using an organic electron donor adsorbed in the zeolite framework. The silver atom in BEA nanosized crystals is found to be stable on the microsecond timescale.