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International audience; Novel norbornene-based imine-stabilized silylium ions 2 have been synthesized via the simple reaction of sulfide-stabilized silylium ion 1 with carbonyl derivatives. Those silylium ions were fully characterized in solution and in the solid state by NMR spectroscopy and X-ray diffraction analysis as well as DFT calculations. Unlike the previously reported phosphine-stabilized silylium ion VI, behaving as a Lewis pair, calculations show that 2 have a strong Lewis acid character. Indeed, imine-stabilized silylium ions 2 are able to activate Si-H bonds and catalyzed the hydrosilylation of carbonyl derivatives under mild conditions.

International audience; A stable (amino)plumbylene-substituted phosphaketene 3 was synthesized by the successive reactions of PbCl 2 with two anionic reagents (lithium amidophosphine and NaPCO). Of particular interest, the thermal evolution of 3, at 80 °C, leads to the transient formation of corresponding amino-and phosphanylidene-phosphaketenes (6 and 7), via a reductive elimination at the Pb II center forming new N-P and P-P bonds. Further evolution of 6 gives a new cyclic (amino)phosphanylidene phosphorane 4, which shows a unique reactivity as a phosphinidene. This result provides a new synthetic route to phosphinidenes, extending and facilitating further their access.

The NH bond activation of ammonia, primary and secondary amines by tetramesityldisilene and -digermene was investigated. In each case, a disilyl- or digermylamine was formed as the only product of amine addition. The mechanism of the addition of ammonia to tetramesityldisilene was computed and revealed a three-step reaction pathway: formation of the anti-ammonia-disilene adduct, inversion at the β-silicon, and syn-transfer of the proton to give the syn-product, where each step follows a distinct stereochemical course. Examination of the reaction landscape also revealed several additional insights: (a) that, in the initial step, the formation of the anti-oriented zwitterionic intermediate is kinetically more preferable than formation of the syn-oriented zwitterionic intermediate, (b) that intermolecular transfer of a proton is not energetically feasible in non-polar solvents, and (c) that the bulk of the substituents can have a profound effect on the stereochemical course of the reaction. With this detailed understanding, nucleophilic additions to ditetrelenes can be exploited in the future.

Hetero Diels-Alder (HDA) reactions between 2,3-dimethyl-1,3-butadiene and diethyl ester of aroyl phosphonates catalyzed by AlCl3 to afford (3,6-dihydro-2H-pyran-2-yl) phosphonate derivatives were investigated. Aroyl phosphonates with electron-withdrawing groups generally resulted in better isolated chemical yields. A stoichiometric amount of AlCl3 rather than a catalytic amount was necessary to activate the cycloaddition reaction. The amount of AlCl3 catalyst and its effect on LUMO of ethyl ester benzoyl phosphonate were also investigated by performing density functional theory (DFT) (B97D/6-31+G(d,p)) computations in dichloromethane. An increased loading of AlCl3 induced a considerable decrease in the LUMO energy of ethyl ester of benzoyl phosphonate. The computed Gibbs free activation energy is 17.03 kcal/mol in DCM at 0°C using the same computational level.

Silicon(IV) phthalocyanines (4 and 5) bearing two calixarene groups as axial ligands were synthesized. Surprisingly, both phthalocyanines were obtained as two different isomers (4a–b and 5a–b) depending on the distance between calixarene benzene groups and the phthalocyanine ring. DFT and TD-DFT computations were performed to model plausible structures of these isomers and to simulate electronic absorption spectra. These isomers converted into each other depending on the polarity of the used solvent, temperature and light irradiation. The photophysical and photochemical properties of each isomer were investigated in dimethylsulfoxide (DMSO) for the determination of photodynamic therapy (PDT) activities of these compounds. The more blue-shifted isomers (4b and 5b) showed higher fluorescence quantum yields and singlet oxygen generation compared to more red-shifted counterparts (4a and 5a). This behavior is extremely important for developing activatable photosensitizers for cancer treatment by PDT. Although these photosensitizers produce lower singlet oxygen in normal cells, they produce higher singlet oxygen (six times higher for 5b) in cancer cells since these photosensitizers converted to more blue-shifted isomers by using light irradiation.

The novel 7-hydroxy-3-(3,4,5-trimethoxyphenyl)coumarin ( 1 ) has been synthesized via Perkin reaction and its phthalonitrile derivatives ( 2 , 3 , 4 and 5 ) have also been prepared from the reaction of this coumarin ( 1 ) with 3-nitrophthalonitrile, 4-nitrophthalonitrile or 4,5-dichlorophthalonitrile compounds for the first time in this study. The newly synthesized compounds have been fully characterized by 1 H NMR, MALDI-TOF, FT-IR, UV–vis and fluorescence spectral data as well as elemental analysis. The exact structure of the coumarin substituted phthalonitrile derivatives ( 2 , 3 and 5 ) have also been determined using X-ray diffraction. The electronic absorption and fluorescence properties of these new compounds have been studied in different solvents. The chemosensor behaviors of these compounds to metal ions have also been examined by fluorescence spectroscopy and these compounds exhibited as fluorescence chemosensor for the determination of Fe 3+ ions in solution. Fe 3+ complex structures of mono-coumarin ring substituted derivatives ( 1–4 ) have been investigated by using density functional theory computations.

WOS:000330850300014 PubMed ID: 23323992 Monoamine oxidase (MAO, EC 1.4.3.4) is responsible from the oxidation of a variety of amine neurotransmitters. MAO inhibitors are used for the treatment of depression or Parkinson's disease. They also inhibit the catabolism of dietary amines. According to one hypothesis, inactivation results from the formation of a covalent adduct to a cysteine residue in the enzyme. If the adduct is stable enough, the enzyme is inhibited for a long time. After a while, enzyme can turn to its active form as a result of adduct breakdown by beta-elimination. In this study, the proposed inactivation mechanism was modeled and tested by quantum chemical calculations. Eight heterocyclic methylthioamine derivatives were selected to represent the proposed covalent adducts. Activation energies related to their beta-elimination reactions were calculated using ab initio and density functional theory methods. Calculated activation energies were in good agreement with the relative stabilities of the hypothetical adducts predicted in the literature by enzyme inactivation measurements. Marmara University Scientific Research Projects Commission (BAPKO)Marmara University [BSE-087/051201] This work was supported by the Marmara University Scientific Research Projects Commission (BAPKO), project no.: BSE-087/051201.

Because of discrepancies in the available experimental data, an extensive theoretical investigation of the formation of the Vilsmeier-Haack (VH) complex has been carried out. The barriers to complex formation calculated using eight different density functional methods (BLYP, B2-PLYP, B3LYP, B3PW91, MPW1K, M06-2X, and PBE1PBE), MP2, and extrapolation techniques (CBS-QB3, G3B3) with several basis sets (6 -aEuro parts per thousand 31 + G**, 6 -aEuro parts per thousand 311++G**, 6 -aEuro parts per thousand 311 + (3df,2p), aug-cc-pVDZ, and aug-cc-pVTZ) were compared with experimental data. For the overall reaction, MP2/aug-cc-pVDZ and M06-2X/6-31 + G(d,p) perform best compared to the CBS techniques. The results help clarify some open mechanistic questions. Excellence Cluster Engineering of Advanced Materials; Deutsche ForschungsgemeinschaftGerman Research Foundation (DFG) We thank the Excellence Cluster Engineering of Advanced Materials (funded by the Deutsche Forschungsgemeinschaft) for financial support.

The aromaticity of 1,3,4-thiadiazole-2-thione and its oxygen analogs including their tautomeric forms, and 1,3,4-thiadiazole, 1,3,4-oxadiazole, furan, thiophene, cyclopentadiene, the cyclopentadienyl anion and the cyclopentadienyl cation has been examined by harmonic oscillator measure of aromaticity (HOMA), aromatic stabilization energy (ASE), differential heat of hydrogenation (Δ Δ HH), and nucleus independent chemical shifts (NICS (0)), calculated at the HF/6-31G**, B3LYP/6-31G**, B3LYP/6-311G**, and B3LYP/6-311++G** levels. A principal component analysis (PCA) of the data set generated from these aromaticity results has been presented and compared with similar analyses in the recent literature. It has been shown that aromaticity is at least a two-dimensional phenomenon, independent of the level of the computational method employed. We observed that the sulfur-containing heterocyclic compounds are more aromatic than their oxygen analogs according to geometrical aromaticity measurements. In addition, our calculations of the energies of the tautomeric forms showed that the carbonyl and thiocarbonyl tautomers are more stable than the hydroxy and mercapto forms, which is in good agreement with the experimental findings in the literature.

A series of zinc phthalocyanines (ZnPcs) tetra-substituted with 1,3-di[2-(2-ethoxyethoxy)ethoxy]-2-propanol (1a) or 1,3-di[2-(2-ethoxyethoxy)ethoxy]-2-propanethiol (1b) at peripheral (β) (6a–b) and non-peripheral (α) (7a–b) positions have been synthesized and characterized. The spectroscopic, photophysical (fluorescence quantum yields and lifetimes) and photochemical (singlet oxygen generation and photodegradation) properties of these newly synthesized phthalocyanines have been investigated in DMSO. The effects of the position of the substituents on the phthalocyanine skeleton and the nature of the linker heteroatom on their spectroscopic, photophysical and photochemical properties have been determined. The quenching behavior of the zinc phthalocyanines by 1,4-benzoquinone has been studied in DMSO. All of the zinc(II) Pc complexes (6a–b and 7a–b) showed similar electronic absorption spectra in various solvents (chloroform, dichloromethane, DMF, DMSO, THF and toluene). However, complex 7a gave an extra red-shifted band at 742 nm in chloroform and dichloromethane. DFT and TD-DFT computations were performed on the model structures (8a–d, pp-8a–d and 9a–d) to find out the cause of the extra red-shifted Q band (J-type aggregation or protonation of the Pc ring). The computational results showed that monoprotonation of a meso nitrogen atom leads to the formation of this extra band. Photophysical and photochemical measurements indicated that these newly synthesized ZnPc derivatives are promising candidates for use as photosensitizers in the application of PDT.

Molecular-dynamics (MD) simulations of urea crystals of different shapes (cubic, rectangular prismatic, and sheet) have been performed using our previously published force field for urea. This force field has been validated by calculating values for the cohesive energy, sublimation temperature, and melting point from the MD data. The cohesive energies computed from simulations of cubic and rectangular prismatic urea crystals in vacuo at 300 K agreed very well with the experimental sublimation enthalpies reported at 298 K. We also found very good agreement between the melting points as observed experimentally and from simulations. Annealing the crystals just below the melting point leads to reconstruction to form crystal faces that are consistent with experimental observations. The simulations reveal a melting mechanism that involves surface (corner/edge) melting well below the melting point, and rotational disordering of the urea molecules in the corner/edge regions of the crystal, which then facilitates the translational motion of these molecules.

We describe an improved force field parameter set for the generalized AMBER force field (GAFF) for urea. Quantum chemical computations were used to obtain geometrical and energetic parameters of urea dimers and larger oligomers using AM1 semiempirical MO theory, density functional theory at the B3LYP/6-31G(d,p) level, MP2 and CCSD ab initio calculations with the 6-311++G(d,p), aug-cc-pVDZ, aug-cc-pVTZ, and aug-cc-pVQZ basis sets, and with the CBS-QB3 and CBS-APNO complete basis set methods. Seven different urea dimer structures were optimized at the MP2/aug-cc-pVDZ level to obtain accurate interaction energies. Atomic partial charges were calculated at the MP2/aug-cc-pVDZ level with the restrained electrostatic potential (RESP) fitting approach. The interaction energies computed with these new RESP charges in the force field are consistent with those obtained from CCSD and MP2 calculations. The linear dimer structure calculated using the force field with modified geometrical parameters and the new RESP charge set agrees well with available experimental data.

The new annulation reaction of trichloronitroethylene with aniline results in the formation of a quinoxalinone-N-oxide derivative. The mechanism of this one-pot annulation reaction between trichloronitroethylene (TCNiE) and anilines has been extensively investigated with B3LYP/6-31+G** methodology. Five different paths (1-5) were proposed and modeled by using this method. These paths were compared in terms of the activation energies of their rate-determining steps and in regard to the experimental findings. Paths 3 and 5, proceeding via four-membered heterocyclic rings, were found to be the most plausible paths with activation energies of 32 and 29 kcal/mol for the rate-determining steps, respectively. The effects of substituent, solvent, temperature, and computational method on these steps were also investigated. The results showed that path 5 is the most plausible mechanism for the annulation reaction of trichloronitroethylene with aniline.