Platinum(II)-Catalyzed Novel Synthesis of 3,4-Fused Furans

A novel synthesis of 3,4-fused furans (both tricyclic and bicyclic) through platinum-catalyzed cyclization of 3-(2-formylcycloalkenyl)-acrylic amides 2 in methanol is described (up to 90% yield). Tricyclic 3,4-fused dihydrofuran derivatives were also obtained via reductive cyclization of 2. The substrates 2 were obtained from β- bromovinyl aldehydes by a Pd-catalyzed Heck reaction.     

Unexpected influence of stereochemistry on the cytotoxicity of highly efficient Ti(IV) salan complexes: new mechanistic insights

The effect of stereochemistry on the cytotoxicity of highly active and hydrolytically stable N-methylated Ti(IV) salan complexes is reported. Four bis(isopropoxo) complexes incorporating N-methylated salan ligands with different aromatic substitution patterns have been prepared in racemic and optically active forms for the first time by ligand-to-metal chiral induction from trans-diaminocyclohexyl-based chiral ligands. The configuration of the metal center that derives from that of the ligand has an enormous influence on cytotoxicity, with the racemic mixture mostly being more active than the single enantiomers that are of either similar or different activity. This implies that the active species is a salan-bound heterochiral polynuclear compound, interacting with a chiral target. Four additional complexes of achiral salan and chiral labile sec-butoxo ligands, analyzed as racemic and as homochiral, revealed no influence of stereochemistry, supporting early dissociation of the labile ligands to give the polynuclear products.     

Different ortho and para electronic effects on hydrolysis and cytotoxicity of diamino bis(phenolato) "salan" Ti(IV) complexes

Bis(isopropoxo) Ti(IV) complexes of diamino bis(phenolato) "salan" ligands were prepared, their hydrolysis in 1:9 water/THF solutions was investigated, and their cytotoxicity toward colon HT-29 and ovarian OVCAR-1 cells was measured. In particular, electronic effects at positions ortho and para to the binding phenolato unit were analyzed. We found that para substituents of different electronic features, including Me, Cl, OMe, and NO(2), have very little influence on hydrolysis rate, and all para-substituted ortho-H complexes hydrolyze slowly to give O-bridged clusters with a t(1/2) of 1-2 h for isopropoxo release. Consequently, no clear cytotoxicity pattern is observed as well, where the largest influence of para substituents appears to be of a steric nature. These complexes exhibit IC(50) values of 2-18 μM toward the cells analyzed, with activity which is mostly higher than those of Cp(2)TiCl(2), (bzac)(2)Ti(OiPr)(2) and cisplatin. On the contrary, major electronic effects are observed for substituents at the ortho position, with an influence that exceeds even that of steric hindrance. Ortho-chloro or -bromo substituted compounds possess extremely high hydrolytic stability where no major isopropoxo release as isopropanol occurs for days. In accordance, very high cytotoxicity toward colon and ovarian cells is observed for ortho-Cl and -Br complexes, with IC(50) values of 1-8 μM, where the most cytotoxic complexes are the ortho-Cl-para-Me and ortho-Br-para-Me derivatives. In this series of ortho-substituted complexes, the halogen radius is of lesser influence both on hydrolysis and on cytotoxicity, while OMe substituents do not impose similar effect of hydrolytic stability and cytotoxicity enhancement. Therefore, hydrolytic stability and cytotoxic activity are clearly intertwined, and thus this family of readily available Ti(IV) salan complexes exhibiting both features in an enhanced manner is highly attractive for further exploration.     

The influence of intrinsic and surface states on the emission properties of colloidal nanocrystals

Time Resolved Photoluminescence (TRPL) measurements on the picosecond time scale (temporal resolution of 17 ps) on colloidal CdSe and CdSe/ZnS Quantum Dots (QDs) were performed, to elucidate the role of intrinsic and surface states on the emission process. Transient PL spectra reveal three emission peaks with different lifetimes (60 ps, 460 ps and 9–10 ns, from the bluest to the reddest peak). The energy separations among the states, together with their characteristic decay times, allow us to attribute the two higher energy peaks to ±1^U and ±1^L bright states of the fine structure picture of spherical CdSe QDs, and the third one to surface states emission, respectively. We show that the contribution of surface emission to the PL results to be different for the two samples studied (67% in the CdSe QDs and 32% in CdSe/ZnS QDs), confirming the decisive role of the ZnS shell in the improvement of the surface passivation.     

Variation in viscosity and ion conductivity of a polymer-salt complex exposed to gamma irradiation

We study changes in microstructure and resulting changes in the properties of PEO(1 − x)-NH₄ClO₄(x) samples where x = 0.18, when irradiated with gamma doses varying up to 50 kGy. Viscosities of aqueous solutions of the irradiated samples give an idea of the change in molecular weight and show correlation with ion conductivity. On the whole, there is a chain scission on irradiation, though there is evidence of some cross-linking at higher doses. The ion conductivity shows a strong increase for an irradiation of 35 kGy. DSC studies indicate a decrease in crystallinity with gamma dose.     

On the conversion XCN ⟷ XNC via an efficient and economic perturbative wave function approach

The energetics, structures, reaction paths and mechanisms for the conversion XCN ? XNC, with X = H, Li, CH₃ and H₂B have been investigated through the use of improved virtual orbitals (IVO) in a second-order multireference perturbation theory (MRPT) treatment within the framework of state-specific (SS) parametrisation of the wave function for the target state (IVO-SSMRPT). Due to its flexibility, IVO-SSMRPT formulation allows us to take into account the major part of the coupling between the dynamic and nondynamic correlation effects in an accurate manner. The results obtained by our calculations agree well with the state-of-the-art electronic structure methods and reference values which illustrates that IVO-SSMRPT, when applied judiciously, can be very accurate for reaction surfaces of XCN ? XNC isomerisation, barrier and bond-parameters.     

Characterization and growth of CdS nanoparticles by a cost effective chemical reduction method

A simple chemical reduction method is followed to grow CdS nanoparticles at room temperature with different duration of time. The grown samples are ultrasonicated in ethanol. The dispersed samples are characterized using electron diffraction techniques. Simultaneously optical absorption, photoluminescence and longtime photorelaxation of these samples are studied at room temperature. An increase in band gap is observed in each case as compared to bulk CdS. Also particle size increases with increase of growth time and hence there is decrease of band gap with increase of growth duration. Simultaneously long time relaxation increases with increase of growth time. An attempt is made to correlate the structural, optical, electrical and opto‐electrical properties. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Pd-Catalyzed Regioselective Domino C−C Bond Formation to Access N-Fused Benzimidazo-Indolo-Isoquinoline Heterocycles

Regioselective synthesis of N-fused benzimidazo-indolo-isoquinoline heterocycles via Pd-catalyzed domino coupling reaction of 1-(1-methyl-1H-indol-2-yl)-1H-benzimidazoles and aryl halides was developed. This one pot methodology proceeded via a five-member carbopalladacycle intermediate and provided direct and facile route to access structurally complex polyheterocycles in moderate to good yields. These unique hybrid molecules resembled structural similarity with naturally isolated alkaloids. Notably, the present domino process occurred through activation of three C−H bonds and the simultaneous formation of two new C−C bonds in one-shot. These molecules exhibited strong solid and solution phase fluorescence and their emission spectra in both the medium are reported here.