Properties of the discotic-nematic to isotropic transition: influence of short range orientational order

The present investigation concerns the analysis of the influence of short range orientational correlation on the thermodynamic properties of discotic-nematic liquid crystals. Two-site cluster approximation is applied to the orientational molecular coordinates to include the short range orientational correlation. The role of short range orientational order, dispersion interaction, molecular length-to-width ratio and pressure on the thermodynamic and orientational behaviour of discotic nematogens close to the discotic-nematic to isotropic transition are analysed. It is observed that the short range orientational order has a strong influence on the thermodynamic properties and that the transition properties of both the calamitic and discotic mesogens exhibit quite similar behaviour.     

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.     

Synthesis of 1,3-Dioxanes Catalyzed by TsOH-SiO2 Under Solvent-Free Conditions

Silica-supported p-toluene sulfonic acid is found to be an excellent catalyst for the Prins reaction to produce 1,3-dioxanes in good yields from olefins and aliphatic aldehydes in dichloromethane at room temperature and solventless microwave irradiation within a short reaction time.     

A microwave-assisted, copper-catalyzed three-component synthesis of dihydropyrimidinones under mild conditions

The synthesis of dihydropyrimidinones via a clean multi-component Biginelli reaction under microwave irradiation is reported. The copper-catalyzed process proved to be simple, efficient, economical, and environmentally friendly.     

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.     

Exploring naphthyl derivatives as SARS-CoV papain-like protease (PLpro) inhibitors and its implications in COVID-19 drug discovery

Molecular Diversity - Novel coronavirus disease 2019 (COVID-19) emerges as a serious threat to public health globally. The rapid spreading of COVID-19, caused by severe acute respiratory syndrome...     

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.