Catalytic Enantioselective Nazarov Cyclization: Construction of Vicinal All‐Carbon‐Atom Quaternary Stereocenters

The diastereoselective asymmetric synthesis of vicinal all‐carbon‐atom quaternary stereocenters is a challenging problem in organic synthesis for which only few solutions have been described. A catalytic asymmetric Nazarov cyclization of fully substituted dienones that provides cyclopentenone derivatives with vicinal quaternary stereocenters in high optical purity and as single diastereoisomers is now reported.     

Entropically driven photochemical upconversion

Conventional photochemical upconversion (UC) through homo-geneous triplet-triplet annihilation (TTA) is subject to several enthalpic losses that limit the UC margin. Here, we address one of these losses: the triplet energy transfer (TET) from the sensitizer to the emitter molecules. Usually, the triplet energy level of the emitter is set below that of the sensitizer. In our system, the triplet energy level of the emitter exceeds that of the sensitizer by ～600 cm(-1). Choosing suitable concentrations for the sensitizer and emitter molecules, we can exploit entropy as a driving force for the migration of triplet excitation from the sensitizer to the emitter manifolds. Thereby we obtain a new record for the peak-to-peak TTA-UC energy margin of 0.94 eV. A modified Stern-Volmer analysis yields a TET rate constant of 2.0 × 10(7) M(-1) s(-1). Despite being relatively inefficient, the upconverted fluorescence is easily visible to the naked eye with irradiation intensities as low as 2 W cm(-2).     

PaDEL‐DDPredictor: Open‐source software for PD‐PK‐T prediction

ADMET (absorption, distribution, metabolism, excretion, and toxicity)‐related failure of drug candidates is a major issue for the pharmaceutical industry today. Prediction of PD‐PK‐T properties using in silico tools has become very important in pharmaceutical research to reduce cost and enhance efficiency. PaDEL‐DDPredictor is an in silico tool for rapid prediction of PD‐PK‐T properties of compounds from their chemical structures. It is free and open‐source software that, has both graphical user interface and command line interface, can work on all major platforms (Windows, Linux, and MacOS) and supports more than 90 different molecular file formats. The software can be downloaded from http://padel.nus.edu.sg/software/padelddpredictor . © 2012 Wiley Periodicals, Inc.     

Colloid surface engineering via deposition of multilayered thin films from polyelectrolyte blend solutions

Multilayer thin films were constructed on polystyrene colloidal particles by depositing alternating layers of poly(allylamine hydrochloride) (PAH) at pH 7.5 and varying composition blends of poly(acrylic acid) (PAA) and poly(styrenesulfonate) (PSS) at pH 3.5. Following the deposition of each layer, microelectrophoresis experiments showed alternating zeta-potentials, suggesting the formation of multilayered films on the particles. Scanning and transmission electron microscopy were used to examine the surface morphology of the colloidal particles, with homogeneous surface coatings apparent for films deposited from PAA/PSS blend solutions containing up to 90 wt % PAA. The colloidal stability of these particles is greater than those coated with individual PAH and PAA layers. In the case of the blend PAA/PSS = 25:75 wt %, up to 20 layers were assembled without compromising the colloidal stability of the dispersion. The results demonstrate that the deposition of layers from PE blend solutions containing a strong and weak PE can be used as a facile method for controlling the surface properties and hence the colloidal stability of core-shell particles, as well as the thickness and morphology of the coatings. Control of these parameters is important for subsequent processing and application of these particles in controlled delivery, photonics, catalytic, and separation applications.     

Isolation of cis- and trans-[SnR2] configurational isomers of the octahedral complex,dichlorobis(4-chlorophenyl)tin(IV)-4,4′-dimethyl-2,2′-bipyridyl

The coordinative interaction between dichlorobis(4-chlorophenyl)tin(IV) and the chelating ligand, 4,4′-dimethyl-2-2′-bipyridyl (dmbipy), has allowed the isolation of both cis- and trans-[SnR₂] configurational isomers of the derived complex, [Sn(4-ClC₆H₄)₂Cl₂(dmbipy)], constituting the first such case reported for octahedral [SnR₂X₂L₂] systems.