A rhodium(I)-catalyzed formal allenic Alder ene reaction for the rapid and stereoselective assembly of cross-conjugated trienes

A rhodium(I)-catalyzed allenic Alder ene reaction to prepare cross-conjugated trienes has been discovered. The scope and limitations are currently being investigated, and the results obtained to date are reported on. This method shows enticing functional group compatibility by tolerating terminal and internal alkynes, hydroxyl, sulfonamide, ether, and diester groups. Progress has been made to increase the stereoselectivity of the olefinic side chain via an unprecendented iridium(I) catalyzed Alder-ene reaction.     

Quantum dots tailored with poly(para-phenylene vinylene)

In polymernanoparticle composites, uniform dispersion of the nanoparticles carries advantages over cases where nanoparticle aggregation dominates. Such dispersion has been particularly difficult to obtain in the case of composites prepared from nanoparticles and conjugated polymers. Here, we show that cadmium selenide nanocrystals, or quantum dots, can be integrated into thin films of poly(para-phenylene vinylene) (PPV) without aggregation. The two key departures from previous studies of quantum-dot/electronic polymer composites are (1) the synthesis of high-quality quantum dots directly in novel, functional ligands, thus eliminating the need for ligand exchange, and (2) polymerization chemistry that grafts PPV to the quantum dot surface. Solid-state photoluminescence spectra of composite materials prepared by these novel techniques reveal the critical importance of the quantum dot-polymer interface that will enable new investigations in nanoparticle-based light-emitting devices.     

The first total synthesis of 15-deoxy-Delta12,14-prostaglandin J2 and the unambiguous assignment of the C14 stereochemistry

[reaction: see text] The first total synthesis of 15-deoxy-Delta12,14-prostaglandin J2 is reported. The highly unsaturated cyclopentenone prostaglandin was obtained via a silicon-tethered allenic [2 + 2 + 1] cycloaddition reaction developed in our group. In addition, the stereochemistry at C14 has been assigned unambiguously.     

Observation of enhanced energy transfer in individual quantum dot-oligophenylene vinylene nanostructures

The temporal and spectral properties of luminescence from individual CdSe quantum dot-oligophenylene vinylene nanostructures (single quantum dots with conjugated organic ligands coordinated to the surface) are profoundly modified relative to blended films of the same components. These kinds of composite quantum dot-conjugated organic systems have attracted significant interest as a way to improve efficiency in photovoltaic device applications. By direct functionalization of the dot surface with the conjugated organic ligands, we realize a significant enhancement in energy transfer and luminescence stability.     

Nonviral gene delivery using poly‐D/L aspartate‐diethylenetriamine cationic polymers and polyethylene glycol: A two‐step approach

Cationic polymers have received much attention as promising nonviral vectors for gene transfer. However, development of polymers with low cell toxicities and high transfection efficiencies continue to be a significant problem and a major hurdle to their success. Poly‐D /L aspartate‐diethylenetriamine poly(D /L Asp‐DET) polymers were synthesized and evaluated as nonviral gene delivery agents. Poly(D /L Asp‐DET) polymers display endosome buffering capacity. The polymers condense plasmid DNA above N:P ratios of 1 and form polyplex particles of ～50–100 nm, with zeta potentials between neutral and +40 mV. Transmission electron microscopy shows the polyplexes to be uniform in size and shape. Polyplexes maintain the structural integrity of DNA following incubation in nucleases and also show high transfection efficiencies with minimal toxicity in both HCT‐116 and PC‐3 cell culture. However, it is found that these poly(D /L Asp‐DET)/DNA polyplexes immediately aggregate in salt and serum conditions, making them unsuitable for use in vivo. Therefore, the polyplexes were further modified by covalent addition of polyethylene glycol (PEG). Introduction of this second step produces PEG‐polyplexes of uniform size (below 100 nm), with neutral zeta potentials that are also stable in both salt and serum conditions. These results suggest poly(D /L Asp‐DET) cationic polymers as potentially safe and efficient nonviral gene delivery agents. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

An allenic Pauson-Khand-type reaction: a reversal in pi-bond selectivity and the formation of seven-membered rings

[reaction: see text] Treatment of alkynyl allenes with [Rh(CO)(2)Cl](2) results in a formal [2 + 2 + 1] cycloaddition reaction. This reaction occurs with complete regioselectivity for a variety of substrates affording only 4-alkylidene cyclopentenones in good yields. Moreover, seven-membered rings have been prepared in high yields.     

Magnetic and Mössbauer effect study of laves phases of U x Fe100−x (x=32, 33.3 and 35)

⁵⁷Fe Mössbauer effect measurements have been made on U _x Fe_100?x (x=32, 33.3, and 35) samples at 300 and 78 K. Laves phase structure was maintained for all three samples. Mössbauer spectra of the three samples were found to be a symmetric quadrupole doublet at 300 K. Such spectra were converted into a set of two overlapping six lines pattern at 78 K. The values of the hyperfine fields have been found to vary systematically with the iron content in the samples. The Curie temperatures, as determined by the ac susceptibility measurements, have been found to increase by increasing the amount of iron in the samples.     

High-speed computers as a supplement to graphical methods--V. HALTAFALL, a general program for calculating the composition of equilibrium mixtures

A computer program, HALTAFALL, is described which calculates the equilibrium concentrations of the species in mixtures of any number of components, which can form any number of complexes and solid phases, provided concentrations (or partial pressures) can be used in the equilibrium calculations. Of course, the equilibrium constants must be known and enough data be given about the gross composition. Some applications are indicated. The flexible input rules make it applicable to a variety of problems. From the input information, the program itself devises an efficient plan for solving the simultaneous equations. The program also provides an efficient means of finding out which of many possible solid phases can actually appear in a certain equilibrium mixture.