Palladium-catalyzed double carbonylation using near stoichiometric carbon monoxide: expedient access to substituted 13C2-labeled phenethylamines

A novel and general approach for (13)C(2)- and (2)H-labeled phenethylamine derivatives has been developed, based on a highly convergent single-step assembly of the carbon skeleton. The efficient incorporation of two carbon-13 isotopes into phenethylamines was accomplished using a palladium-catalyzed double carbonylation of aryl iodides with near stoichiometric carbon monoxide.     

Stereoselective Synthesis,Configurational Assignment and Biological Evaluations of the Lipid Mediator RvD2n-3 DPA

Herein we report the first total synthesis of RvD2_{n-3 DPA}, an endogenously formed mediator biosynthesized from the omega-3 fatty acid n-3 docosapentaenoic acid. The key steps are the Midland Alpine borane reduction, Sonogashira cross-coupling reactions, and a Z-selective alkyne reduction protocol, yielding RvD2_{n-3 DPA} methyl ester in 13 % yield over 12 steps (longest linear sequence). The physical property data (UV chromophore, chromatography and MS/MS fragmentation) of the synthetic lipid mediator matched those obtained from biologically produced material. Moreover, synthetic RvD2_{n-3 DPA} also carried the potent biological activities of enhancing macrophage uptake of Staphylococcus aureus and zymosan A bioparticles.     

Complexes formed in solution between vanadium(IV)/(V) and the cyclic dihydroxamic acid putrebactin or linear suberodihydroxamic acid

An aerobic solution prepared from V(IV) and the cyclic dihydroxamic acid putrebactin (pbH(2)) in 1:1 H(2)O/CH(3)OH at pH = 2 turned from blue to orange and gave a signal in the positive ion electrospray ionization mass spectrometry (ESI-MS) at m/z(obs) 437.0 attributed to the monooxoV(V) species [V(V)O(pb)](+) ([C(16)H(26)N(4)O(7)V](+), m/z(calc) 437.3). A solution prepared as above gave a signal in the (51)V NMR spectrum at δ(V )= -443.3 ppm (VOCl(3), δ(V) = 0 ppm) and was electron paramagnetic resonance silent, consistent with the presence of [V(V)O(pb)](+). The formation of [V(V)O(pb)](+) was invariant of [V(IV)]:[pbH(2)] and of pH values over pH = 2-7. In contrast, an aerobic solution prepared from V(IV) and the linear dihydroxamic acid suberodihydroxamic acid (sbhaH(4)) in 1:1 H(2)O/CH(3)OH at pH values of 2, 5, or 7 gave multiple signals in the positive and negative ion ESI-MS, which were assigned to monomeric or dimeric V(V)- or V(IV)-sbhaH(4) complexes or mixed-valence V(V)/(IV)-sbhaH(4) complexes. The complexity of the V-sbhaH(4) system has been attributed to dimerization (2[V(V)O(sbhaH(2))](+) ? [(V(V)O)(2)(sbhaH(2))(2)](2+)), deprotonation ([V(V)O(sbhaH(2))](+) - H(+) ? [V(V)O(sbhaH)](0)), and oxidation ([V(IV)O(sbhaH(2))](0) -e(-) ? [V(V)O(sbhaH(2))](+)) phenomena and could be described as the sum of two pH-dependent vectors, the first comprising the deprotonation of hydroxamate (low pH) to hydroximate (high pH) and the second comprising the oxidation of V(IV) (low pH) to V(V) (high pH). Macrocyclic pbH(2) was preorganized to form [V(V)O(pb)](+), which would provide an entropy-based increase in its thermodynamic stability compared to V(V)-sbhaH(4) complexes. The half-wave potentials from solutions of [V(IV)]:[pbH(2)] (1:1) or [V(IV)]:[sbhaH(4)] (1:2) at pH = 2 were E(1/2) -335 or -352 mV, respectively, which differed from the expected trend (E(1/2) [VO(pb)](+/0) < V(V/IV)-sbhaH(4)). The complex solution speciation of the V(V)/(IV)-sbhaH(4) system prevented the determination of half-wave potentials for single species. The characterization of [V(V)O(pb)](+) expands the small family of documented V-siderophore complexes relevant to understanding V transport and assimilation in the biosphere.     

Using arbitrary trial distributions to improve intramolecular sampling in configurational-bias Monte Carlo

A new formulation of configurational-bias Monte Carlo that uses arbitrary distributions to generate trial bond lengths, angles and dihedrals is described and shown to provide similar acceptance rates with substantially less computational effort. Several different trial distributions are studied and a linear combination of the ideal distribution plus Gaussian distributions automatically fit to the energetic and ideal terms is found to give the best results. The use of these arbitrary trial distributions enables a new formulation of coupled–decoupled configurational bias Monte Carlo that has significantly higher acceptance rates for cyclic molecules. The chemical potential measured via a modified Widom insertion is found to be ill-defined in the case of a molecule that has flexible bond lengths due to the unbounded probability distribution that describes the distance between any two atoms. We propose a simple standard state that allows the computation of consistent chemical potentials for molecules with flexible bonds. We show that the chemical potential via Widom insertion is not computed properly for molecules with Coulombic interactions when the number of trials for any of the nonbonded selection steps is greater than one. Finally, we demonstrate the power of the new algorithms by sampling the side-chain conformations of a polypeptide.     

Surface-induced phase behavior of polymer/nanoparticle blends with attractions

In an athermal blend of nanoparticles and homopolymer near a hard wall, there is a first order phase transition in which the nanoparticles segregate to the wall and form a densely packed monolayer above a certain nanoparticle density. Previous investigations of this phase transition employed a fluids density functional theory (DFT) at constant packing fraction. Here we report further DFT calculations to probe the robustness of this phase transition. We find that the phase transition also occurs in athermal systems at constant pressure, the more natural experimental condition than constant packing fraction. Adding nanoparticle-polymer attractions increases the nanoparticle transition density, while sufficiently strong attractions suppress the first-order transition entirely. In this case the systems display a continuous transition to a bulk layered state. Adding attractions between the polymers and the wall has a similar effect of delaying and then suppressing the first-order nanoparticle segregation transition, but does not lead to any continuous phase transitions.     

Tris(2-(1H-pyrazol-1-yl)pyridine)cobalt(III) as p-type dopant for organic semiconductors and its application in highly efficient solid-state dye-sensitized solar cells

Chemical doping is an important strategy to alter the charge-transport properties of both molecular and polymeric organic semiconductors that find widespread application in organic electronic devices. We report on the use of a new class of Co(III) complexes as p-type dopants for triarylamine-based hole conductors such as spiro-MeOTAD and their application in solid-state dye-sensitized solar cells (ssDSCs). We show that the proposed compounds fulfill the requirements for this application and that the discussed strategy is promising for tuning the conductivity of spiro-MeOTAD in ssDSCs, without having to rely on the commonly employed photo-doping. By using a recently developed high molar extinction coefficient organic D-π-A sensitizer and p-doped spiro-MeOTAD as hole conductor, we achieved a record power conversion efficiency of 7.2%, measured under standard solar conditions (AM1.5G, 100 mW cm(-2)). We expect these promising new dopants to find widespread applications in organic electronics in general and photovoltaics in particular.     

Computational investigations of pore forming peptide assemblies in lipid bilayers

This Letter presents the first application of a three-dimensional numerical molecular theory based modeling approach to study the structure and energetics of assemblies of peptides embedded in lipid bilayers. Coarse-grained models were used for both the peptides and lipids. Both barrel-stave and toroidal pore morphologies for the lipids near the peptide assemblies are found, but at different assembly sizes. The free energy of the assembly is found to have a global free energy minimum for a solution with a membrane-spanning toroidal pore. A pairwise approximation to this free energy is found to underpredict the free energy minimum associated with the membrane-spanning pores.     

Comparison of random-walk density functional theory to simulation for bead-spring homopolymer melts

Density profiles for a homopolymer melt near a surface are calculated using a random-walk polymeric density functional theory, and compared to results from molecular dynamics simulations. All interactions are of a Lennard-Jones form, for both monomer-monomer interactions and surface-monomer interactions, rather than the hard core interactions which have been most investigated in the literature. For repulsive systems, the theory somewhat overpredicts the density oscillations near a surface. Nevertheless, near quantitative agreement with simulation can be obtained with an empirical scaling of the direct correlation function. Use of the random phase approximation to treat attractive interactions between polymer chains gives reasonable agreement with simulation of dense liquids near neutral and attractive surfaces.