Photoinitiated charge transport in supramolecular assemblies of a 1,7,N,N'-tetrakis(zinc porphyrin)-perylene-3,4:9,10-bis(dicarboximide)

We report the synthesis and photophysical characterization of a multichromophore array, (Z3PN)4PDI, consisting of four zinc 5-phenyl-10,15,20-tri(n-pentyl)porphyrins (Z3PN) attached to the 1,7,N,N'-positions of perylene-3,4:9,10-bis(dicarboximide) (PDI). The dynamics of energy and charge transport within this system were compared to those of two model compounds, N,N'-(Z3PN)2PDI and 1,7-(Z3PN)2PDI. The symmetry of the lowest unoccupied and highest occupied molecular orbitals of PDI results in significantly different electronic couplings between Z3PN and PDI when they are connected at the 1,7-positions vs the N,N'-positions of PDI. This results in two distinct pathways for electron transfer in (Z3PN)4PDI. Using a combination of metal-ligand binding with the bidentate ligand 1,4-diazabicyclo[2.2.2.]octane (DABCO) and pi-pi stacking, (Z3PN4)PDI forms a supramolecular assembly, [[(Z3PN)4PDI]2-DABCO4]2, in toluene solution. The structure of this hierarchical assembly is characterized with the use of solution-phase X-ray scattering techniques and demonstrates both efficient light harvesting and facile charge separation and transport using multiple pathways.     

Screening a fragment cocktail library using ultrafiltration

Ultrafiltration provides a generic method to discover ligands for protein drug targets with millimolar to micromolar K(d), the typical range of fragment-based drug discovery. This method was tailored to a 96-well format, and cocktails of fragment-sized molecules, with molecular masses between 150 and 300 Da, were screened against medical structural genomics target proteins. The validity of the method was confirmed through competitive binding assays in the presence of ligands known to bind the target proteins.     

A comparative study of energy consumption and physical properties of microfibrillated cellulose produced by different processing methods

Microfibrillated celluloses (MFCs) with diameters predominantly in the range of 10–100 nm liberated from larger plant-based fibers have garnered much attention for the use in composites, coatings, and films due to large specific surface areas, renewability, and unique mechanical properties. Energy consumption during production is an important aspect in the determination of the “green” nature of these MFC-based materials. Bleached and unbleached hardwood pulp samples were processed by homogenization, microfluidization, and micro-grinding, to determine the effect of processing on microfibril and film properties, relative to energy consumption. Processing with these different methods affected the specific surface area of the MFCs, and the film characteristics such as opacity, roughness, density, water interaction properties, and tensile properties. Apparent film densities were approximately 900 kg/m³ for all samples and the specific surface area of the processed materials ranged from approximately 30 to 70 m²/g for bleached hardwood and 50 to 110 m²/g for unbleached hardwood. The microfluidizer resulted in films with higher tensile indices than both micro-grinding and homogenization (148 Nm/g vs. 105 Nm/g and 109 Nm/g, respectively for unbleached hardwood). Microfluidization and micro-grinding resulted in films with higher toughness values than homogenization and required less energy to obtain these properties, offering promise for producing MFC materials with lower energy input. It was also determined that a refining pretreatment required for microfluidization or homogenization can be reduced or eliminated when producing MFCs with the micro-grinder. A summary of the fiber and mechanical energy costs for different fibers and processing conditions with economic potential is presented.     

Observations of plasma line splitting in the ionospheric incoherent scatter spectrum

Wide-bandwidth ionospheric incoherent scatter (IS) spectra obtained using the Arecibo IS radar show the occurrence of a split in the plasma line (i.e., two plasma lines) when the plasma frequency is close to the second harmonic of the electron gyrofrequency. This split is predicted in the IS theory for a magnetized plasma, but observations have never been reported. Here we present the experimental results and theoretical calculations supporting the observations. These results may assist in understanding the behavior of Langmuir waves in the magnetized plasma and are a validation of what historically was a somewhat controversial aspect of the IS theory.     

Compressed sensing for resolution enhancement of hyperpolarized 13C flyback 3D-MRSI

High polarization of nuclear spins in liquid state through dynamic nuclear polarization has enabled the direct monitoring of 13C metabolites in vivo at very high signal-to-noise, allowing for rapid assessment of tissue metabolism. The abundant SNR afforded by this hyperpolarization technique makes high-resolution 13C 3D-MRSI feasible. However, the number of phase encodes that can be fit into the short acquisition time for hyperpolarized imaging limits spatial coverage and resolution. To take advantage of the high SNR available from hyperpolarization, we have applied compressed sensing to achieve a factor of 2 enhancement in spatial resolution without increasing acquisition time or decreasing coverage. In this paper, the design and testing of compressed sensing suited for a flyback 13C 3D-MRSI sequence are presented. The key to this design was the undersampling of spectral k-space using a novel blipped scheme, thus taking advantage of the considerable sparsity in typical hyperpolarized 13C spectra. Phantom tests validated the accuracy of the compressed sensing approach and initial mouse experiments demonstrated in vivo feasibility.