Enhancing the photocatalytic efficiency of TiO(2) nanopowders for H(2) production by using non-noble transition metal co-catalysts

Co and Ni-nanoclusters are attractive alternatives to Pt catalysts for hydrogen generation. These earth abundant elements when loaded onto the TiO(2) nanopowders surface act as efficient co-catalysts. Co, Ni-decorated TiO(2) photocatalysts display only three (3) times lower catalytic activities for H(2) evolution under UV illumination compared with Pt-decorated TiO(2) photocatalysts.     

Unusual molecular conformations in fluorinated, contorted hexabenzocoronenes

Fluorinated, contorted hexabenzocoronenes (HBCs) have been synthesized in a facile manner via Suzuki-Miyaura coupling of fluorinated phenyl boronic acids followed by photocyclization and Scholl cyclization. In addition to the molecular conformation observed in previous HBC derivatives, close-contact fluorine-fluorine intramolecular interactions result in a metastable conformation not previously observed. Heating the metastable HBCs above 100 °C irreversibly converts them to the stable conformation, suggesting that the metastable conformation arises from a kinetically arrested state during cyclization.     

Multi-source facility location–allocation and inventory problem

We consider a joint facility location–allocation and inventory problem that incorporates multiple sources of warehouses. The problem is motivated by a real situation faced by a multinational applied chemistry company. In this problem, multiple products are produced in several plants. Warehouse can be replenished by several plants together because of capabilities and capacities of plants. Each customer in this problem has stochastic demand and certain amount of safety stock must be maintained in warehouses so as to achieve certain customer service level. The problem is to determine number and locations of warehouses, allocation of customers demand and inventory levels of warehouses. The objective is to minimize the expected total cost with the satisfaction of desired demand weighted average customer lead time and desired cycle service level. The problem is formulated as a mixed integer nonlinear programming model. Utilizing approximation and transformation techniques, we develop an iterative heuristic method for the problem. An experiment study shows that the proposed procedure performs well in comparison with a lower bound.     

An integrated digital microfluidic chip for multiplexed proteomic sample preparation and analysis by MALDI-MS

To realize multiplexed sample preparation on a digital microfluidic chip for high-throughput Matrix Assisted Laser Desorption/Ionization Mass Spectrometry (MALDI-MS), several fluidic functions need to be integrated. These include the generation of multiple droplets from a reservoir and parallel in-line sample purification. In this paper, we develop two critical new functions in handling protein solutions and standard proteomic reagents with electrowetting-on-dielectric (EWOD) actuation, leading to an integrated chip for multiplexed sample preparation for MALDI-MS. The first is a voltage sequence designed to generate a series of droplets from each of the three reservoirs--proteomic sample, rinsing fluid, and MALDI reagents. It is the first time that proteomic reagents have been dispensed using EWOD in an air (as opposed to oil) environment. The second is a box-in-box electrode pattern developed to allow droplet passing over dried sample spots, making the process of in-line sample purification robust for parallel processing. As a result, parallel processing of multiple sample droplets is demonstrated on the integrated EWOD-MALDI-MS chip, an important step towards high-throughput MALDI-MS. The MS results, collected directly from the integrated devices, are of good quality, suggesting that the tedious process of sample preparation can be automated on-chip for MALDI-MS applications as well as other high-throughput proteomics applications.     

Role of interface in dispersion and surface energetics of polymer nanocomposites containing hydrophilic POSS and layered silicates

Three different hydrophilic nanofillers--natural and synthetic layered silicate as well as octaammonium polyhedral oligomeric silsesquioxane (POSS)--were incorporated into polyamide-6 by a solution-mixing method. The surfaces of the resulting polymer nanocomposites were characterized by X-ray diffraction, polarized optical microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and contact angle measurements. All polymer nanocomposites displayed enhancement in surface hydrophilicity as well as increase in surface free energy due to surface enrichment of the nanofillers. The degree of enhancement was found to depend on both nanofiller type and dispersion state. Interfacial interactions in the form of hydrogen bonding played an important role in affecting the dispersion state of the layered silicates. Exfoliated layered silicates caused a larger increase in hydrophilicity than aggregated layered silicate. On the other hand, aggregated POSS molecules were able to induce a large increase in hydrophilicity. Significant spreading of water was also observed on surfaces containing POSS molecules. Surface models have been proposed to explain these phenomena.     

Encapsidation of nanoparticles by red clover necrotic mosaic virus

Icosahedral virus capsids demonstrate a high degree of selectivity in packaging cognate nucleic acid genome components during virion assembly. The 36 nm icosahedral plant virus Red clover necrotic mosaic virus (RCNMV) packages its two genomic ssRNAs via a specific capsid protein (CP) genomic RNA interaction. A 20-nucleotide hairpin structure within the genomic RNA-2 hybridizes with RNA-1 to form a bimolecular complex, which is the origin of assembly (OAS) in RCNMV that selectively recruits and orients CP subunits initiating virion assembly. In this Article, an oligonucleotide mimic of the OAS sequence was attached to Au, CoFe2O4, and CdSe nanoparticles ranging from 3 to 15 nm, followed by addition of RNA-1 to form a synthetic OAS to direct the virion-like assembly by RCNMV CP. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements were consistent with the formation of virus-like particles (VLPs) comparable in size to native RCNMV. Attempts to encapsidate nanoparticles with diameters larger than 17 nm did not result in well-formed viral capsids. These results are consistent with the presence of a 17 nm cavity in native RCNMV. Covalent linkage of the OAS to nanoparticles directs RNA-dependent encapsidation and demonstrates that foreign cargo can be packaged into RCNMV virions. The flexibility of the RCNMV CP to encapsidate different materials, as long as it is within encapsidation constraint, is a critical factor to be considered as a drug delivery and diagnostic vehicle in biomedical applications.     

One stone kills four birds: a novel diazaperinone 12H-pyrazino[2′,3′:3,4]pyrrolo[1,2-a]perimidin-12-one recognizes four different metal ions

A novel diazaperinone 12H-pyrazino[2′,3′:3,4]pyrrolo[1,2-a]perimidin-12-one has been successfully synthesized through a one-step condensation. Single crystal X-ray analysis shows that the product is of planar structure with strong π?π interactions and H-bonding. Interestingly, the 12H-pyrazino[2′,3′:3,4]pyrrolo[1,2-a]perimidin-12-one can recognize three different metal cations Cu²⁺, Ag⁺ and Hg²⁺ via naked eye visualization, and shows turn-on fluorescence for Fe³⁺ and Ag⁺ among the 22 metal cations.     

Posttranslational hydroxylation of human phenylalanine hydroxylase is a novel example of enzyme self-repair within the second coordination sphere of catalytic iron

Phenylalanine hydroxylase, a mononuclear non-heme iron enzyme, catalyzes the hydroxylation of phenylalanine to tyrosine in the presence of oxygen and reduced pterin cofactor. X-ray structural studies have established the coordination around the iron metal center and point to significant interactions within the second coordination sphere. One such interaction involves Tyr325 in human phenylalanine hydroxylase (hPAH), which forms a hydrogen-bonding network with an aqua ligand on iron and the pterin cofactor. The full-length tetramer (1-452) and truncated dimer (117-424) Tyr325Phe hPAH mutant enzymes showed similar kinetics, thermal stabilities, and oligomerization profiles as their corresponding wild-type proteins. The possibility of in vivo posttranslational hydroxylation that would restore the activity of hPAH was examined by mass spectrometry on the trypsin digested full-length (1-452) hPAH Tyr325Phe point mutant. The amino acid tags obtained by ESI-MS/MS confirmed the presence of a Phe325 in the peptide corresponding to the doubly charged precursor ion at m/z 916.4 (L A T I F W F T V E F G L C K), and its hydroxylated counterpart in the peptide corresponding to the m/z 924.4 (L A T I F-OH W F T V E F G L C K) byproduct ion series comprising the fragments y(5)-y(12). Furthermore, the point mutation Tyr325Ala resulted in an enzyme that was totally inactive and did not display any evidence of hydroxylation. These results demonstrate the importance of Tyr325 for proper conformation of the active site, substrate binding, and catalysis. The rescue of the Tyr325Phe mutant in hPAH via self-hydroxylation presents a novel example of oxidative repair on the molecular level.