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.     

Annealing sequence dependent open-circuit voltage of inverted polymer solar cells attributable to interfacial chemical reaction between top electrodes and photoactive layers

The ability to laminate and delaminate top metal contacts during the processing and testing of inverted polymer solar cells has led us to uncover the peculiar dependence of their open-circuit voltage (V(oc)) on the annealing sequence. Specifically, thermally annealing inverted polymer solar cells having bulk-heterojunction photoactive layers after top electrode deposition above 100 °C leads to lower V(oc) compared to analogous devices with unannealed photoactive layers or photoactive layers that have been annealed prior to metal electrode deposition. This reduction in V(oc), however, can be reversed when the top electrodes are replaced. This observation is thus a strong indication that such changes in V(oc) with annealing sequence are manifestations of changes at the top electrode-photoactive layer interface, and not structural changes in the bulk of the photoactive layer. Electronic characterization conducted on the photoactive layers and metal contacts after dissection of the polymer solar cells via delamination suggests the reduction of V(oc) on thermal annealing in the presence of the metal top contacts to stem from an interfacial chemical reaction between the photoactive layers and the metal electrodes. This chemically generated interfacial layer is removed upon electrode delamination, effectively reverting the V(oc) to its original value prior to thermal annealing when the top electrodes are replaced.     

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.     

Identification of alpha-galactosyl epitope mimetics through rapid generation and screening of C-linked glycopeptide library

A general methodology has been established for rapid generation and screening of combinatorial glycopeptide library and subsequent mass spectrometric sequencing to identify the mimetics of Galalpha(1,3)Gal epitopes. Using this approach, several active glycopeptide sequences were recognized and found to inhibit the binding of human natural anti-Gal antibodies with comparable IC(50)s to synthetic Galalpha(1,3)Gal oligosaccharides. The most active glycopeptides detected from the library included Gal-Tyr-Trp-Arg-Tyr, Gal-Thr-Trp-Arg-Tyr, and Gal-Arg-Trp-Arg-Tyr. These glycopeptides showed higher affinities to anti-Gal antibodies than known Galalpha(1,3)Gal peptide mimetics, such as DAHWESWL and SSLRGF. Our results suggest that, by combining a peptide sequence (the "functional" mimic part) with a terminal alpha-linked galactose moiety (the "structural" mimic part), the resulting glycopeptide could be a very good Galalpha(1,3)Gal mimetic. Analysis of these active glycopeptides provided first-hand information regarding the binding site of anti-Gal antibodies to facilitate the structurally based design of more potent and stable inhibitors.     

Analysis of norethindrone in plasma by high-performance liquid chromatography

The lack of specificity of some radioimmunological assays for the determination of norethindrone has been reported. This paper describes a high performance liquid chromatographic (HPLC) method that is sufficiently sensitive and specific for the determination of plasma samples containing 2 ng/ml norethindrone. Plasma samples were collected from 8 human volunteers. The solvents used for the mobile phase were methanol, HPLC grade acetonitrile, HPLC grade, and double glass-distilled water. The HPLC (Waters Associates, Milford, Massachusetts) was used at a nominal attenuation of .005 absorbance units full scale (AUFS) and fed into a 5 mV recorder, giving an overall response of 0.0025 AUFS. The HPLC was also fitted with an ultraviolet detector (254 nm). The organic solvent extract from plasma is chromatographed on a reversed phase column using the HPLC. Tritiated norethindrone was added to 2.0 ml of plasma containing from 2 to 20 ng/ml of norethindrone and was extracted using the procedure as described. The organic extract was then transferred into a scintillation vial and evaporated to dryness. A Beckman LS 150 scintillation counter with an automatic quench correction device was used to determine radioactivity. The results show that the extraction efficiency and reproducibility are comparable at plasma concentrations ranging between 2-20 ng/ml. No interfering compounds (metabolites and endogenous substances) were extracted using HPLC. Data analysis of a number of spiked plasma samples ranging from 2 ng/ml-20 ng/ml suggests the accuracy and precision of the method. In another experiment, 40 mg of norethindrone was dissolved in ethanolic saline and orally administered in a mini-pig. The plasma norethindrone concentration was readily detected. The experiments illustrate the stronger specificity of the new method compared to reported radioimmunoassays.     

Photochromism of novel molybdate/alkylamine composite thin films.

Novel inorganic/organic composite films of molybdates with photochromic properties have been prepared by self-assembly using alkylammonium ions as a supramolecular template. Both 1-hexadecylammonium/polyoxomolybdate (C16-Mo) and 1-octadecylammonium/polyoxomolybdate (C18-Mo) composite films have been successfully fabricated. The elemental analysis and thermal gravimetric analysis show that the main product in the C16-Mo film was (C16H33NH3)4Mo8O26. The X-ray diffraction (XRD) results indicate that the composite films were lamellar in nature. The IR, Raman and X-ray photoelectron spectroscopy (XPS) results show that the polyoxomolybdate anions present as MoO6 octahedra and that the Mo species exists as Mo6+ in the freshly prepared films. The alkyl chains in the 1-hexadecylammonium chains were linear and the alkyl groups are an all-trans configuration. Upon UV irradiation of the C16-Mo films, some Mo6+ was reduced to Mo5+, some -NH3+ became -NH2 with a concomitant increase in the concentration of -OH groups on the molybdate moieties, and the films were colored. Thus, the photochromism of the films involves the reduction of Mo6+ to Mo5+, coupled with a proton transfer from 1-hexadecylammonium ions to an oxygen atom at the Mo site. In contrast to thin films of transition-metal oxides, which all show photochromism in the blue region of the electromagnetic spectrum, these composite films show photochromism in the violet region with the greatest absorbance change at 472 nm.     

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.     

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.     

Drug screening of pharmaceutical discovery compounds by micro-size exclusion chromatography/mass spectrometry.

Micro-size exclusion chromatography coupled with capillary liquid chromatography (capLC) and mass spectrometry (MS) provides a rapid and simple approach to the preliminary screening of active ligands toward a specific target macromolecule. In this study, the effectiveness of this technique is demonstrated by a number of small molecule ligands with known binding affinities towards the protein target. All ligands were incubated together with a target protein under native conditions. Separation was then achieved by microcentrifugation where the high molecular weight (MW) compounds were selectively passed through the size-exclusion material. The retained low MW compounds were then recovered and analyzed by capLC/MS. The absence of the ligand indicated strong affinity towards the target, while ligand detection indicated inactivity. This assay demonstrated the drugs that were acting as strong inhibitors of Co-PDF from those showing to be comparatively inactive. The relative binding rank order of the drugs towards Co-PDF was also determined. The results were validated by a corresponding set of control experiments in which the target molecules were excluded from the process. In principle, high-throughput micro-size exclusion chromatography, coupled with capLC/MS, offers a powerful technique as a preliminary screen in determining both the strong binding affinity and the relative affinity rank ordering of ligands towards a specific target macromolecule, and is complementary with other analytical drug screening techniques.