Influence of the sulfonate countercation on the thermal stability of nafion perfluorosulfonate membranes

We report a strong dependence of the thermal stability of Nafion® perfluorosulfonate ionomer on the nature of the counterion associated with the fixed sulfonate site. These results were obtained using thermal gravimetric analysis on a series of alkali metal and alkyl ammonium cation-exchanged Nafion films. We have found that the temperature of decomposition of Nafion is inversely dependent on the size of the exchanged cation; i.e., Nafion films show improved thermal stability as the size of the counter cation decreases. We attribute this inverse relationship of thermal stability with counterion size to an initial decomposition reaction which is strongly influenced by the strength of the sulfonate-coun-terion interaction. © 1993 John Wiley & Sons, Inc.     

Characterization of single- and double-stranded DNA on gold surfaces

Single- and double-stranded deoxy ribonucleic acid (DNA) molecules attached to self-assembled monolayers (SAMs) on gold surfaces were characterized by a number of optical and electronic spectroscopic techniques. The DNA-modified gold surfaces were prepared through the self-assembly of 6-mercapto-1-hexanol and 5'-C(6)H(12)SH -modified single-stranded DNA (ssDNA). Upon hybridization of the surface-bound probe ssDNA with its complimentary target, formation of double-stranded DNA (dsDNA) on the gold surface is observed and in a competing process, probe ssDNA is desorbed from the gold surface. The competition between hybridization of ssDNA with its complimentary target and ssDNA probe desorption from the gold surface has been investigated in this paper using X-ray photoelectron spectroscopy, chronocoulometry, fluorescence, and polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS). The formation of dsDNA on the surface was identified by PM-IRRAS by a dsDNA IR signature at approximately 1678 cm(-)(1) that was confirmed by density functional theory calculations of the nucleotides and the nucleotides' base pairs. The presence of dsDNA through the specific DNA hybridization was additionally confirmed by atomic force microscopy through colloidal gold nanoparticle labeling of the target ssDNA. Using these methods, strand loss was observed even for DNA hybridization performed at 25 degrees C for the DNA monolayers studied here consisting of attachment to the gold surfaces by single Au-S bonds. This finding has significant consequence for the application of SAM technology in the detection of oligonucleotide hybridization on gold surfaces.     

Supramolecular assembly on surfaces: manipulating conductance in noncovalently modified mesoscale structures

Molecules capable of complementary hydrogen bonding were used to control the noncovalent self-assembly and electronic properties of a chemically well-defined surface mesostructure. In this work, we patterned a footprint region for molecular assembly on a surface and used moieties featuring complementary recognition to tune the current-voltage properties of the patterned region. With the appropriate functionalities on the complementary moieties, we were able to increase and decrease the observed conductance in surface-bound mesoscale structures imaged by scanning tunneling microscopy (STM).     

Differential inhibition of postnatal brain,spinal cord and body growth by a growth hormone antagonist

Background  

Growth hormone (GH) plays an incompletely understood role in the development of the central nervous system (CNS). In this study, we use transgenic mice expressing a growth hormone antagonist (GHA) to explore the role of GH in regulating postnatal brain, spinal cord and body growth into adulthood. The GHA transgene encodes a protein that inhibits the binding of GH to its receptor, specifically antagonizing the trophic effects of endogenous GH.     

Multifunctional gold nanoparticle-peptide complexes for nuclear targeting

The ability of peptide-modified gold nanoparticles to target the nucleus of HepG2 cells was explored. Five peptide/nanoparticle complexes were investigated, particles modified with (1) the nuclear localization signal (NLS) from the SV 40 virus; (2) the adenovirus NLS; (3) the adenovirus receptor-mediated endocytosis (RME) peptide; (4) one long peptide containing the adenovirus RME and NLS; and (5) the adenovirus RME and NLS peptides attached to the nanoparticle as separate pieces. Gold nanoparticles were used because they are easy to identify using video-enhanced color differential interference contrast microscopy, and they are excellent scaffolds from which to build multifunctional nuclear targeting vectors. For example, particles modified solely with NLS peptides were not able to target the nucleus of HepG2 cells from outside the plasma membrane, because they either could not enter the cell or were trapped in endosomes. The combination of NLS/RME particles (4) and (5) did reach the nucleus; however, nuclear targeting was more efficient when the two signals were attached to nanoparticles as separate short pieces versus one long peptide. These studies highlight the challenges associated with nuclear targeting and the potential advantages of designing multifunctional nanostructured materials as tools for intracellular diagnostics and therapeutic delivery.     

Laser-induced temperature jump electrochemistry on gold nanoparticle-coated electrodes

Laser-induced temperature jumps (LITJs) at gold nanoparticle-coated indium tin oxide (ITO) electrodes in contact with electrolyte solutions have been measured using temperature-sensitive redox probes and an infrared charge-coupled device. Upon irradiation with 532 nm light, interfacial temperature changes of ca. 20 degrees C were recorded for particle coverages of ca. 1 x 1010 cm-2. In the presence of a redox molecule, LITJ yields open-circuit photovoltages and photocurrents that are proportional to the number of particles on the surface. When ssDNA was used to chemisorb nanoparticles to the ITO surface, solution concentrations as low as 100 fM of target ssDNA-modified nanoparticles could be detected at the electrode surface.     

Zum papierchromatographischen Verhalten einiger Abbauprodukte des Vitamins C

Zusammenfassung Die Abbauprodukte des Vitamins C, die 2,3-Diketo-L-gulonsäure und dis L-Threonsäure, wurden hergestellt und ihre Lösungen papierchromatographisch charakterisiert. Der in Chromatogrammen von Ascorbinsäure enthaltendem Material häufig auftretende Fleck mit dem R_f-Wert 0,11–0,14 ist als der 2,3-Diketo-L-gulonsäure zugehörig erkannt worden. Der R_f-Wert der als Vergleichssubstanz herangezogenen 2-Keto-L-gulonsäure beträgt 0,14–0,16, der ihrer Alkalisalze 0,10–0,12.     

Supramolecular control of valence-tautomeric equilibrium on nanometer-scale gold clusters

This communication describes the preparation and characterization of a valence tautomer complex covalently attached to gold nanoparticles. Variable-temperature IR spectroscopy is used to determine the equilibrium thermodynamic parameters for the valence tautomerization. These results are compared with a nonsurface combined valence tautomer complex. The results show that surface confinement attenuates both DeltaH degrees and DeltaS degrees . We attribute these changes to a reduced accessible molecular surface area.