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Fold Enhancement (fold + enhancement)

Distribution by Scientific Domains

Chemistry	33%

Selected Abstracts

Metal Ion Complementarity: Effect of Ring-Size Variation on the Conformation and Stability of Lead(II) and Cadmium(II) Complexes with Pendant-Armed Crowns

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2007
Martín Regueiro-Figueroa
Abstract The binding tendencies of the pendant-armed crown ethers L1,L3 [L1 = N,N, -bis(benzimidazol-2-ylmethyl)-1,7-diaza-12-crown-4, L2 = N,N, -bis(benzimidazol-2-ylmethyl)-1,10-diaza-15-crown-5) and L3 = N,N, -bis(benzimidazol-2-ylmethyl)-4,13-diaza-18-crown-6] towards PbII and CdII have been investigated. The X-ray crystal structure of [Cd(L3)](ClO4)2·EtOH shows that, in the solid state, the CdII ion is eight-coordinate and fits quite well into the crown hole, favouring an anti arrangement of the organic receptor. NMR measurements recorded in acetonitrile solution indicate that increasing the crown size induces a conformational change in the series of CdII complexes. The conformation goes from a syn arrangement for L1 to an anti arrangement for L3, passing through a syn [lrarr2] anti equilibrium in the complex derived from L2. On the contrary, no conformational change was observed for the corresponding PbII complexes, which have a syn conformation in all cases. These results have been confirmed by means of density functional theory (DFT) calculations performed by using the B3LYP model. The binding constants obtained from UV/Vis titration experiments in DMSO solution demonstrate that a decrease in the crown size provokes a 102 -fold enhancement of the stability for this series of CdII complexes, whereas for PbII a gradual decrease of the binding constants is observed. Receptor L1 shows a certain degree of selectivity for CdII over PbII, with a selectivity factor > 102. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Conjugated Polyelectrolyte,Metal Nanoparticle Platforms for Optically Amplified DNA Detection

ADVANCED MATERIALS, Issue 5 2010
Yusong Wang
A conjugated polyelectrolyte (CPE)-silver nanoparticle platform for DNA-sensing applications is fabricated (see figure), which provides over 17-fold enhancement of dye emission intensity, as compared to the intrinsic dye emission observed atop a conventional glass surface. Examination of the distance-dependence amplification process reveals that the role of the silver nanoparticles is to increase the effective field experienced by the light-harvesting CPE, and the metal enhanced fluorescence of the CPE could be translated into higher dye signal intensities for the detection platform. [source]

Surface plasmon enhanced light emission from semiconductor materials

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2008
Koichi Okamoto
Abstract Surface plasmon (SP) coupling technique was used to enhance light emissions from semiconductor nanocrystals with evaporated metal layers. We found that the SP coupling can increase the internal quantum efficiencies (IQE) of emission from CdSe-based nanocrystals regardless of the initial efficiencies. This suggests that this technique should be much effective for various materials that suffer from low quantum efficiencies. We also obtained 70-fold enhancement of emission from silicon nanocrystals in silicon dioxide. Obtained IQE value is 38%, which is as large as that of a compound semiconductor with direct transition. The SP coupling technique would bring a great improvement to silicon photonics. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Directional Surface Plasmon-Coupled Emission from a 3 nm Green Fluorescent Protein Monolayer

BIOTECHNOLOGY PROGRESS, Issue 6 2005
Yordan Kostov
High-sensitivity detection schemes are of great interest for a number of applications. Unfortunately, such schemes are usually high-cost. We demonstrate a low-cost approach to a high-sensitivity detection scheme based on surface plasmon-coupled emission (SPCE). The SPCE of a monomolecular layer of green fluorescent protein (GFP) is reported here. The protein was electrostatically attached to a thin, SiO2 -protected silver film deposited on a quartz substrate. The visible, directional emission of GFP was observed at a sharp, well-defined angle of 47.5° from the normal to the coupling prism, and the spectrum corresponded to that of GFP. The SPCE resulting from the reverse Kretschmann configuration showed a 12-fold enhancement over the free space fluorescence. The directional emission was 97% p-polarized. The directionality and high polarization can be coupled with the intrinsic spectral resolution of SPCE to be used in the design miniaturized spectrofluorometers. The observation of SPCE in the visible region of the spectrum from a monolayer of protein opens up new possibilities in protein-based sensing. [source]

Development of Auxotrophic Agrobacterium tumefaciens for Gene Transfer in Plant Tissue Culture

BIOTECHNOLOGY PROGRESS, Issue 3 2004
Jason I. Collens
Auxotrophic strains of Agrobacterium tumefaciens were generated for use in liquid co-culture with plant tissue for transient gene expression. Twenty-one auxotrophs were recovered from 1,900 tetracycline-resistant insertional mutants generated with a suicide vector transposon mutagenesis system. Twelve of these auxotrophs were characterized on a nutrient matrix. Isolates were screened for growth in plant cell and root culture, and three auxotrophs were identified that had limited growth: adenine (ade-24), leucine (leu-27), and cysteine (cys-32). Ade-24 displayed poor T-DNA delivery in a transient expression test delivering GUS from a binary vector, while cys-32 displayed the best ability to deliver DNA of these three auxotrophs. The growth yield of cys-32 on cysteine was assessed to provide a quantitative basis for co-culture nutrient supplementation. The utility of cys-32 for delivering T-DNA to plant tissues is demonstrated, where an 85-fold enhancement in GUS expression over wild-type A. tumefacienswas achieved. [source]

Photocontrollable Peptide-Based Switches Target the Anti-Apoptotic Protein Bcl-xL

CHEMBIOCHEM, Issue 18 2008
Sabine Kneissl
Abstract Photocontrol of Bcl-xL binding affinity has been achieved by using short BH3 domain peptides for Bak72,87 and Bid91,111 alkylated with an azobenzene crosslinker through two cysteine residues with different sequence spacings. The power to control the conformation of the crosslinker and hence peptide structure was demonstrated by CD and UV/Vis spectroscopy. The binding affinity of the alkylated peptides with Bcl-xL was determined in their dark-adapted and irradiated states by fluorescence anisotropy measurements, and use of different cysteine spacings allowed either activation or deactivation of the binding activities of these peptide-based switches by application of light pulses. Helix-stabilized peptides exhibited high Bcl-xL binding affinity with dissociation constants of 42±9, 21±1, and 55±4 nM for Bak, Bak, and Bid, respectively (superscript numbers refer to the spacing between cysteine residues), and up to 20-fold enhancements in affinity in relation to their helix-destabilized forms. Bak, Bak, and Bid each displayed more than 200-fold selectivity for binding to Bcl-xL over Hdm2, which is targeted by the N-terminal helix of the tumor suppressor p53. Structural studies by NMR spectroscopy demonstrated that the peptides bind to the same cleft in Bcl-xL as the wild-type peptide regardless of their structure. This work opens the possibility of using such photocontrollable peptide-based switches to interfere reversibly and specifically with biomacromolecular interactions to study and modulate cellular function. [source]