870 research outputs found
Extensive homologies between lectins from non-leguminous plants
AbstractSequence studies were performed on lectins from two non-leguminous plants: rice and nettle. Extensive homologies were found between these two proteins and wheat germ agglutinin in support of the conservation of lectin sequences among non-leguminous plants. The number and positions of the cysteine residues were particularly well conserved suggesting a similar folding of the polypeptide chains
Temperature Dependence of Exciton Diffusion in Conjugated Polymers
The temperature dependence of the exciton dynamics in a conjugated polymer is studied using time-resolved spectroscopy. Photoluminescence decays were measured in heterostructured samples containing a sharp polymer-fullerene interface, which acts as an exciton quenching wall. Using a 1D diffusion model, the exciton diffusion length and diffusion coefficient were extracted in the temperature range of 4-293 K. The exciton dynamics reveal two temperature regimes: in the range of 4-150 K, the exciton diffusion length (coefficient) of ~3 nm (~1.5 Ă 10-4 cm2/s) is nearly temperature independent. Increasing the temperature up to 293 K leads to a gradual growth up to 4.5 nm (~3.2 Ă 10-4 cm2/s). This demonstrates that exciton diffusion in conjugated polymers is governed by two processes: an initial downhill migration toward lower energy states in the inhomogenously broadened density of states, followed by temperature activated hopping. The latter process is switched off below 150 K.
Temperature and Field Dependence of the Mobility in Liquid-Crystalline Conjugated Polymer Films
The transport properties of organic light-emitting diodes in which the
emissive layer is composed of conjugated polymers in the liquid-crystalline
phase have been investigated. We have performed simulations of the current
transient response to an illumination pulse via the Monte Carlo approach, and
from the transit times we have extracted the mobility of the charge carriers as
a function of both the electric field and the temperature. The transport
properties of such films are different from their disordered counterparts, with
charge carrier mobilities exhibiting only a weak dependence on both the
electric field and temperature. We show that for spatially ordered polymer
films, this weak dependence arises for thermal energy being comparable to the
energetic disorder, due to the combined effect of the electrostatic and thermal
energies. The inclusion of spatial disorder, on the other hand, does not alter
the qualitative behaviour of the mobility, but results in decreasing its
absolute value.Comment: 9 pages, 8 figures, submitted to Phys. Rev.
Biosynthesis, primary structure and molecular cloning of snowdrop ( Galanthus nivalis L.) lectin
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65530/1/j.1432-1033.1991.tb16339.x.pd
A comparative study of mannose-binding lectins from the amaryllidaceae and alliaceae
A comparative study of the lectins from the families Amaryllidaceae and Alliaceae reveals many common features: all bind-mannose exclusively and have similar molecular structures and amino acid compositions. All these lectins contain subunits of Mr 11 500-14 000 which are not linked by disulphide bonds and occur as dimers (in Allium sativum, A. vineale, A. ursinum, A. moly, Narcissus pseudonarcissus and Clivia miniata) or tetramers (in Galanthus nivalis, Hippeastrum hybrid, Allium cepa and A. porrum. Most of these lectins were shown to occur as complex mixtures of isolectins. In general, the lectin concentration in Amaryllidaceae bulbs is higher than in Alliaceae bulbs. Antisera raised in rabbits against the Galanthus nivalis and the Narcissus cv Carlton lectins gave, upon double immunodiffusion, single precipitation bands and lines of identity with purified lectins from all Amaryllidaceae species, A. cepa and A. porrum. Similar single lines of identity were obtained between purified lectins from other Allium species and Amaryllidaceae lectins when challenged with rabbit anti-daffodil antiserum. However, two immunoprecipitin bands were obtained when the same assay was carried out with antiserum against Galanthus nivalis lectin, one line cross-reacting with the Amaryllidaceae lectins with the formation of a spur. Cross-reactions were also observed between Allium cepa and A. porrum lectins and the lectins from A. moly, A. vineale, A. ursinum and A. sativum. Although all lectins are serologically related, there are differences in their reaction with various antisera.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29508/1/0000595.pd
Exciton bimolecular annihilation dynamics in supramolecular nanostructures of conjugated oligomers
We present femtosecond transient absorption measurements on -conjugated
supramolecular assemblies in a high pump fluence regime.
Oligo(\emph{p}-phenylenevinylene) monofunctionalized with
ureido-\emph{s}-triazine (MOPV) self-assembles into chiral stacks in dodecane
solution below 75C at a concentration of M. We
observe exciton bimolecular annihilation in MOPV stacks at high excitation
fluence, indicated by the fluence-dependent decay of B-exciton
spectral signatures, and by the sub-linear fluence dependence of time- and
wavelength-integrated photoluminescence (PL) intensity. These two
characteristics are much less pronounced in MOPV solution where the phase
equilibrium is shifted significantly away from supramolecular assembly,
slightly below the transition temperature. A mesoscopic rate-equation model is
applied to extract the bimolecular annihilation rate constant from the
excitation fluence dependence of transient absorption and PL signals. The
results demonstrate that the bimolecular annihilation rate is very high with a
square-root dependence in time. The exciton annihilation results from a
combination of fast exciton diffusion and resonance energy transfer. The
supramolecular nanostructures studied here have electronic properties that are
intermediate between molecular aggregates and polymeric semiconductors
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