3 research outputs found
Co-Aggregation of Two Anionic Azo Dyestuffs at a Well-Defined Stoichiometry
The present work investigates the
formation of well-defined heteroaggregates
from a binary mixture of a red and a yellow azo-dyestuff in the presence
of Mg<sup>2+</sup> ions. Combined static and dynamic light scattering
together with laser induced liquid bead ion desorption mass spectrometry
(LILBID-MS) has been applied to characterize the states of the pure
red dye and the pure yellow dye as well as of their mixture in aqueous
solution without Mg<sup>2+</sup>. These experiments indicated that
a structural reorganization on a molecular scale takes place as soon
as the two dyes are combined. Solutions of the combined red and yellow
dye contain micelle-like mixed entities with a size of a few tenths
of nanometers. Upon the addition of Mg<sup>2+</sup>, these micelles
vanish in favor of elongated heteroaggregates, which grow by a stepwise
addition of smaller building units. As unraveled by UV/vis spectroscopy,
the heteroaggregates that are formed from the red and yellow azo dye
in the presence of Mg<sup>2+</sup> obey a stoichiometric ratio of
the two components of 1:1. A new multiangle scattering instrument
allowed us for the first time to follow this aggregation process at
the stoichiometric ratio by time-resolved combined static and dynamic
light scattering, thereby providing further aspects of the worm-like
nature of the growing heteroaggregates
Laser-Induced Liquid Bead Ion Desorption Mass Spectrometry: An Approach to Precisely Monitor the Oligomerization of the β-Amyloid Peptide
In the present work, the recently developed laser-induced
liquid
bead ion desorption mass spectrometry (LILBID MS) is applied as a
novel technique to study Aβ oligomerization, thought to be crucial
in Alzheimer’s disease (AD). The characterization of the earliest
nucleation events of this peptide necessitates the application of
several techniques to bridge the gap between small oligomers and large
fibrils. We precisely monitored in time the transformation of monomeric
Aβ (1-42) into oligomeric Aβ<sub><i>n</i></sub> (<i>n</i> < 20) and its dependence on concentration
and agitation. The distribution shows signs of the hexamer being crucial
in the assembly process. The intensity of the monomer decreases in
time with a time constant of about 9 h. After a lag time of around
10 h, a phase transition occurred in which the total ion current of
the oligomers goes to nearly zero. In this late stage of aggregation,
protofibrils are formed and mass spectrometry is no longer sensitive.
Here fluorescence correlation spectroscopy (FCS) and transmission
electron microscopy (TEM) are complementary tools for detection and
size characterization of these large species. We also utilized the
oligomers of Aβ (1-42) as a model of the corresponding <i>in vivo</i> process to screen the efficacy and specificity of
small molecule inhibitors of oligomerization. The LILBID results are
in excellent agreement with condensed phase behavior determined in
other studies. Our data identified LILBID MS as a powerful technique
that will advance the understanding of peptide oligomerization in
neurodegenerative diseases and represents a powerful tool for the
identification of small oligomerization inhibitors
Influence of Surface Groups on Poly(propylene imine) Dendrimers Antiprion Activity
Prion diseases are characterized by the accumulation
of PrP<sup>Sc</sup>, an aberrantly folded isoform of the host protein
PrP<sup>C</sup>. Specific forms of synthetic molecules known as dendrimers
are able to eliminate protease-resistant PrP<sup>Sc</sup> in both
an intracellular and in vitro setting. The properties of a dendrimer
which govern this ability are unknown. We addressed the issue by comparing
the in vitro antiprion ability of numerous modified polyÂ(propylene-imine)
dendrimers, which varied in size, structure, charge, and surface group
composition. Several of the modified dendrimers, including an anionic
glycodendrimer, reduced the level of protease resistant PrP<sup>Sc</sup> in a prion strain-dependent manner. This led to the formulation
of a new working model for dendrimer/prion interactions which proposes
dendrimers eliminate PrP<sup>Sc</sup> by destabilizing the protein
and rendering it susceptible to proteolysis. This ability is not dependent
on any particular charge of dendrimer, but does require a high density
of reactive surface groups