54 research outputs found
Correlation length of hydrophobic polyelectrolyte solutions
The combination of two techniques (Small Angle X-ray Scattering and Atomic
Force Microscopy) has allowed us to measure in reciprocal and real space the
correlation length of salt-free aqueous solutions of highly charged
hydrophobic polyelectrolyte as a function of the polymer concentration ,
charge fraction and chain length . Contrary to the classical behaviour
of hydrophilic polyelectrolytes in the strong coupling limit, is strongly
dependent on . In particular a continuous transition has been observed from
to when decreased from 100% to
35%. We interpret this unusual behaviour as the consequence of the two features
characterising the hydrophobic polyelectrolytes: the pearl necklace
conformation of the chains and the anomalously strong reduction of the
effective charge fraction.Comment: 7 pages, 5 figures, submitted to Europhysics Letter
On the pearl size of hydrophobic polyelectrolytes
Hydrophobic polyelectrolytes have been predicted to adopt an unique
pearl-necklace conformation in aqueous solvents. We present in this Letter an
attempt to characterise quantitatively this conformation with a focus on ,
the pearl size. For this purpose polystyrenesulfonate (PSS) of various
effective charge fractions and chain lengths has been adsorbed
onto oppositely charged surfaces immersed in water in condition where the bulk
structure is expected to persist in the adsorbed state. \emph{In situ}
ellipsometry has provided an apparent thickness of the PSS layer. In
the presence of added salts, we have found:
( is the monomer size) in agreement with the scaling predictions for
in the pearl-necklace model if one interprets as a measure of the
pearl size. At the lowest charge fractions we have found
for the shorter chains, in agreement with a necklace/globule transition.Comment: 7 pages, 4 figures, 1 table. Published in Europhysics Letters, Vol.
62, Number 1, pp. 110-116 (2003
Ultrasonic particle trapping in microfluidic devices using soft lithography
2007-2008 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Nanostructures via DNA scaffold metallization
金沢大学大学院自然科学研究科物質情報解析金沢大学理学部The critical role of polymers in process of noble metals nanostructures formation is well known, however, the use of DNA chain template in this process is yet largely unknown. In this study we demonstrate different ways of silver deposition on DNA template and report the influence of silver nanostructures formation on DNA conformational state. Metallization of DNA chain proceeds by two different scenarios depending on DNA conformation. If DNA chain is unfolded (elongated) chain, silver reduction leads to the nucleation of silver nanoparticles and their growth on DNA scaffold. Silver nanoparticles assemble on negatively charged DNA template due to electrostatic interactions. During formation of silver nanoparticles, DNA chain, similarly to other polyelectrolytes, plays a role of stabilizing agent, and silver nanoparticles formed in DNA solutions are smaller and have narrower size distributions as compared to the particles formed in DNA-free solutions. Since positive change of thus formed silver nanoparticles is rather low, DNA chain remains in unfolded conformation no matter how high is a concentration of silver nanoparticles. On the other hand, when DNA molecule has been compacted into tight condensate, naturally of a toroid shape, deposition of silver on compacted DNA chain proceeds in a different manner without discretion into nanoparticles. As a result of such silver metal deposition, DNA-templated silver nanorings are formed. By comparison of UV-Vis spectra changes, the detection of transition point between unfolded and compact DNA conformations becomes possible. Metallization of unfolded DNA chain brings nanoparticles of about 30-50 nm size, while deposition of silver metal on a compact DNA condensate gives 100-150 nm metal rings that are distinguished by optical properties. The approach of different scenario of metallization can be used for detection of conformational changes in biopolymers
Multiple Scale Reorganization of Electrostatic Complexes of PolyStyrene Sulfonate and Lysozyme
We report on a SANS investigation into the potential for these structural
reorganization of complexes composed of lysozyme and small PSS chains of
opposite charge if the physicochemical conditions of the solutions are changed
after their formation. Mixtures of solutions of lysozyme and PSS with high
matter content and with an introduced charge ratio [-]/[+]intro close to the
electrostatic stoichiometry, lead to suspensions that are macroscopically
stable. They are composed at local scale of dense globular primary complexes of
radius ~ 100 {\AA}; at a higher scale they are organized fractally with a
dimension 2.1. We first show that the dilution of the solution of complexes,
all other physicochemical parameters remaining constant, induces a macroscopic
destabilization of the solutions but does not modify the structure of the
complexes at submicronic scales. This suggests that the colloidal stability of
the complexes can be explained by the interlocking of the fractal aggregates in
a network at high concentration: dilution does not break the local aggregate
structure but it does destroy the network. We show, secondly, that the addition
of salt does not change the almost frozen inner structure of the cores of the
primary complexes, although it does encourage growth of the complexes; these
coalesce into larger complexes as salt has partially screened the electrostatic
repulsions between two primary complexes. These larger primary complexes remain
aggregated with a fractal dimension of 2.1. Thirdly, we show that the addition
of PSS chains up to [-]/[+]intro ~ 20, after the formation of the primary
complex with a [-]/[+]intro close to 1, only slightly changes the inner
structure of the primary complexes. Moreover, in contrast to the synthesis
achieved in the one-step mixing procedure where the proteins are unfolded for a
range of [-]/[+]intro, the native conformation of the proteins is preserved
inside the frozen core
Anomalous counterion condensation in salt-free hydrophobic polyelectrolyte solutions: Osmotic pressure measurements
The effective charge fraction feff of a highly charged
hydrophobic polyelectrolyte (poly(styrene)-co-styrene sulphonate,
sodium salt) has been measured as a function of the bare
chemical charge fraction f between 0.38 and 1 by
osmotic-pressure measurements complemented by cryoscopy. It was
found that feff is highly reduced, compared to the
prediction of counterion condensation theory and the measurements
we made on a model hydrophilic polyelectrolyte. Furtheremore,
feff varies linearly with the chemical charge fraction and
extrapolates to zero effective charge at a chemical charge
fraction of 0.18, a value close to the limit of solubility of the
polyelectrolyte in water. We relate this anomalous behaviour to
the variations of the local dielectric constant, measured
previously with the same polyelectrolyte, a parameter which is
not considered in the structural models for hydrophobic
polyelectrolytes
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