20 research outputs found
Amyloid-Derived Peptide Forms Self-Assembled Monolayers on Gold Nanoparticle with a Curvature-Dependent β-Sheet Structure
Using a combination of Fourier transform infrared (FTIR) spectroscopy and solid-state nuclear magnetic resonance (SSNMR) techniques, the secondary structure of peptides anchored on gold nanoparticles of different sizes is investigated. The structure of the well-studied CALNN-capped nanoparticles is compared to the structure of nanoparticles capped with a new cysteine-terminated peptide, CFGAILSS. The design of that peptide is derived from the minimal amyloidogenic sequence FGAIL of the human islet polypeptide amylin. We demonstrate that CFGAILSS forms extended fibrils in solution. When constrained at a nanoparticle surface, CFGAILSS adopts a secondary structure markedly different from CALNN. Taking into account the surface selection rules, the FTIR spectra of CFGAILSS-capped gold nanoparticles indicate the formation of β-sheets which are more prominent for 25 nm diameter nanoparticles than for 5 nm nanoparticles. No intermolecular <sup>13</sup>C–<sup>13</sup>C dipolar coupling is detected with rotational resonance SSNMR for CALNN-capped nanoparticles, while CALNN is in a random coil configuration. Coupling is detected for CFGAILSS-capped gold nanoparticles, however, consistent with an intermolecular <sup>13</sup>C–<sup>13</sup>C distance of 5.0 ± 0.3 Å, in agreement with intermolecular hydrogen bonding in a parallel β-sheet structure
Amyloid-Derived Peptide Forms Self-Assembled Monolayers on Gold Nanoparticle with a Curvature-Dependent β-Sheet Structure
Using a combination of Fourier transform infrared (FTIR) spectroscopy and solid-state nuclear magnetic resonance (SSNMR) techniques, the secondary structure of peptides anchored on gold nanoparticles of different sizes is investigated. The structure of the well-studied CALNN-capped nanoparticles is compared to the structure of nanoparticles capped with a new cysteine-terminated peptide, CFGAILSS. The design of that peptide is derived from the minimal amyloidogenic sequence FGAIL of the human islet polypeptide amylin. We demonstrate that CFGAILSS forms extended fibrils in solution. When constrained at a nanoparticle surface, CFGAILSS adopts a secondary structure markedly different from CALNN. Taking into account the surface selection rules, the FTIR spectra of CFGAILSS-capped gold nanoparticles indicate the formation of β-sheets which are more prominent for 25 nm diameter nanoparticles than for 5 nm nanoparticles. No intermolecular <sup>13</sup>C–<sup>13</sup>C dipolar coupling is detected with rotational resonance SSNMR for CALNN-capped nanoparticles, while CALNN is in a random coil configuration. Coupling is detected for CFGAILSS-capped gold nanoparticles, however, consistent with an intermolecular <sup>13</sup>C–<sup>13</sup>C distance of 5.0 ± 0.3 Å, in agreement with intermolecular hydrogen bonding in a parallel β-sheet structure
Response of Villin Headpiece-Capped Gold Nanoparticles to Ultrafast Laser Heating
The
integrity of a small model protein, the 36-residue villin headpiece
HP36, attached to gold nanoparticles (AuNP) is examined, and its response
to laser excitation of the AuNPs is investigated. To that end, it
is first verified by stationary IR and CD spectroscopy, together with
denaturation experiments, that the folded structure of the protein
is fully preserved when attached to the AuNP surface. It is then shown
by time-resolved IR spectroscopy that the protein does not unfold,
even upon the highest pump fluences that lead to local temperature
jumps on the order of 1000 K of the phonon system of the AuNPs, since
that temperature jump persists for too short a time of a few nanoseconds
only to be destructive. Judged from a blue shift of the amide I band,
indicating destabilized or a few broken hydrogen bonds, the protein
either swells, becomes more unstructured from the termini, or changes
its degree of solvation. In any case, it recovers immediately after
the excess energy dissipates into the bulk solvent. The process is
entirely reversible for millions of laser shots without any indication
of aggregation of the protein or the AuNPs and with only a minor fraction
of broken protein–AuNP thiol bonds. The work provides important
cornerstones in designing laser pulse parameters for maximal heating
with protein-capped AuNPs without destroying the capping layer
Cooperative Organization in Iron Oxide Multi-Core Nanoparticles Potentiates Their Efficiency as Heating Mediators and MRI Contrast Agents
In the pursuit of optimized magnetic nanostructures for diagnostic and therapeutic applications, the role of nanoparticle architecture has been poorly investigated. In this study, we demonstrate that the internal collective organization of multi-core iron oxide nanoparticles can modulate their magnetic properties in such a way as to critically enhance their hyperthermic efficiency and their MRI <i>T</i><sub>1</sub> and <i>T</i><sub>2</sub> contrast effect. Multi-core nanoparticles composed of maghemite cores were synthesized through a polyol approach, and subsequent electrostatic colloidal sorting was used to fractionate the suspensions by size and hence magnetic properties. We obtained stable suspensions of citrate-stabilized nanostructures ranging from single-core 10 nm nanoparticles to multi-core magnetically cooperative 30 nm nanoparticles. Three-dimensional oriented attachment of primary cores results in enhanced magnetic susceptibility and decreased surface disorder compared to individual cores, while preserving a superparamagnetic-like behavior of the multi-core structures and potentiating thermal losses. Exchange coupling in the multi-core nanoparticles modifies the dynamics of the magnetic moment in such a way that <i>both</i> the longitudinal and transverse NMR relaxivities are also enhanced. Long-term MRI detection of tumor cells and their efficient destruction by magnetic hyperthermia can be achieved thanks to a facile and nontoxic cell uptake of these iron oxide nanostructures. This study proves for the first time that cooperative magnetic behavior within highly crystalline iron oxide superparamagnetic multi-core nanoparticles can improve simultaneously therapeutic and diagnosis effectiveness over existing nanostructures, while preserving biocompatibility