5 research outputs found
Complementary Surface Second Harmonic Generation and Molecular Dynamics Investigation of the Orientation of Organic Dyes at a Liquid/Liquid Interface
The second-order nonlinear response of two dyes adsorbed at the dodecane/water interface was investigated by surface second harmonic generation (SSHG). These dyes consist of the same chromophoric unit, 2-pyridinyl-5-phenyloxazole, with an alkyl chain located at the two opposite ends. The analysis of the polarization dependence of the SSHG intensity as usually performed points to similar tilt angles of the two dyes with respect to the interface but does not give information on the absolute direction. Molecular dynamics (MD) simulations reveal that both dyes lie almost flat at the interface but have opposite orientations. A refined SSHG data analysis with the width of the orientational distribution yields tilt angles that are in very satisfactory agreement with the MD simulations
Complementary Surface Second Harmonic Generation and Molecular Dynamics Investigation of the Orientation of Organic Dyes at a Liquid/Liquid Interface
The
second-order nonlinear response of two dyes adsorbed at the
dodecane/water interface was investigated by surface second harmonic
generation (SSHG). These dyes consist of the same chromophoric unit,
2-pyridinyl-5-phenyloxazole, with an alkyl chain located at the two
opposite ends. The analysis of the polarization dependence of the
SSHG intensity as usually performed points to similar tilt angles
of the two dyes with respect to the interface but does not give information
on the absolute direction. Molecular dynamics (MD) simulations reveal
that both dyes lie almost flat at the interface but have opposite
orientations. A refined SSHG data analysis with the width of the orientational
distribution yields tilt angles that are in very satisfactory agreement
with the MD simulations
Fluorescence Probing of Thiol-Functionalized Gold Nanoparticles: Is Alkylthiol Coating of a Nanoparticle as Hydrophobic as Expected?
Understanding the interaction of fluorescent dyes with
monolayer-protected
gold nanoparticles (AuNPs) is of fundamental importance in designing
new fluorescent nanomaterials. Among a variety of molecular sensors
and reporters, fluorescent probes based on a 3-hydroxychromone (3HC)
skeleton appear to be very promising. They exhibit the phenomenon
of dual band emission, resulting from excited-state intramolecular
proton transfer (ESIPT), known to be highly sensitive to a nature
of microenvironment surrounding a fluorophore. In this study, dodecanethiol-protected
gold nanoparticles were synthesized, and, owing to the transmission
electron micrograph imaging, their average diameter was found to be
âŒ1.4 nm. Fluorescence titrations of the 3HC ESIPT probes with
AuNPs in toluene solutions demonstrate significant changes in the
intensity ratio of their normal and tautomeric emission bands, suggesting
that the probe molecules become noncovalently bound to a dodecanethiol
layer of AuNPs. Despite expected fluorescence quenching induced by
close proximity to the metal surface, no fluorescence lifetime decrease
was observed, indicating that a bound-fluorophore is shielded from
a nanoparticle core. Further spectral analysis revealed that the ratiometric
fluorescence changes could be interpreted as a consequence of intermolecular
hydrogen bonding between a probe and residual ethanol molecules, trapped
into the dodecanethiol shell of AuNPs during the synthesis. Evidences
for residual traces of ethanol in the ligand shell of the nanoparticles
were also observed in NMR spectra, suggesting that alkylthiol-coated
gold nanoparticles may not be as hydrophobic as one could expect.
To elucidate structural features of dodecanethiol-stabilized gold
nanoparticles at the supramolecular level, a molecular dynamics (MD)
model of AuNP was developed. The model was based on the all-atom CHARMM27
force field parameters and parametrized according to available experimental
data of the synthesized AuNPs. Our MD simulations show that in bulk
toluene the 3HC probe molecule becomes weakly bound to a dodecanethiol
monolayer, so that a fluorophore favors residence in an outer shell
of AuNP. In addition, MD simulations of transfer of AuNP from bulk
ethanol to toluene demonstrate that a small population of ethanol
molecules are able to penetrate deeply into the dodecanethiol layer
and may indeed be trapped into the ligand shell of alkylthiol-functionalized
gold nanoparticles. The results of our fluorescence experiments and
molecular dynamics simulation suggest that 3-hydroxychromones can
be used as a noncovalent fluorescent labeling agent for alkylthiol-stabilized
noble metal nanoparticles
Fluorescence Probing of Thiol-Functionalized Gold Nanoparticles: Is Alkylthiol Coating of a Nanoparticle as Hydrophobic as Expected?
Understanding the interaction of fluorescent dyes with
monolayer-protected
gold nanoparticles (AuNPs) is of fundamental importance in designing
new fluorescent nanomaterials. Among a variety of molecular sensors
and reporters, fluorescent probes based on a 3-hydroxychromone (3HC)
skeleton appear to be very promising. They exhibit the phenomenon
of dual band emission, resulting from excited-state intramolecular
proton transfer (ESIPT), known to be highly sensitive to a nature
of microenvironment surrounding a fluorophore. In this study, dodecanethiol-protected
gold nanoparticles were synthesized, and, owing to the transmission
electron micrograph imaging, their average diameter was found to be
âŒ1.4 nm. Fluorescence titrations of the 3HC ESIPT probes with
AuNPs in toluene solutions demonstrate significant changes in the
intensity ratio of their normal and tautomeric emission bands, suggesting
that the probe molecules become noncovalently bound to a dodecanethiol
layer of AuNPs. Despite expected fluorescence quenching induced by
close proximity to the metal surface, no fluorescence lifetime decrease
was observed, indicating that a bound-fluorophore is shielded from
a nanoparticle core. Further spectral analysis revealed that the ratiometric
fluorescence changes could be interpreted as a consequence of intermolecular
hydrogen bonding between a probe and residual ethanol molecules, trapped
into the dodecanethiol shell of AuNPs during the synthesis. Evidences
for residual traces of ethanol in the ligand shell of the nanoparticles
were also observed in NMR spectra, suggesting that alkylthiol-coated
gold nanoparticles may not be as hydrophobic as one could expect.
To elucidate structural features of dodecanethiol-stabilized gold
nanoparticles at the supramolecular level, a molecular dynamics (MD)
model of AuNP was developed. The model was based on the all-atom CHARMM27
force field parameters and parametrized according to available experimental
data of the synthesized AuNPs. Our MD simulations show that in bulk
toluene the 3HC probe molecule becomes weakly bound to a dodecanethiol
monolayer, so that a fluorophore favors residence in an outer shell
of AuNP. In addition, MD simulations of transfer of AuNP from bulk
ethanol to toluene demonstrate that a small population of ethanol
molecules are able to penetrate deeply into the dodecanethiol layer
and may indeed be trapped into the ligand shell of alkylthiol-functionalized
gold nanoparticles. The results of our fluorescence experiments and
molecular dynamics simulation suggest that 3-hydroxychromones can
be used as a noncovalent fluorescent labeling agent for alkylthiol-stabilized
noble metal nanoparticles