5 research outputs found
Embedding a Metal-Binding Motif for Copper Transporter into a Lipid Bilayer by Cu(I) Binding
Peptide–lipid
interactions are widely involved with biologically
significant phenomena, including the pathogenic mechanisms of protein
misfolding diseases and transmembrane protein folding. In this paper,
the interaction of the cysteine/tryptophan (Cys/Trp) motif, which
is a metal-binding motif of copper transporter (Ctr) proteins, with
a lipid bilayer was studied using fluorescence and circular dichroism
(CD) spectroscopy. The binding of CuÂ(I) to the Cys/Trp motif induced
a large red-edge excitation shift in the Trp fluorescence, indicating
that the Trp residue is located inside the lipid bilayer following
complexation of CuÂ(I) with the Cys/Trp motif. The Stern–Volmer
quenching of the Trp fluorescence also supported the CuÂ(I) binding
peptide embedding in the lipid bilayer. The measurement of the CD
spectra indicated the increase in β-sheet content of the Cys/Trp
motif peptide as a result of CuÂ(I) binding. These results lead to
the conclusion that complexation with CuÂ(I) induces the change in
the secondary structure of the Cys/Trp motif, which results in the
peptide embedding in the lipid bilayer. CuÂ(I)-induced enhancement
of the lipid affinity is discussed in terms of the mechanism for copper
transport by Ctr
Experimental Evaluation of the Density of Water in a Cell by Raman Microscopy
We report direct observation of a
spatial distribution of water
molecules inside of a living cell using Raman images of the O–H
stretching band of water. The O–H Raman intensity of the nucleus
was higher than that of the cytoplasm, indicating that the water density
is higher in the nucleus than that in the cytoplasm. The shape of
the O–H stretching band of the nucleus differed from that of
the cytoplasm but was similar to that of the balanced salt solution
surrounding cells, indicating less crowded environments in the nucleus.
The concentration of biomolecules having C–H bonds was also
estimated to be lower in the nucleus than that in the cytoplasm. These
results indicate that the nucleus is less crowded with biomolecules
than the cytoplasm
Effects of Nanosecond Pulsed Electric Fields on the Intracellular Function of HeLa Cells As Revealed by NADH Autofluorescence Microscopy
The fluorescence
lifetime of the endogenous fluorophore of reduced
nicotinamide adenine dinucleotide (NADH) in HeLa cells is affected
by the application of nanosecond pulsed electric fields (nsPEFs).
In this study, we found that after nsPEF application, the fluorescence
lifetime became longer and then decreased in a stepwise manner upon
further application, irrespective of the pulse width in the range
of 10–50 ns. This application time dependence of the NADH fluorescence
lifetime is very similar to the time-lapse dependence of the NADH
fluorescence lifetime following the addition of an apoptosis inducer,
staurosporine. These results, as well as the membrane swelling and
blebbing after the application of nsPEFs, indicate that apoptosis
is also induced by the application of nsPEFs in HeLa cells. In contrast
to the lifetime, the fluorescence intensity remarkably depended on
the pulse width of the applied nsPEF. When the pulse width was as
large as 50 ns, the intensity monotonically increased and was distributed
over the entire cell as the application duration became longer. As
the pulse width of the applied electric field became smaller, the
magnitude of the field-induced increase in NADH fluorescence intensity
decreased; the intensity was reduced by the electric field when the
pulse width was as small as 10 ns. These results suggest that the
mechanism of electric-field-induced apoptosis depends on the pulse
width of the applied nsPEF
External Electric Field Effects on Excited-State Intramolecular Proton Transfer in 4′‑<i>N</i>,<i>N</i>‑Dimethylamino-3-hydroxyflavone in Poly(methyl methacrylate) Films
The
external electric field effects on the steady-state electronic
spectra and excited-state dynamics were investigated for 4′-<i>N</i>,<i>N</i>-(dimethylamino)-3-hydroxyflavone (DMHF)
in a polyÂ(methyl methacrylate) (PMMA) film. In the steady-state spectrum,
dual emission was observed from the excited states of the normal (N*)
and tautomer (T*) forms. Application of an external electric field
of 1.0 MV·cm<sup>–1</sup> enhanced the N* emission and
reduced the T* emission, indicating that the external electric field
suppressed the excited-state intramolecular proton transfer (ESIPT).
The fluorescence decay profiles were measured for the N* and T* forms.
The change in the emission intensity ratio N*/T* induced by the external
electric field is dominated by ESIPT from the Franck–Condon
excited state of the N* form and vibrational cooling in potential
wells of the N* and T* forms occurring within tens of picoseconds.
Three manifolds of fluorescent states were identified for both the
N* and T* forms. The excited-state dynamics of DMHF in PMMA films
has been found to be very different from that in solution due to intermolecular
interactions in a rigid environment
pH-Dependent Network Formation of Quantum Dots and Fluorescent Quenching by Au Nanoparticle Embedding
A simple approach to the creation of colloidal assemblies is in high demand for the development of functional devices. Here, we present the preparation of CdTe-QD (quantum dot) networks in as little as 1 day simply by pH modification without the use of oxidants. The QD network was tractable in water and casting from a droplet produced a porous networked film on both hydrophobic and hydrophilic solid substrates. Further, we found that citrate-protected gold nanoparticles (AuNPs, <i>d</i> = 5 nm) could be incorporated into the QD networks to afford a QD/Au composite network, and that the fluorescence from the QDs was largely decreased by the addition of a small proportion of AuNPs (QD:AuNP = 99.4:0.6), probably due to the efficient charge transfer through the network. These data indicate that our method is suitable for application to the creation of metal/QD hybrid materials that can be integrated into wet-based processes