6 research outputs found
Simultaneous Resonance Raman Optical Activity Involving Two Electronic States
In the present work, the first observation of strong
resonance
Raman optical activity (RROA) involving more that one resonant electronic
state is reported. The chiral transition metal complex bis-(trifluoroacetylcamphorato)
copperÂ(II), abbreviated CuÂ(tfc)<sub>2</sub>, exhibits both resonance
Raman (RR) and RROA spectra with laser excitation at 532 nm. Vibrational
assignments for this complex were carried out by comparing the non-RR
spectra of CuÂ(tfc)<sub>2</sub> excited at 1024 nm to density functional
theory (DFT) calculations. The theory of the single-electronic-state
(SES) RROA is extended to the next simplest level of theory involving
two resonant electronic states (TES) without interstate vibronic coupling
as an aide to the interpretation of the observed TES-RROA spectra.
Based on measured UVâvis electronic absorbance spectra and
corresponding TD-DFT calculations, the most likely two states associated
with the RROA spectra are identified
Experimental and Theoretical Polarized Raman Linear Difference Spectroscopy of Small Molecules with a New Alignment Method Using Stretched Polyethylene Film
This paper reports the development of the new technique
of Raman
linear difference (RLD) spectroscopy and its application to small
molecules: anthracene and nucleotides adenosine-5â˛-monophosphate,
thymidine-5â˛-monophosphate, guanosine-5â˛-monophosphate,
and cytidine-5â˛-monophosphate. In this work we also present
a new alignment method for Raman spectroscopy where stretched polyethylene
films are used as the matrix. Raman spectra using light polarized
along the orientation direction and perpendicular to it are reported.
The polyethylene (PE) film spectra are consistent with powder samples
and films deposited on quartz. RLD spectra determined from the difference
of the parallel and perpendicular polarized light Raman spectra are
also reported. The equations describing RLD are derived, and RLD spectra
of anthracene and thymidine are calculated from these equations using
Density Functional Theory and assuming perfect orientation of the
samples. Because of the wealth of spectroscopic information in the
vibrational spectra of biomolecules together with our ability to calculate
spectra as a function of orientation, we conclude that RLD has the
potential to provide structural information for biological samples
that currently cannot be extracted from any other method
Rapid Filament Supramolecular Chirality Reversal of HETâs (218â289) Prion Fibrils Driven by pH Elevation
Amyloid
fibril polymorphism is not well understood despite its
potential importance for biological activity and associated toxicity.
Controlling the polymorphism of mature fibrils including their morphology
and supramolecular chirality by postfibrillation changes in the local
environment is the subject of this study. Specifically, the effect
of pH on the stability and dynamics of HET-s (218â289) prion
fibrils has been determined through the use of vibrational circular
dichroism (VCD), deep UV resonance Raman, and fluorescence spectroscopies.
It was found that a change in solution pH causes deprotonation of
Asp and Glu amino acid residues on the surface of HET-s (218â289)
prion fibrils and triggers rapid transformation of one supramolecular
chiral polymorph into another. This process involves changes in higher
order arrangements like lateral filament and fibril association and
their supramolecular chirality, while the fibril cross-β core
remains intact. This work suggests a hypothetical mechanism for HET-s
(218â289) prion fibril refolding and proposes that the interconversion
between fibril polymorphs driven by the solution environment change
is a general property of amyloid fibrils
Rapid Filament Supramolecular Chirality Reversal of HETâs (218â289) Prion Fibrils Driven by pH Elevation
Amyloid
fibril polymorphism is not well understood despite its
potential importance for biological activity and associated toxicity.
Controlling the polymorphism of mature fibrils including their morphology
and supramolecular chirality by postfibrillation changes in the local
environment is the subject of this study. Specifically, the effect
of pH on the stability and dynamics of HET-s (218â289) prion
fibrils has been determined through the use of vibrational circular
dichroism (VCD), deep UV resonance Raman, and fluorescence spectroscopies.
It was found that a change in solution pH causes deprotonation of
Asp and Glu amino acid residues on the surface of HET-s (218â289)
prion fibrils and triggers rapid transformation of one supramolecular
chiral polymorph into another. This process involves changes in higher
order arrangements like lateral filament and fibril association and
their supramolecular chirality, while the fibril cross-β core
remains intact. This work suggests a hypothetical mechanism for HET-s
(218â289) prion fibril refolding and proposes that the interconversion
between fibril polymorphs driven by the solution environment change
is a general property of amyloid fibrils
Is Supramolecular Filament Chirality the Underlying Cause of Major Morphology Differences in Amyloid Fibrils?
The unique enhanced
sensitivity of vibrational circular dichroism
(VCD) to the formation and development of amyloid fibrils in solution
is extended to four additional fibril-forming proteins or peptides
where it is shown that the sign of the fibril VCD pattern correlates
with the sense of supramolecular filament chirality and, without exception,
to the dominant fibril morphology as observed in AFM or SEM images.
Previously for insulin, it has been demonstrated that the sign of
the VCD band pattern from filament chirality can be controlled by
adjusting the pH of the incubating solution, above pH 2 for ânormalâ
left-hand-helical filaments and below pH 2 for âreversedâ
right-hand-helical filaments. From AFM or SEM images, left-helical
filaments form multifilament braids of left-twisted fibrils while
the right-helical filaments form parallel filament rows of fibrils
with a flat tape-like morphology, the two major classes of fibril
morphology that from deep UV resonance Raman scattering exhibit the
same cross-β-core secondary structure. Here we investigate whether
fibril supramolecular chirality is the underlying cause of the major
morphology differences in all amyloid fibrils by showing that the
morphology (twisted versus flat) of fibrils of lysozyme, apo-Îą-lactalbumin,
HET-s (218â289) prion, and a short polypeptide fragment of
transthyretin, TTR (105â115), directly correlates to their
supramolecular chirality as revealed by VCD. The result is strong
evidence that the chiral supramolecular organization of filaments
is the principal underlying cause of the morphological heterogeneity
of amyloid fibrils. Because fibril morphology is linked to cell toxicity,
the chirality of amyloid aggregates should be explored in the widely
used <i>in vitro</i> models of amyloid-associated diseases
Amplified Vibrational Circular Dichroism as a Probe of Local Biomolecular Structure
We
show that the VCD signal intensities of amino acids and oligopeptides
can be enhanced by up to 2 orders of magnitude by coupling them to
a paramagnetic metal ion. If the redox state of the metal ion is changed
from paramagnetic to diamagnetic the VCD amplification vanishes completely.
From this observation and from complementary quantum-chemical calculations
we conclude that the observed VCD amplification finds its origin in
vibronic coupling with low-lying electronic states. We find that the
enhancement factor is strongly mode dependent and that it is determined
by the distance between the oscillator and the paramagnetic metal
ion. This localized character of the VCD amplification provides a
unique tool to specifically probe the local structure surrounding
a paramagnetic ion and to zoom in on such local structure within larger
biomolecular systems