Femtosecond (fs)-laser-induced crystallization as a novel crystallization technique was proposed for the first time by our group, where the crystallization time can be significantly shortened under fs laser irradiation. Similarly, we have further extended our investigation to amyloid fibril formation, also known as a nucleation-dependence process. Here we demonstrate that the necessary time for amyloid fibril formation can be significantly shortened by fs laser irradiation, leading to favorable enhancement. The enhancement was confirmed by both spectral measurements and direct observations of amyloid fibrils. The thioflavin T fluorescence intensity of laser-irradiated solution increased earlier than that of the control solution, and such a difference was simultaneously revealed by ellipticity changes. At the same time before intensity saturation in fluorescence, the number of amyloid fibrils obtained under laser irradiation was generally more than that in the control solution. Besides, such an enhancement is correlated to the laser power threshold of cavitation bubbling. Possible mechanisms are proposed by referring to fs-laser-induced crystallization and ultrasonication-induced amyloid fibril formation.
Characterization
of the secondary structures of two model polypeptides,
poly-l-lysine and poly-l-glutamic acid in aqueous
solutions has been demonstrated by hyper-Raman (HR) spectroscopy for
the first time. Complementary to infrared (IR) and visible Raman spectroscopy,
HR spectroscopy gives the amide I, II, and III bands originating from
the polypeptide backbones and the CCH3 symmetric bending
mode, enabling us to distinguish different conformations. The α-helix
gives the broad and weak amide III band, while the β-sheet and
the random coil show similar spectral patterns with different relative
intensities between the amide I and II bands. HR spectra from aqueous
solutions of the α-helix and the random coil of poly-l-ornithine also possess these spectral features. The HR spectra are
analogous to UV resonance Raman (UVRR) spectra, indicating the signal
enhancement due to the electronic resonance effect via the π–π*
transition. In contrast, the vibrational frequencies of the amide
I band in the HR spectra are much higher than those in the IR, visible
Raman, and UVRR spectra, suggesting the non-coincidence between HR,
IR, and Raman bands. Our finding suggests that HR spectroscopy is
promising to provide complementary information on the secondary structures
of polypeptides in aqueous solutions as a spectral approach differing
from existing vibrational spectroscopic methods.
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