Polarity and Dielectric Property Control Triggered by a Coordinated Solvent Molecule Exchange in Luminescent Mononuclear Aluminium(III) Complexes.

The development of molecule-based multifunctional switchable materials that exhibit a switch of polarity and dielectric property are extremely limited. We have demonstrated solvent-vapour-induced reversible molecular rearrangements between nonpolar crystals [Al(sap)(acac)(sol)] (H2 sap=2-salicylideneaminophenol, acac=acetylacetonate, sol=MeOH (1), EtOH (2)) and polar crystal [Al(sap)(acac)(DMSO)] (3). This crystal-to-crystal structural transformation was accompanied by a switch of second harmonic generation (SHG) and dielectric properties, including the formation of ferroelectric domains, thus reflecting the SHG-active polar Cc space group of 3. This is the first reported example of dielectric properties and polarity switching in luminescent mononuclear aluminium(III) complexes, which exhibit strong green emission in the solid state.

Disassembly of Amyloid Fibril with Infrared Free Electron Laser.

Amyloid fibril causes serious amyloidosis such as neurodegenerative diseases. The structure is composed of rigid ß-sheet stacking conformation which makes it hard to disassemble the fibril state without denaturants. Infrared free electron laser (IR-FEL) is an intense picosecond pulsed laser that is oscillated through a linear accelerator, and the oscillation wavelengths are tunable from 3 µm to 100 µm. Many biological and organic compounds can be structurally altered by the mode-selective vibrational excitations due to the wavelength variability and the high-power oscillation energy (10-50 mJ/cm2). We have found that several different kinds of amyloid fibrils in amino acid sequences were commonly disassembled by the irradiation tuned to amide I (6.1-6.2 µm) where the abundance of ß-sheet decreased while that of α-helix increased by the vibrational excitation of amide bonds. In this review, we would like to introduce the IR-FEL oscillation system briefly and describe combination studies of experiments and molecular dynamics simulations on disassembling amyloid fibrils of a short peptide (GNNQQNY) from yeast prion and 11-residue peptide (NFLNCYVSGFH) from ß2-microglobulin as representative models. Finally, possible applications of IR-FEL for amyloid research can be proposed as a future outlook.

Application study of infrared free-electron lasers towards the development of amyloidosis therapy.

Amyloidosis is known to be caused by the deposition of amyloid fibrils into various biological tissues; effective treatments for the disease are little established today. An infrared free-electron laser (IR-FEL) is an accelerator-based picosecond-pulse laser having tunable infrared wavelengths. In the current study, the irradiation effect of an IR-FEL was tested on an 11-residue peptide (NFLNCYVSGFH) fibril from ß2-microglobulin (ß2M) with the aim of applying IR-FELs to amyloidosis therapy. Infrared microspectroscopy (IRM) and scanning electron microscopy showed that a fibril of ß2M peptide was clearly dissociated by IR-FEL at 6.1 µm (amide I) accompanied by a decrease of the ß-sheet and an increase of the α-helix. No dissociative process was recognized at 6.5 µm (amide II) as well as at 5.0 µm (non-specific wavelength). Equilibrium molecular dynamics simulations indicated that the α-helix can exist stably and the probability of forming interchain hydrogen bonds associated with the internal asparagine residue (N4) is notably reduced compared with other amino acids after the ß-sheet is dissociated by amide I specific irradiation. This result implies that N4 plays a key role for recombination of hydrogen bonds in the dissociation of the ß2M fibril. In addition, the ß-sheet was disrupted at temperatures higher than 340 K while the α-helix did not appear even though the fibril was heated up to 363 K as revealed by IRM. The current study gives solid evidence for the laser-mediated conversion from ß-sheet to α-helix in amyloid fibrils at the molecular level.

Blackbody-Radiation-Induced Population Transfer Dynamics from Highly Vibrationally Excited Levels of the E 0g+ (3P2) Ion-Pair State of I2.

We report the decay dynamics from the highly excited vibrational levels of the E 0g+ (3P2) ion-pair state of I2. Strong UV fluorescence belonging to the D 0u+ (3P2) → X 1Σg+ transition was observed upon the excitation of the E 0g+ (3P2) (vE = 77 and 78) state. The vibrational levels populated in the D 0u+ (3P2) state were found to be located at slightly higher energies than the vibrational levels of the laser-excited E 0g+ (3P2) state. The vibrational levels populated in the D 0u+ (3P2) state were restricted to those which have relatively large Franck-Condon factors between the laser-prepared vibronic levels. The absorption and stimulated emission rate in the presence of thermal radiation strongly suggests that the population in the D 0u+ (3P2) state was induced by the absorption of blackbody radiation. The energy partitioning process in the high vibrational levels in the E 0g+ (3P2) state was found to be totally different from that in the lower levels (vE = 0-2) where amplified spontaneous emission was a major relaxation pathway.

Degradation of Human Serum Albumin by Infrared Free Electron Laser Enhanced by Inclusion of a Salen-Type Schiff Base Zn (II) Complex.

A salen-type Schiff base Zn(II) complex included in human serum albumin (HSA) protein was examined by UV-Vis, circular dichroism (CD), and fluorescence (PL) spectra. The formation of the composite material was also estimated by a GOLD program of ligand-protein docking simulation. A composite cast film of HSA and Zn(II) complex was prepared, and the effects of the docking of the metal complex on the degradation of protein molecules by mid-infrared free electron laser (IR-FEL) were investigated. The optimum wavelengths of IR-FEL irradiation to be used were based on experimental FT-IR spectra and vibrational analysis. Using TD-DFT results with 6-31G(d,p) and B3LYP, the IR spectrum of Zn(II) complex could be reasonably assigned. The respective wavelengths were 1652 cm-1 (HSA amide I), 1537 cm-1 (HSA amide II), and 1622 cm-1 (Zn(II) complex C=N). Degradation of HSA based on FT-IR microscope (IRM) analysis and protein secondary structure analysis program (IR-SSE) revealed that the composite material was degraded more than pure HSA or Zn(II) complex; the inclusion of Zn(II) complex enhanced destabilization of folding of HSA.

Mid-Infrared Amplified Spontaneous Emission from the f' 0g+ (1D2) Ion-Pair State and Spectroscopic Characterization of the Shallow 0g+ (ab) Valence State of I2.

In this paper, we describe amplified spontaneous emission (ASE) from the f' 0g+ (1D2) ion-pair state of I2 populated through a two-step laser excitation technique via the B 3Π(0u+) valence state. The intense infrared emission propagating in the direction of the incident laser beam is assigned to the ASE transition from the f' 0g+ (1D2) state to the F' 0u+ (1D2) ion-pair state. The subsequent ultraviolet fluorescence transition from the F' 0u+ (1D2) state to the 0g+ (bb) state as well as the 0g+ (ab) state is also reported. By Franck-Condon simulation of the cascading F' 0u+ (1D2) → 0g+ (bb) band, we determine the population distributions in the F' 0u+ (1D2) state generated by ASE, which are consistent with the intensity profile of the mid-infrared ASE spectrum. Finally, employing these vibrational distributions for the F' 0u+ (1D2) state, spectral parameters for the shallow 0g+ (ab) state are derived.

Investigation by DFT Methods of the Damage of Human Serum Albumin Including Amino Acid Derivative Schiff Base Zn(II) Complexes by IR-FEL Irradiation.

An infrared free electron laser (IR-FEL) can decompose aggregated proteins by excitation of vibrational bands. In this study, we prepared hybrid materials of protein (human serum albumin; HSA) including several new Schiff base Zn(II) complexes incorporating amino acid (alanine and valine) or dipeptide (gly-gly) derivative moieties, which were synthesized and characterized with UV-vis, circular dichroism (CD), and IR spectra. Density functional theory (DFT) and time dependent DFT (TD-DFT) calculations were also performed to investigate vibrational modes of the Zn(II) complexes. An IR-FEL was used to irradiate HSA as well as hybrid materials of HSA-Zn(II) complexes at wavelengths corresponding to imine C=N, amide I, and amide II bands. Analysis of secondary structures suggested that including a Zn(II) complex into HSA led to the structural change of HSA, resulting in a more fragile structure than the original HSA. The result was one of the characteristic features of vibrational excitation of IR-FEL in contrast to electronic excitation by UV or visible light.

Dissociation of ß-Sheet Stacking of Amyloid ß Fibrils by Irradiation of Intense, Short-Pulsed Mid-infrared Laser.

Structure of amyloid ß (Aß) fibrils is rigidly stacked by ß-sheet conformation, and the fibril state of Aß is profoundly related to pathogenesis of Alzheimer's disease (AD). Although mid-infrared light has been used for various biological researches, it has not yet been known whether the infrared light changes the fibril structure of Aß. In this study, we tested the effect of irradiation of intense mid-infrared light from a free-electron laser (FEL) targeting the amide bond on the reduction of ß-sheet content in Aß fibrils. The FEL reduced entire contents of proteins exhibiting ß-sheet structure in brain sections from AD model mice, as shown by synchrotron-radiation infrared microscopy analysis. Since Aß1-42 fibril absorbed a considerable FEL energy at amide I band (6.17 µm), we irradiated the FEL at 6.17 µm and found that ß-sheet content of naked Aß1-42 fibril was decreased using infrared microscopic analysis. Consistent with the decrease in the ß-sheet content, Congo-red signal is decreased after the irradiation to Aß1-42 fibril. Furthermore, electron microscopy analysis revealed that morphologies of the fibril and proto-fibril were largely changed after the irradiation. Thus, mid-infrared light dissociates ß-sheet structure of Aß fibrils, which justifies exploration of possible laser-based therapy for AD.

Application of mid-infrared free-electron laser tuned to amide bands for dissociation of aggregate structure of protein.

A mid-infrared free-electron laser (FEL) is a linearly polarized, high-peak powered pulse laser with tunable wavelength within the mid-infrared absorption region. It was recently found that pathogenic amyloid fibrils could be partially dissociated to the monomer form by the irradiation of the FEL targeting the amide I band (C=O stretching vibration), amide II band (N-H bending vibration) and amide III band (C-N stretching vibration). In this study, the irradiation effect of the FEL on keratin aggregate was tested as another model to demonstrate an applicability of the FEL for dissociation of protein aggregates. Synchrotron radiation infrared microscopy analysis showed that the α-helix content in the aggregate structure decreased to almost the same level as that in the monomer state after FEL irradiation tuned to 6.06 µm (amide I band). Both irradiations at 6.51 µm (amide II band) and 8.06 µm (amide III band) also decreased the content of the aggregate but to a lesser extent than for the irradiation at the amide I band. On the contrary, the irradiation tuned to 5.6 µm (non-absorbance region) changed little the secondary structure of the aggregate. Scanning-electron microscopy observation at the submicrometer order showed that the angular solid of the aggregate was converted to non-ordered fragments by the irradiation at each amide band, while the aggregate was hardly deformed by the irradiation at 5.6 µm. These results demonstrate that the amide-specific irradiation by the FEL was effective for dissociation of the protein aggregate to the monomer form.

Infrared amplified spontaneous emission from the 0 ((3)P0) and 0 ((1)D2) ion-pair states of molecular bromine.

We report the observation of amplified spontaneous emission for the first time from the 0 ((3)P0) and 0 ((1)D2) ion-pair states of Br2 by using an optical-optical double resonance technique through the B (3)Π(0) valence state as the intermediate state. The strong infrared emission propagating along the incident laser radiation is assigned to the parallel ASE transitions from the 0 ion-pair states down to the nearby 0 ion-pair states. The subsequent UV fluorescence from the 0 states to the high vibrational levels of the ground state is also observed. By the Franck-Condon simulation of the cascade UV fluorescence, we determine the vibrational distributions in the 0 states populated by ASE, which are consistent with the intensity distribution in the dispersed infrared ASE spectrum. The lifetimes of the relevant ion-pair states are evaluated by analyzing the temporal profiles of the UV fluorescence.

Collision induced state-to-state energy transfer dynamics between the 2u ((1)D2) and 2g ((1)D2) ion-pair states of I2.

We report the first observation of collision induced state-to-state energy transfer from the 2u ((1)D2) (v2u = 3-7) ion-pair state of I2 using a perturbation facilitated optical-optical double resonance technique through the c (1)Πg∼ B (3)Π(0) hyperfine mixed double-faced valence state as the intermediate state. The excitation of the 2u ((1)D2) state yielded the weak UV fluorescence from the wide range of vibrational levels in the nearby 2g ((1)D2) state. The vibrational distribution in the 2g ((1)D2) state derived by the Franck-Condon simulation of the UV fluorescence showed that the population in the 2u ((1)D2) state transfers mostly to the 2g ((1)D2) vibronic levels which are located energetically above the laser-prepared level. The radiative lifetimes and the self-quenching rate constants were determined to be 21.3 ± 0.1 and 44.6 ± 0.8 ns, and (1.30 ± 0.01) × 10(-9) and (2.26 ± 0.17) × 10(-9) cm(3) molecule(-1) s(-1) for the 2u ((1)D2) (v2u = 3) and 2g ((1)D2) (v2g = 5) states, respectively. The rate constant for the 2u ((1)D2) - 2g ((1)D2) collision induced state-to-state energy transfer was also evaluated to be (1.89 ± 0.01), (3.07 ± 0.07), and (3.77 ± 0.05) × 10(-10) cm(3) molecule(-1) s(-1) for the v2u = 3, 5, and 7 levels, respectively. The very large self-quenching cross sections for the ion-pair states of I2 could be explained by the harpoon mechanism.

Infrared radiative decay dynamics from the γ 1u ((3)P2), H 1u ((3)P1), and 1u ((1)D2) ion-pair states of I2 observed by a perturbation facilitated optical-optical double resonance technique.

We report the spectroscopic and temporal analyses on the amplified spontaneous emission (ASE) from the single rovibrational levels of the Ω = 1u ion-pair series, γ 1u ((3)P2), H 1u ((3)P1), and 1u ((1)D2), of I2 by using a perturbation facilitated optical-optical double resonance technique through the c (1)Πg ∼ B (3)Π(0u (+)) hyperfine mixed valence state as the intermediate state. The ASE detected in the infrared region was assigned to the parallel transitions from the Ω = 1u ion-pair states down to the nearby Ω = 1g ion-pair states. The subsequent ultraviolet (UV) fluorescence from the Ω = 1g states was also observed and the relative vibrational populations in the Ω = 1g states were derived through the Franck-Condon simulation of the intensity pattern of the vibrational progression. In the temporal profiles of the UV fluorescence, an obvious delay in the onset of the fluorescence was recognized after the excitation laser pulse. These results revealed that ASE is a dominant energy relaxation process between the Ω = 1u and 1g ion-pair states of I2. Finally, the lifetimes of the relevant ion-pair states were evaluated by temporal analyses of the UV fluorescence. The propensity was found which was the longer lifetime in the upper level of the ASE transitions tends to give intense ASE.

Picosecond pulsed infrared laser tuned to amide I band dissociates polyglutamine fibrils in cells.

Amyloid fibrils are causal substances for serious neurodegenerative disorders and amyloidosis. Among them, polyglutamine fibrils seen in multiple polyglutamine diseases are toxic to neurons. Although much efforts have been made to explore the treatments of polyglutamine diseases, there are no effective drugs to block progression of the diseases. We recently found that a free electron laser (FEL), which has an oscillation wavelength at the amide I band (C = O stretch vibration mode) and picosecond pulse width, was effective for conversion of the fibril forms of insulin, lysozyme, and calcitonin peptide into their monomer forms. However, it is not known if that is also the case in polyglutamine fibrils in cells. We found in this study that the fibril-specific ß-sheet conformation of polyglutamine peptide was converted into nonfibril form, as evidenced by the infrared microscopy and scanning-electron microscopy after the irradiation tuned to 6.08 µm. Furthermore, irradiation at this wavelength also changed polyglutamine fibrils to their nonfibril state in cultured cells, as shown by infrared mapping image of protein secondary structure. Notably, infrared thermography analysis showed that temperature increase of the cells during the irradiation was within 1 K, excluding thermal damage of cells. These results indicate that the picosecond pulsed infrared laser can safely reduce amyloid fibril structure to the nonfibril form even in cells.

Far-infrared amplified spontaneous emission and collisional energy transfer between the E 0(g)⁺ (³P2) and D 0(u)⁺ (³P2) ion-pair states of I2.

We report direct observation of far-infrared amplified spontaneous emission from the E 0(g)⁺ ((3)P2) (v(E) = 0 - 3) ion-pair state of I2 by using an optical-optical double resonance technique with the B (3)Πu (0(u)⁺) (v(B) = 19) valence state as the intermediate state. The directional far-infrared emission detected in the wavelength range from 19 to 28 µm was assigned to the vibronic transitions from the E 0(g)⁺ ((3)P2) ion-pair state to the D 0(u)⁺ ((3)P2) ion-pair state. The subsequent UV fluorescence from the D 0(u)⁺ ((3)P2) state was also observed, which consists not only from the vibrational levels populated by the amplified spontaneous emission but also from those populated by collisional energy transfer. Analyses of the vibrational distribution in the D 0(u)⁺ ((3)P2) state revealed that the population transfer through the amplified spontaneous emission was dominant under our experimental conditions.

Mid-infrared free-electron laser tuned to the amide I band for converting insoluble amyloid-like protein fibrils into the soluble monomeric form.

A mid-infrared free-electron laser (FEL) is operated as a pulsed and linearly polarized laser with tunable wavelengths within infrared region. Although the FEL can ablate soft tissues with minimum collateral damage in surgery, the potential of FEL for dissecting protein aggregates is not fully understood. Protein aggregates such as amyloid fibrils are in some cases involved in serious diseases. In our previous study, we showed that amyloid-like lysozyme fibrils could be disaggregated into the native form with FEL irradiation specifically tuned to the amide I band (1,620 cm(-1)). Here, we show further evidence for the FEL-mediated disaggregation of amyloid-like fibrils using insulin fibrils. Insulin fibrils were prepared in acidic solution and irradiated by the FEL, which was tuned to either 1,620 or 2,000 cm(-1) prior to the experiment. The Fourier transform infrared spectroscopy (FT-IR) spectrum after irradiation with the FEL at 1,620 cm(-1) indicated that the broad peak (1,630-1,660 cm(-1)) became almost a single peak (1,652 cm(-1)), and the ß-sheet content was reduced to 25 from 40% in the fibrils, while that following the irradiation at 2,000 cm(-1) remained at 38%. The Congo Red assay as well as transmission electron microscopy observation confirmed that the number of fibrils was reduced by FEL irradiation at the amide I band. Size-exclusion chromatography analysis indicated that the disaggregated form of fibrils was the monomeric form. These results confirm that FEL irradiation at the amide I band can dissect amyloid-like protein fibrils into the monomeric form in vitro.

Revised conformational assignments and conformational evolution of tyrosine by laser desorption supersonic jet laser spectroscopy.

The number of conformers and their structures of tyrosine are reassigned on the basis of resonance enhanced multiphoton ionization (REMPI), ultraviolet-ultraviolet hole burning (UV-UV HB), infrared (IR) dip spectra, and quantum chemical calculations. From comparison between REMPI and UV-UV HB spectra, it was found that 12 conformers coexist in the supersonic jet. The structures of these conformers are determined by the IR spectra and theoretical calculations. The number of conformers is more than that reported in the previous reports (8 conformers), and is rationalized by the systematic formation of conformers from simpler molecules without substituents, just like evolution. The importance of dipole-dipole interaction between an amino-acid chain and hydroxyl group at the benzene ring was also discussed.

Far infrared stimulated emission from the ns and nf Rydberg states of NO.

We report directional far-infrared emission from the υ = 0 vibrational levels of the 9sσ, 10sσ, 11sσ, 9f, and 10f Rydberg states of NO in the gas phase. The emission around 28 and 19 µm from the 9f state was identified as the downward 9f → 8g and subsequent 8g → 7f cascade transitions, respectively. The emission around 38 and 40 µm from the 10f state was identified as the 10f → 9g and 10f → 9dσπ transition, respectively. Following the excitation of the 9sσ, 10sσ, and 11sσ states, the emission around 40, 60, and 83 µm was assigned as the 9sσ → 8pσ, 10sσ → 9pσ, and 11sσ → 10pσ transitions, respectively. In addition to these emission systems originated from the laser-prepared levels, we found the emission bands from the 8f, 9f, and 10f states which are located energetically above the 9sσ, 10sσ, and 11sσ states, respectively. This observation suggests that the upward 8f ← 9sσ, 9f ← 10sσ, and 10f ← 11sσ optical excitation occurs. Since the energy differences between nf and (n + 1)sσ states correspond to the wavelength longer than 100 µm, the absorption of blackbody radiation is supposed to be essential for these upward transitions.

Laser induced amplified spontaneous emission from the f 0(g)(+) (3P0) ion-pair state of I2.

Laser induced amplified spontaneous emission (ASE) from the f 0g (+) ((3)P0) (vf = 1-7) ion-pair state of I2 was directly observed using an optical-optical double resonance technique with the B 0u (+) (vB = 21) valence state as the intermediate state. The emission detected at ~1660 nm was assigned to transitions from the f 0g (+) state to the D 0u (+) ((3)P2) ion-pair state. The transitions observed in the dispersed IR emission spectra were found to be between vibrational levels having the same vibrational quantum numbers in both electronic states, vf = vD. This is due to the almost parallel nature of the potential energy functions of the f 0g (+) and D 0u (+) states, leading to almost unit values for the Franck-Condon factors for vf = vD. That the observed infrared emission is due to ASE is shown by the facts that it propagated in a limited range of solid angles, exhibited a clear threshold against the input-laser power, and had different polarization to that of laser induced fluorescence.

Can Ag+ Permeate through a Potassium Ion Channel? A Bottom-Up Approach by Infrared Spectroscopy of the Ag+ Complex with the Partial Peptide of a Selectivity Filter.

Silver and silver ions have a long history of antimicrobial activity and medical applications. Nevertheless, the activity of Ag+ against bacteria, how it enters a cell, has not yet been established. The K+ channel, a membrane protein, is a possible route. The addition of a channel inhibitor (4-aminopyridine) to modulate the Ag+ uptake could support this view. However, the inhibitor enhances the uptake of Ag+, the opposite result. We have applied cold ion trap infrared laser spectroscopy to complexes of Ag+ and Ac-Tyr-NHMe (a model for GYG) which is a portion of the selectivity filter in the K+ channel to consider the question of permeation. With support from quantum chemical calculations, we have determined the stable conformations of the complex. The conformations strongly suggest that Ag+ would not readily permeate the K+ channel. The mechanism of the unexpected enhancement by the inhibitor is discussed.

Energy Transfer in the 2 u (1 D 2) Ion-Pair State of I2 by Inelastic Collisions with Noble Gas Atoms.

We investigated the energy transfer in the 2 u (1 D 2) ion-pair state of I2 by collision with noble gas atoms, Ar, Kr, and Xe, using an optical-optical double resonance/fluorescence detection technique. By analyzing the temporal profiles of the emission from the laser-excited 2 u (1 D 2) state at various noble gas pressures, the quenching rate constants were determined to be (4.55 ± 0.42) × 10-10, (4.23 ± 0.11) × 10-10, and (6.83 ± 0.16) × 10-10 cm3 molecule-1 s-1 for quenching by Ar, Kr, and Xe, respectively. The 2 g (1 D 2) ion-pair state, lying in the vicinity of the 2 u (1 D 2) state, was identified as a destination state by collision with Ar and Kr. Collision with Xe provided a new reactive pathway forming the excimer XeI(B). The rate constants were determined to be = (9.61 ± 0.63) × 10-11 cm3 molecule-1 s-1 and = (4.87 ± 0.34) × 10-11 cm3 molecule-1 s-1 for the formation of the 2 g (1 D 2) state by collision with Ar and Kr, respectively, and = (6.55 ± 0.19) × 10-11 cm3 molecule-1 s-1 for the formation of XeI(B). The collisional cross sections calculated from the quenching rate constants were considerably larger than the molecular size, owing to the harpoon mechanism.