THz irradiation inhibits cell division by affecting actin dynamics.

Biological phenomena induced by terahertz (THz) irradiation are described in recent reports, but underlying mechanisms, structural and dynamical change of specific molecules are still unclear. In this paper, we performed time-lapse morphological analysis of human cells and found that THz irradiation halts cell division at cytokinesis. At the end of cytokinesis, the contractile ring, which consists of filamentous actin (F-actin), needs to disappear; however, it remained for 1 hour under THz irradiation. Induction of the functional structures of F-actin was also observed in interphase cells. Similar phenomena were also observed under chemical treatment (jasplakinolide), indicating that THz irradiation assists actin polymerization. We previously reported that THz irradiation enhances the polymerization of purified actin in vitro; our current work shows that it increases cytoplasmic F-actin in vivo. Thus, we identified one of the key biomechanisms affected by THz waves.

Gre factors prevent thermal and mechanical stresses induced by terahertz irradiation during transcription.

During transcription in cells, the transcription complex consisting of RNA polymerase, DNA and nascent RNA is exposed to fluctuating temperature and pressure. However, little is known about the mechanism of transcriptional homeostasis under fluctuating physical parameters. In this study, we generated these fluctuating parameters using pulsed local heating and acoustic waves in the reaction system of transcription by Escherichia coli RNA polymerase, using a terahertz free-electron laser. We demonstrated that transcription processes, including abortive initiation and elongation pausing, and the fidelity of elongation are significantly affected by the laser-based local perturbations. We also found that all these functional alternations in the transcription process are almost completely mitigated by the presence of Gre proteins. It is well known that Gre proteins enhance RNA cleavage of polymerase by binding to the pore structure termed secondary channel. Recently, the chaperone activities have also been proposed for Gre proteins, yet the details directly associated with transcription are largely unknown. Our finding indicates that Gre proteins are necessary for maintaining transcriptional homeostasis under thermal and mechanical stresses.

Plane photoacoustic wave generation in liquid water using irradiation of terahertz pulses.

We demonstrate photoacoustic wave propagation with a plane wavefront in liquid water using a terahertz (THz) laser pulse. The THz light can effectively generate the photoacoustic wave in water because of strong absorption via a stretching vibration mode of the hydrogen bonding network. The excitation of a large-area water surface irradiated by loosely focused THz light produces a plane photoacoustic wave. This is in contrast with conventional methods using absorbers or plasma generation using near-infrared laser light. The photoacoustic wave generation and plane wave propagation are observed using a system with a THz free-electron laser and shadowgraph imaging. The plane photoacoustic wave is generated by incident THz light with a small radiant exposure of < 1 mJ/cm2 and delivered 600 times deeper than the penetration depth of THz light for water. The THz-light-induced plane photoacoustic wave offers great advantages to non-invasive operations for industrial and biological applications as demonstrated in our previous report (Yamazaki et al. in Sci Rep 10:9008, 2020).

Propagation of THz irradiation energy through aqueous layers: Demolition of actin filaments in living cells.

The effect of terahertz (THz) radiation on deep tissues of human body has been considered negligible due to strong absorption by water molecules. However, we observed that the energy of THz pulses transmits a millimeter thick in the aqueous solution, possibly as a shockwave, and demolishes actin filaments. Collapse of actin filament induced by THz irradiation was also observed in the living cells under an aqueous medium. We also confirmed that the viability of the cell was not affected under the exposure of THz pulses. The potential of THz waves as an invasive method to alter protein structure in the living cells is demonstrated.

A Study on Blend Ratio-dependent Far-IR and Low-frequency Raman Spectra and WAXD Patterns of Poly(3-hydroxybutyrate)/poly(4-vinylphenol) Using Homospectral and Heterospectral Two-dimensional Correlation Spectroscopy.

An intensive analysis of far-infrared (far-IR), low-frequency Raman, and wide angle X-ray diffraction (WAXD) data has been performed by two-dimensional correlation spectroscopy (2D-COS) as a function of the blend ratio of poly(3-hydroxybutyrate)/poly(4-vinylphenol) (PHB/PVPh). Homospectral 2D-COS revealed that a weak band at 128 cm-1 in the far-IR spectra appeared more clearly in the 2D correlation spectra. Heterospectral 2D-COS (far-IR/low-frequency Raman and far-IR/WAXD) provided very important results that were hardly detected in the conventional 2D-COS. A far-IR peak at 130 cm-1 in the heterospectral 2D-COS had negative correlations with the peaks in the low-frequency Raman spectra at 81, 100, and 110 cm-1 and WAXD profile 8.78 and 11.01°. These results indicated that those peaks have different origins; the 130 cm-1 peak comes from the intermolecular C=O···H-O hydrogen bond between PHB and PVPh, while those for low-frequency Raman and WAXD peaks are the features of PHB crystalline structure.

Exploring the Dynamics of Bound Water in Nylon Polymers with Terahertz Spectroscopy.

Terahertz (THz) spectroscopy was used to observe adsorbed water structure and dynamics within polymer films, ultimately providing a strong rationale for the observed rates of water desorption. The THz absorption spectra of nylon-6 films undergo drastic changes during the hydration and drying processes. Additionally, the structural change from γ to α crystals, induced by the hydration, was observed by the characteristic band of α-nylon-6 at 6.5 THz. Importantly, the THz spectra of adsorbed water, as well as deuterated water, within in the nylon films were observed by the continuous measurement of α-nylon during dehydration. The difference spectra clearly show three absorption bands of water molecules named Peaks I-III, which behave differently between the H2O and D2O materials. The spectra were assigned using a combination of ab initio molecular dynamics simulations and solid-state density functional theory calculations and were compared to previous spectral assignments of bulk water. The results show that the inclusion of H2O and D2O into polymer films results in a distinct set of spectral features that, while similar in frequencies to the dynamics of bulk water, represent significantly different motions owing to the unique chemical environment within the material. These results highlight the significant utility of using THz spectroscopy to study the hydration dynamics and spectral signatures of bound water in this important class of materials.

Low-Frequency Vibrational Modes of Nylon 6 Studied by Using Infrared and Raman Spectroscopies and Density Functional Theory Calculations.

Far-infrared (FIR) and low-frequency Raman bands in the 90?400 cm?1 region of crystalline nylon 6 in ? form were assigned based on comparisons of experimental spectra and quantum mechanical calculations. A fragment methodology was applied in the calculations for explicit consideration of interchain interactions and crystal symmetry. The main features in both Raman and FIR spectra were reproduced well, which enabled the band assignments based on density functional theory and the significant improvement of the conventional assignments for which there had been a big dispute. Temperature dependence of the experimental FIR spectra has revealed that both bands at 222 and 111 cm?1 are characteristic of the ?-form structure. Their intensities linearly decreased with increasing temperature with marked two transition points, which correspond to glass and Brill transitions. Both bands can be indicators of the lattice length of ?-form nylon 6. On the basis of the calculations, the FIR and Raman bands at ?100 cm?1 were successfully assigned to methylene torsion and transverse motion of amide groups in which NH and O atoms move out of the amide plane. Decomposition of the calculated spectra revealed that the intensities at ?100 cm?1 in both spectra mainly originate from the amide groups and only secondarily from the methylene groups. Moreover, the FIR intensities at ?100 cm?1 were nearly perfectly governed by the amide groups, which could be a reason why this FIR band is particularly sensitive to hydrogen bonds among the low-frequency bands. The FIR band at 222 cm?1 was assigned to methylene torsion and transverse motion of NH groups. Both FIR bands at 222 and 111 cm?1 contain perpendicular motions of methylene and amide groups. This will be a reason for their sensitivity to interchain interactions in ?-form nylon 6. Contrarily, the FIR band at 294 cm?1 is in parallel polarization to the chain direction and assigned to a deformation of C?CH2?CH2 and bending motion of C?O in the amide plane. This is the reason why this band is not sensitive to the structural transitions of nylon 6. Our previous works revealed that in regions of 125 and 70 cm?1, there are specific vibrational peaks of crystalline polyesters primarily arising from out-of-plane motion of ester groups. We can find a similarity in 125 and 70 cm?1 regions between crystalline polyesters and nylon 6 that both polymers show specific out-of-plane vibrational peaks around 100 cm?1, which are sensitive to the lattice length among polymer chains.

Actin polymerization is activated by terahertz irradiation.

Polymerization of monomeric actin into filaments has pivotal roles in cell motility, growth, differentiation, and gene expression. Therefore, techniques of manipulating actin polymerization, including actin-binding chemicals, have been developed for understanding and regulating multiple biological functions. Here, we demonstrate that irradiation with terahertz (THz) waves is a novel method of modulating actin polymerization. When actin polymerization reaction is performed under irradiation with 0.46 THz waves generated by a Gyrotron, actin polymerization was observed to be activated by monitoring the fluorescence of pyrene actin fluorophores. We also observed the number of actin filaments under a fluorescence microscope using the polymerized actin probe SiR-actin. The number of actin filaments was increased by 3.5-fold after THz irradiation for 20 min. When the THz irradiation was applied to a steady-state actin solution, in which elongation and depolymerization of actin filaments were equilibrated, increased actin polymerization was observed, suggesting that the THz irradiation activates actin polymerization, at least in the elongation process. These results suggest that THz waves could be applied for manipulating biomolecules and cells.

Terahertz Imaging of the Distribution of Crystallinity and Crystalline Orientation in a Poly(ɛ-caprolactone) Film.

The distribution of crystallinity and the crystalline orientation of a poly(ɛ-caprolactone) (PCL) film have been studied using terahertz (THz) imaging. Terahertz images were developed by using the intensity ratio of the two spectral peaks at 1.42 and 2.03 THz that are assigned to the crystalline modes parallel and perpendicular to the c-axis (I⊥/I ||) of the PCL film. The obtained THz images show that the distribution of crystallinity and crystalline orientation vary considerably between the different regions in the PCL film, even though this inhomogeneity is not visible in the corresponding optical image. Our results clearly illustrate that THz imaging is a promising technique to characterize the physical properties of semi-crystalline polymers.

Low-Frequency Vibrational Modes of Poly(glycolic acid) and Thermal Expansion of Crystal Lattice Assigned On the Basis of DFT-Spectral Simulation Aided with a Fragment Method.

Low-frequency vibrational modes of lamellar crystalline poly(glycolic acid) (PGA) were measured on Raman and far-infrared (FIR) spectra. Among the observed bands, an FIR band at ∼70 cm-1 and a Raman band at 125 cm-1 showed a gradual lower-frequency shift with increasing temperature from 20 °C to the melting point at ∼230 °C. Their polarization direction was perpendicular to the chain axis of PGA. Both spectra were quantum-mechanically simulated with the aid of a fragment method, the Cartesian-coordinate tensor transfer, which enabled an explicit consideration of molecular interactions between two adjacent polymer chains. Good agreement was achieved between the experiment and theory in both spectra. The temperature-sensitive bands at ∼70 cm-1 in FIR and at 125 cm-1 in Raman comprise the out-of-plane C═O bending motion. The temperature-dependent shifts of the low-frequency bands were successfully simulated by the DFT-spectral calculation, exploring that the main origin of the shifts is the thermal expansion of the crystal lattice. This result indicates that the thermally shifted bands may be used as an indicator of the lattice expansion of PGA. Possible changes in intermolecular interactions of PGA under temperature rising were ascribed on the basis of natural bond orbital theory. The steric repulsion between the carbonyl O atom in one chain and the H-C bond in the adjacent chain will be a dominant interaction in the lattice-expanding process, which would cause the observed thermal shifts of the bending modes. Comparisons of the spectral assignment for PGA obtained in this study and that for poly-(R)-3-hydroxybutyrate (PHB) reported by us suggest that crystalline polyesters give vibrational modes composed of out-of-plane bending motion of C═O groups between ∼70 and ∼125 cm-1, the modes of which are sensitive to the thermal expansion of crystal lattice and its concomitant changes in their intermolecular interactions.

Ro-vibrational Spectra of (para-H2 )N -CH4 in He Droplets.

In this work, we report on the infrared spectroscopic study of clusters of CH4 molecules with up to N=80 para-hydrogen molecules assembled inside He droplets. Upon increase of the number of the added para-hydrogen molecules up to about N=12, both the rotational constant, B, and the origin frequency of the υ3 band of CH4 decrease gradually. In the range of 6 ≤N≤12, the spectra indicate some abrupt changes of B and υ3 with both values being approximately constant at N≥12. The origin of this effect is discussed. Comparison of the spectra of methane molecules in para-hydrogen clusters to that in solid para-hydrogen is also presented.

Polymer Morphological Change Induced by Terahertz Irradiation.

As terahertz (THz) frequencies correspond to those of the intermolecular vibrational modes in a polymer, intense THz wave irradiation affects the macromolecular polymorph, which determines the polymer properties and functions. THz photon energy is quite low compared to the covalent bond energy; therefore, conformational changes can be induced "softly," without damaging the chemical structures. Here, we irradiate a poly(3-hydroxybutylate) (PHB) / chloroform solution during solvent casting crystallization using a THz wave generated by a free electron laser (FEL). Morphological observation shows the formation of micrometer-sized crystals in response to the THz wave irradiation. Further, a 10-20% increase in crystallinity is observed through analysis of the infrared (IR) absorption spectra. The peak power density of the irradiating THz wave is 40 MW/cm(2), which is significantly lower than the typical laser intensities used for material manipulation. We demonstrate for the first time that the THz wave effectively induces the intermolecular rearrangement of polymer macromolecules.

Infrared Spectroscopy and Structure of (NO)(n) Clusters.

Nitrogen oxide clusters (NO)n have been studied in He droplets via infrared depletion spectroscopy and by quantum chemical calculations. The ν1 and ν5 bands of cis-ON-NO dimer have been observed at 1868.2 and 1786.5 cm(-1), respectively. Furthermore, spectral bands of the trimer and tetramer have been located in the vicinity of the corresponding dimer bands in accord with computed frequencies that place NO-stretch bands of dimer, trimer, and tetramer within a few wavenumbers of each other. In addition, a new line at 1878.1 cm(-1) close to the band origin of single molecules was assigned to van der Waals bound dimers of (NO)2, which are stabilized due to the rapid cooling in He droplets. Spectra of larger clusters (n > 5), have broad unresolved features in the vicinity of the dimer bands. Experiments and calculations indicate that trimers consist of a dimer and a loosely bound third molecule, whereas the tetramer consists of two weakly bound dimers.

Internal Rotation of Methane Molecules in Large Clusters.

Methane is one of the very few substances that show rotation of individual molecules in the crystalline phase. Here we explore the evolution of the rotation spectrum of methane from single molecules to clusters containing up to about 4 × 10(3) molecules. The clusters were assembled in He droplets at T = 0.38 K and studied via infrared laser spectroscopy in the ν3 region of the methane molecules. Well-resolved rotational structure in the spectra was observed in clusters containing up to about 50 molecules. We have concluded that in distinction to the crystals molecular rotation in methane clusters is confined to the surface and is enabled by low coordination of the molecules. On the contrary the molecules in the cluster's interior are in amorphous state wherein the rotation is quenched. These results demonstrate that even at very low temperature the surface of the methane clusters remains fluxional due to quantum effects.

Rotation of methane molecules in dimers and small clusters.

This work reports on the study of the internal rotation of methane molecules in small clusters containing up to about five molecules. The clusters were assembled in helium droplets at T = 0.38 K by successive capture of single methane molecules and studied by infrared laser spectroscopy of the fundamental CH4 ν3 vibration around 3030 cm(-1). The spectra demonstrate well resolved structure due to internal rotation of the constituent molecules in the clusters. The most resolved spectrum for the dimers shows characteristic splitting of the lines due to anisotropic intermolecular interaction. The magnitude of the splitting is found to be in a good quantitative agreement with the recent theoretical anisotropic intermolecular potentials.

Infrared spectra in the 3 µm region of ethane and ethane clusters in helium droplets.

Ethane and ethane clusters (N ≈ 10(2)-10(4)) were studied inside helium droplets with infrared laser spectroscopy. The spectra were measured in the 2880-3000 cm(-1) range, which covers the ν5, ν(8+11), and ν7 vibrational bands of ethane. Partially resolved rotational fine structure in the spectrum of the monomer reveals solvent-induced band origin blue shifts that are each approximately 1 cm(-1). The effective B(He) and A(He) rotational constants were found to be reduced by 52% and 16% in comparison to their gas phase values, respectively. Spectra of the clusters show the same three bands shifted toward low frequency by approximately 10 cm(-1) because of intermolecular interactions in the clusters. The spectra of the ethane clusters are dominated by the ν7 band, whereas the relative intensities of the ν5 and ν(8+11) bands are about a factor of 5 weaker than for single molecules or for solid ethane, the spectrum of which is also reported here.

Quantum mechanical interpretation of intermolecular vibrational modes of crystalline poly-(R)-3-hydroxybutyrate observed in low-frequency Raman and terahertz spectra.

Low-frequency vibrational bands observed in the Raman and terahertz (THz) spectra in the region of 50-150 cm(-1) of crystalline powder poly-(R)-3-hydroxybutyrate (PHB) were assigned based on comparisons of the Raman and THz spectra, polarization directions of THz absorption spectra, and their congruities to quantum mechanically (QM) calculated spectra. This combination, Raman and THz spectroscopies and the QM simulations, has been rarely adopted in spite of its potential of reliable assignments of the vibrational bands. The QM simulation of a spectrum has already been popular in vibrational spectroscopies, but for low-frequency bands of polymers it is still a difficult task due to its large scales of systems and a fact that interactions among polymer chains should be considered in the calculation. In this study, the spectral calculations with the aid of the Cartesian-coordinate tensor transfer (CCT) method were applied successfully to the crystalline PHB, which include the explicit consideration of an intermolecular interaction among helical polymer chains. The agreements between the calculations and the experiments are good in both the Raman and THz spectra in terms of spectral shapes, frequencies, and intensities. A Raman active band at 79 cm(-1) was assigned to the intermolecular vibrational mode of the out-of-plane C═O + CH(3) vibration. A polarization state of the corresponding far-infrared absorption band at ∼82 cm(-1), perpendicular to the helix-elongation direction of PHB, was reproduced only under the explicit correction, which indicates that this polarized band originates from the interaction among the polymer chains. The calculation explored that the polarization direction of this band was along the a axis, which is consistent with the direction in which weak intermolecular hydrogen bonds are suggested between the C═O and CH(3) groups of two parallel polymer chains. The results obtained here have confirmed sensitivity of the low-frequency vibrational bands to the weak hydrogen bonds among the polymer chains.

Polarization and temperature dependent spectra of poly(3-hydroxyalkanoate)s measured at terahertz frequencies.

Temperature-dependent terahertz (THz) absorption spectra of poly(3-hydroxyalkanoate)s (PHAs) were measured by using a Fourier transform far-infrared (FT-FIR) spectrometer and a THz time-domain spectrometer over a temperature range of 10 K to 465 K with a liquid helium cryostat and a heating cell. Clear differences were observed between the spectra of crystalline and amorphous polyhydroxybutyrate (PHB), indicating that the absorption peaks observed in the THz spectra originated in the higher-order conformation of PHB. The polarization spectra of a stretched PHB sample were measured, and the direction of the vibrational transition moment was determined. The temperature dependences of the spectra reveal frequency shifts and broadening of the absorption peaks with temperature, suggesting large anharmonicity of the vibrational potential. The temperature shift behaviour is quite different in each transition. Some of the transitions show a blue shift, which cannot be explained by a simple anharmonic potential model. Frequency shifts of the peaks were mainly observed below 10 THz, which suggests a large anharmonicity of the vibrational potential at lower frequencies.

Rotation of methane and silane molecules in He droplets.

This work studies the renormalization of the molecular moments of inertia I(G) in liquid helium. For this purpose we have measured the rotational-vibrational spectra of the nu(3) modes of a series of homologous light spherical top molecules such as CH(4), CD(4), SiH(4), and SiD(4) in He droplets. The spectra were fitted to an empirical gas phase Hamiltonian, yielding a set of spectroscopic constants. We found that the additional moment of inertia, DeltaI(He), scales approximately as square of I(G). This is in agreement with the theoretical model which assigns DeltaI(He) to coupling of molecular rotation with vibration of He in the molecular vicinity. Our results also indicate a large increase in the effective centrifugal distortion constants, which is another manifestation of the interaction of the molecular rotors with the He environment. Finally, the mechanism of the relaxation of rotational energy in liquid helium is discussed.

Noninvasive mail inspection system with terahertz radiation.

Using the high penetrability of the terahertz waves and the characteristic absorption spectra in this frequency range, we have built a noninvasive mail inspection system targeting drugs and explosives. The system is composed of two stages; in the first stage, the scattering of a continuous terahertz wave is used for selecting mail that contains concealed powder; in the second stage, the absorption spectrum of the suspicious mail is measured and the material is identified using a terahertz spectrum database. We evaluated the performance and the limits of the inspection system.