Exploring Biomolecular Self-Assembly with Far-Infrared Radiation.

Physical engineering technology using far-infrared radiation has been gathering attention in chemical, biological, and material research fields. In particular, the high-power radiation at the terahertz region can give remarkable effects on biological materials distinct from a simple thermal treatment. Self-assembly of biological molecules such as amyloid proteins and cellulose fiber plays various roles in medical and biomaterials fields. A common characteristic of those biomolecular aggregates is a sheet-like fibrous structure that is rigid and insoluble in water, and it is often hard to manipulate the stacking conformation without heating, organic solvents, or chemical reagents. We discovered that those fibrous formats can be conformationally regulated by means of intense far-infrared radiations from a free-electron laser and gyrotron. In this review, we would like to show the latest and the past studies on the effects of far-infrared radiation on the fibrous biomaterials and to suggest the potential use of the far-infrared radiation for regulation of the biomolecular self-assembly.

Dissolution of a fibrous peptide by terahertz free electron laser.

Fibrous peptides such as amyloid fibrils have various roles in biological system, e.g., as causal factor of serious amyloidosis in human and as functional regulator of cell formation in bacteria and eukaryotes. In addition, the fiber-type format is promising as biocompatible scaffold. Therefore, the dissolution method of peptide fibril is potentially useful at many scenes in medical and material fields: as reductive way of pathogenic amyloid, as modification technique of cell structure, and as fabrication tool of biomaterials. However, the fibril structure is generally difficult to be dissociated due to its rigid stacked conformation. Here, we propose a physical engineering technology using terahertz free electron laser (FEL) at far-infrared wavelengths from 70 to 80 µm. Infrared microscopy analysis of the irradiated fibril of calcitonin peptide as a model showed that ß-sheet was decreased, and α-helix, turn, and others were increased, compared to those of the fibril before the FEL irradiation. Interestingly, the dissociative effect by the far-infrared laser was remarkable than that by the mid-infrared laser tuned to 6.1 µm that corresponds to amide I. In addition, simple heating at 363 K deformed the fibril state but increased the amount of ß-sheet, which was contrast with the action by the FEL, and scanning-electron microscopy and Congo-red staining revealed that the fibril was collapsed power-dependently within a range from 25 to 900 mJ energies supplied with the FEL at 74 µm. It can be considered that irradiation of intense terahertz wave can dissociate fibrous conformation of peptide with little influence of thermal effect.

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.

Electronic-structure-driven magnetic ordering in a Kondo semiconductor CeOs2Al10.

We report the anisotropic changes in the electronic structure of a Kondo semiconductor CeOs(2)Al(10) across an anomalous antiferromagnetic ordering temperature (T(0)) of 29 K, using optical conductivity spectra. The spectra along the a and c axes indicate that an energy gap due to the hybridization between conduction bands and nearly local 4f states, namely the c-f hybridization gap, emerges from a higher temperature continuously across T(0). Along the b axis, on the other hand, another energy gap with a peak at 20 meV becomes visible at 39 K (>T(0)) and fully opens at T(0) because of a charge instability. This result implies that the appearance of the energy gap, as well as the change in the electronic structure along the b axis, induces the antiferromagnetic ordering below T(0).

Pressure transmitting medium Daphne 7474 solidifying at 3.7 GPa at room temperature.

A pressure transmitting medium named Daphne 7474, which solidifies at P(s)=3.7 GPa at room temperature, is presented. The value of P(s) increases almost linearly with temperature up to 6.7 GPa at 100 degrees C. The high pressure realized by a medium at the liquid state allows a higher limit of pressurization, which assures an ideal hydrostatic pressure. We show a volume change against pressure, pressure reduction from room to liquid helium temperature in a clamped piston cylinder cell, pressure distribution and its standard deviation in a diamond anvil cell, and infrared properties, which might be useful for experimental applications.