Dielectric response of hen egg white lysozyme is measured in the far infrared (5-65 cm-1, 0.15-1.95 THz, 0.6-8.1 meV) as a function of hydration. The frequency range is associated with collective vibrational modes of protein tertiary structure. The observed frequency dependence of the absorbance is broad and glass-like. For the entire frequency range, there is a slight increase in both the absorbance and index of refraction with increasing hydration for <0.27 h (mass of H2O per unit mass protein). At 0.27 h, the absorbance and index begin to increase more rapidly. This transition corresponds to the point where the first hydration shell is filled. The abrupt increase in dielectric response cannot be fully accounted for by the additional contribution to the dielectric response due to bulk water, suggesting that the protein has not yet achieved its fully hydrated state. The broad, glass-like response suggests that at low hydrations, the low frequency conformational hen egg white lysozyme dynamics can be described by a dielectric relaxation model where the protein relaxes to different local minima in the conformational energy landscape. However, the low frequency complex permittivity does not allow for a pure relaxational mechanism. The data can best be modeled with a single low frequency resonance (nu approximately 120 GHz=4 cm-1) and a single Debye relaxation process (tau approximately .03-.04 ps). Terahertz dielectric response is currently being considered as a possible biosensing technique and the results demonstrate the required hydration control necessary for reliable biosensor applications.

The phase diagram of water is both unusual and complex, exhibiting a wide range of polymorphs including proton-ordered or disordered forms. In addition, a variety of stable and metastable forms are observed. The richness of H 2 O phases attests the versatility of hydrogen-bonded network structures that include kinetically stable amorphous ices. Information of the amorphous solids, however, is rarely available especially for the stability field and transformation dynamics-but all reported to exist below the crystallization temperature of approximately 150-170 K below 4-5 GPa. Here, we present the evidence of high density amorphous (HDA) ice formed well above the crystallization temperature at 1 GPa-well inside the so-called "no-man's land." It is formed from metastable ice VII in the stability field of ice VI under rapid compression using dynamic-diamond anvil cell (d-DAC) and results from structural similarities between HDA and ice VII. The formation follows an interfacial growth mechanism unlike the melting process. Nevertheless, the occurrence of HDA along the extrapolated melt line of ice VII resembles the ice Ih-to-HDA transition, indicating that structural instabilities of parent ice VII and Ih drive the pressure-induced amorphization.dynamic-DAC | rapid solidication | high pressure kinetics | metastability A bundant in nature, water is a major constituent of planets and living organisms alike. The phase diagram of water exhibits a large number of polymorphs with great diversity in crystalline structure, chemical bonding, and collective interactions (1-3). The hydrogen-bond angles and topology of relatively weak hydrogen bonds (with respect to covalent OH bonds) are subject to large distortions, which, in turn, lead to proton and structural disorders and myriad phases-both stable and metastable (including amorphous). In addition to a large number (approximately 15) of known solid phases of H 2 O, there are many metastable phases. The metastable phases include both crystalline and disordered solids: high-and low-density amorphous (HDA and LDA) at low temperatures (4-11), high-and low-density water (HDW and LDW) (12), as well as crystalline phases of ice IV (13) near the melting line, VII (14) observed in the stability field of ice VI, VII′ (6,15,16) in the ice VIII stability field, and ice III in the ice II field (17). This is in addition to a whole series of intermediate structures arising from amorphorization, dipoleordering transitions, and symmetrization of hydrogen bonding (4, 5, 18). The strength of hydrogen bonds varies in these metastable structures, as does the transition dynamics that is not well understood.Recently, a very high density form of amorphous ice (VHDA) was found by isobaric annealing of HDA at 177 K and 1.9 GPa (7,19). The presence of VHDA is characterized from HDA by its high density-not by the network structure. In fact, the VHDA is a topologically isomorphic phase to HDA, arising from the different interstitial occupancy of oxygen atoms. In this regard, there could be many intermedi...

Pressure-induced physical and chemical transformations of sodium cyanide (NaCN) have been studied up to 50 GPa in diamond-anvil cells, using micro-Raman spectroscopy and angle-resolved synchrotron x-ray diffraction. We observe three phase transitions in this pressure range: NaCN-IIA (orthorhombic, Immm), to NaCN-IIB (orthorhombic, Pmmn) at 4 GPa, to NaCN-III (monoclinic, Cm) at 8 GPa, and to NaCN-IV (tetragonal, P4mm) at 15 GPa, which is stable to 25 GPa. At higher pressures, NaCN-IV undergoes an irreversible chemical change, which occurs over a large pressure range between 25 and 34 GPa. The new material exhibits a broad yet strong Raman band at around 1550 cm(-1), indicating the formation of C=N bonds in a similar configuration of carbon graphite. The absence of sharp diffraction lines in this material suggests an amorphous nature of CN polymer products.

The authors demonstrate a method for rapid determination of protein-ligand binding on solution phase samples using terahertz dielectric spectroscopy. Measurements were performed using terahertz time domain spectroscopy on aqueous solutions below the liquid-solid transition for water. Small ligand binding sensitivity was demonstrated using triacetylglucosamine and hen egg white lysozyme with a decrease in dielectric response with binding. The magnitude of the change increases with frequency.

We have studied the pressure-induced physical and chemical transformations of tetracyanoethylene (TCNE or C6N4) in diamond anvil cells using micro-Raman spectroscopy, laser-heating, emission spectroscopy, and synchrotron x-ray diffraction. The results indicate that TCNE in a quasi-hydrostatic condition undergoes a shear-induced phase transition at 10 GPa and then a chemical change to two-dimensional (2D) C=N polymers above 14 GPa. These phase and chemical transformations depend strongly on the state of stress in the sample and occur sluggishly in non-hydrostatic conditions over a large pressure range between 7 and 14 GPa. The x-ray diffraction data indicate that the phase transition occurs isostructurally within the monoclinic structure (P21∕c) without any apparent volume discontinuity and the C=N polymer is highly disordered but remains stable to 60 GPa-the maximum pressure studied. On the other hand, laser-heating of the C=N polymer above 25 GPa further converts to a theoretically predicted 3D C-N network structure, evident from an emergence of new Raman νs(C-N) at 1404 cm(-1) at 25 GPa and the visual appearance of translucent solid. The C-N product is, however, unstable upon pressure unloading below 10 GPa, resulting in a grayish powder that can be considered as nano-diamonds with high-nitrogen content at ambient pressure. The C-N product shows a strong emission line centered at 640 nm at 30 GPa, which linearly shifts toward shorter wavelength at the rate of -1.38 nm∕GPa. We conjecture that the observed red shift upon unloading pressure is due to increase of defects in the C-N product and thereby weakening of C-N bonds.