Glasses can be formed by many routes. In some cases, distinct polyamorphic forms are found. The normal mode of glass formation is cooling of a viscous liquid. Liquid behavior during cooling is classified between "strong" and "fragile," and the three canonical characteristics of relaxing liquids are correlated through the fragility. Strong liquids become fragile liquids on compression. In some cases, such conversions occur during cooling by a weak first-order transition. This behavior can be related to the polymorphism in a glass state through a recent simple modification of the van der Waals model for tetrahedrally bonded liquids. The sudden loss of some liquid degrees of freedom through such first-order transitions is suggestive of the polyamorphic transition between native and denatured hydrated proteins, which can be interpreted as single-chain glass-forming polymers plasticized by water and cross-linked by hydrogen bonds. The onset of a sharp change in d dT( is the Debye-Waller factor and T is temperature) in proteins, which is controversially indentified with the glass transition in liquids, is shown to be general for glass formers and observable in computer simulations of strong and fragile ionic liquids, where it proves to be close to the experimental glass transition temperature. The latter may originate in strong anharmonicity in modes ("bosons"), which permits the system to access multiple minima of its configuration space. These modes, the Kauzmann temperature T(K), and the fragility of the liquid, may thus be connected.

https://science.sciencemag.org/content/sci/267/5206/1924.full.pdf

Formation of glasses from liquids and biopolymers.

Since the completion of the human genome project in 2003, extraordinary progress has been made in genome sequencing technologies, which has led to a decreased cost per megabase and an increase in the number and diversity of sequenced genomes. An astonishing complexity of genome architecture has been revealed, bringing these sequencing technologies to even greater advancements. Some approaches maximize the number of bases sequenced in the least amount of time, generating a wealth of data that can be used to understand increasingly complex phenotypes. Alternatively, other approaches now aim to sequence longer contiguous pieces of DNA, which are essential for resolving structurally complex regions. These and other strategies are providing researchers and clinicians a variety of tools to probe genomes in greater depth, leading to an enhanced understanding of how genome sequence variants underlie phenotype and disease.

Coming of age: ten years of next-generation sequencing technologies

Water is the most abundant component of biological material, but it is systematically excluded from conventional electron microscopy. This is because water evaporates rapidly under the vacuum conditions of an electron microscope. Cryoelectron microscopy has long been seen as a possible avenue to overcome this limitation, but until recently the direct observation of frozen-hydrated specimens was relatively unsuccessful because of a number of serious difficulties. These were, in particular, due to the absence of a good cryospecimen holder, the inherently low contrast of hydrated specimens and the structural damage due to ice crystals formed during freezing. As a consequence, the cryomethods which have flourished in electron microscopy during the last 20 years were not aimed at preserving the hydration of the specimen in the electron microscope. Freezing was only used as an aid to preparation. The objects ultimately observed in the electron microscope were dry and at room temperature. Such cryomethods have recently been reviewed in detail (Robards and Sleytr 1985).

/pdf/cryo-electron-microscopy-of-vitrified-specimens-46t0snibk6.pdf

Cryo-electron microscopy of vitrified specimens.

https://onlinelibrary.wiley.com/doi/pdf/10.1021/js9601896

Characteristics and Significance of the Amorphous State in Pharmaceutical Systems

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Non-crystalline solid forms of water prepared by the usual two methods of vapour-deposition on a substrate1,2 and by compression of hexagonal ice in a piston cylinder apparatus at 77 K (refs 3,4) do not seem to undergo a glass–liquid transition on heating2,5–7. Neither of these two, or possibly three, non-crystalline forms seem to be interconvertible by a single thermodynamic path involving only temperature or pressure. Also, their molecular structures are thermodynamically discontinuous8, with the structure of bulk water above 273 K and of emulsified water in the supercooled state near 230 K (see also refs 2 and 9). It has been difficult, therefore, to resolve whether or not water supercools to a glassy state in a thermodynamically reversible manner. We now report the results of a calorimetric study of the glassy state of water obtained by rapid cooling or by hyperquenching, demonstrate the reversibility of its glass–liquid transition in the temperature range 113–148 K, and consider the implication to our understanding of its other non-crystalline solid forms.

The glass–liquid transition of hyperquenched water

Pure water can only be vitrified by the very slow condensation of vapour on a metal surface maintained at very low temperatures1,2. Attempts to form vitreous ice by rapid cooling of liquid water invariably lead to formation of ice Ih (ref. 3). (Pryde and Jones4 did report a heat capacity change of rapidly cooled water at 126 K which they attributed to a glass transition, but could not reproduce this result in subsequent experiments.) Dilute aqueous solutions in contrast to concentrated aqueous solutions5 behave similarity to water and separate during freezing, even with the highest cooling rates available, into pure ice and concentrated solute6. We report here that macroscopic parts of samples of pure liquid water and of dilute aqueous solutions can be vitrified completely by jet-freezing of micrometre-sized aqueous droplets distributed in n -heptane as an emulsion—the resulting supercooling effect of ∼40 K being essential for vitrification7.

Complete vitrification in pure liquid water and dilute aqueous solutions

High-density amorphous ice (HDA), further densified on isobaric heating from 77 K to 165 (177) K at 1.1 (1.9) GPa, relaxes at 77 K and 1 bar to the same structural “state” with a density of 1.25 ± 0.01 g cm−3. Its density is higher by ≈9% than that of HDA, and thus it is called very-high-density amorphous ice (VHDA). X-ray diffractogram and Raman spectrum of VHDA clearly differs from that of HDA, and the hydrogen-bonded O–O distance increases from 2.82 A in HDA to 2.85 A in VHDA. Implications for the polyamorphism of the amorphous forms of water are discussed.

https://www.uibk.ac.at/physchem/staff_folder/tloerting/publications/loerting01-pccp.pdf

A second distinct structural “state” of high-density amorphous ice at 77 K and 1 bar

Glass-liquid transition and the enthalpy of devitrification of annealed vapor-deposited amorphous solid water: a comparison with hyperquenched glassy water

Two hydrogen ordered phases of ice were prepared by cooling the hydrogen disordered ices V and XII under pressure. Previous attempts to unlock the geometrical frustration in hydrogen-bonded structures have focused on doping with potassium hydroxide and have had success in partially increasing the hydrogen ordering in hexagonal ice I (ice Ih). By doping ices V and XII with hydrochloric acid, we have prepared ice XIII and ice XIV, and we analyzed their structures by powder neutron diffraction. The use of hydrogen chloride to release geometrical frustration opens up the possibility of completing the phase diagram of ice.

https://science.sciencemag.org/content/sci/311/5768/1758.full.pdf

Erwin Mayer

Papers

The glass–liquid transition of hyperquenched water

Complete vitrification in pure liquid water and dilute aqueous solutions

A second distinct structural “state” of high-density amorphous ice at 77 K and 1 bar

Glass-liquid transition and the enthalpy of devitrification of annealed vapor-deposited amorphous solid water: a comparison with hyperquenched glassy water

The preparation and structures of hydrogen ordered phases of ice.