Winfried Petry

Bio: Winfried Petry is an academic researcher from Technische Universität München. The author has contributed to research in topics: Neutron scattering & Small-angle neutron scattering. The author has an hindex of 40, co-authored 225 publications receiving 6784 citations. Previous affiliations of Winfried Petry include Technical University of Dortmund.

Dynamical transition of myoglobin revealed by inelastic neutron scattering.

Abstract: Structural fluctuations in proteins on the picosecond timescale have been studied in considerable detail by theoretical methods such as molecular dynamics simulation1,2, but there exist very few experimental data with which to test the conclusions. We have used the technique of inelastic neutron scattering to investigate atomic motion in hydrated myoglobin over the temperature range 4–350 K and on the molecular dynamics timescale 0.1–100 ps. At temperatures below 180 K myglobin behaves as a harmonic solid, with essentially only vibrational motion. Above 180 K there is a striking dynamic transition arising from the excitation of non-vibrational motion, which we interpret as corresponding to tor-sional jumps between states of different energy, with a mean energy asymmetry of KJ mol −1. This extra mobility is reflected in a strong temperature dependence of the mean-square atomic displacements, a phenomenon previously observed specifically for the heme iron by Mossbauer spectroscopy3–5, but on a much slower timescale (10−7 s). It also correlates with a glass-like transition in the hydration shell of myoglobin6 and with the temperature-dependence of ligand-binding rates at the heme iron, as monitored by flash photolysis7. In contrast, the crystal structure of myoglobin determined down to 80 K shows no significant structural transition8–10. The dynamical behaviour we find for myoglobin (and other globular proteins) suggests a coupling of fast local motions to slower collective motions, which is a characteristic feature of other dense glass-forming systems.

Thermal motions and function of bacteriorhodopsin in purple membranes: effects of temperature and hydration studied by neutron scattering

Abstract: The internal dynamics of bacteriorhodopsin, the light-driven proton pump in the purple membrane of Halobacterium halobium, has been studied by inelastic neutron scattering for various conditions of temperature and hydration. Light activation can take place when the membrane is vibrating harmonically. The ability of the protein to functionally relax and complete the photocycle initiated by the absorption of a photon, however, is strongly correlated with the onset of low-frequency, large-amplitude anharmonic atomic motions in the membrane. For a normally hydrated sample, this occurs at about 230 K, where a dynamical transition from a low-temperature harmonic regime is observed. In moderately dry samples, on the other hand, in which the photocycle is slowed down by several orders of magnitude, no transition is observed and protein motions remain approximately harmonic up to room temperature. These results support the hypothesis, made from previous neutron diffraction studies, that the "softness" of the membrane modulates the function of bacteriorhodopsin by allowing or not allowing large-amplitude motions in the protein.

Phonon dispersion of the bcc phase of group-IV metals. II. bcc zirconium, a model case of dynamical precursors of martensitic transitions

Abstract: The phonon dispersion of the high-temperature bcc phase of Zr has been measured at several temperatures. The longitudinal L 2/3(1,1,1) mode and the transverse ${\mathrm{T}}_{1}$ 1/2(1,1,0) mode with [11\ifmmode\bar\else\textasciimacron\fi{}0] polarization are of very low energy (i.e., of large amplitude) and overdamped. These phonons achieve the displacements necessary for two martensitic phase transitions. The L 2/3(1,1,1) phonon displaces the lattice toward the high-pressure \ensuremath{\omega} phase and the ${\mathrm{T}}_{1}$ 1/2(1,1,0) phonon shifts the bcc planes into the stacking sequence of the low-temperature hcp phase. These fluctuations are interpreted as dynamical precursors of the low-symmetry phases within the bcc phase. Elastic precursors or central peaks were not found in pure bcc Zr. Furthermore, it is shown that the bcc phase is stabilized mainly by the excess vibrational entropy due to the low-energy phonons.

Formation of glasses from liquids and biopolymers.

Abstract: 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.

Bulk metallic glasses

Abstract: Amorphous alloys were first developed over 40 years ago and found applications as magnetic core or reinforcement added to other materials. The scope of applications is limited due to the small thickness in the region of only tens of microns. The research effort in the past two decades, mainly pioneered by a Japanese- and a US-group of scientists, has substantially relaxed this size constrain. Some bulk metallic glasses can have tensile strength up to 3000 MPa with good corrosion resistance, reasonable toughness, low internal friction and good processability. Bulk metallic glasses are now being used in consumer electronic industries, sporting goods industries, etc. In this paper, the authors reviewed the recent development of new alloy systems of bulk metallic glasses. The properties and processing technologies relevant to the industrial applications of these alloys are also discussed here. The behaviors of bulk metallic glasses under extreme conditions such as high pressure and low temperature are especially addressed in this review. In order that the scope of applications can be broadened, the understanding of the glass-forming criteria is important for the design of new alloy systems and also the processing techniques.

Bulk Glass-Forming Metallic Alloys: Science and Technology

Abstract: The following article is based on the MRS Medal talk presented by William L. Johnson at the 1998 MRS Fall Meeting on December 2, 1998. The MRS Medal is awarded for a specific outstanding recent discovery or advancement that has a major impact on the progress of a materials-related field. Johnson received the honor for his development of bulk metallic glass-forming alloys, the fundamental understanding of the thermodynamics and kinetics that control glass formation and crystallization of glass-forming liquids, and the application of these materials in engineering.The development of bulk glass-forming metallic alloys has led to interesting advances in the science of liquid metals. This article begins with brief remarks about the history and background of the field, then follows with a discussion of multicomponent glass-forming alloys and deep eutectics, the chemical constitution of these new alloys, and how they differ from metallic glasses of a decade ago or earlier. Recent studies of deeply undercooled liquid alloys and the insights made possible by their exceptional stability with respect to crystallization will then be discussed. Advances in this area will be illustrated by several examples. The article then describes some of the physical and specific mechanical properties of bulk metallic glasses (BMGs), and concludes with some interesting potential applications.The first liquid-metal alloy vitrified by cooling from the molten state to the glass transition was Au-Si, as reported by Duwez at Caltech in 1960. Duwez made this discovery as a result of developing rapid quenching techniques for chilling metallic liquids at very high rates of 105–106 K/s.

Dynamic personalities of proteins.

Abstract: Because proteins are central to cellular function, researchers have sought to uncover the secrets of how these complex macromolecules execute such a fascinating variety of functions. Although static structures are known for many proteins, the functions of proteins are governed ultimately by their dynamic character (or 'personality'). The dream is to 'watch' proteins in action in real time at atomic resolution. This requires addition of a fourth dimension, time, to structural biology so that the positions in space and time of all atoms in a protein can be described in detail.