Quasiperiodic structures, or quasicrystals, because of their unique ordering of atoms and a lack of periodicity, possess remarkable crystallographic, physical and optical properties not present in regular crystals.
Figure Caption: Two-dimensional Penrose type quasicrystal made using only two tile shapes: a thick rhomb and a thin rhomb. The structure proposed by Roger Penrose lacks translational symmetry and exhibits five-fold rotational symmetry not allowed in regular crystals.
Periodic structures are known for their predictable symmetry, both rotational and translational, and they were believed to be the only kinds of repeating structures that could occur in nature. From basic solid state physics, these structures are only allowed to exhibit strict 2, 3, 4 or 6-fold rotational symmetry, i.e., upon rotation by a certain angle about a crystallographic axis, the shape would still look identical upon each rotation. It was not believed that there could be a structure that existed which violated these four symmetry rules. Random systems, the other big area of research, looks at amorphous or disordered media like gases.
The introduction of quasicrystals – an ordered structure that lacks periodicity, exhibits some properties similar to periodic structures (such as atomic ordering over large-length scales) while violates rotational symmetry rules associated with them (i.e., a quasicrystal can exhibit 5 or 8 fold rotational symmetry) – was an area initially met with resistance from the research community. Agrawal explores this transition from skepticism to the ultimate acceptance by a growing number of researchers exploring the potential of these unique structures.
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Researchers from the Department of Atomically Resolved Dynamics of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg, the University of Hamburg and the European Molecular Biology Laboratory (EMBL) outstation in the city have developed a new method to watch biomolecules at work. This method dramatically simplifies starting enzymatic reactions by mixing a cocktail of small amounts of liquids with protein crystals. Determination of the protein structures at different times after mixing can be assembled into a time-lapse sequence that shows the molecular foundations of biology.
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Researchers from the Department of Atomically Resolved Dynamics of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg, the University of Potsdam (both in Germany) and the University of Toronto (Canada) have pieced together a detailed time-lapse movie revealing all the major steps during the catalytic cycle of an enzyme. Surprisingly, the communication between the protein units is accomplished via a water-network akin to a string telephone. This communication is aligned with a ‘breathing’ motion, that is the expansion and contraction of the protein.
This time-lapse sequence of structures reveals dynamic motions as a fundamental element in the molecular foundations of biology.
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