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Typically, a molecular solid is ductile when it has isotropic intermolecular interactions. This allows for dislocation between layers of the crystal much like metals. [5] [8] [11] For example, plastic crystals are soft, resemble waxes and are easily deformed. One example of a ductile molecular solid, that can be bent 180°, is hexachlorobenzene ...
For decades hemoglobin was the primary teaching example for the concept of allostery, as well as being an intensive focus of research and discussion on allostery. In 1909, hemoglobin crystals from >100 species were used to relate taxonomy to molecular properties. [6]
A crystal's crystallographic forms are sets of possible faces of the crystal that are related by one of the symmetries of the crystal. For example, crystals of galena often take the shape of cubes, and the six faces of the cube belong to a crystallographic form that displays one of the symmetries of the isometric crystal system. Galena also ...
All crystals have translational symmetry in three directions, but some have other symmetry elements as well. For example, rotating the crystal 180° about a certain axis may result in an atomic configuration that is identical to the original configuration; the crystal has twofold rotational symmetry about this axis.
Important examples of self-assembly in materials science include the formation of molecular crystals, colloids, lipid bilayers, phase-separated polymers, and self-assembled monolayers. [ 23 ] [ 24 ] The folding of polypeptide chains into proteins and the folding of nucleic acids into their functional forms are examples of self-assembled ...
Plastic crystals were discovered in 1938 by Belgian chemist Jean Timmermans [4] by their anomalously low entropy of fusion.He found that organic substances having an entropy of fusion lower than approximately 17 J·K −1 ·mol −1 (~2R, where R is the molar gas constant) had peculiar properties.
In molecular crystals the energetic separation between the top of the valence band and the bottom conduction band, i.e. the band gap, is typically 2.5–4 eV, while in inorganic semiconductors the band gaps are typically 1–2 eV. This implies that molecular crystals are, in fact, insulators rather than semiconductors in the conventional sense.
Examples of network solids include diamond with a continuous network of carbon atoms and silicon dioxide or quartz with a continuous three-dimensional network of SiO 2 units. Graphite and the mica group of silicate minerals structurally consist of continuous two-dimensional sheets covalently bonded within the layer, with other bond types ...