CRYSTALS
Researchers Have Discovered the Crystal-Shape-Directing Quality of Amino Acids
Organic molecules are known to affect crystal growth, but the mechanism has been poorly understood until recently. In a report published in the June 14, 2001, issue of Nature, Christine Orme of the Lawrence Livermore National Laboratory in California and her colleagues describe how the microscopic arrangements of amino acids influence the growth of calcite crystals. These findings buy term paper may have applications in biology and the fabrication of molecular-sized components.
Orme and her team used in situ atomic force microscopy to study the tiny steplike growing surfaces of calcite crystals. Their work revealed that amino acids added to the crystal-growing medium caused normally straight steps to become curved. Moreover, the researchers discovered that addition of the amino acid aspartic acid influenced the direction of the curve. Like human hands, aspartic acid and other organic compounds exist in left- and right-handed mirror image versions of each other, a trait known as chirality. Student Papers Orme’s group discovered that the addition of left-handed aspartic acid influenced the crystal step curve in a fashion opposite that of right-handed aspartic acid. Molecular modeling conducted by the team indicates that the presence of amino acids alters the energy of the minute crystal step, thus causing it to curve. Left- and right-handed amino acids bind preferentially to opposite steps; therefore, curve direction is based on which chiral version of the amino acid is present. Because aspartic acid is a common amino acid found in many organisms, the researchers postulate that nature may take advantage of this mechanism to create the intricate calcite shapes found in shell-forming organisms such as snails and foraminifers. Materials scientists may also eventually exploit this method to guide the direction of growth in nanoscale devices.
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