Tertiary nucleation

In addition, the nucleation may be primary, secondary, or tertiary (Figure 10-7). Primary nucleation is three dimensional a new surface is formed in each direction in space. Secondary nucleation, in contrast, is two dimensional with tertiary nucleation, growth is in one dimension. 

Naturally, one can also propose a tertiary nucleation step for starting growth on a smooth ledge as seen at position 2 in Fig. 3.68. Its nucleation barrier would be even smaller than for secondary nucleation and even less likely to slow the crystal growth significantly. 

Fig. 10.23 Illustration of three basic situations of crystal nucleation. From left to right are primary nucleation in the bulk polymer phase, secondary nucleation on the smooth growth front, and tertiary nucleation at the terrace of the growth front...

Tertiary nucleation involves typically two surfaces being formed and represents the stem attaching to an edge face. 

Fig. 4.13 Schematic pictures of (a) primary nucleation, (b) secondary nucleation, and (c) tertiary nucleation...

Crystal growth occurs by secondary and tertiary nucleation (Fig. 8.2). The initial step is the formation of a secondary nucleus, which is followed by a series of tertiary nucleation events. 

Primary nucleation Secondary nucleation Tertiary nucleation (w 6) (n=4) (ns2)... 

Three basic types of nucleation are considered at various dimensions primary nucleation, secondary nucleation, and tertiary nucleation. Primary nucleation is a three-dimensional nucleus newly formed by thermal fluctuations, with six extra nucleus surfaces if the nucleus is considered to be cubic. Secondary nucleation is two-dimensional nucleation on the advancing surface of nucleus, with four extra surfaces produced. Secondary nucleation is much easier than primary nucleation as its free energy barrier is lower, making crystallization kinetics like a self-acceleration process. Tertiary nucleation is one-dimensional nucleation at the step edge of the spreading layer on the advancing smooth surface of nucleus, with only two extra surfaces produced. Tertiary nucleation is so fast that it can rarely be observed. The schematic pictures of different types of nucleation are shown in Figure 13.8. 

Fig. 5. Protein folding. The unfolded polypeptide chain coUapses and assembles to form simple stmctural motifs such as -sheets and a-hehces by nucleation-condensation mechanisms involving the formation of hydrogen bonds and van der Waal s interactions. Small proteins (eg, chymotrypsin inhibitor 2) attain their final (tertiary) stmcture in this way. Larger proteins and multiple protein assembhes aggregate by recognition and docking of multiple domains (eg, -barrels, a-helix bundles), often displaying positive cooperativity. Many noncovalent interactions, including hydrogen bonding, van der Waal s and electrostatic interactions, and the hydrophobic effect are exploited to create the final, compact protein assembly. Further stmctural...

The nucleation-condensation mechanism can be accommodated in modified framework and hydrophobic-collapse models the framework model must be modified so that formation of secondary structure is linked to the formation of tertiary interactions and the hydrophobic collapse model must have the formation of tertiary interactions linked to the formation of secondary structure. Another variation of concerted structure formation is the hydrophobic zipper. 68 Whatever the distinctions of names, stable tertiary and secondary structural interactions must form concurrently. 

Tertiary structure, the three-dimensional arrangement of secondary structure elements in a protein. Tertiary structure formation is nucleated by supersecondary... 

Protein tertiary structure. Protein tertiary stmctures are the result of weak interactions. When a protein folds, either as it is being made on ribosomes or refolded after it is purified, the first step involves the formation of hydrogen bonds within the structure to nucleate secondary structural (alpha and beta) regions. For example, amide hydrogen atoms can form H-bonds with nearby carbonyl oxygens an alpha helix or beta sheet can zip up, prompted by these small local structures. 

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