Spontaneous chain breaking processes

If the transferred reactive species does not re-initiate monomer, because for example, it is too unreactive or it is purposefully trapped, or if some purely terminative chain breaking process is involved, then the process is termed unimolecular or spontaneous termination. In this case [P]tot remains constant and equal to [I]o, and we must revise eqn (2.13) as follows ... 

The polymerization of mixtures of different racemic cr-amino acids may result in a spontaneous mirror-symmetry breaking process, as proposed for the solid-state polymerization of gwasi-racemates. Thus, in the polymerization of mixtures of different racemic Q -amino adds, the heterochiral chains contain different sequences, resulting in the stochastic mirror-symmetry breaking. ... 

In his interesting paper Professor Nicolis raises the question whether models can be envisioned which lead to a spontaneous spatial symmetry breaking in a chemical system, leading, for example, to the production of a polymer of definite chirality. It would be even more interesting if such a model would arise as a result of a measure preserving process that could mimic a Hamiltonian flow. Although we do not have such an example of a chiral process, which imbeds an axial vector into the polymer chain, several years ago we came across a stochastic process that appears to imbed a polar vector into a growing infinite chain. 

Papirmeister and his colleagues showed that these alkylated purines (guanine and adenine are purines, cytosine and thymine are pyrimidines) are rapidly removed from DNA a depurination process that may occur spontaneously or as a result of activation of endonucleases. Interestingly, it was shown that alkylation of the N3 site of adenine had the greatest sensitizing effects on endonucleases derived from extracts of bacterial and mammalian cells (Papirmeister et al., 1970 Lindahl, 1979). For further details of endonuclease activation, the reader should refer to the original papers. Depurination leads to apurinic sites appearing in DNA and these are attacked by apurinic endonucleases. These specific endonucleases lead to breaks in the DNA chain a critical step in the pathway proposed. Papirmeister summed up the process as ... 

In the process of cell division, each DNA macromolecule duplicates before the cell divides, so that the daughter cells should have an identical DNA sequence to the parent. The DNA duplication process involves the spontaneous splitting of the molecule into two separate chains by the breaking of the hydrogen bonds linking the nitrogenous bases. Each chain then picks up the required bases, phosphates, and sugars from the material in the nucleus to build on a complementary chain, identical to the one from... 

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