Polymers single-strand

Note 1 For a single-strand polymer molecule with skeletal bonds all joined by the same value of valence angle, the contour length is equal to the end-to-end distance of the chain extended to the all-trans conformation. For chains of complex structures, only approximate values of the contour length may be accessible. 

Note 2 The sum of the lengths of all skeletal bonds of a single-strand polymer molecule is occasionally termed contour length . This use of the term in this sense is discouraged. 

As with single-strand polymers, substituents that are part of the CRU are denoted by their names prefixed to the name of the subunit to which they are bound (see Table 7). 

In 1976, the lUPAC Commission on Macromolecular Nomenclature published rules on the nomenclature of regular single-strand organic polymers. These were later revised [1]. A regular single-strand polymer is one which can be described by constitutional repeating units with only two terminals composed of one atom each. 

Note Partial ladder (imperfect ladder, block ladder) polymers [5], in which the sequence of rings is interrupted and a divalent constitutional repeating unit can be identified, are not double-strand polymers. They are named as single-strand polymers. 

In using this nomenclature, the steps to be followed in sequence are the same as those for regular single-strand polymers ... 

The proeedure for structure-based naming of irregular single-strand polymers is as follows ... 

Application of this system should not discourage the use of structure-based nomenclature whenever the copolymer structure is fully known and is amenable to treatment by the rules for single-strand polymers [1, 2]. It is intended that the present nomenclature system supersede the previous recommendations published in 1952 [3]. 

A classification of linear single-strand polymers (lUPAC Recommendations 1988), PureAppl. Chem. 61, 243-254 (1989). 

A single-strand polymer is composed of single-strand macromolecules, the structure of which comprises constitutional units connected in such a way that adjacent constitutional units are joined to each other through two atoms, one on each constitutional unit. 

As for a single-strand polymer, a single preferred CRU must be selected in order to obtain a unique name. The CRU is usually a tetravalent group denoting attachment to four atoms and is named according to the usual rules of organic nomenclature. The name of the polymer is in the form poly(CRU). 

A regular linear polymer that can be described by a preferred CRU in which only one terminal constituent subunit is connected through a single atom to the other identical CRU is a quasi-single-strand polymer. Such polymers are named similarly to single-strand coordination polymers. 

Keratin is a natural single-strand polymer consisting of chains of amino acids, with a high proportion of the two sulfur-containing amino acids cysteine and methionine. Keratin is the polymer of hair and nails. The sulfur atoms account for keratin s ability to bond to arsenic, mercury, and lead. Hair analysis has played an important role in forensic evidence in cases of poisoning, and it has been possible to diagnose the extent to which famous people in history were affected by these toxic elements provided a sample of their hair has been preserved. 

This K is considerably smaller than that of the single-strand polymer at neutral pH, and suggests that the molecules have a rather thick structure. Adopting the interrupted-helix model, we may apply Eq. (97) as in the case of poly-L-proline. Noting that the unit translation distance b0 is 1.70 A for the double-stranded Watson-Crick helix (263 ) [i. e., a distance of 3.40 A for two residues, one in each chain], and taking Mu = 328 for poly(adenylic acid), we obtain r = 22 residues per helical... 

Nucleic acid polymers are known to undergo transitions between single strands and double and triple helices. These transitions are readily detected by NMR because of the large differences in the line widths of a flexible random coil compared to a rigid helix. A mixture of adenosine, a mononucleoside, and poly U, a large single-stranded polymer, is known to form a triple helix at low temperatures.6 The down-... 

The above examples of a stepwise synthesis of a ladder polymer involve the formation of single-stranded polymers via polymerization of suitable monomers to functionalized precursors. These consist of substituted poly(ethylene)- or (polyacetelyne)-type macromolecules, from which attempts are made to carry out a defined polymer-analogous cyclization reaction. 

RNA is chemically very similar to DNA but differs in important ways. The sugar miit is ribose with an added hydroxyl group at the 2 position, and the methylated pyrim-idine uracil (U) replaces thymine. RNA exists in various functional forms but typically as a single-stranded polymer that is much shorter than DNA and that has an irregular three-dimensional structure. Research from recent years has revealed that RNA conformations are not random structures and the folding mechanism of RNA molecules is complex. The secondary structure adopted by an RNA molecule is to a large extent related to its nucleotide sequence. The secondary structure for particular RNA sequences can be as regular as the secondary structure of a protein. It is now known that RNA molecules can further interact to form complex tertiary structures, which are intimately related to novel functions of RNA, such as the catalytic activity of ribozymes, ... 

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