Ring topology

Nitrogen and oxygen are found in level 2 of the Periodic Table, and a further alteration in ring topology may arise when the heteroatom is replaced by an element from a lower level. Here, apart from an increase in atomic diameter, the replacement element may use a hybridization state different than that of the earlier elements. Not only can this affect the shape of the molecule, it can also modify the chemical properties. 

The ring topology is the potential to form unique polymer structures. Like linear polymers, cyclic polymers not only can be branched or cross-linked, but also can form non-covalently linked structures based on their loop topology. These are referred to as topological polymers, including rotaxane, catenane, threaded rings, and rings threaded by network chains. Recently, much attention has been paid to how their particular properties not only differ from linear polymers, but also how they differ from a component of an interlocked polymer system, such as polycatenanes and polyrotaxanes. 

Rotatable Bonds, Unsaturations, Rings, Chains and Ring Topology... 

Currently, the lantibiotic family contains more than 50 members with varying structmes, properties, and biological activities (Fig. lb). Depending on the ring topology of mature lantibiotics, they may have an elongated three-dimensional structure... 

Recently an enzyme was found in planktonic marine cyanobacterium Prochlo-rococcus MIT9313 that could transform up to 29 different linear peptides into a library of polycyclic, conformationally constrained products with highly diverse ring topologies [65]. 

A ring topology directly connects each processing element with two neighboring processing elements. 

In 1995 Muller et al. reported the synthesis and structural characterization of a very high nuclearity cluster M0154 that has a ring topology. The interest generated by this result is partly due to its high nuclearity and partly because of the size of this cluster with an outer diameter... 

Much less is known about more complex ring topologies such as knotted and catenated macromolecular tings (Scheme 12) that are also found in biological materials. Their mechanism of formation and their function are still unclear and increasing efforts are being made to tentatively prepare and investigate their specific characteristics and properties. 

Scaffold abstraction approaches like topological frameworks or reduced graphs were first proposed by Bemis and Murcko [28] and further explored by Xu and Johnson [29]. Groupings into series by some fuzzier similarity are obtained by using different abstraction levels for atom types, bond types, and ring topologies. 

Rosa, A. Orlandini, E. Tubiana, L. Micheletti, C., Structure and Dynamics of Ring Polymers Entanglement Effects Because of Solution Density and Ring Topology. Macromolecides 2011,44,8668-8680. 

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