Cyclic structures, restricted

Although the cyclic structure restricts the conformation of the peptide backbone, there is still considerable conformational flexibility around the Tyr and Phe side chains... 

It was claimed that the hard cyclic structure restricts chain mobility to become an effective tie-down point (thus avoiding the need for chemical cross-linking). When 65% of the formulation was the poly(tetramethylene ether)glycol, elastic fibres similar to the Spandex polyurethane fibres were obtained. 

In their paper Perry et al. proposed that the hard cyclic structure restricted chain mobility and became an effective tie-down point. From subsequent experience with the thermoplastic polyether-polyesters and the S—B—S materials it would seem reasonable to suppose that blocks of the polycarbonate of the cyclic glycol provided the basis of the hard segment rather than single cyclic glycol units randomly positioned along the polymer chain. 

They hypothesized that incorporation of the binding features of this structural water molecule into an inhibitor would be beneficial because of the entropic gain due to its displacement and because the conversion of a flexible linear inhibitor into a rigid, cyclic structure with restricted conformation should provide an additional, positive entropic effect. In the initial design, a cyclohexanone with the ketone oxygen as the structural... 

Timasheff, 1992) for these structures, which can now bind directly between aspartic acids and the flaps, and moreover conversion of a flexible, linear inhibitor into a rigid, cyclic structure with its restriction in conformational freedom would provide an entropic advantage (see Section 2.1). 

One should note that we do not put barriers between organic and inorganic cyclic structures. We have on one hand aromatic organic homocycles such as benzene, cyclopentadienide anions, cyclooctatetrae-nide dianions and tropylium cations, and on the other hand aromatic inorganic homocycles, and then we gradually fuse them into aromatic heterocycles. The only restriction we observe is for discussing only... 

Similarly, substitution only changes the entropy of the lactam very slightly, but decreases considerably the entropy of the linear monomer unit inside a polymer chain by restricting its rotation. In this way, substitution shifts the enthalpy and entropy of polymerization in favour of the cyclic structure and decreased polymerizability. 

Cis-trans isomers (also called geometric isomers) result from restricted rotation (Section 3.4). Restricted rotation can be caused either by a double bond or by a cyclic structure. As a result of the restricted rotation about a carbon-carbon double bond, an alkene such as 2-pentene can exist as cis and trans isomers. The cis isomer has the hydrogens on the same side of the double bond, whereas the trans isomer has the hydrogens on opposite sides of the double bond. 

Cyclic structures with varying potentials exist (e.g., benzene), and such systems retain the degeneracy and real or complex orbital features. Also, j continues to have meaning (restricted) with respect to wavelength and number of nodes. However, angular momentum and energy are no longer simply related to j. 

The extent of the restriction on the mobility of an azobenzene moiety covalently incorporated into higher-order unimer micelles, monitored by photoisomerization and thermal back isomerization rates, is much more pronounced in cyclododecyl domains than in dodecyl domains, which can be related to a difference in the mobility of these aliphatic hydrophobes in the microdomains (52). Cyclododecane is a rigid molecule with much less conformational freedom than dodecane because of its cyclic structure. The latter is a flexible chain that can adopt a variety of conformations. Therefore, cyclododecyl groups may be more tightly associated than dodecyl groups and form a more rigid hydrophobic microdomain. 

The first type of stereoisomers we will look at are cis-trans isomers (also called geometric isomers). These isomers result from restricted rotation. Restricted rotation can be caused either by a cyclic structure or by a double bond. 

In contrast to concrete argument structures, we allow cyclic structures and multiple parents in patterns. However, we need a restriction to rule out inescapable loops, so that recursion is well-founded. 

---