Interchain helical structure

The di-LCPAs in solution and in cast film showed monosignate and bisignate Cotton effects in their CD spectra, respectively. These results suggest the formation of intrachain and interchain helical structures, respectively. In spite of this, the di-LCPAs in solution and in cast film exhibited no CPL [21]. However, (/f)-/(S)-Poly-4 in an N -LC film showed bisignate CPL bands centered around the PL emission band (Fig. 11.12a). (/f)-Poly-4 exhibited positive and negative CPL bands at wavelengths shorter and longer than 530 nm, respectively. (S)-Poly-4 exhibited CPL bands with handedness opposite to those (/ )-Poly-4. The CPL spectra of (/ )-/(S)-Poly-4 in an N -LC film showed gem values of 1.8 x 10 and... 

The DNA isolated from different cells and viruses characteristically consists of two polynucleotide strands wound together to form a long, slender, helical molecule, the DNA double helix. The strands run in opposite directions that is, they are antiparallel and are held together in the double helical structure through interchain hydrogen bonds (Eigure 11.19). These H bonds pair the bases of nucleotides in one chain to complementary bases in the other, a phenomenon called base pairing. 

Hydroxyproline and hydroxylysine Collagen contains hydroxy proline (hyp) and hydroxylysine (hyl), which are not present in most other proteins. These residues result from the hydroxylation of some of the proline and lysine residues after their incorporation into polypeptide chains (Figure 4.6). The hydroxylation is, thus, an example of posttranslational modification (see p. 440). Hydroxy proline is important in stabilizing the triple-helical structure of colla gen because it maximizes interchain hydrogen bond formation. 

The coiled-coil motif is an ideal model system for the following reasons there is only one type of secondary structure present (the a-helix) the a-helical structure can be easily monitored by circular dichroism spectroscopy the two-stranded coiled coil contains two subunits stabilized by both intrachain and interchain interactions and, lastly, its small size reduces the potential complexity in the analysis and interpretation of results encountered in the analysis of globular proteins, which have multiple elements of secondary structure (a-helix, (3-sheet, (3-turns, loops, and regions of undefined structure). 

The interchain periodicity of 5.6 A can typically be visualized in all three common CM-AFM imaging modes, height, deflection and friction (latter one shows highest sensitivity with scan angles of 90°, see also Chap. 2) [34—36]. In the literature, some authors have reported that even the helical structure of the PTFE chains can be resolved in some cases [37], however, this is not obvious in the images shown here. For quantitative work, it is essential that the thermal drift is minimized, hence subsequent up and down scans should match and in particular the inclination angles of the periodic structure should be invariant with this capture direction. 

In the previous section, we reported PMP derivatives bearing chiral side chains having a helicene-like helical structure through intrachain 7r-electron overlap interactions, which lead to a self-assembled whisker morphology due to interchain van der Waals interactions. However, each whisker of the PMP derivative is still randomly oriented, even if it has a self-assembled structure. It is therefore desirable to align the PMP derivative to construct a higher-ordered hierarchical structure and also to evolve an anisotropic nature in its potentially profound op-toelectrical properties. 

The detailed structural analysis of gellan has been performed using X-ray diffraction technique by Chandrasekaran and Radha. The X-ray diffraction study on Li gellan revealed that it possesses an extended double helical molecular structure formed by intertwining of threefold left-handed helical chains of pitch 56.4 A in a parallel fashion [8]. This helical structure is stabilized by means of interchain hydrogen bond between the hydroxymethyl groups of 4-linked glucosyl units in one chain and carboxylate... 

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