Macromolecules helicity

Helix conformation occurs relatively oft i in macromolecules. Helices are distinguished by a number where p gives the number of monomeric units per q complete turns of tl4 helix. The 3i helix of it-poly(propylene) thus exhibits three monomeric units per turn (Figure 4-5). In many macro-molecules, two (e.g., DNA) or three (e.g., collagen) separate helices are... 

In the a modifications of i-PP, bilayers of macromolecules are stacked one on the top of the other in such a way that the top layer on one bilayer and the bottom layer of the bilayer in contact are made up of helices which are enantiomorphous. such helices are regularly anticlined for the ordered a2 modification, more or less at chance isoclined or anticlined for the disordered modifications. 

Fig. 1 Vesicle construct formed from poly(L-lysine)-i)-poly(L-leucme) polypeptides where the poly(L-leucine) block corresponds to the a-helical hydrophobic segments and the poly (L-lysine) block corresponds to the random coil hydrophilic segments. Note that this is one specific example and not all vesicle constructs have a-helical and random coil blocks. Moreover, the amphiphilic copolymer can be comprised of either a pure block copolypeptide or a macromolecule consisting of a polypeptide and another type of polymer. Adapted from [20] with permission. Copyright 2010 American Chemical Society...

Liu S, Kiick KL (2008) Architecture effects on the binding of cholera toxin by helical glycopolypeptides. Macromolecules 41 764—772... 

Liu B, Lewis AK, Shen W (2009) Physical hydrogels photo-cross-linked from self- assembled macromers for potential use in tissue engineering. Biomacromolecules 10 3182-3187 Vandermeulen GWM, Tziatzios C, Duncan R et al (2005) Peg-based hybrid block copolymers containing alpha-helical coiled coil peptide sequences control of self- assembly and preliminary biological evaluation. Macromolecules 38 761-769... 

Vandermeulen GWM, Tziatzios C, Klok HA (2003) Reversible self-organization of poly (ethylene glycol)-based hybrid block copolymers mediated by a de novo four- stranded alpha-helical coiled coil motif Macromolecules 36 4107 114... 

From the atomic to the macroscopic level chirality is a characteristic feature of biological systems and plays an important role in the interplay of structure and function. Originating from small chiral precursors complex macromolecules such as proteins or DNA have developed during evolution. On a supramolecular level chirality is expressed in molecular organization, e.g. in the secondary and tertiary structure of proteins, in membranes, cells or tissues. On a macroscopic level, it appears in the chirality of our hands or in the asymmetric arrangement of our organs, or in the helicity of snail shells. Nature usually displays a preference for one sense of chirality over the other. This leads to specific interactions called chiral recognition. 

Grasdalen, H. and Smidsrod, O. (1981) Iodide-specific formation of K-carrageenan single helices-1-127 NMR spectroscopic evidence for selective site binding of iodide anions in the ordered conformations. Macromolecules, 14, 1842-1845. 

G.S. Manning, Counterion condensation on a helical charge lattice. Macromolecules 34, 4650-4655... 

In proteins in particular the peptide bonds contribute to the CD-spectra of the macromolecule. Here, CD-spectra reflect the secondary structure of proteins, which are derived from CD-spectra of model macromolecules with only one defined secondary structure (like poly-L-lysine at given pH values) or based on spectra of proteins with known structures (e.g.,from X-ray crystallography). The amount of a-helices or -sheets in the unknown structure is calculated by linear combination of the reference spectra [150,151]. 

Several natural and synthetic helical macromolecules such as DNA, polypeptides, and polyisocyanates form, in the appropriate solvent, cholesteric meso-phases. Also self-assembled supramolecular systems formed by guanosine derivatives 2 and 3 (G-wires), which are essentially four-stranded helices (Figure 7.8), behave in a similar way.35... 

Many studies, the first of which began shortly after the discovery of stereoregular polymerization of olefins, demonstrated that macromolecules could adopt stable helical conformations not only in the solid state but also in solution. These efforts have led to the realization that certain helical polymers reach a level of chiral recognition adequate for commercial development as an important aspect of chromatography. Researchers from the leading laboratory in this field, Okamoto, Yashima, and Yamamoto, have written Chapter 3 painting a detailed picture of the current status and future possibilities in this... 

Figure 41 Composition dependence of the enantiomer excess 2fP - 1 of the P helical state of polysilanes 109(P) O 109(S) o, 110 A and 111 (calculated solid curves experimental symbols).326 Reprinted with permission from Sato, T. Terao, K. Teramoto, A. Fujiki, M. Macromolecules 2002, 35, 5355-5357, 2002 American Chemical Society. 

Scheme 31 Induction of PSS helicity in oligosilane by wrapping in 7-cyclodextrin.335 Reprinted with permission from Sanji, T. Kato, M. Tanaka, M. Macromolecules 2005, 38, 4034-4037, 2005 American Chemical Society.

Koe, J. R. Fujiki, M. Nakashima, H. Motonaga, M. Helical Poly(diarylsilylene)s Effects of Higher Order Structure on Optical Activity. In Synthetic Macromolecules with Higher Order Structure, Khan, I. M., Ed. ACS Symposium Series 812 Washington DC, 2002 pp 67-86. 

Although varying considerably in molecular size, any GPCR polypeptide sequence contains seven hydrophobic a-helices that span the lipid bilayer and dictate the typical macromolecule architecture. Seven transmembrane domains bundled up to form a polar internal tunnel and expose the N-terminus and three interconnecting loops, to the exterior, and the C-terminus with a matching number of loops, to the interior of the cell [1-3]. This structural information was recently confirmed by the resolution of the crystal structure of rhodopsin [4,5]. 

It is now more or less believed that the iodine is held as an absorption complex within the helical chain of the macromolecule f3-amylose i.e., a component of most starches. However, another component, a-amylose, is undesirable because it produces a red-colouration with iodine which is not readily reversible, and... 

Concerning the helical stmcture of biological macromolecules in general, they relied on Linus Pauling s discovery of the alpha-helix stmcture of proteins and concerning the helical stmcture of DNA, they relied on Rosalind Franklin s X-ray diffraction pattern of DNA. 

DNA is a structurally polymorphic macromolecule which, depending on nucleotide sequence and environmental conditions, can adopt a variety of conformations. The double helical structure of DNA (dsDNA) consists of two strands, each of them on the outside of the double helix and formed by alternating phosphate and pentose groups in which phosphodiester bridges provide the covalent continuity. The two chains of the double helix are held... 

The problem is further complicated for vinyl polymers with their problems of stereoisomerism. The first descriptions of the conformational state of isotactic polypropylene in solution go back 25 years (178, 179, 192, 193). Corradini, Allegra, and Ganis proposed a model, still essentially valid today, according to which macromolecules possess a local helical structure analogous to that observed in the crystalline state. The helix segments are rather short, only a few monomer units, after which an inversion of the helix sense occurs, with simultaneous alteration of its direction (Figure 15). As a whole this disordered con-... 

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