Mushroom conformation

The same interactions that determine intramolecular structure and aggregatirai also play a role in adsorption to surfaces. When a simple linear macromolecule interacts with a surface and becomes adsorbed, its structure changes from the 3D mushroom conformation to the (quasi)-2D pancake conformation [155]. In the... 

Figure 3 End-grafted polymer chains in a good solvent. If d > 2Rg, the chains assume a conformation similar to that of free chains in solution, for which Rg is the radius of gyration. This is known as the mushroom conformation. If d < 2Rg, the chains stretch out into the solvent to...

Figure 4 Scaling of polymer height from the substrate surface in both mushroom and brush conformations. The quantity d/2Rg gives an indication of the degree of brush formation. In the mushroom conformation, the height, Hm is independent of the grafting density, while in a brush, the height, Hb scales as the cube root of the grafting density, cr, which is 1/d. ...

In other words, the free-energy cost incurred due to interaction between the chains exceeds the contribution due to the entropy elasticity of the chain (Figure 3). In the case of the widely spaced, (or mushroom ) conformation, the height of the polymer layer above the substrate is independent of the grafting density of the chains (number of attached chains per unit area). In the brush conformation, however, the height scales as the cube root of the grafting density (Figure 4), a, which itself is equivalent to 1/d. ... 

FIGURE 17.15 Direct electrochemical contact between an incoming AFM-SECM probe and the redox Fc heads of nanometer-sized, flexible chains (such as PEG or DNA), end-grafted onto an electrode substrate. The Fc heads are alternatively oxidized at the tip and reduced back at the substrate. For clarity, the tip is not drawn to scale. The chains are pictured in the mushroom conformation. (Adapted with permission from Abbou, J., Anne, A., and Demaille, C., Probing the structure and dynamics of end-grafted flexible polymer chain layers by combined atomic force—Electrochemical microscopy. Cyclic voltammetry within nanometer-thick macromolecular poly(ethylene glycol) layers, J. Am. Chem. Soc., 126,10095-10108, 2004. Copyright 2004 American Chemical Society.)... 

Fig. 7. Conformational states of polymer chains grafted at a surface. Influence of grafting density mushroom left) and brush right). 

PEG is a widely used molecule as a component in pharmaceutical formulations. PEG is particularly useful thanks to its low cost and various simple synthetic methods (26). PEG-lipid has been developed as a means of stabilizing conventional liposomes. A lipid moiety has been linked to the large PEGylated head in order to anchor the molecule to the particles. Instead of shielding a direct layer of polymer PEG around the particle, which would be less stable, the idea is to favor hydrophobic interactions between the PEG-lipid and the particle bilayer lipids. This anchor had led to two conformations of the PEG on the particle surface commonly called mushroom and brush regimes (27), representing a more condensed or extended conformations... 

Fig. 2 Schematic representation of surface-anchored polymers in brush (left) and mushroom (middle) conformations in good solvents. Also shown is the conformation of a surface-tethered polymer under poor solvent conditions (right)...

Fig. 18 Schematic of the conformational changes from mushroom to brush state that occur in graft-polymerized PDMAm during the chain propagation process...

L-Cycloserine inhibits many PLP enzymes and is toxic to humans. This observation led Khomutov et al. to synthesize the following more specific "cycloglutamates," structural analogs of glutamic acid with fixed conformations J/k Nature apparently anticipated the synthetic chemist, because it has been reported that the mushroom Tricholoma muscar-... 

In addition to these problems, the classical CD spectrum exhibited by many proteins with a high content of P-sheet secondary structure (Fig. B3.5.6D) is quite different from those for another group of P-structure-containing proteins, of which the first identified was the WW domain (Koepf et al., 1999 not shown), and another is the mushroom inhibitor clitocypin (Fig. B3.5.6C see Kidric et al., 2002, for further examples). P-casein (Fig. B3.5.6B) shows a similar spectrum, but originating from a more complex mix of conformations (Farrell et al., 2001). 

Fig. 8. Schematic representation of the possible conformations of adsorbed (co)polymers prepared using macromonomer technique a brush adsorption of graft copolymer b terminally-attached adsorption c the mushroom-brush transition for strongly overlapping chains proposed by de Gennes [130] and Alexander [155]...

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