Comb molecules

Figure 5.12 Examples of long chain branched molecules produced by macromer incorporation a) three-armed star b)"comb molecule,and c) complexly branched molecule...

Fig. 2. Two limiting cases of a regular comb molecule. The flexible chain sections between two branching points may consist of m monomer units while the/flexible side chains have a length of n monomer units. The one structure (short side chains) resembles a substituted linear chain, the second one (short backbone) has similarity to star molecules...

In recent years the chemistry of preparing dendrimers has become very successful although painfully cumbersome and time consuming [39-47]. This is not the only drawback. Because of space filling it has not been possible to prepare more than five generations. Either the reaction to a higher generation stops completely or, what happens in practice, the outermost shells will develop imperfections. As in the case of comb molecules, corrections have to be made to the properties of this idealized structure. 

Fig. 6 a Schematic drawing of the measured sample, with DNA molecules combed between Re/G electrodes on a mica substrate, b AFM image showing DNA molecules combed on the Re/C bilayer. The large vertical arrow indicates the direction of the solution flow, used to deposit the DNA. The small arrows point towards the combed molecules. Note the forest structure of the carbon film, c DC resistance as a function of temperature on a large temperature scale for three different samples, showing the power law behavior down to 1 K (from [60], with permission Copyright 2001 by Science)... 

Sole (22) has calculated the moments of the distributions of the three principal orthogonal components of obtained by decomposing along the three principal axes of inertia of the chain, for certain star and comb molecules in addition to linear ones and rings he finds that branching or ring closure decreases the high asymmetry found for linear chains. 

Khripin,2008 ssDNA-dispersed SWCNT CHa-modified silicon Proposed a modified random sequential adsorption theory to predict density of combed molecules. 

Molecular combing can be used to demonstrate a number of interesting, and potentially useful, geometries of the combed molecule. These are summarized in Fig. 16.6. 

The amount of branching introduced into a polymer is an additional variable that must be specified for the molecule to be fully characterized. When only a slight degree of branching is present, the concentration of junction points is sufficiently low that these may be simply related to the number of chain ends. For example, two separate linear molecules have a total of four ends. If the end of one of these linear molecules attaches itself to the middle of the other to form a T, the resulting molecule has three ends. It is easy to generalize this result. If a molecule has v branches, it has v 2 chain ends if the branching is relatively low. Branched molecules are sometimes described as either combs or... 

Mannhold, R., Petrauskas, A. Substrucmre versus whole-molecule approaches for calculating log P. QSAR Comb. Sci. 2003, 22, 466-475. 

Sample preparation for AFM analysis is relatively simple. Generally, a desired amount of sample is absorbed onto a smooth and clean substrate surface, for example, a freshly cleaved mica surface. For example, to prepare a food macromolecule sample for AFM imaging in air, the diluted macromolecule solution is disrupted by vortexing. Then, a small aliquot (tens of microliters) of vortexed solution is deposited onto a surface of freshly cleaved mica sheet by pipette. The mica surface is air dried before the AFM scan. A clean surrounding is required to avoid the interference of dust in the air. Molecular combing or fluid fixation may be applied to manipulate the molecule to get more information. 

Ludwig A, Hundhausen C, Lambert MH, et al. Metalloproteinase inhibitors for the disintegrin-like metalloproteinases ADAM 10 and ADAM 17 that differentially block constitutive and phorbol ester-inducible shedding of cell surface molecules. Comb Chem High Throughput Screen 2005 8 161-171. 

Yang, C., Zhong, C. Chirality factors and their application to QSAR studies of chiral molecules. QSAR Comb. Sci. 2005, 24, 1047-1055. 

This approximation is equivalent to assuming that the differences in internal densities and, consequently, in solvent draining, between a branched chain and the homologous linear chain, when included in their corresponding mean sizes, can describe both the friction coefficient and the viscosity. Besides these theoretical considerations, an empirical correlation in terms of a log-log fit of h vs f was employed by Roovers et al. [51]. Kurata and Fukatsu [48] and Ptitsyn [82] performed a more general Kirwood evaluation of the friction coefficient for different types of ideal branched molecules (uniform and randomly distributed stars, combs and random-branched structures). Their results for different structures are included within the limits l[Pg.60]

The result of treating the Flory-Stockmayer ensemble in this way and at the same level of approximation as that of the Cayley tree sketched in the previous section, is that a very similar relaxation spectrum to Eq. (36) is predicted, but with a value for the exponent 0 of 4 rather then 2. A disentanglement transition is also found, as well as the appeafing feature that at each seniority a fixed fraction of the molecules still entangled actually renormalise into linear polymers (like the comb topology) and relax by reptation rather than by further fluctuation [49]. 

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