Packing defect

The membrane is a dynamic assembly and things are diffusing rapidly in the plane of the bilayer. The middle of the bilayer has been likened to olive oil. As with oil, cooling the lipid bilayer will cause the hydrocarbons to become more ordered (structured). The side chains pack closer to each other, and the fluidity of the membrane is lower. Things that disrupt the ability of the side chains to pack in a regular fashion make the membrane more fluid (Fig. 3-4). These include high temperature, lipids with shorter chains (double bonds. The shorter lipids and the m-double bonds cause the occurrence of holes (packing defects). 

F. M. Richards, Packing defects, cavities, volume fluctuations and access to the interior of proteins, Carlsberg Res. Commun. 44, 47-63 (1979). 

In literature the defects in crystalline materials are called O-di-mensional or point defects, 1-dimensional, also called line defects or dislocations and 2-dimensional or packing defects. In this book we will confine ourselves to a brief description of some of the many kinds of defects. 

A secondary transition, with a peak maximum around - 100 °C, is clearly evidenced. It is denoted here as p, but some authors call it y. Indeed, another mechanical transition (referred to as p by these authors) appears in some samples around 80 °C, but it is not characteristic of BPA-PC for it disappears by annealing. This has been attributed to relaxation of packing defects generated by rapid quenching [22-24], This transition will not be consid-... 

Supramolecular 10-105 nm Packing defects, nodular/globular morphology, multiphase structure Materials science Microscopies, scattering methods, thermal analysis... 

As the compression of the surface continues, the vapor phase disappears and the film is in the liquid state, also referred to as liquid expanded (LE, E or Li) state. The area per molecule in this state is in the range of 25-40 A2 for fatty acid films, which is intermediate between those in gaseous and solid (i.e. condensed) states. The surface pressure increases as the area per molecule decreases. The molecules in the liquid expanded state interact strongly with each other but are not closely packed. Defects, such as gauche conformations, can be found in the alkyl tails of the molecules. 

Various kinds of packing defects exist in the ionic crystals of NaCl type. A pair of cation and anion may be shifted from their stable positions toward the surface of the crystal, thus leaving behind a pair of vacancies. This is called the Schottky defect. The cation may leave its stable position and enter into an interstitial site. The formation of an interstitial cation and a vacancy is called the Frenkel defect. In addition to these two common kinds of defects, the presence of impurity atoms, atoms of varied valence, vacancies, and/or interstitial atoms is also possible. Some other important defects are discussed below. 

Cohen J, Kim K, King P, Seibert M, Schulten K. Finding gas diffusion pathways in proteins application to O2 and H2 transport in CpI [FeFe]-hydrogenase and the role of packing defects. Structure. 2005 13(9) 1321-9. 

Solid polymers may contain various stress concentration sources (hereafter referred to as flaws) which are either continuum defects (such as cracks, holes, inclusions, and the like) or quasimolecular flaws (such as regions of orientation, packing defect, crystallinity, or excess free energy) in an otherwise homogeneous and ostensibly structureless glassy polymer. 

Yan [65] has shown that the sintered grain size distribution is similar to the initial particle size distribution. In the proceeding chapters, we have seen that green bodies may have density variations due to various sources. Such packing defects include (1) macroscopic inclusions of organic material which burns out to leave a void, (2) macroscopic voids... 

The volume of space bounded by the solvent-accessible molecular surface is called the solvent-excluded volume because it is the volume of space from which solvent is excluded by the presence of the molecule when the solvent molecule is also modelled as a hard sphere. Moreover, the interstitial volume is the volume consisting of packing defects between the atoms that are too small to admit a probe sphere of a given radius in practice, it is calculated as the difference between the solvent-excluded volume and the van der Waals volume. An analytical method was developed by Connolly able to calculate the solvent-excluded volume [Connolly, 1983b] several other numerical and analytical approaches have been proposed. 

Throughout the book, dehydrons will be referred to in different ways depending on the context. Thus, the terms packing defect, wrapping defect, dehydron, structural deficiency, structural vulnerability will be used synonymously. Far from introducing a notational chaos, this name multiplicity bespeaks of the richness of the concept. 

Fernandez A, Scott LR (2003). Adherence of packing defects in soluble proteins. Phys Rev Lett 91 018102... 

Fernandez A, Berry RS (2003) Proteins with H-bond packing defects are highly interactive with lipid bilayers Implications for amyloidogenesis. Proc Natl Acad Sci USA 100 2391-2396... 

Fig. 4.2 PDB structure of SH3 domain indicating the packing defects in the protein. The backbone is displayed by blue segments representing virtual bonds joining a-carbons, well-wrapped hydrogen bonds are shown as white segments joining a-carbons of paired residues, and dehydrons are shown in green. Some residue labels and side chains are displayed to illustrate hydration patterns. Reprinted with permission from American Institute of Physics [20]. Copyright 2007...

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