Specifications aggregate

Quaternary structure (Section 26.9) The highest level of protein structure, involving a specific aggregation of individual proteins into a larger cluster. 

On the other hand, as biological molecules become larger their tendency to be associated with water molecules, metal ions, and other materials increases. Crystalline proteins, for example, routinely contain 27-65 % of the solvent used for their crystallisation 183). Such associated materials may be difficult to locate by crystallography and it may become a question of terminology whether such molecules should be regarded as inclusion complexes, non-specific aggregates, or merely contaminated biomolecules. 

Morris, E.R., Rees, D.A. and Robinson, G. (1980) Cation-specific aggregation of carrageenan helices Domain model of polymer gel structure. Journal of Molecular Biology, 138, 349-362. 

Unlike electron and scanning tunneling microscopy, the use of fluorescent dyes in monolayers at the air-water interface allows the use of contrast imaging to view the monolayer in situ during compression and expansion of the film. Under ideal circumstances, one may observe the changes in monolayer phase and the formation of specific aggregate domains as the film is compressed. This technique has been used to visualize phase changes in monolayers of chiral phospholipids (McConnell et al, 1984, 1986 Weis and McConnell, 1984 Keller et al., 1986 McConnell and Moy, 1988) and achiral fatty acids (Moore et al., 1986). 

Speed, M. A., Wang, D. I. C., and King, J. (1996). Specific aggregation of partially folded polypeptide chains The molecular basis of inclusion body composition. Nat. Biotechnol. 14, 1283-1287. 

Fig. 5 A proposed mechanism for enhanced emission (or AIEE) in solid-state organic dye nanoparticles. The dye considered here is trans-biphenylethylene (CN-MBE) compound. The geometry is optimized by the density functional theory (DFT) calculation at the B3LYP/6-31G level. Molecular distortion such as twisting and/or subsequent planarization causes prevention of radiationless processes along with specific aggregation such as the /-aggregate in the nanoparticles...

Kim J, McQuade DT, McHugh SK, Swager TM (2000) Ion-specific aggregation in conjugated polymers highly sensitive and selective fluorescent ion chemosensors. Angew Chem IntEd 39 3868-3872... 

Quaternary structure refers to the specific aggregation or association of separate protein chains to form a well-defined structure. Part D of Figure 2.4 compares the quaternary structure of a dimeric protein (two polypeptide chains) to the lower levels of protein structure. The separate protein chains are often referred to as subunits or monomers these subunits may be identical or may be of quite different sequence... 

T n recent years it has become increasingly evident that many important A biological systems, in particular many enzymes, exist in a stable form as specific aggregates of subunits. Frequently, such intermolecular associations play a key role in determining biological activity and its control (1,2,3). To arrive at a full understanding of the function of such macromolecules, it is important to know exactly the molecular weights of their subunits. 

Usually a single, sharp band was observed when the protein was examined by polyacrylamide or starch gel electrophoresis (14, IS) at either pH 7 or 9 (13). Occasionally traces of a slower moving band have been noted, but there is reason to believe that this represents a specific aggregate of pyrophosphatase molecules (see Section II,G and Fig. 4). 

The causes of the variations seen in Figs. 29, 30, and 31 are likely to result from a number of factors including the number of gold(I) ions involved in specific aggregates (dimers, trimers, extended chains, etc.), the distance between the gold(I) ions within any particular aggregate, the relative orientation... 

Impressive materials properties can also be achieved by the solvent-specific aggregation properties of appropriately designed amphiphilic materials. A brief account on the organogel or hydrogel formation by amphiphilic molecules is now presented, citing a few examples from the current literature. Both... 

As a general rule, the abundance is reduced when the number of associated molecules increases. However, some specific aggregates, resulting from particularly important interactions, are present at particularly high abundance. This occurs often with organometallic compounds, as the metal tries to complete its electronic shell. 

MALDI has also been successfully used to study a number of intact non-covalent complexes such as protein quaternary structures [132-135]. However, MALDI has not yet contributed widely to the study of these complexes because it requires the crystallization of the sample with the matrix. Furthermore, the energy deposited to desorb the ions is not clearly known. In consequence, MALDI generally induces dissociation of the non-covalent interactions and leads to the formation of non-specific aggregates. Nevertheless, weak non-covalent interactions can survive during the MALDI process to allow the direct detection of intact complexes if specific methods, which have been developed to preserve these interactions, are followed [136],... 

As well as these, several industries have their own specifications aggregates [22], porcelain [23], ceramic powders [24], plastics [25], coating powders [26], concrete [27] and metals [28], The standard for glass spheres [29] is designed specifically for sieve analysis of glass spheres used in reflective road and pavement markings and other industrial uses. 

In each familiar form of a given disease, a mutation in the gene for a specific aggregated protein [25] was found. Thus, each aggregated protein is intimately connected to a different disease. 

Stability. Current protocols for nonviral delivery systems call for the preparation of the vector at the bedside, due to their aggregation over time [127-129]. Specifically, aggregation of some lipoplex formulations stored as liquids reduced their transfection efficiency [130,131], Electron microscopy was used to show that PEI/DNA complexes did not aggregate, but vectors made with poly-L-lysine and dendrimers did in one study [103],... 

Figure 4. Observed removal efficiencies of specifically aggregated suspensions in varied separation units (sedimentation tanks).

A more realistic approach attempts to describe each equilibrium in terms of its thermodynamic equilibrium constant, molar volumes of specific aggregates, and a heat of reaction to estimate the chemical contribution to excess enthalpy Hchem- The first two parameters contribute to the excess Gibbs energy model. 

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