Aggregation in solution

Chen S-FI, Fluang J S and Tartaglia P (eds) 1992 Structure and Dynamics of Strongly Interacting Colloids and Supramolecular Aggregates in Solution (Dordrecht Kluwer) pp 229-429... 

If polytungstates are considered as formed by the addition of acid to WO , then a series of isopolytungstates appears, in which the degree of aggregation in solution increases with decreasing pH. The relationships of the species, in order of increasing H20" W0 4 ratio, are shown in Table 3. 

Richter D (1992) In Chen SH et al. (eds) Structure and dynamics of strongly interacting colloids and supramolecular aggregates in solutions. Kluwer, Amsterdam, 111... 

Probably the best example of the manifestation of self-assembly processes in dendritic systems via H-bonds is seen in the recent work of Zimmerman et al. [156]. Dendritic wedges possessing tetraacid moieties (67) self-assembling into a hexameric, disc-like framework (68) was confirmed by SEC and -NMR studies. The tetraacid unit (69) is known to form cyclic as well as linear aggregates in solution via carboxylic acid dimerization (Fig. 30). However, with incorporation of larger dendritic wedges on 69, the hexamer form is preferred. 

It is well known that many compounds are able to change their physical form whilst suspended in solution. For example, a compound of interest may change from one polymorphic form to another, while different crystalline aggregations of the same compound can have different solubility profiles. Impurities can mask the true solubility, and aggregation in solution can also change the thermodynamic equilibrium. Finally, errors which have been published in the literature data may in fact magnify from publication to publication. 

Compounds of the porphyrin series, like other aromatic compounds, have a strong tendency to aggregate in solution. In general, aggregation is favoured by increased concentration and by an increased proportion of the poor solvent in a mixed solvent system.67-70 The aggregate shows reduced fluorescence and reduced PDT activity with respect to the monomer.71... 

Solution studies of the complexes outlined in Table 3 are in general agreement that they remain aggregated in solution, with the most common form being dimers.325 Solution studies of 300 in arene solvent indicate that at least two independent aggregates coexist.322 The most likely scenario from the data available is that a dimer-hexamer equilibrium is present in solution. Gas-phase studies of the hydrazides have proved to be problematic due to decomposition of the complexes on volatilization. 

The ease with which dissolution of the acetylated products can be achieved is affected by the method of isolation. In the author s experience, drying of the acetate with alcohol and ether results in apparent insolubility (even though the product was soluble at one stage of the purification process), and should be avoided. Drying, under diminished pressure, of the product precipitated by petroleum ether is sufficient. Chloroform is probably the best solvent. Nitroethane, tetrachlorethane, 2,4-pentanedione, pyridine, methyl acetate, ethyl acetate, and benzene, which have also been suggested, have disadvantages in that either they are unstable or they may cause aggregation in solution.44,116 116... 

Lashuel, H. A., Petre, B. M., Wall, J., Simon, M., Nowak, R. J., Walz, T., and Lansbury, P. T., Jr. (2002). Alpha-synuclein, especially the Parkinson s disease-associated mutants, forms pore-like annular and tubular protofibrils./. Mol. Biol. 322,1089-1102. LeVine, H. (1993). Thioflavine T interaction with synthetic Alzheimer s disease beta-amyloid peptides Detection of amyloid aggregation in solution. Protein Sci. 2, 404—410. Lin, H., Bhatia, R., and Lai, R. (2001). Amyloid beta protein forms ion channels Implications for Alzheimer s disease pathophysiology. FASEB J. 15, 2433-2444. Lorenzo, A., and Yankner, B. A. (1994). Beta-amyloid neurotoxicity requires fibril formation and is inhibited by Congo red. Proc. Natl. Acad. Sci. USA 91, 12243-12247. Luhrs, T., Ritter, C., Adrian, M., Riek-Loher, D., Bohrmann, B., Dobeli, H., Schubert, D., and Riek, R. (2005). 3D structure of Alzheimer s amyl o id-( be la) (1—12) fibrils. Proc. Natl. Acad. Sci. USA 102, 17342-17347. 

Co-polymerizations and homo-polymerizations of monomers such as dienes or 4-methylene dioxolan, in which two or more types of ion may propagate simultaneously, are further examples of enieidic polymerizations. These dienes, of course, also provide examples of eniedic radical and anionic polymerizations. Indeed the idea of dieidic polymerization has been suggested by several authors in relation to anionic polymerizations it arose from the aggregation in solution of the lithium alkyls [135], and similar phenomena. 

Upon immersion in acidic water (pH = 1) these unimolecular inverted micelles form vesicles in which the dendrimer component has a highly distorted conformation with an axial ratio of 1 8 for the highest generations. The amphiphilic dendrimers within the aggregates in solution are thought to have a flattened shape similar to those proposed for dendrimers at the air-water interface (section 16.2.1). 

Yao H, Isohashi T, Kimura K (2006) Detection of spectral inhomogeneities of mesoscopic thiacyanine J aggregates in solution by the apparent CD spectral measurement. Chem Phys Lett 419 21-27... 

GYa G, Sorokin AV, Katrunov IK, Yefimova SL, Lebedenko AN, Malyukin YuV, Yarmoluk SM (2007) Specificity of cyanine dye L-21 aggregation in solutions with nucleic acids. J Fluoresc 17 370-376... 

Sorokin AV (2008) Optical properties and structure of JC-1 J-aggregates in solutions. Biophys Bull 21 115-121... 

Nguyen TQ, Doan V, Schwartz BJ (1999) Conjugated polymer aggregates in solution control of interchain interactions. J Chem Phys 110 4068-4078... 

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