Solubility aggregation

The nitration of d-xylose 69 yields d-xylose tetranitrate, C5HeO (0N02)4, an oily substance insoluble in water, and a crystalline by-product, m.p. 141°, insoluble in water, which is evidently the trinitrate, C5H702 (0N02) 3. Xylosan dinitrate, C5H 02(0N02)2, has been prepared by the action of mixed acid on d-xylose. It consists of little spherical crystal aggregates, soluble in alcohol and melting at 75-80°. 

Because cell-free methods are highly efficient in their incorporation of amino acids, only minute quantities of radiolabeled amino acids are required for analysis by autoradiography. Background translation of endogenous mRNA is also extremely low. This is advantageous because expression conditions can be rapidly screened for their effect on aggregation, solubility, and proteolytic susceptibihty of the expressed construct. Low background translation also means that total and soluble protein yields can be analyzed by auto-... 

Keywords Mesoporous Ti02, sol-gel method, reverse micelles, aggregation, soluble starch. 

Soluble in PBST containing 6M urea and ImM EDTA. Less than 2% were covalent aggregates soluble in PBST/6M urea/lmM EDTA/lOmM DTT. 

Antigens formulations Experimental conditions Reconstituting solvent Aggregate solubility (%) (Average S.D., n = 3) Aggregation mechanism... 

The percentage of aggregate solubility was calculated from the amount of soluble protein recovered in different solvents relative to the total amount of protein aggregates. 

Furthermore, when an amphiphilic maltose neoglycoconjugate (equipped with an eleven-carbon lipophilic spacer) was used in preparation of the GNPs, " supramole-cular aggregates soluble in methanol were also formed (Fig. lOB). The proposed model of aggregation shown in Fig. lOB (middle), and based on TEM micrographs, was confirmed by atomic force microscopy (AFM) imaging (right). 

Many hundreds of studies have reported on the chemical composition of asphaltenes (28—44) and excellent summaries exist. We will only attempt to summarize some key findings here as they relate to aggregation, solubility, and interfacial film formation. 

The issue of water in reverse micellar cores is important because water swollen reverse micelles (reverse microemulsions) provide means for carrying almost any water-soluble component into a predominantly oil-continuous solution (see discussions of microemulsions and micellar catalysis below). In tire absence of water it appears tliat premicellar aggregates (pairs, trimers etc.) are commonly found in surfactant-in-oil solutions [47]. Critical micelle concentrations do exist (witli some exceptions). 

Other solubilization and partitioning phenomena are important, both within the context of microemulsions and in the absence of added immiscible solvent. In regular micellar solutions, micelles promote the solubility of many compounds otherwise insoluble in water. The amount of chemical component solubilized in a micellar solution will, typically, be much smaller than can be accommodated in microemulsion fonnation, such as when only a few molecules per micelle are solubilized. Such limited solubilization is nevertheless quite useful. The incoriDoration of minor quantities of pyrene and related optical probes into micelles are a key to the use of fluorescence depolarization in quantifying micellar aggregation numbers and micellar microviscosities [48]. Micellar solubilization makes it possible to measure acid-base or electrochemical properties of compounds otherwise insoluble in aqueous solution. Micellar solubilization facilitates micellar catalysis (see section C2.3.10) and emulsion polymerization (see section C2.3.12). On the other hand, there are untoward effects of micellar solubilization in practical applications of surfactants. Wlren one has a multiphase... 

The distinction between pairwise and bulk hydrophobic interactions is often made, although some authors doubt the existence of an intrinsic difference between the two ". Pairwise hydrophobic interactions denote the interactions behveen two isolated nonpolar solutes in aqueous solution. They occur in the regime where no aggregation takes place, hence below the critical aggregation concentration or solubility limit of the particular solute. If any breakdown of the hydrophobic hydration shell occurs, it will be only transient. 

Polymers in Solution. Polyacrylamide is soluble in water at all concentrations, temperatures, and pH values. An extrapolated theta temperature in water is approximately —40° C (17). Insoluble gel fractions are sometimes obtained owing to cross-link formation between chains or to the formation of imide groups along the polymer chains (18). In very dilute solution, polyacrylamide exists as unassociated coils which can have an eUipsoidal or beanlike stmcture (19). Large aggregates of polymer chains have been observed in hydrolyzed polyacrylamides (20) and in copolymers containing a small amount of hydrophobic groups (21). 

The methodology for preparation of hydrocarbon-soluble, dilithium initiators is generally based on the reaction of an aromatic divinyl precursor with two moles of butyUithium. Unfortunately, because of the tendency of organ olithium chain ends in hydrocarbon solution to associate and form electron-deficient dimeric, tetrameric, or hexameric aggregates (see Table 2) (33,38,44,67), attempts to prepare dilithium initiators in hydrocarbon media have generally resulted in the formation of insoluble, three-dimensionally associated species (34,66,68—72). These precipitates are not effective initiators because of their heterogeneous initiation reactions with monomers which tend to result in broader molecular weight distributions > 1.1)... 

Amino-4,6-dichlorophenol. This compound (11) forms long white needles from carbon disulfide, and aggregate spheres from benzene. It sublimes at 70—80°C (8 Pa = 0.06 mm Hg) and decomposes above 109 °C. It is freely soluble in benzene and carbon disulfide, and is sparingly soluble in petroleum ether, water, and ethanol. The free base is unstable and the hydrochloride salt (mp 280—285°C, dec) is employed commercially. 

A (4-Hydroxyphenyl)glycine. This derivative (23) forms aggregate spheres or shiny leaflets from water. It turns brown at 200°C, begins to melt at 220°C, and melts completely with decomposition at 245 —247°C. The compound is soluble in alkaU and mineral acid and sparingly soluble in water, glacial acetic acid, ethyl acetate, ethanol, diethyl ether, acetone, chloroform, and benzene. 

Soap is one example of a broader class of materials known as surface-active agents, or surfactants (qv). Surfactant molecules contain both a hydrophilic or water-liking portion and a separate hydrophobic or water-repelling portion. The hydrophilic portion of a soap molecule is the carboxylate head group and the hydrophobic portion is the aUphatic chain. This class of materials is simultaneously soluble in both aqueous and organic phases or preferential aggregate at air—water interfaces. It is this special chemical stmcture that leads to the abiUty of surfactants to clean dirt and oil from surfaces and produce lather. 

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