Solubility cation effects

Even though 3.0-4.4 mmols (from a total of 7.2 mmols) of hydroxyl groups per gram of lignin were cationized by these reagents, the products were completely water soluble and effective flocculants. In this paper we discuss the preparation and testing these cationic lignin derivatives. 

Similarities between reversal of charge spectra for colloids with solubility sequences of salts in bulk solution have been indicated (7, 37)— for example, for salts possessing different cations but the same anion, the solubility sequence of the phosphates is K+ > Na+ > Li+, while it is the reverse for the sulfates (7, 30). In view of this similarity, it is natural to introduce this fact as another possible link to explain the reversal of the specific cation effect in tt-A isotherms, though the precise relationship to monolayers is not clear at this time. 

Biphasic conditions also circumvent the salt solubility problem but classic phase transfer conditions using aqueous sodium hydroxide suffer from competing hydrolysis of the phosphorus(III) esters. However, Kem and co-workers found that butyl esters (their substrate was dibutyl phosphonate) are sufficiently stable to provide Michaelis-Becker products in high yields dialkylphosphine oxides were also suitable substrates.67 Salvatore and co-workers have recently developed an efficient biphasic solid-liquid procedure utilising the cesium cation effect Protocol 7. 

The poly(alkylene oxide)-bound phosphine ligands 1 and 2, as well as a cationic rhodium(I) complex of 1, were demonstrated to possess inverse temperature-dependent solubility. The effects of these solubility properties on catalysis have been demonstrated in the hydrogenation of allyl alcohol in water. An approximately 20-fold decrease in rate is observed when the temperature is raised from 0 °C to 40-50°C [9a], This unusual temperature dependence has been termed smart behavior . 

Table 10.2 summarizes some examples of zeolites based on their classification by chemical composition. Low-silica zeolites (Si/Al < 5) are synthesized in basic conditions (pH >13) using a silicon source, an aluminum source, and alkali hydroxides at moderate temperatures, typically less than 120°C. The identity of the alkaU species used is a determining factor in which phase is obtained from synthesis, as the relative rates of (alumino)silicate hydrolysis and condensation reactions are dependent on the identity of the alkali cation. It is also believed that hydrated alkali cations effectively direct the assembly of (alumino)silicate precursors into fuUy connected three-dimensional structures. Sodium and potassium hydroxide have been used most frequently in low-silica zeolite syntheses due to their low cost and high solubility in... 

Poly(2-dimethylamino)ethyl methacrylate (pDMAEMA) is a water-soluble cationic pol3maer that contains tertiary amines and shows the proton sponge effect to some extent due to pKa=7.5. Approximately 50% of the amines are protonated at pH 7.2 impl3rmg that the other 50% participate in buffering. The absence of primary and secondary amines indicates that pDMAEMA binds relatively loosely to pDNA compared to polycations such as PEI-25K and other high MW PEI. It has been shown to condense pDNA into 150-180 nm size particles and mediate transfection in different cell types. However, complexes with pDMAEMA are not very stable in physiological salt and serum and since they do not possess attributes other than DNA condensation and modest endoso-mal buffering, attempts have been made to modify them (71)... 

Effective methods of continuous treatment are also available. Addition of a chemical product to the furnish always involves a considerable dilution (as the volume of water used in the industry is vast), but treatment directly onto a surface by spray apphcation can be much more concentrated. For this reason it is often more cost-effective if the problem of deposition is defined to a limited part of the papermaking process. The most common method comprises continuous spraying of a water-soluble cationic polymer onto the surface treated. This cationic polymer will then react with anionic water-soluble macromolecules in the furnish (anionic trash) to form a coating. This coating, which is very thin and flexible, is sacrificial, and anything that deposits on this sacrificial coating will be removed from the surface as the deposit is redissolved. Often the polymer is formulated with other materials (like surfactants) to enhance the performance. For centre press rolls spraying a release wax emulsion seems to be the most successful application. 

With the exception of PRs used for direct application, thCTe normally is a negl ible difference in crop response between sources of the common P fertilizers, which indicates in itself that differences in wat solubility is not a major factor in determining P availability. A possible exception to this generalization is that N-P sources are sometimes more efficiently used in banded applications because of N-P interaction created by increased root proliferation in the fertilizer zone and anion/cation effects. The effect of placing ammonium sources with water-soluble P has been shown to be the most beneftdal. 

We have synthesized and Investigated a series of cyclic hexapeptldes containing N-substltuted amino acids, which are cyclo(Sar)6, cyclo(Sar-Sar-Gly>2t cyclo(L-Pro-Sar-Gly)2 and cyclo(Sar-Gly-Gly)2 (3,4,5). It has been reported that the numbers of different conformations due to the cls/trans Isomerism of the N-substltuted peptide bonds decreased In the above order, and that the first two cyclic hexapeptldes, which are very flexible, bound alkali metal cations effectively. The prollne residue made the cyclic hexapeptlde more soluble In organic solvents. These obseirvatlons point to cyclo(L-Pro-Sar-Sar)2 which could be a synthetic lonophore transporting selectively metal Ions through a hydrophobic meud>rane. 

Once formed phosphonium salts could have a significant effect on cellular processes, particularly on mitochondrial function. Ph3PMe has been used as a probe to measure membrane potentials, for instance in thyroid cells lymphocytes Escherichia and human granulocytes The lipid-soluble cation distributes itself across the membrane in accordance with the membrane potential Monovalent lipophilic cations which have significant membrane permeability are concentrated in mitochondria. For instance the laser dye Rhodamine 123 has been used as a specific probe for the localisation of mitochondria in living cells It has also been shown to have in vivo antitumour activity ... 

Aqueous ammonia can also behave as a weak base giving hydroxide ions in solution. However, addition of aqueous ammonia to a solution of a cation which normally forms an insoluble hydroxide may not always precipitate the latter, because (a) the ammonia may form a complex ammine with the cation and (b) because the concentration of hydroxide ions available in aqueous ammonia may be insufficient to exceed the solubility product of the cation hydroxide. Effects (a) and (b) may operate simultaneously. The hydroxyl ion concentration of aqueous ammonia can be further reduced by the addition of ammonium chloride hence this mixture can be used to precipitate the hydroxides of, for example, aluminium and chrom-ium(III) but not nickel(II) or cobalt(II). 

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