Labile aluminium

Fairman, B., Sanz-Medel, A., Gallego, M., Quintela, M.J., Jones, P. and Benson, R. (1994) Method comparison for the determination of labile aluminium species in natural waters. Anal. Chim. Acta, 286, 401-409. 

Several procedures using Chelex-100 (a styrene/divinylbenzene co-polymer with iminodiacetate functional groups) have also been developed. For batch systems, where conditioned resin is stirred with the water sample for up to 4 h, the labile aluminium fraction is calculated from the difference between the total aluminium concentration in the sample found before and after ion-exchange has taken place. The resin has to be very carefully preconditioned in a nitric acidified solution (pH 5.0) of Ca(N03)2 and MgS04 (at concentrations normally found in natural waters) [173,174],... 

Organolithium or Grignard compounds derived from aryl or heteroaryl halides react with diphenyl phosphorazidate to give labile phosphinoyltriazenes, which on reductive work-up with aluminium hydride afford good yields of aryl or heteroaryl amines (equation 7)34. 

An important consequence of acidification is mobilization of metals from terrestrial watersheds [14]. Particularly important is the release of aluminium because of its toxic effects on freshwater biota especially on fish [15]. Not all A1 forms are toxic. Only cationic species contained within the operational forms termed labile A1 (LAI) or inorganic monomeric A1 (Ali) are gUl-reactive and hence affect fish health [16]. It has been shown that concentrations of soluble aluminium increase with decreasing pH from a pH of ca. 6.3 [17]. 

Amino-4-methoxy-l-methoxymethylnaphthalene 120, obtained from the chloromethyl derivative 111, is transformed into azide 121. The latter undergoes photolytic heterocyclization to the labile 5-methoxyben-zo[cd]indole 117 which, on reduction by lithium aluminium hydride followed by acetylation, is converted into the stable l-acetyI-5-methoxy-l, 2-dihydrobenzo[o/]indole 119 (R = OMe) [71JCS(C)721]. The reduction of methyl or phenyl 8-nitro-1 -naphthyl ketones by hydrogen and platinum dioxide or by iron in acetic acid leads to a mixture of products (59M634). 

Mineral Salts Immunostimulatory adjuvants Lipid particles Particulate adjuvants Mucosal adjuvants Aluminium hydroxide, aluminium phosphate, calcium phosphate Saponins (e.g., QS21), MDP derivatives, bacterial DNA (CpG oligos), LPS, MPL and synthetic derivatives, lipopeptides, cytokines (e.g., GM-CSF, IL-2, IL-12) Liposomes, virosomes, iscoms, cochleates, emulsions (e.g., Freunds adjuvant, SAF, MF59 ) Poloxamer particles, virus-like particles, PLG microparticles Cholera toxin (CT), mutant toxin (e.g., LTK63, LTR72), heat labile enterotoxin (LT), microparticles, polymerized liposomes, chitosan... 

Direct evidence for a combination of catalytic fluorination and chlorination [4] was obtained from radiotracer studies in which fluorinated chromia catalysts were labelled with the short-lived (t /2 = 110 min) / + emitting isotope fluorine-18 [11]. Using this isotope it was possible to probe the interactions between HF and various fluorinated chromia catalysts more directly than had been possible hitherto. Three types of surface F-containing species were differentiated, weakly adsorbed HF which was easily removed by an inert gas flow, non-labile F, believed to be bound directly to surface Crin, and catalytically active F which could be incorporated into the organic products [12]. The controversy between dismutation (concerted F-for-Cl and Cl-for-F transfers) and non-concerted halogen exchange processes has been resolved more recently and the evidence is described later in the chapter. What is clear from this early work however, is the importance of aluminium and chromium(III) oxides as catalyst precursors. Fluorination of the surfaces of these oxides is slow (cf [12]) and although there are many references to alu-... 

A substantial fraetion of the ionic character of A1 - O bond and the absenee of the own eleetrons in the valence shell of AF make the complexes kinetieally labile that allows to obtain crystal aluminium hydroxides (gibbsite, bayerite, boemite, norstandite and diaspore) using the reactions in water solutions [33,34]. 

Cyclization of azobenzene and its derivatives tends only to occur under acid conditions. The reaction of the conjugate acids of azobenzene with anhydrous aluminium chloride, stannic chloride, and ferric chloride in 1,2-dichIoroethane has now been reported in detail.144 Benzo[c]cinnoline is formed, but the production of benzidine suggests that the reaction involves photodisproportionation. Similar cyclization is observed with the conjugate acids of azobenzenedicar-boxylic acids.145 With these compounds the reaction also occurs in 98% sulphuric acid to yield, from the 2,2 -isomer, benzo[c]cinnoline-4,7-dicarboxylic acid (90) and indazolo[2,1 - ]indazole-6,12-dione (91) in equal amounts the 3,3 -and 4,4/-dicarboxylic acids of azobenzene likewise give the corresponding cinnolines.145 It is important to note here that benzo[c]cinnoline is light-labile in 148... 

Some authors claim that detection limits (DLs) of 5 mgL are easily obtainable [167] using the batch PCV detection method. However, it has been reported that daily DLs range between 5 and 10 mg L and that personnel who are highly acquainted with the method were needed to achieve DLs down to <10 mg L [168]. This poses a problem when the non-labile or monomeric organic fraction of aluminium to be measured is very small. Errors for Alni can become high, and, because the Driscoll method is a subtraction method, the uncertainty of the calculated Ali fraction (Alim—Alni) can become unacceptable. To increase the precision, sample throughput and practicality of the Driscoll method, several flow injection analysis (FIA) systems have been designed both for the PCV method [169,170] and for detection with a fluorimetric determination of the 8-hydroxyquinoline-5-sulfonic acid (8-HQS) aluminium complex in a micellar medium (cetyltri-methylammonium bromide, CTAB) [168,171]. 

One interlaboratory method comparison exercise for aluminium speciation has been organized within the framework of the BCR project on A1 speciation [184]. Results obtained using a standard Driscoll/PCV method for the determination of the labile monomeric aluminium fraction were tested and compared to three other aluminium speciation procedures. Each of the three participant laboratories carried out both the standard Driscoll method, used as... 

The thioenol ethers are stable towards base and lithium aluminium hydride -but are reconverted to the parent compound on dilute acid hydrolysis. Raney nickel desulphurization can be used to form the diene . Hydrogen peroxide oxidation will convert the acid-labile thioenol ether to an acid-stable sulphoxidoenol ether . The sulphoxidoenol ether may be desulphurized with Raney nickel to the diene, or with lithium aluminium hydride reconverted to the thioenol ether for hydrolysis to the (x,j3-unsaturated ketone . These reactions are depicted in equation (80). 

Although the equilibria involved in this type of complexation may be rather labile and require further detailed investigations, yet examples of the isolation of a few well-defined heterometallic alkoxides from mixtures of component alkoxides may be mentioned here. For example, bimetallic isopropoxides of lanthanides with aluminium can be conveniently volatilized out of a reaction mixture of Ln(OPr )3 and Al(OIV)3 (Eq. 3.7) ... 

Metallation has also been tried as a method for imparting weather- and heat-resistance to polymers. The heat stability of poly(vinyl alcohol) improves on treatment with aluminium isopropoxide which reacts at hydroxy groups with the elimination of propan-2-ol. About 12% of the hydroxy groups can be substituted in this way and these are believed to comprise mainly vicinal hydroxy groups and possibly end and other labile groups. A similar stabilizing effect was noted when free hydroxy groups in poly(vinyl butyral) were removed by this means. 

There is also evidence that commercial poly(vinyl chloride) is slightly branched. When the polymer is treated with lithium aluminium hydride a type of polyethylene is obtained, the infrared spectrum of which indicates about 20 branches per polymer chain. Branching occurs during polymerization by transfer of hydrogen from within the polymer to growing radicals. The most labile hydrogen atoms in poly(vinyl chloride) are those in the —CHCl— groups since the resultant free radical has resonance stability ... 

Low pressure polyethylene might contain minute traces of oxygen or nitrogen or sulfur chain transfer catalyst residues. These are usually labile and can be ignored from the foodstuff contamination point of view. Polymers such as polyethylene, polypropylene and polystyrene manufactured by a catalysed low pressure route will however, usually contain appreciable catalyst residues usually appearing in the form of aluminium, chromium, magnesium and titanium, also possibly lithium and sodium. As the example quoted in Table 3.1 indicates these impurities can occur in the polymer at levels approaching 100 ppm. 

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