Monohydroxy complexes

The inadvertent activation of a mineral can often result in an undesirable response to flotation. A typical example is quartz, a highly unreactive mineral whose recovery by flotation is therefore difficult. However, in the presence of metal cations, it can be activated to respond to anionic collectors, as shown by the data13 in Figure 3. It is of interest that the pH value at which flotation is effective can be related to that at which the monohydroxy complexes of the metal ions are predominantly stable, suggesting a specific adsorption of these species onto the quartz surface. In some cases this can be used for the selective depression of the quartz minerals in, for example, the flotation of pyrite in the presence of cationic collectors such as the long-chain amines. 

Metal ions in aqueous solution generally hydrolyze to form a series of mononuclear ind polynuclear hydroxy complexes. Iron(III) for example forms [FeOH] ", [Fe(OH)2], Fe(OH)3(aq), [Fe(OH)4] , [Fe2(OH)2] and probably other polynuclear species. The formation af a monohydroxy complex (equation 1) can be used as a guide to the degree of electron withdrawal by the cation. Typical pJCa values for various cations are listed in Table 2. (The pJCa values of and HjO are -1.7 and 15.7 respectively.) The tetrahedrally coordinated [Be(H20)4] ion is more acidic than expected when compared with octahedrally coordinated aqua ions of divalent metals. Each hydrogen must carry a somewhat greater portion of the positive charge than it would in an octahedral complex, and this makes removal of a proton easier. Similar considerations apply to square planar Pd (aq). Mercury(II) and tin(II) are also more acidic than would be expected. The high acidity of mercury(II) is due to the unusual stability of linear H2O—Hg—OH, while Sn (aq) has between two and three coordinated water molecules in the inner coordination sphere. ... 

Aluminum salts of carboxylic acids, aluminum carboxylates, may occur as aluminum tricarboxylates (normal aluminum carboxylates), Al(OOCR)2 monohydroxy (monobasic) aluminum dicarboxylates, (RCOO)2Al(OH) and dihydroxy (dibasic) aluminum monocarboxylates, RCOOAl(OH)2. Aluminum carboxylates are used in three general areas textiles, gelling, and pharmaceuticals. Derivatives of low molecular weight carboxyUc acids have been mainly associated with textile appHcations those of fatty carboxyUc acids are associated with gelling salts and more complex carboxylates find appHcations in pharmaceuticals. 

In an attempt to prepare monohydroxy derivatives from dinitrofurazans, a complex mixture of compounds was obtained (98MI1, 99ZOR1555). 

Even more efficient bimetallic cooperativity was achieved by the dinuclear complex 36 [53]. It was demonstrated to cleave 2, 3 -cAMP (298 K) and ApA (323 K) with high efficiency at pH 6, which results in 300-500-fold rate increase compared to the mononuclear complex Cu(II)-[9]aneN at pH 7.3. The pH-metric study showed two overlapped deprotonations of the metal-bound water molecules near pH 6. The observed bell-shaped pH-rate profiles indicate that the monohydroxy form is the active species. The proposed mechanism for both 2, 3 -cAMP and ApA hydrolysis consists of a double Lewis-acid activation of the substrates, while the metal-bound hydroxide acts as general base for activating the nucleophilic 2 -OH group in the case of ApA (36a). Based on the 1000-fold higher activity of the dinuclear complex toward 2, 3 -cAMP, the authors suggest nucleophilic catalysis of the Cu(II)-OH unit in 36b. The latter mechanism is comparable to those of protein phosphatase 1 and fructose 1,6-diphosphatase. 

LAH complexes of the monohydroxy carbohydrate derivatives 1,2 3,4-di-O-isopropylidene-a-D-galactopyranose (39) and 1,2 5,6-di-O-isopropylidene-a-D-glucofuranose (40) have been reported to effect asymmetric reduction of... 

Cuticle. The cuticle of adult nematodes is relatively impermeable and is composed primarily of a complex of several proteins. These proteins include collagens, fibroids, elastoids, and keratoids, possibly hardened by tanning with pol3rphenols or quinones. Sometimes lipide materials are also present (8, 10y 52). When such lipide materials are present on the adult cuticle, they probably take the form of hydroxy fatty acids or esters of fatty acids with monohydroxy alcohols. Such materials may form ring compounds. Regardless of the exact chemical nature, the lipides are unquestionably one of the chief barriers to permeability. These materials are commonly difficult to demon-... 

Kinetic Data for Uncatalyzed and Acid-Catalyzed Cleavage of Monohydroxy-Bridged Rhodium(III) Complexes... 

A 1,10-phenanthroline-containing polyamine macrocycle (78) was designed to complex with Zn2+ ion and, because of the rigidity of the phenanthroline moiety, leave some free binding sites at the metal for ligands such as water, which easily depro-tonate to give stable hydroxo species. The hydrolysis of methyl acetate in the gas phase by such a monohydroxy-Zn(II) complex [Zn(78)(OH)]+ has been investigated by quantum mechanical procedures and some pathways delineated.78... 

In the process of lanthanide complex formation with the porphyrins, the ligand loses two protons and yields lanthanide hydroxy porphyrin or lanthanide porphyrin X, where X = C1, Br, NOJ, etc. Many lanthanide complexes with substituted porphyrins have been prepared by heating a mixture of porphyrin and the lanthanide salt in imidazole melt in the range 210-240°C. When the complex formation is complete the solvent (i.e.) imidazole is eliminated by either sublimation [81] or by dissolution of the mixture in benzene, followed by washing with water [82]. Further purification requires column chromatography. The starting material can be anhydrous lanthanide chloride or hydrated lanthanide acetylacetonate. After purification the final product tends to be a monohydroxy lanthanide porphyrin complex. 

Complexes 11, 1010, after line 3 from bottom]. When a partly epoxidized fatty ester or glyceride carrying residual unsaturation is hydrogenated to the corresponding monohydroxy product at a low pressure over palladium-on-carbon catalyst in ethanol, the presence of silver nitrate in the solution provides complete protection to the ethenoid linkages, probably by7r-complex formation.173... 

HPLC. Many HPLC methods have been described in the literature (Hornero-Mendez and Minguez-Mosquera, 1998 Schoefs, 2002, 2003, 2004 Thompson et al., 2000). When the carotenoid composition is complex, as in passiflora fruit, which contains more than 10 carotenoids, it might be necessary to first separate the different groups of carotenoids. This can be done using an open column packed with alumina. Fraction 1, which contains carotenes and epoxi-carotenoids, is eluted with petroleum ether fraction 2, which is composed of monohydroxy- and keto-carote-noids, is eluted with 70-90% diethyl ether in petroleum ether and fraction 3, made up of polyhydroxy-carotenoids, is eluted with 0—30% ethanol in ether. The pigments contained in individual fractions can be further separated using particular TLC or HPLC methods (Mercadante et al., 1998). 

If the monohydroxy chelate is considered the reactive species, it is possible that it would react as a bifunctional catalyst, as is indicated by formula III, wherein the metal chelate donates a hydroxyl group to the substrate while simultaneously assisting in the removal of the fluoride ion by coordination. Another possibility would involve coordination of the complex with the negative oxygen rather than with the fluoride ion. The term push-pull mechanism has been employed to describe this type of function. 

SEM). Thus, at physiological pH, the monoaqua complex is present mostly in its less reactive monohydroxy form."... 

The reaction of l,2-dichloro-4,5-dinitrobenzene with dilute aqueous sodium hydroxide results in substitution of a nitro-group by hydroxide. However, in hydroxide concentrations greater than 2 mol-dm", only the formation of monohydroxy- and dihydroxy-adducts (42) is observed, and acidification yields the original reactant. The cyanide adduct (43) of 1,3,5-trinitrobenzene has been observed by electrospray ionization mass spectrometry, using acetonitrile as the cyanide source. X-ray structures of the stable crystalline adducts formed from 4,6-dinitrobenzofiiroxan and dodecyl- and hexadecyl-amine have been reported. There has also been a report, related to the destruction of energetic materials, of Meisenheimer complex formation during the alkaline hydrolysis of 2,4,6-trinitrotoluene and 2,4-dinitroanisole. ... 

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