Bivalent metal ions

In the previous section efficient catalysis of the Diels-Alder reaction by copper(II)nitrate was encountered. Likewise, other bivalent metal ions that share the same row in the periodic system show catalytic activity. The effects of cobalt(II)nitrate, nickel(II)nitrate, copper(II)nitrate and zinc(ll)nitrate... 

Further evidence for an increased efficiency of complexation in the presence of micellar aggregates with bivalent metal counterions is presented in Table 5.4. The apparent rate constants of the reaction of 5.1c with 5.2 in the presence of micelles of Co(DS)2, Ni(DS)2, Cu(DS)2 and Zn(DS)2 are compared to the rate constants for the corresponding bivalent metal ion - dienophile complexes in the absence of micelles. The latter data are not dependent on the efficiency of the formation of the catalyst - dienophile complex whereas possible incomplete binding will certainly be reflected in the former. The good correlations between 1 and and the absence of a correlation between and... 

Pseudoalums are a series of double sulfates, such as iron(lI) aluminum sulfate [22429-82-9], FeSO Al2(SO 24H20, containing a bivalent metal ion in place of the univalent element of ordinary alums. These pseudoalums have different crystal stmctures from those of the ordinary alums. 

Carbopol is widely used in cosmetic and pharmaceutical practice as a gel-former. Carbopol resins are hydrophilic polymers which swell in water solutions and transform into the gel form at neutralization. At the elaboration of special cosmetic preparations in which carbopol is used, the problem of raw materials compatibility appears. For example, some extracts of aromatic pectin containing materials destroy the gel structure of carbopol. High contents of bivalent metal ions, in particular calcium ions, destructively influence onto the gel-making ability of the system too. 

Reducing agent stable a Bivalent metal ion free... 

Analysis of six metals by microplate and microluminometric technologies 181 Predictive relative toxicity of nine bivalent metal ions (Ca, Cd, Cu, Hg, 182... 

The reaction of V(ll) with Oj to give substantial amounts of V(IV) must represent a two electron oxidation step (Sec. 5.7.2) since V(Ill) reacts more slowly with O2 than would account for the appearance of V(IV). The suggested mechanismresembles that for other bivalent metal ions,... 

The properties of bilirubin UDP-glucosyl- and bilirubin UDP-xylosyl-transferase from rat liver closely parallel each other with regard to activation by digitonin and dependence on pH and bivalent metal ions. Considerable fractions of the enzyme activities (especially of the glucosyl-transferase) functioned independently of added bivalent cation (F3). The observations are compatible with identical enzyme locations, at least for the metal ion-stimulated activities. 

The combination of the LB technique and the neutron activation method of analysis was used to determine the stoichiometry of the interaction between fatty acid (arachidic acid) and metal ions dissolved in the subphase. The experimental data were used to estimate the stability constants of arachidic acid and bivalent metal ions (Cd and Ba). The data were explained as an interaction between metal ions and the monolayer as an adsorption process ... 

Representative thermodynamic data for the reaction of monovalent and bivalent metal ions with the two isomers (A and B) of dicyclohexyl-18-crown-6 are given in Table 13. From these and similar reactions... 

Enzyme catalysed racemisation is an attractive method. The enzymes are known as racemases and they often need cofactois like pyrodoxyl phosphate (PEP) or bivalent metal ions to function properly. The snbstrates used in racemisation reactions have two features in common, i) the stereocentre carries a proton, ii) adjacent to the stereocentre is a carbonyl gronp or another function that make the proton at the stereocentre acidic. Most racemases work on amino acids and df-hydroxy acids. The principle of those needing PEP is formation of a Schiffs base between the aldehyde of PEP and the amino group of the amino acid (like in Figure 2.6). 

Bivalent Metal Ions. The relative reaction rates of the vanadium (I I)-zinc (II) series have been discussed often (8 34, 35, 40 41, 111). The important features, which are well shown by examination of Table I, are ... 

A corresponding reaction of acetate ion with AJP is also catalyzed by a bivalent metal ion. The reaction probably results in the formation of an acyl phosphate, which has not been identified as such but has been identified by trapping of the product with hydroxylamine. The best catalyst is beryllium ion, which catalyzes optimally at molar ratios of 1 to 1 or less. Acetate ion is presumably the reactive species, since the pH optimum of the reaction is 5. It is concluded from the pH effects in this study and in the transphosphorylation reaction that a complex of the metal ion and nucleophile must occur. Since acetate ion is a monodentate ligand, the mechanism postulated for the phosphorylation reaction above cannot be completely applicable to this case (36). 

Tetracyclines have the tendency to form chelates with bivalent metal ions. As a consequence of their affinity to calcium, tetracyclines tend to accumulate in the bones of treated animals. Although their chelates with calcium show considerable stability, tetracyclines can be extracted from bones containing these drugs and, therefore, may be present in soups and meals when bones from treated animals are cooked (80, 81). The extractability of chlortetracycline from bone tissue is strongly pH-dependent, being higher at low pH values. This can be easily explained by the dependence of the dissociation constant of the chelate from the pH value. 

Anthranilic acid (2-aminobenzoic acid) is an N—O bidentate which commonly forms 2 1 complexes with a variety of bivalent metal ions. d Avignon and Brown16 provided details of some of the structures and applications of these chelates. The synthesis of ternary complexes of 2-aminobenzoic acid and l-nitroso-2-naphthol with a variety of transition metal ions has been reported.17 An X-ray structure shows an unusual N monodentate coordination mode to rhodium for the ligand.18... 

Complexes of pyridine-2-carboxylic acid (picolinic acid, picH) and its substituted derivatives commonly exhibit the N—O bidentate nature of this aromatic amino acid. From aqueous solutions chelates are obtained with the coordinated carboxylic group deprotonated, or neutral ligand forms may be isolated from non-aqueous media.26 Bis chelates are common in either case with bivalent metal ions. The tris chelates of trivalent cobalt27 and manganese28 have been structurally characterized recently. The latter is tetragonally distorted in a structure similar to Mnin(oxine)3. 

Metallothionein proteins are the most abundant intracellular, metal-binding proteins (Andrews, 2000). Four metallothionein isoforms have been identified in the mouse (MT-I-MT-IV) and are clustered within 50 kilobases of each other. In humans, there is one MTII gene and a cluster of MT I genes on chromosome 16 (Searl et al., 1984 West et al., 1990 Heuchel et al., 1995). The mammalian metallothioneins generally consist of 61 amino acids and 20 of these are cysteines (Heuchel et al., 1995). These cysteines are important for the binding of such bivalent metal ions, such as zinc, copper and cadmium. 

By complexing phthalocyanine or tetraphenylporphyrin molecules with different bivalent metal ions, their oxidation potential may be changed, and this also appeared to change their catalytic activity. In Fig. 3 this is shown graphically. 

J. M. Lowenstein (1958). Transphorylations catalysed by bivalent metal ions. J. Biochem., 70, 222-231. 

M. Tetas and J. Lowenstein (1963). The effect of bivalent metal ions on the hydrolysis of adenosine di- and triphosphate. Biochemistry, 2, 350-365. 

---