Hydroxysulfate compounds

The only crystalline phase which has been isolated has the formula Pu2(OH)2(SO )3(HaO). The appearance of this phase is quite remarkable because under similar conditions the other actinides which have been examined form phases of different composition (M(OH)2SOit, M=Th,U,Np). Thus, plutonium apparently lies at that point in the actinide series where the actinide contraction influences the chemistry such that elements in identical oxidation states will behave differently. The chemistry of plutonium in this system resembles that of zirconium and hafnium more than that of the lighter tetravalent actinides. Structural studies do reveal a common feature among the various hydroxysulfate compounds, however, i.e., the existence of double hydroxide bridges between metal atoms. This structural feature persists from zirconium through plutonium for compounds of stoichiometry M(OH)2SOit to M2 (OH) 2 (S0O 3 (H20) i,. Spectroscopic studies show similarities between Pu2 (OH) 2 (SOO 3 (H20) i, and the Pu(IV) polymer and suggest that common structural features may be present. 

Hydroxysulfate compounds, structure 56-57 Hypostoichiometric Pu dioxide condensed phase, vapor pressures and vapor compositions.124-41... 

Previous studies of the hydrothermal hydrolysis of tetravalent Th, U and Np (1-4) have shown a remarkable similarity in the behavior of these elements. In each case compounds of stoichiometry M(0H)2S0i, represent the major product. In order to extend our knowledge of the hydrolytic behavior of the actinides and to elucidate similarities and differences among this group of elements, we have investigated the behavior of tetravalent plutonium under similar conditions. The relationships between the major product of the hydrothermal hydrolysis of Pu(IV), Pu2(OH)2(SO.,)3 (H20) t, (I)> and other tetravalent actinide, lanthanide and Group IVB hydroxysulfates are the subject of this re-... 

The structure of saxitoxin (7,2) is shown in Figure 1, accompanied by 11 derivatives formed by N-l-hydroxyl, 11-hydroxysulfate, and 21-sulfo substitutions (3—13). Structural relationships among these compounds are summarized in Figure 2. The purpose of these diagrams is to summarize structural relationships, not to suggest synthetic or biosynthetic transformations. 

Compounds bearing the 11-hydroxysulfate substituent epimerize, the conversion from beta to alpha predominating (1,2,23,24,27). 

In addition to these passive processes shellfish have been shown to actively modify the saxitoxins. Shimizu has shown (40) that scallops can remove both the N-l-hydroxyl and 11-hydroxysulfate groups from the saxitoxins. Sullivan has shown ( ) that enzymes in littleneck clams can remove the sulfamate or carbamate side chain, yielding the decarbamoyl toxins. This activity was not detected in either mussels or butter clams. With both sorts of modification the products are compounds that have higher potency and are likely to be bound in shellfish more strongly. 

Eq. (10.12), may oxidize the dissolved SO2 to sulfate in the outer layers. The species within rectangular boxes represent the solution constituents and those in ovals represent the corrosion products. Dotted ovals represent reactions or chemical compounds for which there is no evidence by laboratory or field studies. The chemical reactions that have been described and confirmed by laboratory studies are presented as sohd arrows. The dotted arrows represent the mechanisms that are uncertain. TMI in the upper part of Fig. 10.3 stands for transition metal ions and soot catalyzes the S(IV) to S(VI). The ferrous cations react with reduced sulfur to produce several insoluble sulfides. Multistep processes including Fe(II), Fe(III), and OH produce hydroxysulfate mixed salts [5]. 

Odnevall and Leygraf found that there is a structural resemblance between hydroxycarbonate, hydroxychloride, hydroxysulfate and sodium zinc chlorohydroxysulfate [24], since these compounds have layered structures with sheets of Zn in octahedral and tetrahedral coordination, with the main difference being the chemical content and bonding between the sheets. This structural resemblance may facilitate the transformation from one phase into another under appropriate environmental eonditions. 

A quantitative analysis of the species detected on the surface of zinc exposed to different environments is shown in Table 3. The most probably compounds in less aggressive environments are ZnO and Zn(OH)2. In sulfur environments, the relative percentages also correspond with ZnSOs and zinc hydroxysulfates (Zn4S04(0H)e). Furthermore, in presence of NO2, the relative percentage of sulfate increases with respect to the sulfite. 

XPS analysis confirms the presence of zinc hydroxysulfate as the major component, along with zinc sulfite, zinc hydroxide and zincite. Nitrogen compounds have not detected and for this reason it may be inferred that the accelerating effect of NO2 is an indirect effect. 

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