Bicarbonate complex

Uranium can enter the human body orally, by inhalation, and through the skin and mucous membranes. Uranium compounds, both soluble and insoluble, ate absorbed most readily from the lungs. In the blood of exposed animals, uranium occurs in two forms in equiUbrium with each other as a nondiffusible complex with plasma proteins and as a diffusible bicarbonate complex (242). 

In the literature (2), the possible formation of plutonyl bicarbonate complex is discussed. In order to verify whether we are dealing with bicarbonate or carbonate complexes, the Pu(IV) solutions prepared in NaHC03 and Na2C03 solutions are examined by spectrophotometry. The absorption spectra measured up to 900 nm show no visible difference for both solutions. For this reason it is believed that the Pu(IV) ion forms carbonate complexes irrespective of carbonate or bicarbonate ions present in solution. 

Firstly, the reaction between [Tp jZnOH and C02 rapidly gives the dinuclear bridging carbonate complex [TpPr 2]Zn 2(/i.-T)1,T)2-C03) (Scheme 24) (153), so that the postulated bicarbonate complex... 

For some other examples of bicarbonate complexes that have not been structurally characterized by x-ray diffraction see ... 

Synthesis of functional models of carbonic anhydrase has been attempted with the isolation of an initial mononuclear zinc hydroxide complex with the ligand hydrotris(3-t-butyl-5-methyl-pyrazolyl)borate. Vahrenkamp and co-workers demonstrate the functional as well as the structural analogy to the enzyme carbonic anhydrase. A reversible uptake of carbon dioxide was observed, although the unstable bicarbonate complex rapidly forms a dinuclear bridged complex. In addition, coordinated carbonate esters have been formed and hydrolyzed, and inhibition by small ions noted.462 A number of related complexes are discussed in the earlier Section 6.8.4. 

Inorganic ligands in aqueous solutions, and in particular in natural freshwaters, include, in addition to H2O and OH, the major ions carbonate and bicarbonate, chloride, sulfate and also phosphate [29], The distribution of metal ions between these ligands depends on pH and on the relative concentrations of the ligands. The pH is a master variable with regard to the occurrence of hydrolysed species and to the formation of carbonate and bicarbonate complexes. 

We have also studied the coordination of the monocarbonate, bicarbonate, and tricarbonate complexes of neptunyl in water, by using both explicit water molecules and a continuum solvent model.84 The monocarbonate complex was shown to have a pentacoordinated structure, with three water molecules in the first coordination shell, and the bicarbonate complex has a hexacoordinated structure, with two water molecules in the first coordination shell. Overall good agreement with experimental results was obtained. 

The use of CO2 as a reagent for synthetic purposes would be highly desirable, due not only to the vast availabiUty of this gas but also its environmental concerns. The stoichiometric activation of CO2 has been achieved with the iridium-PCP complex 29 comprising an alkyl rather than an aryl skeleton (Scheme 12.12) [32]. The addition of CO2 to the dihydride complex results in C=0 insertion into the iridium-hydride bond, and affords the formate complex 30. However, this complex is not stable and disproportionates spontaneously into the virtually insoluble bicarbonate complex 31 and the carbonyl dihydride 32. Such disproportionation is suppressed when the iridium metal center is replaced by rhodium [33], which is generally assumed to have a lower hydride affinity than iridium. 

The acid catalyzed aquation of the chelated carbonato complexes involves three steps (i) the initial rapid protonation pre-equilibrium of the exocyclic oxygen, (ii) carbonate ring opening, and (iii) decarboxylation of the resulting bicarbonate complex [see Eq. (30)]. 

Complexes of carbonic or carboxylic acid anions have been used as hydroformylation catalysts for various alkenes. The bicarbonate complex [Rh(H)2(02COH)(PPr 3)2] as catalyst enabled 1-hexene to be converted to aldehydes using paraformaldehyde as source of hydrogen and carbon monoxide in place of the more usual gas mixture.338 The acetate complex [Rh(OAc)CO(PPh3)2] (74) has been shown to effect the selective hydroformylation of cyclic dienes. The cyclohexadienes gave predominantly dialdehydes, whereas 1,3- and 1,5-cyclooctadiene gave the saturated monoaldehydes.339... 

The Cu(l) bicarbonate complex previously mentioned (77) was synthesized by the reactions summarized in Scheme 7, which includes C02 insertion into copper hydroxide and alkoxide species. The insertion reaction of C02 with metal hydroxides to form bicarbonates is believed to occur... 

Methylation of the various RR NC02Cu,(/-BuNC) compounds, prepared by the addition of C02 and three equivalents of /-BuNC to a benzene solution of RR NCu [Eq. (36)], has resulted in formation of the corresponding carbamates (see Table IV) (101). These researchers have as well found the copper(I) bicarbonate complexes, HOC02CuL3 (32a, L = PEt3 and 32b, L = /-BuNC), to be effective at carboxylation of cyclohexanone in the presence of a stoichiometric quantity of water (71). The transcarboxylation of cyclohexanone [depicted in Eq. (44)] is proposed to proceed via a dicopper(I) complex (33). 

Uranium. About 50% of plasma uranium is bound, as the uranyl ion, to bicarbonate, which is filtered by the glomerulus. As a result of acidification in the proximal tubule, the bicarbonate complex dissociates, followed by reabsorption of the bicarbonate ion the released UO22"1" then becomes attached to the membrane of the proximal tubule cells. The resultant loss of cell function is evidenced by increased concentrations of glucose, amino acids, and proteins in the urine. 

The lanthanides show ability to form complexes with hydroxide and carbonate ions. Although the lanthanide hydroxides and carbonates are very insoluble, some soluble complexes like Eu(OH) and Eu(C03)2 may be formed. Although HCOJ is the predominant species in the pH range studied, bicarbonate complexes are not formed [147, 148],... 

A suspension of polymeric cupric dimethoxide in pyridine reacts with CO2 to yield the cupric methyl carbonate. The CO2 moiety is, however, very labile the insertion could be reversed by heating the reaction mixture at 80" under a stream of nitrogen [SO]. Another reversible carbon dioxide carrier was found in copper(I) rerr-butoxide, which was stabilized by rerr-butyl isocyanide. The rerr-butyl carbonato complex was formed during the reaction with CO2 [811. Carbon dioxide also reacts with ROCu(PPh3)2 0 produce (ROCOj)Cu(PPhj>3, Hydrolysis or thermolysis of these alkylcarbonato complexes gives the binuctear carbonato copper (I) complex (PPhj>2 CuCK Oj Cu(PPhj)2, which can be further convened into the bicarbonate complex f(HC)C02)Cu(PPh3)3] by reaction with CO2 in moist solvents [82],... 

Once uranium is in the systemic circulation, it is transported as various complexes in the blood. The predominant form of uranium is as a bicarbonate complex, the stability of which is highly dependent on the pH of the solution (ATSDR, 1999 Chevari and Likhner, 1968). In the kidneys, the bicarbonate complex is filtered at the renal glomerulus and excreted in the urine (Adams and Spoor, 1974 ATSDR, 1999 Blantz, 1975 Bowman and Foulkes, 1970 Brady... 

In aqueous solutions iron can occur in two valency states, Fe and Fe (Latimer, 1954). In the presence of anions, iron forms numerous complex ions. Preliminary assessment of the role of sulfate and chloride complexes in the transport of iron has shown that these compounds are stable only in very acid environments. Carbonate and bicarbonate complexes are unstable (Singer and Stimm, 1970), and phosphate complexes are of no importance in connection with the low concentrations of phosphoric acids in natural waters. Thus the main role in the migration of iron is played by simple and hydrated ions (Kalinin and Kashik, 1968). Unfortunately the stability of... 

In the opinion of most investigators, in connection with the prevalent chloride-sulfuric acid composition of volcanogenic waters iron is transported in them mainly in the form of hydrochloric and sulfuric acid complexes. Only in deep hot springs containing a large amount of COj does iron presumably migrate in the form of bicarbonate complexes. Evidence for this is the formation of iron-bearing carbonate (ankerite) in zones below the limit of steam formation, while chiefly carbonates without iron (cdlcite) are formed in the near-surface zone. 

Uranium is usually found in compounds which can be metabolized and recomplexed to form other compounds. In body fluids, tetravalent uranium is likely to oxidize to the hexavalent form followed by formation of uranyl ion. Uranium generally complexes with citrate, bicarbonates, or protein in plasma (Cooper et al. 1982 Bounce and Flagg 1949 Stevens et al. 1980). The stability of the carbonate complex depends on the pH of the solution, which will differ in different parts of the body (BEIRIV 1988). The low-molecular-weight bicarbonate complex can be filtered at the renal glomerulus, and be excreted in urine at levels dependent on the pH of the urine. The uranium bound to the protein (primarily transferrin) is less easily filtered and is more likely to remain in blood. In the blood, the uranyl ion binds to circulating transferrin, and to proteins and phospholipids in the proximal tubule (Wedeen 1992). 

The mechanism for the renal toxicity observed in cases of adult exposure to uranium is believed to be due to the retention of uranium in the kidney. This is the result of the reabsorption of bicarbonate from the ultrafiltrate in the proximal tubule and the resulting release of the U02 ion from a bicarbonate complex. Newborn humans have relahvely inefficient tubular secretion and reabsorption compared to older children or adults, and whether this would increase or decrease the susceptibility of newborns to uranium toxicity is not known. 

Precipitation potential of the calcium ion Precipitation potential of CaCOs Carbonate complex of calcium ion Bicarbonate complex of calcium ion Hydroxide complex of calcium ion... 

The, M -7 -C02-bridged complex (C0)3(dmb)Re-C(0)-0-Re(dmb)(C0)3 is isolated (together with several unidentified species) on standing from an acetone solution of /flc-Re(dmb)(CO)3(COOH). Their IR data are summarized in Table 8. Neither yac-Re(dmb)(C0)3(02CH) nor yac -Re(dmb)(CO)3(H) has been observed as a product in the decomposition of/ac-Re(dmb)(CO)3(COOH) [84]. However, yac-Re(dmb)(CO)3(COOH) in DMSO containing small amounts of water is transformed into the bicarbonate complex, yac -Re(dmb)(CO)3(OC(0)OH) [100]. The detail mechanisms involving these species need to be elucidated. 

In the previous studies, the ligand OH-of the model complex was reacted with CO2 to produce CO32- complexes, such as [LZn( i-C03)ZnL], where L=HB(3,5-i -Pr2pz)3[8]. Since the dimerization does not take place in vivo, these complexes are not preferred as an enzyme model. H NMR evidence showed that the [LZn(OH)], where L=HB(3-But-5-Mepz)3, is reacted with CO2 in benzene to produce bicarbonate complex [LZn(0C02H)], reversibly[9]. 

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