Cobalt complexes triphosphates

Introduction of the cobalt atom into the corrin ring is preceeded by conversion of hydrogenobyrinic acid to the diamide (34). The resultant cobalt(II) complex (35) is reduced to the cobalt(I) complex (36) prior to adenosylation to adenosylcobyrinic acid i7,i -diamide (37). Four of the six remaining carboxyhc acids are converted to primary amides (adenosylcobyric acid) (38) and the other amidated with (R)-l-amino-2-propanol to provide adenosylcobinamide (39). Completion of the nucleotide loop involves conversion to the monophosphate followed by reaction with guanosyl triphosphate to give diphosphate (40). Reaction with a-ribazole 5 -phosphate, derived biosyntheticaHy in several steps from riboflavin, and dephosphorylation completes the synthesis. 

The rate of hydrolysis of bidentate triphosphate in [Co(NH3)4HnP3Oi0] has been studied by phosphomolybdate analysis and 31P NMR.297,298 Both the X-ray crystal structure299 and the 31P NMR spectrum of [Co(NH3)4H2P3O 0] are consistent with structure (91) in which one terminal phosphate residue is not bonded to the metal centre. Kinetic studies establish that hydrolysis of the chelated ligand occurs at some two thirds of the rate for the free ligand. Hubner and Milbum300 have noted large rate increases of ca. 10s for cobalt(III) complexes with a 3 1 metal pyrophosphate stoichiometry. 

Reactions involving the formation and hydrolysis of phosphate and polyphosphate esters are of vital importance in biological systems in which it is found that magnesium ions are almost invariably implicated. The formation and decomposition of adenosine triphosphate are the fundamental reactions involved in energy storage in living systems. In this context, it is perhaps relevant to note that the hydrolysis of ATP is enhanced, albeit in a very modest manner, by some cobalt(m) complexes. 

The hydrolysis of adenosine 5 -triphosphate (ATP) in the presence of various cobalt(III) complexes has been studied. Complexes such as [Co(en)3] which have no available sites for coordination of the substrate display no catalytic activity. Complexes having one site or two sites in a trans configuration such as tetraethylenepentaminecobalt(III) or bis(dimethylgly-oximato)cobalt III) slightly enhance ATP hydrolysis. However, complexes with two available sites in a cis configuration such as cis-a- or crs-jS-Co(trien) exhibit considerable activity. Both the reactions ATP+HjO- ADP+Pj and ATP+H20- AMP+PPi occur with these systems. The complex [Co(dien)] effectively enhances the hydrolysis of ATP to ADP+Pj. At pH 4.0 the uncatalyzed hydrolysis rate constant for ATP hydrolysis is 1.18xl0 s at 50 °C. For ATP UxlO M) and [Co (dien)] "" (2xlO M) at pH 4.0, = 1.75X 10 at 50°C, a rate... 

Triphosphates and pyrophosphates can be estimated in the presence of each other and ortho and cyclic metaphosphates, with tris(ethylenediamine) cobalt chloride. At pH = 3.5, this latter reagent will form an insoluble triphosphate complex but not a pyrophosphate complex. Conversely at pH = 6.5, a pyrophosphate but not a triphosphate complex can be precipitated. Under either of these conditions ortho and cyclic metaphosphates will not give precipitates. 

Azab HA, El-Nady AM, Hassan A, Azkal RSA (1994) Potentiometric studies of binary and ternary complexes of cobalt(II) with adenosine-5 -mono-, -di- and -triphosphate and some biologically important polybasic oxygen acids. Monatsh Chem 125 1059-1066... 

An excellent review concerned with the metal-ion-promoted hydrolysis of nucleoside S -triphosphates has appeared. Although most of the metal-accelerated reactions of phosphates involve cobalt(III), Sargeson has recently described some reactions of iridium(III) complexes. The hydrolysis of [(H3N)5lr0P)(=0)(0R)(0Ar)] (Ar = 4-nitrophenyl R = Et or Ar) obeys a two-term rate law (5). It is suggested that the preliminary step is an... 

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