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Mercury(II) thiolate and selenolate interactions, and chelation therapy


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Arnold, Alan Peter 1982 , 'Mercury(II) thiolate and selenolate interactions, and chelation therapy', PhD thesis, University of Tasmania.

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This thesis is an account of a study of some aspects of the
biological chemistry of mercury. The interactions of mercury
compounds with both simple and naturally occurring thiols, some
selenols, and several antidotes for mercury poisoning have been
The dithiol antidotes 2,3-dimercaptosuccinic acid (DISH 4 ) and
the sodium salt of 2,3-dimercaptopropane-l-sulfonate (Unithiol,
Na[UH 2 ]) form isolable complexes of stoichiometry (MeHg) 2 ENSH 2and
Na[(MeHg) 2 U]. The mercury(II) complexes Hg(DMSH 2 ).2H 20 and Na[HgU]
have polymeric structures, (-Hg-S'S-), similar to that reported for
the Hg(II) complex of the classic heavy metal antidote, British AntiLewisite
(BALH 2 ). The stability constants for the interaction of MeHg(II) with
several monothiols in aqueous solution have been determined potentiometrically.
High stability of complexes with a-mercaptocarboxylic
acids and a-mercaptoamines (log 3 110 (1`15-17) necessitated the use of a
titration method involving iodide competition. 2,3-Dimercaptosuccinic
acid forms a MeHg(II) complex with log = similar to that
expected for interaction of MeHg(II) with a monothiol; but BALH 2and
Unithiol form complexes with log fi lo2-3 orders of magnitude higher,
suggesting the presence of chelation.
Implications of the results obtained from both synthetic and
solution studies for the use of dithiols as antidotes for MeHg(II)
poisoning are discussed.
A computer program for the potentiometric evaluation of ligand
hydrolysis constants has been written. The algorithm uses a rigorous least-squares procedure and can be applied to mixtures of multiprotic
acids or bases. Any titration parameter can be refined.
Complexes of 400 with selenols have been prepared and the first
structural studies of Hg(II) selenolates obtained. Comparison of
vibrational spectra and X-ray powder diffraction patterns for these
complexes and their thiol analogs allows assignment of structures for
some complexes and suggests that, for Hg(SeR) 2 , polymeric structures
may be more common than for Hg(SR) 2 . Thus., Hg(SeR) 2 (R.Me, Et, Bu t )
are polymeric and Hg(SeCH 2CO2H) 2 is linear,'but for a large number Of
analogous thiolate complexes, only Hg(SBU ) 2 is known to be polymeric.
Single crystal X-ray diffraction studies show a polymeric structure
for Hg(SeMe) 2 based on .distorted tetrahedral geometry for mercury with
bridging selenolate groups . The structure of [Bu tSeHgCl(py) m]4 :is similar to those previously
reported for the sulfur analogs with pyridine.and 47methylpyridine, and
is isomorphous with the latter. The structure is based on an eightMembered
ring of alternating Hg and Se atoms (-Hg-SeBu t
7 )4 having a
centre of symmetry and two mercury environments, 'Hg(u 7SeBu t ) 2 (u-C1) 2 . 1
and 'Hg(u-SeBu ) 2Cl(py)', with a dichloro bridge linking the former
mercury atoms. The complex [EtSeHgC1(py)] 4 has a similar structure but
a dichloro bridge is absent and all mercury atoms have the environment
'Hg(U.-SeEt) 2C1(py) . .
The first valid comparison between Hg-S and Hg-Se bond lengths
for analogous thiolate and selenolate complexes of Hg(II) indicates
that the Hg-Se bond lengths are slightly shorter than expected from
comparisons of sulfur and selenium covalent radii.
Possible synthetic routes to selenium analogs of antidotal dithiois
are discussed. Although selenium analogs of BALH 2 and 1 .,3-dimercapto-2-
propanol (DMPH ) could not be isolated the new compounds selenetan-3-ol, 1a-diselenan-4-ol and 1-bromo-3-selenocyanato-2-propanol were obtained
from their attempted syntheses. The'Hg(II) derivatives of the selenium
analogs, Hg(SeBAL) and Hg(SeDMP), were isolated as intractable polymers.
These polymers have tetrahedral geometry for Hg(II) in contrast to linear
geometry for their thiol analogs, consistent with structural differences
between simple complexes Hg(XR) (X=S,Se). The compounds 27 (benzylseleno)-
fumaric.acid and 2-(benzylseleno)succinic acid have been prepared as intermediates
towards a projected synthesis of SeDMSH4.

Item Type: Thesis - PhD
Authors/Creators:Arnold, Alan Peter
Keywords: Mercury, Chelation therapy, Biochemistry
Copyright Holders: The Author
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Copyright 1982 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
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Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1983. Bibliography: l. 367-400

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