Lanthanide‐Ion Complexation by D‐Glucuronic and D‐Galacturonic Acids

Abstract

To assess the potential of naturally occurring substances in the treatment of heavy-metal intoxication, the interaction between D-galacturonic and ~-glucuronic acids with several trivalent lanthanide ions has been studied in aqueous solutions by means of a spectrophotometric method (27"; 0 . 1~ NaC10,; pH 4.0). Values for the overall stability constants for [LnL] and [LnL,] (Ln = La, Ce, Pr, Nd, Gd, or Lu) complexes are presented and discussed.The interpretation of the data shows that, similarly to acetates, the COOH group coordinates metal ions in both [LnL] and [LnL,] complexes. The 1 :I complexation is supplemented by the ring C(5)-0-atom. Moreover, the C(4)-0-atom seems to play an important role in the steric hindrance of the chelating ligand molecules.Introduction. -Lanthanide ions are found in living organisms in trace amounts only, and they are considered to play no biological role 111. They interact, however, with biological materials in specific ways, which along with their unique magnetic and spectroscopic properties make them very informative substitution probes for Ca-, Mg-or Zn-containing biological materials [2]. Because of their chemical similarity, lanthanides may also act as substitution probes for the actinides, especially for those radioactive elements available only in submicroquantities.Foreign chemicals entering into the organism are usually converted into compounds that can be excreted. For heavy metals deposited into the organism, there is no physiological process that will eliminate them rapidly from the body. Their excretion rate is so slow that, in a normal life span, only a fraction of the deposited metals can be removed from the body. Events such as the Chernobyl fallout have stimulated studies leading to the development of new therapeutic methods for the removal of immobilized radioactive materials. The strategy for this removal has been mainly based on the use of high-affinity chelating agents which migrate preferentially to certain organs in vivo. A toxic metal bound to a constituent of living organisms (usually a protein) is transformed into a metal chelate which is readily excreted. It has long been known that the increase in stability constant of a metal complex parallels an increase in excretion rate [3-51.The majority of artificial chelating agents that are commerically available have been developed for purposes other than the removal of toxic metal ions from mammalian body. The most popular chelating agents EDTA (ethylenediaminetetraacetic acid) and DTPA (diethylenetriaminepentaacetic acid) have several COOH groups which are ionized under physiological conditions. Therefore, they cannot pass through cell membranes to any significant extent [6] [7]. As a result, EDTA and DTPA are very effective in

Structure and Thermodynamics of Eu(III) and Cm(III) Complexes with Glucuronic Acid

“…There is, however, evidence in the literature that a smaller cation cannot form as a stable complex with GlcA. Fuks and Bünzli found a trend toward smaller complex formation constants for smaller lanthanide cations (i.e., Gd and Lu) . Balt et al postulated a 1:2 complex for Yb­(III) with GlcA in which both ligands bind only through O-5 and O-6 without any participation of the ring hydroxyl groups.…”

“…The formation constants for the Ln:GlcA 1:1 complexes are in the range log β 11 = 1.13−1.60 17,24 and those for the 1:2 complex in the range log β 12 = 3.61−3.92. 17 For Cr(III) 1:1 and 1:2 complexes are described in the literature with lower complex formation constants (log β 11 = −0.13 and log β 12 = −2.24, respectively). 22 We have studied the complex formation of GlcA with Cm(III) and Eu(III) as representatives of the trivalent actinides and a homologue, respectively.…”

“…Some prior studies regarding the complexation behavior of GlcA with Ln­(III) − and trivalent transition metals , can be found in the literature. To our knowledge, no studies of the complexation of An with GlcA exist to date.…”

“…Some studies also report stability constants, but none have given sufficient information for an extrapolation to standard conditions. The formation constants for the Ln:GlcA 1:1 complexes are in the range log β 11 = 1.13–1.60 , and those for the 1:2 complex in the range log β 12 = 3.61–3.92 . For Cr­(III) 1:1 and 1:2 complexes are described in the literature with lower complex formation constants (log β 11 = −0.13 and log β 12 = −2.24, respectively) …”

Opening the Egg Box: NMR spectroscopic analysis of the interactions between s-block cations and kelp monosaccharides

“…Both GalA and GlcA are found abundantly in nature (in pectins and hemicelluloses, respectively), and their metal-binding properties have been much more widely investigated than that of the algal uronates, hence providing a useful comparison. [42][43][44][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63] To our knowledge, the work presented herein represents the most extensive investigation of the complexation of metal ions to mono-uronates to-date, and will help to inform future studies of the behaviour and applications of their parent polysaccharides.…”