Evidence for these properties has been derived for DNA oligomers using NMR spectroscopy, among other techniques. Third, because of charge–charge repulsion, the effective compensation of negative charge on the nucleic acid by the cation counterions is modeled to be slightly less than 1:1. Second, the effective concentration of cations in this mobile layer becomes independent of the bulk at a relatively low threshold concentration.
#Metal ion bonding methionine full#
First, the cations are considered to maintain full hydration and to be “territorially”or diffusely bound, meaning that they are mobile, not localized on the nucleic acid. Three important properties of the ions involved in counterion condensation are the following. In its ideal form this theory assumes a linear polyanionic chain consisting of regularly spaced charges and of infinite length, in a medium of constant dielectric constant. 8.29.3.1 Nucleic Acids are Polyelectrolytes: Counterion Condensation TheoryĪ formal theoretical model for the association of cations with polyelectrolytes is provided by counterion condensation theory. In order to put these sites into perspective within the complexities of a nucleic acid polyanion, this section provides a brief description of all three categories. The bulk of this chapter will describe metal sites in category (c), which are specific metal sites that have been localized in X-ray or spectroscopic studies of nucleic acid structures. Specific “site-binding,” in which at least one cation aqua ligand is replaced by a ligand from the nucleic acid. Nonspecific “site-binding,” association of hydrated cations with pockets of negative electrostatic potential created by the nucleic acid structure and (c) “territorial” binding, a mobile charged layer of hydrated cations associated with the nucleic acid polyanion (b) Three general types of cation interactions with nucleic acid oligonucleotides (after Misra and Draper 6). Similar studies have been described on the uptake of nickel, copper, zinc and cadmium ions by fungal biomass ( Bosecker, 1993)Īnother example is the removal of manganese by a unique bacterial culture, which oxidizes dissolved Mn(II) to Mn(IV), which then precipitates as manganese dioxide at neutral pH ( Mita and Kato, 1999).įigure 5. The metal uptake is, however, inhibited by chloride ions, which is a drawback limiting the application of this approach. This makes it possible to recover some of the metals. The less strongly bound metal ions are stripped by transferring to a medium of pH 2.0. An interesting study by Greene and McPherson (1987) has shown that from a 0.1 mM solution at pH 5.0 the following metal ions are adsorbed with relative bond strength Ag(I)>Al(III)>Cu(II)>Pb(II)>Cd(II)>Ni(II)>Cr(III)>Co(II). The cell walls of chlorella vulgaris, a common green alga containing a complex mixture of sugars and proteins has a high sorptive capacity for a variety of metal ions. An interesting and very economical method is based on the uptake of metal ions by the cell walls of organisms in green alga. Many examples have been described from time to time. The metals are then desorbed by hydrochloric acid.īiotechnological methods, which involve biosorption by organisms in naturally occurring substances like algae and fungi have been applied to remove several metals. Almost 100% peat moss floats in 3 minutes of flotation time. The adsorption capacities for the peat moss are in sequence of Pb > Ni > Cu > Cd, and the adsorption kinetics are in the same sequence, as shown by Aldrich and Feng (2000).Īfter the metal uptake the peat mass is floated using cetyl trimethyl ammonium bromide as collector with a dosage of 12.5 mg/L at pH 6.4 and a feed content of 0.5 g/L. These constituents contain polar functional groups such as alcohols, aldehydes, ketones, acids and phenolic residues that can form chemical bonds or complex with the metal ions from solutions ( Chen et al., 1990). Peat moss is a complex material containing lignin and cellulose as its major constituents ( Coupal and Lalancette, 1976). M and PM denoting metal and peat moss respectively.
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