Self-assembled ionophores

Details Self-assembled ionophores Self-assembled ionophores

1999-11-24

2002-09-10

Raymond, Richard L. (Department: 1624)

Organic compounds -- part of the class 532-570 series

Organic compounds

Four or more ring nitrogens in the bicyclo ring system

C534S010000, C544S230000, C544S276000, C588S253000

Reexamination Certificate

active

06448400

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to ionophores which have the capacity to spontaneously assemble in solution. More particularly, the present invention concerns ionophore composed of hydrogen-bonded monomers of 5′-(t-butyl-dimethylsilyl)-2′,3′-O-isopyoidene-isoguanosine, or 5′-(t-butyl-dimethylsilyl)-2′,3′-O-isopropylidene-thio-isoguanosine, and use of these ionophores for removing 137-cesium ions (
137
Cs
+
) from nuclear waste.
2. Description of the Related Art
The United States faces a crisis in nuclear waste management. Safety and health issues surrounding nuclear waste have caused considerable interest in methods for separating radioactive isotopes
4,5,9
Cesium-137 (
137
Cs
+
) is a major product from uranium fission. Due to its 30 year half-life, much of the
137
Cs
+
produced during the nuclear age still exists.
137
Cs
+
and
90
Sr are the major heat sources in radioactive waste at Hanford Nuclear Reservation. Different methods for
137
Cs
+
removal and/or recovery from nuclear waste have been described, including selective precipitation as phospho-tungstate salts, inorganic ion exchanges, and solvent extraction using crown ethers.
4,5
Since the Na
+
concentration in nuclear waste is 10
3
-10
4
times that of
137
Cs
+
, ionophores with high Cs
+
/Na
+
selectivity are required to separate
137
Cs
+
from nuclear waste.
There are few Cs
+
-selective ionophores known. Due to its large size, selective extraction of Cs
+
(r=1.67 Å) from solutions containing Na
+
(r=0.97 Å) and K
+
(r=1.33 Å) is challenging. Initially, design of Cs
+
ionophores relied on large-ring crown ethers. Specifically, 21-c-7 and 23-c-8 have been proposed as ionophores for
137
Cs
+
extractions.
6
The use of large-ring crown ethers poses special challenges because of their flexibility. Thus, both the Cs
+
binding constants and Cs
+
selectivities of large-ring crown ethers are relatively modest.
10
Better results have been obtained using rigid macrocycles, such as calixarenes.
7,12-14
While their Cs
+
binding constants and Cs
+
/K
+
selectivities are often impressive, these rigid ionophores have two major problems: 1) they are difficult to synthesize and are available only in small quantities; and 2) due to high association constants, cation recovery from the ionophore complex is difficult.
SUMMARY OF THE INVENTION
The present invention solves the problems noted above by providing an ionophore useful for removing
137
Cs
+
from nuclear waste. The term “ionophore” as used herein refers to molecule or an assembly of molecules which either has the capacity to bind one or more ions, or is actually bound to one or more ions. The ionophore of the present invention comprises a plurality of monomers, wherein each monomer is noncovalently bound to another monomer, preferably through hydrogen bonding. Ideally, the ionophore is capable of spontaneously assembling in a solution containing the plurality of monomers. These inophores self-assemble at concentrations as low as 1 &mgr;M in CHCl
3
or CH
3
CN. The ionophore advantageously comprises identical monomers such as 5′-(t-butyl-dimethylsilyl)-2′,3′-O-isopropylidene-isoguanosine, 5′-(t-butyl-dimetlhylsilyl)-2′,3′-O-isopropylidene-thio-isoguanosine, or 2′,3′-Di-O-acetyl-5′-(t-butyl-dimethylsilyl)-isoguanosine. The ionophore may contain four or eight monomers. The ionophore is capable of forming a complex with an ion. This ion is preferably a cation such as Cs
+
, Na
+
, K
+
, Ag
+
, Hg
+2
, Pb
+2
, or Cd
+2
, preferably Cs
+
, and most preferably
137
Cs
+
. Ideally, the binding affinity of the ionophore for Cs
+
is greater than the binding affinity of the ionophore for Na
+
or K
+
. The present invention includes the complex comprising the ionophore and the ion. Also, the present invention includes a micelle comprising a plurality of the ionophores, wherein each monomer comprises a hydrophobic moiety making micelle formation possible, wherein the ion is bound to one of the ionophores of the micelle; the hydrophobic moiety-containing monomer preferably has the following structure:
wherein R is H or —SiR″
3
, where R″ is a hydrocarbon (CH
2
)
m
CH
3
wherein m=0-22, or an ester C=O(CH
2
)
n
CH
3
, wherein n=0-22.
Additionally, the present invention is also directed to three methods:
(1) a method for forming the complex comprising the steps of adding the plurality of monomers to a solution containing the ion;
(2) a method for removing the ion from a solution comprising adding the plurality of monomers to the solution, and removing the resultant complex from the solution; and
(3) a method for removing the ion from an aqueous solution comprising adding a plurality of the hydophobic moiety-containing monomers to the solution. In method (3), the monomers form a composition comprising a micelle, wherein the micelle is composed of the ionophores, and the ionophores have ions bound thereto. The composition is then removed from the solution, preferably by ultrafiltration.


REFERENCES:
Davis et al., Journal of Organic Chemistry, vol. 60, No. 13, pp. 4167-4176, Jun. 30, 1995.

Affiliated with

Also associated with

Rating

Self-assembled ionophores does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Self-assembled ionophores, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Self-assembled ionophores will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2841020