Ind. Eng. Chem. Res. 2000, 39, 3405-3411
3405
Contributions of Professor Reed M. Izatt to Molecular Recognition Technology: From Laboratory to Commercial Application Neil E. Izatt,* Ronald L. Bruening, Krzysztof E. Krakowiak, and Steven R. Izatt IBC Advanced Technologies, Inc., 856 East Utah Valley Drive, American Fork, Utah 84003
Professor Reed M. Izatt has been a scientific pioneer in the discovery and development of molecular recognition technology (MRT). From early involvement in the field of macrocyclic chemistry to recent commercialization, Professor Izatt has made significant contributions to the field. Initial work focused on understanding factors important to selectivity, including cation geometry requirements, ionic radius, ligand cavity dimensions, ligand donor atom type and placement, ring number, and ring substituents. Subsequently, ligands were incorporated into useful formats including beads, membranes, and columns. Important applications were found in analytical and process industries. MRT enables the separation, recovery, and purification of specific species often from complex and difficult matrixes. Professor Izatt’s scientific work has led to commercial separations including among others chloride ion, mercury, copper, lead, cesium, strontium, radium, palladium, rhodium, antimony, bismuth, gold, iron, and aluminum. Introduction The pioneering scientific work of Professor Reed M. Izatt and his associates at Brigham Young University (BYU) laid the foundation for the development and commercialization of novel separations and chelation projects at IBC Advanced Technologies, Inc. (IBC). Dr. Izatt and co-workers were involved at an early stage in the rapidly evolving field of macrocyclic chemistry. Pederson,1 Busch,2 Lehn,3 and their associates had reported a variety of macrocycles and observed that these molecules showed unusual selectivities for cations, including alkali-metal ions. The rapid development of our knowledge of the coordination chemistry of alkalimetal ions is due, in large part, to the availability of macrocycles and to the characterization of their metal complexation properties. Early work by Frensdorff,4 Lehn and Sauvage,3 and Izatt et al.5 showed that certain crown ether macrocycles have remarkable selectivities for alkali-metal, alkaline-earth-metal, and post-transition-metal ions as measured by equilibrium constants (K) for the interactions. Some of these results are given in Table 1. Structures of the macrocycles used in the paper are given in Figure 1. The results in Table 1 show the effect on complex stability and selectivity of matching crown ether cavity and metal ion radii, macrocycle donor atom type, and number of crown ether rings. For example, the ionic radii of K+ and Ba2+, which are nearly identical, most closely match the radius of the 18C6 cavity6,7 and have the largest log K values in the alkali-metal and alkalineearth-metal groups, respectively. The substitution of two sulfur atoms for two oxygen atoms in 18C6 results in a reversal of complex stability in the cases of K+ and Ag+. The additional ring in 2.2.2 as compared to 18C6 results in much more stable complexes with the alkali-metal ions and increased selectivity for K+. These and similar initial promising results fueled an intensive and enduring effort by an increasing number and variety of scientists worldwide to synthesize novel macrocycles * To whom correspondence should be addressed. E-mail:
[email protected]. Fax: (801) 763-8491. Phone: (801) 763-8400.
Table 1. log K (H2O) Values6-8 at 25 °C for the Interaction with Crown Ethers of Alkali-Metal Ions, Alkaline-Earth-Metal Ions, Ag+, and Pb2+ Mn+
ionic radius, Å
log K
Na+ K+ Rb+ Cs+ Ag+
0.95 1.33 1.48 1.69 1.26
0.8 2.03 1.56 0.99 1.50
18C6
Ca2+ Sr2+ Ba2+ Pb2+
0.99 1.13 1.35 1.20
4.0 (Cl-) and
