Average N-Np
length: 2.77 Å
Average N-U length:
2.63 Å
Slightly distorted
ring
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| Transition Metal Complexation | ||
| Similar to their smaller counterparts, expanded porphyrins and expanded Schiff base complexes have been found to possesss interesting metal coordination characteristics. Therefore, the Sessler group is interested in metal complexation to a number of their macrocycles. Current research is focused on both complexation with transition metals and also the less studied f-block elements. |
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| The large central core of many expanded porphyrins and expanded Schiff base macrocycles make them excellent candidates to coordinate f-block elements. A considerable amount of research has focued on Lanthanide coordination--namely Gd or Lu-- coordination to Texaphyrin. More recently, efforts have been made to complex the transactinide elements (U, Np and Pu). For this project, collaboration between the Sessler group and Los Alamos National Laboratories in New Mexico has been established. The goal of this work remains to sense, coordinate and separate radioactive cations, such as UO2+, NpO2+ and PuO2+, in order to optimize process chemistry and waste management. This research has already produced the first all-aza coordinated neptunyl complex (shown below). |
| Isoamethyrin-NpO2+
Complex |
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Average N-Np
length: 2.77 Å |
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| Sessler, J. L.; Seidel, D. S.; Vivian, A. E.; Lynch, V.; Scott, B.; Keogh, D. W. Angew. Chem., Int Ed. Eng. 2001, 40, 591-594 | |
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| Complexes
containing two or more transition metal centers are of interest due to
their
similarity to active sites in a number of biologically important
enzymes. However, the majority of these complexes have relied on
multiple ligands rather than single multifunctional macrocycles.
As poly-pyrrolic macrocycles in nature are well known for their ability
to coordinate one transition metal
center (chlorophyll, coenzyme B12 etc.) our group is interested in
exploiting larger poly-pyrrolic macrocycles to coordinate two or more
transition metals. |
| Positive
Homotropic Allosteric Binding of Ag(I) Cations |
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| It has been shown
through UV-vis titrations that, for the synthesis shown above,
coordination of a second Ag(I) cation to the macrocycle occurs through
postive homotropic allosteric binding. As this coorperative
behavior is similar to binding observed with hemoglobin, we believe
further research in this area may provide useful insights into metal
complexation with biological systems. |
| Sessler,
J. L., Tomat, E., Lynch, V. M. Positive Homotropic Allosteric Binding
of Silver(I) Cations in a Schiff Base Oligopyrrolic Macrocycle. J.Am. Chem. Soc. 2006,
128 ( |
| Giving
Iron a Choice... |
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|
 7 |
 9 |
| The
free base of macrocycle 4* is reacted with Fe2Mes4
to produce the macrocycle shown above. The Fe-O-Fe angle is
roughtly
124° and the Fe(III)s can be described as a distored square pyramid. |
The
acid salt of macrocycle 4 is reacted under the same conditions as complex 7. Here, the Fe-O-Fe bridge is linear and both Fe(III)s are in a distorted trigonal bipyramidal conformation. |
| Veauthier, Jacqueline M.; Cho,
Won-Seob; Lynch, Vincent M.; Sessler, Jonathan L. Calix[4]pyrrole
Schiff Base Macrocycles. Novel Binucleating Ligands for m-Oxo Iron
Complexes. Inorganic Chemistry 2004,
43(4), 1220-1228. |
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| *Numbering scheme followed from
paper. |
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| Page Last Updated on 2/24/03
Comments to Patricia Melfi |