An Octadentate Luminescent Eu(III) 1,2-HOPO Chelate with PotentAqueous Stability Page: 1 of 4
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to Digital Library by the UNT Libraries Government Documents Department.
The following text was automatically extracted from the image on this page using optical character recognition software:
An Octadentate Luminescent Eu(III) 1,2-HOPO Chelate with
Potent Aqueous Stability
Evan G. Moore, Christoph J. Jocher, Jide Xu, Eric J. Werner and Kenneth N.
Department of Chemistry, University of California, Berkeley, CA, 94720-1460.
RECEIVED DATE (will be automatically inserted after manuscript is accepted)
The synthesis, characterization, and photophysical
properties of two novel ligands, 5LINMe-1,2-HOPO (1)
and H(2,2)-1,2-HOPO (2), which utilize the 1,2-HOPO
chelate as a sensitizer for Eu(III) are reported. In
addition, the former ligand was structurally
characterized as the Eu(III) complex by X-ray
crystallography. The [Eu(1)2]- complex of the
tetradentate ligand (1) is stable in aqueous solution, to
a limiting concentration of ca. 7x10-9 M, and retains
the superior photophysical performance noted for the
1,2-HOPO sensitizer. By contrast, the octadentate
ligand (2) has vastly improved stability as the [Eu(2)]-
complex upon further dilution, to a limiting
concentration of ca. 5x10-" M, which is beyond the
minimum detectable concentration of most
fluorimeters. The presence of a single coordinated
water molecule for the latter complex reduces the
overall metal centered luminescence.
Organic complexes of luminescent lanthanides such as
Eu(III) have become increasingly useful for biological
assays and in high throughput screening applications,'2
where their long lived luminescence can allow significant
improvement in signal to noise ratio. Several Ln(III)
chelates are commercially available (eg. LanceTM - Perkin
Elmer, LanthaScreenTM - Invitrogen) and fluorescent assay
platforms such as Dissociation-Enhanced Lanthanide
Fluorescent Immuno Assay (DELFIA) are well developed,3
offering increased sensitivity compared to colorimetric
assay formats such as Enzyme-Linked Immuno Sorbent
Assay (ELISA).4 Nonetheless, the quantum yield of these
commercial luminescence agents are far from optimized
(ca. 2-10 %), and the improvement of this crucial parameter
while maintaining sufficient aqueous solubility and stability
for biological compatibility is a challenging area of active
We recently reported6 the exceptional photophysical
performance of tetradentate 1-hydroxypyridin-2-one
derivatives such as 5LIO-1,2-HOPO (3) that form stable
ML2 complexes with Eu(III). These ligands simultaneously
fulfill the criteria of both high thermodynamic stability and
excellent photophysical properties. Herein, we extend this
family to include an amino linked version 5LINMe-1,2-
HOPO (1) (Chart 1) which was developed as a model for
H(2,2)-1,2-HOPO (2), the first example of an octadentate
1,2-HOPO derivative for Eu(III) luminescence. The latter
forms an ML complex with improved stability upon
dilution in aqueous solution, a feature required for the
practical development and application of these complexes
in biological assays.
N H HORN
N-OH O OH
H H O HO-N
Chart 1. Structures of 5LIO-1,2-HOPO (3) (top left), 5LINMe-1,2-HOPO
(1) (bottom left) and H(2,2)-1,2-HOPO (2) (right).
The syntheses of 5LINMe-1,2-HOPO and H(2,2)-1,2-
HOPO are straightforward (see Scheme S1, Supp. Info.).
Boc amidation of N-(2-aminoethyl)-ethane-1,2-diamine
(dien) followed by reductive amination with formaldehyde
provides the protected backbone which was converted to
the 5LINM amine by reaction with TFA. Alternately, the
(H(2,2)) may be prepared using literature methods.7
Reaction of either backbone with the thiazaolide activated
1,2-HOPO precursor6' s yields the benzyl protected ligands,
which were deprotected under acidic conditions with 1:1
(v/v) AcOH:HCl (12 M). Complexation with EuCl3.6H20
in MeOH at reflux gave the desired complexes on cooling
in good yield and analytically pure form. An X-ray quality
crystal of the [Eu(5LINMe-1,2-HOPO)2] complex, as the
potassium salt, was grown by slow evaporation of a ca.
500 pM solution in 0.1 M KCl at ca. pH 8.
As shown in Figure 1, the anion Eu(III) complex of (1)
forms an ML2 species, with an overall eight coordinate
To whom correspondence should be addressed. Email: email@example.com. Fax (Int.) +1 (510) 486 5283
Here’s what’s next.
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
Moore, Evan G.; Jocher, Christoph J.; Xu, Jide; Werner, Eric J. & Raymond,Kenneth N. An Octadentate Luminescent Eu(III) 1,2-HOPO Chelate with PotentAqueous Stability, article, February 26, 2007; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc901582/m1/1/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.