Angewandte
Communications
Chemie
Luminescence Sensors
Coordinatively Unsaturated Lanthanide(III) Helicates: Luminescence
Sensors for Adenosine Monophosphate in Aqueous Media
Jashobanta Sahoo, Rajendran Arunachalam, Palani S. Subramanian,* Eringathodi Suresh,
Abstract: Coordinatively unsaturated double-stranded heli-
cates [(H2L)2Eu2(NO3)2(H2O)4](NO3)4, [(H2L)2Tb2(H2O)6]-
(NO3)6, and [(H2L)2Tb2(H2O)6]Cl6 (H2L = butanedioicacid-
transport across membranes, DNA synthesis, or cell signal-
ing.[6] Adenosine monophosphate (AMP) controls important
processes in the regulation of carbohydrate metabolism,
including glycogen phosphorylase and phosphofructoki-
nase.[7]
Surprisingly, probes for the sensing of AMP (especially in
the presence of ADP and ATP) are rare.[8] Odashima and co-
workers[9] and Shaoꢁs group[10] had reported electrochemical
detection methods. Fluorescent nano-silica sandwich com-
plexes by Qu and co-workers[11] and a Cu complex by Lin[12]
were reported. A guanidinium-based tweezer type receptor
has been reported by Schmuck et al.[13] and a pyridinium-
based tripodal chemosensor by Ghosh and co-workers.[14] The
preferential binding order of receptors generally follows
ATP > ADP > AMP, owing to the decreasing charge–charge
interaction.
The present study introduces highly charged luminescent
cationic lanthanide helicates to selectively recognize the less-
charged AMP over ADP and ATP. Although various organo-
fluorophores[15] were reported for sensing of AMP, most of
these fluorophores bind generally through the phosphate
terminals. In the present case, the receptor favors a bridging
of AMP by involving both terminal moieties of the phosphate
and the adenosine coordinating to the two metal centers. The
receptor itself is a novel kind of luminescent coordinatively
unsaturated double-stranded dinuclear helicate formed from
two bis(tridentate) ligands H2L (Figure 1) and two europium-
(III) or terbium(III) ions. The coordination sites at the metal
ions are filled up by water molecules or anions. Those co-
ligands in principle can be substituted by anionic species.
However, a thorough screening of possible anionic co-ligands
for the helicate revealed that only AMP results in a significant
change of the luminescent properties.
1,4-bis[2-(2-pyridinylmethylene)hydrazide])
are
easily
obtained by self-assembly from the ligand and the correspond-
ing lanthanide(III) salts. The complexes are characterized by
X-ray crystallography showing the helical arrangement of the
ligands. Co-ligands at the metal ions can be easily substituted
by appropriate anions. A specific luminescence response of
AMP in presence of ADP, ATP, and other anions is observed.
Specificity is assigned to the perfect size match of AMP to
bridge the two metal centers and to replace quenching co-
ligands in the coordination sphere.
I
n 1987 J.-M. Lehn introduced the term helicate for
oligonuclear coordination compounds with two or more
linear ligands wrapping around two or more metal ions.[1]
This marked the beginning of intensive studies of helical
metal complexes. Early on the interest mainly arose from
mechanistic aspects.[2]
In the early investigations of helicates, properties and
function played only a minor role. An exception was the
pioneering work of Piguet and Bꢀnzli on lanthanide helicates,
which focused on some special features, such as photophysics
or magnetism.[3,4] Nowadays, more and more helicates are
used as structurally well-defined entities to interact with
biochemical or biological systems.[5]
Nucleoside phosphates are the building blocks of DNA,
a double-helical species found in nature. They themselves are
unique species, which regulate the energy conversion in
organisms. Furthermore, adenosine triphosphate (ATP),
adenosine diphosphate (ADP), or adenosine monophosphate
(AMP) play a key role in many cellular functions, for example
Ligand H2L was prepared by reaction of succinic acid
dihydrazide with 2-pyridine carboxaldehyde. Treating H2L
with Eu(NO3)3, TbCl3, and Tb(NO3)3 results in the respective
dinuclear LnIII complexes [Eu2(H2L)2(NO3)2(H2O)4](NO3)4,
[*] J. Sahoo, R. Arunachalam, Dr. P. S. Subramanian, Dr. E. Suresh
Central Salt and Marine Chemicals Research Institute (CSIR-
CSMCRI), Academy of Scientific and Innovative Research (AcSIR)
Bhavnagar, 364002, Gujarat (India)
E-mail: siva140@yahoo.co.in
Dr. A. Valkonen, Prof. Dr. K. Rissanen
University of Jyvaskyla, Department of Chemistry
Nanoscience Center
P.O. Box. 35, 40014 University of Jyvaskyla (Finland)
Prof. Dr. M. Albrecht
Institut fꢀr Organische Chemie, RWTH Aachen University
Landoltweg 1, 52074 Aachen (Germany)
E-mail: markus.albrecht@oc.rwth-aachen.de
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under
Figure 1. Ligand H2L and AMP.
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
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