1. Current Research and
Current research focuses on molecular recognition
chemistry based on metal complexes with alkali and lanthanide
ions. Coordination chemistry for these ‘hard’ cations is
investigated using multi-dentate macrocyclic ligands with which
structurally well-defined and kinetically stable complexes can be
formed. The complexes are also used to construct a new type of
receptors showing unique binding properties.
Combination with photochemistry is another project, because photon is
one of the most useful tools to communicate with molecules and to know
the events happening on a molecular level. Functional dyes such
as porphyrins and carotenoids are incorporated for this purpose as well
as highly luminescent lanthanide cations and their complexes.
(1) Molecular Recognition Chemistry
Three-dimensional alkali metal
complexes and their assembly
“Armed macrocycles,” made by introducing metal-binding
sidearms on the nitrogen atoms of polyazamacrocycles, can form stable
1:1 complexes with the large and hard alkali metal cations, with the
cooperative coordination of the parent rings and their sidearms.
The stability constants of those metal complexes are so large that we
can use them as unique template molecules or building blocks to
construct more elaborate systems for molecular recognition and sensing.
Alkali metal complexes of cholesterol-armed macrocycles
spontaneously formed stable aggregates of 10-100 nm-size in aqueous
ethanol solutions. These cationic aggregates can incorporate
hydrophobic anions in their chiral hydrophobic cavities.
Enantiomers of dansyl amino acids showed fluorescence with quite
different intensity that enabled "visual sensing of chirality" of amino
(2) Photochemistry of Lanthanide Complexes
Among the trivalent lanthanide cations, Tb3+
and Eu3+ ions are known to show long-lived luminescence
based on f-f transition in the visible region. To make use of
these ions as photofunctional devices, we developed water-soluble
lanthanide complexes highly emissive in aqueous solutions. Our
goal is to develop lanthanide complexes which can respond to a
particular environment, such as a concentration of protons, anions, or
organic molecules. Recently, new approaches to obtain highly
luminescent Tb3+ complexes were developed based on
supramolecular self-assembly of designed ligands.
Anion sensing by lanthanide
Anions can bind to lanthanide ions to form highly
coordinated complexes in solutions. Anion coordination perturbs
the luminescence behaviors of lanthanide complexes which leads to the
luminescence sensing of anions. We have been trying to synthesize
various types of lanthanide complexes with high selectivity and
sensitivity toward specific anions.
2. Selected Publications
1. (review) "Luminescent Lanthanide Complexes as Analytical Tools in Anion Sensing, pH Indication and Protein Recognition," S. Shinoda and H. Tsukube, Analyst, 136, 431-435 (2011).
2. "Mixed-Metal Complexes Incorporating Platinum and Lanthanide Centers for Selective Binding and Chirality Sensing of Succinates," S. Shinoda, A. Mizote, M. Eiraku Masaki, M. Yoneda, H. Miyake, and H. Tsukube, Inorg. Chem., 50, 5876-5878 (2011).
3. "Mechanical Tuning of Molecular Recognition to Discriminate the Single-Methyl-Group Difference between Thymine and Uracil," T. Mori, K. Okamoto, H. Endo, J. P. Hill, S. Shinoda, M. Matsukura, H. Tsukube, Y. Suzuki, Y. Kanekiyo, and K. Ariga, J. Am. Chem. Soc., 132, 12868-12870 (2010).
4. "Combinatorial Screening of Lanthanide Complex Library for Luminescence Sensing of Amino Acids," S. Shinoda, K. Yano, and H. Tsukube, Chem. Commun., 46, 3110-3112 (2010).
5. "Experimental and Theoretical Approaches Toward Anion-Responsive Tripod–Lanthanide Complexes: Mixed Donor Ligand Effects on Lanthanide Complexation and Luminescence Sensing Profiles," Y. Kataoka, D. Paul, H. Miyake, T. Yaita, E. Miyoshi, H. Mori, S. Tsukamoto, H. Tatewaki, S. Shinoda, and H. Tsukube, Chem.–Eur. J., 14, 5258-5266 (2008).
6. " "Pocket Dendrimers" as Nanoscale Receptors for Bimolecular Guest Accommodation," S. Shinoda, M. Ohashi, and H. Tsukube, Chem.–Eur. J., 13, 81-89 (2007).
7. "Mechanical Control of Enantioselectivity of Amino Acid Recognition by Cholesterol-Armed Cyclen Monolayer at the Air-Water Interface," T. Michinobu, S. Shinoda, T. Nakanishi, J. P. Hill, K. Fujii, T. N. Player, H. Tsukube, and K. Ariga, J. Am. Chem. Soc., 128, 14478-14479 (2006).
8. "Cholesterol-Armed Cyclens for Helical Metal Complexes Offering Chiral Self-Aggregation and Sensing of Amino Acid Anions in Aqueous Solutions," S. Shinoda, T. Okazaki, T. N. Player, H. Misaki, K. Hori, and H. Tsukube, J. Org. Chem., 70, 1835-1843 (2005).
9. "Luminescent Lanthanide Complexes with Stereo-Controlled Tris(2-pyridylmethyl)amine Ligands: Chirality Effects on Lanthanide Complexation and Luminescence Properties," T. Yamada, S. Shinoda, H. Sugimoto, J. Uenishi, and H. Tsukube, Inorg. Chem., 42, 7932-7937 (2003).
10. "Ester-Armed Cyclens having Quadruple Helicated Geometry: Remarkably Stable and Selective Na+ Ion Encapsulation," S. Shinoda, T. Nishimura, M. Tadokoro, and H. Tsukube, J. Org. Chem., 66, 6104-6108 (2001).