Chi-Tung Yeung

Impressive Europium Red Emission Induced by Two-Photon Excitation for Biological Applications

Three triazine-based europium(III) complexes were synthesized that demonstrated strong two-photon induced europium emission with a high two-photon absorption cross-section. The modified triazine ligand of complex 3 initiated over 100% enhancement of the two-photon absorption cross-section (σ(2): 320 GM) when compared with complex 1 (σ(2): 128 GM) in a solution of DMSO. Europium complex 3 is also stable in vitro, and power-dependence curves were obtained in vitro to confirm the two-photon-induced f-f emission in HeLa cells.

Copper Complexes of Chiral Tetradentate Binaphthyl Schiff‐Base Ligands: Syntheses, X‐ray Crystal Structures and Activity in Catalytic Asymmetric Cyclopropanation of Alkenes

A number of new chiral monomeric binaphthyl Schiff-base ligands H2L [where H2L = 2,2′-bis(3-R1-5-R2-2-hydroxybenzylideneamino)-1,1′-binaphthyl] and a series of chiral copper(II) complexes [CuL] were prepared in good or nearly quantitative yields. Some of the free ligands and the [CuL] complexes were structurally characterized by X-ray crystallography. Almost all the [CuL] complexes were found to be active catalysts for the asymmetric cyclopropanation of alkenes with ethyl or tert-butyl diazoacetate. Enantioselectivities of up to 77% ee were observed. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

In Vitro Imaging and Human Serum Albumin Responsive Dimeric Lanthanide DO3A Complex

Two series of dimeric DO3A (1,4,7,10-tetraazacyclodecane-1,4,7-triacetate) lanthanide complexes (LnL(1)-LnL(2), Ln = Eu, Gd, and Tb) have been synthesized with two different bridged chromophores. The X-ray structures of dimeric LnL(1) (Ln = Gd and Tb) complexes show that each metal ion has nine coordination numbers with eight directly bound donor atoms of the ligand and one oxygen donor from the water molecule. Photophysical measurements indicate that the bridged antenna in LnL(2) gives a higher efficiency than that of LnL(1) and is responsive to the protein Human Serum Albumin (HSA), giving an f-f luminescence signal enhancement with a binding constant log K = 4.84. In vitro imaging of EuL(1) and EuL(2) in HeLa cells has been recorded, and EuL(2) has demonstrated a higher rate of cellular uptake and low cytotoxicity (IC(50) = 3 mM).

Responsive two-photon induced europium emission as fluorescent indicator for paralytic shellfish saxitoxin.

A water-soluble europium(III) complex (1) has been synthesized and demonstrated to be a specific fluorescence probe for the paralytic shellfish toxin saxitoxin, a neurotoxin that blocks the voltage-gated sodium channels on cell membranes. Saxitoxin binds to the europium complex (K(B) = 6.1 × 10(4) M(-1)) and triggers a two-photon induced f-f emission enhancement by over 100% and increases the two-photon absorption cross-section from 9 to 36 GM.

Stereolabile chiral biphenyl hybrids: crystallization-induced dynamic atropselective resolution involving supramolecular interactions

Crystallization-induced dynamic atropselective resolutions of three simple chiral biphenyl hybrids, (1R,1′R)-1,1′-(biphenyl-2,2′-diyl)diethanol 1, (1R,1′R)-1,1′-(biphenyl-2,2′-diyl)bis(ethane-1,1-diyl)diacetate 2 and (1S,1′S)-1,1′-(biphenyl-2,2′-diyl)bis(2,2′-dimethylpropan-1-ol) 3 were achieved. The axial chirality of the biphenyl backbones of 1–3 were found to be determined by (i) the steric bulkiness at the α position of the ortho-substituents, and (ii) the intermolecular interactions between the molecules. 1, which possesses the least sterically demanding methyl substituents, was found to form stereoselectively the S-atropisomer and gave enantiomerically pure supramolecular right-handed helices through strong and directional intermolecular hydrogen bonds in its crystal.