Ho-Lun 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.

New binuclear double-stranded manganese helicates as catalysts for alkene epoxidation

New binuclear double-stranded helicates were formed between manganese(ii) perchlorate and chiral phenyl- and polyphenyl-bridged oligopyridines; they are active catalysts for alkene epoxidation.

Stereoselective formation of helical binuclear metal complexes: synthesis, characterization, and crystal structures of chiral bis-rhenium(I) quaterpyridine complexes

A series of single-stranded helical Re(I) complexes, of formula [Re(2)(L)Br(2)(CO)(6)], were prepared by reacting [Re(CO)(5)Br] with chiral quaterpyridines L1-4. By (1)H and (13)C NMR analysis, all the crude complexes consisted of a pair of stereoisomers. Sterically more demanding ligand L4 induced a higher ratio (80:20) than L1-3 (about 56:44). Stereochemically pure complexes could be obtained by recrystallization in CH(2)Cl(2). X-ray crystallographic analysis of single crystals from purified complexes showed a single-stranded helical structure with a bridging ligand wrapped around two distorted octahedral rhenium metals, both of which possessed one bromide ligand and three carbonyl ligands in a fac coordination. The helical core is established by extensive noncovalent electrostatic interactions and chiral information is transmitted from the ligand to the helix through these interactions. Solution behavior was studied by CD spectroscopy, and the strong Cotton effect confirms the integrity of the helical structure in solution. The diastereoselectivity of helicates is proposed to be induced by steric interaction between the bromine atom and the substituent of the bridging ligand.

Diastereoselective formation of a dicopper(I) helicate with a chiral tetradentate pyridylthiazole ligand

Reaction of a pinene-based pyridylthioamide with 1,4-dibromo-2,3-butanedione in refluxing methanol yielded a new chiral pyridylthiazole ligand L which forms a dinuclear double-stranded helicate with Cu(i) ions; this helicate has opposite helical chirality when compared with its quaterpyridine analogue.

Stereoselective formation of a single-stranded helicate : Structure of a bis(palladium-allyl)quaterpyridine complex and its use in catalytic enantioselective allylic substitution

Chiral C2-symmetric quaterpyridine L reacts with [Pd(eta3-C3H5)Cl]2 to form a chiral single-stranded helical binuclear palladium complex of formula [Pd2(eta3-C3H5)2(L)]2+; the complex can efficiently catalyze allylic substitution of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate with enantioselectivity up to 85%.

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.