Zeng Huang

Enantioselective Gel Collapsing: A New Means of Visual Chiral Sensing

An optically active BINOL-terpyridine based Cu(II) complex (R)-2 was prepared. Sonication of (R)-2 in CHCl(3) led to the formation of a stable gel. The interaction of this gel with chiral amino alcohols was studied. It was found that (S)-phenylglycinol (0.10 equiv) could break the gel network of (R)-2 (3.75% w/v, g/mL) in CHCl(3) to cause gel collapsing but (R)-phenylglycinol (0.10 equiv) could not. Similar enantioselective gel collapsing was also observed with (R)- and (S)-1-amino-2-propanol. This study demonstrates that chiral molecular gels are potentially useful for visual chiral discrimination. Complex (R)-2 in solution also exhibited significant enantioselective fluorescent enhancement in the presence of a variety of amino alcohols.

Zn(II) promoted dramatic enhancement in the enantioselective fluorescent recognition of functional chiral amines by a chiral aldehyde

The addition of Zn2+ dramatically enhanced the enantioselective fluorescent responses of 3,3′-diformyl-1,1′-bi-2-naphthol toward chiral functional amines in methanol. One enantiomer of the chiral substrates, including diamines, amino alcohols and amino acids, was found to turn on the emission of this molecular probe at λ > 500 nm much more than the other enantiomer. This emission signal is greatly red-shifted from most of the other BINOL-based enantioselective fluorescent sensors whose fluorescent signals are generally at 400 ± 50 nm. Thus, a new window is opened for the use of BINOLs to observe chiral recognition events. The fluorescent responses of the new probe in the presence of Zn2+ toward a chiral diamine have also allowed a visual discrimination of these two enantiomers because of their different emitting color and intensity. The mass spectroscopic analyses for the reaction of the probe plus Zn2+ with the two enantiomers of a chiral diamine have revealed that the chirality match and mismatch between the probe and the substrate have produced different reaction products, generating very different fluorescent responses.

Highly selective fluorescent recognition of Zn2+ in water by terpyridine–CuCl2

TpyCuCl2 is found to exhibit highly selective fluorescence enhancement in the presence of Zn2+ in water solution and can be used to discriminate Zn2+ from a broad range of metal cations.

Highly selective ratiometric fluorescent recognition of histidine by tetraphenylethene–terpyridine–Zn( ii ) complexes

TPE–monoTpy and TPE–diTpy compounds (TPE = tetraphenylethene, Tpy = 2,2′:6′,2′′-terpyridine) were prepared and showed significant red shifts in fluorescence upon coordination to Zn(NO3)2 in THF : HEPES (1 : 4) solutions. These in situ prepared Zn(II) complexes have achieved highly selective ratiometric fluorescent recognition of histidine even in the presence of other natural amino acids and metal cations. This fluorescent recognition of histidine is visually observable with distinctive color changes from yellow to blue under UV irradiation. The mechanism for the interaction of the Zn(II) complexes with histidine was studied by UV-Vis absorption, NMR and MS.

Spectroscopic studies on the interaction of terpyridine-CuCl2 with cysteine

Interaction of the classical coordination complex TpyCuCl2 (Tpy = terpyridine) with cysteine was studied. Addition of cysteine to the solution of TpyCuCl2 was found to give greatly enhanced fluorescence. UV-vis absorption and mass spectroscopic analyses were conducted to investigate this reaction under various conditions. These studies indicate that in a pure water solution (pH = 6.10–6.55), cysteine can reduce Cu(II) to generate TpyCuSCH2CH(NH2)CO2H with greatly enhanced fluorescence. In a HEPES buffer solution (pH = 7.40), the Tpy ligand can be further displaced off the copper center, contributing to the enhanced fluorescence.