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Zhenlin Zhong

Publications and source records attributed to Zhenlin Zhong.

8 recordsLinked to original sources
PubMed2005

An artificial siderophore for the detection of iron(III).

An artificial siderophore in the form of a squaraine dye (1) has been synthesized. The bidentate ligand chelates to Fe(III) between the deprotonated hydroxyl group on the ortho position of the ring adjacent to the carbonyl group of the cyclobutadiene ring. The optical response is due to a subtle geometry change of 1 on chelation to Fe(III). This artificial siderophore forms a 2 ratio 1 ligand ratio metal complex, as indicated by a sigmoidal isotherm (K(a)= 10(7) M(-1)). The optical response on the addition of Fe(III) is observed at low concentrations in comparison to other metal salts. The X-ray crystal structure and calculated structures of dye (1) are also included, and will be discussed.

Cations↗
PubMed2005

Large pKa shifts of alpha-carbon acids induced by copper(II) complexes.

A series of synthetic receptors (4-6) incorporating metal ions, specifically copper(II), were examined for their ability to enhance the acidity of active methylene compounds. The copper(II) complexes were observed to reduce the pKa of 1,3-diketone carbon acids in acetonitrile by as much as 12 pKa units. The relatively large pKa reduction achieved by the complex is attributed to the electrostatic interaction between the anionic pi system of the enolate and the copper(II) ions. The cage structure and hydrogen bonding sites in receptors 4 and 5 lead to a very modest further enhancement of the acidity relative to that with 6. This study provides insight into the way in which metalloenzymes stabilize an enolate intermediate.

Acids↗
PubMed2005

Guidelines in implementing enantioselective indicator-displacement assays for alpha-hydroxycarboxylates and diols.

Enantioselective association events between boronic acid receptors and bifunctional substrates such as alpha-hydroxycarboxylates and vicinal diols were exploited to develop enantioselective indicator-displacement assays. It was found that the sensitivity of the assay could be tuned by using either colorimetric or fluorescent indicators. Mathematical principles were established for concurrent determination of concentration and enantiomeric excess (ee) of a chiral analyte, which has been a challenge to the high-throughput analysis of chiral samples. Furthermore, experimental protocols were optimized to maximize the chiral resolution of the assay and to improve the accuracy of the ee measurements.

Alcohols↗
PubMed2004

Rate of enolate formation is not very sensitive to the hydrogen bonding ability of donors to carboxyl oxygen lone pair acceptors; a ramification of the principle of non-perfect synchronization for general-base-catalyzed enolate formation.

Two series of structures (1 and 2) possessing intramolecular hydrogen bonds to the lone-pair electrons of carbonyl oxygens have been examined to reveal the influence of the pK(a) of the hydrogen-bond donor on the rate of general-base-catalyzed enolate formation. The geometry of the hydrogen bonds is well accepted to be appropriate for intramolecular hydrogen-bond formation. Yet, as revealed by Brønsted plots, both series show very little dependence of the rate of enolate formation on the hydrogen-bond donor ability. The intramolecular hydrogen bonds give rate enhancements only on the order of 10-100-fold, and corrected Brønsted alpha-values are slightly below 0.1. The results can be understood by interpreting them in light of the Principle of Non-Perfect Synchronization. The results are consistent with the proton transfer occurring through an asynchronous transition state with the developing negative charge localized on carbon. We postulate that catalysts of enolate formation will be most effective if the binding groups are focused on stabilizing negative charge that is forming on the enolate carbon rather than on the enolate oxygen.

Alcohols↗
PubMed2002

A colorimetric sensing ensemble for heparin.

A receptor possessing ammoniums and a novel amino acid with a boronic acid side chain was designed and synthesized. The receptor shows good affinity and selectivity for heparin over similar polysaccharides possessing lower anionic charge density. The affinity for heparin is similar to that for a heparin disaccharide, indicating that disaccharidic units are the likely sites for binding to the receptor. The receptor has a potential use for creating a colorimetric assay for heparin.

Anticoagulants↗