Yintang Zhang

On the Origin of the Relative Stability of Wells–Dawson Isomers: A DFT Study of α-, β-, γ-, α*-, β*-, and γ*-[(PO4)2W18O54]6– Anions

Density functional theory calculations have been carried out to investigate α-, β-, γ-, α*-, β*-, and γ*-[(PO(4))(2)W(18)O(54)](6-) Wells-Dawson isomers, which exhibited stability in the order of α > β > γ > γ* > β* > α*, reproduced the experimental observations (α > β > γ), and confirmed the hypothesis of Contant and Thouvenot (γ* > β* > α*). Energy decomposition analysis reveals that both the spatial arrangement of the host W(18)O(54) cage (eclipsed or staggered) and its structural distortion induced by the encapsulated guest anions are two dominant factors in control of the stability order, while the influences of host-guest interaction and distortion of the guest anions are very small. A building block decomposition approach is designed and provides an effective means to clarify the detailed relationship between the local distortion and energy. By using this method, it is found that the eclipsed belt, and in particular the staggered belt, significantly distort the two caps inside the Wells-Dawson structure. Notably, there is a direct relationship between the overall stability and distortion in the belts, which is proven to be partly originating from the dominance in the quantity of the belt building blocks over that of the caps (12:6). Besides, half-unit {XW(9)} decomposition confirms that [(XO(4))(2)W(18)O(54)](n-) (X = Si, Ge, Al, and Ga) are thermodynamically instable because of the notable electrostatic repulsion between two {XW(9)} units induced by the highly charged guest anions.

On the Origin of the Inverted Stability Order of the Reverse-Keggin [(MnO4)(CH3)12Sb12O24]6−: A DFT Study of α, β, γ, δ, and ε Isomers

Density functional theory calculations have been carried out to investigate the alpha, beta, gamma, delta, and epsilon isomers of [(MnO(4))Me(12)Sb(12)O(24)](6-) (Me = CH(3)) anions, which are simplified Baker-Figgis models of Keggin-type antimonate complexes in experiments. It is found that the stability order of the five isomers (alpha < beta < gamma < delta < epsilon) perfectly reverses to the well-known trend of the classical Keggin [PW(12)O(40)](3-) anions (alpha > beta > gamma > delta > epsilon), despite their significant similarities in frameworks. On the basis of the building block decomposition method, the stabilizing effect of the edge-sharing [Sb(2)(mu-O)(2)Me(2)] fragment inside gamma, delta, and epsilon structures is confirmed and found to originate from its two energy-favorable components rather than itself as an indivisible unit. Similar behavior is also held by the destabilizing [W(2)(mu-O)(2)O(2)] fragment in [PW(12)O(40)](3-); however, the well-accepted electrostatic repulsion between the short W(VI)-W(VI) contacts cannot be taken as direct evidence. Notably, in the assembly of the [(MnO(4))Me(12)Sb(12)O(24)](6-) structure, all of the octahedral building units incline to compress axially and elongate horizontally, and this is exactly opposite to the deformation pattern observed in the building blocks of Keggin tungstates, which tend to elongate axially and compress horizontally, thus giving rise to the inverted stability order. Furthermore, energy decomposition analysis reveals that the intrinsic property of the anion comes from the spatial arrangements of the metal-oxygen cage and does not change significantly with the type and charge of the encapsulated anion.

A highly selective long-wavelength fluorescent probe for hydrazine and its application in living cell imaging

A highly selective long-wavelength turn-on fluorescent probe has been developed for the detection of N2H4. The probe was prepared by conjugation the tricyanofuran-based D-π-A system with a recognizing moiety of acetyl group. In the presence of N2H4, the probe can be effectively hydrazinolysized and produce a turn-on fluorescent emission at 610nm as well as a large red-shift in the absorption spectrum corresponding to a color change from yellow to blue. The sensing mechanism was confirmed by HPLC, MS, UV-vis, emission spectroscopic and theoretical calculation studies. The probe displayed high selectivity and sensitivity for N2H4 with a LOD (limit of detection) of 0.16μM. Moreover, the probe was successfully utilized for the detection of hydrazine in living cells.

Naked-eye detection of Cys using simple molecular systems of curcumin and Hg2+

A sensing ensemble for cysteine was assembled conveniently by simply mixing curcumin (Cur) and Hg2+ in buffered acetonitrile/HEPES (10 mM, 7/3, v/v, pH 7.4) solutions. In the ensemble, Hg2+ serves as the receptor, and Cur functions as the indicator in sensing the analyte. The detection can be performed either spectroscopically, by the decrease of the UV-Vis absorbance at 430 nm and the increase of the UV-Vis absorbance at 355 nm, or visually by the color change from colorless to yellow upon addition of an aqueous solution of the analyte to the solution of the ensemble.

A highly selective and ratiometric fluorescent probe for cyanide by rationally altering the susceptible H-atom

A highly selective and ratiometric fluorescent probe for cyanide was rationally designed and synthesized. The probe comprises a fluorophore unit of naphthalimide and a CN- acceptor of methylated trifluoroacetamide group. For these previous reported trifluoroacetamide derivative-based cyanide chemosensors, the H-atom of amide adjacent to trifluoroacetyl group is susceptible to be attacked by various anions (CN- itself, F-, AcO-, et al.) and even the solvent molecule, which resulted in the bewildered reaction mechanism and poor selectivity of the assay. In this work, the susceptible H-atom of trifluoroacetamide was artfully substituted by alkyl group. Thus a highly specific fluorescent probe was developed for cyanide sensing. Upon the nucleophilic addition of cyanide anion to the carbonyl of trifluoroacetamide moiety of the probe, the ICT process of the probe was significantly enhanced and leading to a remarkable red shift in both absorption and emission spectra of the probe. This fluorescent assay showed a linear range of 1.0-80.0µM and a LOD (limit of detection) of 0.23µM. All the investigated interference have no influence on the sensing behavior of the probe toward cyanide. Moreover, by coating on TLC plate, the probe can be utilized for practical detection of trace cyanide in water samples.

A sensitive gold nanoparticle-based aptasensor for colorimetric detection of Aβ1–40 oligomers

In this work, a gold nanoparticle-based label-free homogeneous phase colorimetric bioassay was developed for the detection of Aβ1–40 oligomers (AβO), important biomarkers for diagnosis and monitoring progression of Alzheimers disease (AD). The prepared AβO-aptamer decorated AuNPs tended to aggregate in a solution with high concentrations of salt, and displayed a purple color with a maximum absorption peak at 650 nm, a characteristic absorption of aggregated AuNPs. In the presence of AβO, the specific binding of the target with the aptamer generated folded aptamer structures, which can stabilize AuNPs towards the salt-induced aggregation more effectively than AuNPs stabilized by the aptamer alone, and thus achieved a hypsochromic shift in the absorption spectra. On the basis of this sensitive spectral transformation, the proposed aptasensor was successfully applied for the detection of AβO with a dynamic range of 1–600 nM and a low detection limit of 0.56 nM. The reliability and practicality of this aptasensor was demonstrated by analysis of AβO in artificial cerebrospinal fluid (aCSF). We anticipate that the proposed facile colorimetric assay for AβO will provide applicable information for early diagnosis of AD.

Recent progress in the development of fluorescent probes for hydrazine

Hydrazine (N2 H4 ) is an important and commonly used chemical reagent for the preparation of textile dyes, pharmaceuticals, pesticides and so on. Despite its widespread industrial applications, hydrazine is highly toxic and exposure to this chemical can cause many symptoms and severe damage to the liver, kidneys, and central nervous system. As a consequence, many efforts have been devoted to the development of fluorescent probes for the selective sensing and/or imaging of N2 H4 . Although great efforts have been devoted in this area, the large number of important recent studies have not yet been systematically discussed in a review format so far. In this review, we have summarized the recently reported fluorescent N2 H4 probes, which are classified into several categories on the basis of the recognition moieties. Moreover, the sensing mechanism and probes designing strategy are also comprehensively discussed on aspects of the unique chemical characteristics of N2 H4 and the structures and spectral properties of fluorophores.