RESUMO
Electrochemiluminescence (ECL), integrating the characteristics of electrochemistry and fluorescence, has the advantages of high sensitivity and low background. However, only a few studies have been reported for enantioselective sensing based on the ECL-active platform because of the huge challenges in constructing tunable chiral ECL luminophores. Here, we developed a facile strategy to design and prepare ECL-active chiral covalent organic frameworks (COFs) Ph-triPy+-(R)-Ru(II) for enantioselective sensing. In such an artificial structure, the ionic skeleton of COFs was beneficial to the electron transfer on the working electrode surface and the chiral Ru-ligand was used as the chiral ECL-active luminophore. It was found that Ph-triPy+-(R)-Ru(II) coupled with sodium persulfate (Na2S2O8) as the coreactant exhibited obvious ECL signals. More importantly, a clear difference toward l- and d-enantiomers was observed in the response of the ECL intensity, resulting in a uniform recognition law. That is, for amino alcohols, d-enantiomers (1 mM) measured by Ph-triPy+-(R)-Ru(II) showed a higher ECL intensity compared with l-enantiomers. Differently, amino acids (1 mM) gave an inverse recognition phenomenon. The ECL intensity ratios between l- and d-enantiomers (1 mM) are in the range of 1.25-1.94 for serine, aspartic acid, glutamic acid, valine, leucine, leucinol, and valinol. What is more interesting is that the ECL intensity was closely related to the concentration of l-amino alcohols and d-amino acids, whereas their inverse configurations remained unchanged. In a word, the present concept demonstrates a feasible direction toward chiral ECL-active COFs and their potential for efficient enantioselective sensing.
RESUMO
To date, achieving enantioselective electroanalysis for electrochemically silent chiral molecules is still highly desired. Here, an ionic covalent organic framework (COF) consisting of the pyridinium cation was derived from the tripyridinium Zincke salt and 1,4-phenylenediamine in a one-pot reaction. The electrochemical measurements revealed that the ionic backbone contributed to the electron transfer with a low charge transfer resistance. Besides, the π-π+ interaction between the pyridinium cation and ferrocenyl unit can promote the absorption of electroactive chiral ferrocenyl reagents into the hole of COF, so as to afford the electrochemical signals by themselves, replacing the testing enantiomers. As a result, the electroactive complex used as an electrochemical platform was highly effective at enantiomerically recognizing amino alcohols (prolinol, valinol, leucinol, and alaninol) and amino acids (methionine, serine, and penicillamine), giving the ratios of current intensity between l- and d-enantiomers in the range of 1.46-1.72. Moreover, the density functional theory calculations determined the possible intermolecular interactions between the testing enantiomers and chiral selector: namely, hydrogen bonds and electrostatic attractions. Overall, the present work offers an effective strategy to enlarge the electrochemical scope for chiral recognition based on electroactive chiral COFs.
RESUMO
Although electroactive chiral covalent-organic frameworks (CCOFs) are considered an ideal platform for chiral electroanalysis, they are rarely reported due to the difficult selection of suitable precursors. Here, a facile strategy of liquid-liquid interfacial polymerization was carried out to synthesize the target electroactive CCOFs Ph-Py+-(S,S)-DPEA·PF6- and Ph-Py+-(R,R)-DPEA·PF6-. That is, a trivalent Zincke salt (4,4',4â³-(benzene-1,3,5-triyl)tris(1-(2,4-dinitrophenyl)pyridin-1-ium)) trichloride (Ph-Py+-NO2) and enantiopure 1,2-diphenylethylenediamine (DPEA) were dissolved in water and chloroform, respectively. The Zincke reaction occurs at the interface, resulting in uniform porosity. As expected, the cyclic voltammetry and differential pulse voltammetry measurements showed that the tripyridinium units of the CCOFs afforded obvious electrochemical responses. When Ph-Py+-(S,S)-DPEA·PF6- was modified onto the surface of a glassy carbon electrode as a chiral sensor, the molecules, which included tryptophan, aspartic acid, serine, tyrosine, glutamic acid, mandelic acid, and malic acid, were enantioselectively recognized in the response of the peak current. Very importantly, the discriminative electrochemical signals were derived from Ph-Py+-(S,S)-DPEA·PF6-. The best peak current ratios between l- and d-enantiomers were in the range of 1.31-2.68. Besides, a good linear relationship between peak currents and enantiomeric excess (ee) values was established, which was successfully harnessed to determine the ee values for unknown samples. In a word, the current work provides new insight and potential of electroactive CCOFs for enantioselective sensing in a broad range.
RESUMO
A chiral metal-organic framework (CMOF) was synthesized by introducing L-histidine (L-His) to zeolitic imidazolate framework-8 (ZIF-8) and then grafting with carboxymethyl-ß-cyclodextrin (CM-ß-CD). Compared with L-His-ZIF-8, the CM-ß-CD-functionalized L-His-ZIF-8 (L-His-ZIF-8-CD) showed significantly enhanced discrimination ability for the tryptophan (Trp) enantiomers owing to the inherent chirality of CM-ß-CD. The specificity of the chiral interface was also studied, and the results indicated that the discrimination ability for Trp enantiomers is significantly stronger than that for the enantiomers of cysteine (Cys) and tyrosine (Tyr), which might be due to the better matching between the indole ring of Trp and the chiral cavity of CM-ß-CD.
RESUMO
Efficient discrimination of amino acids (AAs) isomers is of significant importance for life science and analytical chemistry. Here, a dual-mode chiral discrimination strategy is proposed for visual and electrochemical chiral discrimination of tryptophan (Trp) isomers. Shikimic acid chiral ionic liquids (SCIL) is coordinated with copper ions (Cu2+), and the obtained SCIL-Cu2+ can form ternary complexes with the Trp isomers. Owing to the inherent chirality of SCIL and the reverse homochirality of L-Trp and D-Trp, the ternary complex of SCIL-Cu-D-Trp has higher stability than SCIL-Cu-L-Trp, as revealed by the calculated stability constants (K) and changes in Gibbs free energy (ΔG). The difference in the stability can be utilized for the chiral discrimination of L-Trp and D-Trp, resulting in discernible differences in colors and the electrochemical signals of the Trp isomers. Besides Trp, the isomers of phenylalanine (Phe) can also be discriminated by the proposed dual-mode chiral discrimination strategy with the SCIL-Cu2+ complex.
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Although several studies related with the electrochemiluminescence (ECL) technique have been reported for chiral discrimination, it still has to face some limitations, namely, complex synthetic pathways and a relatively low recognition efficiency. Herein, this study introduces a facile strategy for the synthesis of ECL-active chiral covalent organic frameworks (COFs) employed as a chiral recognition platform. In this artificial structure, ruthenium(II) coordinated with the dipyridyl unit of the COF and enantiopure cyclohexane-1,2-diamine was harnessed as the ECL-active unit, which gave strong ECL emission in the presence of the coreactant reagent (K2S2O8). When the as-prepared COF was used as a chiral ECL-active platform, clear discrimination was observed in the response of the ECL intensity toward l- and d-enantiomers of amino acids, including tryptophan, leucine, methionine, threonine, and histidine. The biggest ratio of the ECL intensity between different configurations was up to 1.75. More importantly, a good linear relationship between the enantiomeric composition and the ECL intensity was established, which was successfully employed to determine the unknown enantiomeric compositions of the real samples. In brief, we believe that the proposed ECL-based chiral platform provides an important reference for the determination of the configuration and enantiomeric compositions.
Assuntos
Técnicas Biossensoriais , Estruturas Metalorgânicas , Aminoácidos , Medições Luminescentes/métodos , Estereoisomerismo , Metionina , Técnicas Biossensoriais/métodos , Técnicas Eletroquímicas/métodosRESUMO
Chiral analysis with simple devices is of great importance for analytical chemistry. Based on the photothermal (PT) effect, a simple chiral sensor with a portable laser device as the light source and a thermometer as the detection tool was developed for the chiral recognition of tryptophan (Trp) isomers and the sensitive sensing of one isomer (L-Trp). Gold nanorods (GNRs), which have outstanding photo-thermal conversion ability due to their localized surface plasma resonance (LSPR) effect, are used as PT reagents, and biomacromolecules bovine serum albumin (BSA) are used as natural chiral sources, and thus, GNRs@BSA was obtained through Au-S bonds. The resultant GNRs@BSA displays higher affinity toward L-Trp than D-Trp owing to the inherent chirality of BSA. Under the irradiation of near-infrared (NIR) light, the temperature of GNRs@BSA//L-Trp is greatly lower than that of GNRs@BSA//D-Trp due to its greatly decreased thermal conductivity, and thus chiral discrimination of Trp isomers can be achieved. In addition, the developed PT effect-based chiral sensor can be used for sensitive detection of L-Trp, and the linear range and limit of detection (LOD) are 1 µM-10 mM and 0.43 µM, respectively.
Assuntos
Ouro , Limite de Detecção , Nanotubos , Soroalbumina Bovina , Triptofano , Ouro/química , Soroalbumina Bovina/química , Nanotubos/química , Triptofano/análise , Triptofano/química , Estereoisomerismo , Bovinos , Animais , Temperatura , Espectrometria de FluorescênciaRESUMO
This study reports an imaging method for gigahertz surface acoustic waves in transparent layers using infrared subpicosecond laser pulses in the ablation regime and an optical pump-probe technique. The reflectivity modulations due to the photoelastic effect of generated multimodal surface acoustic waves were imaged by an sCMOS camera illuminated by the time-delayed, frequency-doubled probe pulses. Moving the delay time between 6 . 0 n s to 11 . 5 n s , image stacks of wave field propagation were created. Two representative samples were investigated: wafers of isotropic fused silica and anisotropic x-cut quartz. Rayleigh (SAW) and longitudinal dominant high-velocity pseudo-surface acoustic wave (HVPSAW) modes could be observed and tracked along a circular grid around the excitation center, allowing the extraction of angular profiles of the propagation velocity. In quartz, the folding of a PSAW was observed. A finite element simulation was developed to predict the measurement results. The simulation and measurement were in good agreement with a relative error of 2 % to 5 %. These results show the potential for fast and full-field imaging of laser-generated ultrasonic surface wave modes, which can be utilized for the characterization of thin transparent samples such as semiconductor wafers or optical crystals in the gigahertz frequency range.