Chelerythrine (CH) and ethoxychelerythrine (ECH) are chemical reference substances for quality control of Chinese herbal medicines, and ECH is the dihydrogen derivative of CH. In this study, their ...fluorescence and absorption spectra, as well as their structural changes in different protic solvents were compared. It was observed that their emission fluorescence spectra in methanol were almost the same (both emitted at 400 nm), which may be attributed to the nucleophilic and exchange reactions of CH and ECH with methanol molecules with the common product of 6-methoxy-5,6-dihydrochelerythrine (MCH). When diluted with water, MCH was converted into CH, which mainly existed in the form of positively charged CH+ under acidic and near-neutral conditions with the fluorescence emission at 550 nm. With the increase of pH value of the aqueous solution, CH+ converted to 6-hydroxy-5,6-dihydrochelerythrine (CHOH) with the fluorescence emission at 410 nm. The fluorescence quantum yields of MCH and CHOH were 0.13 and 0.15, respectively, and both the fluorescence intensities were much stronger than that of CH+. It is concluded that CH and ECH can substitute each other in the same protic solvent, which was further verified by high-performance liquid chromatography. This study will help in the investigation of structural changes of benzophenanthridine alkaloids and will provide the possibility for the mutual substitution of standard substances in relevant drug testing.
In this work, the origins for the spectral difference between two isoflavones, formononetin (F) and ononin (FG), are revealed via a comparison study of the fluorescence molecular structure. The ...fluorescence enhancement of FG in hot alkaline conditions is reported for the first time. For F, there is almost no fluorescence under acidic conditions, but when the pH is >4.8, its fluorescence begins to increase due to the deprotonation of 7-OH. Under a pH between 9.3 and 12.0, the anionic form of F produces a strong and stable fluorescence. The fluorescence quantum yield (Yf) of F is measured to be 0.042. FG shows only weak fluorescence in aqueous solutions under a wide range of pH until it is placed in hot alkaline solutions, which is attributed to the cleavage reaction of the γ-pyrone ring in FG. The Yf of FG is determined to be 0.020. Based on the fluorescence sensitization methods of F and FG, the quantitative analysis and detection of two substances can be realized. The limit of the detections for F and FG are 2.60 ng·mL
and 9.30 ng·mL
, respectively. The linear detection ranges of F and FG are 11.7~1860 ng·mL
and 14.6~2920 ng·mL
, respectively. Although the structural relationship between F and FG is glycoside and aglycone, under hot alkaline conditions, the final products after the cleavage and hydrolysis reactions are essentially different. The different fluorescence characteristics between F and FG pave a way for further identification and a quantitative analysis of the corresponding components in Chinese herbal medicine.
HPLC-FTIR analysis using a novel apparatus with CuO powder as an interface is reported. This apparatus initially serves as a reservoir for the dilute eluted solution of HPLC, and then acts as an ...enrichment device by combining diffusion and evaporation processes. It can be used not only to effectively remove the mobile phase of the eluted solution, but also to enrich the analyte within a tiny spatially resolved separated sample spot whose size is suitable for obtaining spectra using an FTIR microscope. An experimental demonstration using benzamide and sodium dodecyl benzene sulfonate shows that this apparatus is readily applicable in the analysis of real-world mixture samples.
A simple, low toxic, sensitive strategy based on the localized surface plasmon resonance light scattering (LSPR-LS) properties of silver nanoparticles (AgNPs) is introduced for the detection of ...gallic acid (GA). It was found that the silver ammonium complex, Ag(NH3)2+(aq), could be reduced in the alkaline medium by GA at room temperature; this reaction formed dispersed AgNPs. Transmission electron microscopy analyses were performed to ascertain the formation of AgNPs. UV-visible spectra revealed the localized surface plasmon resonance (LSPR) absorption at 410 nm corresponding to the LSPR of AgNPs. On these basis, we could quantify the GA concentration in the range of 4 × 10−7 – 5 × 10−6 mol L−1 in the optimized experimental conditions. This method was used for determining the concentration of GA in artificial samples with satisfactory results. The detailed mechanism underlying this special phenomenon was elucidated.
The localized surface plasmon resonance light scattering (LSPR-LS) of the silver nanoparticles (AgNPs) formed through the modified “silver mirror reaction” is given, which can serve as the strategy ...for the detection of hydroquinone (HQ) in tap water. The inserted is the TEM image of the formed AgNPs.
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► This is the first report on the determination of Hydroquinone by LSPR-LS. ► The assay is based on LSPR-LS of the formed AgNPs via the modified mirror reaction. ► The formed AgNPs are characterized by TEM, UV–vis and LS, respectively. ► The mechanism for the reaction system is proposed. ► A method for the determination of Hydroquinone in tap water samples was established.
In this contribution, a simple strategy for the detection of hydroquinone (HQ) is proposed based on the localized surface plasmon resonance light scattering (LSPR-LS) of the silver nanoparticles (AgNPs) formed through the modified silver mirror reaction. The redox reaction between HQ and silver ammonia occurred in the coexistence of sodium hydroxide and ammonia at room temperature, where silver ammonia was reduced by HQ and resulted in the formation of AgNPs without adding the AgNPs seeds. The formed AgNPs were demonstrated to be monodisperse and uniform by transmission electron microscopy (TEM) image. We also studied the localized surface plasmon resonance absorption (LSPR-A) and LSPR-LS spectra using both a UV–vis spectrophotometer and a common spectrofluorometer, and obtained a good agreement between experiments. By carefully optimizing the amount of NaOH and ammonia of the reaction conditions, we were able to obtain the highest net intensity of LSPR-LS on the concentrations of HQ. On the basis of experimental studies, the LSPR-LS intensity enhanced linearly over the range 0.4–2.5
μmol
L
−1 with the corresponding limits of determination (3
σ) of 70.6
nmol
L
−1. With that, the present approach was applied to detect HQ in water samples with satisfactory results.
► A modified reference spectrum is used to construct 2D asynchronous spectra. ► Computer simulation show intensities and s/n ratio of cross peaks are improved. ► Experiments on real chemical system ...show intensities of cross peaks are enhanced.
In this paper, a modified reference spectrum is utilized to generate 2D asynchronous spectra constructed by using the AOSD approach that is developed in our previous work. Mathematical analysis suggests that it is possible to enhance the intensity of cross peaks by using the modified reference spectrum. Computer simulation indicates that both intensity of cross peaks and signal-to-noise ratio of 2D spectra are improved significantly by adopting the modified reference spectrum. As a result, 2D asynchronous spectrum can be used to probe weak intermolecular interactions under the influence of spectral noise. Furthermore, experiments on acetonitrile/butanone/CCl4 system demonstrate that intensities and signal-to-noise ratio of cross peaks that reflect intermolecular interactions between acetonitrile and butanone can be enhanced remarkably by using the modified reference spectrum.
The influence of the sequence of the concentration series is investigated on the 2D asynchronous spectra generated by the asynchronous orthogonal sample design (AOSD) approach. We prove that the ...requirement of the AOSD is also satisfied when the sequence of the concentration series changes, if the initial concentration series satisfies the requirement of the AOSD. Changing the sequence of concentration series produces the same absolute intensity of the 2D asynchronous spectra when only three solutions are used. However, different outcomes can be gained when four solutions are adopted. Studies on a real chemical system indicate that the sensitivity of the cross peak from asynchronous spectra can be improved significantly when the suitable sequence of concentration series is adopted.
Fluorescence spectra of hymecromone (4MU) aqueous solutions are investigated at different pHs. Two fluorescent species of 4MU, neutral molecular form and anion form, are considered to be the main ...fluorescent forms. Quantum yields of the two forms are measured to be 0.74 at pH 5.98 and 0.95 at pH 9.75, respectively. The ionization constant of 7-hydroxyl proton of 4MU is determined to be pKa=7.85±0.03 by a pH-fluorescence method. Addition of methanol into 4MU aqueous solution leads to a blue shift of maximum emission wavelength from 445 nm to 380 nm, and a decrease in fluorescence intensity. 3D fluorescence spectra of Chinese patent drug Compound Dantong Capsule (CDC) and its four component herbal drugs are also investigated. Based on their fluorescent properties, a novel fluorimetric method is proposed for the selective determination of 4MU in CDC without preseparation. The new method is suitable for the routine quality evaluation of CDC.
A novel fluorimetric method for determination of paeonol, an active component of Chinese herbal medicine, is proposed. The method is based on the reaction of paeonol with aluminum ion in pH 4.4 ...HAc-NaAc buffer to form a fluorescent Al(III)-paeonol complex. The maximum excitation wavelength and emission wavelength of the complex were 296 nm and 455 nm, respectively. The fluorescence quantum yield of the complex was determined to be 0.053 at an excitation wavelength of 296 nm. A linear calibration curve covered the concentration range 0.017–1.2 μg/mL. The method has been applied to the analysis of paeonol in medicinal crop Cynanchi Paniculati Radix (Xuchangqing), and the results demonstrated that this method can be used for quality evaluation of crude drug Xuchangqing.
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