Exploring in vivo violacein biosynthesis by application of multivariate curve resolution on fused UV–VIS absorption, fluorescence, and liquid chromatography–mass spectrometry data

In this work, the application of multivariate curve resolution-alternating least squares (MCR-ALS) is proposed for extracting information from multitechnique fused multivariate data (UV–VIS absorption, fluorescence, and liquid chromatography–mass spectrometry) gathered during the biosynthesis of violacein pigment. Experimental data sets were pretreated and arranged in a row-wise augmented data matrix before their chemometric investigation. Five different chemical components were resolved. Kinetic and spectral information about these components were obtained and their relationship with violacein biosynthesis was established. Three new chemical compounds with molar masses of 453, 465, and 479 u, until now not reported in the literature, were identified and proposed as intermediates in the biosynthesis of other indolocarbazoles. The precursor (tryptophan), one intermediate (deoxyviolacein), and the final product (violacein) of violacein biosynthesis were identified and characterized using the proposed approach. The chemometric procedure based on the MCR-ALS method has proved to be a powerful tool to investigate violacein biosynthesis and its application can be easily extended to the study of other bioprocesses.     

Ultrafast quantitation of six quinolones in water samples by second-order capillary electrophoresis data modeling with multivariate curve resolution–alternating least squares

This paper presents the development of a capillary electrophoresis method with diode array detector coupled to multivariate curve resolution–alternating least squares (MCR-ALS) to conduct the resolution and quantitation of a mixture of six quinolones in the presence of several unexpected components. Overlapping of time profiles between analytes and water matrix interferences were mathematically solved by data modeling with the well-known MCR-ALS algorithm. With the aim of overcoming the drawback originated by two compounds with similar spectra, a special strategy was implemented to model the complete electropherogram instead of dividing the data in the region as usually performed in previous works. The method was first applied to quantitate analytes in standard mixtures which were randomly prepared in ultrapure water. Then, tap water samples spiked with several interferences were analyzed. Recoveries between 76.7 and 125 % and limits of detection between 5 and 18 μg L^?1 were achieved.     

Liquid chromatographic analysis of Hg(II) binding by thiol-rich peptides using both UV–vis and electrochemical detection

An existing method for HPLC determination of thiol-containing peptides has been successfully adapted to the analysis of mixtures of glutathione (GSH) and some related peptides with their Hg(II) complexes as a first approach to the study of phytochelatin extracts. The separation was achieved in a C18 column with a mobile phase of 0.1% trifluoroacetic acid (TFA) and 0.1% TFA/acetonitrile. Non-derivative UV–vis detection at 202 nm used in the original method has been complemented with amperometric detection at 1.2 V on glassy carbon electrode. Two different Hg(II)–GSH complexes were observed by both detection modes and confirmed by mass spectrometry.     

Determination of nicotine in tobacco with second-order spectra data of charge-transfer complex in ethanol–water binary solvents processed by parallel factor analysis

A new spectrophotometric method for the determination of nicotine in mixtures without pre-separation has been proposed. Nicotine could react with 2,4-dinitrophenol through a charge-transfer reaction to form a colored complex. The second-order data from the visible absorption spectra of the complex in a series of ethanol–water binary solvents with various water volume fractions could be expressed as the combination of two bilinear data matrices. With the bilinear model, the second-order spectra data of mixtures containing nicotine and other interferents could be analysed by using second-order calibration algorithms, and the determination of nicotine in the mixtures could be achieved. The algorithm used here was parallel factor analysis. The method has been successfully used to determine nicotine in tobacco samples with satisfactory results.     

Online UV–visible spectroscopy and multivariate curve resolution as powerful tool for model-free investigation of laccase-catalysed oxidation

The laccase-catalysed transformation of indigo carmine (IC) with and without a redox active mediator was studied using online UV–visible spectroscopy. Deconvolution of the mixture spectra obtained during the reaction was performed on a model-free basis using multivariate curve resolution (MCR). Thereby, the time courses of educts, products, and reaction intermediates involved in the transformation were reconstructed without prior mechanistic assumptions. Furthermore, the spectral signature of a reactive intermediate which could not have been detected by a classical hard-modelling approach was extracted from the chemometric analysis. The findings suggest that the combined use of UV–visible spectroscopy and MCR may lead to unexpectedly deep mechanistic evidence otherwise buried in the experimental data. Thus, although rather an unspecific method, UV–visible spectroscopy can prove useful in the monitoring of chemical reactions when combined with MCR. This offers a wide range of chemists a cheap and readily available, highly sensitive tool for chemical reaction online monitoring.     

Semi-automated alignment and quantification of peaks using parallel factor analysis for comprehensive two-dimensional liquid chromatography–diode array detector data sets

Parallel factor analysis was used to quantify the relative concentrations of peaks within four-way comprehensive two dimensional liquid chromatography–diode array detector data sets. Since parallel factor analysis requires that the retention times of peaks between each injection are reproducible, a semi-automated alignment method was developed that utilizes the spectra of the compounds to independently align the peaks without the need for a reference injection. Peak alignment is achieved by shifting the optimized chromatographic component profiles from a three-way parallel factor analysis model applied to each injection. To ensure accurate shifting, components are matched up based on their spectral signature and the position of the peak in both chromatographic dimensions. The degree of shift, for each peak, is determined by calculating the distance between the median data point of the respective dimension (in either the second or first chromatographic dimension) and the maximum data point of the peak furthest from the median. All peaks that were matched to this peak are then aligned to this common retention data point. Target analyte recoveries for four simulated data sets were within 2% of 100% recovery in all cases. Two different experimental data sets were also evaluated. Precision of quantification of two spectrally similar and partially coeluting peaks present in urine was as good as or better than 4%. Good results were also obtained for a challenging analysis of phenytoin in waste water effluent, where the results of the semi-automated alignment method agreed with the reference LC–LC MS/MS method within the precision of the methods.     

A novel liquid chromatographic method with fluorescence detection for quantitation of tadalafil and dapoxetine hydrochloride in pharmaceutical dosage form and human plasma北大核心CSCD

Tadalafil( TAD)and dapoxetine HCl( DAP)are recently co-formulated and both show native fluo-rescence. Therefore,a novel,accurate,specific and sensitive reversed-phase high performance liquid chroma-tographic method with fluorescence detection was developed and validated for their separation and quantitation in dosage form and human plasma using avanafil as an internal standard( IS). Separation was achieved using isocratic elution within 7. 0 min on C18 column and acetonitrile-0. 15% triethylamine( 40∶60,v/v;pH 4)as a mobile phase. The flow rate was 1. 0 mL/min and the detection was time-programmed at 330,410 and 370 nm for TAD,DAP and IS,respectively,after excitation at 236 nm. The linear ranges from 0. 01 to 30. 00 μg/mL for each drug with the limits of detection of 4. 20 and 7. 20 ng/mL for TAD and DAP,respectively. The method was validated in accordance to the International Conference on Harmonization( ICH)guidelines and was successful-ly applied to spiked human plasma with mean recoveries of 98. 17% and 98. 83% for TAD and DAP respectively.     

FT-MIR and UV–vis data fusion strategy for origins discrimination of wild Paris Polyphylla Smith var. yunnanensis

Paris Polyphylla Smith var. yunnanensis (Franch.) Hand.-Mazz has multiple therapeutic properties and the origins may affect clinical efficacy. Tracing the geographical origin is important to the authentication and quality assessment of this species. 177 wild samples collected from central, southeast and northwest Yunnan Province, China, were analyzed by single analytical method and data fusion strategies (low- and mid-levels) using Fourier transform mid-infrared (FT-MIR) and ultraviolet-visible (UV–vis) spectroscopies combined with chemometrics (partial least squares discrimination analysis (PLS-DA) and support vector machines grid search (SVM-GS)), for categorizing samples from different geographic origins. According to the results, mid-level data fusion strategy presented a better generalization performance and accuracy rates based on latent variables selected by PLS-DA than single analytical method and low-level data fusion strategy. Accuracy rates were almost 100% when both of the PLS-DA and SVM-GS were employed for classifying samples picked from southeast and northwest districts based on mid-level dataset. For samples collected from central of Yunnan where was divided into seven categories in this paper, the accuracy rates of training set and test set of PLS-DA and SVM-GS were preferable (>87%). Based on the mid-level data set, both of the classification results of PLS-DA and SVM-GS presented satisfying accuracy for 177 samples. Additionally, as small as possible parameters showed in mid-level data set, it suggested that this method was robust and generalized. Therefore, the comprehensive method was established for the origin traceability of wild P. Polyphylla Smith var. yunnanensis, which is meaningful for the quality control of herbal medicines.     

Two dimensional assisted liquid chromatography – a chemometric approach to improve accuracy and precision of quantitation in liquid chromatography using 2D separation,dual detectors,and multivariate curve resolution

Comprehensive two-dimensional liquid chromatography (LC × LC) is rapidly evolving as the preferred method for the analysis of complex biological samples owing to its much greater resolving power compared to conventional one-dimensional (1D-LC). While its enhanced resolving power makes this method appealing, it has been shown that the precision of quantitation in LC × LC is generally not as good as that obtained with 1D-LC. The poorer quantitative performance of LC × LC is due to several factors including but not limited to the undersampling of the first dimension and the dilution of analytes during transit from the first dimension (¹D) column to the second dimension (²D) column, and the larger relative background signals. A new strategy, 2D assisted liquid chromatography (2DALC), is presented here. 2DALC makes use of a diode array detector placed at the end of each column, producing both multivariate ¹D and two-dimensional (2D) chromatograms. The increased resolution of the analytes provided by the addition of a second dimension of separation enables the determination of analyte absorbance spectra from the ²D detector signal that are relatively pure and can be used to initiate the treatment of data from the first dimension detector using multivariate curve resolution–alternating least squares (MCR–ALS). In this way, the approach leverages the strengths of both separation methods in a single analysis: the ²D detector data is used to provide relatively pure analyte spectra to the MCR–ALS algorithm, and the final quantitative results are obtained from the resolved ¹D chromatograms, which has a much higher sampling rate and lower background signal than obtained in conventional single detector LC × LC, to obtain accurate and precise quantitative results. It is shown that 2DALC is superior to both single detector selective or comprehensive LC × LC and 1D-LC for quantitation of compounds that appear as severely overlapped peaks in the ¹D chromatogram – this is especially true in the case of untargeted analyses. We also anticipate that 2DALC will provide superior quantitation in targeted analyses in which unknown interfering compounds overlap with the targeted compound(s). When peaks are significantly overlapped in the first dimension, 2DALC can decrease the error of quantitation (i.e., improve the accuracy by up to 14-fold compared to 1D-LC and up to 3.8-fold compared to LC × LC with a single multivariate detector). The degree of improvement in performance varies depending upon the degree of peak overlap in each dimension and the selectivities of the spectra with respect to one another and the background, as well as the extent of analyte dilution prior to the ²D column.     

Quantitative control and identification of copper species in Cu–SAPO-34: a combined UV–vis spectroscopic and H2-TPR analysis

Research on Chemical Intermediates - A series of Cu–SAPO-34 catalysts with different copper contents were prepared using a modified ion-exchange method, i.e., impregnation–activation....     

Rapid and sensitive method for the determination of acetaldehyde in fuel ethanol by high-performance liquid chromatography with UV–Vis detection

A high-performance liquid chromatography (HPLC) method for the determination of acetaldehyde in fuel ethanol was developed. Acetaldehyde was derivatized with 0.900 mL 2,4-dinitrophenylhydrazine (DNPHi) reagent and 50 L phosphoric acid 1 mol L^–1 at a controlled room temperature of 15°C for 20 min. The separation of acetaldehyde-DNPH (ADNPH) was carried out on a Shimadzu Shim-pack C₁₈ column, using methanol/LiCl_(aq) 1.0 mM (80/20, v/v) as a mobile phase under isocratic elution and UV–Vis detection at 365 nm. The standard curve of ADNPH was linear in the range 3–300 mg L^–1 per injection (20 L) and the limit of detection (LOD) for acetaldehyde was 2.03 g L^–1, with a correlation coefficient greater than 0.999 and a precision (relative standard deviation, RSD) of 5.6% (n=5). Recovery studies were performed by fortifying fuel samples with acetaldehyde at various concentrations and the results were in the range 98.7–102%, with a coefficient of variation (CV) from 0.2% to 7.2%. Several fuel samples collected from various gas stations were analyzed and the method was successfully applied to the analysis of acetaldehyde in fuel ethanol samples.     

A strategy for qualitative and quantitative profiling of Angelicae Pubescentis Radix and detection of its analgesic and anti-inflammatory components by spectrum–effect relationship and multivariate statistical analysis

This study established a spectrum–effect relationship method for screening and quantifying the analgesic and anti-inflammatory active ingredients in Angelicae Pubescentis Radix (AP) by ultra-high-performance liquid chromatography–quadrupole mass spectrometry detector analysis (UPLC–QDA). First, the fingerprint of AP was established to determine the common peaks. Next, six batches of AP samples, with significant differences, were selected for evaluation of pharmacological activity. Subsequently, the spectrum–effect relationship was used to screen the active ingredients. Finally, the screened ingredients were quantified using UPLC–QDA. In total, 21 common peaks were identified and four effective compounds (bergapten, columbianetin acetate, osthole and isoimperatorin) were selected using the gray relational analysis and partial least squares regression analysis. Quantitative analysis showed that the content of the four effective compounds was the highest in a randomly selected batch, S7 (Hubei). To our knowledge, this is the first attempt that evaluated the quality and spectrum–effect relationship of AP by quantitative analysis and chemometrics. This study identified the key pharmacologically active components of AP and thereby improved the quality evaluation system of AP. This method has broad application prospects for screening effective components and will be helpful in establishing more reliable, scientific and reasonable quality standards for AP and other traditional Chinese medicines.     

A fluorescence “on–off” sensor for the highly selective and sensitive detection of Cu2+ ion

In an attempt to obtain a model of copper(II) ion-selective sensors, a new 1,8-naphthalimide-based fluorescence chemosensor, N-allylamine-4-[(E)-4-(([2-aminoethyl]imino)methyl) benzene-1,3-diol]-1,8-naphthalimide (NABN), was designed and synthesized. The sensor NABN is fully characterized by melting point analysis, fourier transform infrared spectra, Ultraviolet–visible (UV–vis) spectra, fluorescence spectra, ¹H NMR and ¹³C NMR spectroscopy, and mass spectrometry. NABN showed an unrivaled sensing behavior and an ardent selectivity toward copper(II) ion over other competitive metal ions tested in solution (N,N-Dimethylformamide (DMF)/Tris–HCl buffer, 1:1, v/v, pH = 7.2). The sensor showed a linear fluorescence quenching toward copper(II) ion in the range 0–50 μM, with a detection limit of 1.92 × 10⁻⁷ M estimated. Job's method indicated the formation of a 2:1 coordinative mode of the sensor with copper(II) ion with a high threshold of binding constant of 4 × 10¹² M⁻¹. Combining the above results, the quenching response of NABN toward Cu(II) ions could be ascribed to the strong, intrinsic paramagnetic behavior of Cu(II).     

Rapid gas chromatographic analysis of less abundant compounds in distilled spirits by direct injection with ethanol–water venting and mass spectrometric data deconvolution

The principal trace secondary compounds common to fermentation-derived distilled spirits can be rapidly quantified by directly injecting 5 μL of spirit without sample preparation to a narrow-bore 0.15 mm internal diameter capillary column. The ethanol–water is removed in an initial solvent venting step using a programmed temperature vapourization injector, followed by splitless transfer of the target analytes to the column. The larger injection facilitates trace analysis and ethanol–water removal extends column lifetime. Problems of coelution between analytes or with sample matrix were surmounted by using mass spectral deconvolution software for quantification. All operations in the analysis from injection with solvent venting to data reduction are fully automated for unattended sequential sample analysis. The synergy of the various contributory steps combines to offer an effective novel solution for this analysis. Applications include quantification of low ppm amounts of acids and esters and sub-ppm profiling of trace compounds from both the raw material malt and the ageing in wood barrels.     

A novel fourth-order calibration method based on alternating quinquelinear decomposition algorithm for processing high performance liquid chromatography–diode array detection– kinetic-pH data of naptalam hydrolysis

Five-way high performance liquid chromatography–diode array detection (HPLC–DAD)–kinetic-pH data were obtained by recording the kinetic evolution of HPLC–DAD signals of samples at different pH values and a new fourth-order calibration method, alternating quinquelinear decomposition (AQQLD) based on pseudo-fully stretched matrix forms of the quinquelinear model, was developed. Simulated data were analyzed to investigate the performance of AQQLD in comparison with five-way parallel factor analysis (PARAFAC). The tested results demonstrated that AQQLD has the advantage of faster convergence rate and being insensitive to the excess component number adopted in the model. Then, they have been successfully applied to investigate quantitatively the kinetics of naptalam (NAP) hydrolysis in two practical systems. Additionally, the serious chromatographic peak shifts were accurately corrected by means of chromatographic peak alignment method based on abstract subspace difference. The good recoveries of NAP were obtained in these samples by selecting the time region of chromatogram. The elution time, spectral, kinetic time and pH profiles resolved by the chemometric techniques were in good agreement with experimental observations. It demonstrates the potential for the utilization of fourth-order data for some complex systems, opening up a new approach to fourth-order data generation and subsequent fourth-order calibration.     

High-throughput characterization of sediment organic matter by pyrolysis–gas chromatography/mass spectrometry and multivariate curve resolution: A promising analytical tool in (paleo)limnology

Molecular-level chemical information about organic matter (OM) in sediments helps to establish the sources of OM and the prevalent degradation/diagenetic processes, both essential for understanding the cycling of carbon (C) and of the elements associated with OM (toxic trace metals and nutrients) in lake ecosystems. Ideally, analytical methods for characterizing OM should allow high sample throughput, consume small amounts of sample and yield relevant chemical information, which are essential for multidisciplinary, high-temporal resolution and/or large spatial scale investigations. We have developed a high-throughput analytical method based on pyrolysis–gas chromatography/mass spectrometry and automated data processing to characterize sedimentary OM in sediments. Our method consumes 200 μg of freeze-dried and ground sediment sample. Pyrolysis was performed at 450 °C, which was found to avoid degradation of specific biomarkers (e.g., lignin compounds, fresh carbohydrates/cellulose) compared to 650 °C, which is in the range of temperatures commonly applied for environmental samples. The optimization was conducted using the top ten sediment samples of an annually resolved sediment record (containing 16–18% and 1.3–1.9% of total carbon and nitrogen, respectively). Several hundred pyrolytic compound peaks were detected of which over 200 were identified, which represent different classes of organic compounds (i.e., n-alkanes, n-alkenes, 2-ketones, carboxylic acids, carbohydrates, proteins, other N compounds, (methoxy)phenols, (poly)aromatics, chlorophyll and steroids/hopanoids). Technical reproducibility measured as relative standard deviation of the identified peaks in triplicate analyses was 5.5 ± 4.3%, with 90% of the RSD values within 10% and 98% within 15%. Finally, a multivariate calibration model was calculated between the pyrolytic degradation compounds and the sediment depth (i.e., sediment age), which is a function of degradation processes and changes in OM source type. This allowed validation of the Py–GC/MS dataset against fundamental processes involved in OM cycling in aquatic ecosystems.     

A strategy for the rapid discovery and validation of active diterpenoids as quality markers in different habitats of Langdu using ultrahigh-performance liquid chromatography–tandem mass spectrometry with multivariate statistical analysis

Langdu, known as a traditional Chinese medicine, was identified as the roots of species of Euphorbia ebracteolata Hayata and Euphorbia fischeriana Steud, displaying anti-tuberculosis activity. To clarify the potent quality markers of Langdu, this research first developed a fast and sensitive ultrahigh-performance liquid chromatography–tandem mass spectrometry method for the quantification of 13 diterpenoids in Langdu. The developed method was further applied in the analyses of 12 authentic E. ebracteolata and E. fischeriana samples collected in northern and southeastern China. Then, the anti-tuberculosis evaluation of 12 batches of Langdu samples was performed in vitro. Finally, partial least squares discrimination analysis was used in the discrimination of E. ebracteolata and E. fischeriana from different origins and processing methods. Jolkinolide A ( 1 ), jolkinolide E ( 3 ), yuexiandajisu D ( 6 ), and ebractenone A ( 11 ) were identified as key, potent diterpenoids for the quality control of E. ebracteolata Hayata and E. fischeriana Steud. The present study established a qualitative chemical analysis method for Langdu (E. ebracteolata and E. fischeriana) and suggested the key bioactive components that will improve qualitative control methodology for this important medicine.     

Dispersive liquid–liquid microextraction combined with high-performance liquid chromatography-UV detection as a very simple,rapid and sensitive method for the determination of bisphenol A in water samples

Dispersive liquid–liquid microextraction (DLLME) coupled with high-performance liquid chromatography (HPLC)-UV detection was applied for the extraction and determination of bisphenol A (BPA) in water samples. An appropriate mixture of acetone (disperser solvent) and chloroform (extraction solvent) was injected rapidly into a water sample containing BPA. After extraction, sedimented phase was analyzed by HPLC-UV. Under the optimum conditions (extractant solvent: 142 μL of chloroform, disperser solvent: 2.0 mL of acetone, and without salt addition), the calibration graph was linear in the range of 0.5–100 μg L⁻¹ with the detection limit of 0.07 μg L⁻¹ for BPA. The relative standard deviation (RSD, n = 5) for the extraction and determination of 100 μg L⁻¹ of BPA in the aqueous samples was 6.0%. The results showed that DLLME is a very simple, rapid, sensitive and efficient analytical method for the determination of trace amount of BPA in water samples and suitable results were obtained.     

Growth,geometrical analysis,FMO, MEP UV–vis,nonlinear optical and antibacterial properties of pure and 2-furoic acid doped Guanidinium carbonate single crystal

In the presence of distilled water, the adaption of the slow evaporation solution growth approach resulted in the successful development of single crystals of Pure and doped GC (FAGC). The cell characteristics of the produced FAGC crystals were investigated using single-crystal X-ray diffraction analysis. The theoretical analysis was carried out using the DFT method, and the HOMO-LUMO energy band difference was estimated. The Molecular optimized geometry, MEP and HOMO-LUMO energy distance were computed using the B3LYP level of theory using a 6-31G (d,p) basis set. The FT-IR spectrum probes the modes of vibration of various functional groups in pure and doped GC (FAGC) crystals. According to UV–visible NIR transmittance experiments, the formed crystal exhibits a high transmittance in the whole visible range. The relative SHG efficiency of pure and doped crystals (FAGC) was carried out by the Kurtz perry technique. The Antibacterial activity demonstrates that both the pure and the dopant have antibacterial action against dangerous microorganisms.     

Rhodium-catalyzed cyclopropanations of 2-aryl-2H-chromenes with dialkyl malonate esters. A comparison of α-diazo derivatives and phenyliodonium ylides

Rhodium-catalyzed reactions of 2-aryl-substituted 2H-chromenes with α-diazo esters prepared from dimethyl and tert-butyl methyl malonates were investigated, and the results were compared with reactions carried out with phenyliodonium ylides prepared from the same esters. The phenyliodonium ylide prepared from dimethyl malonate was found to give superior yields of cyclopropane products compared to the corresponding α-diazo equivalent. However, this result was reversed with tert-butyl methyl malonate when Rh₂(S-TBSP)₄ was used to decompose the diazo compound. All reactions gave 1,1-cyclopropane diesters as single diastereomers.