Direct determination of sulfite in food samples by a biosensor based on plant tissue homogenate

In the work described here, a biosensor was developed for the determination of sulfite in food. Malva vulgaris tissue homogenate containing sulfite oxidase enzyme was used as the biological material. M. vulgaris tissue homogenate was crosslinked with gelatin using glutaraldehyde and fixed on a pretreated Teflon membrane. Sulfite was enzymatically converted to sulfate in the presence of the dissolved oxygen, which was monitored amperometrically. Sulfite determination was carried out by standard curves, which were obtained by the measurement of consumed oxygen level related to sulfite concentration. Several operational parameters had been investigated: the amounts of plant tissue homogenate and gelatin, percentage of glutaraldehyde, optimum pH and temperature. Also, some characterization studies were done. There was linearity in the range between 0.2 and 1.8 mM at 35 °C and pH 7.5. The results of real sample analysis obtained with the biosensor agreed well with the enzymatic reference method using spectrophotometric detection.     

Syntheses of (±)-17α- and (±)-17β-hydroxytacamonine; determination of configuration at C-17

Both (±)-17α-hydroxytacamonine (3) and its 17β-isomer (4) were synthesized in two steps (one-pot) from aldehyde mixture 5/6 via the cyanohydrin reaction. NMR spectral characterization of isomer 3 revealed it to be unidentical with natural 17-hydroxytacamonine, whereas spectral data of isomer 4 were in agreement with those published for the natural isomer. The configuration at C-17 was confirmed by NOE difference spectroscopy.     

New liquid chromatographic-chemometric approach for the determination of sunset yellow and tartrazine in commercial preparation

A new liquid chromatographic (LC)-chemometric approach was developed for the determination of sunset yellow (SUN) and tartrazine (TAR) in commercial preparations. This approach uses LC and chemometric calibration methods, i.e., classical least-squares (CLS), principal component regression (PCR), and partial-least squares (PLS), simultaneously. The combined LC-chemometric approaches, denoted as LC-CLS, LC-PCR, and LC-PLS, are based on photodiode array (PDA) detection at multiple wavelengths. Optimum chromatographic separation of SUN and TAR with allura red as the internal standard (IS) was obtained by using a Waters Symmetry C18 column, 5 microm, 4.6 x 250 mm, and 0.2 M acetate buffer (pH 5)-acetonitrile-methano-bidistilled water (55 + 20 + 15 + 10, v/v) as the mobile phase at a flow rate of 1.9 mL/min. The LC data sets consisting of the ratios of analyte peak areas to the IS peak area were obtained by using PDA detection at 5 wavelengths (465, 470, 475, 480, and 485 nm). LC-chemometric calibrations for SUN and TAR were separately constructed by using the relationship between the peak-area ratio and the training sets for each colorant. LC-chemometric approaches were tested for different synthetic mixtures containing SUN and TAR in the presence of the IS. These LC-chemometric calibrations were applied to a commercial preparation of the 2 colorants. The experimental results of the LC-chemometric approaches were compared with those obtained by a developed classical LC method using single-wavelength detection.     

Multicomponent quantitative resolution of binary mixtures by using continuous wavelet transform

Continuous 1-dimensional wavelet transform (WT) was applied to the quantitative analysis of a vitamin combination of thiamine hydrochloride (THI) and pyridoxine hydrochloride (PYR) with strongly overlapping signals. Absorbance data from the UV-Vis absorption spectrum of width 1150 were subjected to Gauss1 and Gauss2 WTs. Because of its flexibility, data processing, and its high signal amplitude, the continuous WT method is a powerful tool for analysis of multicomponent mixtures. By measuring the amplitude signals corresponding to the selected zero-crossing points of the transformed signal, we obtained the calibration curve. The validation of the calibration graphs was confirmed with different mixtures of THI and PYR at various concentration ratios. A brief explanation of the continuous wavelet method is given. MATLAB 6.5 software was used to perform the calculations. The results of our study were compared with those obtained by spectroscopic, chemometric, and liquid chromatographic methods, and good agreement was found.     

Aldehyde Intermediates in the Synthesis of Tacamine-Type Indole Alkaloids: Preparation of (±)-apotacamine

The synthesis of aldehyde intermediates suitable for the preparation of indole alkaloids of the tacamine ( 1 ) type is described. The four possible aldehydes 4–7 were prepared from methyl 5-ethylnicotinate ( 8 ) in a few simple steps using a base-catalyzed epimerization as the final step (Schemes 1 and 2). The key aldehyde 4 , which is an analogue of the important vincamine intermediate 3 (‘Oppolzer's aldehyde’), was finally converted into the indole alkaloid (±)-apotacamine ( 21 ).     

A novel biosensor for specific determination of hydrogen peroxide: catalase enzyme electrode based on dissolved oxygen probe

A biosensor for the specific determination of hydrogen peroxide was developed using catalase (EC 1.11.1.6) in combination with a dissolved oxygen probe. Catalase was immobilized with gelatin by means of glutaraldehyde and fixed on a pretreated teflon membrane served as enzyme electrode. The electrode response was maximum when 50 mM phosphate buffer was used at pH 7.0 and at 35 degrees C. The biosensor response depends linearly on hydrogen peroxide concentration between 1.0x10(-5) and 3.0x10(-3) M with a response time of 30 s. The sensor is stable for >3 months so in this period >400 assays can be performed.     

The Color Reaction of Mercury(II) with the New Reagent 2-Methylthiophenyldiazoaminoazobenzene and Its Application

A new and very sensitive and selective chromogenic reagent, 2-methylthiophenyldiazoaminoa-zobenzene (MTDAA), was synthesized and studied in detail for the determination of trace mercury(II) in water samples. The method is based on the color reaction between MTDAA and mercury(II). It was found that mercury(II) reacts with MTDAA in Na₂B₄O₇-NaOH buffer solution (pH = 10.0) to form 1 : 2 red complexes; these show maximum absorption at 520 nm. Beer’s law is obeyed in 0–15 µg of mercury(II) in 25 mL of solution. The apparent molar absorptivity of the complex is 1.33 × 10⁵ L/(mol cm); its limit of quantification, limit of detection, and relative standard deviation are 0.75 ng/mL, 0.27 ng/mL, and 1.0%, respectively, giving better sensitivity. The influence of the reaction variables and the effect of interfering ions are reported; most of the metal ions in water samples can be tolerated in considerable amounts. Only a few ions can interfere with the determination of trace mercury(II), but these can be eliminated by prior extraction. The proposed method is sensitive, simple, and rapid. It has been applied to the determination of trace mercury(II) in water samples with satisfactory results.__________From Zhurnal Analiticheskoi Khimii, Vol. 60, No. 7, 2005, pp. 703–706.Original English Text Copyright © 2005 by Guo, Din, Tian, Liu, Chang, Meng.The text was submitted by the authors in English.     

Studies with enaminones: The reaction of enaminones with aminoheterocycles. A route to azolopyrimidines,azolopyridines and quinolines

The enaminones 1b,d,f react with 4‐phenyl‐3‐methyl‐5‐pyrazoleamine 3a to yield the pyrazole derivatives 4a‐c that cyclised readily on reflux in pyridine solution in presence of hydrochloric acid to yield the pyrazolo[1,5‐a]pyrimidines 5a‐c. Similarly 3(5)‐amino‐1H‐triazole (3b) reacted with 1b,d,f to yield the triazolo[1,5‐a]pyrimidines 5d‐f. In contrast attempted condensation of the 5‐tetrazoloamine (3c) with 1a,d,e resulted in its trimerisation and only triaroylbenzene 8a,d,e was isolated. The reaction of 1a,b,d with anthranilonitrile 9a and the reaction of 1a‐c with the 2‐aminocyclohexene thiophene‐3‐nitrile 10a afforded the cis enaminones 11a‐c and 12a‐c. Similarly, reaction of 1a‐c with the methylanthranilate 9b and reaction of 1b,e with ethyl 2‐aminocyclohexene thiophene‐3‐carboxylate 10b afforded the cis enaminones 11d‐f and 12d,e respectively. Attempted cyclization of 11a‐c into quinoline failed. Successful cyclization of 11d into the quinolinone 13 could be affected, on heating for five minutes in a domestic microwave oven at full power. The reaction of 1a‐c,f with piperidine afforded the trans enaminones 14a‐d. Similarly, trans 14e was formed from the reaction of 1b with morpholine. The coupling reaction of 1b with excess of benzene diazonium chloride afforded the formazane 16. The enaminone 2 reacted with heterocyclic amines to yield the pyridones 17,18.     

Glycan–protein cross-linking mass spectrometry reveals sialic acid-mediated protein networks on cell surfaces

A cross-linking method is developed to elucidate glycan-mediated interactions between membrane proteins through sialic acids. The method provides information on previously unknown extensive glycomic interactions on cell membranes. The vast majority of membrane proteins are glycosylated with complicated glycan structures attached to the polypeptide backbone. Glycan–protein interactions are fundamental elements in many cellular events. Although significant advances have been made to identify protein–protein interactions in living cells, only modest advances have been made on glycan–protein interactions. Mechanistic elucidation of glycan–protein interactions has thus far remained elusive. Therefore, we developed a cross-linking mass spectrometry (XL-MS) workflow to directly identify glycan–protein interactions on the cell membrane using liquid chromatography-mass spectrometry (LC-MS). This method involved incorporating azido groups on cell surface glycans through biosynthetic pathways, followed by treatment of cell cultures with a synthesized reagent, N-hydroxysuccinimide (NHS)–cyclooctyne, which allowed the cross-linking of the sialic acid azides on glycans with primary amines on polypeptide backbones. The coupled peptide–glycan–peptide pairs after cross-linking were identified using the latest techniques in glycoproteomic and glycomic analyses and bioinformatics software. With this approach, information on the site of glycosylation, the glycoform, the source protein, and the target protein of the cross-linked pair were obtained. Glycoprotein–protein interactions involving unique glycoforms on the PNT2 cell surface were identified using the optimized and validated method. We built the GPX network of the PNT2 cell line and further investigated the biological roles of different glycan structures within protein complexes. Furthermore, we were able to build glycoprotein–protein complex models for previously unexplored interactions. The method will advance our future understanding of the roles of glycans in protein complexes on the cell surface.

The cell surface glycocalyx is highly interactive defined by extensive covalent and non-covalent interactions. A method for cross-linking and characterizing glycan–peptide interactions in situ is developed.