Ionic-liquid-based MS probes for the chemo-enzymatic synthesis of oligosaccharides

A new N-benzenesulfonyl-based ionic-liquid mass spectroscopy label (I-Tag2) for covalent attachment to substrates has been prepared. I-Tag2 was used to monitor oligosaccharide elongation and serve as a purification handle. Starting from chemically synthesized I-Tag2-labelled N-acetyl glucosamine (GlcNAc) 1, I-Tag2-LacNAc (Galβ(1-4)GlcNAc) 2 and I-Tag2-Lewis(X) (Galβ(1-4)[Fucα(1-3)]GlcNAc) 3, which are oligosaccharides of biological relevance, were enzymatically prepared. The apparent kinetic parameters for the enzyme catalysed transformations with β-1,4-galactosyltransferase (β-1,4-GalT) and fucosyltransferase VI (FucT VI) were measured by LC-MS demonstrating the applicability and versatility of the new I-Tags in enzymatic transformations with glycosyltransferases.     

Traceless chemical ligations from O-acyl serine sites

Chemical ligation via O- to N-acyl transfer of O-acylated serine containing peptides affords serine containing native peptides via 8- and 11-membered cyclic transition states opening the door to a wide variety of potential applications to peptide elaboration. The feasibility of these traceless chemical ligations is feasible as supported by computation.     

Tautomers of anthrahydroquinones: enzymatic reduction and implications for chrysophanol, monodictyphenone, and related xanthone biosyntheses

Reduction of emodin by sodium dithionite resulted in the formation of two tautomeric forms of emodin hydroquinone. Subsequent conversion by the short-chain dehydrogenase/reductase (SDR) MdpC into the corresponding 3-hydroxy-3,4-dihydroanthracen-1(2H)-one implies that deoxygenation is the first step in monodictyphenone biosynthesis. Implications for chrysophanol formation as well as reaction sequences in the related xanthone, ergochrome, and bianthraquinone biosyntheses are discussed.     

Synthesis,characterisation and supramolecular interaction of Rh-biphenylic-imidazole-phenanthroline with antibiotics

A novel rhodium biphenylic imidazole phenanthroline metal-organic complex (BIP-MC) has been synthesised and characterised as a stable supramolecule. The structure of compound was established on the basis ESI, ¹H NMR and UV–vis spectroscopic data. The selectivity of BIP-MC as a new fluorescent chemosensor for various antibiotics has been explored. The supramolecular interaction of amoxicillin with BIP-MC enhanced the fluorescence activity of BIP-MC. A linear response of the sensor was observed in the measuring ranges of excitation 240–298 nm and emission 290–360 nm with detection limits of up to 10 μg/ml at an optimum pH 8.0. Based on the observations made here, a new quantitative method for the determination of this drug in synthetic samples without the use of separation of matrix is developed. It is also inferred that the possible fluorescence enhancement is due to the formation of exciplex between the BIP-MC and amoxicillin. These finding will thus help in pharmacokinetics studies of drugs. The sensor was used for the direct assay of amoxicillin antibiotic in commercial pharmaceutical preparations.     

Synthesis and Reactivity of Hydrolysis Products of Cyclic Phosphites with Amino Substituents

Abstract

Hydrolysis of several cyclic aminophosphites are discussed and compared with that of cyclic chloro/ phenoxy phosphites. An X-ray structure of a hydrolysis product, (C₆H₁₁NH₃)⁺O^?P(O)(H)(2,2′-OC₆H₄-C₆H₄OH) has been determined.     

Separation and determination of m-phenoxybenzaldehyde reaction products by capillary gas chromatography

A capillary GC method employing an internal standard has been developed and successfully used for quantitative determination both of the raw materials used for the manufacture of m-phenoxybenzaldehyde and for the components of the reaction mixtures obtained at various stages of the development of the process. A complete analysis can be performed in a single temperature programmed run.     

Electrospun EGNPs reinforced precursor carbon nanofibril composites by using RSM

Response surface methodology (RSM),based on five‐level, four variable Box‐Benkhen technique was investigated for modeling the average fiber diameter of electrospun polyacrylonitrile (PAN) nanofibers. The four important electrospinning parameters were studied including applied voltage (kV), Berry's number, deposition distance from nozzle to collector (cm), and spinning angle (? in degree). The measured fiber diameters were in a good agreement with the predicted results by using RSM technique. High‐regression coefficient between the variables and the response (R² = 87.74%) indicates excellent evaluation of experimental data by second‐order polynomial regression model. The optimum PAN average fiber diameters of 208 and 37‐nm standard deviation were collected at 19 kV, Berry's number = 10, 25^° spinning angle, and 16‐cm deposition distance. The PAN/N,N‐dimethylformamide (DMF) polymer solution with the optimum weight concentration (10 wt.%) was selected to study the effect of dispersing exfoliated graphite nanoplatelets (EGNPs) in PAN/DMF solution on the electrospun EGNP/PAN fibril composite diameter. Five different EGNPs weight concentrations (2, 4, 6, 8, and 10 wt.%) were dispersed in the optimized PAN/DMF polymer solution. Morphology of EGNPs/PAN fibril composites and its distribution were investigated by scanning electron microscopy (SEM) to show the minimum fiber diameter for the above‐mentioned 5 wt. % of EGNPs. A minimum fibril composite diameter of 182 nm was obtained at 10 wt.% of EGNPs. Morphological characteristics of electrospun fibers and their distribution were tested by Raman spectroscopy, SEM, differential light scattering, and high‐resolution transmission electron microscopy.     

DBU-catalyzed transprotection of N-Fmoc-cysteine di- and tripeptides into S-Fm-cysteine di- and tripeptides

The transprotection of N-Fmoc-cysteine containing di- and tripeptides possessing a free SH group to produce the corresponding S-Fm-cysteine di- and tripeptides bearing a free amino group is accomplished efficiently with DBU in dry THF. The N-Fmoc to S-Fm transformation mechanism is discussed. S-Fm-Cysteine di- and tripeptides readily form amide bonds on coupling with N-(Pg-α-aminoacyl)benzotriazoles and N-(Pg-α-dipeptidoyl)benzotriazoles to give larger peptides.     

Synthesis and Ring Transformation of Pyrrolo[2,3-d][1,3]oxazine to Pyrrolo[2,3-d]Pyrimidines

A convenient route is reported for the synthesis of fused pyrrolo[2,3-d][1,3]oxazine and pyrrolo[2,3-d]-pyrimidine derivatives from 2-amino-1-benzyl-3-t-butoxycarbonyl]-4,5-dimethylpyrrole.     

Determination of arsenic, selenium, and antimony in cloud water by inductively coupled plasma mass spectrometry

The capability of inductively coupled plasma mass spectrometry in determining trace levels of As, Se, and Sb in cloud water was evaluated. Preliminary studies focused on identifying and eliminating potential interferences in the cloud water matrix, the choice of appropriate internal standards, and system optimization. The detection limits for As, Se, and Sb were 20, 100, 20 pg/mL using pneumatic nebulization, and 5, 25, 5 pg/mL, respectively, using ultrasonic nebulization with a precision of better than 5% RSD. The accuracy was demonstrated by the analysis of a NIST commercial reference material, SRM 1643d. In all cases, the results from ICP-MS analysis agreed within 4% of the certified values. Comparative analysis of cloud water samples obtained from a site downwind from large pollution sources (Whiteface Mountain, New York) and Changlagali Pakistan, a rural mountain peak, was carried out by hydride generation atomic absorption (HGAA) spectrometry. There was excellent agreement between the ICP-MS and HGAA results. Received: 31 July 1997 / Revised: 28 October 1997 / Accepted: 31 October 1997