Clathrate and Inclusion Compounds. Part 13 [1]. Vibrational and NMR Spectroscopic Studies of Carboxylic Acid Guests in Urea

Infrared, Raman and solid state¹³C NMR spectra have been recorded for arange of inclusion compounds of urea containingstraight chain aliphatic carboxylic acids(butyric – decanoic) as guests. Inclusioncompounds are not formed with formic, acetic andpropionic acids. Thiourea does not forminclusion compounds with any of the C1 to C10acids. The vibrational and NMR data support theconclusion that the acids are present ashydrogen bonded dimers in the channels of thehost. The alkyl chain ¹³C chemical shiftvalues are very different from those of acidguests in the cavities formed in Dianin'scompound. These suggest that the alkyl chainsare present in the all-trans conformation,although weak bands observed in the spectrum ofthe decanoic acid inclusion compound lend somesupport to suggestions based on MM calculationsthat other conformations might be present.     

ROM polymerization-capture-release: application to the synthesis of unsymmetrical porphyrazinedithiols and peripherally metalated derivatives

Crossover Linstead macrocyclization of a doubly norbornenyl-functionalized dimercaptomaleonitrile with dipropylmaleonitrile gave a crude mixture of porphyrazines containing the hexapropylporphyrazinedithiol magnesium complex. The mixture was subjected to ring-opening metathesis polymerization to yield the insoluble porphyrazinedithiol-functionalized polymers. Cleavage from the polymer backbone using mercury(II) acetate followed by reaction with electrophiles gave access to a range of thioporphyrazinedithiol derivatives including solitaire porphyrazines. Studies into the possible uses of hexapropyl-2,3-di-(carboxymethylthio)porphyrazine in sensing metal cations in solution are described.     

Acylated flavone glycosides from the roots of Saussurea lappa and their antifungal activity

The isolation of four novel acylated flavonoid glycosides from the roots of Saussurea lappa and their identification using a combination of 1D and 2D NMR and mass spectrometry is described. The in vitro antifungal and antibacterial activities of the isolated compounds and their mixture were tested on nine fungal and four bacterial strains, using the microdilution method. The compounds and mixture showed moderate to high antifungal activity against most of the fungi tested, compared to a miconazole standard, while only one compound and the mixture showed antibacterial activity against all strains tested.     

Determination of the components of analgesic mixtures using high-performance thin-layer chromatography

A spectrodensitometric method is described for the determination of the components of two analgesic mixtures. For the first mixture (paracetamol-ascorbic acid-caffeine-phenylephrine), the pharmaceutically active components were separated from each other and closely related degradation products and impurities on high-performance thin-layer chromatography (F254) plates using methylene chloride-ethyl acetate-ethanol-formic acid (3.5 + 2 + 4 + 0.5) and methylene chloride-ethyl acetate-ethanol (5 + 5 + 1) as the developing systems. The other mixture (phenazone-phenacetin-caffeine) was separated efficiently from the degradation products using the same plates and acetonitrile-chloroform (1 + 1) as the mobile phase. The proposed method was used to determine these mixtures in commercial tablets.     

Liquid chromatography-electrospray mass spectrometry as a tool for the analysis of sulfated oligosaccharides from mucin glycoproteins.

An approach for analyzing sulfated oligosaccharide alditol mixtures by liquid chromatography-electrospray mass spectrometry (LC-ESI-MS) is described. Two columns, an amino-bonded column and a porous graphitized carbon column (PGC) were used. Oligosaccharides were eluted with linear gradients of acetonitrile and water, with 5 mM ammonium hydrogencarbonate or formate buffers at a basic pH. The methods were evaluated on a mixture of sulfated oligosaccharide alditols prepared from mucin glycoproteins from pig stomach. Results from LC-ESI-MS of the mixture were compared with the structural information obtained by high energy collision fragmentation using fast atom bombardment tandem mass spectrometry (FAB-MS-MS). The separation ability of the two columns was also tested using a more complex mixture of sulfated oligosaccharides from pig colon, where several isomers were detected. The potential use of in-source collision-induced dissociation (CID) to gain sequence information of sulfated oligosaccharides was also evaluated. The major fragment ions obtained by in-source CID of the trisaccharide Hex-3HexNAcol6-HexNAc6-SO3 were sufficient for assigning the oligosaccharide sequence and the position of the sulfate group within the monosaccharide moiety. The LC-ESI-MS approach should be a valuable tool for characterization of mucin glycosylation and alterations during pathological conditions.     

tert-Butyl (phenylsulfonyl)alkyl-N-hydroxycarbamates: the first class of N-(Boc) nitrone equivalents

[reaction: see text] tert-Butyl (phenylsulfonyl)alkyl-N-hydroxycarbamates 1 have been easily prepared from aldehydes and tert-butyl N-hydroxycarbamate in a methanol-water mixture using sodium benzenesulfinate and formic acid. These sulfones 1 behave as N-(Boc)-protected nitrones 4 in the reaction with organometallics to give N-(Boc)hydroxylamines. Some chemical transformations showing their interest as building blocks in organic synthesis are described.     

High-throughput bioassay-guided fractionation: a technique for rapidly assigning observed activity to individual components of combinatorial libraries,screened in HTS bioassays

In this paper, we describe an automated, high-throughput analytical tool for the unambiguous characterization of the active component(s) of a combinatorially derived reaction mixture. We call this technique high-throughput bioassay-guided fractionation (BGF). The novel aspects of this communication are the systematization of the BGF concept, the application of BGF to combinatorial chemistry, and the high-throughput nature of the identification technique. The identification of the active component in a well mixture is an essential step for subsequent resynthesis or isolation of the active component(s) or for removal of intractable wells from further consideration. We believe the technique described is also applicable to any mixture library, provided the expected component (or components) of each well is (are) known. Example mixture libraries would include collections of synthetic chemicals and collections of purified natural products. The mixture need not come from libraries produced using parallel synthesis. The BGF tool described herein allows full utilization of highly diverse combinatorial libraries, thereby obviating costly up-front purification or extensive prescreening characterization efforts.     

A simplified method for the determination of fenpropathrin residues in fruits

Summary A simple and efficient method is described for the determination of fenpropathrin in oranges, pears, apples and strawberries. The procedure is based on the extraction of each homogenized fruit sample with hexane:acetone (1∶1, v/v) mixture, followed by a cleanup technique on a column packed with florisil, using a hexane:ethyl ether (7∶3, v/v) mixture, and gas chromatographic analysis with electron capture detection (ECD). The fortification levels (0.5;1.0;2.0 mg kg⁻¹) were selected according to the maximum residue limits (MRLs) established for fenpropathrin by Brazilian legislation. Mean recoveries from five replicates of fortified fruit samples ranged from 83 % to 98%, with coefficients of variation from 1.4 to 13.5 and detection limits varying from 0.1 to 0.2 mg kg⁻¹.     

Use of Carbon-13 Labelled Dioxins Mixture for Analysis of Polychlorinated Dibenzo-p-Dioxins in Environmental Samples by GC-MS

Abstract

Positive identification and quantitation of polychlorinated dibenzo-p-dioxins (PCDD) in complicated environmental samples is described using a C-13 labelled dioxin mixture as an internal reference standard. Environmental samples are spiked with the C-13 labelled dioxin mixture and monitored for labelled and unlabelled dioxins using GC-MS in the electron impact selected ion monitoring (EISIM) mode. The C-13 labelled dioxin mixture and a municipal solid waste (MSW) incinerator fly ash extract show the same number of isomers in each tetra to octa-chlorodioxin congener groups. Quantitation of the C-13 labelled dioxin mixture was carried out using a reference standard mixture of unlabelled dioxins consisting of at least one isomer for each congener group. The C-13 labelled dioxin standard is highly useful for the determination of retention windows for tetra- to octa-chlorodioxins, identification of dioxins in each congener group, and calculation of the recovery of dioxins in samples that require extensive sample clean-up prior to GC-MS analysis. Its application for retention time window determination and as an internal reference standard for quantitation of dioxins in MSW incinerator fly ash extract and identification of dioxins in a complex sample from a PCB fire is demonstrated.     

Silica-immobilized formylsalicylic acid as a selective phase for the extraction of iron(III)

The immobilization of formylsalicylic acid compounds on the surface of amino group-containing silica gel phases is described. The resulting phases were tested for the extraction of iron(III) and showed an exchange capacity of 0.95-0.96 mmol g(-1). The other metal ions tested showed lower metal capacity values than iron(III). The selectivity of the phases tested for the extraction of iron(III) from a mixture containing several other metal ions was evaluated using atomic absorption spectrometry. A method for the recycling of immobilized silica gel after metal extraction is described for practical applications.     

Application of the least-squares method in the matrix form: simultaneous spectrophotometric determination of rifampicin and isoniazid in binary pharmaceutical formulations

A least-squares method in the matrix form is described for the simultaneous determination of rifampicin and isoniazid in a mixture. The method allows the rapid analysis of binary pharmaceutical formulations with minimum error. The concentration of each component in the mixture has been determined spectrophotometrically by measuring the absorbance of the mixture at 5-nm intervals from 230 to 290 nm. To calculate the matrix of the proportionality constant a standard mixture was used for each component. All data analyses were performed on a personal computer.     

Convenient preparation of trans-arylalkenes via palladium(II)-catalyzed isomerization of cis-arylalkenes

A convenient method for the isomerization of cis-arylalkenes to their trans isomers using a palladium(II) catalyst is described. The reaction conditions are mild and general across a range of arylalkenes. The synthesis of a trans-resveratrol derivative from a mixture of alkene isomers was also completed.     

HPLC-NMR of fatty alcohol ethoxylates

The application of HPLC-NMR for the analysis of a mixture of fatty alcohol ethoxylates (FAEs) is described. The use of the new generation, cryogenically cooled probes is investigated in respect of the sensitivity advantage that they provide. The FAE mixture is separated using liquid chromatography at the critical point of adsorption. The ability of the method to differentiate between the different end groups and the degree of polymerization of the mixture constituents is investigated. Both on-flow and stop-flow HPLC-NMR techniques were used together with two-dimensional NMR spectroscopy. The results are compared with those obtained by using an evaporative light scattering detector for the HPLC.     

The synthesis and conformation of oxygenated trianglimine macrocycles

The synthesis of series of D(2h) and C(2v) symmetric oxygenated aromatic dicarboxaldehydes, using dilithiation methodology, is described along with their reactivity in the [3+3] cyclocondensation reaction with (1R,2R)-diaminocyclohexane to give oxygenated trianglimine macrocycles. Macrocycles derived from C(2v) symmetric dialdehydes give macrocycles with a stereogenic aromatic plane with complete diastereocontrol, as a mixture of rotamers.     

L-羟脯氨酸寡肽混合物的高效液相色谱分离与质谱分析

研究了三氯氧磷辅助下L-羟脯氨酸的成肽反应,建立了采用反相高效液相色谱-质谱/质谱联用技术分离鉴定羟脯氨酸寡肽混合物的方法,优化了L-羟脯氨酸寡肽混合物的色谱分离条件。实验以YWG C8柱(10 μm,250 mm×10 mm)为分离柱,以乙腈-0.06%三氟乙酸水溶液(体积比为2∶98)为流动相进行等度洗脱,在正离子模式下对洗脱物进行了电喷雾电离串联质谱鉴定。结果显示,分离出的各组分分别为L-羟脯氨酸二肽、L-羟脯氨酸环二肽和L-羟脯氨酸三肽。     

荧光偏振发射平台法及其应用

本文从原理上叙述荧光偏振发射平台法,并用荧光单体-单体混合物及单体-聚合物体系进行验证试验。前者如荧光黄-罗丹明S(或四碘荧光素、或罗丹明B),后者如罗丹明6G-罗丹明6G聚合物体系,结果满意。     

A new high-performance liquid chromatographic method with evaporative light scattering detector for the analysis of phospholipids. Application to Iberian pig subcutaneous fat

A new method for the analysis of phospholipids by normal-phase HPLC is described using a silica column. Addition of ammonia and triethylamine to a gradient based on chloroform/methanol/water promoted a good and rapid separation of phospholipid classes (20 min run). The use of an evaporative light scattering detector permitted an accurate analysis of a mixture of phospholipids. Calibration curves were linear within different range for each phospholipid class. The LOD and LOQ obtained were below 0.03 and 0.05 mg kg⁻¹ for all cases, respectively. Besides, a new method for the separation of phospholipids from total lipids before HPLC analysis by a solid-phase extraction (SPE) with Si cartridges has been developed. This methodology gave a good recovery ranging from 97 to 117%. The method was validated with a standard mixture of phospholipids. This method has been applied to characterize the phospholipid fraction of subcutaneous fat from Iberian pig. Cardiolipin, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, phosphatidylcholine, and sphingomyelin have been described for first time in these samples. The fatty acid composition of the different phospholipid classes and their HPLC electrospray ionization mass spectrometry have been used for characterizing the molecular species present in each one.     

Direct determination of lead in biological samples by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) after furnace-fusion in the sample cuvette-tungsten boat furnace

The newly conceived electrothermal vaporization (ETV) system using a tungsten boat furnace (TBF) sample cuvette was designed for the direct analysis of solid samples with detection by inductively coupled plasma mass spectrometry (ICP-MS). Into this small sample cuvette, a solid mixture of the biological samples and diammonium hydrogenphosphate powder as a fusion flux was placed and situated on a TBF. Tetramethylammonium hydroxide solution was added to the mixture. After the on-furnace digestion had been completed, the analyte in the cuvette was vaporized and introduced into the ICP mass spectrometer. The solid samples were analyzed by using a calibration curve prepared from the aqueous standard solutions. The detection limit was estimated to be 5.1 pg of lead, which corresponds to 10.2 ng g(-1) of lead in solid samples when a prepared sample amount of 1.0 mg was applied. The relative standard deviation for 8 replicate measurements obtained with 100 pg of lead was calculated to be 6.5%. The analytical results for various biological samples are described.     

Methyl mercapturate synthesis: an efficient, convenient and simple method

A safe and simple method for methyl S-arylmercapturate synthesis is described. Thirteen such compounds, to be used afterwards in metabolism studies, have been obtained with yields ranging from 71 to 99.6%. These compounds were obtained using a sulfa-Michael addition and synthesized by adding the corresponding thiophenols to a mixture composed of methyl 2-acetamidoacrylate (MAA), potassium carbonate and a phase transfer catalyst, Aliquat 336. MAA, the initial synthon, was itself isolated in quasi quantitative yield following a fully described synthesis.