Abstract: Electrochemical oxidation of the corresponding carboxylates (Kolbe reaction) offers a simple and efficient means to solidly attach a monolayer of arylmethyl groups on carbon surfaces. The starting molecules are easily accessible, and the presence of appropriate substituents on the phenyl rings makes this type of derivatization a convenient starting point for further chemical modifications. The extent of the surface modification can be followed by cyclic voltammetry as a function of the number of successive potential cycles. The presence of the groups on the surface, their arrangement, and their concentration are determined by the same technique as well as by X-ray photoelectron spectroscopy and scanning electron tunneling microscopy after transfer of the derivatized electrode into a pure electrolyte solution. The fact that reductive and oxidative cyclic voltammograms of the derivatized electrodes can be obtained demonstrates that the grafted groups are in electrical contact with the electrode by means of ...

Abstract: A highly activated ester containing a fixed positive charge, S-pentafluorophenyl [tris(2,4,6-trimethoxyphenyl)phosphonium]acetate bromide (TMPP-AcSC6F5 bromide), has been synthesized as a reagent for N-terminal modification of peptides Stable in aqueous acetonitrile solution during extended storage, TMPP-AcSC6F5 bromide reacts with unprotected peptides through p-(dimethylamino)pyridine (DMAP)-promoted amidation in aqueous acetonitrile (15 min, ambient temperature) to form N-TMPP-Ac derivatives of peptides These peptide derivatives are readily amenable to analysis by fast atom bombardment (FAB) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry Greater than 90% conversion has been observed in transforming low-nanomole quantities of analyte using molar ratios of 1:5:10 (peptide/reagent/DMAP) For reactions at the picomole level a slightly modified stoichiometry, with molar ratios of 1:10:500, is employed Owing to the high reaction efficiency and the tolerance to moderate excess re

Abstract: A selective and sensitive high-performance liquid chromatographic (HPLC) method has been developed for the measurement of colistin residues in milk and in four bovine tissues (i.e., muscle, liver, kidney, and fat). The sample treatment consists of protein precipitation using 10% (w/v) trichloroacetic acid, solid-phase purification on C18 cartridges, and precolumn derivatization of colistin with ortho-phthalaldehyde and 2-mercaptoethanol in borate buffer (pH 10.5). This latter step is performed automatically, and the resulting reaction mixture is injected into a switching HPLC system including a precolumn and an analytical column packed with end-capped LiChrospher RP18 (5 microns). Washing the precolumn and final elution onto the analytical column are conducted using acetonitrile-0.01M phosphate buffer (pH 7.0) mixtures with respective proportions of 65:35 and 68:32 (v/v). Detection is carried out by spectrofluorometry (excitation wavelength, 340 nm; emission wavelength, 440 nm). The retention times of the derivatives corresponding to the two main components of colistin (i.e., polymyxins E2 and E1) are approximately 14 and 18 min, respectively. The structural study of the derivatives corresponding to polymyxins E1 and E2 is carried out by HPLC coupled with electrospray mass spectrometry; data obtained confirms that the derivatization process occurs with the five amino groups of the analytes. Selectivity is obtained in the HPLC system versus other coadministered anti-infective drugs (beta-lactams, aminoglycosides, tetracyclines, and sulphonamides) and endogenous compounds. Quantitation is performed using the sum of the peak areas of polymyxin E1 and polymyxin E2 derivatives. Testing linearity affords correlation coefficients greater than 0.990 for calibration curves in the range of 10-500 microL/L for milk, 50-1000 micrograms/kg for muscle and fat, and 100-1000 micrograms/kg for kidney and liver. Relative standard deviation values are less than 10% at a concentration of 25 micrograms/L in milk and 100 micrograms/kg in tissues (six replicates); recoveries are higher than 60%.

Abstract: A high-performance liquid chromatographic method for the determination of primary and secondary amino acids in green beans is described. Hydrochloric acid hydrolysates of 15 representative samples of bean proteins are derivatized with phenylisothiocianate, and the resulting phenylthiocarbamyl derivatives are separated on a reversed-phase column by gradient elution with sodium acetate buffer and acetonitrile-water (60:40 [v/v]) and detected by ultraviolet detection at 254 nm. Recoveries range from 93.5 to 97.5%, method precision (relative standard deviation) ranges from 1.26 to 3.98%, and detection limits range from 8.11 to 13.3 pmol/μL.

Abstract: This survey gives a short overview of the various reagents and procedures that can be used for pre-, post- and on-column derivatization in capillary electrophoresis. First there is an introduction about capillary electrophoresis as an analytical technique; this is followed by a discussion of the pros and cons of the various modes of derivatization and a comparison with liquid chromatography. In the following paragraphs the reagents for a number of functional groups are discussed. The emphasis is on derivatization of the amino group. Most of the information on the reagents and derivatization procedures is listed in tables together with information on the detection mode, analytes, sensitivity and samples. In addition to the amino group, information is given on labeling of aldehyde, keto, carboxyl, hydroxyl and sulfhydryl groups.

Abstract: Hydrothermal reaction of lacunary [(PO4)W11O35]7- with rhodium acetate dimer yields the novel dirhodium-substituted Keggin anion, [(PO4)W11O35{Rh2(OAc)2}]5- (1) An X-ray structure determination of the guanidiunium salt of the dimethyl sulfoxide derivative of 1 confirms the structure deduced from proton and tungsten NMR spectroscopy Oxidation of 1 to an unstable RhII,III derivative, and synthesis of other polytungstate analogs is possible The tetrabutylammonium salt of 1 exhibits modest catalytic reactivity for cyclopropanation

Abstract: Using the wet-chemistry technique, we selectively reduced the surface of the PEEK film (PEEK-OH), and covalently fixed hexamethylene diisocyanate by addition onto the hydroxyl functions. The resulting PEEK-NCO film displayed free isocya nate termini, the basic hydrolysis of which gave the PEEK-NH2 film in 85% extent of derivatization. The PEEK-NCO film reacted with trifluoroethylamine in toluene, trifluoroethylamine in PBS buffer, GABA, and lysine in PBS buffer to furnish, respectively, the PEEK-CF3(A), PEEK-CF3(B), PEEK-CO2H, and PEEK(NH2)CO2H films in 80%, 45%, 30%, and 25% extents of derivatization, as determined from the F/C and N/C atomic ratios recorded in the corresponding XPS spectra. The surface reactivity of the PEEK-NH2 and PEEK-NCO films was assayed by coupling with appropriate H-3 labels followed by liquid scintillation counting of the sample-associated radioactivity. The PEEK-NH2, PEEK-CO2H, and PEEK-(NH2)CO2H films were used as substrates for the cultivation of CaCo2 epithelial cells; the presence of surface amine and carboxyl functions significantly improves the cellular adhesion and growth. (C) 1997 John Wiley & Sons, Inc.

Abstract: Measurement of plasma homocysteine may be of value in several clinical conditions including homocystinuria, atherosclerosis, thrombophilia, and folate/vitamin B12 deficiency. The increasing interest in measuring total homocysteine in plasma has led to the development of several different methods (1). A widely used technique for measuring total plasma homocysteine is reversed-phase HPLC with fluorescence detection after derivatization of plasma thiols with ammonium 7-fluorobenzo-2-oxa-1,3-diazole-4-sulfonate (SBD-F) (2)(3). Most published methods use external calibration alone for quantitation of homocysteine because of the difficulty in selecting an internal standard. We have modified this method by adding cysteamine hydrochloride as an internal standard to the plasma or homocysteine calibrator to compensate for variations in thiol derivatization and sample injection procedures. HPLC was carried out by an isocratic system with fluorescence detection (SFM 25 spectrofluorometer), autosampler (SA 360), and HPLC pump (325) supplied by Kontron Instruments. Chemicals were obtained from Sigma. The method has been adapted from that of Ubbink et al. (2) on the basis of the chemical description provided by Araki and Sako (3). The plasma or homocysteine calibrator (150 μL) was incubated with 100 mL/L tri- n -butylphosphine in dimethylformamide (15 μL) for 30 min at 4 °C to reduce and release protein-bound thiols. Deproteinization was achieved by the addition of 100 g/L trichloroacetic acid (150 μL) and centrifugation. An aliquot of the supernatant (50 μL) was mixed with sodium hydroxide (10 μL, 1.55 mol/L), borate buffer (125 μL, 0.125 mol/L, pH 9.5, containing 4 mmol/L EDTA), and SBD-F (50 μL, 1 g/L) and incubated for 60 min at 60 °C. The SBD-F derivative from the supernatant (20-μL aliquot) was eluted isocratically from the Spherisorb ODS2 [4.6 mm (i.d.), 5-μm particles] analytical column (Jones Chromatography). The mobile phase was 0.1 mol/L KH2PO4, pH 2.0, containing 40 …

Abstract: The surface reduction of amorphous poly(aryl ether ether ketone) (PEEK) film was successfully achieved by wet chemistry using a solution of NaBH4 in DMSO at 120 degrees C for 3 h. The resulting PEEK-OH film was fully characterized by MIR, W-visible, and H-1 NMR spectroscopies; all the data were consistent with those of the references, 4-(4-methoxyphenoxy)benzhydrol and bulk-reduced PEEK (''PEEK-OH''). The surface of PEEK-OH film was analyzed by X-ray photoelectron spectroscopy (XPS). From the fine structures of the Cls and Ols peaks, we could determine a ratio of reduction reaching 75-85% of the monomer units contained in the 10 outermost atomic layers. The surface reactivity of the hydroxyl groups was assayed by derivatization with [H-3]acetic anhydride followed by liquid scintillation counting (LSC) of the sample-associated radioactivity. The PEEK-OH film was reacted with p-nitrophenyl chloroformate to furnish an activated surface (PEEK-OCO2PNP), the basic hydrolysis of which allowed the indirect spectrophotometric assay of the reactive OH groups. The PEEK-OCO2PNP film was further used to covalently fix amine derivatives via a carbamate Linkage. Using [H-3]lysine and trifluoroethylamine, we were able to assay the surface reactivity by LSC and XPS respectively. The ratios of surface derivatization were within 5-30%. The PEEK-OH film was used as substrate for the cultivation of CaCo2 epithelial cells; the presence of surface hydroxyl functions moderately improves the polymer biocompatibility.

Abstract: Solid-phase extraction and group separation by anion exchange chromatography were combined with capillary column liquid chromatography-mass spectrometry (LC/MS) to permit a thorough characterization of bile acids and intact conjugates of bile alcohols in human urine. Groups of compounds were separated according to acid strength and were analysed on a capillary column, 0.25 x 500 mm, packed with 5 microns particles of Chromasil C18, and connected via a fused silica capillary to the continuous-flow fast atom bombardment (CF-FAB) or electrospray (ES) sources of an AutoSpec-TOFFPD hybrid mass spectrometer. Acetonitrile:water mixtures containing 30 mM ammonium acetate pH 7.2 were used as mobile phases, with 5% glycerol added for FAB Ionisation. Bile acids were analysed directly or after derivatization of carboxyl groups with 4-aminobenzenesulphonic acid. Negative-ion spectra (m/z 1000 or 800 to 300 or 100) were recorded using the point detector or, in the case of ES ionization, the focal plane array detector (FPD). Deprotonated molecules of bile acids containing a sulphonic acid group were detected with a spectral signal to noise ratio of 5:1 when about 90 fmol were injected onto the column of the LC/CF-FAB system. The corresponding peak in the reconstructed ion chromatogram gave a signal-to-noise ratio of about 25:1. The sensitivity could be increased 20-50 times by using ES ionization and the FPD. Bile acids without a sulphonic acid group gave about 70% of the signal of sulphonic acids using ES ionization. The capillary column LC/MS systems were evaluated by analyses of urine from an infant with cholestatic liver disease. More than 150 different bile acids and bile alcohol conjugates were detected, some of which were partially characterized using collision induced dissociation (CID) of the deprotonated molecules and B/E linked scans. A number of compounds were detected for the first time, e.g. di-, tri-, and tetra-hydroxycholestanoic acids conjugated with N-acetylhexosamine and cholestenediol, cholestenetriol and cholestanetriol doubly conjugated with sulphuric acid and glucuronic acid. The relative merits of ES and FAB ionization are discussed.

Abstract: As part of a program to develop methods for the verification of alleged exposure to sulphur mustard, we synthesized and characterized three amino acid adducts presumably formed by alkylation of haemoglobin: 4-(2-hydroxyethylthioethyl)-l-aspartate, 5-(2-hydroxyethylthioethyl)-l-glutamate and N1- and N3-(2-hydroxyethylthioethyl)-l-histidine. Suitable derivatization methods for GC/MS analysis were developed for these adducts as well as for the cysteine and the N-terminal valine adduct. Incubation of human blood with [35S]sulphur mustard in vitro followed by acidic hydrolysis of isolated globin and derivatization with Fmoc-Cl afforded three major radioactive peaks upon HPLC analysis, one of which coeluted with the synthetic Fmoc derivative of N1/N3-(2-hydroxyethylthioethyl)-l-histidine. After pronase digestion of globin the adducts of histidine, glutamic acid, aspartic acid, cysteine and N-terminal valine could be tentatively identified and quantitated. Final identification was obtained from GC/MS analysis. The most abundant adduct, N1/N3-(2-hydroxyethylthioethyl)-l-histidine, could not be sensitively analysed by GC/MS. A convenient LC-tandem MS procedure was developed for this compound, enabling the detection of exposure of human blood to 10␣μM sulphur mustard in vitro.

Abstract: The structures of stachybotrin C and parvisporin have been determined by spectroscopic analyses and chemical derivatization. Stachybotrin C contains a unique pyrano-isoindolinone ring system, while parvisporin has a hydroxyl farnesyl phenol structure.