Bridget K. Stein

Analysis of various organic and organometallic compounds using nanostructure-assisted laser desorption/ionization time-of-flight mass spectrometry (NALDI-TOFMS).

Nanostructure-assisted laser desorption/ionization time-of-flight mass spectrometry (NALDI-TOFMS) has been developed recently as a matrix-free/surface-assisted alternative to matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). The NALDI surface of silicon nanowires is already very effective for the analysis of small to medium sized, polar organic molecules in positive ion mode. The current study examined this technology for the analysis of several nonpolar organic, organometallic, and ionic compounds in positive ion mode, as well as a fluorinated compound and various acids in negative ion mode. NALDI data are compared and contrasted with MALDI data for the same compounds, and the higher sensitivity of NALDI is highlighted by the successful characterization of two porphyrins for a sample amount of 10 amol per spot.

First General Solvent‐Free Synthesis of Symmetrical Triindolylmethanes Using Acid‐Washed Montmorillonite Clay

Abstract Dry reaction of indoles and alkylindoles (1a–h) with triethyl orthoformate (2.5 equiv.) on acid‐washed montmorillonite K10 clay at room temperature afforded in <5 min–4 hr the respective symmetrical TIMs (2a–h) in good to high yields along with the formylindole 3 and the formyl‐TIM 4 from 1g and 1h, respectively.

Water soluble platinum(II) and palladium(II) complexes of alkyl sulfonated phosphines

Abstract The reactions of the alkylsulfonated phosphines LM=Ph 2 P(CH 2 ) n SO 3 Na/K ( n =2, 3, 4) with K 2 PtCl 4 and K 2 PdCl 4 have been studied in homogeneous aqueous solution as a function of pH. In homogeneous acidic solution the protonated phosphines react to give cis - and trans -PtCl 2 (LH) 2 . The biphasic reaction between 1,5-cyclooctadiene platinum(II) chloride in dichloromethane and acidified aqueous LNa/K gives a higher proportion of the cis isomer. In neutral solution the initial reaction to give [PtCl(LNa/K) 3 ] + Cl − is followed by slow formation of cis -PtCl 2 (LNa/K) 2 . K 2 PdCl 4 reacts more rapidly to give PdCl 2 (LNa/K) 2 . In homogeneous alkaline solution rapid oxidation of the phosphine occurs with only small amounts of platinum complex being observable. The biphasic reaction yields phosphine oxide in the aqueous layer and a small amount of the chelate complexes PtL 2 in the organic. Representative complexes have been isolated and characterised and the mechanisms for the reactions discussed. The electrospray mass spectra of solutions of the isolated complexes have been recorded in both positive and negative ionisation modes. The positive ionisation spectra are complicated, but platinum and palladium containing ions derived from loss of chloride, H + and HCl are observed in the negative ionisation spectra.

Characterisation of organometallic and coordination compounds by solvent-free matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry.

Insoluble or low solubility organometallic and coordination compounds have been characterised by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry, with solvent-free sample preparation being the key step toward successful analysis.

Accurate mass measurement by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry. I. Measurement of positive radical ions using porphyrin standard reference materials: Accurate mass MALDI of positive radical ions using porphyrins

A method for the accurate mass measurement of positive radical ions by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) is described. Initial use of a conjugated oligomeric calibration material was rejected in favour of a series of meso-tetraalkyl/tetraalkylaryl-functionalised porphyrins, from which the two calibrants required for a particular accurate mass measurement were chosen. While all measurements of monoisotopic species were within +/-5 ppm, and the method was rigorously validated using chemometrics, mean values of five measurements were used for extra confidence in the generation of potential elemental formulae. Potential difficulties encountered when measuring compounds containing multi-isotopic elements are discussed, where the monoisotopic peak is no longer the lowest mass peak, and a simple mass-correction solution can be applied. The method requires no significant expertise to implement, but care and attention is required to obtain valid measurements. The method is operationally simple and will prove useful to the analytical chemistry community.

Oxidation of guanine Nucleosides to 4-amidinocarbamoyl-5-hydroxyimidazoles by dimethyldioxirane

Abstract Final oxidation products generated from guanosine and 2′-deoxyguanosine by reaction with dimethyldioxirane have been identified as 4-amidinocarbamoyl-5-hydroxyimidazoles.

Accurate mass measurement by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry. II. Measurement of negative radical ions using porphyrin and fullerene standard reference materials

A method for the accurate mass measurement of negative radical ions by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) is described. This is an extension to our previously described method for the accurate mass measurement of positive radical ions (Griffiths NW, Wyatt MF, Kean SD, Graham AE, Stein BK, Brenton AG. Rapid Commun. Mass Spectrom. 2010; 24: 1629). The porphyrin standard reference materials (SRMs) developed for positive mode measurements cannot be observed in negative ion mode, so fullerene and fluorinated porphyrin compounds were identified as effective SRMs. The method is of immediate practical use for the accurate mass measurement of functionalised fullerenes, for which negative ion MALDI-TOFMS is the principal mass spectrometry characterisation technique. This was demonstrated by the accurate mass measurement of six functionalised C(60) compounds.