Arlene P. Rothwell

Characterization of betaines using electrospray MS/MS

Betaines are an important class of naturally occurring compounds that function as compatible solutes or osmoprotectants. Because of the permanent positive charge on the quaternary ammonium moiety, mass spectrometric analysis has been approached by desorption methods, including fast atom bombardment and plasma desorption mass spectrometry. Here we show that electrospray ionization MS gives comparable results to plasma desorption MS for a range of authentic betaine standards and betaines purified from plant extracts by ion exchange chromatography. A distinct advantage of electrospray ionization MS over plasma desorption MS is the capability of obtaining product ion spectra via MS/MS of selected parent ions, and hence structural information to discriminate between ions of identical mass.

Measuring calcium absorption and utilization in humans.

Purpose of reviewCalcium metabolism is comprised primarily of absorption, urinary excretion, endogenous secretion and bone turnover. This review evaluates recent findings relating to the role of genetic and environmental factors, especially diet, on perturbing parameters of calcium metabolism. Calcium dynamics are studied with the use of isotopic tracers. We also cover state-of-the-art methods for stable calcium isotope ratio analysis and offer insights on experimental design. Recent findingsSome progress has been made identifying genetic and hormonal regulators of calcium absorption. Much progress has been made in understanding the role of diet on influencing calcium retention, especially with regard to dietary protein and salt. Long-held views on dietary factors thought to contribute to bone loss through urinary calcium loss have been shown to have no impact on net calcium retention because of compensatory changes in other aspects of calcium metabolism. SummaryMuch more work needs to be done on understanding genetic regulators of calcium metabolism. Despite recent advances in our knowledge of dietary influences on calcium metabolism, more studies are needed on the role of environmental factors, especially physical activity.

DISCOVERY OF 3-METHYL-2-BUTEN-1-YL ACETATE, A NEW ALARM COMPONENT IN THE STING APPARATUS OF AFRICANIZED HONEYBEES

We analyzed the alarm pheromone components from five colonies of Africanized honeybees and three colonies of European honeybees collected in Mexico. Analyses revealed a novel alarm pheromone component that was only present in appreciable quantities in the Africanized bee samples. Analysis of the mass spectrum and subsequent synthesis confirmed that this compound is 3-methyl-2-buten-1-yl acetate (3M2BA), an unsaturated derivative of IPA. In Africanized honeybees, sampling from stings of guards showed that 3M2BA was present at levels of 0–38% the amount of isoamyl acetate (IPA). Behavioral assays from three colonies each of Africanized and European bees showed that 3M2BA recruited worker bees from hives of both Africanized bees and European bees at least as efficiently as isopentyl acetate IPA, a compound widely reported to have the highest activity for releasing alarm and stinging behavior in honeybees. However, a mixture of of 3M2BA and IPA (1:2) recruited bees more efficiently than either of the compounds alone. None of the compounds differed in their efficacy for inducing bees to pursue the observers.

Trinuclear nickel clusters, [Ni3(μ3-L)(μ3-I)(μ2-dppm)3]n+ (L = I−, CO, CNCH3, CN-2,6-Me2C6H3, CN-i-C3H7, CN-t-C4H9, CN-n-C4H9, NO+) and the “dimer of trimer” hexanuclear nickel clusters {[Ni3(μ3-I)(μ2-dppm)3]2(μ3,μ3′,η1,η1′- CN-R-NC)}2+, (R = −(CH2)6−, p-C6H4): characterization of large clusters by mass spectrometry

Abstract The mass spectra of a series of trinuclear nickel clusters of the general formula [Ni3(μ3-L)(μ3-I)(μ2-dppm)3]n+, where L = I− (1), CO (2), CNCH3 (3), CN-2,6-Me2C6H3 (4, CN-i-C3H7 (5), CN-t-C4H9 (6), CN-n-C4H9 (7), and NO+ (8) and n = 0, 1, 2 were measured by Plasma Desorption (PD) and Fast Atom Bombardment (FAB) mass spectrometry. Strong molecular ion peaks were observed for all of the trinuclear clusters except 8 by both techniques. Ion fragmentation followed similar pathways in both ionization modes. Dimers of trinuclear clusters, {[Ni3(μ3-I)(μ2-dppm)3]2(μ3,μ3′,η1,η1′-CN-R-NC)}2+ where R = −(CH2)6− (9) and 1,4-C6H4 (10) were prepared by the reaction of two equivalents of 1 with one equivalent of the appropriate diisocyanide, CN-R-NC. Clusters 9 and 10 were not distinguishable from simple trimers such as 3–7 by 31P NMR and optical spectroscopies, but were unambiguously identified by PD and FAB mass spectrometry. The parent ions are different for the two techniques: MI+ in the former case and M+ in the latter.

Chlorine/UV Process for Decomposition and Detoxification of Microcystin-LR

Microcystin-LR (MC-LR) is a potent hepatotoxin that is often associated with blooms of cyanobacteria. Experiments were conducted to evaluate the efficiency of the chlorine/UV process for MC-LR decomposition and detoxification. Chlorinated MC-LR was observed to be more photoactive than MC-LR. LC/MS analyses confirmed that the arginine moiety represented an important reaction site within the MC-LR molecule for conditions of chlorination below the chlorine demand of the molecule. Prechlorination activated MC-LR toward UV254 exposure by increasing the product of the molar absorption coefficient and the quantum yield of chloro-MC-LR, relative to the unchlorinated molecule. This mechanism of decay is fundamentally different than the conventional view of chlorine/UV as an advanced oxidation process. A toxicity assay based on human liver cells indicated MC-LR degradation byproducts in the chlorine/UV process possessed less cytotoxicity than those that resulted from chlorination or UV254 irradiation applied separately. MC-LR decomposition and detoxification in this combined process were more effective at pH 8.5 than at pH 7.5 or 6.5. These results suggest that the chlorine/UV process could represent an effective strategy for control of microcystins and their associated toxicity in drinking water supplies.

Surface-supported group 5 metal organometallic compounds for catalytic arene hydrogenation

The Group 5 metal alkylidyne bridged compounds [(Me3SiCH2)2M(µ-CSiMe3)2M(CH2SiMe3)2](M = Nb, Ta) supported on silica will catalyse the exhaustive hydrogenation of a variety of aromatic substrates.

Hydrolysis of thioesters in an ion trap

The alkenyldiarylmethanes are a class of non-nucleoside reverse transcriptase inhibitors that are currently being developed as potential antivirals for the treatment of HIV infection and AIDS. As part of our continuing investigations on the alkenyldiarylmethanes, a series of thioester analogues were prepared in an effort to improve upon the metabolic stability of the parent lead compound. Hydrolysis of the thioester moieties was consistently observed during ion trap electrospray ionization (ESI) mass spectrometry to the extent that the parent molecular ion was weak in intensity or simply could not be detected. The same hydrolysis observations were also made when the analogues were analyzed by ion trap electron impact (EI) ionization, indicating the hydrolysis event was the result of the ion trap and not ionization technique. Ion-trap-mediated hydrolysis has been observed previously in prior alkenyldiarylmethane studies and prevented characterization of certain intermediates; thus, we wished to investigate whether modifying instrument parameters and protocols affected the instrument-mediated hydrolysis event. Unfortunately, varying the maximum injection time and the number of microscans performed, independent of each other, had little effect on the intensities of the parent ions [MH(+)] or the hydrolysis products] MH(+) -HSCH(3)].

Fast atom bombardment, electron impact and chemical ionization mass spectrometry of the neutral 18-electron species M(CO)2(CNR)2(PR′3)2 (MMo or W)

Abstract The molybdenum(0) and tungsten(O) complexes of the type M(CO) 2 (CNR) 2 (PR′ 3 ) 2 have been studied using a variety of mass spectral techniques, viz. fast atom bombardment (FAB), electron impact (EI), and both positive- and negative-ion chemical ionization (PICI and NICI) mass spectrometry. The FABMS technique gave the most structurally informative spectra with the observation of the molecular ions M + (100% relative abundance in the case of MW) and in some instances the pseudomolecular ion (M + H) + . Fragmentation ions arising from competitive ligand loss (CO versus RNC versus PR′ 3 ) were observed, as well as those formed by loss of H from fragment ions and dealkylation of RNC ligands. The EI and PICI spectra were not especially useful due to the relatively low thermal stability of these complexes, while the NICI spectra gave an abundance of ions that resulted from ligand redistribution reactions. Of special note were anions that contained M(CO) 4 and M(CO) 3 fragments. Dealkylation of the RNC ligands to give cyanometallate anions was also prevalent.