Albert A. Tuinman

‘Fluorine dance’ on the fullerene surface

Abstract A facile fluorine migration process (‘fluorine dance’) leads to the formation of the most thermodynamically stable isomers during the high temperature fluorination of [60]fullerene.

Highly fluorinated fullerenes as oxidizers and fluorinating agents

Contrary to the chemistry of “standard” fluorocarbons, highly fluorinated fullerenes (C60F44 - C60F46) display distinct oxidizing and fluorinating properties. They liberate iodine from NaI solutions, oxidize isopropanol to acetone, and fluorinate aromatic compounds in the presence of acid catalysts such as BF3·Et2O. Fluoroaromatic products are also generated in the reaction of these fluorofullereness with organolithium reagents. Even the relatively unreactive heterocycle pyridine is fluorinated by the higher fluorofullerenes. Reaction mechanisms are proposed to explain these observations.

Characterizing the electrospray-ionization mass spectral fragmentation pattern of enzymatically derived hyaluronic acid oligomers

Oligosaccharides derived from hyaluronic acid by action of bovine testicular hyaluronidase (BTH) (hyaluronate 4-glycanohydrolase, E.C. 3.2.1.35) were characterized by mass spectrometry (MS) with electrospray-ionization mass spectrometry (ESIMS) and compared with results obtained by matrix-assisted laser desorption/ionization. Both oligomers with an odd number and even number of sugar units with molecular masses up to 8 kDa were observed in the ESI spectra. However, the generation of odd-numbered oligomers is not consistent with the regiospecificity of the enzyme and with the MALDI results, which indicated even-numbered oligomers exclusively. In addition, a third method of characterization, high-performance anion-exchange chromatography (HPAEC), showed only even-numbered oligomers. Relative intensities of the odd-numbered oligomers demonstrated in ESIMS a cone-voltage dependence suggesting the odd-numbered oligomers resulted from collisional activation. In order to achieve results by ESI that mirror results from other techniques, the cone voltage must be kept low and precisely controlled. This study displays the usefulness and possible vulnerabilities of ESIMS when utilized for carbohydrate analysis without corroborating data from other methods of analysis.

POTASSIUM NITRITE REACTION WITH 11-NOR-DELTA9-TETRAHYDROCANNABINOL-9-CARBOXYLIC ACID IN URINE IN RELATION TO THE DRUG SCREENING ANALYSIS

Recently potassium nitrite has been used as an adulterant to interfere with the analysis of 11-nor-delta 9-tetrahydro-cannabinol-9-carboxylic acid (THC-COOH) in urine. A comprehensive study of the THC-COOH and nitrite reaction chemistry and stability under various conditions is presented. Reverse phase high performance liquid chromatography (HPLC) and negative electrospray mass spectrometry (ESMS) results are given to substantiate the derived reaction mechanism and properties leading to reaction termination. The addition of potassium carbonate as a buffering agent prior to or following sample void as a means of preventing the formation of a nitroso-complexed form of the 11-nor-delta 9+-tetrahydrocannabinol-9-carboxylic acid is evaluated.

Comparison of the repeatability of quantitative data measured in high-performance liquid chromatography with UV and atmospheric pressure chemical ionization mass spectrometric detection

A detailed comparison of the repeatability of the retention times, the peak efficiencies and the peak areas of a dozen probe compounds achieved in HPLC, using either HPLC-UV or HPLC-MS for detection purpose, is reported. Three groups of conventional analytes, each one separated under a different set of experimental conditions, were selected for this study. Most of the compounds are basic, the other ones being neutral. The repeatabilities of the retention times do not exhibit any influence of the mode of detection. However, the repeatabilities of the peak areas and the column efficiencies are generally (although not always) better in HPLC-UV than that in HPLC-MS. On average, the precision for the UV peak area detection was 2.5% versus 6.8% for MS detection. Experimental results show that the response factor of the UV detector is more constant than that of the MS detector, probably because the HPLC flow-rate was sufficiently stable. The results obtained in the different tests are discussed.

Fast atom bombardment-induced condensation of glycerol with ammonium surfactants. I: Regioselectivity of the adduct formation

Fast atom bombardment promotes condensation between trimethyl tetradecyl ammonium cations and the glycerol matrix. Bond formation at both the head and tail of the surfactant is demonstrated by low energy collision-induced dissociation (ClD) of deuterium-labeled precursors, with a preponderance of the reaction apparently occurring at the tail. Two distinct ClD pathways are identified for each kind of adduct (head- and tail-attack). Evidence is presented for the detection of distonic radical cations of the surfactant, complexed (solvated) with glycerol.

Studies of low-energy electron attachment at surfaces

Abstract Studies of the formation of negative ions at heated metal surfaces are reported under two experimental conditions: (1) laser desorption/ablation ionization and (2) heated metal wires in the presence of fluorine gas. In condition (1), nanoclusters of boron nitride/graphite are first produced by laser ablation of boron nitride mixed with graphite in a heated (∼1100 °C) rare gas followed by laser desorption negative ionization to yield a wide variety of cluster anions. The negative ion mass spectra for laser ablation/desorption ionization of small cluster ions from fullerenes, graphite, or most carbon containing metals (e.g. stainless steel) show common features (Cn− for n = 1 to ∼10, with even > odd alternation). The laser serves to heat the surface, produce clusters, and provides free and “quasifree” electrons for attachment and to dissociate larger negative ions/neutrals to produce low-mass cluster anions. Laser desorption of C60H36 and C60F48 at high laser power results in intense H− and F− ion signals, respectively. In the case of C60H36, the H− ion production is attributed to dissociative electron attachment, i.e. e + C60H36 → C60H35 + H−. For the case of C60F48, both dissociative attachment and photodissociation of C60F48− are believed responsible for the F− ion yield. These observations form the basis for the development of intense pulsed ion sources of H− and F− ions for use in energy production (fuel injection into fusion reactors), spallation neutron devices, lithography, and other applications. In condition (2), heated metal wires of Al, Au, Au/Pd, Nb, Ni/Cr, Pt, Re, Ta, Ti, V, W, and Zr are “burned” in a low pressure vapor of fluorine gas (∼10−4 Torr) resulting in a wide variety of molecular anions (e.g. Al2F9−; AuF2,3−; NbF6−; ReF5,6−; TaF6−; Ti4,5−; VF4,5−; WF5,6−; ZrF5−, and Zr2F9−) of varying intensity. Also of interest are the occurrences of F3− and the “impurity” ion Na2F3−.

Ionic Properties of Hydrogenated and Fluorinated Fullerenes

Using mass spectrometry, the ionization potentials (IP) of C{sub 60}H{sub n} for even-numbered n=2-12 were determined to be 6.75-7.5 eV, and for odd-numbered n were below 6.75 eV (for C{sub 60}, IP is 7.65 eV). Electron affinities (EA) of these species rapidly decrease with increasing n. IPs and EAs for C{sub 60}F{sub x}, on the other hand, both increase dramatically upon fluorination. A second electron can be added to gaseous C{sub 60}F{sub 48}{sup {minus}}; the resulting doubly charged anion is more stable than the singly charged anion.

Fast-atom bombardment-induced condensation of glycerol with ammonium surfactants II: Time dependence of mass spectra and tandem mass spectra.

Studies of fast-atom bombardment (FAB)-induced condensation between trimethyltetradecylammonium cations and glycerol have been extended to consider spectral time dependence. To enhance reproducibility of time dependence, a modified FAB target was used. FAB mass spectrometry of deuterium-labeled surfactants and FAB/collision-induced dissociation (CID) of nonlabeled material demonstrate that products of condensation at the surfactant “head group” predominate early in the analysis, while tail adducts become prominent later. This time dependence correlates with the expected surface activity of the products. It is incompatible with gas-phase reaction, but consistent with reaction in the condensed phase. Subtle variations in the surface activities of various condensation products (derived from changes in the number of hydroxyls from the reactive glycerol radical or in the position of attack along the surfactant chain) are reflected in the time dependence of FAB and CID spectra. CID spectra of deuterium-labeled cations provide evidence for intramolecular hydrogen transfer from the surfactant tail to the head within a surfactant radical. This transfer shows no significant kinetic isotope effect.

Mass spectrometric signature of S-prenylated cysteine peptides.

The fast atom bombardment mass spectra of peptides containing S-prenylated cysteine display signature fragmentations characteristic of this modified amino acid. The fragmentation is independent of the nature of the cysteine carbonyl substituent, easily differentiates prenyl from nonprenyl alkylation, and readily identifies the oligomer count of the prenyl. This screening method, which requires little time, effort, or material (compared with previous analysis methods based on chemical degradation), greatly facilitates the identification of these prenylated proteins.