Paul M. Mayer

Methods to determine the biological composition of particulate matter collected from outdoor air

Abstract Associations between increased morbidity and exposure to ambient air particulates have been the subject of intense study. Few data exist on the presence of cells or cell materials of fungi, bacteria and pollen in fine particle samples (

THE MECHANISMS OF COLLISIONAL ACTIVATION OF IONS IN MASS SPECTROMETRY

This article is a review of the mechanisms responsible for collisional activation of ions in mass spectrometers. Part I gives a general introduction to the processes occurring when a projectile ion and neutral target collide. The theoretical background to the physical phenomena of curve-crossing excitation (for electronic and vibrational excitation), impulsive collisions (for direct translational to vibrational energy transfer), and the formation of long-lived collision intermediates is presented. Part II highlights the experimental and computational investigations that have been made into collisional activation for four experimental conditions: high (>100 eV) and intermediate (1-100 eV) center-of-mass collision energies, slow heating collisions (multiple low-energy collisions) and collisions with surfaces. The emphasis in this section is on the derived post-collision internal energy distributions that have been found to be typical for projectile ions undergoing collisions in these regimes.

Chemical composition of acid–base fractions separated from biooil derived by fast pyrolysis of chicken manure

Our earlier investigations on the chemical composition of biooils derived by the fast pyrolysis of chicken manure revealed the presence of more than 500 compounds. In order to simplify this heterogeneous and complex chemical system, we produced four biooil fractions namely strongly acidic fraction A, weakly acidic fraction B, basic fraction C and neutral fraction D on the basis of their solubilities in aqueous solutions at different pHs. The yield (wt/wt.%) for fraction A was 3%, for fraction B 21.3%, for fraction C 2.4% and for fraction D 32.4%, respectively. The four fractions were analyzed by elemental analyses, Fourier Transform infrared spectrophotometry (FTIR), (1)H and (13)C nuclear magnetic spectroscopy (NMR), and electrospray ionization mass spectrometry (ESI-MS). The major components of the four fractions were saturated and unsaturated fatty acids, N-heterocyclics, phenols, sterols, diols and alkylbenzenes. The pH separation system produced fractions of enhanced chemical homogeneity.

An assessment of theoretical procedures for the calculation of reliable radical stabilization energies

The performance of a variety of theoretical methods in computing stabilization energies of the substituted methyl and vinyl radicals ˙CH2F, ˙CH2CN, ˙CH2CHCH2, ˙CH2CHO, CH2C˙F and CH2C˙CN is examined. The influence of electron correlation (UHF, UMP2, PMP2, RMP2, UB3-LYP, UQCISD, UQCISD(T), UCCSD(T), URCCSD(T) and RRCCSD(T)) and basis set size (from 6-31G(d) to 6-311++G(3df,3pd)) on stabilization energies is evaluated, as well as the performance of compound methods such as G2, G3, CBS-Q and CBS-APNO and their variants. The results indicate that generally reliable radical stabilization energies can be obtained at modest cost using RMP2/6-311+G(2df,p)//RMP2/6-31G(d) energies. A slightly less accurate but more economical procedure is RMP2/6-311+G(d)//B3-LYP/6-31G(d). UMP2 and PMP2 are unsuitable for obtaining radical stabilization energies for spin-contaminated radicals, while UB3-LYP appears generally to overestimate stabilization energies.

On the dissociation of the naphthalene radical cation: new iPEPICO and tandem mass spectrometry results.

The dissociation of the naphthalene radical cation has been reinvestigated here by a combination of tandem mass spectrometry and imaging photoelectron photoion coincidence spectroscopy (iPEPICO). Six reactions were explored: (R1) C(10)H(8)(•+) → C(10)H(7)(+) + H (m/z = 127); (R2) C(10)H(8)(•+) → C(8)H(6)(•+) + C(2)H(2) (m/z = 102); (R3) C(10)H(8)(•+) → C(6)H(6)(•+) + C(4)H(2) (m/z = 78); (R4) C(10)H(8)(•+) → C(10)H(6)(•+) + H(2) (m/z = 126); (R5) C(10)H(7)(+) → C(6)H(5)(+) + C(4)H(2) (m/z = 77); (R6) C(10)H(7)(+) → C(10)H(6)(•+) + H (m/z = 126). The E(0) activation energies for the reactions deduced from the present measurements are (in eV) 4.20 ± 0.04 (R1), 4.12 ± 0.05 (R2), 4.27 ± 0.07 (R3), 4.72 ± 0.06 (R4), 3.69 ± 0.26 (R5), and 3.20 ± 0.13 (R6). The corresponding entropies of activation, ΔS(‡)(1000K), derived in the present study are (in J K(-1) mol(-1)) 2 ± 2 (R1), 0 ± 2 (R2), 4 ± 4 (R3), 11 ± 4 (R4), 5 ± 15 (R5), and -19 ± 11 (R6). The derived E(0) value, combined with the previously reported IE of naphthalene (8.1442 eV) results in an enthalpy of formation for the naphthyl cation, Δ(f)H°(0K) = 1148 ± 14 kJ mol(-1)/Δ(f)H°(298K) = 1123 ± 14 kJ mol(-1) (site of dehydrogenation unspecified), slightly lower than the previous estimate by Gotkis and co-workers. The derived E(0) for the second H-loss leads to a Δ(f)H° for ion 7, the cycloprop[a]indene radical cation, of Δ(f)H°(0K) =1457 ± 27 kJ mol(-1)/Δ(f)H°(298K)(C(10)H(6)(+)) = 1432 ± 27 kJ mol(-1). Detailed comparisons are provided with values (experimental and theoretical) available in the literature.

Concerning the heats of formation of CH2NH and CH2NH

Energy-resolved electron impact was used to measure the appearance energy of CH 2 NH + from azetidine and propargylamine and the adiabatic ionization energy of CH 2 NH formed in the pyrolysis of azetidine. The heats of formation of CH 2 NH and CH 2 NH + were determined to be 22 ± 3 and 250± 2 kcal mol −1 , respectively, although the presence of a competitive shift makes the results upper limits. A review of past thermochemical determinations leads to a selected value for Af H 298 0 (CH2NH) of 21 ± 4 kcal tool −1 .

Epicuticular Compounds of Drosophila subquinaria and D. recens : Identification, Quantification, and Their Role in Female Mate Choice

The epicuticle of various Drosophila species consists of long-chain cuticular hydrocarbons (CHCs) and their derivatives that play a role in waterproofing and a dynamic means of chemical communication. Here, via gas chromatography and mass spectrometry, we identified and quantified the epicuticular composition of D. recens and D. subquinaria, two closely related species that show a pattern of reproductive character displacement in nature. Twenty-four compounds were identified with the most abundant, 11-cis-Vaccenyl acetate, present only in males of each species. Also exclusive to males were five tri-acylglycerides. The 18 remaining compounds were CHCs, all shared between the sexes and species. These CHCs were composed of odd carbon numbers (C29, C31, C33, and C35), with an increase in structural isomers in the C33 and C35 groups. Saturated hydrocarbons comprise only methyl-branched alkanes and were found only in the C29 and C31 groups. Alkenes were the least prevalent, with alkadienes dominating the chromatographic landscape in the longer chain lengths. Sexual dimorphism was extensive with 6/8 of the logcontrast CHCs differing significantly in relative concentration between males and females in D. recens and D. subquinaria, respectively. Males of the two species also differed significantly in relative concentration of six CHCs, while females differed in none. Female-choice mating trials revealed directional sexual selection on male CHCs in a population of each species, consistent with female mate preferences for these traits. The sexual selection vectors differed significantly in multivariate trait space, suggesting that different pheromone blends determine male attractiveness in each species.

Threshold photoelectron study of naphthalene, anthracene, pyrene, 1,2-dihydronaphthalene, and 9,10-dihydroanthracene

Threshold photoelectron spectra (TPESs) were obtained for naphthalene, anthracene, pyrene, 1,2-dihydronaphthalene, and 9,10-dihydroanthracene using imaging photoelectron photoion coincidence spectroscopy, from threshold to a photon energy of ∼20 eV. Outer valence Greens function calculations at the OVGF∕cc-pVTZ level of theory were used to assign molecular orbitals to the observed TPES features. There is generally good agreement between the predicted and observed bands. Threshold regions for each molecule exhibit vibrational structure which is readily assigned based on previous PES studies. While the measured adiabatic ionization energies (IE(a)) for naphthalene, anthracene, and pyrene are in good agreement with previous works, new values are reported for the two dihydro species (1,2-dihydronaphthalene, 8.010 ± 0.010 eV and 9,10-dihydroanthracene, 8.335 ± 0.010 eV). A comparison is also made with the G3∕∕B3LYP composite method, which consistently overestimates the IE values by 0.06-0.09 eV. The double ionization energies for anthracene and pyrene have been measured to be 19.3 ± 0.2 and 19.8 ± 0.2 eV, respectively.

The effects of methyl substitution on the structure and thermochemistry of the cyanomethyl radical and cation

Energy-resolved electron impact appearance energy (AE) measurements were performed to determine the heat of formation of the cyanomethyl radical and cation as well as the ionization energy (IE) of the methyl substituted analogues, CH3ĊHCN and (CH3)2ĊCN. The results were ΔfH0298 (CH2CN) = 58 ± 3 kcal mol−1, ΔfH0298 (+CH2CN) = 287 ± 1 kcal mol−1, IE (CH3ĊHCN) = 9.25 ± 0.02 eV and IE ((CH3)2ĊCN) = 8.48 ± 0.02 eV, the latter two values yielding the corresponding cationic heats of formation, 263 ± 2 kcal mol−1 and 236 ± 2 kcal mol−1. The results were used to explore both π delocalization and the predictability of thermochemical properties in nitrile substituted cations and radicals.

Experiment and theory combine to produce a practical negative ion calibration set for collision cross‐section determinations by travelling‐wave ion‐mobility mass spectrometry

RATIONALE There are relatively few cross-section measurements for negatively charged ions. Available calibrants provide sufficient cross-section coverage for the 390 Å(2) to 641 Å(2) and 1174 Å(2) to 3395 Å(2) ranges. This is not particularly well suited for determining the collision cross-sections of smaller ions, such as small peptides. METHODS Molecular mechanics/molecular dynamics (MM/MD) simulations, coupled with simulated annealing, were used to find the low-energy molecular conformations of polystyrene (PS) oligomers of length 3-9 (singly deprotonated) and 5-13 (doubly deprotonated). The trajectory method in MOBCAL was employed to derive their respective collision cross-sections, Ω. A calibration plot relating corrected Ω values to drift times in a Waters Synapt G2 mass spectrometer was used to predict the Ω values for the -2 to -6 charge states of dT(10) DNA. RESULTS The in silico design of a reliable negative ion calibration set for ion mobility spectrometry successfully resulted in the use of α,ω-carboxy-terminated PS oligomers to determine the collision cross-sections of negatively charged ions in the range 132-388 Å(2). All charge states of dT(10) DNA were predicted to within 3% of the referenced values for these ions. CONCLUSIONS α,ω-Carboxy-terminated PS oligomers were found to be an excellent choice to calibrate ion mobility spectrometers to obtain cross-sections for moderately sized ions. Oligomers with fewer, or weaker, interactions among the internal side chains (like poly(ethylene glycol) oligomers) tend to have a wide range of low-energy molecular conformations resulting in large standard deviations in their theoretically predicted collision cross-sections.