Gas‐phase rate coefficients for the reactions of O(3P), S(3P), Se(3P), and Te(3P) with alkenes: Application of perturbation frontier molecular orbital theory,correlations, and structure–activity relations (SARs)

The kinetics of the reactions of the atoms O(³P), S(³P), Se(³P), and Te(³P) with a series of alkenes are examined for correlations relating the logarithms of the rate coefficients to the energies of the highest occupied molecular orbitals (HOMOs) of the alkenes. These correlations may be employed to predict rate coefficients from the calculated HOMO energy of any other alkene of interest. The rate coefficients obtained from the correlations were used to © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 351–356, 2006     

Observations on the detection of b‐ and y‐type ions in the collisionally activated decomposition spectra of protonated peptides

Tandem mass spectrometric data from peptides are routinely used in an unsupervised manner to infer product ion sequence and hence the identity of their parent protein. However, significant variability in relative signal intensity of product ions within peptide tandem mass spectra is commonly observed. Furthermore, instrument‐specific patterns of fragmentation are observed, even where a common mechanism of ion heating is responsible for generation of the product ions. This information is currently not fully exploited within database searching strategies; this motivated the present study to examine a large dataset of tandem mass spectra derived from multiple instrumental platforms. Here, we report marked global differences in the product ion spectra of protonated tryptic peptides generated from two of the most common proteomic platforms, namely tandem quadrupole‐time‐of‐flight and quadrupole ion trap instruments. Specifically, quadrupole‐time‐of‐flight tandem mass spectra show a significant under‐representation of N‐terminal b‐type fragments in comparison to quadrupole ion trap product ion spectra. Energy‐resolved mass spectrometry experiments conducted upon test tryptic peptides clarify this disparity; b‐type ions are significantly less stable than their y‐type N‐terminal counterparts, which contain strongly basic residues. Secondary fragmentation processes which occur within the tandem quadrupole‐time‐of‐flight device account for the observed differences, whereas this secondary product ion generation does not occur to a significant extent from resonant excitation performed within the quadrupole ion trap. We suggest that incorporation of this stability information in database searching strategies has the potential to significantly improve the veracity of peptide ion identifications as made by conventional database searching strategies. Copyright © 2009 John Wiley & Sons, Ltd.     

Assessment of compliance of analytical results with regulatory or specification limits

 In some cases the compliance of a measurement result with a limit value will be unclear and a 'judgment' is required based on agreed criteria. Recent developments in the estimation of measurement uncertainty have opened up the possibility of a more rational approach to such problems. This paper briefly reviews some of the issues and current practices and suggests a pragmatic way forward. Received: 26 August 1998 · Accepted: 31 August 1998     

On a deception game with three boxes

This paper clarifies the status of a deception game posed by Spencer. We show the value of this game is zero.     

Comparison of singlet methylene removal rates by group IV hydrides

The technique of laser flash photolysis/laser absorption has been used to obtain an absolute removal rate constant of (3.85 ± 0.18) × 10^?10 cm³ molecule^?1 s^?1 for singlet methylene, ¹CH₂ (ã¹A₁), with germane (GeH₄) at ambient temperature. The removal rate constant is compared with the values for methane (CH₄) and silane (SiH₄) which have been determined previously. © 1995 John Wiley & Sons, Inc.     

Asymptotic analysis of a model for substitutional-interstitial diffusion

A substitutional-interstitial model for impurity diffusion in semi-conductors is discussed. In particular we consider a surface-source problem and obtain asymptotic solutions in the limit of the surface concentration of impurity being much greater than the equilibrium vacancy concentration. In the absence of vacancy generation, a double error function impurity curve is obtained. These double profiles reproduce some of the qualitative features of diffusion in many III–V semiconductor systems. We also discuss how vacancy generation modifies the analysis and show that in the limit of high vacancy generation, the problem becomes one of linear diffusion with the diffusion curves then being single error function complements.