Unraveling structure-reactivity relationships in SNV reactions: kinetics of the reactions of methoxybenzylidenemalononitrile, 2-(methylthiobenzylidene)-1,3-indandione, 2-(benzylthiobenzylidene)-1,3-indandione, and methyl beta-methylthio-alpha-nitrocinnamate with OH- and thiolate ions in aqueous DMSO.

The kinetics of the title reactions were determined in 50% DMSO-50% water (v/v) at 20 degrees C; n-BuS-, HOCH2CH2S-, and MeO2CCH2S- were used as thiolate ions. The reactions with the thiolate ions gave rise to two separate kinetic processes. The first refers to rapid, reversible attachment of RS- to the substrate leading to a tetrahedral intermediate (k1RS), k(-1)RS, the second to the conversion of the intermediate to products (k2RS). In most cases all of the rate constants (k1RS, k(-1)RS and k2RS could be determined. In combination with results from previous studies, a detailed discussion regarding the effects of activating substituents and leaving groups on rate and equilibrium constants as well as on intrinsic rate constants is presented. The reaction with OH- only allowed a determination of k1OH for nucleophilic attack on the substrate; in this case the tetrahedral intermediate remains at steady-state levels under all conditions.     

FTIR Emission Spectra, Molecular Constants, and Potential Curve of Ground State GeO

Extensive new high-temperature, high-resolution FTIR emission spectroscopy measurements for the five common isotopomers of GeO are combined with previous diode laser and microwave measurements in combined isotopomer analyses. New Dunham expansion parameters and an accurate analytical potential energy function are determined for the ground X1Sigma+ state. Copyright 1999 Academic Press.     

Ferrichrome: Surprising stability of a cyclic peptide-FeIII complex revealed by mass spectrometry

Ferrichrome, a fungal siderophore that is also utilized by some bacterial species, was studied with liquid secondary ion mass spectrometry (LSIMS) and matrix-assisted laser desorption ionixation (MALDI) mass spectrometry. A strong ionic signal corresponding to a Fe^III complex was observed with LSIMS in the positive ion mode. Switching the polarity of the mass spectrometer did not necessarily result in reduction of ferric ion, although certain conditions led to appearance of a Fe^II complex signal as well. The results of the structural studies of the metal ion-cyclic peptide complex with collisionally induced dissociation allowed unambiguous identification of the chelation sites. The action of the siderophore on Fe^III was studied by in vitro chelation of ferric ion (from ferric citrate) by the iron-free ferrichrome. Effective chelation of ferric ion was compared to actions of the iron-free ferrichrome on other metal ions. Unlike LSIMS, desorption with MALDI did not form selectively molecular ions of intact ferrichrome: the spectra contained abundant peaks corresponding to the cyclic peptide itself and its nonspecific association with alkali metal ions.     

Carolyn Eisele's place in Peirce studies

Carolyn Eisele's unique, ongoing career as a scholar is sketched, and the importance of her contributions to Peirce Studies and other fields is emphasized. The essay concludes with a series of suggestions about how to interpret Peirce's works based on themes related to the pioneering efforts of Dr. Eisele.