ABSTRACT
Sulfenic acid (HSOH, 1) has been synthesized in the gas-phase by low-pressure high-temperature (1150 degrees C) pyrolysis of di-tert-butyl sulfoxide (tBu(2)SO, 2) and characterized by means of matrix isolation and gas-phase IR spectroscopy. High-level coupled-cluster (CC) calculations (CCSD(T)/cc-pVTZ and CCSD(T)/cc-pVQZ) support the first identification of the gas-phase IR spectrum of 1 and enable its spectral characterization. Five of the six vibrational fundamentals of matrix-isolated 1 have been assigned, and its rotational-resolved gas-phase IR spectrum provides additional information on the O-H and S-H stretching fundamentals. Investigations of the pyrolysis reaction by mass spectrometry, matrix isolation, and gas-phase FT-IR spectroscopy reveal that, up to 500 degrees C, 2 decomposes selectively into tert-butylsulfenic acid, (tBuSOH, 3), and 2-methylpropene. The formation of the isomeric sulfoxide (tBu(H)SO, 3 a) has been excluded. Transient 3 has been characterized by a comprehensive matrix and gas-phase vibrational IR study guided by the predicted vibrational spectrum calculated at the density functional theory (DFT) level (B3LYP/6-311+G(2d,p)). At higher temperatures, the intramolecular decomposition of 3, monitored by matrix IR spectroscopy, yields short-lived 1 along with 2-methylpropene, but also H(2)O, and most probably sulfur atoms. In addition, HSSOH (6), H(2), and S(2)O are found among the final pyrolysis products observed at 1150 degrees C in the gas phase owing to competing intra- and intermolecular decomposition routes of 3. The decomposition routes of the starting compound 2 and of the primary intermediate 3 are discussed on the basis of experimental results and a computational study performed at the B3LYP/6-311G* and second-order Møller-Plesset (MP2/6-311G* and RI-MP2/QZVPP) levels of theory.
ABSTRACT
The allelic variations of the regulatory operon agr (groups I-IV) and the cap polymorphism (capsular types 5 and 8) were used as a typing scheme for rapid strain designation in Staphylococcus aureus. In combining 10 agr subgroups resolved by restriction fragment length polymorphism (RFLP) analysis with the two cap polymorphisms 12 types could be defined. To assess whether this type designation is informative for the population structure of the species S. aureus, agr and cap types were determined in clonal lineages defined by pulsed-field gel electrophoresis (PFGE) of a collection of 219 isolates. agr groups and cap types were both linked to certain clone complexes. However, little correlation was found between the two polymorphic loci. By PFGE cluster analysis 11 prevalent and 52 sporadic clones were defined. Most of the prevalent clones (9/11) could be discriminated by agr/cap typing. Thus, this technique allows a first subdivision of isolates and an inter-center comparable designation of S. aureus clones preceding a more detailed clonal analysis by PFGE or multi-locus sequence typing (MLST). To get insight into agr diversification, sequence analysis of the variable and conserved part of agr from selected S. aureus clones was performed. Strains of agr-I displayed the highest sequence divergence on the nucleotide and amino acid level, suggesting an early diversification of this group. When analyzing the relationship between the four agr interference groups we could show: (i) one intermediate between agr-I and agr-IV alleles; (ii) agr-IV sequences seem to bridge the agr-I and -III groups and (iii) two cases of horizontal transfer of the variable gene cassette from an agr-I strain to an agr-II strain. Thus, stepwise evolutionary progression and rare events of recombination were evident in the diversification of the agr locus.
