Electronic structure of paramagnetic clusters of transition metal ions. 3. Magnetic properties and scattered wave description of the electronic structure of the hexanuclear octahedral cluster [Fe6(μ3−S)8(PEt3)6] (BPh4)2

Spin-polarized Xα–SW calculations of [Fe₆(μ₃?S)₈(PH₃)₆]²⁺ as a model of the cluster [Fe₆(μ₃?S)₈(PEt₃)₆] (BPh₄)₂ have been performed. The highest occupied energy levels are well separated from empty levels, and up to a maximum of eight electrons can be unpaired, giving a maximum spin state with S = 4. This electronic state is consistent with the magnetic data of [Fe₆(μ₃?S)₈(PEt₃)₆](BPh ₄)₂, which have been interpreted using the Heisenberg–Dirac–Van Vleck exchange spin Hamiltonian. The S = 4 state arises from the magnetic coupling between five low-spin (S_i = 1/2) and one intermediate-spin (S = 3/2) iron(III) center. © 1994 John Wiley & Sons, Inc.     

Heptametallic,Octupolar Nonlinear Optical Chromophores with Six Ferrocenyl Substituents

New complexes with six ferrocenyl (Fc) groups connected to Zn^II or Cd^II tris(2,2′‐bipyridyl) cores are described. A thorough characterisation of their BPh₄^? salts includes two single‐crystal X‐ray structures, highly unusual for such species with multiple, extended substituents. Intense, visible d(Fe^II)→π* metal‐to‐ligand charge‐transfer (MLCT) bands accompany the π→π* intraligand charge‐transfer absorptions in the near UV region. Each complex shows a single, fully reversible Fe^III/II wave when probed electrochemically. Molecular quadratic nonlinear optical (NLO) responses are determined by using hyper‐Rayleigh scattering and Stark spectroscopy. The latter gives static first hyperpolarisabilities β₀ reaching as high as approximately 10^?27 esu and generally increasing with π‐conjugation extension. Z‐scan cubic NLO measurements reveal high two‐photon absorption cross‐sections σ₂ of up to 5400 GM in one case. DFT calculations reproduce the π‐conjugation dependence of β₀, and TD‐DFT predicts three transitions close in energy contributing to the MLCT bands. The lowest energy transition has octupolar character, whereas the other two are degenerate and dipolar in nature.     

Comparison between post-Hartree-Fock and DFT methods for the study of strength and mechanism of cleavage of Hg(SINGLE BOND)C bond

A parallel MP2 and DFT study was performed for mercury dihalides and for representative organomercury compounds including a Hg(SINGLE BOND)C bond. From a methodological point of view, medium-size basis sets provide reliable general trends for a number of properties already at the HF level. However, quantitative results can only be obtained including correlation energy by post-Hartree-Fock (even at the MP2 level) or density functional models and adding f-polarization functions on Hg. At this level, geometrical parameters are sufficiently accurate for most purposes and reliable thermodynamic data can be obtained using isodesmic reactions. The advantage of the DF approach resides, besides the shorter computation times, in the lower dependence of the results on the basis set. From a more general point of view, all the computations indicate that Hg(SINGLE BOND)C bond breaking is favored, decreasing the electronegativity of further substituents. We have next investigated the reaction mechanism for cleavage of the Hg(SINGLE BOND)C bond by halogenic acids. Our results show that the reaction occurs through a one-step mechanism in which, however, bond forming and breaking are not completely synchronous. © 1997 John Wiley & Sons, Inc.     

MALDI-TOF/TOF de novo sequence analysis of 2-D PAGE-separated proteins from Halorhodospira halophila, a bacterium with unsequenced genome

Because protein identifications rely on matches with sequence databases, high-throughput proteomics is currently largely restricted to those species for which comprehensive sequence databases are available. The identification of proteins derived from organisms with unsequenced genomes mainly depends on homology searching. Here, we report the use of a simplified, gel-based, chemical derivatization strategy for de novo sequence analysis using a MALDI-TOF/TOF mass spectrometer. This approach allows the determination of de novo peptide sequences of up to 20 amino acid residues in length. The protocol was applied on a proteomic study of 2-D PAGE-separated proteins from Halorhodospira halophila, an extremophilic eubacterium with yet unsequenced genome. Using three different homology-based search algorithms, we were able to identify more than 30 proteins from this organism using subpicomole quantities of protein.     

A case study of de novo sequence analysis of N-sulfonated peptides by MALDI TOF/TOF mass spectrometry

The simplicity and sensitivity of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry have increased its application in recent years. The most common method of "peptide mass fingerprint" analysis often does not provide robust identification. Additional sequence information, obtained by post-source decay or collision induced dissociation, provides additional constraints for database searches. However, de novo sequencing by mass spectrometry is not yet common practice, most likely because of the difficulties associated with the interpretation of high and low energy CID spectra. Success with this type of sequencing requires full sequence coverage and demands better quality spectra than those typically used for data base searching. In this report we show that full-length de novo sequencing is possible using MALDI TOF/TOF analysis. The interpretation of MS/MS data is facilitated by N-terminal sulfonation after protection of lysine side chains (Keough et al., Proc. Natl. Acad. Sci. U.S.A. 1999, 96, 7131-7136). Reliable de novo sequence analysis has been obtained using sub-picomol quantities of peptides and peptide sequences of up to 16 amino acid residues in length have been determined. The simple, predictable fragmentation pattern allows routine de novo interpretation, either manually or using software. Characterization of the complete primary structure of a peptide is often hindered because of differences in fragmentation efficiencies and in specific fragmentation patterns for different peptides. These differences are controlled by various structural parameters including the nature of the residues present. The influence of the presence of internal Pro, acidic and basic residues on the TOF/TOF fragmentation pattern will be discussed, both for underivatized and guanidinated/sulfonated peptides.     

Physical Appearance and Voice in Male-To-Female Transsexuals

It has been suggested that sex judgments of male-to-female transsexuals based on the voice may be influenced by the physical appearance of the clients. To explore this hypothesis, a listener experiment was designed in which a panel of 22 laypersons and 22 students in speech-language pathology rated the “femaleness” of fourteen male-to-female transsexuals from video-recorded speech samples in three modes of presentation: auditory-only presentation, visual-only presentation, and audiovisual presentation. Results indicate that appearance and voice are indeed interacting factors. Ratings from the auditory-only presentation were significantly lower than ratings from the audiovisual presentation and ratings from the visual-only presentation were significantly higher than those from the audiovisual presentation. It follows that the success of voice training in male-to-female transsexuals is not solely dependent on vocal characteristics and that speech pathologists should consider incorporating physical appearance as a treatment and outcome variable in the voice training of male-to-female transsexuals.     

Voice and Physical Appearance in Female-to-Male Transsexuals

The study aims to investigate if a similar interaction between physical appearance and voice could be found in female-to-male transsexuals as had been observed in male-to-female transsexuals. A panel of judges rated “maleness” of seven female-to-male transsexuals from video-recorded speech samples using three modes of presentation: auditory-only presentation, visual-only presentation, and audiovisual presentation. For the group of transsexuals as a whole, no significant differences were found between scores given in the auditory-only mode or the visual-only mode and those given in the audiovisual mode. Analysis of individual results, however, yielded significant differences in some individuals and there was some relation with hormone treatment. There was no significant correlation between the ratings of “maleness” in the auditory-only mode and fundamental frequency. Physical appearance in female-to-male transsexuals appears not to be a strong influencing factor in general, but may interact with gender recognition based on the voice in some individuals. The absence of a correlation between fundamental frequency and rating of maleness could mean that in female-to-male transsexuals, fundamental frequency is a relatively less important factor for gender expression or perhaps also that a higher voice in males is more accepted than a lower voice in females.