Synthesis and study of a novel hybrid UV photoinitiator: p-benzoyldiphenyliodonium hexafluorophosphate (PhCOPhI+PhPF)

A novel hybrid photoinitiator, p-benzoyldiphenyliodonium hexafluorophosphate (PhCOPhI⁺PhPF⁻₆), was synthesized, characterized, and studied. It absorbs UV light not only below 300 nm, but above 300 nm as well. When exposed to UV light, it undergoes an asymmetrical photocleavage to produce cation-radicals and radicals which could induce cationic and radical polymerizations respectively. Compared with the simple iodonium salt PhI⁺PhPF⁻₆, and bimolecular sensitization system PhCOPh/PhI⁺PhPF⁻₆, the covalently bonded photosensitization system PhCOPhI⁺PhPF⁻₆ is much more efficient as a photoinitiator. Oxygen has a small negative effect on the cationic polymerization photoinitiated by PhCOPhI⁺PhPF⁻₆, while isopropanol has a small positive influence only in argon atmosphere. © 1996 John Wiley & Sons, Inc.     

Novel blends from agave fibers and poly(methyl methacrylate)

Cellulose-rich fibers were isolated from Agave lechuguilla (AL) and Agave fourcroydes (AF) growing in the Mexican northeast. These fibers are a valuable feedstock for the preparation of blends with synthetic polymers like poly(methyl methacrylate), PMMA. Blends of different types of agave fibers (dewaxed, mercerized, and grafted) and PMMA were prepared and investigated by means of tension measurements and dynamic mechanical analysis. The fiber-containing blends are more stable than the plain PMMA. Surprisingly, the mechanical stability of the blends is practically independent of the pretreatment of the fibers. Methyl methacrylate (MMA) was grafted onto the biopolymer fibers initiated by the cerammonium nitrate redox initiator. Grafting yields of 26.5% were realized with fibers from AL while up to 75.8% MMA was grafted onto fibers from AF. The materials were characterized by means of FTIR spectroscopy and DSC.     

Enzyme kinetics of multiple alternative substrates

An innovative theoretical approach that enables the complete characterisation of enzyme–substrate and enzyme–substrate–competitor reactions is generalised to systems with multiple alternative substrates. Based on the quasi‐steady‐state assumption, time‐dependent closed form solutions are presented for cases with even, weak and mixed substrate competition. The analytic framework should facilitate the development of computational fitting procedures for progress curves, simplifying the measuring process and increasing the reliability of reaction constant estimates. This revised version was published online in July 2006 with corrections to the Cover Date.     

Modifying the structure of dinuclear ruthenium complexes with antitumor activity

In order to modulate the structure of a recently developed series of antitumor‐active, dinuclear Ru(II)–arene compounds, complexes 1c – 4c were synthesized. The complexes were modified with respect to their pyridinone moieties and the spacer linking the two metal centers. More particularly, the series of dinuclear ruthenium(II) complexes was extended to compounds with longer spacers, i.e. tetradecane and 3,7,10‐trioxotridecane, and the pyridinone ring was modified by replacing the methyl group by an ethyl group and by shifting the position of the methyl group. The organometallic ruthenium compounds were obtained from the reaction between [RuCl₂(η⁶‐p‐isopropyltoluene)]₂ and ligands 1b – 4b with yields ranging from 41 to 67%. All compounds were characterized by standard methods: MS, ¹H and ¹³C NMR spectroscopy and elemental analysis. Copyright © 2008 John Wiley & Sons, Ltd.     

Differences in voice quality between men and women: Use of the long-term average spectrum (LTAS)

The goal of this study was to determine if there are acoustical differences between male and female voices, and if there are, where exactly do these differences lie. Extended speech samples were used. The recorded readings of a text by 31 women and by 24 men were analyzed by means of the Long-term Spectrum (LTAS), extracting the amplitude values (in decibels) at intervals of 160 Hz over a range of 8 kHz. The results showed a significant difference between genders, as well as an interaction of gender and frequency level. The female voice showed greater levels of aspiration noise, located in the spectral regions corresponding to the third formant, which causes the female voice to have a more “breathy” quality than the male voice. The lower spectral tilt in the women's voices is another consequence of this presence of greater aspiration noise.     

The role of Fe during hydride formation in the Mg–Fe system: a Mössbauer investigation

The mechanically assisted hydriding of Mg_1???x Fe _x powder mixtures with x?=?0.02, 0.03, 0.10, 0.20 and 0.33 was studied. The hydriding kinetics up to saturation was followed from the hydrogen absorption during milling. All the steady state samples and some partially hydrided ones, with x?=?0.03 , were characterized by X-ray diffraction and Mössbauer spectroscopy. The catalytic action of Fe in the H₂ sorption by Mg based systems and the influence of complex ternary hydride formation in such processes are discussed.     

N-Acyl-2-benzoxazolinones in titanium-mediated aldol reactions

N-Acyl-2-benzoxazolinones readily form trichlorotitanium enolates that react rapidly with aldehydes to provide crystalline syn-aldol adducts in high yield. The resulting products are simply converted to amides, esters, and thioesters. A simple, economical synthesis of 3-hydroxy-2-methylpentanoate N-propionylcysteamine thioesters based on these findings is presented.