The synthesis of a leukotriene with SRS-like activity

The synthesis and biological characteristics of an SRS-like leukotriene are described.     

Dephasing maps for quantum stochastic systems

Stochastic time evolution in a nonseparable and nonintegrable quantum system is manifested by rapid dephasing of gaussian wavepackets, whose topological distribution in the coordinate-momentum space defines its irregular regions, while wavepackets initiated in regular regions exhibit quasiperiodic evolution. A gradual transition from quasiperiodic to chaotic dynamics with increasing energy is observed.     

Silver(I)-catalyzed addition of zirconocenes to glycal epoxides. A new synthesis of alpha-C-glycosides

[reaction: see text] Hydrozirconation of terminal alkynes, followed by AgClO4-catalyzed in situ addition of the resultant alkenylzirconocenes to 1,2-anhydrosugars (glycal epoxides) leads to alpha-C-glycosides in moderate to high yields.     

Self-assembling porphyrin-modified peptides

[structure: see text] We report the synthesis and characterization of a novel supramolecular assembly that features long-range electronic coupling between porphyrins covalently attached to a designed peptide scaffold. The resulting construct self-assembles to form extended organized aggregates in which the porphyrins engage in exciton coupling.     

Electrochemical nitric oxide sensor preparation: a comparison of two electrochemical methods of electrode surface modification

Platinum electrodes modified with Mn(II) 5-(N-(8-pyrrole-yl-3,6-dioxa-1-aminooctane)phenylamide-10,15,20-trimethoxyphenylporphyrin (Mn(II)triOMeTCPPyP) using multi-sweep cyclic voltammetry and differential pulse amperometry were evaluated as electrocatalytic surfaces for the oxidation of nitric oxide. The electrodes modified using the pulse amperometric approach were more sensitive towards the detection of nitric oxide. The increased sensitivity led to the attainment of a wider linear dynamic range for the quantification of nitric oxide.     

Passive mode-locking by use of waveguide arrays

A novel mode-locking technique is presented in which the intensity-dependent spatial coupling dynamics of a waveguide array is used to achieve temporal mode-locking in a passive optical fiber laser. By use of the discrete, nearest-neighbor spatial coupling of the waveguide array, low-intensity light can be transferred to the neighboring waveguides and ejected (attenuated) from the laser cavity. In contrast, higher-intensity light is self-focused in the waveguide and remains largely unaffected. Numerical studies of this pulse shaping mechanism (intensity discrimination) show that using current waveguide arrays and standard optical fiber technology produces stable and robust mode-locked soliton-like pulses.     

Effects of informational maskers within and across trials

The across-trial effect of maskers in conditions of informational masking was evaluated from performance on occasional trials in which the signal was presented alone. For 6 of 12 listeners participating in the study, a significant number of errors were obtained on signal-alone trials; in some cases equivalent to that signal+ masker trials. On immediately preceding trial blocks for which there were no intervening maskers, performance for these signals was perfect. The results indicate that informational maskers can have a significant effect on signal threshold, both within and across trials.     

Classification and identification of recorded and synthesized impact sounds by practiced listeners, musicians, and nonmusicians

Three experiments were conducted to test the viability of a low-parameter modal model for synthesizing impact sounds to be used in commercial and psychoacoustic research. The model was constrained to have four physically based parameters dictating the amplitude, frequency, and decay of modes. The values of these parameters were selected by ear to roughly match the recordings of ten different resonant objects suspended by hand and struck with different mallets. In experiment 1, neither 35 professional musicians nor 187 college undergraduates could identify which of the two matched sounds was the real recording with better than chance accuracy, though significantly better than chance performance was obtained when modal parameters were selected without the previously imposed physical constraints. In experiment 2, the undergraduates identified the source corresponding to the recorded and synthesized sounds with the same level of accuracy and largely the same pattern of errors. Finally, experiment 3 showed highly practiced listeners to be largely insensitive to changes in the acoustic waveform resulting from an increase in the number of free parameters used in the modal model beyond 3. The results suggest that low-parameter, modal models might be exploited meaningfully in many commercial and research applications involving human perception of impact sounds.     

Forced folding and structural analysis of metastable proteins

A significant fraction of the proteins encoded by the human and other genomes appears to be significantly unfolded in vitro. This will undoubtedly hamper attempts to characterize their structure by classical crystallographic or solution NMR methods. Here we show that encapsulation of a metastable protein within the restricted volume a reverse micelle can be used to force fold the protein and allow its characterization by modern methods of NMR spectroscopy. This may have significant utility in the context of structural proteomics. In addition, variation of the inner volume of the reverse micelle can be used to probe the character of the manifold of unfolded states.