A cross-linked reverse micelle-encapsulated palladium catalyst

Cross-linked reverse micelle-palladium catalysts are effective and stable cross-coupling catalysts; cross-linking is crucial for stability.     

Probing dipeptide trans/cis stereochemistry using pH control of thiopeptide analogues, and application to the PepT1 transporter

The stereochemistry of thiodipeptides of proline [e.g. Ala-Psi[CS-N]-Pro] can be controlled using pH, allowing the trans-preference for substrates of the peptide transporter PepT1 to be confirmed.     

Comparison of solid-phase and solution-phase chiral auxiliaries in the alkylation/iodolactonization sequence to gamma-butyrolactones

Five prolinol-based chiral auxilaries have been compared for the stereoselective synthesis of gamma-butyrolactones via the sequence of N-acylation, C(alpha)()-allylation, and iodolactonization under both solution-phase and solid-phase conditions. Comparisons of stereoselectivity of both the C(alpha)()-allylation and iodolactonization processes indicate that incorporation of a non-C(2)-symmetric auxiliary as a polymer cross-link gives results superior to those obtained either in solution or with other non-C(2)-symmetric auxiliaries and comparable to those observed using a polymer-supported pseudo-C(2)-symmetric auxiliary.     

Sonoluminescence quenching by organic acids in aqueous solution: pH and frequency effects

The quenching of sonoluminescence from aqueous solutions by acrylic and methacrylic acids is dependent on whether the acid is ionised in solution, as controlled by the pH, but also by the frequency of ultrasound used.     

Enhancement of proton acceleration by hot-electron recirculation in thin foils irradiated by ultraintense laser pulses

MeV-proton production from solid targets irradiated by 100-fs laser pulses at intensities above 1x10(20) W cm(-2) has been studied as a function of initial target thickness. For foils 100 microm thick the proton beam was characterized by an energy spectrum of temperature 1.4 MeV with a cutoff at 6.5 MeV. When the target thickness was reduced to 3 microm the temperature was 3.2+/-0.3 MeV with a cutoff at 24 MeV. These observations are consistent with modeling showing an enhanced density of MeV electrons at the rear surface for the thinnest targets, which predicts an increased acceleration and higher proton energies.     

Practical low-noise stretched-pulse Yb(3+)-doped fiber laser

We report on the development of what we consider to be a practical and highly stable stretched-pulse laser based on Yb(3+) -doped silica fiber. The Fabry-Perot cavity uses nonlinear polarization rotation as the mode-locking mechanism, and a semiconductor saturable-absorber mirror to ensure robust self-starting and incorporates a diffraction grating pair to compensate for the normal dispersion of the fiber. Use of a single-mode grating-stabilized telecommunications-qualified pump laser diode ensures reliable, low-noise operation (~0.05% amplitude fluctuations at 10-Hz measurement bandwidth). The laser generates high-quality, 60-pJ pulses of <110-fs duration at a repetition rate of ~54 MHz (3-mW average power).