Multiple Equilibrium States of Slightly Extensible Elastic Strings

We consider the equilibrium states of elastic strings loaded transversely by their own weight. We are interested in the relation between the equilibrium states of inextensible strings and those of strings which are nonlinearly elastic and slightly extensible. The inextensible string has a unique concave equilibrium state while the concave equilibrium states of a nonlinearly elastic string come in pairs. In this paper we explore the relation between the two models. This revised version was published online in August 2006 with corrections to the Cover Date.     

Syntheses of 3-Chloro-7-[(Chlorocarbonyl)Methoxy]-4-Methylcoumarin

Two efficient syntheses of 3-chloro-7-[(chlorocarbonyl)methoxy]-4-methylcoumarin are described, one utilizing traditional chemistry starting from 3-chloro-7-hydroxy-4-methylcoumarin, while the other uses a novel reagent, sulfuryl chloride/thionyl chloride, in a one-pot reaction starting from 7-(carboxymethoxy)-4-methylcoumarin.     

Palladium catalyzed asymmetric sulfonylation mediated chiral β-hydroxy- and β-(o-diphenylphosphino)benzoyloxy (o-diphenyl phosphino)benzamides

The palladium catalyzed asymmetric allylic sulfonylation reaction has been investigated employing β-hydroxy- and β-(o-diphenylphosphino)benzoyloxy (o-diphenyl phosphino)benzamides as chiral, non-racemic ligands. The bisphosphine β-benzoyloxybenzamide ligands proved to be the best ligands for this process. Competitive transition states for the (1S,2R)-norephedrine derived ligand 14 are compared and a rationale is provided for the observed enantioselectivities.     

Focusing of dispersive phonons in GaAs

The ballistic propagation of highly dispersive phonons in GaAs in analyzed with both a bond-charge model (BCM) and a shell model, and compared to imaging experiments. When scattering is neglected, both models predict dispersive focusing pattern which depend strongly on the selected group velocities. In contrast, velocity-selected phonon images obtained with a PbBi tunnel-junction detector on a 0.7-mm thick crystal, display well-defined caustic lines whose angular positions do not shift at longer delay times. When isotope scattering is considered in the calculation, however, the shell model reproduces the experimental focusing structures remarkably well.For highly dispersive phonons, the bond-charge and shell models predict markedly different phonon-focusing patterns. In particular, a concentration of heat flux along [100] is predicted by BCM forv=1.7–2.0 THz slow-transverse (ST) phonons., but this effect is absent in the shell model. Both models predict new focusing structures in the fasttransverse (FT) mode at high frequencies. Our calculations which include isotope scattering indicate that to observe these new structures considerable technical advances are required in the phonon-imaging experiments.     

Measurement of a phonon hot spot in photoexcited Si

High frequency phonons are produced by the thermalization of photoexcited electronhole pairs in a semiconductor. Inelastic and elastic scattering processes determine the frequency down-conversion and diffusion of this thermal energy. Simple estimates of the anharmonic and isotope scattering processes suggest that the acoustic phonons will undergo a quasi-diffusive propagation process. In particular, non-equilibrium phonons high-resolution phonon-imaging experiments presented here show well defined ballistic pulses and sharp phonon-focusing caustics. We explain this discrepancy in terms of a phonon hot spot which acts to efficiently down-convert the high-frequency phonons very near the excitation spot. We present the first measurements of the size of a phonon hot spot, which depends upon excitation power.     

Perfluoroaryl Bicyclic Cell‐Penetrating Peptides for Delivery of Antisense Oligonucleotides

Exon‐skipping antisense oligonucleotides are effective treatments for genetic diseases, yet exon‐skipping activity requires that these macromolecules reach the nucleus. While cell‐penetrating peptides can improve delivery, proteolytic instability often limits efficacy. It is hypothesized that the bicyclization of arginine‐rich peptides would improve their stability and their ability to deliver oligonucleotides into the nucleus. Two methods were introduced for the synthesis of arginine‐rich bicyclic peptides using cysteine perfluoroarylation chemistry. Then, the bicyclic peptides were covalently linked to a phosphorodiamidate morpholino oligonucleotide (PMO) and assayed for exon skipping activity. The perfluoroaryl cyclic and bicyclic peptides improved PMO activity roughly 14‐fold over the unconjugated PMO. The bicyclic peptides exhibited increased proteolytic stability relative to the monocycle, demonstrating that perfluoroaryl bicyclic peptides are potent and stable delivery agents.     

Effects related to Stevenson's rule in mass spectral intensity correlations

According to Stevenson's rule, there is a possibility that the chloromethyl and bromomethyl ions in the spectra of alkylhalides may not be formed from the molecular ion by processes described by electronic ground states alone. Since ion intensities at 75 eV are generally considered to be governed by appearance potentials, the operation of Stevenson's rule should influence correlations of intensity data according to the kinetic approach to mass spectra. Deviations from linearity were obtained in correlations of CH₂Br⁺ intensities, but not in those of CH₂CL⁺. Stevenson's rule is of help in explaining the deviations, but by its nature it is not absolute in predicting their occurrence with certainty. Consequently caution must be exercised in the interpretation of new data, particularly for aliphatic compounds.