Latency of auditory brain-stem responses and otoacoustic emissions using tone-burst stimuli

A comparison of the latency of auditory brain-stem responses (ABR) and evoked otoacoustic emissions (EOAE) has led to an interpretation for the travel of transients in the peripheral auditory system that is consistent with both sets of data. The "cochlear echo" theory for the origin of the EOAE indicates that the latency of a particular frequency component back to the ear canal should be twice the forward latency of its characteristic place in the cochlea. The latency of wave V of the ABR to tone-burst stimuli can be described as the sum of two components: (1) a component that varies with intensity and frequency in an orderly and predictable manner and (2) a component that is independent of both intensity and frequency. Because the EOAE data can be predicted by taking twice the value of component (1) of the ABR latency, this component is interpreted to be due to mechanical travel through the cochlea. A consequence of this interpretation is that the remaining neural component of the ABR latency must be relatively independent of frequency and intensity.     

Lithiation and electrophilic substitution of 8-chlorodibenz[b,f][1,4]-oxazepine-10-tert-butylcarbamate: The preparation of novel fused heterocyclic derivatives of 8-chlorodibenzoxazepine

Lithiation of 8-chlorodibenz[b,f][1,4]oxazepine-10-tert-butylcarbamate ( 1 ) is described. Electrophilic substitution of the resulting N-Boc dibenzoxazepine α- lithioamine 2 with ketones, aldehydes, nitriles, iso-cyanates and imines, followed by an in-situ cyclization, gave fused carbamates 5–26 , fused 2H-imidazol-2-ones 27–29 , fused hydantoins 30–32 , and fused ureas 33–35 , respectively, in 11–66% yield.     

Reactions of N-heterocyclic carbenes (NHCs) with one-electron oxidants: possible formation of a carbene cation radical

One-electron oxidation of N-heterocyclic carbenes (NHCs) has been carried out using oxidising agents such as tetracyanoethylene (TCNE) and ferrocenium [Cp(2)Fe](+); the formation of carbene radical cations is postulated.     

Atomic origin of hysteresis during cyclic loading of Si due to bond rearrangements at the crack surfaces

The atomistic origin of fatigue failure in micron-sized silicon devices is not fully understood. Two series of density-functional theory calculations on cubic diamond Si explore the effect of surface bond formation on crack healing in systems which exhibit strong surface reconstruction. Both series introduce a separation between Si(100) layers (i.e., the crack) and allow the ions to relax to their minimum-energy configuration. The initial surface ionic positions are either bulk terminated or 2 x 1 reconstructed. A plot of the energy versus the introduced separation reveals that once the surfaces reconstruct, the crack is no longer able to return to the equilibrium configuration. Rather, the healed crack interface contains defects which places the flawed energy minimum at a finite strain of 3% and an increased energy of 1.13 Jm2 relative to the equilibrium configuration. The irreversible plastic deformation supports the mechanism proposed by Kahn et al. [Science 298 1215 (2002)] that invokes mechanically induced subcritical cracking to explain the delayed onset of failure.     

The Zygmund Morse-Sard Theorem

The classical Morse-Sard Theorem says that the set of critical values off:R ^n+k →R ⁿ has Lebesgue measure zero iff ∈C ^k+1. We show theC ^k+1 smoothness requirement can be weakened toC ^k+Zygmund. This is corollary to the following theorem: For integersn >m >r > 0, lets = (n ?r)/(m ?r); iff:R ⁿ →R ^m belongs to the Lipschitz class Λ _s andE is a set of rankr forf, thenf(E) has measure zero.     

Identification of 4-amino-4-deoxychorismate synthase as the molecular target for the antimicrobial action of (6s)-6-fluoroshikimate

(6S)-6-Fluoroshikimate has antimicrobial activity. The molecular basis of this effect had not been identified, but there was speculation that (6S)-6-fluoroshikimate is first converted in vivo into 2-fluorochorismate, which then could inhibit 4-amino-4-deoxychorismate synthase (ADCS). 2-Fluorochorismate was prepared from E-fluorophosphoenolpyruvate and erythose-4-phosphate by the sequential reactions of DAHP synthase, dehydroquinate synthase, dehydroquinase, shikimate dehydrogenase, EPSP synthase, and chorismate synthase. Inhibition studies on ADCS showed that it was inhibited rapidly and irreversibly by 2-fluorochorismate. Electrospray mass spectrometry of the inactivated enzyme showed an additional mass of 198 +/- 10 Da. A novel peptide of 1087.6 Da was identified in the HPLC trace for the tryptic digest of 2-fluorochorismate-inactivated ADCS. Sequencing of this peptide by MS/MS showed that the peptide corresponded to residues 272-279 with a modification of 206.1 Da on Lys-274. This observation is particularly exciting in the context of a recent proposal for the catalytic mechanism of ADCS.     

Preparation of a DSCG-like bisbenzofuran

The preparation of 6,6′-[(2-hydroxy-1,3-propanediyl)]bis(oxy)]bis(3-hydroxy)]-2-benzofurancarboxylic acid) diethyl ester trisodium salt trihydrate ( 6 ), a compound structurally related to disodium cromoglycate (DSCG), is described.     

A semi-micro synthesis of selenophene

A semi-micro preparation of selenophene is described which offers a convenient technique for the production of milligram quantities of the heterocycle. Selenophene is synthesized from bis-(trimethylsilyl)-1,3-butadiyne and sodium hydrogen selenide generated in situ from selenium and sodium borohydride in DMF-water. J. Chem. Soc., 14, 1115 (1977)     

Capillary electrochromatography of Triton X-100

Nonionic surfactants such as Triton X-100 (TX-100) are comprised of a mixture of oligomers with a varying degree of length in the ethoxylate chain. The development of chromatographic methods for resolution of the various oligomers of TX-100 is of environmental importance, and can be useful for quality control and characterization in industrial manufacture. Capillary electrochromatography (CEC) is fast becoming a capable separation technique that combines the benefits of both high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE). This report presents a novel CEC method for separation of the various TX-100 oligomers. A comparison of monomeric vs. polymeric stationary phases for separation of TX-100 was conducted. Since the oligomers of TX-100 were better resolved on a monomeric phase as compared to polymeric phase, a systematic mobile phase tuning was performed utilizing a monomeric CEC-C18-3 microm-100 A stationary phase. Various mobile phase parameters such as acetonitrile (ACN) content, Tris concentration, pH, voltage, and temperature were manipulated in order to achieve the optimum separation of oligomers in less than 30 min.