CH3O(X2E) production from 266 nm photolysis of methyl nitrite and reaction with NO

The CH₃O($\text{X}$²E) radical produced by the 266 nm photolysis of CH₃ONO is characterized by laser-induced fluorescence. Using a flowing gas cell the reaction rate of CH₃O($\text{X}$²E) with NO is measured to be (2.08 ± 0.12) × 10^?11 cm³ s^?1 molecule^?1 based upon disappearance of CH₃O and appearance of HNO detected by laser induced fluorescence. Upper limits for CH₃O reactions with CH₄, CO, N₂O, NH₃, CH₃OH, (CH₃)₃CH and CH₂CHCH₂CH₃ are reported. These reactions are all too slow to measure under our experimental conditions.     

Interwell excitons in GaAs superlattices

The formation of spatially indirect excitons in superlattices with narrow minibands is investigated experimentally. The interwell exciton is similar to the first Wannier–Stark localized exciton of an electrically biased superlattice. However, in the present case the localization is mediated by the Coulomb interaction of the electron and the hole without external fields.     

Heisenberg and the German bomb

Many natural and human-made nonlinear oscillators exhibit the ability to adjust their rhythms due to weak interaction: two lasers, being coupled, start to generate with a common frequency; cardiac pacemaker cells fire simultaneously; violinists in an orchestra play in unison. Such coordination of rhythms is a manifestation of a fundamental nonlinear phenomenon--synchronization. Discovered in the 17th century by Christiaan Huygens, it was observed in physics, chemistry, biology and even social behaviour, and found practical applications in engineering and medicine. The notion of synchronization has been recently extended to cover the adjustment of rhythms in chaotic systems, large ensembles of oscillating units, rotating objects, continuous media, etc. In spite of essential progress in theoretical and experimental studies, synchronization remains a challenging problem of nonlinear sciences.     

PHOTODYNAMIC ACTION OF CHEMICALLY RELATED FLAVONES

Abstract— Flavone, polyhydroxyflavones (apigenin, fisetin, kaempferol, luteolin, myricetin, quercetin, resokaempferol and robinetin), polymethoxyflavones and acetylated and benzylated flavones were tested for photodynamic activity using Tetrahymena pyriformis T as the test organism. Among these compounds, polymethoxyflavones showed the highest order of activity, followed by flavone and then flavone derivatives with OH and OCH₃ groups. Resokaempferol was the only active polyhydroxyflavone, the remainder being inactive such as the benzyl-derivative. The methoxyl group in the 5–position and an increase in number of methoxyl groups from one to three in the phenolic portion of the flavonoid tended to decrease photodynamic activity. Tetrahymena killed photodynamically by polymethoxyflavones were morphologically altered by blister-like blebs. Polymethoxyflavones showed the lowest cytotoxicity and the greatest photodynamic activity among those flavonoids tested. The majority of the favonoids in this series have absorption spectra in the 320–370 nm region.     

Mechanism of solid|liquid interfacial reactions. The reactive dissolution of p-chloranil in aqueous solution as studied by the channel flow cell with electrochemical detection and atomic force microscopy

A quantitative study of the hydrolytic dissolution of solid p-chloranil at alkaline pH using a combination of the channel flow cell and in situ atomic force microscopy measurements shows that the dissolution is driven by reaction of the substrate with hydroxide ions at, or very close to, the dissolving surface. The dissolution rate equation, deduced from the channel flow cell for single crystals of p-chloranil, is rate/mol cm⁻² s⁻¹ = 3.8 × 10⁻⁷ [OH⁻]₀ where [OH⁻]₀/M is the hydroxide ion concentration adjacent to the solid surface. An analogous rate law is derived for pressed pellet substrates. The novel application of the atomic force microscope to make absolute measurements of surface averaged dissolution rates is described. Comparison with the independent channel flow cell data reveals good mechanistic agreement and consistency of rate constants provided it is recognised that a thick stagnant diffusion layer can be present under the usual conditions employed for AFM.     

Structural characterization of a degradation product of tin ethyl etiopurpurin (SnET2): Comparison of the long‐range heteronuclear correlations detected using conventional GHMBC and IMPEACH‐MBC in conjunction with submicro NMR probe technology

During the terminal heat sterilization of the lipid emulsion final dose formulation of the photodynamic therapeutic (PDT) agent tin ethyl etiopurpurin (SnET2), a new degradant was observed at very low levels. The degradant, which was prone to photo‐instability, was isolated by preparative chromatography and subsequently characterized by mass spectrometry and NMR methods. Reproducible parent ion clusters were only observable via negative ion APCI methods. Because of the limited isolate sample, NMR characterization was done using 1.7 mm SMIDG (SubMicro Inverse‐Detection Gradient) NMR probe technology in conjunction with the accordion‐optimized IMPEACH‐MBC long‐range heteronuclear shift correlation experiment. The “static” 8 Hz optimization of the GHMBC experiment failed to allow the observation of a number of long‐range correlations that were of critical importance to the determination of the structure of the impurity. In contrast, all of the correlations required to assemble the structure were obtained from an IMPEACH‐MBC experiment optimized for long‐range heteronuclear couplings in the range from 2–10 Hz.     

Finite Element Methods for a Model for Full Waveform Acoustic Logging

A model is defined to simulate the propagation of waves in aradially symmetric, isotropic, composite system consisting ofa fluid-filled well bore ^f through a fluid-saturated poroussolid ^p. Biot's equations of motion are chosen to describe thepropagation of waves in ^p, while the standard equation of motionfor compressible inviscid fluids is used for ^f, with appropriateboundary conditions at the contact surface between ^f and ^p.Also, absorbing boundary conditions for the artificial boundariesof ^p are derived for the model, their effect being to make themtransparent for waves arriving normally First, results on the existence and uniqueness of the solutionof the differential problem are given and then a discrete-time,explicit finite element procedure is defined and analysed, withfinite element spaces suited for radially symmetric problemsbeing used for the spatial discretisation.     

An experimental and theoretical investigation of the chemical shielding tensors of (13)C(alpha) of alanine, valine, and leucine residues in solid peptides and in proteins in solution

We have carried out a solid-state magic-angle sample-spinning (MAS) nuclear magnetic resonance (NMR) spectroscopic investigation of the (13)C(alpha) chemical shielding tensors of alanine, valine, and leucine residues in a series of crystalline peptides of known structure. For alanine and leucine, which are not branched at the beta-carbon, the experimental chemical shift anisotropy (CSA) spans (Omega) are large, about 30 ppm, independent of whether the residues adopt helical or sheet geometries, and are in generally good accord with Omega values calculated by using ab initio Hartree-Fock quantum chemical methods. The experimental Omegas for valine C(alpha) in two peptides (in sheet geometries) are also large and in good agreement with theoretical predictions. In contrast, the "CSAs" (Deltasigma) obtained from solution NMR data for alanine, valine, and leucine residues in proteins show major differences, with helical residues having Deltasigma values of approximately 6 ppm while sheet residues have Deltasigma approximately 27 ppm. The origins of these differences are shown to be due to the different definitions of the CSA. When defined in terms of the solution NMR CSA, the solid-state results also show small helical but large sheet CSA values. These results are of interest since they lead to the idea that only the beta-branched amino acids threonine, valine, and isoleucine can have small (static) tensor spans, Omega (in helical geometries), and that the small helical "CSAs" seen in solution NMR are overwhelmingly dominated by changes in tensor orientation, from sheet to helix. These results have important implications for solid-state NMR structural studies which utilize the CSA span, Omega, to differentiate between helical and sheet residues. Specifically, there will be only a small degree of spectral editing possible in solid proteins since the spans, Omega, for the dominant nonbranched amino acids are quite similar. Editing on the basis of Omega will, however, be very effective for many Thr, Val, and Ileu residues, which frequently have small ( approximately 15-20 ppm) helical CSA (Omega) spans.