First structural characterization of binary AsIII and SbIII azides

The highly explosive molecules As(N(3))(3) and Sb(N(3))(3) were obtained in pure form by the reactions of the corresponding fluorides with (CH(3))(3)SiN(3) in SO(2) and purification by sublimation. The crystal structures and (14)N NMR, infrared, and Raman spectra were determined, and the results compared to ab initio second-order perturbation theory calculations. Whereas Sb(N(3))(3) possesses a propeller-shaped, pyramidal structure with perfect C(3) symmetry, the As(N(3))(3) molecule is significantly distorted from C(3) symmetry due to crystal packing effects.     

Low probe concentration can cause problems in multilocus DNA fingerprinting (cautionary notes III)

The power of multilocus DNA fingerprinting depends on the reliability with which the uniqueness of an individual's profile can be demonstrated. This cautionary note stresses the importance of the probe concentration in this procedure. In case of a probe shortage, DNA fragments rich in tandem repeats have the potential to impede hybridization in other parts of the gel, and thus interfere with bands that are part of a DNA fingerprinting profile.     

Solution conformational preferences of glutaric, 3‐hydroxyglutaric, 3‐methylglutaric acid,and their mono‐ and dianions

Conformational preferences of glutaric, 3‐hydroxyglutaric and 3‐methylglutaric acid, and their mono‐ and dianions have been investigated with the aid of NMR spectroscopy. In contrast to succinic acid, glutaric acid displays essentially statistical conformational equilibria in polar and non‐polar solutions of high and low hydrogen‐bonding ability with no clear evidence for intramolecular hydrogen‐bonding interactions. The acid ionization constant ratios, K ₁/K₂, in D₂O and DMSO of glutaric, 3‐hydroxyglutaric, and 3‐methylglutaric acids also indicate that intramolecular interactions are much less important than, or indeed insignificant, for shorter‐chain acids. FTIR studies on 3‐methylglutaric acid indicate some preference for either association with solvent or dimerization, depending on the solvent, rather than intramolecular hydrogen bonding. Copyright © 2008 John Wiley & Sons, Ltd.     

High-precision frequency-domain measurements of the optical properties of turbid media

We report high-precision measurements of the absorption and the reduced scattering coefficients for turbid media. Using a frequency-domain measurement technique for a point-source infinite-medium geometry, we find that the standard deviations of multiple measurements of the absorption coefficient mu(a) and the reduced scattering coefficient mu(s)(?) are less than 0.6%, and three independently derived values for mu(a) and mu(s)(?) agree to better than 1%. Measurements of mu(a) agree with measurements of a nonscattering medium to within 1.2%. To obtain high precision requires attention to proper conditions for the spherical photon-density wave model, the detection linearity, and the ratio of the absorption rate to the source modulation rate. Frequency-domain amplitude and phase measurements deviate from fitted curves by 0.1% and 0.06 degrees rms, respectively.     

Frequency-domain technique for optical property measurements in moderately scattering media

We demonstrate a reflection geometry frequency-domain technique that is suitable for measurement of the optical properties of a medium with moderate scatter and absorption (mu(s) and mu(a) ~ 1 m(-1)). Variations in absorption and scatter produce opposing tends in the amplitude signal and common trends in the phase signal, allowing unique determination of absorption and scattering coefficients for a given phase function. An analytical model based on single-scattering events gives good agreement with experimental measurements.     

Synthesis of 2′-Iodo Analogues of β-Rhodomycins1

Abstract

10-O-(R/S)Tetrahydropyranosyl-β-rhodomycinone (5a,b) was prepared via 7,9-O-phenylboronyl-β-rhodomycinone (3) from β-rhodomycinone (1). Glycosidation of 5a,b with 3,4-di-O-acetyl-1,5-anhydro-2,6-dideoxy-L-arabino-hex-1-enitol (3,4-di-O-acetyl-L-rhamnal) (6) and 3,4-di-O-acetyl-1,5-anhydro-2,6-dideoxy-L-lyxo-hex-1-enitol (3,4-di-O-acetyl-L-fucal) (7) using N-iodosuccinimide gave the corresponding 7-O-glycosyl-β-rhodomycinones 8a,b, 9a,b and 10a,b, 11a,b. After cleavage of the THP-ether and O-deacetylation 7-O-(2,6-dideoxy-2-iodo-α-L-manno-hexopyranosyl)-β-rhodomycinone (14) and 7-O-(2,6-dideoxy-2-iodo-α-L-talo-hexopyranosyl)-β-rhodomycinone (16) were obtained.     

Material Discrimination in Nanoparticle Hetero-Aggregates by Analysis of Scanning Transmission Electron Microscopy Images

Hetero-contacts are interfaces between different materials at the nanoscale leading to novel functional properties. In hetero-aggregates, primary particles of at least two different materials are mixed at primary particle or cluster level. Double flame spray pyrolysis (DFSP) is a versatile technique for the controlled synthesis of such materials. Characterization of hetero-aggregates by scanning transmission electron microscopy (STEM) requires acquisition and evaluation of many aggregate images in order to derive statistically significant results. Usually, STEM energy dispersive X-ray spectroscopy (EDXS) is used to acquire elemental maps providing the material distribution of the primary particles within hetero-aggregates. However, the acquisition of a single EDXS map takes up to several minutes. For this reason, determination of material types of primary particles from the intensity in high-angle annular dark field STEM images alone is desirable. These images can be acquired within a couple of seconds. In the present work, a method is suggested which allows for achieving this objective. It can be applied to distinguish materials with a significant difference in their atomic number and hence sufficient material contrast in the STEM images.     

A rank-one algorithm for unconstrained function minimization

A rank-one algorithm is presented for unconstrained function minimization. The algorithm is a modified version of Davidon's variance algorithm and incorporates a limited line search. It is shown that the algorithm is a descent algorithm; for quadratic forms, it exhibits finite convergence, in certain cases. Numerical studies indicate that it is considerably superior to both the Davidon-Fletcher-Powell algorithm and the conjugate-gradient algorithm.     

Observation of resonance recombination lines in electron excited auger spectra of Gd

Combined measurements of electron excited N_4,5 Auger spectra and photoelectron emission on clean and oxidized Gd lead to a distinction between Auger lines originating from 4d → continuum and 4d → 4? resonance excitations. Several Auger structures are identified as due to the direct recombination of 4d⁹4?⁸ states with the 4f and valence electrons. The shape of the most prominent Auger line for oxidized Gd agrees perfectly with the Fano profile of the 4? photoemission intensity.