Nondestructive distinction between aflatoxin B1 and ethoxyquin in thin-layer chromatography

A rapid and simple method has been developed for the nondestructive distinction between aflatoxin B1 and the feed antioxidant, ethoxyquin. These two chemicals exhibit similar RF values in certain solvent systems and produce a similar bluish fluorescence under long UV (366 nm) radiation. The method involves the in situ generation of fluorescence spectra of the respective thin-layer chromatography spots. Since it is nondestructive, the method affords ancillary study of the separated aflatoxins.     

Conformational study of protonated,neutral, and deprotonated formamide

Neutral, protonated, and deprotonated formamide isomers were studied at the 3-21G SCF level with complete geometry optimization. Ten stable structures, ten first-order saddle points, and three second-order saddle points (conformational maxima) are reported. [Total energies are reported in hartrees (1 hartree = 627.51 kcal/mol = 2625.5 kJ/mol) and energy differences are reported in kJ/mol (1 kJ/mol = 0.239 kcal/mol).] Rotational barriers and proton affinities are discussed and compared to isoelectronic amidine species.     

Divide and conquer: rat liver tissue proteomics based on the analysis of purified constituents

Comparative proteome data of normal and diseased tissue samples are difficult to interpret. Proteins detected in tissues are derived from different cell types and blood constituents. Pathologic or toxicant-induced aberrations may affect the proteome profile of tissues in several ways since different cell types may respond in very different and highly specific manners. The aim of this study was to analyze the proteome profiles of purified rat liver primary cells and of blood plasma in comparison to liver whole tissue. Moreover, we investigated alterations of these profiles induced by the liver toxicant N-nitrosomorpholine (NNM) used as a model compound. Whole liver samples, pure hepatocytes and Kupffer cells as well as blood plasma were obtained from saline- or NNM-treated rats. Proteins were separated by 2-D PAGE and their amounts were estimated by fluorography. Selected proteins were identified by MS analysis of tryptic digests. Among them we identified proteins exclusively expressed in the analysed constituents. Several of these proteins were assigned in the proteome profile of whole-tissue homogenates. Furthermore, we identified several proteins that were modified, up-regulated or down-regulated due to NNM treatment in total liver homogenates. Some of these protein alterations were specifically detected in primary cells isolated from NNM-treated rats. Thus, we demonstrated the successful assignment of NNM-induced proteome alterations in rat liver to the cell type of origin. The currently applied approach may help to better understand pathologic processes at a whole-tissue level.     

Short-time restricted diffusion in a static gradient and the attenuation of individual coherence pathways

We experimentally explore some of the implications of a recent theoretical study [J. Magn. Reson. 64 (2003) 145] for the measurement of restricted diffusion in connected porous media in a static gradient. In particular, we examine how restriction affects the short-time attenuation of different coherence pathways, all excited with the same sequence of slice-selective radiofrequency (RF) pulses, and how the various pathways make the transition to the long-time or tortuosity regime. We confirm that every pathway contains equivalent diffusional information and, for short times, yields the surface-to-volume ratio (S/V) of the confining space. We find also, in agreement with the theoretical predictions, that different pathways are controlled by different time scales and, thus, exhibit different sensitivity to restriction. This property might be exploited when designing optimal sequences to study restricted motion.     

Effect of internal gradients in the nuclear magnetic resonance measurement of the surface-to-volume ratio

We consider a system of spins diffusing in a static inhomogeneous (nonuniform-gradient) magnetic field B in a restricted geometry and in the presence of surface relaxation. We show that the short-time diffusional decay of nuclear magnetization is controlled by the field scattering kernel F(t) identical with [B(t)-B(0)](2), which is a measure of the average field inhomogeneity sampled by the spins in time t and does not depend on the particular sequence of radio-frequency pulses used. Magnetization in arbitrary sequences can be straightforwardly computed by evaluating elementary integrals of F(t). Diffusion takes place while the field is on, so that the spins precess as they diffuse, in contrast to the simpler problem of purely classical diffusion considered in [P. P. Mitra, P. N. Sen, and L. M. Schwartz, Phys. Rev. B 47, 8565 (1993)] which is applicable only to the ideal pulsed-field gradient experiment. We compute the short-time asymptotic form of F(t) and find that it depends on the surface-to-volume ratio (S/V) of the pore space as well as on the average of the gradients over the bounding surface. In a system with nonuniform gradients that vary faster near the surface than in the bulk, as for internal susceptibility fields, this gradient surface average may be much larger than the gradients in the bulk, significantly enhancing the apparent S/V. We discuss the application of our results to the widely used Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence as well as proposing a modification of it, which we term "padded" CPMG, that may be preferable in systems with significant surface relaxation. We indicate how each sequence can be used to probe the internal fields.     

Relationships between experienced listener ratings of multichannel audio quality and naïve listener preferences

The preferences of a large number of na?ve listeners were elicited in response to a selection of multichannel audio items that had been degraded in quality by using band-limiting and down-mixing algorithms. Relationships were sought between these preference ratings and the quality judgements of experienced listeners in an attempt to determine whether one could be predicted from the other. Results suggest that a simple regression model can be used to do this with adequate results, but that a better prediction can be successfully based on experienced listener ratings of timbral and spatial fidelity. There is a difference between na?ve and experienced listeners in the weightings of the fidelities and their relationship to overall quality.     

2-Chloroacetaldehyde induces epsilondA DNA adducts in DNA of Raji cells as demonstrated by an improved HPLC-fluorimetry method

Etheno adducts in DNA are promutagenic lesions and are formed from vinyl chloride, urethane, and lipid peroxidation-derived products such as 4-hydroxynonenal. Such adducts were induced in a B-lymphoid cell line (Raji) by a metabolite of vinyl chloride, 2-chloroacetaldehyde. By modification of a method of Bedell et al., etheno dA was determined in 20 microg DNA by HPLC-fluorimetry. Our method has a detection limit of 5 fmol which is one two-hundredth that of the original method. By use of this method initial evidence was found that cigarette smoke can also induce etheno dA adducts in Raji cell DNA.     

Double inelastic interactions in pd collisions in the 1.6–4.3 GeV/c incident p momentum range

We present results on $\text{p}\text{d}$ multiplicity distributions at 3.9 and $\text{4.3}\text{GeV}\text{/c}\text{p}$ incident momenta obtained from a bubble chamber experiment. An excess is observed for the even-prong multiplicities as compared with $\text{p}$ collisions on free protons. This excess as well as that observed in other existing $\text{p}\text{d}$ data in the 1.6–2.9 GeV/c range was analysed in terms of double interaction processes inside the deuteron.