A quantitative N NMR investigation of tautomeric equilibria of two 1-hydroxybenzimidazoles

¹⁵N nuclear shielding data are used in a study of the tautomeric equilibria of two 1-hydroxybenzimidazoles. The nitrogen signal assignments are supported by INDO-S/SOS shielding calculations. The observation of the N-3 signal is shown to give a quantitatively reliable estimate of the position of equilibrium. In the unsubstituted 1-hydroxybenzimidazole the amount of the hydroxy from present in the equilibrium mixture is found to be proportional to the pK_a value of the solvent employed.     

Frequency dependence of ferromagnetic resonance in amorphous magnets: Ferromagnetic and reentrant alloys

We report measurements on magnetic resonance in a number of transition metal-glass former complexes. Data were taken over a wide range of frequencies (2–35 GHz) and temperatures (2–300 K). In the ferromagnetic regime all the systems have a term in their linewidth which points strongly to noncolinearity of spin in glassy magnets even in a nominally saturated state. At low temperatures, in the reentrant alloys, there is a characteristic exponential term describing the increase in linewidth, with reducing T. Such a contribution appears in most random spin systems. There is no adequate microscopic picture to account for many of the results.     

An improved computer model of struvite solution chemistry

The computer model of the solution chemistry of struvite has been improved. Firstly, with ammonia as the prime calculation point in the liquid phase, the algorithm is smaller and faster. Secondly, the incorporation of distilled magnesium hydrogen phosphate in the model significantly increased the concentrations in solution. Thirdly, estimates of the activity coefficients are included. These improvements have but a marginal (5–10%) improvement in the fit. However, proceeding with this flexible modelling procedure using the symbolic manipulator, Maple, easily allows the inclusion of all possible species. The addition of associated ammonium phosphates improves the fit. The relative standard deviation of the fit of both Taylor's data and the data of Webb is improved from 0.5 to 0.2. Estimates of the association constants are included.     

Observation of new laser transitions and saturation effects in optically pumped NO

We report investigations of an NO laser employing specially profiled magnetic fields of up to 3.4T, and F₂ pump laser intensities as great as 20 MW cm^–2. We have observed laser oscillation at 226 nm on a rotational branch of the B'-X/it(3–11) band of NO for the first time, in addition to the previously reported oscillation at 218 nm on the B'-X/it(3–10) band. We have also observed visible laser emission on a rotational branch of the B ²-B ² II(3–1) band of NO. Saturation of the NO laser pulse energy with pump intensity has been observed, the total NO laser pulse energy having been increased to 490 J. The possibility of increasing the NO laser pulse energy towards 1 mJ per transition is discussed.     

The Effect of Diet Quality on δ(13)C and δ(15)N in the Tissues of Locusts, Locusta migratoria L

Abstract Locust nymphs were raised from hatching to adult locusts on either seedling wheat (C(3)) or maize (C(4)), to determine whether relative enrichments/depletions of (15)N and (13)C within body tissues are influenced by diet. The maize contained less hexose sugars and protein per gram than wheat. The isotopic spacing between the food and the whole insect was found to differ between the two diets. The lower quality maize diet showed an overall +5.1‰ enrichment in δ(15)N compared to + 2.8‰ for wheat, possibly due to increased fractionation due to protein recycling. The maize diet resulted in increased depletion in lipid and trehalose and depletion in chitin relative to diet. The results for both δ(15)N and δ(13)C suggest that substrate recycling was occurring on the low quality maize diet. Therefore diet quality determines the enrichment/depletion in δ(15)N and δ(13)C within organisms.     

Synthesis of hydroxy and methoxy perylene quinones, their spectroscopic and computational characterization, and their antiviral activity

Hydroxy and methoxy perylene quinones are synthesized in an attempt to isolate the essential spectroscopic and biological features of light-induced antiviral agents such as hypericin and hypocrellin. Unlike their naturally occurring counterparts, these synthetic quinones bear the carbonyl, hydroxyl, and methoxy groups in the "bay region." The hydroxy and methoxy compounds have rich absorption spectra with broad features in the visible (approximately 450-800 nm) and relatively more intense and narrow features at wavelengths < or = 350 nm. High-level ab initio quantum mechanical calculations assign the features in the absorption spectra to electronic transitions from S0 to S2 and to higher-lying electronic states. The calculations indicate that in the ground state the trans dihydroxy isomer is 12.5 kcal/mol lower in energy than the cis dihydroxy isomer and is thus the only species present. The lowest-energy trans methoxy ground state isomer and the lowest-energy cis methoxy ground state isomer are found to be degenerate. An additional cis methoxy isomer 6.3 kcal/mol higher in energy than the global minimum is assumed to contribute to the spectrum and is also considered. Finally, the synthetic compounds exhibit similar light-induced antiviral activity to each other, but significantly less than that of hypericin.