Announcement

Thermal decomposition of FeSO₄-H₂O in carbon monoxide has been studied up to 900°C by thermoanalytical methods and the reaction products and intermediates identified by Mössbauer, IR and X-ray diffraction techniques. The main reaction products are elemental iron and ferrous sulphide; at higher temperatures, cementite is formed as well. For comparison, experiments have also been carried out in hydrogen atmosphere.     

N.m.r. studies on aromatic compounds. I—13C n.m.r. spectra of some mono- and disulpho-substituted hydroxycarboxylic acids

Carbon-13 n.m.r. spectra of 3-hydroxy-4-sulpho-2-naphthoic, 3-hydroxy-5-sulpho-2-naphthoic, 3-hydroxy-7-sulpho-2-naphthoic, 5-sulphosalicylic, 3-hydroxy-5,7-disulpho-2-naphthoic, 1-hydroxy-4,7-disulpho-2-naphthoic, and 3,5-disulphosalicylic acids were recorded with and without proton noise-decoupling. Analyses of the spectra were carried out for all compounds except 3-hydroxy-5-sulpho-2-naphthoic acid which dimerized. The fine splitting caused by long-range coupling was used in identifying the lines of the ¹³C n.m.r. spectra.     

Highly impermeable vesicles composed of conformationally restricted phosphatidylethanolamine

Vesicles composed of a phosphatidylethanolamine derivative with a cyclopropyl-containing interfacial region are twenty-seven times less permeable than vesicles composed of a closely related analogue.     

SENSITIVITY OF HemA MUTANT Escherichia coli CELLS TO INACTIVATION BY NEAR-UV LIGHT DEPENDS ON THE LEVEL OF SUPPLEMENTATION WITH δ-AMINOLEVULINIC ACID

Abstract— Four strains carrying all four possible combinations of the alleles nur, nur⁺, uvr A6 and uvr A ⁺ were transduced to hemA8 . The hemA8 mutation blocks the synthesis of δ-aminolevulinic acid (δ-ALA), one of the first steps in the synthesis of porphyrin and, ultimately, cytochromes essential for aerobic respiration. The cells were grown either with or without δ-ALA and treated with broad-spectrum near-ultraviolet light (NUV; 300–400 nm). hemA8 defective cells grown without δ-ALA were resistant to inactivation by NUV while hemA8 cells were sensitive to such inactivation when supplemented with δ-ALA. The sensitivity to NUV inactivation conferred by the nur gene was retained in the hemA8 derivatives. The sensitivity of such cells to NUV inactivation can be controlled by varying the level of δ-ALA supplementation. The level of δ-ALA supplementation did not influence the sensitivity of the cells to inactivation by far-UV light (FUV; 200–300 nm). The near-UV sensitivity of hemA⁺ cells was not significantly altered when grown with δ-ALA suppiementation suggesting that endogenously formed δ-ALA supports the normal, regulated level of porphyrin synthesis. These results can be interpreted to mean that porphyrin components of the respiratory chain in E. coli represent chromophores involved specifically in broad-spectrum NUV inactivating events.     

Estimation of line tension and contact angle from heterogeneous nucleation experimental data

Using the classical nucleation theory corrected with line tension and experimental data of heterogeneous nucleation of n-nonane, n-propanol, and their mixture on silver particles of three different sizes, the authors were able to estimate the line tensions and the microscopic contact angles for the above mentioned systems. To do this they applied generalized Young's equation for the line tension and calculated the interfacial tensions using Li and Neumann's equation [Adv. Colloid Interface Sci. 39, 299 (1992)]. It has been found that, for both unary and binary systems, the line tension is negative and the resulting microscopic contact angle derived from experimental nucleation data is most of the time larger than the macroscopic one. This is in contrast to earlier studies where the influence of line tension has not been accounted for. The values of the three phase contact line tension obtained in this way are of the same order of magnitude as the estimations for other systems reported in literature. The line tension effect also decreases considerably the nucleation barrier.     

Connection between the virial equation of state and physical clusters in a low density vapor

We carry out Monte Carlo simulations of physical Lennard-Jones and water clusters and show that the number of physical clusters in vapor is directly related to the virial equation of state. This relation holds at temperatures clearly below the critical temperatures, in other words, as long as the cluster-cluster interactions can be neglected--a typical assumption used in theories of nucleation. Above a certain threshold cluster size depending on temperature and interaction potential, the change in cluster work of formation can be calculated analytically with the recently proposed scaling law. The breakdown of the scaling law below the threshold sizes is accurately modeled with the low order virial coefficients. Our results indicate that high order virial coefficients can be analytically calculated from the lower order coefficients when the scaling law for cluster work of formation is valid. The scaling law also allows the calculation of the surface tension and equilibrium vapor density with computationally efficient simulations of physical clusters. Our calculated values are in good agreement with those obtained with other methods. We also present our results for the curvature dependent surface tension of water clusters.     

A model to predict the steady-state concentration of hydroxyl radicals in the surface layer of natural waters

A model was developed to predict the steady-state [*OH] in the surface layer of natural waters as a function of nitrate, inorganic carbon (IC) and dissolved organic matter (DOM). The parameter values were studied in the range detected in shallow high-mountain lakes, to which the model results are most relevant. Calculations indicate that [*OH] increases with increasing nitrate and decreasing IC, and conditions are also identified where [*OH] is directly proportional, inversely proportional or independent of DOM. Based on the model results it is possible to predict the half-life time, due to reaction with *OH, of given dissolved compounds, including organic pollutants, from the water composition data.     

Spectrophotometric characterisation of surface lakewater samples: implications for the quantification of nitrate and the properties of dissolved organic matter

Filtered lakewater samples, mainly collected in the province of Torino (Piedmont, NW Italy) were characterised from a spectrophotometric point of view. Spectral data were then used for the direct determination of nitrate by three-wavelength photometry, which should account for the spectral interference by dissolved organic matter (DOM), and the results compared with nitrate quantification by ion chromatography. The spectrophotometric method proved very suitable for nitrate measurement, with unity slope (micro +/- sigma = 0.99 +/- 0.03) of the correlation plot (spectral vs. ion chromatography data) up to 0.1 mM nitrate, and with r2 = 0.97 for 26 data points. Lakewater spectra were also used for the characterisation of DOM by means of the specific absorption at 285 and 254 nm (absorbance vs. NPOC, the latter to quantify the DOM amount), and the E2/E3 and E3/E4 indexes. The latter two make only use of radiation absorption data (250 vs. 365 and 300 vs. 400 nm). It could be concluded that lakewater DOM is mainly composed of autochthonous material (biologically produced aliphatic compounds and only a minor fraction of aromatic groups), with generally low molecular weight and degree of aromaticity. Some exceptions could be found in high-mountain lakes, but it should also be considered that NPOC measurement cannot be avoided if DOM origin is to be studied. From the absorption spectrum alone it is possible to get indication on the aromaticity degree of radiation-absorbing DOM, but most of the autochthonous DOM would escape spectrophotometric characterisation.