Synthesis of 1,3-bridged β-lactams embedded in a macrocyclic structure

A new approach to N1-C3 bridged macrocyclic β-lactams has been developed. Orthogonal functional groups' protection combined with RCM has allowed the construction of the bicyclic systems bearing a β-lactam motif. These systems could represent a structural alternative to the actual lactamic antibiotics and may be further transformed into a broad variety of compounds.     

Emission spectroscopy of flame fronts in aluminum suspensions

Spatially resolved emission spectra from Bunsen-type flames stabilized in aluminum suspensions in air and oxygen–argon/helium mixtures were obtained using a mechanical-optical scanning system. A low resolution (1.5 nm) spectrometer was used to acquire the broad spectra over the 350–1000 nm range, and a high-resolution (0.04 nm) instrument was used for observation of AlO molecular bands and non-ionized atomic aluminum. The temperature of condensed phase emitters in the flame was derived using polychromatic fitting of the continuum spectra to Planck’s law. AlO temperature was found by fitting of the theoretically calculated shape of the band to experimental data. Peak temperatures of the condensed emitters were found to be approximately 3250 K in aluminum-air flames and approximately 3350 K for oxygen–argon/helium flames. Temperatures derived from AlO spectra coincide with the temperature of the condensed emitters with measurement accuracy and are only 100–200 °C lower than the computed equilibrium flame temperatures. The radial distribution of the temperature profile of the continuous emitters was found via Abel deconvolution and recovered the double-front structure of the Bunsen flame cone, with the outer flame being attributed to a diffusion flame of the fuel-rich products with ambient air. The observation of atomic aluminum lines seen in emission from the outer flame edge and partial self-absorption from the inner flame confirms the structure associated with the double-front structure. The implications of these results for the regime of particle combustion in a dust flame are discussed.     

On the Use of Metal Purine Derivatives (M=Ir,Rh) for the Selective Labeling of Nucleosides and Nucleotides

The reactions of neutral or cationic Ir^III and Rh^III derivatives of phenyl purine nucleobases with unsymmetrical alkynes produce new metallacycles in a predictable manner, which allows for the incorporation of either photoactive (anthracene or pyrene) or electroactive (ferrocene) labels in the nucleotide or nucleoside moiety. The reported methodology (metalation of the purine derivative and subsequent marker insertion) could be used for the postfunctionalization and unambiguous labeling of oligonucleotides.     

Synthesis and characterisation of [6]-azaosmahelicenes: the first d4-heterometallahelicenes

[6]-Azaosmahelicenes, the first d(4)-heterometallahelicenes, have been synthesised and fully characterised. Their optical properties (UV-Vis absorption and luminescence) are reported.     

Comparison of the silver nitrate and bacterial denitrification methods for the determination of nitrogen and oxygen isotope ratios of nitrate in surface water

Nitrogen (N) and oxygen (O) isotope ratios of NO are often used to trace dominant NO pollution sources in water. Both the silver nitrate (AgNO₃) method and the bacterial denitrification method are frequently used analytical techniques to determine δ¹⁵N‐ and δ¹⁸O‐NO in aqueous samples. The AgNO₃ method is applicable for freshwater and requires a concentration of 100–200 µmol of NO for isotope determination. The bacterial denitrification method is applicable for seawater and freshwater and for KCl extracts of soils with a NO concentration as low as 1 µmol. We have carried out a thorough method comparison using 42 real surface water samples having a wide range of δ¹⁵N‐ and δ¹⁸O‐NO values and NO concentrations. Various correction pairs using three international references and blanks were used to correct raw δ¹⁵N‐ and δ¹⁸O‐NO values. No significant difference between the corrected data was observed when using various correction pairs for each analytical method. Both methods also showed excellent repeatability with high intraclass correlation coefficients (ICC). The ICC of the AgNO₃ method was 0.992 for δ¹⁵N and 0.970 for δ¹⁸O. The ICC of the bacterial denitrification method was 0.995 for δ¹⁵N and 0.954 for δ¹⁸O. Moreover, a positive linear relationship with a high correlation coefficient (r ≥ 0.88) between the two methods was found for δ¹⁵N‐ and δ¹⁸O‐NO. The comparability of the methods was assessed by the Bland‐Altman technique using 95% limits of agreement. The average difference between results obtained by the bacterial denitrification and the AgNO₃ method for δ¹⁵N was ?1.5‰ with 95% limits of agreement ?3.6 and +0.5‰. For δ¹⁸O this was +2.0‰, with 95% limits of agreement ?3.3 and +7.3‰. We found that for δ¹⁵N and for δ¹⁸O, 97% of the differences fell within these 95% limits of agreement. In conclusion, the AgNO₃ and the bacterial denitrification methods are highly correlated and statistically interchangeable. Copyright © 2010 John Wiley & Sons, Ltd.     

A pseudo Newton-Raphson method for function minimization

A pseudo Newton-Raphson algorithm for function minimization is presented. As in all such algorithms, an estimate of the inverse Hessian is calculated. In this case, the estimate is of the formXZX ^T , whereZ is a diagonal matrix; and this feature permits the use of the simple procedures to maintain the positive definiteness ofZ, and hence of the restriction ofXZX ^T to the range ofX. The algorithm is shown to have finite convergence for quadratic functions and asymptotic convergence for a fairly general class of functions. Some numerical results are presented, and the extension of the algorithm to deal with linear equality and inequality constraints is briefly discussed.R. Mamen acknowledges with gratitude the financial support afforded by an Athlone Fellowship and a National Research Council of Canada Post-Graduate Bursary. Dr. S. C. Chuang made useful comments on some of the proofs. Some of the results are closely related to those of Allwright (Ref. 1).     

Error assessment of nitrogen and oxygen isotope ratios of nitrate as determined via the bacterial denitrification method

Currently, bacterial denitrification is becoming the accepted method for δ¹⁵N‐ and δ¹⁸O‐NO determination. However, proper correction methods with international references (USGS32, USGS34 and USGS35) are needed. As a consequence, it is important to realize that the corrected isotope values are derived from a combination of several other measurements with associated uncertainties. Therefore, it is necessary to consider the propagated uncertainty on the final isotope value. This study demonstrates how to correctly estimate the uncertainty on corrected δ¹⁵N‐ and δ¹⁸O‐NO values using a first‐order Taylor series approximation. The bacterial denitrification method errors from 33 batches of 561 surface water samples varied from 0.2 to 2.1‰ for δ¹⁵N‐NO and from 0.7 to 2.3‰ for δ¹⁸O‐NO, which is slightly wider than the machine error, which varied from 0.2 to 0.6‰ for δ¹⁵N‐N₂O and from 0.4 to 1.0‰ for δ¹⁸O‐N₂O. The overall uncertainties, which are composed of the machine error and the method error, for the 33 batches ranged from 0.3 to 2.2‰ for δ¹⁵N‐NO and from 0.8 to 2.5‰ for δ¹⁸O‐NO. In addition, the mean corrected δ¹⁵N and δ¹⁸O values of 132 KNO₃‐IWS (internal working standard) measurements were computed as 8.4 ± 1.0‰ and 25.1 ± 2.0‰, which is a slight underestimation for δ¹⁵N and overestimation for δ¹⁸O compared with the accepted values (δ¹⁵N = 9.9 ± 0.3‰ and δ¹⁸O = 24.0 ± 0.3‰). The overall uncertainty of the bacterial denitrification method allows the use of this method for source identification of NO. Copyright © 2010 John Wiley & Sons, Ltd.