Determination of the types of nitrogen in steels containing aluminium or titanium by an extraction method with hydrogen

The extraction method with hydrogen, hitherto used to determine mobile nitrogen in steels over the temperature range 350–450°C, has been employed at higher temperatures to determine nitrogen bound as aluminium nitride, or as titanium nitride or carbonitride. In steels containing only silicon and titanium as deoxidizers, the nitrogen remaining after passage of hydrogen at 600 or 750°C is present as titanium nitride or carbonitride and can be determined by difference. In steels containing only silicon and aluminium as deoxidizers, the nitrogen remaining after passage of hydrogen at 600°C is present as aluminium nitride and can also be determined by difference. This was verified by determining the aluminium nitride indirectly. The nitrogen released from both the aluminium and titanium steels in hydrogen at 600°C probably results from dissociation of submicroscopic particles of manganese silicon nitride.     

An Integer Goal Programming Model for Determining Military Aircraft Expenditures

The decision-making process involved in the procurement of military weapon systems, although quite critical and complex, still encompasses the basic characteristics of a capital budgeting problem. Given a number of expenditure items and a limited budget, it is desired to procure those weapon systems that will achieve the goals and objectives of the government and/or military in the most efficient manner. Since these objectives are typically numerous and diverse, traditional decision-making techniques are not applicable. As such, integer goal programming is suggested as a technique to be employed to determine the number of military aircraft to be procured, given conflicting expenditure, budget and effectiveness goals. This method is demonstrated via a case example in which the solution results are presented.     

The determination of mobile nitrogen in vanadium steels by the extraction method with hydrogen

Some slope-intercept and graphical solution methods are proposed for calculation of the molar absorptivity (?) and the overall formation constant (β_n) of a complex which forms exclusively in solution. The data required for applying these methods are obtained from points selected from one or more continuous variations curves. The validity and applicability of the methods proposed are demonstrated by appropriate examples.     

Simplest Monodentate Imidazole Stabilization of the oxy‐Tyrosinase Cu2O2 Core: Phenolate Hydroxylation through a CuIII Intermediate

Tyrosinases are ubiquitous binuclear copper enzymes that oxygenate to Cu^II₂O₂ cores bonded by three histidine Nτ‐imidazoles per Cu center. Synthetic monodentate imidazole‐bonded Cu^II₂O₂ species self‐assemble in a near quantitative manner at ?125 °C, but Nπ‐ligation has been required. Herein, we disclose the syntheses and reactivity of three Nτ‐imidazole bonded Cu^II₂O₂ species at solution temperatures of ?145 °C, which was achieved using a eutectic mixture of THF and 2‐MeTHF. The addition of anionic phenolates affords a Cu^III₂O₂ species, where the bonded phenolates hydroxylate to catecholates in high yields. Similar Cu^III₂O₂ intermediates are not observed using Nπ‐bonded Cu^II₂O₂ species, hinting that Nτ‐imidazole ligation, conserved in all characterized Ty, has functional advantage beyond active‐site flexibility. Substrate accessibility to the oxygenated Cu₂O₂ core and stabilization of a high oxidation state of the copper centers are suggested from these minimalistic models.     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.