Ion chromatographic method for the simultaneous determination of nitrite and nitrate by post-column indirect fluorescence detection

This short paper highlights the suitability of ion chromatography with post-column indirect fluorescence detection to determine simultaneously nitrite and nitrate based on the quenching of tryptophan native fluorescence. The method uses an enhanced fluorescence mobile phase containing tryptophan and detects the suppression of fluorescence of the mobile phase due to the elution of the target ions. The phenomenon of fluorescence quenching of tryptophan is highly induced by the presence of phosphate ions. The quenched fluorescence intensity exhibits concentration dependence in the range 1-25 mg/l and 3-65 mg/l for nitrite and nitrate, respectively. The relative standard deviation for five replicates of a standard solution containing a mixture of 5 mg/l of nitrite and 10 mg/l of nitrate lies around 2.8%. This simple coupling technique results in a relatively sensitive, fast, and accurate method, allowing for both qualitative and quantitative analysis of nitrite and nitrate. The method can easily be implemented to real samples such as foodstuffs, fertilizers and soils and is proven to be precise and accurate when compared with reference methods.     

An efficient route to 3-aryl-substituted quinolin-2-one and 1,8-naphthyridin-2-one derivatives of pharmaceutical interest

Reaction of arylacetic ester enolates with 2-alkoxy-4H-3,1-benzoxazin-4-ones offers a short and versatile synthetic route to 3-aryl-4-hydroxyquinolin-2(1H)-ones, through the cyclization of the beta-ketoesters produced. Similar reactions of 4H-pyrido[2,3-d][1,3]oxazin-4-ones with ester enolates afford 1-acyl-4-hydroxy-1,8-naphthyridin-2(1H)-ones in a convenient two-step, one-pot procedure.     

Waiting time analysis of a two-stage queueing system with priorities

A two-stage queueing system with two types of customers and non-preemptive priorities is analyzed. There is no waiting space between stages and so the blocking phenomenon is observed. The arrivals follow a Poisson distribution for the high priority customers and a gamma distribution for the low priority customers, while all service times are arbitrarily distributed. We derive expressions for the Laplace transform of the waiting time density of a low priority customer both in the transient and the steady state.     

Acid-Catalyzed Rearrangements for a Diastereoselective Entry into a New Fused Hexacyclic Heterocycle: (5RS,7aRS,12RS,14aRS,)-4,5,7a,11,12,14,14a-octahydro-5,12-dimethyl-diindolo [1,7-bc: 1′,7′-gh][2,6] naphthyridine

The title compound 1 was obtained in 10.3% overall yield via two acid-catalyzed rearrangements and pyrrolidine formation. Thus, bi-oxindole 6 afforded exclusively the thermodynamically stable cis-diazachrysene 7 which, after allylation, followed by aza-Claisen rearrangement gave alcohol 2 . Pyrolytic ring closure of the latter yielded 1 in highly diastereoselective fashion.     

Trapping without traps by correlated random walks

Correlated random walk of particles in the infinite cluster of percolating lattices in two dimensions is investigated. For infinitely strong forward correlations (no change of direction except at the boundaries) trapping of the particles in small regions of the infinite cluster is observed.     

Editorial: Hierarchical and bilevel programming

Approximately twenty years ago the modern interest for hierarchical programming was initiated by J. Bracken and J.M. McGill [9], [10]. The activities in the field have ever grown lively, both in terms of theoretical developments and terms of the diversity of the applications. The collection of seven papers in this issue covers a diverse number of topics and provides a good picture of recent research activities in the field of bilevel and hierarchical programming. The papers can be roughly divided into three categories; Linear bilevel programming is addressed in the first two papers by Gendreau et al and Moshirvaziri et al; The following three papers by Nicholls, Loridan & Morgan, and Kalashnikov & Kalashnikova are concerned with nonlinear bilevel programming; and, finally, Wen & Lin and Nagase & Aiyoshi address hierarchical decision making issues relating to both biobjective and bilevel programming.