Plasmachemical surface functionalised beads: versatile tailored supports for polymer assisted organic synthesis

Plasmachemical surface modification of porous polystyrene beads with allylamine or diaminopropane provides reactive amine functionality exclusively at accessible surface sites, allowing faster reactions than classically prepared materials.     

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.     

Analysis of Light Scattering Data on the Calcium Ion Sensitivity of Caseinate Solution Thermodynamics: Relationship to Emulsion Flocculation

We describe the quantitative interrelation between the thermodynamic parameters of caseinate submicelles in the presence of calcium ions (0-14 mM) in aqueous medium and the capacity of the protein to induce depletion flocculation in oil-in-water emulsions at pH 7.0 and ionic strength 0.05 mol dm(-3). Measurements have been made by static and dynamic multiangle laser light scattering of the weight-average molecular weight, the radius of gyration, the hydrodynamic radius, and the second virial coefficient of caseinate submicelles in aqueous solution. Successive thermodynamic approximations with and without consideration of correlations between caseinate submicelles have been used to calculate the osmotic pressure in caseinate aqueous solutions and the free energy of the depletion interaction between droplets in oil-in-water emulsions stabilized by caseinate. Numerical results from both thermodynamic approximations are in reasonably good agreement with experiment, predicting a pronounced decrease in the strength of the depletion attraction at concentrations of Ca(2+) in the range 4-8 mM (with a minimum value at 8 mM). This correlates well with the great enhancement of stability of these emulsions with respect to flocculation in comparison with systems having no added ionic calcium and emulsions with lower (2 mM) or higher (10 mM) Ca(2+) contents. Nevertheless, the allowance for interactive correlations between caseinate submicelles seems to lead to a better prediction of emulsion flocculation on a qualitative level over the whole range of Ca(2+) concentrations studied (2-14 mM). The calculated pronounced decrease in depletion interaction strength is attributable to marked changes in weight-average molecular weight and mean size of aggregates, and to more positive values of the second virial coefficient of caseinate submicelles with increasing Ca(2+) content. Finally, we discuss the part played by the electrical charge on the protein in determining the overall strength of the flocculation-inducing attractive interactions between droplets. Copyright 2001 Academic Press.     

Teaching decimal – binary conversion through an interactive exhibit

This note is a presentation of a didactic proposition about how to comprehend the conversion from the decimal into the binary system and vice versa with the aid of an interactive exhibit.