An exact and heuristic approach for the <Emphasis Type="Italic">d</Emphasis>-minimum branch vertices problem

Given a connected graph \(G=(V,E)\), the d-Minimum Branch Vertices (d-MBV) problem consists in finding a spanning tree of G with the minimum number of vertices with degree strictly greater than d. We developed a Miller–Tucker–Zemlin based formulation with valid inequalities for this problem. The results obtained for different values of d show the effectiveness of the proposed method, which has solved several instances faster than previous methods. Also, an heuristic is proposed for this problem, that was tested on several instances of the Minimum Branch Vertices problem, which is the d-MBV problem, when \(d = 2\).     

Extended analysis of the Kr V spectrum

The spectrum of four-times-ionized krypton (Kr V) has been observed in the 230–4900 Å wavelength range, resulting in 91 new classified lines. We were able to identify 21 new energy levels belonging to the 4s²4p5d, 4s²4p5s, 4s²4p6s, 4s²4p5p and 4s4p²4d configurations. Relativistic Hartree–Fock calculations were used to predict energy levels and transitions.     

E´tude the´orique de la conformation de la 1,1-dime´thylhydrazine et du complexe (CH3)2N-NH2 · BF3

CNDO/2 calculations are performed in order to determine the preferred conformations of 1,1-dimethylhydrazine and 1,1-dimethylhydrazine-boron trifluoride complex. In each case, the calculations reveal the existence of an equilibrium between gauche and trans forms (25 % of trans form in the free molecule, 65 % in the complex). In agreement with experiment, the results confirm that BF₃ is attached to the nitrogen atom bearing the methyl groups.     

Kinetic study of the reaction between hydroxylated polybutadienes and isocyanates. II. Reaction with 3-isocyanatomethyl-3,5,5-trimethylcyclohexylisocyanate (IPDI) and dimer diacid diisocyanate (DDI)

A comparative kinetic study of the reaction of three different hydroxylated liquid poly-butadienes (M?_n ? 3000)–R-45M, R-45HT and H-034–with 3-isocyanatomethyl–3,5,5-trimethylclohexylisocyanate (IPDI) and dimer diacid diisocyanate (DDI) was carried out in toluene solution. An analytical method was used to follow the kinetics of the reactions, at four different temperatures. In the second-order plots, a discontinuity was observed in the reaction with IPDI, in contrast to the reactions with DDI which showed straight-line plots. In all studied reactions, the R-45M polybutadiene was about twice as reactive as R-45HT and H-034. The latter hydroxylated polybutadienes (R-45HT and H-034) showed similar reactivities.     

The photo-oxidation of EPDM rubber: Part III—Mechanistic aspects and stabilization

The kinetics of the photo-oxidation of crude EPDM rubber has been studied in order to propose a mechanism for the sequence of reactions which occurs during the photo-degradation process. The presence of the unsaturation markedly affects the kinetics of the photo-oxidation of EPDM in comparison with that of EPM. We have also studied the stabilization effect of a hindered amine and a hindered phenol on EPDM and compared this with crude EPM rubber. These stabilizers showed poor efficiency, which is explained by the presence of impurities which act as sensitizers for the degradation of the crude rubber.     

Nature of the interference of nitric acid in the determination of nickel and vanadium by atomic absorption spectrometry with electrothermal atomization

Effects of the concentration of nitric acid in the determination of nickel and vanadium in the presence of other metals by flarneless atomic absorption spectrometry have been studied. Specific complexation of the metals in the aqueous phase suppresses the interferences. A method has been developed which allows the use of calibration curves from dilute acidic solutions in the determination of samples with high nitrate concentrations. The method is suitable for solutions reproducing the mineralization of airborne particulates.     

Bisubstrate Inhibitors for the Enzyme Catechol O‐Methyltransferase (COMT): Dramatic Effects of Ribose Modifications on Binding Affinity and Binding Mode

Inhibition of the enzyme catechol O‐methyltransferase (COMT) is of significant interest in the therapy of Parkinson's disease. Described herein are structural analogs of the potent bisubstrate inhibitor (?)‐ 1 (IC₅₀=9 nM ; Table 1) for COMT, with target modifications of the central ribose moiety. Their synthesis involves, as key intermediates, adenosine derivatives, which are transformed to the potential bisubstrate inhibitors by a similar sequence of six steps (Schemes 1–4). The compounds were submitted to an enzymatic assay for determination of their in vitro inhibitory activity against COMT, and the inhibition mechanism with respect to the binding side of the cofactor S‐adenosylmethionine (SAM) was analyzed by kinetics measurements (Fig. 3). Both binding affinity and binding mode were exceedingly sensitive towards modifications of the ribose moiety (Table 1). Removal of the 2′‐OH group upon changing from (?)‐ 1 to (?)‐ 2 (IC₅₀=28 μM ) led to a reduction in binding affinity by more than three orders of magnitude. At the same time, competitive inhibition kinetics with respect to the SAM binding site was maintained, thereby supporting a bisubstrate binding mode. Unlike (?)‐ 2 , the dideoxyribose inhibitor (?)‐ 3 (IC₅₀=3 μM ) showed a mixed and the cyclopentane derivative (+)‐ 4 (IC₅₀=1 μM ) an uncompetitive inhibition mechanism with respect to the SAM binding site. In the complex of the latter, the adenine‐substituted cyclopentane ring orients most probably towards the surface of the enzyme into the surrounding solution. The enantiomeric compounds (?)‐ 5 (IC₅₀=43 μM ) and (+)‐ 5 (IC₅₀=141 μM ), wherein the ribose had been replaced by a pyrrolidine ring, showed only low binding affinity.     

Assuring the reliability of mass spectrometry for the routine determination of traces of doping in horse-urine

Summary This paper describes an analytical method using a nuclear-related technique for the detection of forbidden doping substances in the urine of race horses. The proposed method, adapted from the Méthode Alcaline Sur C-18 developed by the French Laboratoire de Contr?le Antidopage, is based on gas chromatography separation followed by mass spectrometry (GC-MS). The method was validated for caffeine, identified as the most frequent doping substance in the Brazilian horseracing activity. This validation is also a major requirement to achieve ISO/IEC 17025 laboratory accreditation. The validation has led to several metrological challenges because the decisions are largely based on qualitative results (“false-positive” and/or “false-negative”) and the degree of accuracy, as well as the traceability had to be determined in the absence of certified matrix reference materials.     

Alcoylation d'acridanone-9. Premiers exemples de O-alcoylation dans cette série de composés

The results of nucleophilic substitution of the 2-methoxy-9-acridone are discussed in terms of competition between both ionic sites N^? and O^?, of the molecule. They are the first examples of O-alkylation of substituted 9-acridone.