On Rump’s characterization of <Emphasis Type=Italic>P</Emphasis>-matrices

The necessary and sufficient P-matrix condition by Rump (Linear Algebra Appl 363:237–250, 2003) is simplified by showing that one of its assumptions can be deleted without affecting validity of the result.     

Pyrazinecarboxamides as potential elicitors of flavonolignan and flavonoid production in Silybum marianum and Ononis arvensis cultures in vitro

The effect of new synthetic pyrazinecarboxamide derivatives as potential elicitors of flavonolignan and flavonoid production in Silybum marianum and Ononis arvensis cultures in vitro was investigated. Both tested elicitors increased the production of flavonolignans in S. marianum callus and suspension cultures and flavonoids in O. arvensis callus and suspension cultures. Compound I, 5-(2-hydroxybenzoyl)-pyrazine-2-carboxamide, has shown to be an effective elicitor of flavonolignans and taxifoline production in Silybum marianum culture in vitro. The maximum content of silydianin (0.11%) in S. marianum suspension culture was induced by 24 h elicitor application in concentration of 1.159 × 10?3 mol/L. The maximum content of silymarin complex (0.08%) in callus culture of S. marianum was induced by 168 h elicitor application of a concentration 1.159 × 10?? mol/L, which represents contents of silydianin (0.03%), silychristin (0.01%) and isosilybin A (0.04%) compared with control. All three tested concentrations of compound II, N-(2-bromo-3-methylphenyl)-5-tert-butylpyrazin-2-carboxamide increased the flavonoid production in callus culture of O. arvensis in a statistically significant way. The best elicitation effect of all elicitor concentrations had the weakest c? concentration (8.36 × 10?? mol/L) after 168 h time of duration. The maximum content of flavonoids (about 5,900%) in suspension culture of O. arvensis was induced by 48 h application of c? concentration (8.36 × 10?? mol/L).     

Insights into Antimalarial Activity of N-Phenyl-Substituted Cinnamanilides

Due to the urgent need of innovation in the antimalarial therapeutic arsenal, a series of thirty-seven ring-substituted N-arylcinnamanilides prepared by microwave-assisted synthesis were subjected to primary screening against the chloroquine-sensitive strain of P. falciparum 3D7/MRA-102. The lipophilicity of all compounds was experimentally determined as the logarithm of the capacity factor k, and these data were subsequently used in the discussion of structure-activity relationships. Among the screened compounds, fourteen derivatives exhibited IC₅₀ from 0.58 to 31 µM, whereas (2E)-N-(4-bromo-2-chlorophenyl)-3-phenylprop-2-enamide (24) was the most effective agent (IC₅₀ = 0.58 µM). In addition, (2E)-N-[2,6-dibromo-4-(trifluoromethyl)- phenyl]-3-phenylprop-2-enamide (36), (2E)-N-[4-nitro-3-(trifluoromethyl)phenyl]-3-phenylprop- 2-enamide (18), (2E)-N-(2-bromo-5-fluorophenyl)-3-phenylprop-2-enamide (23), and (2E)-3-phenyl-N-(3,4,5-trichlorophenyl)prop-2-enamide (33) demonstrated efficacy in the IC₅₀ range from 2.0 to 4.3 µM, comparable to the clinically used standard chloroquine. The results of a cell viability screening performed using THP1-Blue™ NF-κB cells showed that none of these highly active compounds displayed any significant cytotoxic effect up to 20 μM, which makes them promising Plasmodium selective substances for further investigations.     

About a new class of matroid-inducing packing families

Let T be a family of graphs. A T-packing of a graph G is a subgraph of G, components of which are isomorphic to members of T. We are concerned with families T, such that in every graph G, the subsets of vertices that can be saturated by some T-packing form a collection of independent sets of a matroid. The main purpose of this paper is to introduce a new class of families with this property.     

Steric Effects on Reaction Rates. Part IX. Force-Field Parameters for Bridgehead and Rigid Tertiary Carbenium Ions

Molecular-mechanics calculations for strain of carbenium ions are tested using Bentley's unified reactivity scale for bridgehead solvolysis as reference. Excellent correlations are obtained for solvolytic bridgehead reactivity with the calculated steric-energy difference (ΔE_st) between substrate (R? H or R? OH) and cation (R⁺). After adjustment of appropriate force-field parameters, the approach is successfully extended to the rigid, but planar cations derived from structures 15 – 20 ; however, the general set of parameters cannot be applied to highly strained systems such as the cation formed from 17 . With all of the 18 sets of parameters tested, the 2-endo-norbornyl derivative 16 , is adequately correlated, while the exo isomer 15 exhibits enhanced reactivity by a factor of ca. 10² to 10³.     

Kinetics of the heterogeneous electron transfer reaction of triplet pyrene in micelles to Br2− radicals in aqueous solution

A combined flash photolysis and pulse radiolysis experiment was carried out to produce triplet pyrene (P) molecules in micelles of cetyltrimethylammonium bromide and Br₂^? in the surrounding aqueous medium. The reaction ³P_mic + Br → P + 2 Br^? was followed by optical absorption measurements in the 10^?8?10^?4–sec range. This reaction possesses a “fast” and a “slow” component with respective rate constants of 2.3 × 10⁶ sec^?1 and 1 × 10⁹M^?1 · sec^?1. The fast component is related to the probability of a Br₂^? radical meeting a triplet pyrene containing micelle on the first encounter (only 16% of the micelles contained a triplet molecule). Reactions involving more than one Br₂^? radical–micelle encounter are ascribed to the slow component. The presence of two components reflects the fact that the residence time of a Br₂^? radical in the vicinity of a cationic micelle is substantially longer than the diffusion time of the radical between micelles. Thus the conditions met in micellar chemistry differ dramatically from those in ordinary solution kinetics where the encounter time is generally much shorter than the time between encounters. Some considerations on the energetics of this electron transfer reaction are also presented.     

Configuration interaction calculations of the valence and the inner valence levels of the CS molecule

CI calculations were performed on the energies and relative intensities of the outer and inner valence levels of the CS molecule. Breakdown of the one-particle model is discussed in terms of CI, and the results are compared with the analogous investigations using the Green's function technique.     

Calculation of vibrational structure in the core and valence esca spectra of CO and N2

The vibrational excitations in the core and valence ESCA bands of CO and N₂ have been investigated by means of Franck—Condon (FC) analysis. FC factors obtained from optimized geometries and from the force constants of the neutral ground and ionized states are compared with those obtained from calculated ionized-state energy gradients. Geometries, force constants, and energy gradients are calculated both from frozen-orbital energies and from OS RHF wavefunctions. The differences between the results of the methods employed are discussed in the light of experimental data.     

New Reasons to Motivate Trope Theory: Endurantism and Perdurantism

In this paper, I argue that (non-presentist) endurantism is incompatible with the view that properties are universals. I do so by putting forward a very simple objection that forces the endurantist to embrace tropes, rather than universals. I do not claim that this is bad news for the endurantist—trope theory seems to me by all means more appealing than universals—rather, I would like to see this result as a further motivation to embrace tropes. I then also put forward a (more controversial) reason to believe that at least some versions of perdurantism also require tropes rather than universals.     

Mean field calculation of effective permeability based on fractal pore space

Effective permeability for porous rocks is calculated using mean field theory. We make two simplifying assumptions about the internal conductances in a network representation of the porous rock: (i) Pore space is characterized by a uniform fractal scaling; (ii) the internal conductances depend only on the characteristic pore sizes. Within these approximations, it is possible to derive a simple probability density for the internal conductances which is used for calculating effective permeability. Good agreement between calculations and experimental data of permeability vs. porosity is achieved.