Letter to the editor

The meaning of semiotics for mathematical research and education is discussed, and further practical applications are proposed. An example of matrix notation exhibits some related arguments.     

Power loss of an energetic charged particle moving parallel to a graphene sheet

In this work we analyze the energy loss of a fast charged particle moving parallel to a two-dimensional (2D) graphene sheet. The response dynamics of the 2D graphene sheet are modeled using the random phase approximation in the degenerate limit (zero temperature). We determine the energy loss and stopping power for motion parallel to the graphene sheet as a function of the distance of the charged particle from the 2D sheet and of its velocity.     

Antifolate chemistry: synthesis of 4-[N-[(6RS)-2-methyl-4-oxo-3,4,7,8-tetrahydro-6H-cyclopenta[g]quinazolin-6-yl]-N-(prop-2-ynyl)amino]benzoic acid via a (propargyl)Co2(CO)6+ complex

A new route to compound 3 (4-[N-(6RS)-2-methyl-4-oxo-3,4,7,8-tetrahydro-6H-cyclopenta[g]quinazolin-6-yl]-N-(prop-2-ynyl)amino]benzoic acid), a crucial intermediate for the synthesis of potent inhibitors of thymidylate synthase (TS), is described. In this sequence the C6-N10 bond was constructed first, by the reductive amination of 5-acetamido-6-bromoindan-1-one 6 with tert-butyl 4-aminobenzoate, then the cyclopenta[g]quinazolinone ring was formed and the propargyl group was introduced on the N10-position using the (propargyl)Co2(CO)6+ complex as the electrophilic propargyl reagent.     

Monitoring of Polycyclic Aromatic Hydrocarbon Levels in Mussels (Mytilus galloprovincialis) from Aquaculture Farms in Central Macedonia Region,Greece, Using Gas Chromatography–Tandem Mass Spectrometry Method

A new sensitive and selective gas chromatography tandem mass spectrometry (GC-MS/MS) method was developed for the analysis of 26 polycyclic aromatic hydrocarbons (PAHs), including 16 Environmental Protection Agency (EPA) and 15 + 1 European Union (EU) PAHs, in mussel samples from aquaculture farms in Thermaikos and Strymonian Gulf, Central Macedonia Region, in three sampling periods. Concentrations were found at moderate to low values at all sampling sites, without exceeding maximum levels set by EU. Low molecular weight PAHs were predominant in all samples. Seasonal variation of the concentrations was observed; values were slightly higher in the winter period. Use of diagnostic ratios for potential sources of PAHs showed both petrogenic and pyrolitic origin. In comparison to other related studies of mussels from the Mediterranean Sea, Greek mussels cultivated in the studied gulfs are low in contaminants due to minimal environmental pollution effects. Low concentrations of PAHs are in compliance with the low values of other POPs which were found in the mussels.     

Simulation of polymer network formation: Connectivity considerations

The issue of connectivity in polymer networks is discussed by employing graph theory. Several topics are addressed, including the theory of rubberlike elasticity and computer simulations of network formation. The formulation of the partition function is reviewed and new applications are presented on the irradiation cure of polybutadiene and the sulfur vulcanization of cis(1,4)-polyisoprene and cis(1,4)-polybutadiene.     

Inverse gas chromatographic investigation of the effect of hydrogen in carbon monoxide adsorption over silica supported Rh and Pt-Rh alloy catalysts, under hydrogen-rich conditions

Selective CO oxidation (SCO) has attracted scientific and technological interest due to its application to the operation of proton electrolyte membrane fuel cells (PEM-FCs). CO adsorption, being an elementary step of SCO, is studied over silica supported monometallic Rh and Rh0.50 + Pt0.50 alloy catalysts, under various hydrogen atmospheres, namely: 25% H2 + 75% He, 50% H2 + 50% He and 75% H2 + 25% He carrier gas mixture compositions. The investigation of CO adsorption is done by utilizing reversed-flow gas chromatography (RF-GC). As a result rate constants for the adsorption (k1), desorption (k(-1)) and irreversible CO binding (k2) over the studied catalysts as well as the respective activation energies are determined. The variation of the rate constants and the activation energies against the nature of the used catalyst (monometalic or alloy) and the amount of hydrogen in the carrier gas gives useful information for the selectivity as well as the activity of CO oxidation over group VIII noble metals. At low temperatures and under H2-rich conditions compatible with the operation of PEM fuel cells the activity of the monometallic and the alloy catalysts is expected to be similar, however the selectivity of Rh0.50 + Pt0.50 alloy catalyst is expected to be higher, making Pt-Rh alloy catalyst as a better candidate for CO preferential oxidation (PROX). The low energy barrier values found in the present work, most likely are referred to high surface amounts of CO. The desorption barriers determined are in any case much lower than the respective activation energies found for CO desorption in the absence of hydrogen indicating a H2-induced desorption, which can explain the observed in the literature rate enhancement of SCO oxidation.     

Occurrence and distribution of selected pharmaceutical compounds on sewage-impacted section of River Acheloos,Western Greece

The occurrence of eight pharmaceutical compounds (PhCs), two metabolites and caffeine was investigated in River Acheloos, located in Western Greece, during a twelve-month monitoring period (March 2007–February 2008). Solid-phase extraction (SPE) was used for the extraction and pre-concentration of the target pollutants and gas chromatography mass spectrometry (GC–MS) for the detection and quantification. Recoveries were determined between 74.0–100.4% for distilled water and 72.6–95.1% for the river water, whereas the relative standard deviation was less than 9.4% for distilled water and 8% for the river water, respectively. The limits of detection ranged between 1–40 ng L^?1. Two pharmaceuticals (paracetamol and carbamazepine), caffeine and the metabolite (salicylic acid), have been detected in all the analysed samples. Maximum concentration levels determined in river samples reached 305 ng L^?1 recorded for paracetamol. The concentrations of target compounds were significantly higher in the samples collected at the sampling station situated after the wastewater treatment plant (WWTP) of Agrinio City compared to the samples collected in upper and lower parts of the river. Seasonal variations were attributed mainly to river flow variations and removal percentages by WWTP. Risk quotient method for median environmental concentrations revealed minimal to median risk with the exception of triclosan, ibuprofen and diclofenac, which presented high risk when maximum environmental concentrations were used.     

Chromeno[2,3-c]pyrroles by one-pot multicomponent domino addition–amination reaction

A new aspect concerning chromone chemistry leading to the one-pot synthesis of chromeno[2,3-c]pyrroles is described. The synthesis involves a multicomponent reaction of 3-formylchromones with isocyanides and azodicarboxylates, whereupon novel chromeno[2,3-c]pyrrole derivatives were formed in good yields. The structures of the products were elucidated by 1D and 2D NMR experiments and were unambiguously confirmed by the use of crystal X-ray diffraction analysis. Full assignment of all ¹H and ¹³C NMR chemical shifts has been achieved. A plausible mechanistic scheme is proposed.