Carbon acidity of the alpha-pyridinium carbon of a pyridoxamine analog

We report second-order rate constants of kDO = 120 dm(3) mol(-1) s(-1) and kB = 6.4 x 10(-4) dm(3) mol(-1) s(-1) for exchange for deuterium of the first alpha-methylene proton of the 4-(aminomethyl)pyridine dication in D2O at 25 degree C and I= 1.0 (KCl). These data are consistent with a carbon acid pKa between 17 and 19 for ionization of this simple carbon acid and they show that the effect of an alpha-pyridinium substituent on carbon acidity is similar to that of an alpha-ester substituent.     

Configuration with internally coupled valves to overcome shortcomings in the simultaneous determination of nitrite and nitrate by flow-injection analysis

A configuration with internally coupled valves and a reductant column located in the loop of the secondary valve is proposed for the simultaneous determination of nitrite and nitrate. Depending on the column characteristics, a washing stream flowing in the opposite direction to the sample may or may not be required. The washing step may conveniently be performed by use of the proposed configuration.     

Scale-free networks from varying vertex intrinsic fitness

A new mechanism leading to scale-free networks is proposed in this Letter. It is shown that, in many cases of interest, the connectivity power-law behavior is neither related to dynamical properties nor to preferential attachment. Assigning a quenched fitness value x(i) to every vertex, and drawing links among vertices with a probability depending on the fitnesses of the two involved sites, gives rise to what we call a good-get-richer mechanism, in which sites with larger fitness are more likely to become hubs (i.e., to be highly connected).     

Corrigendum to “Gaussian bounds for degenerate parabolic equations” [J. Funct. Anal. 255 (2) (2008) 283–312]

We rectify an error in the proof of the Gaussian estimates for the heat kernel associated to certain weighted elliptic equations.     

1H and 13C NMR data,occurrence, biosynthesis,and biological activity of Piper amides

Alkamides are the major and characteristic chemical compounds of the plants belonging to the Piper genus. These compounds are responsible for the flavor of pepper spices and for its broad use in cuisine across many regions of the world. Humans are in contact every day with these substances, which additionally show a broad variety of pharmacological activities, making them an important research target. A large amount of NMR data for these natural products is dispersed throughout literature. Its organization will help those research groups interested in their identification and structural elucidation. This review summarizes the ¹H and ¹³C NMR data of 268 Piper amides in a systematic and orderly way, with a discussion on their biological activities, biosynthetic aspects, and NMR analysis of typical and relevant aspects of this information.     

Fe(III)-Catalyzed direct C3 chalcogenylation of indole: The effect of iodide ions

A mild and efficient iron (III)-catalyzed C3 chalcogenylation of indoles has been developed and the role of the iodide ions in this transformation was investigated. EPR experiments revealed the reduction of Fe(III) to Fe(II) under the reaction conditions, supporting the formation of molecular iodine in the system, which in effect catalyze the reaction. The scope of the chalcogenylation was broad and the synthesis of more functionalized 3-selenylindoles was explored.