Unimolecular rearrangements of ketene-O,O-acetals and fragmentations occurring in the gas phase

Gas phase skeletal rearrangements of regioisomeric 3‐cyano‐2‐methoxy‐3a‐alkylfuro[2,3‐b]‐ and [3,2‐b]indoles were evidenced by product ions [M ? 32]^+?, consistent with loss of methanol, on electron ionization in their mass spectra. The rearranged products occurring in gas phase were demonstrated to have elemental composition and fragmentation properties identical to those of authentic samples of 2‐indolyl cyanomalonates. Isotopic labeling experiments support the formation mechanism of the [M ? 32]^+? ion. Additional thermal gas‐phase reaction products were characterized by comparison with an authentic sample. Copyright © 2011 John Wiley & Sons, Ltd.     

Line graph of combinations of generalized Bethe trees: Eigenvalues and energy

We characterize the eigenvalues and energy of the line graph L(G) whenever G is (i) a generalized Bethe tree, (ii) a Bethe tree, (iii) a tree defined by generalized Bethe trees attached to a path, (iv) a tree defined by generalized Bethe trees having a common root, (v) a graph defined by copies of a generalized Bethe tree attached to a cycle and (vi) a graph defined by copies of a star attached to a cycle; in this case, explicit formulas for the eigenvalues and energy of L(G) are derived.     

New pentacoordinated Schiff-base diorganotin(IV) complexes derived from nonpolar side chain α-amino acids

In this work we report the synthesis and spectroscopic characterization of twenty new pentacoordinated diorganotin(IV) compounds. These compounds have been prepared in good yields by multicomponent reactions (MCRs) of α-amino acids (isoleucine, leucine, methionine, phenylalanine and aminophenylacetic acid), 2,4-dihydroxybenzaldehyde, 2-hydroxy-4-methoxybenzaldehyde and either di-n-butyltin(IV) oxide or diphenyltin(IV) oxide. All compounds were characterized by IR spectroscopy, ¹H, ¹¹⁹Sn and ¹³C NMR spectroscopy and mass spectrometry. Each compound has a coordinative N→Sn bond and shows the expected ¹¹⁹Sn NMR chemical shift indicative of a pentacoordinated or hexacoordinated tin atom in CDCl₃ and DMSO-d₆, respectively. These compounds were also tested in tumoral cell lines, HeLa, HCT-15 and MCF-7, in order to evaluate the antiproliferative activity and to obtain the medial inhibitory concentrations (IC₅₀) values.     

Mechanism of the organocatalyzed decarboxylative Knoevenagel-Doebner reaction. A theoretical study

We have investigated important intermediates and key transition states of the organocatalyzed Knoevenagel condensation using density functional theory and two different basis sets (6-31 G(d,p) and 6-311++G(2df,2pd)), both in gas phase and simulating the bulk solvent (pyridine) using the PCM method. Calculated structures for reactants, intermediates, and key transition states suggest that the secondary amine catalyst is essential, both for activating the aldehyde for nucleophilic attack, and in the possible decarboxylation pathways. The calculated results are shown to agree with available experimental information. On the basis of the results obtained, the studied mechanism may be important in the understanding of vinylphenol production during malting and brewing of wheat and barley grains.     

Characterization of pristine and purified organobentonites

Pristine and purified Argel sodium bentonites were organically modified with quaternary ammonium and phosphonium surfactants by ion exchange reaction in order to investigate the effect of the chemical identity of the surfactant and of the clay purification procedure in the intercalation process, final structure and thermal stability of organobentonites. The bentonites were characterized by X-ray diffraction analysis, thermogravimetric analysis and Fourier transform infrared spectroscopy. The bentonite purification treatment and, especially, the chemical structure of surfactant affected the thermal behavior of the organobentonites. The phosphonium modified bentonites were thermally more stable than those modified with ammonium, particularly the purified bentonite. These results seem to be promising regarding to the potential application of phosphonium modified Argel bentonites for the melt processing preparation of nanocomposites with polymeric matrices requiring high processing temperatures.     

The Construction of Open GdIII Metal–Organic Frameworks Based on Methanetriacetic Acid: New Objects with an Old Ligand

The preparation, X‐ray crystallography and magnetic investigation of the first examples of methanetriacetate (mta)‐containing lanthanide(III) complexes of formulae [Gd(mta)(H₂O)₃]_n ? 4 n H₂O ( 1 ) [Gd(mta)(H₂O)₃]_n ? 2 n H₂O ( 2 ) and [Gd₂(mta)₂(H₂O)₂]_n ? 2 n H₂O ( 3 ) are described herein. This tripodal ligand promotes the formation of 6³ networks; thus 1 consists of a honeycomb structure, whereas in 2 two of these layers are condensed to form a rare five‐connected two‐dimensional (4⁸6²) network. Compound 3 can be seen as an aggregation of 6³ layers leading to a three‐dimensional (6,6)‐connected binodal (4¹²6³)(4⁹6⁶)‐ nia net, in which the gadolinium(III) ions and the mta ligands act as octahedral and as trigonal prismatic nodes, respectively. The magnetic properties of 1 – 3 were investigated in the temperature range 1.9–300 K. A close fit to the Curie law ( 1 ) and weak either antiferro‐ [J=?0.0063(1) cm^?1 ( 2 )] or ferromagnetic [J=+0.0264(6) cm^?1 ( 3 )] interactions between the Gd^III ions are observed; the different exchange pathways involved [extended tris‐bidentate mta ( 1 ) and μ‐O(1);κ²O(1),O(2) ( 2 and 3 ) plus single syn–syn carboxylate‐mta ( 3 )] accounting for these magnetic features. The nature and magnitude of the magnetic interactions, between the Gd^III ions in 1 – 3 , agree with the small amount of data existing in the literature for these kind of bridges.     

Different coordination modes of the thiosaccharinate anion in dinuclear and one dimensional polymeric silver–azine complexes

The effect of substituted pyridines bases upon the coordination of thiosaccharinate (tsac, C₇H₄NO₂S₂⁻ in ternary silver complexes is analyzed. Four crystalline silver-substituted pyridine complexes with tsac as a coordinating counter anion, [Ag(tsac)(3-methylpyridine)₂]_n, [Ag₂(tsac)₂(4-methylpyridine)]_n, [Ag₂(tsac)₂(quinoline)₂] and [Ag(tsac)(4-methyloxypyridine)]_n were synthesized and characterized by means of spectroscopic (IR and Raman, UV–Vis, and ¹H and ¹³C NMR) and X-ray diffraction techniques. The thiosaccharinate anion showed its versatility coordinating to the metal in each complex by a different way. In the 3-Mepy complex it was coordinated in a μ₂-S mode and in the 4-MeOpy complex it was bound in a μ₃-S form both resulting in polymeric chains. In the 4-Mepy complex the anion was bound in a μ₂-S,N head to head mode and in the quinoline complex in a μ₂-S,N head to tail mode, both showing dinuclear arrangements.