Palladium-Catalyzed Allylic Coupling of 1,2,3-Triazolo[4,5-d]pyrimidines (8-Azapurines)

The palladium-catalyzed coupling of the sodium salt of 7-amino-1,2,3-triazolo[4,5-d]pyrimidine (8-azaadenine, 1) with allylic phosphates or carbonates resulted in mixtures of 2- and 3-substituted 1,2,3-triazolopyrimidines, which were separated by chromatography. 1-Substituted triazolopyrimidines were not isolated from these reactions. Regioselectivity (and stereoselectivity) was also observed for substitution of the allylic moiety when more than one isomer is possible from the reaction. The use of 5-amino-1,2,3-triazolo[4,5-d]pyrimidin-7-ones (8-azaguanine, 2), instead of 8-azaadenine, also resulted in mixtures. Alternate syntheses of the 3-allyl-1,2,3-triazolo[4,5-d]pyrimidines confirmed the structures of these compounds.     

Rapid crack growth in a thermoelastic solid under mixed-mode thermomechanical loading

A two-dimensional steady-sate analysis of semi-infinite brittlecrack growth at a constant subcritical rate in an unboundedfully-coupled thermoelastic solid under mixed-mode thermomechanicalloading is made. The loading consists of normal and shear tractionsand heat fluxes applied as point sources (line loads in theout-of-plane direction). A related problem is solved exactly in an integral transformspace, and robust asymptotic forms used to reduce the originalproblem to a set of integral equations. The equations are partiallycoupled and exhibit operators of both Cauchy and Abel types,yet can be solved analytically. The temperature change field at a distance from the moving crackedge is then constructed, and its dominant term is found tobe controlled by the imposed heat fluxes. The role of this termis, indeed, enhanced if the heat fluxes serve to render thecrack as a net heat source/sink for the solid, as opposed tobeing a transmitter of heat across its plane. More generally,the influence of the thermoelastic coupling on this field, aswell as other functions, is found to increase with crack speed.     

Thermal degradation and flame retardance in copolymers of methyl methacrylate with diethyl(methacryloyloxymethyl)phosphonate

Methyl methacrylate (MMA) has been free radically copolymerized, both in bulk and in solution, with diethyl(methacryloyloxymethyl)phosphonate (DEMMP), to give polymers which are significantly flame retarded when compared with PMMA, as indicated by the results of limiting oxygen index (LOI) measurements, UL 94 tests, and the results of cone calorimetric experiments. The physical and mechanical properties of the copolymers are similar to those of PMMA, except that the bulk copolymers are slightly crosslinked, and are better than those of PMMA flame retarded to a similar extent by some phosphate and phosphonate additives. Examination of the some of the gaseous products of pyrolysis and combustion, and of chars produced on burning, show that flame retardation occurs in the copolymers by both a condensed-phase and a vapour-phase mechanism. The condensed-phase mechanism is shown to involve generation of phosphorus acid species followed by reaction of these with MMA units giving rise to methacrylic acid units. The methacrylic acid units subsequently form anhydride links, which probably impede depolymerization of the remaining MMA sequences, resulting in evolution of less MMA (the major fuel when MMA-based polymers burn). By undergoing decarboxylation, leading to interchain cyclisation and, eventually, to aromaticisation, the anhydride units are probably also the principal precursors to char.     

In situ vinylindole synthesis. Diels-alder reactions with maleimides to give tetrahydrocarbazoles

Tetrahydrocarbazoles have been prepared in one-flask syntheses from indoles, ketones or aldehydes, and maleimides, with acid catalysis. The reactions involve a condensation of the indole with the ketone or aldehyde, followed by an in situ trapping of the vinylindole in a Diels-Alder addition with a maleimide. Isomerization of the double bond into the indole nucleus gave the tetrahydrocarbazoles which were isolated ( 6, 9 , and 10 ). Variation of the indole, carbonyl compound, and maleimide has been explored. The predominant stereochemistry of the tetrahydro ring in the products is all-cis, although a second stereoisomer has been isolated. Two regioisomers were generated from all unsymmetrical 2-alkanones, except 2-butanone, which gave the single isomer 9a . Aromatization of tetrahydrocarbazoles 6 to carbazoles 7 was accomplished with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone.     

The crystal structure of a novel product from the acid-catalyzed condensation of 1-benzylindole with acetone

The acid-catalyzed condensation of 1-benzylindole with acetone in the presence of N-phenylmaleimide gave a tetrahydrocarbazole, (4,5,10,10b-tetrahydro-5-methyl-2-phenyl-10-(phenylmethyl)pyrrolo[3,4-a]carbazole-1,3[2H, 3aH]-dione (1), as the major product and a novel spiro compound, 1,3,4,4-tetrahydro-1,1,3,3-tetramethyl-4,4-bis(phenylmethyl)-1,3(2H, 2H)-spiro[cyclopent[b]indole] (2), as the minor product. The structure of the spiro compound was determined by an X-ray crystallographic determination. The acid-catalyzed condensation of 1-benzylindole with acetone in the absence of N-phenylmaleimide gave a bisindole, (1,1-bis(phenylmethyl)-3,3-(1-methylethylidene)diindole (3), as the major product and the spiro-compound as the minor product.     

Diels-alder reactions of 3-(2-nitrovinyl)indoles: Formation of carbazoles and bridged carbazoles

The Diels-Alder reactions of 1-substituted-3-(2-nitrovinyl)indoles 3 with quinones and acetylenes give aromatized 1:1 adducts (- nitrous acid) ( 1 ) or (- nitrous acid, -2 hydrogens) 2,5 . Likewise, dimerization (-2 nitrous acids) of 3 gives aromatized 2-(3-indolyl)carbazoles 4 . In contrast, 3 reacts with maleimides 6 to give 1:2 adducts (- nitrous acid or -2 hydrogens) 10 and 11 , respectively, along with smaller amounts of 1:1 adducts (- nitrous acid, -2 hydrogens; or -4 hydrogens) 12 and 13 , respectively. A mechanism for formation of the nitro products 11 and 13 is discussed. A 1:2 adduct (-2 hydrogens) 19 was also obtained from a Diels-Alder reaction between maleimide and the vinylindole produced in situ by condensing 1-methylindole with acetone. The stereochemisty of this 1:2 adduct has been determined by X-ray crystallography.     

Synthetic magnetic opals

We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there exists no report in literature on any BiNi compound which is magnetic.     

Structure Determination of the Products from the Acid-Catalyzed Condensation of Indole with Acetone

Four of the previously reported compounds obtained from the acid-catalyzed condensation of indole with acetone are now assigned the following structures: cis-4,4a,9,9a-tetrahydro-2-(1H-indol-3-yl)-4,4-dimethyl-3H-carbazole (2a), 1,1',4,4'-tetrahydro-1,1,1',1'-tetramethyl-3,3'(2H,2'H)-spirobi[cyclopent[b]indole] (4), 4,4a-dihydro-2-(3-1H-indolyl)-4,4-dimethyl-3H-carbazol-4a-ol (7), and 5-(2-aminophenyl)-1,3,4,5-tetrahydro-1,1,4,4-tetramethylcyclopent[kl]acridine (8). The structure of the novel rearrangement product 8 was solved by an X-ray crystal structure determination. The two previously reported autoxidation products of 4 are now assigned the following structures: 1,3',4,4'-tetrahydro-1,1,4',4'-tetramethyl-cis-dispiro[cyclopent[b]indole-3(2H),2'(5'H)-furan-5',3"-[3H]-indol]-2"(1"H)-one (5) and 1,4-dihydro-1,1,5',5'-tetramethylspiro[cyclopent[b]indole-3(2H),3'(4'H)-1-benzazocine]-2'(1'H),6'(5'H)-dione (6).     

Functional neural network analysis in frontotemporal dementia and Alzheimer's disease using EEG and graph theory

Background  

Although a large body of knowledge about both brain structure and function has been gathered over the last decades, we still have a poor understanding of their exact relationship. Graph theory provides a method to study the relation between network structure and function, and its application to neuroscientific data is an emerging research field. We investigated topological changes in large-scale functional brain networks in patients with Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD) by means of graph theoretical analysis of resting-state EEG recordings. EEGs of 20 patients with mild to moderate AD, 15 FTLD patients, and 23 non-demented individuals were recorded in an eyes-closed resting-state. The synchronization likelihood (SL), a measure of functional connectivity, was calculated for each sensor pair in 0.5–4 Hz, 4–8 Hz, 8–10 Hz, 10–13 Hz, 13–30 Hz and 30–45 Hz frequency bands. The resulting connectivity matrices were converted to unweighted graphs, whose structure was characterized with several measures: mean clustering coefficient (local connectivity), characteristic path length (global connectivity) and degree correlation (network 'assortativity'). All results were normalized for network size and compared with random control networks.