New epoxyisoindolines by intramolecular diels-alder reactions of some methyl-substituted allylaryl-2-furfurylamines

N-Alkenyl-N-(5-substituted-2-furfuryl)-N-p-toluidines 1–10 have been selected to study the intramolecular Diels-Alder reaction of furans. New epoxyisoindolines 11–20 were prepared and fully characterised.     

On the Wiener index of a graph

A modification of the Weiner index which properly takes into account the symmetry of a graph is proposed. The explicit formulae for the modified Wiener index of path, cycle, complete bipartite, cube and lattice graphs are derived and compared with their standard Wiener index.     

Slater orbital molecular integrals with numerical fourier transform methods. I. (coplanar) multicenter exchange integrals over 1s orbitals

Slater orbital r₁₂^?1 integrals are calculated with a numerical Fourier-transform method based on a formulation first given by Bonham, Peacher and Cox. Spherical wave expansions are introduced that decouple the Feynman integrations for the charge distribution Fourier transforms. The Feynman integrals are evaluated semianalytically, and their properties are analyzed in detail. The final computational step involves a numerical integration over charge distribution quantities. Results for (coplanar) multicenter exchange integrals over 1s orbitals are given. As long as the charge distributions are overlapping considerably, the method gives good results, even when these distributions are highly asymmetric. The method as presently implemented fails when highly disconnected charge distributions are involved.     

Method for simultaneous luminescence sensing of two species using optical probes of different decay time, and its application to an enzymatic reaction at varying temperature

Chemical sensing, imaging and microscopy based on the use of fluorescent probes has so far been limited almost exclusively to the detection of a single parameter at a time. We present a scheme that can overcome this limitation by enabling optical sensing of two parameter simultaneously and even at identical excitation and emission wavelengths of two probes provided (a) their decay times are different enough to enable two time windows to be recorded, and (b) the emission of the shorter-lived probe decays to below the detectable limit while that of the other still can be measured. We refer to this new scheme as the dual lifetime determination (DLD) method and show that it can be widely varied by appropriate choice of probes and experimental settings. DLD is demonstrated to work by sensing oxygen and temperature independently from each other by making use of two probes, one for oxygen (a platinum porphyrin dissolved in polystyrene), and one for temperature [a europium complex dissolved in poly(vinyl methylketone)]. DLD was applied to monitor the consumption of oxygen in the glucose oxidase-catalyzed oxidation of glucose at varying temperatures. The scheme is expected to have further applications in cellular assays and biophysical imaging. Figure Principle behind the dual lifetime determination (DLD) method     

New compounds in the reaction of aromatic amines and 5-hydroxy-4-pyrone-2-carboxylate. The influence of a methoxy group

Unlike most of other aromatic amines, 4-methoxyaniline with methyl comenate ( 1 ) in the mixture of acetic acid and methanol (1:1) gave two unexpected products with azomethyne moiety. The structures of new compounds were determined from their characteristic spectroscopic behaviour and were confirmed by X-ray crystallographic measurements.     

Unusual random walks

For most structures (molecules, graphs, lattices) a count of random walks for nonequivalent sites will give different numbers, particularly for walks of many steps. Occasionally one finds the same count of walks for nonequivalent sites. These have been termed “unusual walks” and have been closely examined in the case of trivalent graphs. While it remains to be understood what structural factors are critical, some regularities have been observed and are discussed. Unusual walks within a single structure signal “isospectural” points in a graph. A number of structures possessing unusual walks have been displayed, and a few constructive steps which do not alter the “unusual” characteristics of selected vertices have been indicated.     

Yttrium calix[4]arene complexes. Silylation and silylamine elimination reactions on model oxo surfaces

The synthesis and the spectroscopic and structural characterization of lower-rim-silylated and rare-earth-metalated calix[4]arenes are presented. Hexamethyldisilazane, HN(SiMe3)2, reacted in a selective manner with [p-tert-buttylcalix[4]arene]H4 (1) in refluxing mesitylene to give the 1,3-silylated product [p-tert-butylcalix[4]arene(SiMe3)2]H2 (2) in high yield. The molecular structure of compound 2, as revealed by X-ray crystallography, shows the pinched cone conformation of the calixarene bowl, featuring hydrogen bonding between the phenylsilyl ether and phenolic oxygen atoms (O...O, 2.838 A). From the reaction of the sterically more crowded tetraphenyldimethyldisilazane, HN(SiMePh2)2, only starting material could be recovered. In contrast, tetramethyldisilazane, HN(SiHMe2)2, afforded the tetrakis-silylated product [p-tert-butylcalix[4]arene(SiHMe2)4] (3) in hexane solution at ambient temperature. A single-crystal X-ray diffraction study of compound 3 established the 1,2-alternate conformation, which is also present in solution, as indicated by 1H NMR spectroscopy. The yttrium complex Y[N(SiHMe2)2]3(THF)2 (4) exchanged all of its silylamide ligands when treated with an equimolar amount of 1 in toluene at ambient temperature to yield compound 5, as indicated by IR and NMR spectroscopy. The molecular structure of 5 revealed a centrosymmetric dimer of composition [Y(p-tert-butylcalix[4]arene(SiHMe2)(THF)]2. Three of the deprotonated phenolic oxygen atoms of the calixarene bowl bind to the metal center, two as terminal ligands and one in a bridging mode, while the fourth undergoes in situ silylation (nu(SiH) 2127 cm-1). The distorted-trigonal-bipyramidal coordination geometry is completed by a THF molecule. Bis-silylated 2 reacted with 4 to form the heteroleptic complex (Y[p-tert-butylcalix[4]arene(SiMe3)2][N(SiHMe2)2]) (6). Crystal data: C50H72O4Si2 (2), triclinic, P1, a = 12.8914(3) A, b = 14.9270(5) A, c = 15.1652(4) A, alpha = 77.293(2) degrees, beta = 65.019(2) degrees, gamma = 72.234(2) degrees, Z = 2; C52H80O4Si4 (3), triclinic, P1, a = 10.1774(2) A, b = 14.1680(2) A, c = 18.7206(2) A, alpha = 95.8195(8) degrees, beta = 95.5294(8) degrees, gamma = 98.1098(7) degrees, Z = 2; C100H132O10Si2Y2, 2(C6H6) (5), triclinic, P1, a = 13.2625(4) A, b = 14.5894(3) A, c = 17.0458(5) A, alpha = 65.0986(14) degrees, beta = 77.8786(8) degrees, gamma = 85.5125(13) degrees, Z = 1.