RESUMEN

The organic glass-forming materials 1,3-bis(1-naphthyl)-5-(2-naphthyl)benzene (2) and its partially deuterated analogue, 1,3-bis(1-naphthyl-d(7))-5-(2-naphthyl)benzene (2-d(14)), have been synthesized on a gram scale using Suzuki coupling reactions. Detailed spectroscopic studies afford complete NMR assignments (1H, 2H, 13C) for both compounds. Modest energy barriers for the interconversion of atropisomers (ca. 15 kcal/mol) result in a propensity for these materials to form supercooled liquids and glasses, rather than undergoing crystallization. The preparation of these materials enables detailed studies of physical properties of organic glasses and molecular diffusion in condensed phases.

RESUMEN

A ditopic structure containing two heterocyclic DeAP units and programmed to self-assemble is used as an initiation unit for the synthesis of polylactide and polystyrene. The resultant polymers self-assemble into higher molecular weight structures with a lower molecular weight distribution. The largest discrete nanoscale polymeric assembly is proposed to be a hexameric star with a molecular weight of ca. 92.7 kDa. All polymeric assemblies generally exhibit PDI values of 1.3 to 1.5, which are lower than the PDI value of the corresponding polymeric arms. A hexameric assembly is stabilized by 30 hydrogen bonds, including six AADD.DDAA contacts. The hexameric star is formed under conditions that are at least partially controlled by kinetics.

Asunto(s)

Polímeros/química , Espectroscopía de Resonancia Magnética , Estructura Molecular , Peso Molecular , Espectrometría de Masa por Láser de Matriz Asistida de Ionización Desorción

RESUMEN

An exceptionally strong quadruply hydrogen-bonded complex is formed between 2,7-diamido-1,8-naphthyridine 3 (DAN) and the butylurea of guanosine 6 (UG) in chloroform. The UG unit can be prepared in four steps from guanosine on a 10 g scale in excellent yields without chromatographic purification. The association constant (Kassoc approximately 5 x 10(7) M(-1)) for the UG.DAN complex determined by fluorescence energy transfer from the naphthyridine unit of 3 to coumarin 343 covalently linked UG (18) is among the highest reported for a neutral DNA base-pair analogue. The weak self-association of DAN (Kdimer < 10 M(-1)) and UG (Kdimer ca. 200-300 M(-1)) means that the UG.DAN complex forms with unparalleled fidelity.

Asunto(s)

Guanosina/análogos & derivados , Naftiridinas/química , Cristalografía por Rayos X , Guanosina/química , Enlace de Hidrógeno , Cinética , Resonancia Magnética Nuclear Biomolecular , Espectrometría de Fluorescencia , Espectrofotometría Ultravioleta , Urea/análogos & derivados , Urea/química

RESUMEN

Irradiation (lambda = 670 or >613 nm) of 4,5-benzodiazocycloheptatriene (15), matrix isolated in argon at 10 K, produces primarily 2,3-benzobicyclo[4.1.0]hepta-2,4,6-triene (9) accompanied by small amounts of triplet 4,5-benzocycloheptatrienylidene (2) and 2-naphthylcarbene (10). A reversible photoequilibrium is established in which 9 is converted to 10 at lambda = 290 nm and then regenerated at lambda = 360 nm. Similarly, matrix-isolated 2,3-benzodiazocycloheptatriene (16) produces 4,5-benzobicyclo[4.1.0]hepta-2,4,6-triene (11) at lambda = 670 or >613 nm, but without detection of 2,3-benzocycloheptatrienylidene (4). Irradiation of 11 at lambda = 290 nm induces ring opening to triplet 1-naphthylcarbene (12), which, in turn, cyclizes back to 11 at lambda = 342 or >497 nm. The diazo compounds and photoproducts are characterized by IR, UV/visible, and ESR spectroscopy, where appropriate, and by comparison of the experimental and B3LYP/6-31G calculated IR spectra for each species. Alternate rearrangement products such as allenes 6, 7, and 8 are not detected in the photolysis of either diazo compound.