Synthesis and spectroscopic characterization of solution processable highly ordered polythiophene-carbon nanotube nanohybrid structures.

We report on the synthesis and spectroscopic study of a novel highly ordered nanohybrid structure consisting of a single-walled carbon nanotube (SWNT) coated with highly crystalline regio-regular poly(3-hexylthiophene) (rrP3HT) and discuss the applicability of the nanohybrids in organic photovoltaics. The use of a solvent extraction technique allows the nanohybrids to be produced with a high yield and high purity. We find evidence that the crystallinity of rrP3HT is enhanced in the presence of SWNTs, which introduces a reduced optical band gap and increased carrier mobility in the polymer. Study of the photoluminescence excitation spectra of the SWNTs reveals an efficient energy transfer of excitons created on the rrP3HT to the SWNTs. This energy transfer is expected to limit our ability to use the nanohybrids as a charge separating interface and can therefore explain the low efficiency of P3HT-SWNT solar cells produced to date. In addition, careful consideration of the energy transfer is necessary when attempting to improve state of the art polymer-fullerene photovoltaic devices with SWNTs in order to make use of their high charge carrier mobilities and increased rrP3HT crystallinity.

Acute diverticulitis in patients under 40 years of age: radiologic diagnosis.

During a 4-year period, eight patients 40 years old or younger had surgically proved diverticulitis at our institution. None of these patients had connective-tissue diseases or were on medication (i.e., steroids) that would predispose them to diverticulosis. The presenting clinical symptoms in this group of patients were often misleading, and in only one of the eight cases was the correct clinical diagnosis made at the time of admission. Of the three diagnostic studies that were performed (barium enema, sonography, and CT), barium enema was the most accurate, yielding evidence for diverticulitis in six of seven cases. The degree and extent of diverticulosis in these patients was minimal compared with that in the older patients. CT showed abdominal abscesses in two patients; in one, a mistaken diagnosis of Crohn disease was made; in the other, diverticulitis was correctly identified. In the three patients in whom sonography was performed, the findings were negative for diverticulitis. Our experience suggests that the diagnosis of acute diverticulitis should be considered in patients with abdominal pain who are less than 40 years old.

The effects of polyribonucleotides on the binding of dexamethasone-receptor complex to DNA.

The ability of polyribonucleotides to affect the association of [3H]-Dexamethasone-receptor complex with DNA-cellulose has been investigated. Certain ribopolymers can release the receptor complex DNA. This release is not dependent on the charge of the polymer only, but displays some specificity with regard to the base composition of the ribopolymer. Of the polyribonucleotides examined, polyguanylic acid and polyxanthylic acid were most effective at promoting release of the steroid-receptor from the DNA. Polyadenylic acid and polycytidylic acid had no effect on the association. For a polymer to display activity it must possess a base with an oxygen or sulfur atom at the C-6 position of purines or C-4 position of pyrimidines. Simple nucleotides possessing this structural feature are inactive.