Discovery and optimization of new chromium catalysts for ethylene oligomerization and polymerization aided by high-throughput screening.

High throughput screening (HTS) of a 205 member Schiff base salicylaldimine ligand library derived from salicylaldehydes bearing bulky ortho-substituents, i.e., 9-anthracenyl, 1,4,5,8-tetramethylanthracenyl or triptycenyl, reacted in-situ with (p-tolyl)CrCl2(thf)3, identified two new classes of highly active chromium based systems for the oligomerization and polymerization of ethylene, respectively. The polymerization system comprises bidentate ortho-substituted anthracenyl Schiff bases bearing small primary or secondary alkyl imine substituents. The oligomerization catalysts are based upon tridentate ortho-triptycenyl-substituted Schiff bases with pyridylmethyl or quinolyl substituents. Validation tests confirmed polymerization productivities of up to 3000 g x mmol(-1)h(-1)bar(-1) for the polymerization catalyst systems while the oligomerization catalysts gave productivities up to 10 000 g x mmol(-1)h(-1)bar(-1). Key catalyst precursors have been characterized by X-ray crystallography.

Discovery of a new family of chromium ethylene polymerisation catalysts using high throughput screening methodology.

Following a discovery that salicylaldimines bearing bulky ortho-phenoxy substituents and small imine substituents give very active chromium catalysts for ethylene polymerisation, High Throughput Screening (HTS) methodology has been employed to facilitate a further discovery of exceptionally active catalysts based on tridentate salicylaldimine ligands with bulky triptycenyl groups.

Use of human papillomavirus DNA testing to compare equivocal cervical cytologic interpretations in the United States, Scandinavia, and the United Kingdom.

BACKGROUND: Human papillomavirus (HPV) DNA testing may be useful in clarifying equivocal cervical cytologic interpretations. One application might be to standardize the meaning of equivocal interpretations from laboratories in various regions. Because international differences may be particularly marked, international comparisons of emerging data will require clear translations of "equivocal" and similar terms. METHODS: To perform a three-country comparison, the authors selected a morphologically diverse set of 188 conventional Papanicolaou tests initially classified as "squamous atypia" from a study of more than 20,000 women in Portland, Oregon (1989-1990). Previously, five U.S. expert cytopathologists independently interpreted the slides with screening cytotechnologists' marks in place. For this comparison, one British and two Scandinavian reviewers involved in HPV research reviewed the slides after original marks had been removed. The authors compared all eight reviewers' classifications of negative, equivocal, or abnormal in a series of pairwise comparisons using the kappa statistic. They then compared cytologic interpretations with HPV DNA testing. RESULTS: Oncogenic HPV DNA detection was significantly associated with increasingly abnormal interpretations for each reader. The British reader tended to rate tests as more abnormal than the American pathologists did, whereas the Scandinavians tended to rate tests as more normal. Reference to the HPV DNA standard clarified the tendency of readers to render systematically more or less severe interpretations. For example, the Scandinavian cytologists discounted subtle (often HPV-associated) changes in favor of cytologic certainty, making HPV triage of equivocal tests less applicable there. CONCLUSIONS: International research on cytopathology, particularly on the possible uses of HPV DNA testing, will require calibration of local cytologic definitions.