First-principles modeling of the polycyclic aromatic hydrocarbons reduction

Density functional theory modelling of the reduction of realistic nanographene molecules (C42H18, C48H18 and C60H24) by molecular hydrogen evidences for the presence of limits in the hydrogenation process. These limits caused the contentions between three-fold symmetry of polycyclic aromatic hydrocarbon molecules and two-fold symmetry of adsorbed hydrogen pairs. Increase of the binding energy between nanographenes during reduction is also discussed as possible cause of the experimentally observed limited hydrogenation of studied nanographenes.Comment: 18 pages, 7 figures, accepted to J. Phys. Chem.

Male factors determining the outcome of intracytoplasmic sperm injection with epididymal and testicular spermatozoa

Summary. During a period of 8 years, 1079 intracytoplasmic sperm injection (ICSI) procedures with aspirated epididymal or testicular spermatozoa were performed. Epididymal spermatozoa were used in 172 cycles and testicular spermatozoa or spermatids in 907 cycles. Multiple biopsies were obtained from at least two different locations in the testes. Retrieved spermatozoa were used after cryopreservation (frozen) or immediately after aspiration (fresh). Three hundred patients had obstructive azoospermia (OA) or ejaculation failure. In 414 cases, azoospermia was caused by impaired spermatogenesis resulting from maldescended testes, chemotherapy/radiotherapy, or by Sertoli-cellonly syndrome, genetic disorders or unknown aetiology. Transfer rates, pregnancy rates and birth rates per ICSI cycle showed no statistically significant differences between testicular and epididymal spermatozoa in men with OA (28% average birth rates in both cases). However, birth rates differed significantly with regard to the status of spermatogenesis. Treatment of men with nonobstructive azoospermia (NOA) resulted in a birth rate of 19% per cycle. In all patient groups, there was no difference in the birth rates achieved with fresh and cryopreserved spermatozoa. While testicular volume, follicle-stimulating hormone level and age of the male patient are no statistically significant prognostic factors, the underlying cause of azoospermia is the most important factor determining the outcome of ICSI with epididymal and testicular spermatozoa. The pregnancy rate is lower in NOA patients than in those with OA

Polylactones, 53 - Formation of cyclic polyesters in the combined ringexpansion polymerization/ring-opening polycondensation of lactones

Full Paper: Ring-expansion polymerizations of beta-D,L- butyrolactone (beta-BL) or epsilon-caprolactone (epsilon-CL) were initiated with 2,2-dibutyl-2-stanna-1,3,-dioxepane (DSDOP) and the monomer-initiator ratio (M/I) was varied. The resulting tin-containing polylactones were polycondensed in situ either with succinyl chloride (in the case of beta-BL) or with suberoyl chlorid (for epsilon-CL). the reaction conditions were optimized towards high molecular weights by the addition of bipyridine. The isolated tin-free polylactones were characterized by MALDI-TOF mass spectrometry. In the best spectra cyclic poly(epsilon-caprolactone)s were detected up to masses around 10600 Da and cyclic poly(beta-butyrolactone)s up to masses around 17000 Da. In addition to the cyclic polyesters linear chains having alcoholic OH and/or CO2H group were found. these results suggest that the chain growth is limited by cyclization and by incomplete conversion of the functinoal groups