RESUMEN
New nanoarchitectures can be built from polycyclic aromatic hydrocarbons (PAHs) by exploiting the capability of some metal surfaces for inducing cyclodehydrogenation reactions. This bottom-up approach allows the formation of nanostructures with a different dimensionality from the same precursor as a consequence of the diffusion and coupling of the PAHs adsorbed on the surface. In this work we present a thorough study, by means of a combination of X-ray photoemission spectroscopy, near-edge X-ray absorption fine structure and scanning tunneling microscopy with first principle calculations of the structural and chemical transformations undergone by pyridyl-substituted dibenzo[5]helicene on three coinage surfaces, namely Cu(110), Cu(111) and Au(111). Upon annealing, on-surface chemical reactions are promoted affecting the adsorbate/substrate and the molecule/molecule interactions. This thermally induced process favours the transformation from diffusing isolated molecules to polymeric nanographene chains and finally to N-doped graphene.
RESUMEN
BACKGROUND AND PURPOSE: The occurrence of microembolic signals (MES) in patients with transient ischemic attack (TIA) or stroke has already been described, but the diagnostic and prognostic value of this finding is still debated. METHODS: We evaluated 90 consecutive patients admitted for their first hemispheric TIA or ischemic stroke within 72 hours of onset. All of them underwent 30-minute bilateral transcranial Doppler monitoring of middle cerebral arteries, within 72 hours of onset. The monitoring was repeated after an additional 24 hours and after 7 days. We then classified the episodes in the following etiologic categories: cardioembolic, atherothrombotic, small-vessel disease, mixed cases, unknown origin, and other causes. RESULTS: We included 75 patients, with a mean interval of registration of 32.04 +/- 19.39 hours. There were 9 patients with MES (12%). All MES were recorded only on the symptomatic middle cerebral artery, and the majority were recorded during the first or the second registration. No statistically significant difference was found in risk factors and hematologic parameters. Five patients (56%) had atherothrombotic episodes, 3 patients (33%) had cardioembolic episodes, and 1 patient (11%) had a protein S deficit. No patient with MES had small-vessel disease (P = .01). CONCLUSIONS: MES are an infrequent finding in patients with TIA or ischemic stroke within 72 hours of onset, but they can be recorded more easily with serial registration. In our patients, MES were found only on the symptomatic middle cerebral artery and were present in atherothrombotic and cardioembolic episodes but not in small-vessel disease.