Ruthenium‐Catalyzed α‐(Hetero)Arylation of Saturated Cyclic Amines: Reaction Scope and Mechanism

Transition‐metal‐catalyzed sp³ C? H activation has emerged as a powerful approach to functionalize saturated cyclic amines. Our group recently disclosed a direct catalytic arylation reaction of piperidines at the α position to the nitrogen atom. 1‐(Pyridin‐2‐yl)piperidine could be smoothly α‐arylated if treated with an arylboronic ester in the presence of a catalytic amount of [Ru₃(CO)₁₂] and one equivalent of 3‐ethyl‐3‐pentanol. A systematic study on the substrate and reagent scope of this transformation is disclosed in this paper. The effect of substitution on both the piperidine ring and the arylboronic ester has been investigated. Smaller (pyrrolidine) and larger (azepane) saturated ring systems, as well as benzoannulated derivatives, were found to be compatible substrates with the α‐arylation protocol. The successful use of a variety of heteroarylboronic esters as coupling partners further proved the power of this direct functionalization method. Mechanistic studies have allowed for a better understanding of the catalytic cycle of this remarkable transformation featuring an unprecedented direct transmetalation on a Ru^II? H species.     

Evolution of the protein corona of lipid gene vectors as a function of plasma concentration

The concept that the effective unit of interest in the cell-nanomaterial interaction is the particle and its corona of associated proteins is emerging. Here we investigate the compositional evolution of the protein corona of 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) cationic liposomes (CLs) and DOTAP/DNA lipoplexes over a wide range of plasma concentrations (2.5-80%). The composition of the hard corona of lipoplexes is quite stable, but that of CLs does evolve considerably. We show that the protein corona of CLs is made of both low-affinity and competitive-binding proteins whose relative abundance changes with the plasma concentration. This result may have deep biological implications for the application of lipid-based gene vectors both in vitro and in vivo.     

Structural variations and electronic substituent effects in phenylcubane derivatives: a quantum chemical study

Electronic substituent effects in 4-substituted 1-phenylcubane derivatives, Ph–C₈H₆–X, have been investigated from the structural changes caused by the substituent X. The molecular structures of 34 derivatives with charged or dipolar substituents have been determined from quantum chemical calculations at the HF/6-31G* and B3LYP/6-311++G** levels of theory. Geometrical variations caused by substitution appear both in the cubane framework and in the benzene ring, but the two kinds of changes show no correlation. The rather small changes in the benzene ring geometry are caused by long-range polar effects (field effects), while the larger changes in the cubane cage are controlled primarily by electronegativity effects. A structural parameter measuring the long-range polar effect of the substituent, S _F^CUB, has been derived from the geometry of the phenyl group acting as a probe. This parameter correlates well with the calculated gas-phase acidities of 4-substituted cubane-1-carboxylic acids, HOOC–C₈H₆–X, and with other indicators of long-range polar effects obtained from bicyclo[2.2.2]octane derivatives. The correlations can further be improved by introducing a resonance parameter as an additional explanatory variable. This indicates that the electron delocalization resulting from hyperconjugative interactions between substituent and cage modifies the long-range polar effect of the substituent. Strong hyperconjugative interactions between some charged substituents and the cubane cage result in remarkable variations in the cage geometry, superimposed onto those ascribed to electronegativity effects.     

Direct measurement of the 7Be solar neutrino flux with 192 days of borexino data

We report the direct measurement of the 7Be solar neutrino signal rate performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso. The interaction rate of the 0.862 MeV 7Be neutrinos is 49+/-3stat+/-4syst counts/(day.100 ton). The hypothesis of no oscillation for 7Be solar neutrinos is inconsistent with our measurement at the 4sigma C.L. Our result is the first direct measurement of the survival probability for solar nu(e) in the transition region between matter-enhanced and vacuum-driven oscillations. The measurement improves the experimental determination of the flux of 7Be, pp, and CNO solar nu(e), and the limit on the effective neutrino magnetic moment using solar neutrinos.     

Expectations of Fermionic Fields with N Components

In this Letter, we show with a concrete example that the behaviour in N independent components (flavours) of the expectation of fermionic fields can be different from that suggested by its expansion in terms of Feynman graphs. To prove this result, we study the asymptotic behaviour of a nonautonomous discrete time map.     

Cationic oligomerization of isoprene and structure of its oligomers

The results obtained in a study of isoprene cationic oligomerization in the presence of some oxyacids (H₂SO₄, CH₃SO₃H, Nafion^® H) are reported. Oligomers up to pentamers are obtained which were examined through gas chromatography/mass spectrometry analysis either of the reaction products or of the hydrogenated products. The structure of the dimer fraction was investigated and revealed the prevalent presence of α-pinene and p-cymene together with different cyclic unsaturated hydrocarbons. Only small quantities of linear dimers were found. Possible reaction mechanisms are presented.     

X-ray photoelectron spectroscopic study of poly[4,4′-isopropylidenebis(1,4-phenyleneoxyethylene) diacrylate] photocured in the presence of a fluorine containing monomer

A preliminary X-ray photoelectron spectroscopic (XPS) investigation on poly[4,4′-isopropylidenebis(1,4-phenyleneoxyethylene) diacrylate] samples obtained by photocuring on several substrates in the presence of a fluorine containing acrylic monomer is reported. Quantitative calculations based on F_1s/C_1s area ratios and C_1s peak fitting show a noticeable fluorine surface enrichment that ranges, depending on the substrate, from 17 wt.-% to 59 wt.-% of fluorine containing moiety. The calculations also reveal the presence of a concentration gradient at the surface.