The Fluorenyl Cation

The fluorenyl cation is a textbook example for a 4π antiaromatic cation. However, contrasting results have been published on how the annelated benzene rings compensate the destabilizing effect of the 4π antiaromatic five‐membered ring in its core. Whereas previous attempts to synthesize this cation in superacidic media resulted in undefined polymeric material only, we herein report that it can be generated and isolated in amorphous water ice at temperatures below 30 K by photolysis of diazofluorene. Under these conditions, the fluorenylidene is protonated by water to give the fluorenyl cation, which could be characterized spectroscopically. Its absorption in the visible‐light range matches that previously obtained by ultrafast absorption spectroscopy, and furthermore, its IR spectrum could be recorded. The IR bands in amorphous ice very nicely match predictions from DFT and DFT/MM calculations, suggesting the absence of strong interactions between the cation and surrounding water molecules.     

A novel chemo-multienzymatic synthesis of bioactive cyclophellitol and epi-cyclophellitol in both enantiopure forms

A new route to synthesize cyclophellitol and epi-cyclophellitol from racemic starting materials in enantiopure forms has been developed. The synthesis involves a multi-enzymatic biotransformation pathway of the novel cyano-cyclitol (1R,4S,5R,6R)/(1S,4R,5S,6S)-4,5,6-trihydroxycyclohex-2-enecarbonitrile by a cooperative use of lipase, nitrile hydratase, and amidase.     

Reactivity of Functionalized Phosphonates 1. Acid-Base Properties and Reactivity of Methyl Esters of Alpha-Aminophosphonic Acids

Acid-base properties and reactivity of series of alpha-aminophosphonates has been investigated. The reaction of addition of the aminophosphonates to phenylisocyanate was used as a model reaction. The influence of steric and electronic effects of substituents at alpha-carbon or nitrogen in amino group on the mechanism inversion from AdN to AdE is discussed.     

New 9,10‐Secosteroids from Biotransformations of Bile Acids with Rhodococcus ruber

The biotransformations of cholic, deoxycholic, and hyocholic acids with Rhodococcus ruber are reported. In all biotransformations, the C₁₇‐side chain is partially degraded, and the new 9,10‐secosteroids 4a (54%) and 4b (55%) are obtained from cholic and deoxycholic acids, respectively. The loss of H₂O from C(11)? C(12) of secosteroids 4a and 4b affords the compounds 5a (5%) and 5b (20%), respectively. On the other hand, in the biotransformation of hyocholic acid with R. ruber the 9,10‐secosteroid 4c is not detected, but, rearranging to an intramolecular hemiacetal form, it evolves to the final furan derivative 6c (35%) by easy elimination of two molecules of H₂O. The new secosteroids were characterized by IR, NMR, and 2D‐NMR spectroscopy, and mass spectroscopy.     

Starshapedness of level sets of solutions to elliptic PDEs

We investigate how some geometric properties of the domain are inherited by level sets of solutions of elliptic equations. In particular we prove that, under suitable assumptions, solutions of elliptic Dirichlet problems in starshaped rings have starshaped level sets. Our results are applicable to a large class of operators, including fully-nonlinear ones.     

Comparative LC Enantioseparation of Novel PPAR Agonists on Cellulose- and Amylose-Based Chiral Stationary Phases

The LC enantiomeric separation of several dual PPARα/γ agonists on the commercially available Chiralcel OD and Chiralpak AD columns has been evaluated in normal phase mode using a mobile phase consisting in a mixture of n-hexane, 2-propanol and trifluoroacetic acid at constant volume ratio. Most compounds were separated as underivatized acids without requiring time consuming analysis. Some complementary selectivity was evidenced on the two investigated chiral stationary phases related to the different accessibility of the active sites of the helical cavities. Additional information on the chiral recognition mechanism were deduced from the chromatographic behaviour of some selected methyl esters.     

Performance of an active well coincidence counter for HEU samples

Neutron coincidence counting is the reference NDA technique used in nuclear safeguards to measure the mass of nuclear material in samples. For high-enriched uranium (HEU) samples active neutron interrogation is generally performed and the most common device used by nuclear inspectors is the Active Well Coincidence Counter (AWCC).Within her master thesis at the Polytechnic of Milan, the first author performed an intensive study on the characteristics and performances of the AWCC in order to assess the ²³⁵U mass in HEU oxide samples at the PERLA laboratory of JRC. The work has been summarised in this paper that starts with the optimisation of the use of AWCC for nuclear safeguards, describing the calibration procedure, reporting results of a series of verification measurements, summarising the performances that can be obtained with this instruments during inspections at fuel production plants and concluding with the discussion of uncertainties related to these measurements.