2-difluoromethylene-4-methylenepentanoic acid, a paradoxical probe able to mimic the signaling role of 2-oxoglutaric acid in cyanobacteria

2-Difluoromethylene-4-methylenepentanoic acid (DFMPA), a seemingly deviated analog of 2-oxoglutaric acid (2-OG), could surprisingly mimic its signaling function in cyanobacteria. Computer modeling revealed the favorable binding of DFMPA toward the 2-OG receptor, NtcA, via mutual conformational changes, suggesting that structural alteration of 2-OG is tolerated for it to exercise its signaling role. This extremely useful finding could be exploited for the design of affinity probes with which to study new 2-OG receptors in related signaling pathways.     

Steady-state and time-resolved investigations of a crown thioether conjugated with methylacridinium and its complexes with metal ions

The crown thioether 9-[4-(4,7,10,13-tetrathia-1-azacyclopentadecyl]phenyl-N-methylacridinium perchlorate (TCMA) was synthesized and characterized with the aim to verify its ability to interact selectively with metal ions and substantiate the possibility to detect easily the presence of heavy metals in fluid samples. The spectroscopic properties of TCMA, alone and in the presence of metal ions, were therefore studied in polar solvents (MeCN and H(2)O); in particular, steady-state UV-Vis spectrophotometric and fluorimetric techniques were used together with transient absorption spectroscopy with fs time resolution to investigate the spectral and dynamic properties of the lowest excited singlet state of TCMA and of TCMA/metal ion complexes. The absorption in the Vis region is characterized by a charge-transfer nature with the methylacridinium moiety acting as the electron-acceptor and the anilic group as the electron-donor. No emission from the S(1) was detected both in MeCN and H(2)O, while a small S(2)→ S(0) fluorescence emission (λ(max) = 485 nm and ?(F) = 0.0011) was detected in water. Time-resolved measurements with fs resolution of TCMA in MeCN have shown that the relaxed S(1) state is reached ～0.6 ps after the laser pulse, while the S(1)→ S(0) time constant is 3.7 ps. Among the investigated metal ions, only Fe(3+) (in MeCN) and Hg(2+) (in MeCN and H(2)O) were able to form stable complexes (association constant, K(ass) = 1-11 × 10(4) M(-1)) with TCMA. The S(1) state of the TCMA/M(n+) complexes emits with low quantum yield (?(F) = 0.0023-0.014) and decays with time constants much longer than TCMA itself, at least in the case of TCMA/Hg(2+) in MeCN. This study showed that TCMA is a good candidate for colorimetric/fluorimetric sensing of Hg(2+) in aqueous media owing to its high selectivity towards metal ions.     

Manifestation of the bound state \bar NN (1870) in the annihilation process \bar pd \to p_s 5\pi

It is shown that the existence of an N?N bound state with a mass of approximately 1870 MeV and width 10 MeV follows from analysis of the experimental data on the momentum distribution of recoil protons in the annihilation process p?d→p _s5π.     

The LAPEX experiment for observation of the supernova SN 1987A in hard X-rays

Summary The LAPEX payload is described in the configuration that will be launched to observe the supernova SN 1987A. The balloon flight will be performed from Alice Springs (Australia) in April 1989 as a part of a NASA balloon campaign. The experiment will allow simultaneous observations of source and background in order to minimize systematic errors due to background variations. The limiting flux sensitivity of the instrument in the (20÷200) keV energy band is 4·10⁻⁶ ph/(cm²s keV) or ∼2.5 mCrab for a 10⁴ s observation of SN 1987A. The presence of a⁵⁷Co emission line in the SN 1987A photon spectrum could be detected down to an intensity level of ∼8·10⁻⁵ photons/cm²s as at 99.7% confidence level. The high resolution of the event timing (<0.1 ms) will make it possible to detect millisecond pulsations with amplitudes down to ∼4% of the expected average flux from SN 1987A in the (20÷60) keV band. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

Nanostructured silicon as a photonic material

Photonics applications of silicon are presented. In particular it is demonstrated that silicon when rendered low dimensional, e.g. in form of nanocrystals or quantum wires, can be turned into an active photonic materials which shows light amplification characteristics, non-linear optical effects, photon confinement in both one and two dimensions, photon trapping with evidences of light localization, and gas sensing properties.