NEW CHIRAL AMINOPHOSPHINE AND DIAMINES LIGANDS, CORRESPONDING TRANSITION METAL COMPLEXES, THEIR APPLICATIONS IN ASYMMETRIC SYNTHESIS AND DEVELOPMENT OF HYBRID SYSTEM (ARTIFICIAL METALLOENZYMES)

Transition metal complexes containing chiral bidentate ligands are robust catalytic system for the preparation of chiral compounds as fine chemicals, fragrances and insecticides. Bifunctional P-ligands, N-ligands or P-N ligands are preferentially used for the preparation of late transition metals complexes (Rh, Ru, Pd, Ir, Pt) to modify their catalytic performance. While the reduction of olefin and carbonyl groups has been widely investigated, the asymmetric reduction of imines is relatively underdeveloped, although enantiopure amines play an important role in the preparation of many products. The asymmetric hydrogenation of cyclic imines is more difficult in comparison to the acyclic analogue because aromatic compounds are more stable, the reaction requires harsher conditions and it suffers from easy deactivation of the catalysts due to the poisoning. The interest of both academic and industrial research groups has increased in recent years in asymmetric hydrogenation of cyclic and acyclic imines, with a focus on the discovery of catalytic system with excellent enantioselectivity and activity under low hydrogen pressure or alternative source of hydrogen. Moreover, the development of ATH in aqueous media is emerged as a valid alternative to the use of organic solvents for its no toxic, economic and environmental compatible profile. Since the pioneering work of Noyori and Ikariya groups in 1995, the catalysts of choice in ATH reductions of ketones have been established to be the ruthenium(II) complexes chelating different substituted 1,2-diamines such as DPEN and its derivatives. In particular the monotosylated compounds were revealed as the most efficient ones. All these types of catalysts were based on the presence of ligands forming a five membered ring in coordination to the metal centre. Some examples of symmetric 1,4 diamines and few examples of 1,3-diamines were reported in literature, mainly used as a typical ruthenium complex [(diphosphine)-RuCl2-(diamine)] for hydrogenation of simple aromatic and aliphatic ketones. In this PhD thesis are reported the synthesis of simple asymmetric monotosylated 1,3-aminophosphine and monotosylated 1,3-diamines, up to now poorly investigated. The evaluation of their catalytic performances and their application for the preparation of artificial hydrogen transferases are also investigated. Chiral benzyl alcohols, used as synthons for the preparation of bidentate ligands, were obtained by biotransformation. Screening results revealed Rhodotorula rubra MIM 147 as an efficient catalytic system for this purpose. The first generation of this type of ligand was based on chiral 1,3 tosyl aminophosphine compounds able to use for the preparation of chelating six member ring complexes containing Ir(I) and Ru(II). Chelating aminophosphines have a combination of hard (N) and soft (P) Lewis base centers which make these ligands particularly useful in a variety of catalytic reactions. In fact these precatalysts, in hydrogenation reaction of several prochiral substrates such as ketones, imines and inactivated double bonds, showed a wide activity without stereoselectivity. Second generation of ligands containing linear and branched 1,3 tosyl diamines in which the tosyl moiety was present in different position, were synthesised to improve stereoselectivity. In respect to the tosyl aminophosphines: they are more easy to synthesise, to functionalize and are more easy to handle because are not air sensitive. Moreover these compounds are water soluble and act as suitable ligands for hydrogen transfer reaction conditions. [Ru (p-Cymene) (Tsdiamine)] complex (S-9a) results the best catalyst for the reduction of acetophenone in water used under ATH conditions (e.e.=56%, Yield=97%), revealing the importance of stereogenic centre to be in proximity of the amine involved in the catalytic cycle. The Ts moiety contribute to increase both the reaction conversion and enantioselectivity through a steric and/or an electronic effects. Considering different hydrogen donors, the used of HCOONa was revealed the best choice. Ligand (S-9) was used for the preparation of [IrCp*Tsdiamine] complex (S-9b) and applied in the reduction of cyclic imines in ATH reaction conditions. Substrates were reduced in excellent yield, in aqueous medium even if the enantioselectivity was low. The conformation of chelating six member ring seems to play a primary role for the enantiodiscrimination of the substrate adopting a chair conformation in this condition. Starting from the assumption that the reduction of these substrates is not easy to obtain, the results using this catalyst, encouraged our research to improve the stereoselectivity of the system, and for this reason, transition metal catalysts was applied in the development of artificial metallo enzymes. This hybrid system results from the incorporation of a catalytically competent organometallic moiety within a macromolecule. For this work was exploited the biotin-streptavidine technology. In fact tethering a biotin anchor to a catalyst precursor ensures that, in presence of streptavidine (Sav), the metal moiety is quantitatively incorporated within the host protein. Meta and para biotinylated aminosulfonamide iridium d5-pianostool complexes were prepared and their performances were evaluated in combination with Sav wild type and 10 different mutants in position 112. After this chemo-genetic optimization, the para-biotinylated aminosulfonamide iridium d5-pianostool complex (S-33a) embedded in combination with Sav S112C allowed to obtain an imine reductase able to reduce dihydroisoquinolines with good activity and enantioselectivity (e.e.=66%,Yield=90%), in aqueous solution using HCOONa as hydrogen donor

Constraining the optical emission from the double pulsar system J0737-3039

We present the first optical observations of the unique system J0737-3039 (composed of two pulsars, hereafter PSR-A and PSR-B). Ultra-deep optical observations, performed with the High Resolution Camera of the Advanced Camera for Surveys on board the Hubble Space Telescope could not detect any optical emission from the system down to m_F435W=27.0 and m_F606W=28.3. The estimated optical flux limits are used to constrain the three-component (two thermal and one non-thermal) model recently proposed to reproduce the XMM-Newton X-ray spectrum. They suggest the presence of a break at low energies in the non-thermal power law component of PSR-A and are compatible with the expected black-body emission from the PSR-B surface. The corresponding efficiency of the optical emission from PSR-A's magnetosphere would be comparable to that of other Myr-old pulsars, thus suggesting that this parameter may not dramatically evolve over a time-scale of a few Myr.Comment: 16 pages, 3 figures, ApJ accepte

Executive functions, math anxiety and math performance in middle school students

Previous studies mainly investigated working memory (WM) and math anxiety (MA) leaving almost unexplored other aspects of executive functions (EFs) in middle school period. Filling the gap in the literature, the aims of this study were: (1) to better examine the relationship between MA and math performance, (2) to better examine the relationship between EFs and math performance and (3) to investigate the interplay between EFs and MA on math performances. This study confirmed a significant and negative relationship between MA and math performance, indicates a significant and positive relationship between visuospatial WM and math performance, shifting and math performance and highlight a scarcely investigated indirect influence of MA through the measure of shifting on math performance. Our findings shed further light on the mediating role of EFs between MA and math performance and underline some future perspectives

The relationship betweens math anxiety and arithmetic reasoning: The mediating role of working memory and self-competence

The complex interplay between cognitive and emotional factors at the base of maths achievement started to be evaluated and quantified in the last few years. Only a few studies, anyway, examine at the same time, the role of working memory (visuospatial and verbal subsystem) and maths anxiety together with self-competence, on maths attainment. To investigate the specific link between these three factors, in a large developmental sample, we enrol 335 students from the 3rd, 5th, and 7th grades. In respect to emotional and motivational factors, data indicates a direct influence of maths anxiety on maths performance. Furthermore, the results highlight that maths anxiety differently impacts working memory subsystems. In fact, we observe a significant and indirect effect of MA, through the visuospatial system, on maths achievement. Our results provide further support to the hypothesis that maths anxiety is a special type of anxiety, most likely impacting the visuospatial rather than the verbal working memory subsystem. Data is discussed in terms of a possible mechanism underlying maths anxiety and visuospatial working memory at the base of this specificity, and in relation to the role of self-competence in this interplay

Detection of continuum radio emission associated with Geminga

A deep Very Large Array observation of the Geminga pulsar field led to the discovery, at a higher than 10 sigma significance level, of radio emission trailing the neutron star proper motion. This 10-arcsec-long radio feature, detected with a flux of 0.4 mJy at 4.8 GHz, is marginally displaced (2.7\pm1.8 arcsec) from the pulsar (which, at any rate, is unlikely to contribute with magnetospheric pulsed emission more than 15% to the total observed radio luminosity, about 1E26 erg/s) and positionally coincident with the X-ray axial tail recently discovered by Chandra and ascribed to the pulsar wind nebula (PWN). Overall, the Geminga radio tail is compatible with the scenario of a synchrotron-emitting PWN, but the present data do not allow us to discriminate between different (and not always necessarily mutually exclusive) possible processes for producing that. If this radio feature does not result from intrinsic peculiarities of Geminga, but its proximity and radio-quiet nature (both helping in not hindering the faint diffuse radio emission), other relatively near and energetic radio-quiet pulsars could show similar structures in dedicated interferometric observations.Comment: Version accepted by MNRAS Letters (new title and substantial changes in response to referees reports); 5 pages, 2 colour figure

Long Term Study of the Double Pulsar J0737-3039 with XMM-Newton: pulsar timing

The relativistic double neutron star binary PSR J0737-3039 shows clear evidence of orbital phase-dependent wind-companion interaction, both in radio and X-rays. In this paper we present the results of timing analysis of PSR J0737-3039 performed during 2006 and 2011 XMM-Newton Large Programs that collected ~20,000 X-ray counts from the system. We detected pulsations from PSR J0737-3039A (PSR A) through the most accurate timing measurement obtained by XMM-Newton so far, the spin period error being of 2x10^-13 s. PSR A's pulse profile in X-rays is very stable despite significant relativistic spin precession that occurred within the time span of observations. This yields a constraint on the misalignment between the spin axis and the orbital momentum axis Delta_A ~6.6^{+1.3}_{-5.4} deg, consistent with estimates based on radio data. We confirmed pulsed emission from PSR J0737-3039B (PSR B) in X-rays even after its disappearance in radio. The unusual phenomenology of PSR B's X-ray emission includes orbital pulsed flux and profile variations as well as a loss of pulsar phase coherence on time scales of years. We hypothesize that this is due to the interaction of PSR A's wind with PSR B's magnetosphere and orbital-dependent penetration of the wind plasma onto PSR B closed field lines. Finally, the analysis of the full XMM-Newton dataset provided evidences of orbital flux variability (~7%) for the first time, involving a bow-shock scenario between PSR A's wind and PSR B's magnetosphere.Comment: Comments: 16 Pages, 6 Figures. Accepted for publication in Astrophysical Journal (Draft Version