Recent advances in structure and function of cytosolic IMP-GMP specific 5′nucleotidase II (cN-II)

Cytosolic 5′nucleotidase II (cN-II) catalyses both the hydrolysis of a number of nucleoside monophosphates (e.g., IMP + H2O→inosine + Pi), and the phosphate transfer from a nucleoside monophosphate donor to the 5′position of a nucleoside acceptor (e.g., IMP + guanosine →inosine + GMP). The enzyme protein functions through the formation of a covalent phosphoenzyme intermediate, followed by the phosphate transfer either to water (phosphatase activity) or to a nucleoside (phosphotransferase activity). It has been proposed that cN-II regulates the intracellular concentration of IMP and GMP and the production of uric acid. The enzyme might also have a potential therapeutic importance, since it can phosphorylate some anti-tumoral and antiviral nucleoside analogues that are not substrates of known kinases. In this review we summarise our recent studies on the structure, regulation and function of cN-II. Via a site-directed mutagenesis approach, we have identified the amino acids involved in the catalytic mechanism and proposed a structural model of the active site. A series of in vitro studies suggests that cN-II might contribute to the regulation of 5-phosphoribosyl-1-pyrophosphate (PRPP) level, through the so-called oxypurine cycle, and in the production of intracellular adenosine, formed by ATP degradation

AN IR-193 AND AU-197 MOSSBAUER INVESTIGATION OF IRIDIUM(I), IRIDIUM(III) AND IRIDIUM(I) GOLD(I) COMPLEXES

Comparison of the Ir-193 and Au-197 Mossbauer spectra of the series trans-(Ph3P)2Ir(CO)X, trans,cis-(Ph3P)2(H)2Ir(CO)(X) (X = Cl or pz-N; pzH = 3,5-dimethyl-, 3,5-dimethyl-4-nitro-, 3,5-bis(trifluoromethyl)pyrazole) and trans-(Ph3P)2(CO)Ir[mu-(3,5-dimethylpyrazolato-N,N')]AuX' (X' = Cl, Br) shows that even the substituents on the heterocycle influence the electron density at the iridium nucleus and that the bridging pyrazolato ligand transmits electronic effects from gold to iridium through three bonds. The Mossbauer parameters are sensitive to the ligand X but not to the presence of conformers

Maintenance of natural ester transformers. Case studies

In the last two decades, the number of applications of natural esters (NE) transformers is steeply growing, requiring also proper monitoring and maintenance of the quality of the insulating liquid. Nevertheless, reference values and alert limits are not yet completely available with reference to different classes of the transformers. Some helps may be sorted out from the recent publication (2021-01) of the IEC 62975 "Natural esters - Guidelines for maintenance and use in electrical equipment"which contains useful additional information for the operators in NE transformers.To overcome this situation, there is an effort to look for similarities with traditional transformers insulated with mineral oil (MO) for which a great amount of information on chemical-physical analysis are already available. In the present paper, case studies of some Natural Ester (NE) transformers maintenance have been presented and discussed. The acquired data will be also useful with the aim of adjusting the Health Index evaluation in order to guarantee support for maintenance decisions of the operators in this sector

NMR-STUDY OF THE CHEMICAL-EXCHANGE OF THE HYDRIDO LIGANDS IN THE BIS(BIS(DIPHENYLPHOSPHINO)ETHANE)TRIHYDRIDODIPLATINUM(II) CATION BY T1, T2, AND HD ISOTOPIC PERTURBATION

Proton longitudinal and transverse relaxation rates of hydrido resonances of different isotopomers in [H3Pt2(Dpe)2][BF4] [Dpe = bis(diphenylphosphino)ethane] show significant differences in the satellite peaks with respect to the central ones that can be used to evaluate the activation energy of the intramolecular exchange process and the chemical shift separation between bridging and terminal sites. An alternative route to get an estimation of the chemical shift values of the bridging and terminal hydrides in this derivative has been pursued by considering the isotopic shift of the three H-3, H2D, and HD2 isotopomers at different temperatures

Synthesis and VT-NMR study of cationic hydride platinum clusters

The synthesis of three trinuclear platinum hydrides [Pt3(L-L)3(H)3]+ (L-L = 1,2-bis(diphenylphosphino)ethane, dppe, l; 1-diphenylphosphino-2-diphenylarsinoethane, dppae. 2; 1,2-bis(diphenylarsino)ethane, dpae, 3) is reported. The complexes were characterized by IR, FAB-MS, and NMR (1H,31P and195Pt) spectroscopic techniques. The fast exchange of the hydride ligands, observed at ambient temperature, is frozen out at low temperature. The low-temperature1H and31P NMR spectra are consistent with an open array of Pt atoms in the clusters, in keeping with a 16-electron configuration on each platinum atom. Two of the hydride ligands are terminally bonded to two metal centers, whereas the third one is \u3bc3-coordinated, interacting more tightly with the unique platinum atom

REACTION OF PLATINUM(II) DERIVATIVES WITH BIS(PYRAZOLYL)PROPANE - CLEAVAGE OF A C(SP3)-N BOND IN A BIS(PYRAZOLYL)ALKANE PROMOTED BY PLATINUM(II) DERIVATIVES - CRYSTAL-STRUCTURE OF CIS-PT(PYRAZOLE)2CL2

The reactions of bis(pyrazolyl)propane (CH3)2C(pz)2, (pzH = pyrazole), with PtCl2, (RCN)2PtCl2 and K2[PtCl4 have been investigated, and the results compared with those described previously for the corresponding palladium(II) derivatives. In contrast with the behaviour of the palladium analogues, the platinum derivatives promote the rupture of the ligand: simple adducts of pyrazole, cis- or trans-Pt(pzH)2Cl2, or species containing the ligand [HNC(R)pz], formally arising from the insertion of a nitrile into the NH bond of pyrazole, are obtained. For comparison, the reaction of the platinum derivatives with pyrazole itself has been investigated under various conditions. The crystal structure of cis-Pt(pzH)2Cl2 has been determined by X-ray diffraction: monoclinic, space group C2/c, a 9.180(1), b 15.084(1), c 15.1445(9) \uc5, \u3b2 101.536(7)\ub0, Z - 8, R = 0.039, Rw = 0.040 for 2125 observed reflections