Piani grafici a caratteristica 3

Sunto Si dimostra che un piano grafico finito di caratteristica 3 sopra un quasicorpo associativo d'ordine q² il cui centro sia un campo d'ordine ≥ q è necessariamente pascaliano, e che non esistono piani diHughes di caratteristica 3.

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Summary It is proved: a) Any graphic finite plane of characteristic 3 on an associative near-field of order q² whose center is a field having order ≥ q, is necessarily pascalian ; b) There is noHughes plane of characteristic 3.

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A Giovanni Sansone nel suo 70^o compleanno.     

A perturbation solution of Michaelis–Menten kinetics in a “total” framework

In this paper we expand the equations governing Michaelis–Menten kinetics in a total quasi-steady state setting, finding the first order uniform expansions. Our results improve previous approximations and work well especially in presence of an enzyme excess.     

Ruthenium piano-stool complexes bearing imidazole-based PN ligands

A variety of piano-stool complexes of cyclopentadienyl ruthenium(II) with imidazole-based PN ligands have been synthesized starting from the precursor complexes [CpRu(C₁₀H₈)]PF₆, [CpRu(NCMe)₃]PF₆ and [CpRu(PPh₃)₂Cl]. PN ligands used are imidazol-2-yl, -4-yl and -5-yl phosphines.Depending on the ligand and precursor different types of coordination modes were observed; in the case of polyimidazolyl PN ligands these were κ¹P-monodentate, κ²P,N-, κ²N,N- and κ³N,N,N- chelating and μ-κP:κ²N,N-brigding. The solid-state structures of [CpRu(1a)₂Cl ]·H₂O (5^.H₂O) and [{CpRu(μ-κ²-N,N-κ’¹-P-2b)}₂](C₆H₅PO₃H)₂(C₆H₅PO₃H₂)_2, a hydrolysis product of the as well determined [{CpRu(2b)}₂](PF₆)₂^.2CH₃CN (7b^.2CH₃CN) were determined (1a = imidazol-2-yldiphenyl phosphine, 2b = bis(1-methylimidazol-2-yl)phenyl phosphine, 3a = tris(imidazol-2-yl)phosphine). Furthermore, the complexes [CpRu(L)₂]PF₆ (L = imidazol-2-yl or imidazol-4-yl phosphine) have been screened for their catalytic activity in the hydration of 1-octyne.     

The Si?Sn Chemical Bond: An Integrated Thermochemical and Quantum Mechanical Study of the SiSn Diatomic Molecule and Small Si–Sn Clusters

The silicon–tin chemical bond has been investigated by a study of the SiSn diatomic molecule and a number of new polyatomic Si_xSn_y molecules. These species, formed in the vapor produced from silicon–tin mixtures at high temperature, were experimentally studied by using a Knudsen effusion mass spectrometric technique. The heteronuclear diatomic SiSn, together with the triatomic Si₂Sn and SiSn₂ and tetratomic Si₃Sn, Si₂Sn₂, and SiSn₃ species, were identified in the vapor and studied in the overall temperature range 1474–1944 K. The atomization energy of all the above molecules was determined for the first time (values in kJ mol^?1): 233.0±7.8 (SiSn), 625.6±11.6 (Si₂Sn), 550.2±10.7 (SiSn₂), 1046.1±19.9 (Si₃Sn), 955.2±26.8 (Si₂Sn₂), and 860.2±19.0 (SiSn₃). In addition, a computational study of the ground and low‐lying excited electronic states of the newly identified molecules has been made. These electronic‐structure calculations were performed at the DFT‐B3LYP/cc‐pVTZ and CCSD(T)/cc‐pVTZ levels, and allowed the estimation of reliable molecular parameters and hence the thermal functions of the species under study. Computed atomization energies were also derived by taking into account spin–orbit corrections and extrapolation to the complete basis‐set limit. A comparison between experimental and theoretical results is presented. Revised values of (716.5±16) kJ mol^?1 (Si₃) and (440±20) kJ mol^?1 (Sn₃) are also proposed for the atomization energies of the Si₃ and Sn₃ molecules.     

The behaviour of stereoisomeric ions in the gas phase: 2—Negative and positive chemical ionization of cyclohexanehexacarboxylic methyl esters

The positive ion chemical ionization (CI (isobutane)), negative ion chemical ionization (NICI) electron attachment (CH₄, He) and NICI (OH^?) spectra of the title compounds have been studied in detail with the aid of deuterium-labelled derivatives. The obtained results show that under CI conditions the stereospecificity is retained. Interesting correlations with the condensed phase epimerization yields are emphasized.