Giuseppe Giordano

31P and 13C NMR investigation of the system tetracarbonyldi-μ-chlorodirhodium(I) — tertiary phosphine

13C and 31P{1H} NMR data at low temperature prompted us to characterize cis-[Rh(CO)2(PR3)Cl] (3) (3a, PR3  PPh3; 3b, PR3  PMe2Ph), as surprisingly stable products of the reaction between [{Rh(CO)2(μ-Cl)}2] (1) and tertiary phosphines in toluene (P : Rh = 1). Every attempt to isolate solid 3a led to the cis- and trans- halide-bridged dimers [{Rh(CO)2(μ-Cl)}2] (5a) and 6a which are formed from 3a by slow decarbonylation, a process which is greatly accelerated by the evaporation of the solvent under vacuum. The analogous reaction of 1 with dimethylphenylphosphine follows a similar pathway; in this case, however, low temperature NMR spectra allowed us to characterize the pentacoordinated dinuclear species [{Rh(CO)2(μ-Cl)}2] (2b) as the unstable intermediate of the bridge-splitting process. The reaction of 3 with a second equivalent of phosphine (P : Rh = 2) leads, at room temperature, to the well known product trans-[Rh(CO)(PR3)2Cl] (8) accompanied by evolution of CO; however our data show that when the reaction is performed at 200 K, decarbonylation is prevented and spectroscopic evidence of trigonal bipyramidal pentacoordinate [Rh(CO)2(PR3)2Cl] (7), stable only at low temperature, can be obtained.

Crystal structure of [Pd(μ3-2-propenyl)(dps)][Pd(μ3-2-propenyl)Cl2]. NMR evidence of binuclear μ3-allyl palladium(II) species with bridging dps

Abstract The reactions of di-2-pyridyl sulfide (dps) with (μ3-allyl)palladium chloride dimers gave the ionic compounds [Pd(μ3-allyl)(dps)][Pd(μ3-allyl)Cl2] (allyl=2-propenyl (1), 2-methyl-2-propenyl (2), 2-butenyl (3)). The structure of 1 has been determined by X-ray diffraction methods. Crystals are triclinic, space groupP 1 , with Z=2 in a unit cell of dimensions a=8.840(1), b=8.928(1), c=12.317(2) A, α= 98.82(1), β=90.46(1), γ=95.46(1)°. The structure has been solved from diffractometer data by direct and Fourier methods and refined by full-matrix least-squares on the basis of 3855 observed relections to R and Rw values of 0.0269 and 0.0339, respectively. Compound 1 consists of discrete complex ion pairs, containing allyl groups coordinated to both the cationic and anionic palladium centres. In the cationic portion the dps acts as a chelate ligand and adopts an N,N inside conformation. The six-membered chelate ring shows a boat conformation. The cation and anion are connected by a short Pd2…Cl2 interaction (3.073(1) A) which determines pseudo-five-coordination for the cation. At low temperature the 1H NMR spectra in CD3OD of 1 and 2 confirm the presence of the cation and the anion while in CDCl3 they also indicate the presence of a binuclear species with bridging dps. The 1H NMR spectra, at variable temperature, show that 1, 2 and 3 in solution undergo dynamic processes. In CDCl3, a lower energy process makes the π-allyl groups equivalent at room temperature, a higher energy process determines the magnetic equivalence of syn and anti π-allyl protons at high temperature.

Effects of Picotamide on Release of Endothelin-1, Thromboxane, and Prostacycline After Treadmill Stress in Patients with Peripheral Artery Disease

To assess the effects of picotamide, an antithromboxane receptor and antithromboxane synthase drug, on vascular function and endothelin-1 release, 20 patients with peripheral arterial disease, without hypertension or diabetes mellitus, receiving placebo and pico tamide (900 mg/day) were studied. The modifications of vascular parameters were evaluated by arterial distensibility index and postischemic hyperemia test (postischemic perfusion index and recovery time). Endothelin-1, prostacycline, and thromboxane B2 were determined under resting conditions and after treadmill test. Picotamide treatment caused a decrease of resting thromboxane B2 and endothelin-1 concentrations, produced an improvement of the vascular function as seen by the increase of vascular parameters reported, and attenuated the ischemic treadmill-induced increase of thromboxane B 2, but not of endothelin-1. These data confirm that the picotamide improved vascular flow by the reduction of thromboxane-mediated effects, reduced resting endothelin-1 levels, but did not attenuate endothelin-1 concentrations induced by the treadmill stress.

Isomerization mechanism of dinuclear chloro-bridged rhodium(I) complexes

Abstract At room temperature the cis- and trans-halide-bridged dimers [{Rh(CO) (PPh3)(μ-Cl)}2] give rise to a rather fast equilibrium of interconversion. NMR spectra provide evidence that during the reaction neither rhodium-phosphorus nor rhodium-carbon bonds are broken. These results suggest that the equilibrium takes place through dissociation of the dinuclear Rh1 species into the tricoordinated 14-electron T-shaped fragments [Rh(CO)(PPh3)Cl]. In keeping with this suggestion, the rate of the isomerization is accelerated by the presence in solution of small amounts of cis-[Rh(CO)2(PPh3)(μ-Cl)], a complex which can be considered a precursor of the tricoordinated fragment [Rh(CO)(PPh3)Cl].

Paul Feyerabend: un ruolo euristico per il dissenso

Nel 1934, Gaston Bachelard scriveva che «l’osservazione scientifica e sempre un’osservazione polemica; essa conferma oppure smentisce una tesi anteriore, uno schema preliminare, un piano di osservazione; essa mostra dimostrando; essa dispone gerarchicamente le apparenze; trascende l’immediato; essa ricostruisce il reale dopo avere ricostruito i propri schemi»

The Controversy over Specialism: From Ortega to Morin—Stages on a Journey Toward Complexity

The author proposes an analysis on a key issue in 20th-century thought: the struggle against disciplinary specialism. This problem is stressed by the reflections of philosophers and scientists such as Ortega y Gasset, Erwin Chargaff, Werner Heisenberg, Konrad Lorenz, Karl Popper, Paul Feyerabend, and Edgar Morin.

EFFECTS OF CLORICROMENE ON THE LEVELS OF ENDOTHELIN AND ON THE MICROCIRCULATORY FUNCTION IN PERIPHERAL ATHEROSCLEROTIC ARTERIOPATHIES

The effects of cloricromene on plasma endothelin-1 (ET-1) levels and on microcirculatory function in 9 patients with peripheral atherosclerotic arteriopathy (PAA) and in healthy control subjects were studied. ET-1 levels and microcirculatory function were evaluated both under basal conditions and 30, 60, and 90 min after acute administration of cloricromene (30 mg i.v.). PAA patients had significantly increased levels of ET-1 and impaired vascular parameters (studied by means of Winsors Index, Goslings Index, postischemic perfusion index and recovery time) when compared to control subjects. The acute administration of cloricromene (30 mg i.v.) did not change plasma ET-1 both in control subjects and in patients with PAA. In contrast, cloricromene produced a significant improvement in the postischemic perfusion index and in recovery time in arteriopathic patients. Control subjects and patients with PAA also underwent a cold pressor test (CPT) under basal conditions and (72 h later) 30 min after an acute intravenous administration of cloricromene (30 mg i.v.). CPT caused a higher increase in ET-1 in the patients with PAA compared to the control group, and a reduction in the vascular flow at the femoral level, while the pretreatment with cloricromene prevented both the increase in the levels of ET-1 and the reduction of the femoral vascular flow observed after the cold stimulus in patients with PAA. Our data show that cloricromene, besides ameliorating the microcirculatory function, is able to interfere with dynamic mechanisms, such as those induced by the CPT, capable of stimulating the release of ET-1 at the vascular level.

Effects of gallopamil on epinephrine and norepinephrine plasmatic levels and on txb2 and beta-tg release in patients with coronary artery disease during adrenergic stimulus with cold pressor test

We investigated the effect of gallopamil administration during a cold pressor test (CPT) in 18 patients suffering from chronic angina (CA) and in 21 healthy subjects. CA patients showed increased basal levels of beta-thromboglobulin and thromboxane B2 compared to control patients and normal plasma levels of catecholamines. CPT caused plasma catecholamines, beta-thromboglobulin and TxB2 levels to rise. This rise was greater in CA patients than in control patients. Administration of gallopamil (50 mg kg-1 three times a day for 30 days) reduced plasma levels of catecholamines, beta-thromboglobulin and TxB2 blood concentrations either under basal conditions or after CPT. Our data suggest that gallopamil is able to modulate the response induced by adrenergic stress.