Single-ion versus dipolar origin of the magnetic anisotropy in iron(III)-oxo clusters: a case study.

A multitechnique approach has allowed the first experimental determination of single-ion anisotropies in a large iron(III)-oxo cluster, namely [NaFe6(OCH3)12(pmdbm)6ClO4 (1) in which Hpmdbm = 1,3-bis(4-methoxyphenyl)-1,3-propanedione. High-frequency EPR (HF-EPR). bulk susceptibility measurements, and high-field cantilever torque magnetometry (HF-CTM) have been applied to iron-doped samples of an isomorphous hexagallium(III) cluster [NaGa6(OCH3)12-(pmdbm)6]ClO4, whose synthesis and X-ray structure are also presented. HF-EPR at 240 GHz and susceptibility data have shown that the iron(III) ions have a hard-axis type anisotropy with DFe = 0.43(1) cm(-1) and EFe = 0.066(3) cm(-1) in the zero-field splitting (ZFS) Hamiltonian H = DFe[S2(z) - S(S + 1)/3] + Fe[S2(x) - S2(y)]. HF-CTM at 0.4 K has then been used to establish the orientation of the ZFS tensors with respect to the unique molecular axis of the cluster, Z. The hard magnetic axes of the iron(III) ions are found to be almost perpendicular to Z, so that the anisotropic components projected onto Z are negative, DFe(ZZ)= -0.164(4) cm(-1). Due to the dominant antiferromagnetic coupling, a negative DFe(ZZ) value determines a hard-axis molecular anisotropy in 1, as experimentally observed. By adding point-dipolar interactions between iron(III) spins, the calculated ZFS parameter of the triplet state, D1 = 4.70(9) cm(-1), is in excellent agreement with that determined by inelastic neutron scattering experiments at 2 K, D1 = 4.57(2) cm(-1). Iron-doped samples of a structurally related compound, the dimer [Ga2(OCH3)2(dbm)4] (Hdbm = dibenzoylmethane), have also been investigated by HF-EPR at 525 GHz. The single-ion anisotropy is of the hard-axis type as well, but the DFe parameter is significantly larger [DFe = 0.770(3) cm(-1). EFe = 0.090(3) cm(-1)]. We conclude that, although the ZFS tensors depend very unpredictably on the coordination environment of the metal ions, single-ion terms can contribute significantly to the magnetic anisotropy of iron(III)-oxo clusters, which are currently investigated as single-molecule magnets.

Does the measurement of portal flow velocity have any value in the identification of patients with cirrhosis at risk of digestive bleeding?

Upper gastrointestinal bleeding is a leading cause of death in patients with liver cirrhosis. In most cases haemorrhage originates from oesophageal varices or from congestive gastropathy, and the evaluation of the bleeding risk is based on oesophagogastroduodenoscopic data. The aim of this prospective study was to determine whether the measurement of portal flow velocity by Duplex-Doppler, compared with endoscopic data, can help in detecting patients with cirrhosis at risk of bleeding. One hundred and seventy-three patients underwent endoscopy to ascertain the size of the varices and the severity of congestive gastropathy. For each patient maximal portal flow velocity measurements were obtained. No difference in portal flow velocity was observed between patients with or without oesophageal varices or congestive gastropathy. During a 2-year observation period, 27 patients (15.6%) had at least one episode of acute digestive bleeding. Stepwise multiple logistic regression analysis demonstrated a correlation between oesophageal varices and congestive gastropathy endoscopic grading and the incidence of bleeding; only the former was entered into the final regression equation (p < 0.001). No relationship between the max portal flow velocity value and incidence of bleeding was found. This study shows that portal flow velocity is unrelated to the degree of the endoscopic abnormalities in patients with liver cirrhosis and that it has no value in the identification of patients with cirrhosis at risk of upper gastrointestinal bleeding.

[Roxatidine in the treatment of gastroduodenal mucosal lesions in hepatic cirrhosis]. / La roxatidina nel trattamento del danno mucoso gastroduodenale in corso di cirrosi epatica.

In about 50% of patients with liver cirrhosis, upper digestive bleeding is not due to oesaphageal varices rupture, but to a group of peculiar mucosal lesions usually referred as "congestive gastropathy" and "hepatogenic ulcer". The pathogenesis of such mucosal damage is still unclear: an important causative role is commonly thought to be played by portal hypertension, but the role of peptical pathway and of the mucosal barrier impairment must not be underscored as well. Aim of this study was to evaluate the effect of roxatidine in the long-term treatment of mucosal damage in 19 patients with liver cirrhosis. Patients showed a good tolerance and no side effects. The improvement of endoscopic pattern after a three months period of roxatidine therapy was statistically significant; moreover there was no occurrence of digestive bleeding. In conclusion, H2 antagonist may be considered as the drug of choice for the treatment of mucosal damage in patients with liver cirrhosis, for both its safety and effectiveness.