Structural rearrangements and reaction intermediates in a di-Mn water oxidation catalyst.

By using first-principles molecular dynamics simulations combined with metadynamics to simulate rare events we analyse competing reaction coordinates for a di-Mn water oxidation catalyst ([(bis(imino)pyridine)(H(2)O)Mn(IV)(µ-O)(2)Mn(V)(O)(bis(imino)pyridine)](3+)). The catalytic water oxidation cycle of the complex is examined by addressing the thermodynamic accessibility of the hydroperoxo species that is considered a critical and rate-limiting intermediate. To achieve this, hybrid quantum-mechanics/molecular-mechanics (QM/MM) and full QM simulations have been performed for an explicit treatment of the water environment that plays an active role in the reaction processes. Starting from a likely active species for the O-O bond formation, we observe that during the water approach to the oxo ligand a facile structural rearrangement of the complex takes place, leading to the opening of one µ-O bridge and the release of a water ligand, and resulting in two pentacoordinated Mn centers. This complex appears weakly active in the water oxidation process, since a concerted reaction is required to establish a Mn-OOH hydroperoxo intermediate. The slow kinetics of a concerted reaction can allow other processes, including linear degradation of the catalyst, to take precedence over catalytic water oxidation.

Acetyl group orientation modulates the electronic ground-state asymmetry of the special pair in purple bacterial reaction centers.

Recent experimental data point to an asymmetric ground-state electronic distribution in the special pair (P) of purple bacterial reaction centers, which acts as the primary electron donor in photosynthesis. We have performed a density functional theory investigation on an extended model including the bacteriochlorophyll dimer and a few relevant surrounding residues to explore the origin of this asymmetry. We find strong evidence that the ground-state electron density in P is intrinsically asymmetric due to protein-induced distortions of the porphyrin rings, with excess electron charge on the P(M) bacteriochlorophyll cofactor. Moreover, the electron charge asymmetry is strongly modulated by the specific orientation of the C3(1) acetyl group, which is hydrogen bonded to His168. The electronic excitation has a significant charge transfer character inducing a displacement of electron charge from P(L) to P(M), in agreement with experimental data in the excited state. These results are relevant for the understanding of the unidirectional electron transfer path in photosynthesis.

DFT study of the active intermediate in the Fenton reaction.

Density functional theory has been used to investigate the nature of the oxidizing agent in the Fenton reaction. Starting from the primary intermediate [FeII(H2O)5H2O2]2+, we show that the oxygen-oxygen bond breaking mechanism has a small activation energy and could therefore demonstrate the catalytic effect of the metal complex. The O-O bond cleavage of the coordinated H2O2, however, does not lead to a free hydroxyl radical. Instead, the leaving hydroxyl radical abstracts a hydrogen from an adjacent coordinated water leading to the formation of a second Fe-OH bond and of a water molecule. Along this reaction path the primary intermediate transforms into the [FeIV(H2O)4(OH)2]2+ complex and in a second step into a more stable high valent ferryl-oxo complex [FeIV(H2O)5O]2+. We show that the energy profile along the reaction path is strongly affected by the presence of an extra water molecule located near the iron complex. The alternative intermediate [FeII(H2O)4(OOH-)(H3O+)]2+ suggested in the literature has been also investigated, but it is found to be unstable against the primary intermediate. Our results support a picture in which an FeIV-oxo complex is the most likely candidate as the active intermediate in the Fenton reaction, as indeed first proposed by Bray and Gorin already in 1932.

Spontaneous formation and stability of small GaP fullerenes

We report the spontaneous formation of a GaP fullerene cage in ab initio molecular dynamics simulations starting from a bulk fragment. A systematic study of the geometric and electronic properties of neutral and ionized GaP clusters suggests the stability of heterofullerenes formed by a compound with zinc blende bulk structure. We find that GaP fullerenes up to 28 atoms have high symmetry, closed electronic shells, large highest occupied molecular orbital-lowest unoccupied molecular orbital energy gaps, and do not dissociate when ionized. We compare our results for GaP with those obtained by other groups for the corresponding BN clusters.

[Case histories of extranodal non-Hodgkin's lymphomas with primary gastrointestinal appearance]. / Contributo casistico sui linfomi non-Hodgkin extranodali a primitivo esordio gastrointestinale.

Authors refer results obtained in 24 cases of primary NHL of gastrointestinal tract. These cases were observed in the period 1981-1990. All cases can be included as primary extranodal lymphomas satisfying criteria of the literature. Sixty-six per cent (16/24) had a gastric localization half cases were centrocytic-centroblastic lymphomas followed by immunoblastic, centroblastic, follicular centrocytic-centroblastic and lymphocytic-well-differentiated. In intestinal localisation (34% of cases), the most represented was lymphocytic poor-differentiated, followed by mixed centrocytic lymphoma. Therapeutic strategy was: surgery in all patients followed by chemotherapy (CHOP 14/24) or by radiotherapy plus chemotherapy (8/24). Surgery alone was adopted in 2 out 24 patients. Patients who received radiotherapy plus chemotherapy had a sandwich treatment (CVP = 4/8, CHOP = 4/8) consisting of splint course of 3 cycles followed by radiotherapy and completed with other 3 drugs cycles. Sixteen out 24 patients were valuable (4 patients were lost during the follow-up due to problems other than the disease; 4 patients are still under treatment). In the 16 valuable patients we had a complete remission (CR) with a median free-disease survival of 82 months (range: 12-116 months) by means of the primary treatment. Four out 16 patients relapsed. In these patients the free-disease survival was range 8-108 months. All patients reached a second CR by means of chemotherapy (CCNU + VIP16) or radiotherapy. No cases of second tumor insorgence was observed.

[Neoplasms with unknown primary location]. / Neoplasie a sede primitiva ignota.

Neoplasms with unknown primary location (U.P.L.N.) represent an important chapter of oncological pathology which has not yet been completely defined regarding diagnostics, therapy and prognosis. U.P.L.N. recur in clinical practice in 0.5%-10% of cases and show equal sharing in both sexes: still mortality is high. This is in agreement with the biological behavior of U.P.L.N. which is that of a neoplastic illness, systemic from the onset and therefore immediately aggressive. Treatments commonly used only slightly alter the course of the disease. If the general state of the patients allows it, treatment must include every available therapeutical remedy (CHR, RDT, CHM) conveniently evaluated in every single case and preferably under the guidance of the apparent histotype and of the onset seat. The histotype of an U.P.L.N. sensibly affects the prognosis of the patient: there is an improvement in well differentiated and lodged forms and conversely, there is a sharp impairment with fast evolution in the less differentiated and variably metastasized forms. In our case-report, the U.P.L.N. rate has been 5.37% on 1786 cancer diagnoses from February 1980 until January 1988. In 65% of these cases, the histotype sustaining the pathology was represented by adenocarcinoma, in 21% by epidermoid carcinoma and in the remaining 14% by undifferentiated carcinoma. The clinical onset most frequently observed has involved the lymph nodes, followed by involvement of the serosa, bones, lungs and liver. Complex therapeutic treatments have not provided clear results, but the use of anthracyclines and cyclophosphamide seems promising. Finally, we suggest the use of immunomodulators (such as interferons, thymus hormone, lymphokines) in association with the classic chemotherapeutics.

[Clinical contribution to the knowledge of retroperitoneal tumors of the pelvic excavation]. / Contributo clinico alla conoscenza dei tumori retroperitoneali dello scavo pelvico.

Two cases of primitive retroperitoneal tumors of the pelvic excavation have been reported: a neurinosarcoma and a liposarcoma. Particular, this work emphasizes the rarity of the neurinosarcoma in that seat, the atypical clinical presentation, the complex diagnostic researches performed and the problems of the differential diagnosis. In the diagnosis of these neoplasms, the Authors emphasize, the main role performed by the "classic" radiology and its most recently acquired means as (ECO, TAC, EMR). These can give precise informations about the seat and the size of the neoplasms and especially, about it's relationship with the adjacent tissues. By using these new means, other examinations some what dangerous, can be avoided. The Authors conclude that from the therapeutical point of view, surgery is still the main weapon against these neoplasms, even if sometimes it is demolishing and does not sensibly improve the prognosis. Surgery can be associated with radiotherapy and/or chemotherapy.