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Biomedical subjects

S Santucci

Publications and source records attributed to S Santucci.

At least 19 recordsLinked to original sources
PubMed2005

Soft-x-ray photoemission spectroscopy and ab initio studies on the adsorption of NO2 molecules on defective multiwalled carbon nanotubes.

The adsorption of NO(2) molecules on defective multiwalled carbon nanotubes has been studied by soft-x-ray photoemission. The valence band and carbon core-level spectra have been acquired before, during, and after NO(2) exposure. The spectra show a reversible decrease of the density of states at the top of the valence band when NO(2) molecules are adsorbed on the (carbon nanotubes) CNTs. No shift of the C 1s spectra has been observed. Theoretical calculations, using density-functional theory, have been performed on the CNT + NO(2) system, considering semiconducting nanotubes with different diameters and introducing a Stone-Wales [Chem. Phys. Lett. 128, 501 (1986)] defect. The calculation confirms the decrease of the density of states at the top of the valence band in the CNT + NO(2) system, while close to the adsorption site new states appear very close to the Fermi level.

Journal Article↗
PubMed2004

Electronic structure of crystalline copper phthalocyanine.

The electronic structure of copper-phthalocyanine (CuPc) has been studied both experimentally and theoretically. Experiments have been performed on alpha and beta crystalline phases, using photoemission spectroscopy to probe core levels and valence band spectra. Different photon energies have been used, in order to probe different sample depths. Only minor differences have been observed in the experimental data on the two different phases, except for a small charge effect on the beta phase crystal. First-principles calculations have been performed using the density functional for molecular and three-dimensional periodic solids (Dmol(3)) code on both the single CuPc molecule and the beta phase, allowing the identification of the different atomic and angular contributions to the experimental density of states. In particular, the highest occupied molecular level is mainly due to Cu and N states. The comparison between theoretical data obtained for the CuPc in the beta phase and in the single molecule shows that the interchain interaction between the molecules is negligible, whereas slightly stronger intrachain interactions occur.

Journal Article↗
PubMed2004

Ozone adsorption on carbon nanotubes: the role of Stone-Wales defects.

First-principles calculations within the density functional theory have been performed in order to investigate ozone adsorption on carbon nanotubes. Particular emphasis is placed on the effects of Stone-Wales-like defects on the structural and electronic properties of (i) ideal tubes and (ii) tubes in the presence of ozone. Our results show that structural deformations induced on the pure carbon nanotubes by Stone-Wales defects are similar, as expected, to those induced on graphite; for the (10,0) tube, the semiconducting character is kept, though with a small reduction of the band gap. As for the ozone adsorption, the process on ideal nanotubes is most likely physisorption, though slightly stronger if compared to other previously studied molecules and consistent with the strong oxydizing nature of O(3). However, when ozone adsorbs on Stone-Wales defects, a strong chemisorption occurs, leading to relevant structural relaxations and to the formation of a CO covalent bond; this is consistent with experimental observations of CO functional groups, as well as of the liberation of CO gas phase and of the formation of C vacancies, thus explaining the consumption of the nanotube film upon ozone exposure.

Journal Article↗
PubMed2003

Physiopathology of multiple sclerosis.

Pleiotropy and redundancy are distinctive elements of the immune response. Recent research into the inflammatory component of multiple sclerosis (MS) indicates that, as expected, pleiotropy and redundancy characterize various physiopathological mechanisms of the disease. A certain degree of redundancy is becoming apparent also as far as the degenerative component is concerned. Cumulatively, these data suggest that treatments that target single pathogenetic pathways are unlikely to provide a definitive solution. Combination therapies may offer, in principle, some advantage, although there is a need for more information on the aetiology of the disease.

Animals↗
PubMed2001

Direct visualization of defect density waves in 2D.

A scanning tunneling microscopy investigation of the 1/3 of a monolayer alpha phase of Sn on Si(111) reveals a new low temperature phase, which is electronic and not structural. This phase consists of a one-dimensional incommensurate electronic wave that coincides with a periodic modulation of the population of the substitutional Si defects, i.e., a defect density wave.

Journal Article↗
PubMed2000

Numerical verification of bona fide stochastic resonance

The notion of stochastic resonance as an input/output synchronization mechanism is reestablished quantitatively, based on accurate numerical simulation of a simple two-state model, namely, the Schmitt trigger. The corresponding phenomenological criterion known as bona fide stochastic resonance is thus proven applicable throughout the entire range of the input parameters. Claims to the contrary are briefly discussed.

Journal Article↗
PubMed2000

Intrawell stochastic resonance versus interwell stochastic resonance in underdamped bistable systems

We show that, for periodically driven noisy underdamped bistable systems, an intrawell stochastic resonance can exist, together with the conventional interwell stochastic resonance, resulting in a double maximum in the power spectral amplitude at the forcing frequency as a function of the noise intensity. The locations of the maxima correspond to matchings of deterministic and stochastic time scales in the system. In this paper we present experimental evidence of these phenomena and a phemonological nonadiabatic description in terms of a noise-controlled nonlinear dynamic resonance.

Journal Article↗
PubMed1995

Bovine papillomavirus type 1 E1 ATPase activity does not depend on binding to DNA nor to viral E2 protein.

Replication of bovine papillomavirus type 1 (BPV-1) DNA has been shown to require two viral proteins known to interact in a molecular complex: E2, a transcription activator, and E1, another nuclear phosphoprotein, which binds to the replication origin and for which helicase/ATPase activities have previously been reported. Here we characterize the BPV-1 E1 ATPase activity. In contrast to Seo et al. (Proceedings of the National Academy of Sciences, USA, 90, 702-706, 1993), we were able to detect this activity in the absence of nucleic acid in partially purified preparations of either E1 protein or of E1-E2 protein complex. Measurements of specific activity and kinetic parameters gave similar values for preparations of various kinds. ATPase activity was quantitatively retained by immunoprecipitates obtained by using anti-E1 or, in the case of E1-E2 complex, anti-E2 antibodies. Significantly, preparations of bacterially expressed glutathione S-transferase-E1 fusion protein exhibited levels of DNA-independent ATPase activity comparable to those of baculovirus-expressed E1. The presence of nucleic acids of various types, including stoichiometric amounts of a BPV-1 ori DNA fragment containing E1 and E2 binding sites, did not grossly affect E1 ATPase activity, the most notable effect being a 2-fold stimulation by unspecific ssDNA. Altogether, our results indicate that BPV-1 E1 possesses an intrinsic ATPase activity which does not depend on the presence of nucleic acid; moreover, they render unlikely any modulation of E1 ATPase activity due to binding either E2 protein or target DNA sequences, or as a result of protein phosphorylation.

Adenosine Triphosphatases↗
PubMed1995

Bovine papillomavirus E1 protein binds specifically DNA polymerase alpha but not replication protein A.

Extracts prepared from either mouse cells or monkey cells were examined for the ability to support in vitro bovine papillomavirus type 1 (BPV1) DNA replication, and they were used in parallel as a source of host replication proteins for affinity chromatography. DNA synthesis exhibited an absolute requirement for BPV1 E1 protein. In contrast to previous observations, we found that low levels of E1 were highly efficient in initiating DNA replication in the absence of the BPV1 transcription factor E2. Surprisingly, COS-1 cell extract allowed a high rate of BPV1 DNA replication, supporting an efficient production of mature circular DNA molecules, whereas in mouse cell extracts, the replication products mostly consisted of replicative intermediates. Submitting the extracts to affinity chromatography allowed specific binding of DNA polymerase alpha-primase to E1 protein, up to a total depletion of the extract, regardless of the origin of the cell extract. Furthermore, replication protein A was not retained on E1 affinity columns, even when E2 was complexed with E1. These data confirm that the interactions between E1 and DNA polymerase alpha-primase do not exhibit cell-type specificity, as had already been suggested by data from in vivo and in vitro replication assays, but they imply that other cellular proteins may affect the level of E1-dependent replication.

Animals↗
PubMed1994

Clinical findings in two African-American families with the nevoid basal cell carcinoma syndrome (NBCC).

The nevoid basal cell carcinoma syndrome (NBCC) is an autosomal dominant multisystem disorder with variable expressivity. We present the clinical findings on 11 African-American NBCC cases from 2 families and a review of the literature of NBCC in African-Americans. The 2 new families, as well as those previously reported, suggest minimal expression of the basal cell carcinomas and full expression of the other components of the syndrome. The 3 most common findings in the 11 cases were jaw cysts, palmar and/or plantar pits, and calcification of the falx cerebri. Only 44% (4/11) of these cases had one or more confirmed basal cell carcinomas. This frequency is substantially less than that observed in whites (90% with basal cell carcinomas). The relative lack of these skin tumors in African-Americans partly reflects ultraviolet radiation protection resulting from increased skin pigmentation. Future research should help identify the specific mutation(s) in blacks as well as other modifying genes and environmental exposures that may contribute to the varied manifestations of the syndrome.

Abnormalities, Multiple↗