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C Arcangeli

Publications and source records attributed to C Arcangeli.

At least 19 recordsLinked to original sources
PubMed2002

Quenching of majority-channel quasiparticle excitations in cobalt.

The low-energy electronic excitations in cobalt are studied by a theoretical method that includes many-body effects and a realistic description of the band structure. Angle-resolved photoemission spectra measured on a thick film of hexagonal close-packed Co on Cu(111) agree well with calculated spectral functions. Because of many-body effects no sharp quasiparticle peaks exist for binding energies larger than 2 eV and in this energy region the spectrum is essentially incoherent. The many-body corrections are much stronger in the majority-spin channel and drastically affect the spin polarization of the spectra.

Journal Article↗
PubMed2001

Molecular dynamics simulation and essential dynamics study of mutated plastocyanin: structural, dynamical and functional effects of a disulfide bridge insertion at the protein surface.

A molecular dynamics simulation (1.1 ns) at 300 K, of fully hydrated Ile21Cys, Glu25Cys plastocyanin mutant has been performed to investigate the structural, dynamical and functional effects of a disulfide bridge insertion at the surface of the protein. A detailed analysis of the root mean square fluctuations, H-bonding pattern and dynamical cross-correlation map has been performed. An essential dynamics method has also been applied as complementary analysis to identify concerted motions (essential modes), that could be relevant to the electron transfer function. The results have been compared with those previously obtained for wild-type plastocyanin and have revealed that the mutant shows a different pattern of H-bonds, with several interactions lost and a higher flexibility, especially around the electron transfer copper site. The analysis of dynamical cross-correlation map and of essential modes, has shown that the mutant performs different functional concerted motions, which might be related to the binding recognition with its electron transfer partners in comparison with the wild-type protein.

Algorithms↗
PubMed2001

Concerted motions in copper plastocyanin and azurin: an essential dynamics study.

Essential dynamics analysis of molecular dynamics simulation trajectories (1.1 ns) of two copper containing electron transfer proteins, plastocyanin and azurin, has been performed. The protein essential modes have been analysed in order to identify large concerted motions which could be relevant for the electron transfer function exerted by these proteins. The analysis, conducted for temporal windows of different lengths along the protein trajectories, shows a rapid convergence and indicates that for both the proteins the predominant internal motions occur in a subspace of only a few degrees of freedom. Moreover, it is found that for both the proteins the likely binding sites (i.e. the hydrophobic and negative patches) with the reaction partners move in a concerted fashion with a few structural regions far from the active site. Such results are discussed in connection with the possible involvement of large concerted motions in the recognition and binding interaction with physiological electron transfer partners.

Azurin↗
PubMed2001

Low-frequency vibrational modes in proteins: a neutron scattering investigation.

The low-frequency dynamics of plastocyanin, an electron transfer copper protein, has been investigated by incoherent neutron scattering at different temperatures. The contribution to the dynamic structure factor arising from H/D exchangeable and non-exchangeable protein protons has been evaluated by analyzing two differently exchanged protein samples. The dynamic structure factor of a hydrated plastocyanin sample with all the exchangeable hydrogens (about 150) replaced by deuterium exhibits an excess of vibrational modes, at about 3.5 meV, reminiscent of the boson peak found in other proteins and glassy systems. When only fast exchangeable hydrogens (about 50) are substituted by deuterium, the protein, besides the above-mentioned peak, shows an additional peak at about 1 meV. These vibrational peaks are discussed in connection with the topological disorder of the systems and the fluctuations of the intramolecular hydrogen bonds.

Biophysical Phenomena↗
PubMed2001

Structural and optical properties of silicon nanocrystals grown by plasma-enhanced chemical vapor deposition.

Silicon nanocrystals (Si-nc) embedded in SiO2 matrix have been prepared by high temperature thermal annealing (1000-1250 degrees C) of substoichiometric SiOx films deposited by plasma-enhanced chemical vapor deposition (PECVD). Different techniques have been used to examine the optical and structural properties of Si-nc. Transmission electron microscopy analysis shows the formation of nanocrystals whose sizes are dependent on annealing conditions and deposition parameters. The spectral positions of room temperature photoluminescence are systematically blue shifted with reduction in the size of Si-nc obtained by decreasing the annealing temperature or the Si content during the PECVD deposition. A similar trend has been found in optical absorption measurements. X-ray absorption fine structure measurements indicate the presence of an intermediate region between the Si-nc and the SiO2 matrix that participates in the light emission process. Theoretical observations reported here support these findings. All these efforts allow us to study the link between dimensionality, optical properties, and the local environment of Si-nc and the surrounding SiO2 matrix.

Computer Simulation↗
PubMed2000

In situ Raman microspectroscopic identification and localization of carotenoids: approach to monitoring of UV-B irradiation stress on Antarctic fungus.

The in situ Raman microspectroscopic properties of an Antarctic fungus are investigated to assess the nature and the spatial localization of the main chromophores and to study their spectral changes under enhanced UV-B irradiation. The Raman spectroscopic features of spores in situ are consistent with those of carotenoid-like pigments. In particular, the Raman shifts seem to be related either to the frequency modes of long conjugated double-bond carotenoids or to protein bound beta-carotene. The spectroscopic analysis at different spore depths clearly shows the strongest Raman signal arises from cell wall and membrane structures. The intensity of such a signal shows a drastic reduction upon UV-B irradiation without any significant frequency change. The use of Raman microspectroscopy for nondestructively monitoring the UV-B effects on Arthrobotrys ferox spores is also discussed.

Antarctic Regions↗
PubMed2000

Two-photon autofluorescence microscopy and spectroscopy of Antarctic fungus: new approach for studying effects of UV-B irradiation.

We combined two-photon fluorescence microscopy and spectroscopy to provide functional images of UV-B (280-315 nm) induced stress on an Antarctic fungus. Two-photon excitation microscopy was used to characterize the distribution of autofluorescence inside the spore and the hyphae of the fungus. The imaging analysis clearly shows that the autofluorescence response of spores is higher than that of hyphae. The imaging analysis at different depths shows that, strikingly enough, the spore autofluorescence originates from the cell wall and membrane fluorophores. The spectroscopic results show moreover that the fluorescence spectra of spores are redshifted upon UV-B irradiation. Tentative identification of the chromophores involved in the autofluorescence response and their biological relevance are also discussed on the basis of a previous steady-state fluorescence spectroscopic study performed on both whole spore suspension and organic-soluble extracts.

Image Processing, Computer-Assisted↗
PubMed1999

A molecular dynamics simulation study of the solvent isotope effect on copper plastocyanin.

The effect of heavy water on the structure and dynamics of copper plastocyanin as well as on some aspects of the solvent dynamics at the protein-solvent interfacial region have been investigated by molecular dynamics simulation. The simulated system has been analyzed in terms of the atomic root mean square deviation and fluctuations, intraprotein H-bond pattern, dynamical cross-correlation map and the results have been compared with those previously obtained for plastocyanin in H2O (Ciocchetti et al. Biophys. Chem. 69 (1997), 185-198). The simulated plastocyanin structure in the two solvents, averaging 1 ns, is very similar along the beta-structure regions, while the most significant differences are registered, analogous to the turns and the regions likely involved in the electron transfer pathway. Moreover, plastocyanin in D2O shows an increase in the number of both the intraprotein H-bonds and the residues involved in correlated motions. An analysis of the protein-solvent coupling evidenced that D2O makes the H-bond formation more difficult with the solvent molecules for positively charged and polar residues, while an opposite trend is observed for negatively charged residues. On the other hand, the frequency of exchange of the solvent molecules involved in the protein-solvent H-bond formation is significantly depressed in D2O. The results are discussed also in connection with protein functionality and briefly with some experimental results connected with the thermostability of proteins in D2O.

Journal Article↗
PubMed1999

Long-term molecular dynamics simulation of copper azurin: structure, dynamics and functionality.

A long-term molecular dynamics simulation (1.1 ns), at 300 K, of fully hydrated azurin has been performed to put into relationship the protein dynamics to functional properties with particular attention to those structural elements involved in the electron transfer process. A detailed analysis of the root mean square deviations and fluctuations and of the intraprotein H-bonding pattern has allowed us to demonstrate that a rigid arrangement of the beta-stranded protein skeleton is maintained during the simulation run, while a large mobility is registered in the solvent-exposed connecting regions (turns) and in the alpha-helix. Moreover, the structural elements, likely involved in the electron transfer path, show a stable H-bonding arrangement and low fluctuations. Analysis of the dynamical cross-correlation map has revealed the existence of correlated motions among residues connected by hydrogen bonds and of correlated and anti-correlated motions between regions which are supposed to be involved in the functional process, namely the hydrophobic patch and the regions close to the copper reaction center. The results are briefly discussed also in connection to the current through-bond tunneling model for the electron transfer process. Finally, a comparison with the structural and the dynamical behaviour of plastocyanin, whose structure and functional role are very similar to those of azurin, has been performed.

Journal Article↗
PubMed1999

Incoherent neutron scattering of copper azurin: a comparison with molecular dynamics simulation results.

The low-frequency dynamics of copper azurin has been studied at different temperatures for a dry and deuterium hydrated sample by incoherent neutron scattering and the experimental results have been compared with molecular dynamics (MD) simulations carried out in the same temperature range. Experimental Debye-Waller factors are consistent with a dynamical transition at approximately 200 K which appears partially suppressed in the dry sample. Inelastic and quasielastic scattering indicate that hydration water modulates both vibrational and diffusive motions. The low-temperature experimental dynamical structure factor of the hydrated protein shows an excess of inelastic scattering peaking at about 3 meV and whose position is slightly shifted downwards in the dry sample. Such an excess is reminiscent of the "boson peak" observed in glass-like materials. This vibrational peak is quite well reproduced by MD simulations, although at a lower energy. The experimental quasielastic scattering of the two samples at 300 K shows a two-step relaxation behaviour with similar characteristic times, while the corresponding intensities differ only by a scale factor. Also, MD simulations confirm the two-step diffusive trend, but the slow process seems to be characterized by a decay faster than the experimental one. Comparison with incoherent neutron scattering studies carried out on proteins having different structure indicates that globular proteins display common elastic, quasielastic and inelastic features, with an almost similar hydration dependence, irrespective of their secondary and tertiary structure.

Azurin↗
PubMed1998

Minimal carcinoma in prostate needle biopsy specimens: diagnostic features and radical prostatectomy follow-up.

Prostate cancer screening and early detection efforts have resulted in the identification of smaller volume carcinomas of the prostate. We evaluated the diagnostic features of minimal (< 1 mm) carcinoma in sextant needle biopsy specimens of the prostate and in follow-up analyzed the features of the corresponding carcinomas in the whole gland. We reviewed specimens from 50 consecutive patients who had minimal carcinoma in needle biopsy tissue and who had undergone radical prostatectomy. Histologic grade, tumor size, pathologic stage, and margin status of the 50 carcinomas in the whole gland in which the carcinoma size was minimal in the sextant needle biopsy specimen were compared with those of 50 carcinomas in the whole gland in which carcinoma size was greater than 1 mm in the needle biopsy specimen. The most common morphologic features of these minimal carcinomas were nucleomegaly (96%), infiltrative growth pattern (88%), intraluminal secretions (78%), prominent nucleoli (64%), associated high-grade prostatic intraepithelial neoplasia (40%), amphophilic cytoplasm (36%), hyperchromatic nuclei (30%), and intraluminal crystalloids (22%). Perineural invasion (2%), collagenous micronodules (2%) and mitotic figures (2%) were uncommon. The mean tumor volume in the whole gland of carcinomas corresponding to minimal carcinoma in a needle biopsy specimen was significantly smaller (P=.029) at 1.1 mL than it was in carcinomas with tumor greater than 1 mm in the needle biopsy specimen at 1.6 mL, but other pathologic features of carcinoma in the whole gland were not significantly different. In conclusion, a constellation of morphologic attributes is important for establishment of a diagnosis of minimal carcinoma of the prostate in needle biopsy specimen. Most (82%) of the corresponding prostate cancers in the whole gland were pathologically significant.

Aged↗
PubMed1993

[Late ventricular potentials in patients with dilated cardiomyopathy. Correlations with spontaneous ventricular tachycardia and clinical course].

In a series of 55 patients with dilated cardiomyopathy, the presence of noninvasive recordings of late ventricular potentials (LVP) was correlated to ventricular tachycardia (VT), as detected by a 24-hour Holter monitoring obtained one week within LVP recording. LVPs were found in 12/55 patients (21.8%) and in 2 of a series of 66 normal subjects of the same age and sex. In all patients with LVP either non sustained (11 cases) or sustained (1 case) VT was present at Holter monitoring. In the other 43 patients without LVP only 13 (30%) had non sustained VT (p < 0.01). During the follow-up period (mean 17 months) six patients died suddenly; three of them had LVP and VT (sustained in one); two had non sustained VT, but no LVP; one had neither. This study suggests that the presence of LVP predicts VT recording in ambulatory ECGs. On the contrary, VT may be recorded in patients without LVP. Further studies are necessary to ascertain the value of LVP as a marker of sudden death in patients with dilated cardiomyopathy.

Action Potentials↗
PubMed1990

Human breast milk T lymphocytes display the phenotype and functional characteristics of memory T cells.

Naive (unsensitized) and memory (antigen-primed) T cells can be phenotypically distinguished on the basis of the high or low intensity with which they express a number of immunologically relevant lymphocyte membrane antigens, including CD45R, CDw29, UCHL1, LFA-1, LFA-3, CD2 and Pgp-1. Here we report that in contrast to the two major T cell subsets found in the blood, milk T lymphocytes are almost exclusively composed of the one which exhibits the CD45Rlow, CDw29, UCHL1, LFA-1high memory T cell phenotype. In addition, while milk and autologous blood cells expressed similar levels of CD3 surface antigens, CD2 and ICAM-1 expression was approximately twofold greater on the milk T lymphocytes. This agrees with the finding that whereas colostrum T cells respond poorly to PHA, they proliferate and produce interferon-gamma normally when stimulated with either the anti-CD3 or anti-CD2 monoclonal antibodies. The selective colonization of the mammary gland during lactation by a population of T lymphocytes which displays the phenotype and functional characteristics of memory T cells may be one of the mechanisms whereby the suckling infant benefits form its mother's immunological experience.

Antibodies, Monoclonal↗
PubMed1990

Activation of cord T lymphocytes. II. Cellular and molecular analysis of the defective response induced by anti-CD3 monoclonal antibody.

Despite the fact that the percentage of circulating CD3-positive cells is similar in cord and adult blood, the proliferative response induced by anti-CD3 monoclonal antibody (mAb) was impaired in the majority of human cord peripheral blood mononuclear cell (PBMC) samples we tested. The cell proliferative defect was associated with low interleukin 2 (IL 2) gene expression and scant IL 2 production. However, interleukin 2 receptor was fully expressed at both the mRNA and protein levels. Such a finding is consistent with the observation that exogenous recombinant IL 2 is able to boost the anti-CD3-mediated response of cord PBMC. Furthermore, when anti-CD3 and phorbol myristate acetate (PMA) were added together, they exerted a very marked synergistic effect on both the proliferation of, and IL 2 production by, cord PBMC. The addition of allogeneic antigen presenting cells plus soluble anti-CD3 or Sepharose-coupled anti-CD3 mAb to the cord T cell cultures had no significant effect on proliferation, whereas both elicited good mitogenesis of adult T cells. Moreover, addition of exogenous recombinant interleukin 1 to anti-CD3-stimulated T cells failed to trigger any proliferation in either adult or cord samples. Since the combination of PMA and calcium ionophore A23187 is effective in triggering optimal proliferation of cord T cells, the defect would seem to be associated with a failure in transmembrane transduction of the activation signals provided by the anti-CD3 stimulus for the cord T cell.

Antigen-Presenting Cells↗