Detecting exponential dichotomy on the real line: SVD and QR algorithms

In this paper we propose and implement numerical methods to detect exponential dichotomy on the real line. Our algorithms are based on the singular value decomposition and the QR factorization of a fundamental matrix solution. The theoretical justification for our methods was laid down in the companion paper: “Exponential Dichotomy on the real line: SVD and QR methods.”     

A simple apparatus for the direct measurement of optical gain spectra

A simple apparatus which allows direct recording of optical gain and induced absorption spectra is presented. It makes use of the very sensitive method based on the modulation of the length of the illuminated sample surface. It can easily be assembled with elements usually present in any spectroscopy laboratory and does not need calibration. The sensitivity of the system and the main sources of error are analysed in detail.     

Comparative analysis of different computer handling systems for gamma-spectrometric data developed at C.C.R. Ispra

Three different computer systems for gamma-spectrometric data-handling have been developed at the Joint Nuclear Research Center of Ispra. The systems are: (1) batchwise treatment of the data with a large computer, (2) time-shared teleprocessing by means of a centralised computer, (3) use of a small computer at the laboratory site. The paper describes both hardware and software of the three systems with emphasis on their practical use and on advantages and disadvantages in routine application. A partial analysis of the running costs of the systems is also presented.     

Ion trap tandem mass spectrometric determination of F2-isoprostanes

A new tandem mass spectrometry (MS/MS) method based on the use of an ion trap mass spectrometer for the identification and quantitation of F(2)-isoprostanes has been developed. It consists of two solid-phase extractions and two derivation steps followed by gas chromatography/negative ion chemical ionization tandem mass spectrometry (GC/NICI-MS/MS) analysis. This method is highly selective and sensitive and it has been successfully applied to biological samples.     

Increased sensitivity of autoantibody determination by coupled-particle light-scattering assay by poly(ethylene glycols)-modified beads

New kinds of coatings by using polyethylene glycols were studied and were applied to a qualitative homogeneous immunoassay that exploits the agglutination reaction for the detection of autoimmune antibodies in a complex matrix. We used a piece of new technology, the Copalis^™, which uses a special optical-sizing flow particle analysis and a semiconductor laser as a light source.

Polystyrene microbeads coated with the antigen were used as markers and were put in contact with the serum sample. Different polyethylene glycols were synthesised and tested, optimising the experimental parameters. Human serum specimens were evaluated and we obtained a higher sensitivity with good discrimination between negative and positive samples. All the experimental steps are easy, rapid and enable us to process many samples in a short period of time.     

Molecular characterization of homo- and heterodimeric mercury(II)-<Emphasis Type="Italic">bis</Emphasis>-thiolates of some biologically relevant thiols by electrospray ionization and triple quadrupole tandem mass spectrometry

A series of 24 compounds of general formula R(1)S-Hg-SR(2), R(1) and R(2) being biologically relevant thiol-containing amino acids and peptides (cysteine, homo-cysteine, penicillamine, N-acetyl-cysteine, N-acetyl-penicillamine, cysteinyl-glycine, gamma-glutamyl-cysteine and glutathione) were prepared by direct reaction of mercury(II) ions and thiols in water at millimolar concentration. The obtained products were characterized by electrospray ionization and triple quadrupole tandem mass spectrometry. The source spectra of equimolar mixtures of two different thiols reacting with a stoichiometric amount of mercury(II) show the peak clusters of the three theoretically expected bis-thiolato-mercury(II) complexes with relative intensities close to the theoretically expected 1:2:1 ratio, thus pointing at lack of substantial discrimination between the different thiols, the only observed exception being homo-cysteine, which is less reactive than cysteine and penicillamine. The fragment spectra are structure-specific for the different ligands bound to the metal ion and allow a stand-alone discrimination of some constitutional isomer pairs. Among the peculiar fragmentation processes observed, loss of neutral ammonia from protonated symmetrical and unsymmetrical mercury(II)-bis-thiolates with free, protonizable amino groups leads to the formation of thiirane-carboxylic bound species; this process is suppressed when the protonated amino group is in the gamma-position with respect to the sulfur atom, as in the case of compounds with homo-cysteine. This unusual behavior may hint at unforeseen mechanisms for the interaction of mercury(II) with biological structures, ultimately leading to cellular and organ toxicity. Compounds with N-acetylated amino acids show distinctive fragment ions to which the connectivity of a protonated 2-methyl-oxazoline-5-carboxylic acid may be proposed on the basis of the loss of water and of the elements of formic acid. Finally, the adducts of mercury(II) with glutathione and gamma-glutamyl-cysteine feature a distinctive decomposition channel by loss of a pyroglutamic unit, much the same as protonated glutathione, glutathione disulfide, the S-glutathionyl adducts of biologically occurring electrophiles and other (pseudo)-peptides with gamma-glutamyl bonds.     

Interaction of Natural and Modified β-Cyclodextrins with a Biological Membrane Model of Dipalmitoylphosphatidylcholine

Lipid vesicles made up of dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) were used as a biological membrane model to investigate the interaction between natural and modified β-cyclodextrins and these membrane bilayers. Differential scanning calorimetry was used to study the thermotropic behavior of the DPPC vesicles and any change caused by the presence of cyclodextrins. The presence of dimethyl-β-cyclodextrin (DM-β-CyD) triggered a reduction in the enthalpy values related to the main transition peak from gel state to liquid crystal phase of DPPC aqueous dispersions, as a function of the DM-β-CyD molar fraction: the larger the amount of DM-β-CyD, the greater the reduction in ΔHvalues. This effect was probably due to the ability of DM-β-CyD to extract and to complex the DPPC molecules forming the phospholipid vesicles. The presence of β-cyclodextrin (β-CyD) or hydroxypropyl-β-cyclodextrin (HP-β-CyD) caused no particular alteration in the thermotropic parameters of DPPC vesicles, whereas trimethyl-β-cyclodextrin (TM-β-CyD) at molar fractions higher than 0.12 caused broadening of the transition peak due to a possible interaction with the hydrophobic part of the bilayers. Experiments on DPPC–cholesterol (10 mol%) vesicles showed the capability of β-CyD and TM-β-CyD to extract cholesterol from the ordered bilayer structures, triggering an alteration in the lipid constituents of the membranes. HP-β-CyD caused no variation in the thermotropic parameters of the DPPC–cholesterol (10 mol%) vesicles. The findings show that HP-β-CyD seems the most suitable molecular drug carrier forin vivoadministration.     

Intercomparison of suspended particles sampling methodologies

Sampling and sample preparation/processing are known to carry large, but typically unknown uncertainty contribution to the final analytical data and there is a lack of qualitative and quantitative data on the comparability of results achieved by the different sampling methods. To this end, an intercomparison programme was founded by the European Commission, in which different institutions participated using their own ”in-situ” methods (”ANPA”, ”EDF” and ”MIDIYA”) for collection of water and suspended material in freshwater bodies. The main criterion for this intercomparison was the agreement among the ¹³⁷Cs activity concentrations in the dissolved phase (Bq l^–1), those associated with the suspended particles (Bq g^–1) and the concentrations of total suspended material (TSM) in the water body (mg l^–1). The results show that the sampling systems provide TSM concentration results with low accuracy; on the contrary, they are recommended for the determination of ¹³⁷Cs activity concentration in the dissolved phase. Concerning the determination of radiocaesium activity concentration in the suspended particles, the ”EDF” system provides the more reliable results. Received: 10 December 2001 Accepted: 4 March 2002     

Essential oil composition and biological activity from Artemisia caerulescens subsp. densiflora (Viv.) Gamisans ex Kerguélen & Lambinon (Asteraceae), an endemic species in the habitat of La Maddalena Archipelago

The purpose of this study was to investigate the composition of the essential oil obtained from a population of Artemisia caerulescens subsp. densiflora growing in Razzoli, an island in the La Maddalena Archipelago (Sardinia, Italy). A. caerulescens sups. densiflora Viv. (Asteraceae), a wild herb, seldom studied in the Mediterranean, represents one of the many rare endemic species growing in North Sardinia. The essential oil composition was analysed by means of GC/MS analysis, which showed davana ethers as the major volatile components, accounting together for 17.5%, followed by (E)-nerolidol (4.5%), β-oplopenone (3.3%), cis-sabinene hydrate (5.2%) and terpinen-4-ol (4.7%). The oil was tested for antioxidant activity by means of DPPH test, inhibition of lipid oxidation test and hypochlorous acid test, which showed a quite interesting scavenger capacity. For the first time, we reported the cytotoxic activity of the essential oil of A. caerulescens subsp. densiflora, against three human tumour cell lines (A375, MDA-MB231 and HCT116), with IC₅₀ values in the range 5.20–7.61 μg/mL, which deserved further studies to support its use as chemopreventive agent. Finally, the antimicrobial activity of the essential oil, displayed on a panel of human pathogens, was very low.