Emilio Francesco Orsega

3D laser ablation-ICP-mass spectrometry mapping for the study of surface layer phenomena – a case study for weathered glass

In this work, a multi-elemental 3D laser ablation-ICP-mass spectrometry mapping procedure for high-resolution depth information retrieval to investigate surface layer phenomena is presented. The procedure is based on laser drilling on a virtual grid on the surface, followed by extraction of depth maps along the z-axis (for each element monitored). Using a burst of 50 laser pulses at 1 Hz on each point of the grid, a penetration rate of ca. 150 nm per pulse (in glass) was obtained and a lateral resolution in the order of the laser beam diameter. By ultrafast ICP-MS monitoring of individual ablation pulses (58 ms for a set of 19 elements) using a laser ablation cell with fast signal washout (less than 0.5 s for whole laser pulse), the corresponding peak areas could be consistently integrated, resulting in spatial elemental data associated with individual pulses. The usual laser drilling limitations such as pulse mixing and signal tailing are avoided with this approach. After manipulation of the spatial elemental datasets and quantification, stacks of 50 2D depth maps (for each element monitored) were produced which could be visualized as volume images or time-lapse movies. As a proof of concept, this approach was successfully used to investigate the degradation mechanisms of a medieval, weathered glass artifact by colocalization analysis of selected cross-sectional 2D elemental images in arbitrary planes of the volume images. It was shown that degradation must have started as a result of dealkalinization leading to depletion of alkalis/earth alkalis in glass surface layers and enrichment of network formers (Si and Al), and subsequent worsening by cracking and formation of corrosion pits and so-called spatiotemporal Liesegang rings indicative of radial leaching.

A study of the pH dependence of the activity of porcine Cu,Zn superoxide dismutase

Abstract The enzyme activity of porcine Cu,Zn superoxide dismutase, which has an unusually high isoelectric point, decreases almost linearly with increasing pH between pH 7.5 and 12.0, while EPR and NMR parameters of the copper are titrated only above pH 9.5. Elimination of lysine charges by succinylation abolishes the pH dependence of activity between pH 7.5 and 9.5 and produces identical pH-activity curves for both bovine and porcine enzymes. The pH dependence of activity of the succinylated proteins overlaps that of the spectroscopic parameters of the copper in both enzymes. These results indicate that lysines play a critical role in the rate determining step of the mechanism of the Cu,Zn superoxide dismutases.

A rotating disk electrode for kinetic studies of superoxide dismutases: applicability in a wide pH range and for continuous monitoring of enzyme inactivation.

A rotating disk electrode coated with a thin mercury film is described. It is suitable for electrochemical determinations of the catalytic constant of superoxide dismutase in a much wider pH range than that accessible to polarographic methods. In particular this is the only direct method, except for pulse radiolysis, that allows mechanistic studies of the enzyme in the physiological pH range. Furthermore, the continuous response of this electrode allows enzyme activity changes characterized by half-lives in the range from a few to 10(3) s. to be followed.

Zanzibar and Indian Ocean trade in the first millennium CE: the glass bead evidence

Recent archaeological excavations at the seventh- to tenth-century CE sites of Unguja Ukuu and Fukuchani on Zanzibar Island have produced large numbers of glass beads that shed new light on the island’s early interactions with the wider Indian Ocean world. A selected sample of the beads recovered was analyzed by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to determine the origins of the glass used to make the beads and potential trade relationships are considered. The data show that two major glass types can be identified: mineral-soda glass, m-Na-Al, produced in Sri Lanka (and possibly South India) and plant ash soda glass. The latter comprises three subtypes: two with low alumina concentrations and different quantities of lime (here designated v-Na-Ca subtypes A and B) and one with high alumina (designated v-Na-Al). The v-Na-Ca subtype A beads are chemically similar to Sasanian type 1 glass as well as Zhizo beads found in southern Africa, while v-Na-Ca subtype B compares reasonably well with glasses from Syria and the Levant. While the mineral-soda beads were made in South Asia, it appears likely that at least some of the plant ash beads were made in South or Southeast Asia from imported raw and/or scrap Middle Eastern glass. In contrast, during this period, all beads imported into southern Africa were made of Middle Eastern glass from east of the Euphrates (v-Na-Ca subtype A) and appear to have arrived on ships from Oman and the Persian Gulf. These data suggest that the two sections of the African coast were engaged in different Indian Ocean trade circuits.

817—Application of short controlled drop-time polarography to the study of superoxide ion dismutation in aqueous solutions

Abstract A short controlled drop-time mercury electrode was utilized to generate the superoxide ion, O 2 − , in aqueous solutions and to study the dismutation processes of this ion. In particular, by the method of the catalytic currents, it was possible to measure the activity of superoxide dismutases, a class of metallo-enzymes present in aerobic cells. The use of this electrode minimizes the contribution of the spontaneous dismutation of the O 2 − to the limiting currents and, as a consequence, it makes enzyme activity measurements possible down to physiological pH values. The advantages with respect to other physicochemical methods are discussed.

Electron spin resonance of γ-iradiated single crystals of calcium formate

Abstract The electron spin resonance spectra of CO 2 − in an irradiated single crystal of calcium formate have been recorded. The 13 C hyperfine splitting tensor has been measured and the orientation of the CO 2 − molecule with respect to the crystallographic axes is compared with that of the undamaged HCO 2 − molecules. The results show that there is a reorientation of the CO 2 group when the CH bond is broken.

Tuning the activity of Cu,Zn superoxide dismutase through site-directed mutagenesis: a relatively active monomeric species

Abstract An enzymatically active monomeric analog of human copper,zinc superoxide dismutase (SOD) was produced by replacing four hydrophobic residues at the dimer interface of wild-type SOD (WT) with hydrophilic residues in a manner which has maintained the overall protein charge (i.e., Phe50Glu, Gly51Glu, Val148Lys, Ile151Lys). This analog has been characterized by (1) molecular weight determination, (2) several spectroscopic techniques probing catalytic site geometry and (3) enzymatic activity measurements at various ionic strengths. At physiological ionic strength the present monomer has sizable activity being five times that of a previously reported monomeric analog carrying only two of these substitutions with an overall charge two units more negative than WT (i.e., Phe50Glu, Gly51Glu). Unlike the catalytic activity of the latter analog, this one reveals an ionic strength dependency like that of WT. Enzymatic behavior is discussed with regard to factors affecting substrate diffusion towards the catalytic site.

An EPR study on ancient and newly synthesised Egyptian blue

Two sets of ancient Roman Egyptian blue (EB) samples and one set of EB samples synthesised in our lab, were analysed by EPR spectroscopy, a technique not commonly used in this field. The spectroscopic parameters obtained were used to attempt the discrimination of the provenance and of the manufacturing techniques of the investigated samples. The results obtained show that EPR technique could be very useful for this purpose. Furthermore, the similarity of the obtained parameters between the ancient and new samples testify the successful attempt to reproduce the EB according to the chemical knowledge.

Copper,Zinc superoxide dismutase activity evaluation using mercury microelectrodes

Abstract The activity of bovine Cu,Zn superoxide dismutase (SOD) was determined by steady-state voltammetry using mercury microelectrodes having close hemisphere shapes. The measurements were carried out in aerated aqueous solutions saturated with the surfactant triphenylphosphine oxide (TPO). The influence of pH on oxygen reduction process, either in the presence or in the absence of SOD, was studied over the range 7.5–12.3. Well-defined steady-state voltammetric waves, whose heights were reproducible within 2%, were obtained. A theoretical equation was derived for the calculation of the kinetic constant involved in the SOD-catalysed dismutation of the superoxide ion. The results obtained with the approach employed here agreed satisfactorily with those obtained by a dropping mercury electrode with a short dropping time.

A rotating disk electrode study of the catalytic waves produced by dismutation of O2− in the presence of superoxide dismutase

Abstract An equation is derived for the catalytic currents controlled by different dismutation processes of superoxide ion and by diffusion at a rotating disk electrode. Experimental data confirming the theoretical conclusions are presented for Cu, Zn superoxide dismutase.