Silvano Bellandi

Trace Copper(II) or Zinc(II) Ions Drastically Modify the Aggregation Behavior of Amyloid-beta(1-42): An AFM Study

Formation of amyloid-beta (Abeta){1-42} amyloid fibrils, a characteristic feature of Alzheimers disease (AD), was monitored in situ through atomic force microscopy (AFM). Well-structured amyloid fibrils slowly formed in solution within 24 hours for which high quality AFM pictures could be obtained. Remarkably, addition of either copper(II) or zinc(II) ions to the incubation medium, even at extremely low molar ratios, dramatically changed the Abeta {1-42} aggregation profile and prevented fibril formation. Aggregates of different morphology appeared in accordance with previous observations: small globular aggregates upon addition of zinc; ill-structured micro-aggregates in the case of copper. The implications of these AFM results are discussed in the context of current concepts for AD metallobiology.

Analysis of snow from Antarctica: a critical approach to ion-chromatographic methods

Ion-chromatographic methods for anion and cation determination in snow samples from Antarctica are evaluated with regard to sensitivity and selectivity. An eluent-step change method is proposed to determine simultaneously mono- and divalent cations with detection limits lower than 1 μg/L. Special attention is given to the determination of the ammonium ion at trace levels in the presence of high sodium concentrations and the problems of sample contamination by the laboratory environment are evaluated. Two alternative methods, one using isocratic and the other a gradient elution, are proposed for the determination of fluoride, acetate, formate and methanesulphonate ions. Both methods are discussed to evaluate their use in snow sample analysis.

Chemical characterization of cloud episodes at a ridge site in Tuscan Appennines, Italy

Cloudwater samples were collected from November 1992 to March 1995 in Vallombrosa, a mountain site of the Tuscan Apennines (central Italy). Chemical analyses show that all examined inorganic ions contributed significantly to the total ionic content (TIC). The ratio SO42−/NO4− ranged from 0.92 to 3.46 and was >1 for 86% of samples. There is a wide range in the chemical composition of the cloudwater. The total ionic content ranged from 640 to 7476 μeq l−1 and pH from 3.17 to 6.22. The liquid water content (LWC) ranged from 0.06 to 0.94 g m−3 and electrical conductivity from 47 to 485 μΩ−1. The total ionic content decreases while the liquid water content increases. Also analyzed were soluble trace metals (Fe, Pb, Cu, Mn, Cd, Al), synthetic anionic surfactants and the methanesulphonic acid. Chemical analyses evidenced in some cases a high concentration of organic matter. The meteorological analysis for a few samples of individual passages was carried out for the possibility of establishing a correspondence between meteorological events and chemical composition. The sources (marine, crustal and anthropogenic) of chemical components were deduced.

Selective electrodesorption based atomic layer deposition (SEBALD): a novel electrochemical route to deposit metal clusters on Ag(111).

The possibility of synergic effects of some metals on the catalytic activity of silver led us to study the way to perform controlled deposition on silver. In fact, many metals of technological interest such as Co, Ni, and Fe cannot be deposited at underpotential on silver, and any attempt to control the deposition at overpotential, even at potentials slightly negative of the Nernst value, did not allow an effective control. However, due to the favorable energy gain involved in the formation of the corresponding sulfides, these metals can be deposited at underpotential on sulfur covered silver. The deposition is surface limited and the successive electrodesorption of sulfur leaves confined clusters of metals. The method can also be used to obtain metal clusters of different size. In fact, the alternate underpotential deposition of elements that form a compound is the basis of the electrochemical atomic layer epitaxy (ECALE), and the reiteration of the basic cycle allows us to obtain sulfide deposits whose thickness increases with the number of cycles. Therefore, the successive selective desorption of sulfur leaves increasing amounts of metals.

Determination of gold in alloys via potentiometric titration; an alternative to the fire assay

In this paper we report the results of a deep investigation of gold title in jewellery alloys by means of potentiometric titration. After reviewing the suitable reactions for such purpose we focused on the most profitable one, which involves the use of hexadecylpyridinium chloride (CPC). This cation gives rise to selective and quantitative precipitation of AuCl4−. We completely revised a method previously proposed by W.S. Selig in the 80’s, by improving the sampling preparation and by optimizing the titration steps. Then, the new proposed method was tested on a large number of different alloys, commonly used for goldsmithery purposes. The obtained gold titles were compared with the data achieved by fire assay, giving rise to a very good agreement. At the light of these results, the present method can be rightfully considered a cheaper and “greener” alternative to the traditional one.

Acid deposition in the tuscan appennines during the dry period 1988-89

Abstract The typical parameters of acid precipitation are evaluated in the forest of Vallombrosa (Tuscan Appennines) during the dry period 1988-89. Individual rain events (dry and wet deposition) were sampled in a clearing of the forest and below the canopy of an evergreen tree as well as a deciduous broadleaf tree. In atmospheric precipitation the pH values usually vary around 4.4, with neutralization in the hot season due to calcareous material from distant sources. Relatively large concentrations of Pb and Cd are found in rain, but only in a small amount in canopy leachate. Aluminium, manganese and iron are more significantly washed off than Pb and Cd.

Quasi -Seasonal Neutralization of Acid Rain in Tuscany: Can Saharan Dust be Responsible?

Rainwater is often acidic (pH in the range 4–4.5 in many cases) in coastal, inland and mountain zones of Tuscany (central Italy). Neutralized rainfalls, i. e. exhibiting pH > 5.6, usually occur in spring and autumn; sometimes Saharan dust is visibly evident, in which cases a pH > 7 is generally found. When the contribution from Saharan dust is not evident, the neutralization (pH 5.6–7) appears to be due to local atmospheric dust or, in samples collected near to the shoreline, to marine aerosol. Collection of single rainfall, or fractions of single events, is recommended to distinguish among the various contributions to the neutralization.