Radiation-Induced Polymerization of Vinylidene Chloride in Bulk and Included in Thiourea Crystals

Vinylidene chloride (VDC) or 1,1-dichloroethylene was polymerized with γ radiation in bulk or as inclusion complex in thiourea crystals (inclusion polymerization). The resulting poly(vinylidenechloride) (PVDC) samples obtained from the two different polymerization techniques were characterized by FT-IR and electronic absorption spectroscopies, by ozonolysis and by thermal analysis (TGA, DTG and DTA). It was found that two selective secondary reactions occur in the two PVDC samples, respectively obtained from bulk polymerization or from inclusion polymerization. In the former case, the main reaction is only a crosslinking reaction, while in the latter case, with the PVDC included into the thiourea channels, the crosslinking reaction is fully inhibited and instead a dehydrohalogenation reaction takes place producing the polyene structures. The presence of polyene structures in the PVDC synthesized by the inclusion polymerization was demonstrated by electronic absorption spectroscopy and by ozonolysis experiments. The presence of polyene segments in the PVDC causes a reduction in the thermal stability of the polymer, lowers its melting point and reduces its crystallinity.     

Synthesis and Study of the Thermal and Chiro-Optical Properties of Polyacetylenes with Bulky Side Groups: Poly(1-ethynyl-4-biphenyl), Poly(1-ethynyl-4- phenoxybenzene) and Poly(1-ethynyl-4-pentylbenzene)

The monosubstituted acetylenes 1-ethynyl-4-biphenyl, 1-ethynyl-4-phenoxybenzene and 1-ethynyl-4-pentylbenzene were polymerized to the corresponding polyacetylenes with bulky side substituents: PEBIP, PEPHENO and PEPB, respectively, using a Rh(I) complex as polymerization catalyst. The FT-IR and UV-VIS spectra of PEBIP, PEPHENO and PEPB were studied using the corresponding spectra of polyphenylacetylene (PPA), polytolylacetylene (PETOL) and poly(1-ethynyl-naphthalene) PEN as reference. Based on the spectral analysis, high cis-trasoid structures were assigned to PEBIP, PEPHENO and PEPB. The specific optical rotation of PEBIP, PEPHENO and PEPB was measured in the chiral solvent α (-)pinene and, only for PEPB, also in α (+)pinene. It was found that even at low concentration PEBIP, PEPHENO and PEPB cause changes in the specific optical rotation of the chiral medium where they have been dissolved. This phenomenon has not been observed when toluene or atactic polystyrene are dissolved in the same chiral solvent in similar concentration. This suggests that the polyacetylenes with bulky side groups are able to rearrange in a helical configuration (prevalently right-handed or vice-versa, depending on the type of chiral medium used) once hosted in a chiral medium giving a contribution to the chirality of the solvent where they have been dissolved. The thermal stability of PEBIP, PEPHENO and PEPB was studied under N₂ flow by thermal analysis (TGA, DTG and DTA) in comparison to reference monosubstituted polyacetylenes PPA, PETOL and PEN. The results show that the thermal stability of monosubstituted polyacetylenes is greatly improved by the presence of bulky substitutents as theoretically expected, and similarly, also the char-forming tendency increases with the bulkiness of the side groups.     

Mixed micellar aggregates of nonionic surfactants with short hydrophobic tails

Mixed micelle formation by aqueous mixtures of pentaethylene glycol monohexyl ether (C₆E₅) and diethylene glycol monohexyl ether (C₆E₂) has been investigated by determining the temperature-composition phase diagrams and measuring the intradiffusion coefficients. In binary aqueous solutions, C₆E₅ shows a high tendency to micellize, while C₆E₂, because of its too short hydrophilic head, presents a macroscopic phase separation in a water-rich and a surfactant-rich phases. The temperature-composition phase diagrams obtained for the ternary water-C₆E₅---C₆E₂ mixtures present a micellar region in which both surfactants co-aggregate. The dimensions of this micellar region depend on the relative ratio between the two surfactants molalities. By analysing the micelle intradiffusion coefficient, measured through the PGSE-NMR technique, the hydrodynamic radius of the aggregates has been estimated at 25 °C. It is similar to that of triethylene glycol monohexyl ether (C₆E₃) in binary aqueous solution. The experimental evidences suggest that in mixed ethoxylated surfactants the micellar behaviour is mainly determined by the mean number of ethoxylic units per surfactant molecule, independently of their distribution.     

Determination and assessment of the contents of essential and potentially toxic elements in Ayurvedic medicine formulations by inductively coupled plasma-optical emission spectrometry

Traditional Ayurvedic remedies are easily available nowadays not only in India, their country of origin, but also in Western countries. Some of these products contain high concentrations of potentially toxic elements as main or secondary ingredients, in addition to elements essential for human health; for these reasons, it is interesting to determine their elemental composition. In this study we assessed the concentrations of fifteen elements (Al, As, Ca, Cd, Cr, Cu, Fe, Hg, K, Mg, Mn, Na, Pb, Si and Zn) in five products of the Parpati family, a group of Ayurvedic medicines containing high concentrations of mercury, manufactured in various places in India. Concentrations were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES) or (for Pb and Cd) by graphite furnace atomic absorption spectrometry (GF-AAS) after sample mineralization. We compared the calculated daily intake of each element with reference values, considering maximum tolerable intake levels or recommended nutrient amounts. The experimental results were treated with chemometric pattern recognition techniques. We found differences in the composition of products of the same denomination manufactured by different companies and strong correlations among groups of variables. As expected, the daily intake of mercury upon consumption of Parpati medicines largely exceeded the tolerable intake level of this element.     

On the action of ozone at high concentration on various grades of polyethylene and certain straight chain paraffins

The surface functionalisation of UHMWPE (ultra high molecular weight polyethylene) was successfully achieved by the action of ozone (10% by weight in oxygen) under mild conditions. The kinetics of the gas-solid reaction between O₃ and UHMWPE in powder form were measured in an IR gas cell and the pseudo-first-order rate constant was k′_UHMWPE = 1.9 × 10⁻⁴ s⁻¹. The resulting surface-oxidized UHMWPE was studied by FT-IR spectroscopy and the nature of the surface functionalities was determined. Furthermore, the surface-oxidized UHMWPE was studied by DSC (differential scanning calorimetry). It was evident that ozone attacks and oxidizes the amorphous phase of UHMWPE preserving the crystalline phase because after the ozone treatment there was an increase in the % of crystallinity. Two other polyethylene grades having respectively M_w = 15,000 Da (defined as LMWPE = low molecular weight polyethylene) and M_w = 4000 Da (defined as VLMWPE = very low molecular weight polyethylene) were studied as model compounds in comparison to UHMWPE in their reaction with ozone. Commercial liquid paraffin and n-dodecane were used as model compounds to study the reaction between high ozone concentration and alkanes.     

Enantio- and chemo-selective HPLC separations by chiral-achiral tandem-columns approach: the combination of CHIROBIOTIC TAG and SCX columns for the analysis of propionyl carnitine and related impurities

We describe a new tandem-columns chiral-achiral HPLC arrangement by using a chiral column (CHIROBIOTIC TAG) connected in series with an achiral column (Spherisorb S5 SCX), based on a strong cationic exchange mechanism; this approach is very useful for the analysis of chiral molecules, containing cationic groups in their structures. We used this special combination to develop an easy and convenient procedure for the enantio- and chemo-selective dosage of propionyl L-carnitine (1) and relative impurities (2-6), which allowed for the simultaneous separation and quantitation within 30 min. Under the best chromatographic conditions (acetonitrile-10 mM sodium dihydrogen phosphate 65:35, v/v (pHa 6.80) as the mobile phase and UV detection at 205 nm], all the individual peaks were well separated. The applicability of the method, fully validated, was demonstrated by the analysis of a pharmaceutical batch of propionyl L-carnitine, where we found the following contents: 98.5% for 1 (drug substance); 0.15% for 3; 0.1% for 5 and 0.2% for 6. The enantiomeric excess (e.e.%) measured for the drug substance was 98.9%. Finally, a single mixed-bed column, packed with a binary mixture of the chiral and achiral phases, in a 1:1 ratio, gave similar chromatographic results as the tandem-columns approach, and thus, offered an easy alternative solution to the separation of the considered mixture.     

A cognitive analysis of dragging practises in Cabri environments

Dragging in Dynamical Geometry Software (DGS) is described by introducing a hierarchy of its functions. This is suitable for classifying different attitudes and aims of students who investigate a geometric problem, such as exploring, conjecturing, validating and justifying. Moreover the hierarchy has cognitive features and can be used to describe the twofold modulities namely ascending and descending in which students interact with external representations (e.g. Cabri drawings). Switching from one modality to the other through dragging often allows them to produce fruitful conjectures and to pass from the empirical to the theoretical side of the question. The genesis of such different functions in students does not happen automatically but is the consequence of specific didactical interventions of the teacher in the pupils' apprenticeship of Cabri practises. A worked-out example illustrates the theoretical concepts introduced in the paper.