Viscoelastic gels of guar and xanthan gum mixtures provide long-term stabilization of iron micro- and nanoparticles

Iron micro- and nanoparticles used for groundwater remediation and medical applications are prone to fast aggregation and sedimentation. Diluted single biopolymer water solutions of guar gum (GG) or xanthan gum (XG) can stabilize these particles for few hours providing steric repulsion and by increasing the viscosity of the suspension. The goal of the study is to demonstrate that amending GG solutions with small amounts of XG (XG/GG weight ratio 1:19; 3 g/L of total biopolymer concentration) can significantly improve the capability of the biopolymer to stabilize highly concentrated iron micro- and nanoparticle suspensions. The synergistic effect between GG and XG generates a viscoelastic gel that can maintain 20 g/L iron particles suspended for over 24 h. This is attributed to (i) an increase in the static viscosity, (ii) a combined polymer structure the yield stress of which contrasts the downward stress exerted by the iron particles, and (iii) the adsorption of the polymers to the iron surface having an anchoring effect on the particles. The XG/GG viscoelastic gel is characterized by a marked shear thinning behavior. This property, coupled with the low biopolymer concentration, determines small viscosity values at high shear rates, facilitating the injection in porous media. Furthermore, the thermosensitivity of the soft elastic polymeric network promotes higher stability and longer storage times at low temperatures and rapid decrease of viscosity at higher temperatures. This feature can be exploited in order to improve the flowability and the delivery of the suspensions to the target as well as to effectively tune and control the release of the iron particle

Relationship of Treatment Delay with Surgical Defect Size from Keratinocyte Carcinoma (Basal Cell Carcinoma and Squamous Cell Carcinoma of the Skin)

Larger keratinocyte carcinoma (KC) lesions are associated with higher morbidity. This study examined the association of potentially modifiable characteristics, including treatment delay, with KC defect size after Mohs micrographic surgery (MMS). A stratified random sample of patients treated for KC with MMS were selected for telephone interview. Two hundred and nineteen interviews were completed (refusal rate 24%). Regression models were used to examine the predictors to defect size and delay. Anatomic site, age, histology, and gender predicted defect size (R2=0.39) and were used as control variables. Self-reported delay between initial physician examination and MMS predicted defect size (p=0.0004), with greater than 1 y delay being associated with a doubling of defect size (adjusted odds ratio (OR) 2.0; 95% confidence interval (CI) 1.3–3.1). Delays of this duration were associated with initial examination by a primary provider (unadjusted OR 3.9; 95% CI 1.7–8.8), misdiagnosis (unadjusted OR 6.8; 95% CI 2.5–18.7), being treated without biopsy (unadjusted OR 23.3; 95% CI 6.5–83.7), and multiple surgical removals (unadjusted OR 6.2; 95% CI 2.5–15.5). All but provider specialty were independent predictors of delay. Attention to processes of care delivery for KC may have a greater impact on morbidity than efforts are earlier detection by the public

Palaeomagnetic dating of the Neostromboli succession

The Neostromboli volcanic succession is characterized by packages of lava flow units and scoria beds erupted from the summit of the Stromboli volcano, and by scoria cones and lava flows poured out from lateral vents and fissures. Available radiometric ages constrain Neostromboli activity in the 14\u20134 ka BP age window, but the chronological relations of central vs. peripheral activity are still poorly understood. Furthermore, radiometric and palaeomagnetic ages for some of the peripheral eruptions are strikingly inconsistent. Here we report on the palaeomagnetic dating of thirty-four sites from Neostromboli products. Seventeen are new palaeomagnetic directions, while additional seventeen ages are recalculated - using published directions by Speranza et al. (2008) - with the recent SHA.DIF.14K palaeo-secular variation (PSV) field model. We show that the beginning of Neostromboli succession could be much younger than the commonly accepted 4814 ka onset, providing our oldest data an age of 489 ka. The improved geochronological resolution allowed by palaeomagnetic dating suggests that the early stages of the Neostromboli activity occurred at 9\u20138 ka BP and were characterized by summit lava flow units blanketing both the SW and northern volcano flanks; after 487.5 ka lateral eruptions from peripheral cones and fissures became dominant. We suggest that the intense flank activity enabled magma-water interaction thus yielding explosive activity and repeated collapse events, leading to the Sciara del Fuoco formation. Our work confirms that PSV analysis of Holocene volcanics may yield eruption chronology definition with an accuracy unlikely to be achieved with other radiometric techniques

Comparative studies on solution characteristics of mannuronan epimerized by C-5 epimerases

Both dilute and concentrated solutions of bacterial Mannuronan (MANNA) and its epimerized products by AlgE1 at 5 and 24 h, named MANNAEp1t5h and MANNAEp1t24h, respectively, and AlgE4 (MANNAEp4) have been studied as a function of variables such as polymer concentration and ionic strength (NaCl) in order to investigate the macromolecular solution properties of these innovative polyuronic acids having the same charge density but different composition and sequence of b-D-mannuronic acid (-M-), a-L-guluronic acid (-G-) or MGblocks. Measurements of intrinsic viscosity [h] as a function of ionic strength, I, by capillary viscometry has led to an estimate of the Smidsrød- Haug parameter B, an index useful to characterize the stiffness of polymeric chains. The results are largely consistent with much of the published data relative to chain extension and conformational freedom around the torsional angles of the glycosidic linkages occurring in alginates. Steady shear rheometry provided information about the coil-overlapping parameter c*, which marks the transition from dilute to concentrated solution. The slopes of the double logarithmic plots of hsp vs. c[h] both at low and high degrees of coil overlap suggest that all samples solutions behave like linear polymer entangled network systems. The value of c* is strictly influenced by the stiffness of the chains, and hence by the primary structure. Dynamic shear rheometry shows that the frequency dependence of dynamic viscosity is only partially superimposable to the shear rate dependence of viscosity. Such behaviour may be ascribed to the presence of semiflexible polymeric coils in a non-totally destructured entangled state. By solvent/non-solvent (H2O/isopropanol) fractionation carried out on mannuronan, a set of samples with different average molecular weights and narrow polydispersities were obtained. Triple detection GPC allowed the evalutation of the Mark–Houwink–Sakurada parameters as well as of the characteristic ratio CN for one of the fractionated MANNA samples. The chain persistence length was estimated by the wormlike chain model

Acid gel formation in (pseudo) alginates with and without G blocks produced by epimerising mannuronan with C5 epimerases

The main scope of this paper is the characterization, in terms of viscoelastic and mechanical properties, of acid gels formed from solutions of mannuronan ALG (0%G/0%GG) and its enzymatically epimerised products. The epimerised products were obtained using recombinantly produced mannuronan C5 epimerases named AlgE1 and AlgE4, which catalyse the conversion of mannuronic residues into guluronic (G) and guluronic-mannuronic (GM) blocks, respectively. The products used in this study resulted from either the action of AlgE1 on mannuronan for 5 and 24 h (named ALG(44%G/32%GG) and ALG (68%G/59%GG), respectively) or AlgE4 on mannuronan (named ALG (47%G/0%GG)). d-gluconic acid-δ-lactone (GDL) was used as H+-donor to produce acidic gels. ALG (0%G/0%GG) yields strong, stable solid-like structures. As predicted by circular dichroism measurements performed at different pH, gelation of ALG (47%G/0%GG) occurs at lower values of pH (∼1) than those obtainable using GDL. Hydrochloric acid was therefore added to ALG (47%G/0%GG) solutions yielding rapid sol-gel transitions and gels with a remarkable resistance to thermal treatment. The introduction of guluronic residues along the chain (ALG (44%G/32%GG)) causes a reduction in the storage modulus at the equilibrium with respect to that of ALG (0%G/0%GG) and the occurrence of negligible syneresis at the highest polymer concentrations. The increase in the average length of the G blocks (ALG (68%G/59%GG)) is accompanied by a further increase in the storage modulus without the occurrence of any significant syneresis. © 2006 Elsevier Ltd. All rights reserved.The main scope of this paper is the characterization, in terms of viscoelastic and mechanical properties, of acid gels formed from solutions of mannuronan ALG (0%G/0%GG) and its enzymatically epimerised products. The epimerised products were obtained using recombinantly produced mannuronan C5 epimerases named AlgE1 and AlgE4, which catalyse the conversion of mannuronic residues into guluronic (G) and guluronic–mannuronic (GM) blocks, respectively. The products used in this study resulted from either the action of AlgE1 on mannuronan for 5 and 24 h (named ALG(44%G/32%GG) and ALG (68%G/59%GG), respectively) or AlgE4 on mannuronan (named ALG (47%G/0%GG)). Dgluconic acid-d-lactone (GDL) was used as HC-donor to produce acidic gels. ALG (0%G/0%GG) yields strong, stable solid-like structures. As predicted by circular dichroism measurements performed at different pH, gelation of ALG (47%G/0%GG) occurs at lower values of pH (w1) than those obtainable using GDL. Hydrochloric acid was therefore added to ALG (47%G/0%GG) solutions yielding rapid sol–gel transitions and gels with a remarkable resistance to thermal treatment. The introduction of guluronic residues along the chain (ALG (44%G/32%GG)) causes a reduction in the storage modulus at the equilibrium with respect to that of ALG (0%G/0%GG) and the occurrence of negligible syneresis at the highest polymer concentrations. The increase in the average length of the G blocks (ALG (68%G/59%GG)) is accompanied by a further increase in the storage modulus without the occurrence of any significant syneresis

Ionic gel formation of a (pseudo)alginate characterised by an alternating MG sequence produced by epimerising mannuronan with AlgE4

The scope of this paper is the characterization, in terms of viscoelastic and mechanical properties, of ionic gels obtained from solutions of pseudoalginates characterized by a strictly alternating MG sequence (ALG(47%, 0%GG)) in the presence of calcium ions. ALG(47%, 0%GG) was obtained using a recombinantly produced mannuronan C-5 epimerase, named AlgE4 which catalyses the conversion of mannuronic residues into guluronic–mannuronic (GM) blocks. It was established that the kinetics of gelation as well as the mechanical properties and degree of syneresis of the ensuing gels are markedly dependent on both polymer concentration and Ca2+ content. The molecular dynamic investigation was carried out on a comparative basis between poly(MG) vs. poly(G) and demonstrated that in the case of poly(MG) the structural unit composed by two calcium paired MG oligomer enjoy a higher degree of Xexibility in comparison to the equivalent structure based on GG sequence. Furthermore, the electrostatic interaction between Ca2+ ions and carboxylate groups of M and G units is the main driving force to gel formation

Radioactivité dans le lait maternel et contamination de l’environnement

Après l’accident de Tchernobyl, nous avons entrepris un programme de contrôle de la radioactivité artificielle dans le lait maternel, dans la ville de Rome. Cette recherche s’est déroulée en 1986 et en 1987 et est encore en cours. Nous avons confronté les concentrations de césium 134 et 137 mesurées avec celles du lait de vache et du lait en poudre. La dose efficace a été calculée pour les nourrissons. En 1987, nous nous étions assigné un double objectif : 1) vérifier la représentativité des mères qui ont fourni les échantillons par rapport à toutes les mères du Latium ; 2) prélever des échantillons dans le Latium et aussi dans d’autres régions de l’Italie du Nord. Nous visons donc à vérifier l’homogénéité de la contamination du lait maternel dans la région de Rome ainsi qu’à évaluer cette contamination dans les régions les plus frappées par les retombées de Tchernobyl