Physicochemical Aspects of Chitosan Dispersibility in Acidic Aqueous Media: Effects of the Food Acid Counter-Anion

Differences in formation of colloidal dispersions of chitosan in aqueous solutions of citric acid or lactic acid (25, 50 or 100 mM) were quantitatively studied. Protonation enthalpies, electrical conductivity and ζ-potential measurements were additionally undertaken, aiming at better understanding these differences at a molecular level. In dispersion kinetics assays, experimental data were well fitted (R²?>?0.9; MAPE?<?4 %) by a first-order kinetics model with two terms - one accounting for the fast, direct dispersion of biopolymers chains and another accounting for the slow dispersion of chains from lumps. In all cases, maximal dispersibility was reached after about 20?30 min of stirring. For both acids, the higher the acid concentration in the medium, the higher was the chitosan dispersibility. At a given acid concentration, chitosan showed higher dispersibility in lactic acid than in citric acid solutions. Protonation of chitosan -NH₂ groups was strongly exothermic, with ΔH values three times higher for citric acid (triprotic) than lactic acid (monoprotic) (ΔH?=??120 kJ?mol^{- 1} and ΔH?=??40 kJ?mol^{- 1}, respectively), indicating that chitosan -NH₂ protonation itself was not dependent on the type of acid. However, the electrical conductivity of suspensions of powdered chitosan in water evolved differently as these systems were titrated with citric or acid lactic. With citric acid, electrical conductivity remained virtually constant for acid concentration?<?of 15 mM, and then increased linearly as the acid concentration increased until 75 mM. Instead, with lactic acid, electrical conductivity progressively increased with increasing of acid concentration from 0 to 75 mM. The ζ-potential of chitosan dispersed particles was +28.5 mV and +52.1 mV in dispersions containing 10 mM of citric and lactic acids, respectively. The conjoint analysis of data from physicochemical analyses suggested that, contrarily to lactate anions, citrate anions bind more strongly on the electrical double layer of protonated, positively charged chains of chitosan, diminishing the inter-chains electrostatic repulsion, thus leading to a lower dispersibility of this polysaccharide in aqueous solutions of citric acid, compared to equimolar solutions of lactic acid.     

A Short Guide to the Climatic Variables of the Last Glacial Maximum for Biogeographers

Ecological niche models are widely used for mapping the distribution of species during the last glacial maximum (LGM). Although the selection of the variables and General Circulation Models (GCMs) used for constructing those maps determine the model predictions, we still lack a discussion about which variables and which GCM should be included in the analysis and why. Here, we analyzed the climatic predictions for the LGM of 9 different GCMs in order to help biogeographers to select their GCMs and climatic layers for mapping the species ranges in the LGM. We 1) map the discrepancies between the climatic predictions of the nine GCMs available for the LGM, 2) analyze the similarities and differences between the GCMs and group them to help researchers choose the appropriate GCMs for calibrating and projecting their ecological niche models (ENM) during the LGM, and 3) quantify the agreement of the predictions for each bioclimatic variable to help researchers avoid the environmental variables with a poor consensus between models. Our results indicate that, in absolute values, GCMs have a strong disagreement in their temperature predictions for temperate areas, while the uncertainties for the precipitation variables are in the tropics. In spite of the discrepancies between model predictions, temperature variables (BIO1-BIO11) are highly correlated between models. Precipitation variables (BIO12- BIO19) show no correlation between models, and specifically, BIO14 (precipitation of the driest month) and BIO15 (Precipitation Seasonality (Coefficient of Variation)) show the highest level of discrepancy between GCMs. Following our results, we strongly recommend the use of different GCMs for constructing or projecting ENMs, particularly when predicting the distribution of species that inhabit the tropics and the temperate areas of the Northern and Southern Hemispheres, because climatic predictions for those areas vary greatly among GCMs. We also recommend the exclusion of BIO14 and BIO15 from ENMs because those variables show a high level of discrepancy between GCMs. Thus, by excluding them, we decrease the level of uncertainty of our predictions. All the climatic layers produced for this paper are freely available in http://ecoclimate.org/.     

Retinol and retinoic acid increase MMP-2 activity by different pathways in cultured Sertoli cells

Diseases such as atherosclerosis, arthritis and cancer have been related with imbalance in ROS production and failures in regulation of the MMPs. Authors suggested a relationship between MPP activity and ROS. Our research group has demonstrated that retinol 7µM induced changes in Sertoli cell metabolism linking retinol treatment and oxidative stress. We verified MMP activity in Sertoli cells treated with vitamin A using gelatin zymography. We found that retinol (7µM) and retinoic acid (1nM) induced MMP-2 activity in Sertoli cells. Antioxidants reversed retinol-induced but not retinoic acid-induced MMP-2 activity. Moreover, retinol but not retinoic acid increased ROS production quantified by DCFH-DA oxidation. We found that retinol and retinoic acid induced ERK1/2 phosphorylation, but only retinol-increased MMP-2 activity was inhibited by UO126, an ERK1/2 phosphorylation inhibitor. Our findings suggested that retinol-induced MMP-2 activity, but not retinoic acid-induced MMP-2 activity, was related to ERK1/2 phosphorylation and ROS production.     

The invasion of an alien characiform fish and the decline of a native congener in a Neotropical river-floodplain system

Hydrobiologia - Using a long time series, we analyzed trends in abundance of two characiform fishes in the upper Paraná River and its floodplain: the native Schizodon altoparanae and its alien...     

Global phylogeography of sailfish: deep evolutionary lineages with implications for fisheries management

Hydrobiologia - Since the Miocene profound climatic changes have influenced the biology and ecology of species worldwide, such as their connectivity, genetic population structure, and biogeography....     

Niche measures and growth rate do not predict interspecific variation in spatial synchrony of phytoplankton

Limnology - Spatial synchrony occurs when local populations exhibit correlated dynamics over time. Recent studies, both experimental and observational, have indicated that the magnitude of spatial...     

Effect of a denture cleanser on the concentration of volatile sulphur compounds and denture biofilm in institutionalised elderly

doi:10.1111/j.1741‐2358.2009.00341.x
Effect of a denture cleanser on the concentration of volatile sulphur compounds and denture biofilm in institutionalised elderly Objective: To determine the effectiveness of a denture cleanser in reducing the concentration of volatile sulphur compounds (VSC) and its antimicrobial action. Background: Micro‐organisms from the denture biofilm can cause local and systemic disease and halitosis. Denture cleansers are important adjuncts in oral care, but there is limited investigation on their effect in malodour compounds. Material and methods: Nineteen institutionalised elderly who wore at least an upper denture were selected; their VSC concentrations were measured and the denture biofilm was collected. In phase 1, the subjects wore their old denture and data were collected before (B₀) and after 7(A₁), 14(A₂), 28(A₃) days of continuous daily use of the denture cleanser. In phase 2, new dentures were inserted and measurements were made at 30(A_1.1), 60(A_2.2), 90(A_3.3) days of treatment. Results: The VSC concentration increased from B₀ to A₁ (p < 0.05)_, but no differences were found for the others intervals of times. Total micro‐organism data did not show a statistical difference between times in Phase I, but in Phase II, there was a statistical difference (p < 0.05) and a progressive re‐colonisation was observed. Conclusion: Within the limits of this study, it was concluded that the denture cleanser had no antimicrobial effect and VSC levels were not reduced.     

Two- and three-dimensional quantitative structure-activity relationships for a series of purine nucleoside phosphorylase inhibitors

Comparative molecular field analysis (CoMFA), comparative molecular similarity indices analysis, and hologram quantitative structure-activity relationship (HQSAR) studies were conducted on a series of 52 training set inhibitors of calf spleen purine nucleoside phosphorylase (PNP). Significant cross-validated correlation coefficients (CoMFA, q(2)=0.68; CoMSIA, q(2)=0.66; and HQSAR, q(2)=0.70) were obtained, indicating the potential of the models for untested compounds. The models were then used to predict the inhibitory potency of 16 test set compounds that were not included in the training set, and the predicted values were in good agreement with the experimental results. The final QSAR models along with the information gathered from 3D contour and 2D contribution maps should be useful for the design of novel inhibitors of PNP having improved potency.     

Triploidization in the streaked prochilod Prochilodus lineatus inferred by flow cytometry,blood smears and karyological approaches

The streaked prochilod Prochilodus lineatus is an important fish species from the Neotropical region. In this study, a protocol of triploidization was established by temperature shock. Fertilized eggs were shocked at 2 min post-fertilization at 0, 38, 40 and 42°C. At 0°C, the embryos were maintained for 30 min, while the rest for 2 min. Heat shocked embryos and control (during all experiment) were incubated at 27°C. The ploidy status was confirmed by flow cytometry, erythrocyte diameter, conventional cytogenetics (Giemsa staining), chromosome banding and fluorescence in situ hybridization using 5S and 18S rDNA probes. Heat-shock at 40°C produced 96.7% of triploids and such a procedure did not reduce the fertilization, hatching rate and the percentage of normal embryos. The use of chromosome banding and FISH gave rise to effective procedure to identify triploids. The data obtained here is innovative for the species and bring new information for basic and applied studies.