Rheological study of the chitosan/glutaraldehyde chemical gel system

©1998. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ This document is the Accepted, version of a Published Work that appeared in final form in Polymer Gels and Networks . To access the final edited and published work see https://doi.org/10.1016/S0966-7822(98)00032-XChitosan dissolved in 0.1 mol l~1 acetic acid shows an apparent yield stress at very low frequencies, probably due to a structuring process yielding gel-like response. It re#ects complex relaxation mechanisms once chains disentangle and relax, presumably due to incipient hydrophobic contacts reinforced by the relative sti!ness of the chitosan chains, which tend to slow down reptation. When chemical cross-linkages are introduced, the weak self-associated network of chitosan is gradually replaced by a permanent covalent network as the molar ratio of aldehyde/amine groups, R, is increased. At R"0.4 a glass-to-rubber-type transition is observed, while at R"0.5 the form of the mechanical spectrum suggests the co-existence of a chemically cross-linked gel &dissolved' in a second entangled network formed by chitosan chains of restricted mobility. At higher cross-linking levels (R'1) a strong permanent gel is formed. The observed frequency dependence near the rheological gel point suggests several modes of relaxation processes

Mesoscopic Modeling of the Encapsulation of Capsaicin by Lecithin/Chitosan Liposomal Nanoparticles

The transport of hydrophobic drugs in the human body exhibits complications due to the low solubility of these compounds. With the purpose of enhancing the bioavailability and biodistribution of such drugs, recent studies have reported the use of amphiphilic molecules, such as phospholipids, for the synthesis of nanoparticles or nanocapsules. Given that phospholipids can self-assemble in liposomes or micellar structures, they are ideal candidates to function as vehicles of hydrophobic molecules. In this work, we report mesoscopic simulations of nanoliposomes, constituted by lecithin and coated with a shell of chitosan. The stability of such structures and the efficiency of the encapsulation of capsaicin, as well as the internal and superficial distribution of capsaicin and chitosan inside the nanoliposome, were analyzed. The characterization of the system was carried out through density maps and the potentials of mean force for the lecithin-capsaicin, lecithin-chitosan, and capsaicin-chitosan interactions. The results of these simulations show that chitosan is deposited on the surface of the nanoliposome, as has been reported in some experimental works. It was also observed that a nanoliposome of approximately 18 nm in diameter is stable during the simulation. The deposition behavior was found to be influenced by a pattern of N-acetylation of chitosan

Sample contamination explains evidence of close kin proximity in yellowfin tuna (Thunnus albacares) in the Western and Central Pacific Ocean

© 2023 Anderson, Macdonald, Lal, Hampton, Smith and Rico. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.Anderson et al.’s 2019 paper ‘Close Kin Proximity in Yellowfin Tuna (Thunnus albacares) as a Driver of Population Genetic Structure in the Tropical Western and Central Pacific’ provided observations of genetically related individuals among sampled yellowfin tuna. Resampling of some individuals from the original study produced very different sequencing results when compared with the original dataset, one possible explanation of which is cross-contamination among the original samples. Re-analyses produced no indication of strong population structure, including a very slightly and consistent heterozygosity deficit with only one statistically significant pairwise FST value of 0.002. We identified only one pair of genetically similar individuals that could still be an artefact of lingering contamination. These new results therefore support a highly connected population of yellowfin tuna in the study area, although we do not rule out the potential for local adaptation driven by non-observed loci or genetic sub-structure operating at more contemporary scales.Funding was provided by the Western and Central Pacific Fisheries Commission (Project 35b) and the European Union “Pacific-European-Union-Marine-Partnership” Programme (agreement FED/2018/397-941). This publication was produced with the financial support of the European Union and Sweden.Peer reviewe

Supplementary Material: Sample contamination explains evidence of close kin proximity in yellowfin tuna (Thunnus albacares) in the Western and Central Pacific Ocean

Figure S1 Map of the study area with distribution of sample locations, specifying year by color and number of samples by size of circle. Redrawn from Anderson et al. (2019).-- Figure S2 Distribution of observed heterozygosity values in the initial dataset prior to extracting high heterozygosity individuals (blue, ‘Initial’) and the final dataset (red, ‘Final’).-- Table S1 Number of loci retained through quality filtering process. NB: the order of filtering steps changed slightly between manuscripts; also the new dataset was filtered twice, first for extraction of low quality individuals (‘initial’ column) and then for the creation of a final dataset for genetic analysis (‘final’ column). To confirm robustness of results, an ‘alternative updated’ version of the final dataset is also reported here, which extracted the same individuals as the ‘updated final’ dataset prior to employing alternative thresholds in the final filtering steps. MAF = Minor allele frequency, HWE = Hardy-Weinberg expectation, LD = Linkage disequilibrium, LUPS = Loci under potential selection, FDR = False discovery rate.-- Table S2 Adjusted expected heterozygosity (Hnb), observed heterozygosity (Ho) and inbreeding coefficient (FIS) compared between results from original and updated analyses. Results from the new dataset using alternative filtering thresholds are provided in parentheses.-- Table S3 Fixation index (FST) values from the original data are below the diagonal and comparable values from the current study are above the diagonal. Results produced by the alternative new dataset are provided in parentheses above the diagonal. Unlike in the main document that reports p values adjusted by false discovery rate, p values here are adjusted using a Bonferroni correction (alpha value threshold of 0.00238). Significant values are bold.-- Figure S3 Discriminant Analyses of Principal Components produced by A) the original dataset using 62 principal components and 6 degrees of freedom, as recommended by alpha optimization analyses; B) the updated dataset using 60 principal components and 6 discriminant function, also as recommended by alpha optimization and cross validation; and C) the alternatively filtered updated dataset, also using 60 principal components and 6 discriminant function, as recommended by alpha optimization and cross validation. NB: the panel representing the original analysis is a recreation and, due to randomized initial seeding in some R coding, is very near but not an exact copy of the figure from Anderson et al 2019.-- Table S4 The k value representing the most likely number of independent genetic clusters present in a sample (from ADMIXTURE).-- Table S5 Relatedness (r) data summarized as number of dyads recommended as a particular type of relationship. NB: Anderson et al., (2019) only reported dyads that were highlighted by both software programs to increase robustness of observations, and also only focused on half- and full-sib dyads because there were sufficient novel observations without considering more distance degrees of relatedness. In the current study, we report COANCESTRY and RelatedAdmix results separately and incorporate more relationship degrees to better illustrate the change in results. Results from the alternatively filtered updated dataset are reported in parentheses.Peer reviewe

Preparation of chitosan nanoparticles by nanoprecipitation and their ability as a drug nanocarrier

Polysaccharide-based nanoparticles represent a very promising drug delivery platform, particularly for the transmucosal delivery of bioactive macromolecules. Thus, the aim of this paper is to revisit the nanoprecipitation processes for preparing chitosan nanoparticles and to evaluate the influence of the process parameters on their characteristics. Chitosan was dissolved in water as N-(methylsulfonic acid) chitosan or directly in aqueous acetic acid. Methanol was used as the nonsolvent diffusing phase. Nanoparticles became smaller as the polymer concentration decreased or the nonsolvent to solvent volume ratio increased. Particles prepared in acidic media are slightly larger than those precipitated from N-(methylsulfonic acid) chitosan. Replacement of methanol by water in the suspension medium resulted in a notorious increase in their size. On the other hand, very little additions of Tween-80 to the nonsolvent phase render smaller nanoparticles, with a similar mean-size values. Nanoparticles precipitated in methanol have roughly the same dimensions, regardless of the ionic strength of the chitosan solution. These chitosan nanoparticles have good association and loading efficiency values of a model substance showing their ability as a nanocarrier for drug delivery systems

DataSheet_1_Sample contamination explains evidence of close kin proximity in yellowfin tuna (Thunnus albacares) in the Western and Central Pacific Ocean.csv

Anderson et al.’s 2019 paper ‘Close Kin Proximity in Yellowfin Tuna (Thunnus albacares) as a Driver of Population Genetic Structure in the Tropical Western and Central Pacific’ provided observations of genetically related individuals among sampled yellowfin tuna. Resampling of some individuals from the original study produced very different sequencing results when compared with the original dataset, one possible explanation of which is cross-contamination among the original samples. Re-analyses produced no indication of strong population structure, including a very slightly and consistent heterozygosity deficit with only one statistically significant pairwise FST value of 0.002. We identified only one pair of genetically similar individuals that could still be an artefact of lingering contamination. These new results therefore support a highly connected population of yellowfin tuna in the study area, although we do not rule out the potential for local adaptation driven by non-observed loci or genetic sub-structure operating at more contemporary scales.</p

Synthesis of regioselective chitosan copolymers with β-cyclodextrin and poly(N-isopropyl acrylamide)

This work aimed to design a synthetic route under mild conditions allowing the main chitosan chain to be grafted with β-cyclodextrin (β-CD) and poly(N-isopropyl acrylamide) (PNIPAm), at C2 and C6 positions, respectively. For this reason, the regioselectivity of proposed reactions is an important factor to be considered. β-CD is an oligosaccharide with a cyclic structure capable of forming inclusion complexes with hydrophobic molecules. Grafting β-CD onto the chitosan backbone by reductive N-alkylation at C2 position was carried out. With this purpose, the previous preparation of β-CD monoaldehyde was required. PNIPAm is a thermosensitive polymer with a transition temperature near 33 °C. To regioselectively anchor poly(N-isopropyl acrylamide) chains onto chitosan at C6 position, it was required to attach at the C6 position of chitosan an alkyl group for the subsequent grafting of PNIPAm-N3 by means of copper-catalyzed azide-alkyne cycloaddition click reaction. To guarantee the regioselectivity of the functionalization of chitosan with a C6 terminal alkyne, its oxyalkylation with glycidyl propargyl ether in a solvent composed of LiOH/KOH/urea was used. The structure of all derivatives was confirmed by FT-IR and 1H-NMR spectroscopy

DataSheet_2_Sample contamination explains evidence of close kin proximity in yellowfin tuna (Thunnus albacares) in the Western and Central Pacific Ocean.docx

Anderson et al.’s 2019 paper ‘Close Kin Proximity in Yellowfin Tuna (Thunnus albacares) as a Driver of Population Genetic Structure in the Tropical Western and Central Pacific’ provided observations of genetically related individuals among sampled yellowfin tuna. Resampling of some individuals from the original study produced very different sequencing results when compared with the original dataset, one possible explanation of which is cross-contamination among the original samples. Re-analyses produced no indication of strong population structure, including a very slightly and consistent heterozygosity deficit with only one statistically significant pairwise FST value of 0.002. We identified only one pair of genetically similar individuals that could still be an artefact of lingering contamination. These new results therefore support a highly connected population of yellowfin tuna in the study area, although we do not rule out the potential for local adaptation driven by non-observed loci or genetic sub-structure operating at more contemporary scales.</p