| 1. |
- Alves, Luis, et al.
(författare)
-
New Insights on the Role of Urea on the Dissolution and Thermally-Induced Gelation of Cellulose in Aqueous Alkali
- 2018
-
Ingår i: GELS. - : MDPI AG. - 2310-2861. ; 4:4
-
Tidskriftsartikel (refereegranskat)abstract
- The gelation of cellulose in alkali solutions is quite relevant, but still a poorly understood process. Moreover, the role of certain additives, such as urea, is not consensual among the community. Therefore, in this work, an unusual set of characterization methods for cellulose solutions, such as cryo-transmission electronic microscopy (cryo-TEM), polarization transfer solid-state nuclear magnetic resonance (PTssNMR) and diffusion wave spectroscopy (DWS) were employed to study the role of urea on the dissolution and gelation processes of cellulose in aqueous alkali. Cryo-TEM reveals that the addition of urea generally reduces the presence of undissolved cellulose fibrils in solution. These results are consistent with PTssNMR data, which show the reduction and in some cases the absence of crystalline portions of cellulose in solution, suggesting a pronounced positive effect of the urea on the dissolution efficiency of cellulose. Both conventional mechanical macrorheology and microrheology (DWS) indicate a significant delay of gelation induced by urea, being absent until ca. 60 degrees C for a system containing 5wt % cellulose, while a system without urea gels at a lower temperature. For higher cellulose concentrations, the samples containing urea form gels even at room temperature. It is argued that since urea facilitates cellulose dissolution, the high entanglement of the cellulose chains in solution (above the critical concentration, C*) results in a strong three-dimensional network.
|
|
| 2. |
- Schönnesson, LN, et al.
(författare)
-
The power for action - now!
- 2024
-
Ingår i: AIDS care. - 1360-0451. ; , s. 1-5
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
|
|
| 3. |
- Gastineau, R., et al.
(författare)
-
Haslea ostrearia-like Diatoms: Biodiversity out of the Blue
- 2014
-
Ingår i: Advances in Botanical Research. - London : Academic Press Ltd-Elsevier Science Ltd. - 0065-2296. ; 71, s. 441-465
-
Tidskriftsartikel (refereegranskat)abstract
- Diatoms are usually referred to as golden-brown microalgae, due to the colour of their plastids and to their pigment composition, mainly carotenoids (fucoxanthin, diadinoxanthin, diatoxanthin), which mask chlorophylls a and c. The species Haslea ostrearia Gaillon/Bory (Simonsen) appears unique because of its extraplastidial bluish colour, a consequence of the presence of a water-soluble blue pigment at cell apices, marennine. When released in seawater, marenbine can be fixed on gills of oysters and other bivalves, which turn green. This greening phenomenon is economically exploited in Southwestern France, as it gives an added value to oysters. For decades, this singularity ascribed a worldwide distribution to H. ostrearia, first as Vibrio ostrearius, then Navicula ostrearia, last as H. ostrearia, when the genus Haslea was proposed by R. Simonsen (1974). Indeed, this 'birthmark' (presence of blue apices) made H. ostrearia easily recognisable without further scrutiny and identification of the microalga as well as its presence easily deduced from the greening of bivalves. Consequently, the widely admitted cosmopolitan character of H. ostrearia has only been questioned recently, following the discovery in 2008, of a new species of blue diatom in the Black Sea, Haslea karadagensis. The biodiversity of blue diatoms suddenly increased with the finding of other blue species in the Mediterranean Sea, the Canary Islands, etc., the taxonomic characterization of which is in progress. This review thus focuses on the unsuspected biodiversity of blue diatoms within the genus Haslea. Methods for species determination (morphometrics, chemotaxonomy, genomics), as well as a new species, are presented and discussed.
|
|
| 4. |
- Gastineau, R, et al.
(författare)
-
Inheritance of Mitochondrial DNA in the Pennate Diatom Haslea ostrearia (Naviculaceae) during Auxosporulation Suggests a Uniparental Transmission
- 2013
-
Ingår i: Protist. - 1434-4610 .- 1618-0941. ; 164:3, s. 340-351
-
Tidskriftsartikel (refereegranskat)abstract
- We present the first study examining mtDNA transmission in diatoms, using sexual progeny of the pennate species Has lea ostrearia (Naviculaceae). A fragment of the cytochrome oxidase subunit I gene (cox1) with 7 nucleic substitutions between parental clones was used as a parental tracer in 16 F1 clones obtained from two pairs of mating crosses. Each cross involved a parental clone isolated from France (Bay of Bourgneuf) and Sweden (Kattegat Bay). We determined that all progeny possessed only one cox1 parental haplotype. These results suggest that the mitochondrial DNA transmission in H. ostrearia is uniparental. Implications and new topics of investigation are discussed. (C) 2013 Elsevier GmbH. All rights reserved.
|
|
| 5. |
|
|
