| 1. |
- Idström, Alexander, et al.
(författare)
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Dissolution of cellulose in tetrabutylammonium acetate/dimethyl sulfoxide
- 2016
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Ingår i: The 7th workshop on cellulose, regenerated cellulose and cellulose derivatives.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The dissolution of cellulose in tetrabutylammonium acetate (TBAAc)/dimethyl sulfoxide (DMSO) was studied combining experimental and simulation techniques. It was found that the dissolution limit at 40 °C corresponded to a molar ratio close to one acetate per cellulose anhydroglucose units. MD simulations suggested that the acetate ions bind to cellulose by dual hydrogen bonds. This effectively turns cellulose into a polyelectrolyte, attracting the bulky tetrabutylammonium (TBA+) counter ions, which prevent close contact between chains in the dissolved state. This hypothesis was tested by 1H- and 13C-NMR spectroscopy, which confirmed that acetate forms hydrogen bonds to cellulose, and by diffusion NMR spectroscopy, which demonstrated a strong dynamic correlation between bound acetate and tetrabutylammonium in near-quantitative agreement with simulation. The present results suggest that offering hydrogen bonding to the acetate ions is the main driving force for dissolving cellulose and that the TBA+ counter ions form a diffuse layer around the acetate-decorated cellulose chains.
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| 2. |
- Idström, Alexander, et al.
(författare)
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On the dissolution of cellulose in tetrabutylammonium acetate/dimethyl sulfoxide : a frustrated solvent
- 2017
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 24:9, s. 3645-3657
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Tidskriftsartikel (refereegranskat)abstract
- We have found that the dissolution of cellulose in the binary mixed solvent tetrabutylammonium acetate/dimethyl sulfoxide follows a previously overlooked near-stoichiometric relationship such that one dissolved acetate ion is able to dissolve an amount of cellulose corresponding to about one glucose residue. The structure and dynamics of the resulting cellulose solutions were investigated using small-angle X-ray scattering (SAXS) and nuclear magnetic resonance techniques as well as molecular dynamics simulation. This yielded a detailed picture of the dissolution mechanism in which acetate ions form hydrogen bonds to cellulose and causes a diffuse solvation sheath of bulky tetrabutylammonium counterions to form. In turn, this leads to a steric repulsion that helps to keep the cellulose chains apart. Structural similarities to previously investigated cellulose solutions in aqueous tetrabutylammonium hydroxide were revealed by SAXS measurement. To what extent this corresponds to similarities in dissolution mechanism is discussed.
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| 3. |
- Artacho Ruiz, Josep, et al.
(författare)
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The synthesis and characterization of all diastereomers of a linear symmetrically fused tris-Troger's base analogue: New chiral cleft compounds
- 2006
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Ingår i: Chemistry: A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 12:10, s. 2692-2701
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis and characterization of all diastereomers of a linear symmetrically fused tris-Troger's base analogue are described. The diastereomers are unambiguously assigned as syn-anti 1a, anti-anti 1b, and syn-syn 1c isomers, by using X-ray diffraction analysis and NMR spectroscopy. For the first time, the anti-anti and the syn-syn diastereomers of a linear symmetrically fused tris-Troger's base analogue have been synthesized. Molecules 1a and 1c are new cleft compounds and analysis of compound 1a in the solid state shows inclusion of one molecule of CH2Cl2 in the larger aromatic cleft, whereas in isomer 1c disordered solvent molecules are trapped in the extended aromatic cleft. Furthermore, in the solid state, isomer 1c forms infinite open channels along one of the crystallographic axes and perpendicular to this axis there are infinitely extending "wedged-ravines". Importantly, each of the diastereomers 1a-c is resistant to inversion at the stereogenic nitrogen atoms under strongly and weakly acidic conditions in the range from room temperature (RT) to 95 degrees C. This observed configurational stability at the stereogenic nitrogens of 1a-c is unique for analogues of Troger's base in general to date. Finally, the ratio of cleft compounds 1a and 1c significantly increased relative to cavity compound 1b when ammonium chloride was used as an additive in the Troger's base condensation to 1a-c suggesting a templating effect of the ammonium ion.
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| 4. |
- Artacho Ruiz, Josep, et al.
(författare)
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Tröger's Base Twisted Amides: Endo Functionalization and Synthesis of an Inverted Crown Ether
- 2012
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Ingår i: Organic Letters. - : American Chemical Society (ACS). - 1523-7052 .- 1523-7060. ; 14:18, s. 4706-4709
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Tidskriftsartikel (refereegranskat)abstract
- Taking advantage of the unconventional reactivity of twisted mono- and bis-amides of Tröger's base (TB), rac-6 and rac-7, respectively, the first synthesis of a 6-endo-monosubstituted TB analogue, rac-9, and the first rational synthesis of a 6,12-endo,endo-disubstituted TB analogue, rac-11, have been achieved. The bis-TB crown ether, meso-13, was prepared starting from rac-7. Meso-13 constitutes a rare example of a crown ether with an inverted methylene bridge-to-bridge bis-TB conformation both in solution and in the solid state, resulting in a reluctance to act as a receptor for cations.
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| 5. |
- BAYATI, SOLMAZ, et al.
(författare)
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Mixed micelles of oppositely charged poly(N-isopropylacrylamide) diblock copolymers
- 2017
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Ingår i: Journal of Polymer Science, Part B: Polymer Physics. - : Wiley. - 0887-6266. ; 55:19, s. 1457-1470
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Tidskriftsartikel (refereegranskat)abstract
- Mixed micelle formation between two oppositely charged diblock copolymers that have a common thermosensitive nonionic block of poly(N-isopropylacrylamide) (PNIPAAM) has been studied. The block copolymer mixed solutions were investigated under equimolar charge conditions as a function of both temperature and total polymer concentrations by turbidimetry, differential scanning calorimetry, two-dimensional proton nuclear magnetic nuclear Overhauser effect spectroscopy (2D 1H NMR NOESY), dynamic light scattering, and small angle X-ray scattering measurements. Well-defined and electroneutral cylindrical micelles were formed with a radius and a length of about 3 nm and 35 nm, respectively. In the micelles, the charged blocks built up a core, which was surrounded by a corona of PNIPAAM chains. The 2D 1H NMR NOESY experiments showed that a minor block mixing occurred between the core blocks and the PNIPAAM blocks. By approaching the lower critical solution temperature of PNIPAAM, the PNIPAAM chains collapsed, which induced aggregation of the micelles.
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| 6. |
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| 7. |
- Grundberg, Hans, et al.
(författare)
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Absence of reverse anomeric effect in furanosides
- 2006
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 1520-6904 .- 0022-3263. ; 71:16, s. 5892-5896
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Tidskriftsartikel (refereegranskat)abstract
- A series of conformationally restricted N-"furanosides" has been synthesized, where the carbons of the tetrahydrofuran ring are kept in one plane by a rigid norbornane skeleton, permitting only the ring oxygen to move above or below the tetrahydrofuran ring plane. This causes the substituents of the anomeric carbon to occupy a pseudoaxial or a pseudoequatorial position. On protonation of these "norbornane-furanosides" with trifluoromethanesulfonic acid, all three compounds exhibited decreasing coupling constants for the anomeric proton, indicating a shift toward the pseudoaxial conformation. The coupling constant measurements were supported by volume integration of NOESY cross-peaks, which also showed a change toward the pseudoaxial conformation upon protonation of the nitrogen. These results provide no evidence for the so-called reverse anomeric effect; on the contrary they are in full agreement with a small normal anomeric effect.
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| 8. |
- Hagman, Joel, et al.
(författare)
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On the dissolution state of cellulose in cold alkali solutions
- 2017
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; , s. 2003-2015
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Tidskriftsartikel (refereegranskat)abstract
- We have characterized the dissolved state of microcrystalline cellulose (MCC) in cold alkali [2.0 M NaOH(aq)] solutions using a combination of small angle X-ray (SAXS) and static light scattering (SLS), (Formula presented.)H NMR, NMR self-diffusion, and rheology experiments. NMR and SAXS data demonstrate that the cellulose is fully molecularly dissolved. SLS, however, shows the presence of large concentration fluctuations in the solution, consistent with significant attractive cellulose-cellulose interactions. The scattering data are consistent with fractal cellulose aggregates of micrometre size having a mass fractal dimension (Formula presented.). At 25(Formula presented.) the solution structure remains unchanged on the time scale of weeks. However, upon heating the solutions above 35(Formula presented.) additional aggregation occurs on the time scale of minutes. Decreasing or increasing the NaOH concentration away from the “optimum” 2 M also leads to additional aggregation. This is seen as an increase of the SAXS intensity at lower q values. Addition of urea (1.8 and 3.6 M, respectively) does not significantly influence the solution structure. With these examples, we will discuss how scattering methods can be used to assess the quality of solvents for cellulose.
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| 9. |
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| 10. |
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