| 1. |
|
|
| 2. |
- Barauskas, Justas, et al.
(författare)
-
Towards redox active liquid crystalline phases of lipids: a monoolein/water system with entrapped derivatives of ferrocene
- 2003
-
Ingår i: Chemistry and Physics of Lipids. - 0009-3084. ; 123:1, s. 87-97
-
Tidskriftsartikel (refereegranskat)abstract
- The phase and electrochemical behavior of the aqueous mixtures of monoolein (MO) and synthetic ferrocene (Fc) derivatives containing long alkyl chains -(Z)-octadec-9-enoylferrocene (1), (Z)-octadecen-9-ylferrocene (2), and ferrocenylmethyl (Z)-octadec-9-enoate (3)-were studied. At low hydration, the reversed micelles (L-2 phase) and cubic Q(230) phase of MO can accommodate relatively high amounts ( > 6 wt.%) of the Fc-derivative 2, whereas at high hydration, the pseudoternary cubic phase Q(224) is destabilized even at about 2 wt.% of this Fc. Increasing the Fc-derivative content induces L-alpha L-2 and L-alpha --> reversed bicontinuous cubic phase (Q(II)) H-II transitions depending upon hydration. A rough study of the MO system containing compounds I and 3 indicates very similar phase behavior to that of the MO/2/H2O system. Compound 2 apparently has no effect on the lipid monolayer thickness in the pseudoternary L-alpha, H-II and Q(II) liquid crystalline phases of MO. Within a 3D-structure of the Q224 phase, derivatives 1-3 exhibit electrochemical activity on the gold electrode. The one-electron redox conversion processes are electro-chemically quasi-reversible and controlled by diffusion. The values of apparent diffusion coefficient (D-app) and heterogeneous electron-transfer rate constant (k(s)) of Fcs are significantly lo er in the cubic,phase matrix when compared to the acetonitrile solution. By contrast, the MO H-II phase with entrapped Fc-derivatives does not exhibit electrochemical activity on the electrode surface. It is suggested that the diffusional anisotropy and/or localized aggregation of compounds 1-3 within a 2D-structure of the H-II phase account(s) for the latter observation. (C) 2003 Elsevier Science Ireland Ltd. All rights reserved.
|
|
| 3. |
- Mattisson, C, et al.
(författare)
-
Diffusivity measurements using holographic laser interferometry in a cubic lipid-water phase
- 1996
-
Ingår i: Chemistry and Physics of Lipids. - 0009-3084. ; 84:1, s. 1-12
-
Tidskriftsartikel (refereegranskat)abstract
- The diffusion of glucose in a cubic lipid-water phase was studied with holographic laser interferometry. The X-ray diffraction data showed that the structure of the cubic phase could be described as a primitive cubic lattice under the experimental conditions used. The present study shows that holographic laser interferometry is suitable for determining the concentration profile due to diffusion, even for such intriguing structures as cubic lipid-water phases. The concentration profile obtained revealed that the diffusion process can be described by Fick's Second Law, and the effective diffusion coefficient was obtained by fitting a theoretical concentration profile to the experimental data. The diffusion coefficient obtained for glucose was four times smaller than the corresponding coefficient in aqueous bulk solution. The effective diffusion coefficient in the cubic phase is greater than that predicted by models developed for polymer gels.
|
|
| 4. |
- Persson, Mattias, et al.
(författare)
-
Enzymatic fatty acid exchange in digalactosyldiacylglycerol
- 2000
-
Ingår i: Chemistry and Physics of Lipids. - 0009-3084. ; 104:1, s. 13-21
-
Tidskriftsartikel (refereegranskat)abstract
- Six different lipases were screened for their ability of acidolysis between digalactosyldiacylglycerol (DGDG) and heptadecanoic acid in toluene. Lipases from Geotrichum candidum, Alcaligenes sp. and Penicillium camembertii did not catalyse the acidolysis reaction. Rhizopus arrhizus and Rhizomucor miehei (Lipozyme) catalysed the acidolysis but produced a mixture of DGMG, DGDG, acyl-DGMG and acyl-DGDG. The extra acyl group is bound to the primary hydroxyl of the digalactosyl moiety. Candida antarctica also catalysed the acidolysis but the TLC analysis showed bands with higher R(f) values than acyl-DGDG, these probably being different tetra and higher esters. R. arrhizus lipase was the most promising enzyme under the conditions used, with no tetra esters being formed and giving the highest reaction rate of the enzymes investigated. Low water activity (0.06 or 0.11) and high fatty acid concentration (400 mM) increased the formation of acyl-DGDG whilst higher water activities (0.33 and 0.54) increased the amount of DGMG when R. arrhizus lipase was used as catalyst. At a water activity of 0.11 and a fatty acid concentration of 400 mM a yield of 24% modified DGDG was obtained. In this product the fatty acid originally present in the sn-1 position had been exchanged by heptadecanoic acid. Copyright (C) 2000 Elsevier Science Ireland Ltd.
|
|
| 5. |
- Svensson, I., et al.
(författare)
-
Phase behaviour of aqueous systems of enzymatically modified phosphatidylcholines with one hexadecyl and one hexyl or octyl chain
- 1993
-
Ingår i: Chemistry and Physics of Lipids. - 0009-3084. ; 66:3, s. 195-197
-
Tidskriftsartikel (refereegranskat)abstract
- Phosphatidylcholines composed of a hexadecyl chain in the 2-position and a hexyl or octyl chain in the l-position (C6C16PC or C8C16PC) were prepared from dipalmitoylphosphatidylcholine by lipase-catalyzed transesterification; the aqueous phase properties of the products were examined. In the C8C16PC-water system, a lamellar liquid-crystalline phase was dominant. Like all long-chain phosphatidylcholines studied earlier, a liposomal dispersion was formed in the presence of excess water. In the C6C16PC system, a new type of phase behaviour was observed; at high water content, an L3 phase was formed.
|
|
| 6. |
- Virto, Carmen, et al.
(författare)
-
Hydrolytic and transphosphatidylation activities of phospholipase D from Savoy cabbage towards lysophosphatidylcholine
- 2000
-
Ingår i: Chemistry and Physics of Lipids. - 0009-3084. ; 106:1, s. 41-51
-
Tidskriftsartikel (refereegranskat)abstract
- The hydrolysis and transphosphatidylation of lysophosphatidylcholine (LPC), with a partially purified preparation of phospholipase D (PL D) from Savoy cabbage, was investigated. These reactions were about 20 times slower than the hydrolysis of phosphatidylcholine (PC) in a micellar system. For the transfer reaction, 2 M glycerol was included in the media, which suppressed the hydrolytic reaction. Both reactions presented similar V(max) values, suggesting that the formation of the phosphatidyl-enzyme intermediate is the rate-limiting step. The enzyme had an absolute requirement for Ca2+, and the optimum concentration was approximately 40 mM CaCl2. K(Ca)(app) was calculated to be 8.6±0.74 mM for the hydrolytic and 10±0.97 mM for the transphosphatidylation reaction. Both activities reached a maximum at pH 5.5, independent of Ca2+ concentration. Kinetic studies showed that the Km(app) for the glycerol in the transphosphatidylation reaction is 388±37 mM. Km(app) for the lysophosphatidylcholine depended on Ca2+ concentration and fell between 1 and 3 mM at CaCl2 concentrations from 4 to 40 mM. SDS, TX-100, and CTAB did not activate the enzyme as reported for phosphatidylcholine hydrolysis; on the contrary, reaction rates decreased at detergent concentrations at or above that of lysophosphatidylcholine. Copyright (C) 2000 Elsevier Science Ireland Ltd.
|
|
| 7. |
- Virto, Carmen, et al.
(författare)
-
Two-enzyme system for the synthesis of 1-lauroyl-rac-glycerophosphate (lysophosphatidic acid) and 1-lauroyl-dihydroxyacetonephosphate
- 2000
-
Ingår i: Chemistry and Physics of Lipids. - 0009-3084. ; 104:2, s. 175-184
-
Tidskriftsartikel (refereegranskat)abstract
- A combination of two enzymes, phospholipase D (PL D) and C (PL C), was investigated for the production of two lysophospholipids, 1-lauroyl-rac- glycerophosphate (1-LGP) and 1-lauroyl-dihydroxyacetonephosphate (1-LDHAP). The high transphosphatidylation ability of phospholipase D from Streptomyces sp. allowed the formation of 1-lauroyl-phosphatidylglycerol (1-LPG) and 1- lauroyl-phosphatidyldihydroxyacetone (1-LPDHA) from phosphatidylcholine (PC) and 1-monolauroyl-rac-glycerol (1-MLG) and 1-lauroyl-dihydroxyacetone (1- MDHA), respectively. A two-phase system, diethyl ether/water, was chosen for the convenience of the recovery of the water insoluble products. A similar two-phase system was used for hydrolysis of the complex phospholipids by phospholipase C form Bacillus cereus, which released both lysophospholipids. Only trace amounts of phosphatidic acid (PA) were detected showing that the enzyme is highly selective for the release of the diacylglycerol and 1- lauroyl-rac-glycerophosphate and 1-lauroyl-dihydroxyacetonephosphate.
|
|
| 8. |
- Waninge, Rianne, et al.
(författare)
-
Phase equilibria of model milk membrane lipid systems.
- 2003
-
Ingår i: Chemistry and Physics of Lipids. - 0009-3084. ; 125:1, s. 59-68
-
Tidskriftsartikel (refereegranskat)abstract
- The phase behaviour of mixtures of recombined milk membrane lipids dioleoylphosphatidylcholine (DOPC), sphingomyelin (SM), dioleoylphosphatidylethanolamine (DOPE), phosphatidylinositol (PI) and dioleoylphosphatidylserine (DOPS) in 60% water was examined as a function of temperature between 5 and 90 °C. The aim was to examine under which lipid composition the average properties turn from balanced over to hydrophobic. The phase boundaries were determined by small angle X-ray diffraction (SAXD) and differential scanning calorimetry (DSC). The lamellar phase was dominating in the DOPC/SM/DOPE system. The phase boundary for the reversed hexagonal phase was only observed at high DOPE content within the examined temperature interval. The anionic phospholipids PI and DOPS induced a swollen lamellar phase, but no significant change of the transition between the lamellar phase and the reversed hexagonal phase was observed.
|
|
| 9. |
|
|
| 10. |
|
|
