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| 11. |
- Milleding, P, et al.
(författare)
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Surface energy of non-corroded and corroded dental ceramic materials before and after contact with salivary proteins
- 1999
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Ingår i: European Journal of Oral Sciences. - 0909-8836 .- 1600-0722. ; 107, s. 384-392
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Tidskriftsartikel (refereegranskat)abstract
- After sintering and autoglazing, the surface free energy of seven different dental ceramic materials was determined by contact angle measurements, using a Dynamic Adsorption Tester and three different standard probe liquids, before and after in vitro corrosion and also before and after incubation with human whole saliva. The surface free energy was calculated from the Young-Dupre-equation and the polar and non-polar components were determined. The total surface free energy (range 50±5 mN/m) did not differ significantly between the different ceramic materials or between corroded and non-corroded specimens. The basic surface chemical character persisted after corrosion, although reduced to a lower level, which probably reflects ion exchange processes at the exposed surfaces. After saliva incubation the basic component of the surface free energy increased, which may be interpreted as the result of salivary proteins binding to the basic surface with their acidic groups, orienting their basic sites towards the bulk phase. Selective adsorption of proteins to biosurfaces will no doubt influence both microbiological colonisation and cell adhesion, although the exact mechanisms are not known.
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- Gutfelt, S, et al.
(författare)
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Microemulsions as reaction medium for surfactant synthesis
- 1997
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Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 128, s. 265-271
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Tidskriftsartikel (refereegranskat)abstract
- Various microemulsion formulations were evaluated as reaction medium for synthesis of a surface active compound, decyl sulfonate, from decyl bromide and sodium sulfite. The reaction rate was fast both in water-in-oil and in bicontinuous microemulsions based on nonionic surfactant. Two-phase systems with added phase transfer agent (quaternary ammonium salt or crown ether) was much less efficient. It is postulated that the low efficiency of the phase transfer agents in catalyzing the reaction is caused by strong ion pair formation between the product formed, decyl sulfonate, and the phase transfer agent. To prove this point decyl bromide was reacted with two other nucleophiles, sodium cyanide and sodium azide. Neither of these give a reaction product that can form ion pair with the phase transfer agent. With these reagents phase transfer catalysis was almost as efficient as synthesis in microemulsion. It was also demonstrated that the rate of decyl sulfonate formation in microemulsion can be increased further by addition of a small amount of cationic surfactant. The choice of surfactant counterion is decisive of the effect on reaction rate, however. Whereas a small non-polarizable ion, such as acetate, gives a considerable reaction rate increase, a large polarizable ion, such as bromide, slows down the reaction. Bromide is believed to interact so strongly with the interface that it prevents the reacting ion, sodium sulfite to reach into the interfacial zone.
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- Holmberg, K, et al.
(författare)
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Microemulsions as reaction medium for a substitution reaction
- 1996
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Ingår i: Progress in Colloid and Polymer Science. - 0340-255X .- 1437-8027. ; 100, s. 281-285
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Tidskriftsartikel (refereegranskat)abstract
- Synthesis of sodium decyl sulfonate from 1-bromodecane and sodium sulfite was performed in microemulsions based on nonionic surfactant, in liquid crystals and in 2-phase systems with or without a phase transfer agent added. The reactions were fast in both bicontinuous and W/O microemulsion, slower in liquid crystal and very sluggish in 2-phase systems also in the presence of a Q salt or a crown ether. Addition of a small amount of anionic surfactant to the microemulsion systems decreased reaction rate. Addition of cationic surfactant either increased or decreased the reaction rate depending on the choice of counterion.
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| 18. |
- Lam, S, et al.
(författare)
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Surfactants in heterophase polymerization: A study of film formation using atomic force microscopy
- 1997
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Ingår i: Journal of Applied Polymer Science. - 0021-8995 .- 1097-4628. ; 66, s. 187-198
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Tidskriftsartikel (refereegranskat)abstract
- Film formation of three different latices was studied using atomic force microscopy. The latices were made from a mixture of butyl acrylate, styrene and acrylic acid using either a polymerizable or an unreactive aionic surfactant as emulsifier. Sodium 11-crotonoyloxyundecan- 1-ylsulfate and sodium-3-(sulfopropyl)tetradecylmaleate were used as reactive surfactant and the unreactive surfactant was sodium dodecylsulfate (SDS). The conventional surfactant was found to migrate to the surface of the latex film to a much greater extent than the reactive surfactants; however, also the latter were incompletely anchored to the particle. The maleate surfactant was bound to a higher degree than the crotonate, a finding which is in line with the relative reactivities of the two surfactants.
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| 19. |
- Oh, S-G, et al.
(författare)
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Effect of hydrocarbon chain length on yield of lipase catalyzed triglyceride synthesis in microemulsion
- 1996
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 181, s. 341-343
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Tidskriftsartikel (refereegranskat)abstract
- Previous work on lipase catalyzed esterification of glycerol with fatty acids in w/o microemulsions gave monoglyceride as the main reaction product. Only traces of triglyceride were obtained. We show here that the reason triglycerides are not formed in these systems is that the diglyceride formed in the oil-water interfacial zone partitions into the continuous hydrocarbon domain. It is then inaccessible to the enzyme. The yield of triglyceride is increased by using longer hydrocarbons as the oil component. These have poorer solvency for mono- and diglycerides. When the hydrocarbon chain length exceeds that of the glyceride acyl groups, triglyceride is the main reaction product.
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| 20. |
- Oh, S-G, et al.
(författare)
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Microemulsions as reaction media for synthesis of sodium decyl sulfonate II: Role of ionic surfactants
- 1995
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Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 104, s. 217-222
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Tidskriftsartikel (refereegranskat)abstract
- Synthesis of sodium decyl sulfonate in various types of microemulsions based on nonionic surfactants have been reported in our previous paper. As a continuation of this study the effect of ionic surfactants with different counterions on the reaction profile was investigated. As expected, the electrical potential of microemulsion droplets significantly influenced the degree of conversion probably by affecting the diffusion of ionic species into the interfacial region where the reaction occurs. The reaction yield was also highly dependent on the type of counterions. Tetradecyl trimethyl ammonium acetate increased the yield, but sodium dodecyl sulfate and tetradecyl trimethyl ammonium bromide gave decreased conversion. The counterion effect was explained by the competitive association of ions with the surfactant monolayer at the oil/water interface.
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| 21. |
- Oh, S-G, et al.
(författare)
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Microemulsions as reaction medium for synthesis of sodium decyl sulfonate I: Role of microemulsion composition
- 1995
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Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 97, s. 169-179
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Tidskriftsartikel (refereegranskat)abstract
- Reaction kinetics for the formation of sodium decyl sulfonate from alkyl halide and sodium sulfite in microemulsions based on nonionic surfactant were investigated and compared with those in oil-water two-phase systems. Reactions were run at room temperature at various oil-water ratios. Whereas at room temperature almost no reaction occurred in the two-phase systems. all microemulsion-based reactions proceeded at a fair rate. No clear relationship between microemulsion structure and reaction rate could be seen. An equation describing reaction kinetics in the microemulsion system has been derived based on the pseudophase model.
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| 23. |
- Sharma, P, et al.
(författare)
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Cloning and functional expression of the guinea pig neuropeptide Y Y2 receptor
- 1998
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Ingår i: Regulatory Peptides. - : Elsevier BV. - 0167-0115. ; 75-76, s. 23-28
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Tidskriftsartikel (refereegranskat)abstract
- Five neuropeptide Y (NPY) receptor subtypes have been cloned in mammals. The degree of sequence conservation differs considerably between subtypes as well as between evolutionary lineages. To shed further light on this, we have cloned the five NPY receptors in the guinea pig. Here, we report the cloning of the guinea pig Y2 receptor. The Y2 receptor is generally highly conserved, with 90-95% identity between different orders of mammals, including the guinea pig. The guinea pig receptor has a divergent cytoplasmic tail, indicating possible differences in regulation of signalling and/or down regulation. COS-7 cells transiently transfected with the gpY2 receptor show saturable 125I-PYY binding with a Kd = 6 pM. In displacement experiments, the gpY2 receptor was similar to the human and rat receptors with the following rank order of potencies: pNPY > pPYY > pNPY13-36 = pNPY22-36 > [Leu31Pro34]NPY > BIBP3226. Thus, the guinea pig Y2 receptor is well conserved in comparison with human and rat with regard to both amino acid sequence and pharmacological profile.
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