Biomedical subjects

Krister Holmberg

Publications and source records attributed to Krister Holmberg.

15 recordsLinked to original sources

PubMed2006

Incorporation of platinum nanoparticles in ordered mesoporous carbon.

Platinum nanoparticles were incorporated within the pore system of ordered mesoporous carbon (OMC) by impregnating the carbon with a water-in-oil (w/o) microemulsion containing dissolved platinum salt followed by reduction of the platinum ions in situ inside the carbon pore system. The procedure provides preparation of metallic nanoparticles from hydrophilic precursors inside the hydrophobic carbon support structure with simultaneous control of the maximum metal particle size. Electron tomography was used to verify the presence of platinum nanoparticles inside the carbon material.

Journal Article↗

PubMed2006

Water-in-diesel emulsions and related systems.

Water-in-diesel emulsions are fuels for regular diesel engines. The advantages of an emulsion fuel are reductions in the emissions of nitrogen oxides and particulate matters, which are both health hazardous, and reduction in fuel consumption due to better burning efficiency. An important aspect is that diesel emulsions can be used without engine modifications. This review presents the influence of water on the emissions and on the combustion efficiency. Whereas there is a decrease in emissions of nitrogen oxides and particulate matters, there is an increase in the emissions of hydrocarbons and carbon monoxide with increasing water content of the emulsion. The combustion efficiency is improved when water is emulsified with diesel. This is a consequence of the microexplosions, which facilitate atomization of the fuel. The review also covers related fuels, such as diesel-in-water-in-diesel emulsions, i.e., double emulsions, water-in-diesel microemulsions, and water-in-vegetable oil emulsions, i.e., biodiesel emulsions. A brief overview of other types of alternative fuels is also included.

Journal Article↗

PubMed2006

Size control and growth process of alkylamine-stabilized platinum nanocrystals: a comparison between the phase transfer and reverse micelles methods.

Alkylamine-stabilized platinum nanoparticles are synthesized either by the phase-transfer method or in reverse micelles. The phase-transfer method produces nanocrystals that are quite spherical whereas the synthesis in reverse micelles generates a large number of wormlike structures. An alkylamine is used as a stabilizing agent to prevent nanoparticle coalescence, and it is shown that there is an inverse relationship between the alkylamine chain length and the platinum nanoparticle diameter. By comparing alkylamine and alkylthiol analogues, it is found that the integrity of the different crystallites depends on the strength of the interaction between the stabilizing agent and the platinum nanocrystals. The results obtained and the comparison made between the two synthesis methods improve the understanding of the growth mechanisms of platinum nanocrystals in disperse media.

Journal Article↗

PubMed2006

Nonionic ortho ester surfactants as cleavable emulsifiers.

Acid labile surfactants containing an ortho ester link are used as emulsifiers for an aliphatic oil, squalane. The emulsions were made in the presence of a cationic polymer, either polyamine or the corresponding hydrophobically modified polyamine. Spontaneous hydrolysis of the surfactant resulted in emulsions stabilized by polymer together with degradation products from the surfactant. The effect of breakdown of the surfactant on the emulsion was evaluated by means of droplet size measurements and kinetic stability. One linear and one branched nonionic ortho ester surfactant with the same number of oxyethylene units were characterized and used for the purpose. The ortho ester surfactants are complex mixtures of components, ranging from very hydrophilic to very hydrophobic species. The chemical shift of the central methine proton in the ortho ester link is extremely sensitive to the substitution pattern and it was possible to identify by (1)H NMR the components that make up the surfactants, as has been reported earlier. The change in emulsion stability, the change in droplet size and the rate of surfactant hydrolysis were studied at acidic pH at room temperature. Both gas chromatography and (1)H NMR were used in order to monitor the surfactant degradation. The presence of a polymer gave a more sluggish breakdown of the surfactants, probably due to hydrophobic shielding by the polymer. There was a good correlation between increase of droplet size and degree of surfactant decomposition.

Catalysis↗

PubMed2005

Mixed micellar systems of cleavable surfactants.

Previous studies have shown that the alkaline hydrolysis of cleavable ester surfactants is strongly affected by aggregation. The alkaline hydrolysis of the cationic species decyl betainate (DB) is strongly enhanced by micellization, whereas the nonionic species tetra(ethylene glycol)mono-n-octanoate (TEO) is virtually protected when residing in aggregates. In the present work, mixtures of DB and TEO were studied at concentrations above the critical micelle concentration, and the rate of hydrolysis of each surfactant in the presence of the other was assessed. The micellar interaction parameter (beta) was determined from the critical micelle concentrations of various mixtures of the two surfactants. The result (beta = -2.4) indicates a moderate net attraction. The hydrolysis of the surfactants was monitored using 1H NMR. It was shown that the hydrolysis of DB exhibits the main characteristics of the pseudophase ion-exchange model and that the reaction rate decreases with an increasing molar ratio of TEO. There are indications that the hydrolysis rate parallels the expected total counterion binding to the mixed micelles. The hydrolysis of TEO was not affected by the presence of DB. However, complementary experiments showed that it is possible to accelerate or retard the hydrolysis of TEO by coaggregation with stable cationic or anionic surfactants, respectively.

Alkanes↗

PubMed2005

Hydrolyzable nonionic surfactants: stability and physicochemical properties of surfactants containing carbonate, ester, and amide bonds.

A linear and a branched nonionic cleavable surfactants containing a carbonate bond have been prepared from tetra(ethylene glycol) and an alkylchloroformate. The stability of these carbonate surfactants was determined by investigating their hydrolysis and biodegradability characteristics. The hydrolysis was catalyzed by alkali or enzymes (esterase from porcine liver and lipases from Mucor miehei and Candida antarctica B) and was monitored using 1H NMR. It was found that the stability toward alkali was higher for a carbonate surfactant than for a corresponding surfactant with an ester as weak bond. Biodegradation tests resulted in more than 60% degradation after 28 days for both carbonate surfactants. Physicochemical properties, such as critical micelle concentration (CMC), cloud point, area per molecule, and surface tension at the CMC, were determined and compared to those obtained from similar surfactants containing ester, amide, or ether bonds. It was found that the carbonate linkage is hydrophobic and that the oxycarbonyl part of the carbonate group is equivalent, in a formal sense, to an extra methylene group in the alkyl chain of the surfactant.

Journal Article↗

PubMed2005

Use of a mesoporous material for organic synthesis.

A common problem in synthetic organic chemistry is attaining proper contact between lipophilic organic compounds and inorganic salts. Various strategies, for example, phase transfer catalysis (Starks, C. M.; Liotta, C. L.; Halpern, M. Phase Transfer Catalysis: Fundamentals, Applications and Industrial Perspectives; Chapman & Hall: New York, 1994) or use of a microheterogeneous medium such as a microemulsion (Hager, M.; Currie, F.; Holmberg, K. Organic Reactions in Microemulsions. In Colloid Chemistry II; Antonietti, M., Ed.; Topics in Current Chemistry 227; Springer-Verlag: Heidelberg, 2003; p 53) have been worked out to tackle the issue. Here, we report that mesoporous solid materials made from surfactant self-assembly can be used as medium for such reactions. The material is made from silica, and the pore size is large, relatively uniform, and can be controlled with a high degree of precision by the choice of surfactant that is being used as template (Palmqvist, A. E. C. Curr. Opin. Colloid Interface Sci. 2003, 8, 145). The pores are hydrophilic and are filled with an aqueous solution containing the inorganic salt. The porous material is dispersed in the lipophilic organic substrate, that is, 4-tert-butylbenzyl bromide, or in a hydrocarbon solution of this substrate. The reaction occurs at the hydrophilic/lipophilic interface, and, because the interface is large, the reaction is fast. A considerable advantage with this new reaction medium is that the workup procedure is extremely facile. After the reaction is completed, the solid is simply removed by filtering or centrifugation.

Journal Article↗

PubMed2005

Lipopolysaccharide removal by a peptide-functionalized surface.

Five peptides: BPI(85-109); CAP18(106-137); endotoxin inhibitor (EI); GQ33 and GQ33C, derived from lipopolysaccharide (LPS)-binding molecules were investigated for LPS-binding ability with a view to a potential use in extracorporeal therapy. The surface plasmon resonance technique (SPR) was used to monitor the interaction between LPS in solution and the surface-immobilized peptides. The peptides were covalently bound to a model dextran surface via inherent amino groups or via terminally introduced cysteine residues. The results showed that the binding efficacy and binding stability of the peptides varied greatly. The CAP18(106-137) peptide, which exhibited the highest binding efficacy and binding stability, was also immobilized on a poly(ethylene imine)-poly(ethylene glycol) (PEI-PEG) surface through maleimide-terminal PEG. The binding efficacy of the CAP18(106-137) peptide was not significantly affected by the different immobilization methods used in the attachment to a dextran or a PEI-PEG surface. LPS bound selectively to CAP18(106-137) and showed very low unspecific binding to the PEI-PEG surface layer. The EI peptide proved to have a reasonably good binding capacity but a less stable interaction with LPS. The other peptides exhibited much poorer binding efficacy. We believe that the results presented in this work can be of practical value for the development of extracorporeal treatment of patients suffering from septic shock.

Acute-Phase Proteins↗

PubMed2004

Phase-transfer agents as catalysts for a nucleophilic substitution reaction in microemulsions.

The reaction between 4-tert-butylbenzyl bromide and potassium iodide was carried out in microemulsions based on different nonionic surfactants, and the reaction rates were compared with those obtained in two-phase systems with added phase-transfer agent, either a quaternary ammonium salt or a crown ether. The reactions were relatively fast in the microemulsions and extremely sluggish in the two-phase systems without additional phase-transfer agent. Addition of a phase-transfer agent did not accelerate the reaction when a hydrocarbon was used as organic solvent, neither in the two-phase system nor in the microemulsion. When a chlorinated hydrocarbon was used as solvent, phase-transfer catalysis became effective and the rate obtained in the two-phase system with an equimolar amount of phase-transfer agent added was higher than that obtained in the microemulsion. When a catalytic amount of phase-transfer agent was used, the rate in the two-phase system was about the same as the rate obtained in the microemulsion without the phase-transfer agent. The combined approach, that is, use of a microemulsion as the reaction medium and addition of a phase-transfer agent, gave the highest reaction rate. The quaternary ammonium salt (tetrabutylammonium hydrogen sulfate) was a more efficient catalyst in the microemulsion system than the crown ether ([18]crown-6).

Journal Article↗

PubMed2004

A nucleophilic substitution reaction performed in different types of self-assembly structures.

A nucleophilic substitution reaction between 4-tert-butylbenzyl bromide and potassium iodide has been performed in oil-in-water microemulsions based on various C12Em surfactants, i.e., dodecyl ethoxylate with m number of oxyethylene units. The reaction kinetics was compared with the kinetics of reactions performed in other self-assembly structures based on very similar surfactants and in homogeneous liquids. The reaction was fastest in the micellar system, intermediate in rate in the microemulsions, and most sluggish in the liquid crystalline phase. Reaction in a Winsor I system, i.e., a two-phase system comprising an oil-in-water microemulsion in equilibrium with excess oil, was equally fast as reaction in a one-phase microemulsion. The reactions in microemulsion were surprisingly fast compared to reaction in homogeneous, protic liquids such as methanol and ethanol. The rate was independent of the microstructure of the microemulsion; however, the rate was very dependent on the type of surfactant used. When the C12Em surfactant was replaced by a sugar-based surfactant, octyl glucoside, the reaction was much more sluggish. The high reactivity in microemulsions based on C12Em surfactants is belived to be due to a favorable microenvironment in the reaction zone. The reaction is likely to occur within the surfactant palisade layer, where the water activity is relatively low and where the attacking species, the iodide ion, is poorly hydrated and, hence, more nucleophlic than in a protic solvent such as water or methanol. Sugar surfactants become more hydrated than alcohol ethoxylates and the lower reactivity in the microemulsion based on the sugar surfactant is probably due to a higher water activity in the reaction zone.

Journal Article↗

PubMed2004

Surfactant-templated nanomaterials synthesis.

The ability of amphiphilic compounds to self-assemble into well-defined structures can be taken advantage of for synthesis of inorganic materials with nanometer dimensions. The principle, which is biomimetic in character, is discussed with special attention put on three areas: microemulsion-based synthesis of nanoparticles, preparation of mesoporous materials from surfactant templates, and surfactant-mediated crystallization.

Biocompatible Materials↗

PubMed2004

Oxidation of self-organized nonionic surfactants.

Nonionic surfactants containing a polyoxyethylene headgroup are known to slowly undergo oxidative degradation when exposed to air. The oxidation, which starts by abstraction of a hydrogen atom from a methylene group in alpha-position to an ether oxygen, is accelerated by metal ions. Silver ion mediated oxidation of a technical grade surfactant of this type, Brij 30, was investigated in two types of self-assembled systems, a water-in-oil microemulsion and a liquid crystalline phase. It was found that in both systems the longer homologues, i.e., the surfactant homologues that carry a longer polyoxyethylene chain, decompose faster than the shorter homologues. This trend was found to be more pronounced when the surfactant is present in a liquid crystal than in a microemulsion. The difference is explained in terms of differences in accessibility of the polyoxyethylene chains to the silver ions.

Letter↗

PubMed2004

Impact of polymer surface affinity of novel antifouling agents.

In a previous study we found two agents, the alpha(2)-agonist medetomidine ((+/-)-4-[1-(2,3-dimethylphenyl)ethyl]-1H-imidazole) and the alpha(2)-agonist clonidine (2-(2,6-dichloroanilino)-2-imidazoline), that specifically and efficiently impede settlement of the barnacle Balanus improvisus, one of the most serious biofouling organisms in Swedish waters. Medetomidine, but not clonidine, is known to adsorb to solid polystyrene (PS) surfaces in the presence of salt, a feature that is of particular interest in attempts to develop an efficient antifouling surface. We show that medetomidine, but not clonidine, has a significant ability to adsorb to untreated (hydrophobic) PS in two different incubation media: filtered seawater (FSW) and deionized water (mQ). At negatively charged (hydrophilic) PS, medetomidine displays a strong interaction with the surface in both incubation media. At the hydrophilic PS, clonidine also displays a significant interaction with the surface when incubated in mQ and a weaker, but not significant, interaction when incubated in FSW. By studying the effects of time, incubation media, and pH on the adsorption of medetomidine and clonidine, we suggest that medetomidine is associated to hydrophobic PS by means of hydrophobic interactions, while the adsorption of medetomidine and clonidine to hydrophilic PS contains elements of electrostatic interaction. Using time-of-flight secondary ion mass spectroscopy (TOF-SIMS) we detected only weak signals from medetomidine on the hydrophobic PS surfaces, while strong medetomidine signals were observed on hydrophilic PS. This suggests that the adsorbed medetomidine, to a greater extent, desorbed from the hydrophobic rather than from the hydrophilic PS surfaces during exposure to vacuum. The strong surface affinity of medetomidine on both types of surfaces and the preserved antifouling activity are valuable features in designing a marine coating.

Adsorption↗

PubMed2003

Structure and catalytic properties of nanosized alumina supported platinum and palladium particles synthesized by reaction in microemulsion.

Mixtures of nanosized platinum and palladium particles have been prepared by reduction of salt-containing microemulsion droplets using hydrazine as the reducing agent. To avoid possible negative effects of the presence of sulfur compounds during the preparation the microemulsion was made using the sulfur-free nonionic polyoxyethylene 4 lauryl ether surfactant. Transmission electron microscopy showed that the as-prepared mixtures contained crystalline platinum particles of fairly homogeneous size (20 to 40 nm) with adsorbed amorphous palladium particles 2 to 5 nm in size. Catalyst samples were prepared by depositing the nanoparticles on a gamma-Al(2)O(3) support followed by heating in air at 600 degrees C. Alloyed particles of platinum and palladium with sizes ranging from 5 to 80 nm were obtained during the heating. The majority of the particles had the fcc structure and their compositional range was dependent upon the Pt:Pd molar ratio of the microemulsion. A catalyst prepared from a microemulsion with a 20:80 Pt:Pd molar ratio showed the highest catalytic activity for CO oxidation, while pure platinum and palladium catalysts showed higher sulfur resistance. These results differ from the performance of conventional wet-impregnated catalysts, where a 50:50 Pt:Pd molar ratio resulted in the highest catalytic activity as well as the highest sulfur resistance.

Journal Article↗

PubMed2001

Kinetics of the Formation of Nano-Sized Platinum Particles in Water-in-Oil Microemulsions.

The effect of surfactant type and temperature on the kinetics of the formation of platinum nanoparticles in water-in-oil microemulsions by chemical reduction of PtCl(6)(2-) were examined with time-resolved UV-vis absorption spectroscopy. The surfactants used were poly(ethylene glycol)monododecyl ethers (C(12)E(4), C(12)E(5), C(12)E(6)), sodium bis(2-ethylhexyl)sulphosuccinate (AOT), and mixtures of the alcohol ethoxylates and AOT. The oil domain was n-heptane. The microemulsion droplet size was measured by a dynamic light scattering technique (photon correlation spectroscopy) and the final platinum particle size was determined by transmission electron microscopy. The reaction rate for platinum particle formation was approximately the same in microemulsions based on either of the alcohol ethoxylates but considerably lower for microemulsions based on AOT. In microemulsions based on mixtures of an alcohol ethoxylate and AOT the reaction rate was similar to that obtained when alcohol ethoxylate was the sole surfactant. The reaction was observed to be particularly rapid in microemulsions based on combinations of AOT and C(12)E(5) or C(12)E(6), and the rate was relatively independent of the ratio of the nonionic and anionic surfactants. The reaction was found to be of first order for platinum nanoparticles formed in alcohol ethoxylate-, AOT-C(12)E(5)-, and AOT-C(12)E(6)-based microemulsions, whereas in microemulsions with AOT and AOT-C(12)E(4) the reaction rate seemed to be of higher reaction order. The platinum particles were found to be less than 5 nm in average diameter, which was consistent with the microemulsion droplet size. Copyright 2001 Academic Press.

Journal Article↗