Biomedical subjects

Anders Karlsson

Publications and source records attributed to Anders Karlsson.

25 records · Page 2Linked to original sources

PubMed2003

Amperometric detection of exocytosis in an artificial synapse.

A liposome model of exocytosis has been used to examine the nanometer environment of the space between the electrode and the membrane. First, this has been used to test models of coulometric efficiency for different size vesicles with 5- and 33-microm electrodes. The resulting model has a best fit that suggests that the liquid space is approximately 300 nm across the gap. Given this dimension, the volume of the electrode-membrane space is not large enough to accommodate the volume of larger vesicles in cells such as the mast cells of the beige mouse. Second, the model suggests that flow of solution from the exocytosis event is more important than diffusion. Flow from the finite vesicle volume past the electrode leads to less charge passed. Third, and finally, this system can be used to model transport in the synapse and so it is possible to examine the idea that transmitter flows in addition to diffusing from the synapse. This model should be useful in understanding and quantifying the escape of transmitter from synapses in vivo.

Animals↗

PubMed2003

A nanofluidic switching device.

We present a nanofluidic switching function which allows directed transport in lipid bilayer nanotubes ( approximately 100 nm in diameter) between any two or several nanotube-connected vesicle containers (5-10 mum radius) in a large network. Liquid is transported in the form of small vesicular structures (10-15-10-18 L), and the transport direction is controlled by a two-point perturbation technique, where the surface membrane tension is decreased in one container while it is increased in another container. When reaching a target container, the transported vesicular structures could also inject their material into it.

Journal Article↗

PubMed2003

Nanofluidic networks based on surfactant membrane technology.

We explore possibilities to construct nanoscale analytical devices based on lipid membrane technology. As a step toward this goal, we present nanotube-vesicle networks with fluidic control, where the nanotube segments reside at, or very close (<2 microm) to optically transparent surfaces. These nanofluidic systems allow controlled transport as well as LIF detection of single nanoparticles. In the weak-adhesion regime, immobilized vesicles can be approximated as perfect spheres with nanotubes attached at half the height of the vesicle in the axial (z) dimension. In the strong-adhesion regime (relative contact area, Sr* approximately 0.3), nanotubes can be adsorbed to the surface with a distance to the interior of the nanotubes defined by the membrane thickness of approximately 5 nm. Strong surface adsorption restricts nanotube self-organization, enabling networks of nanotubes with arbitrary geometries. We demonstrate LIF detection of single nanoparticles (30-nm-diameter fluorescent beads) inside single nanotubes. Transport of nanoparticles was induced by a surface tension differential applied across nanotubes using a hydrodynamic injection protocol. Controlled transport in nanotubes together with LIF detection enables construction of nanoscale fluidic devices with potential to operate with single molecules. This opens up possibilities to construct analytical platforms with characteristic length scales and volume orders of magnitudes smaller than employed in traditional microfluidic devices.

Liposomes↗

PubMed2002

Effect of temperature on the reversal in the retention order of the enantiomers of mosapride on Chiral-AGP.

The retention order of the enantiomers of mosapride could be controlled by column temperature and mobile phase pH. In the presented paper, temperature studies have been used to study the thermodynamics of the reversal in retention order. A linear relationship was obtained plotting the logarithm of the capacity factor versus the inverted column temperature. However, at higher mobile phase pHs, the logarithm of the separation factor versus the inverted column temperature showed a non-linear behaviour and at the highest mobile phase pH used (pH=7.4), an optimum in the separation factor was observed. The plots showed that the thermodynamics for the two enantiomers of mosapride differ in the studied mobile phase pH interval. Thermodynamic values, enthalpy and entropy were calculated and showed that at a low mobile phase pH, the enantiomeric resolution was caused by differences in enthalpy between the two enantiomers. However, at a higher mobile phase pH, the chiral discrimination was a result of entropy effects. High correlation was obtained between experimental and predicted separation factors at different mobile phase pHs.

Benzamides↗

PubMed2002

Enantiomeric separations of amino alcohols by packed-column SFC on Hypercarb with L-(+)-tartaric acid as chiral selector.

The use of L-(+)-tartaric acid as a chiral mobile phase additive (CMPA) has been investigated in a packed-column SFC system. The CMPA, carbon dioxide, and methanol, containing a high concentration of aliphatic amine additive, were used as the mobile phase and Hypercarb as support [Gyllenhaal O., Karlsson A., SFC of metoprolol and other amino alcohols on Hypercarb (in preparation)]. Good enantioselectivities were obtained for tertiary amine homologues of 2-amino alcohols, used as beta-adrenoreceptor-blocking drugs. Moderate selectivities were observed for aromatic compounds having a second substituent in the ortho-position. The overall retention was influenced by the aromaticity of the analytes as well as the presence of free electron pairs in the molecule. Increased concentrations of CMPA gave higher retention and also increased the enantioselectivity. The practical utility of this present enantioselective system was demonstrated on one batch of (S)-metoprolol that was N-methylated with methyl iodide. The enantiomeric separation was accomplished within 10 min.

Amino Alcohols↗

PubMed2002

Security of quantum key distribution using d-level systems.

We consider two quantum cryptographic schemes relying on encoding the key into qudits, i.e., quantum states in a d-dimensional Hilbert space. The first cryptosystem uses two mutually unbiased bases (thereby extending the BB84 scheme), while the second exploits all d+1 available such bases (extending the six-state protocol for qubits). We derive the information gained by a potential eavesdropper applying a cloning-based individual attack, along with an upper bound on the error rate that ensures unconditional security against coherent attacks.

Journal Article↗

PubMedDate not supplied

New selective method for quantification of organosilanol groups in silicone pre-elastomers.

The silicone elastomers used for drug delivery are normally reinforced by fumed silica, which contains a high density of silanol groups. These inorganic silanol groups have to be deactivated in order to avoid stiffening the uncured pre-elastomer, also called creep hardening. One commonly used way of achieving this deactivation is to mix the material with low molecular mass organosilanols at an elevated temperature. It is important to be able to quantify the nonbonded organosilanols remaining in the material after manufacture. Traditional testing does not distinguish between inorganic silanols and organosilanols. A new selective method for the quantification of organosilanol groups in silicone pre-elastomers has therefore been developed. This method is based on derivatization of the silanol groups with a mixture of dimethylphenylchlorosilane and tetramethyldiphenylsilazane, so that the silanol groups are replaced with a dimethylphenyl group. The derivatized organosilanols are then determined by liquid chromatography using a size exclusion column and a UV detector. No interference was found from other groups normally present in medical grade pre-elastomers, such as vinyls, hydrides, and inorganic bonded silanol on silica or water. The results agreed well with the nonselective Karl Fischer titration for some short chain silanols.

Biocompatible Materials↗