Maria Kempe

Separation of amino acids, peptides and proteins on molecularly imprinted stationary phases.

Stationary phases, to be used in high-performance liquid chromatography, were tailor-made for the separation of amino acids, peptides and proteins. The stationary phases were prepared by molecular imprinting, applying two different approaches. Low-molecular-mass compounds were imprinted in bulk polymers by copolymerization of functional monomers and cross-linkers in the presence of the compound of interest, the print molecule. These polymers were, after extraction of the print molecule, successfully applied as chiral stationary phases, showing high resolution and load capacity. The development of a surface-imprinting approach for the preparation of stationary phases selective for proteins is also discussed.

Molecular imprinting used for chiral separations

Molecular imprinting is a promising technique for the preparation of synthetic polymers of predetermined specificity. Functional monomers are copolymerized with crosslinkers in the presence of the desired molecule, the imprint molecule. The use of these polymers as chiral stationary phases is discussed. Other applications, such as antibody-mimics, enzyme-like catalysts and sensors, are also focused upon.

Direct resolution of naproxen on a non-covalently molecularly imprinted chiral stationary phase

A synthetic polymer selective for (S)-naproxen was prepared by molecular imprinting. 4-Vinylpyridine and ethylene glycol dimethacrylate were copolymerised in the presence of the template, (S)-naproxen. The template was extracted from the polymer, leaving specific recognition sites, complementary to the template. The polymer was utilized as a stationary phase in HPLC. Racemic naproxen was efficiently resolved on the polymer. Furthermore, the polymer was able to separate naproxen from the structurally related ibuprofen and ketoprofen.

Binding Studies on Substrate- and Enantio-Selective Molecularly Imprinted Polymers

A molecularly imprinted polymer was prepared using tert-butyloxycarbonyl-L-phenylalanine as the print molecule and methacrylic acid as the functional monomer. The bulk polymer obtained was ground, sieved, packed into a column and investigated in the HPLC-mode by frontal chromatography to determine the number of binding sites and dissociation constants for the enantiomers interacting with the polymer. The dissociation constant for the L-enantiomer of the print molecule was lower than for the D-enantiomer (6.3 mM and 8.1 mM, respectively). This means that the affinity for the L-enantiomer was higher than for the D-enantiomer. The number of binding sites in the polymer giving rise to these dissociation constants were determined to be 28 μmol per g dry polymer. (Less)

The use of magnetite nanoparticles for implant-assisted magnetic drug targeting in thrombolytic therapy.

Implant-assisted targeting of magnetic particles under the influence of an external magnetic field has previously been verified through mathematical modeling, in vitro studies, and in vivo studies on rat carotid arteries as a feasible method for localized drug delivery. The present study focuses on the development of nanoparticles for the treatment of in-stent thrombosis. Magnetic nanoparticles in the size-range 10-30 nm were synthesized in a one-pot procedure by precipitation of ferrous hydroxide followed by oxidation to magnetite. The nanoparticles were silanized with tetraethyl orthosilicate in the presence of triethylene glycol and/or polyethylene glycol. The surface coated magnetite nanoparticles were activated with either N-hydroxysulfosuccinimide or tresyl chloride for covalent immobilization of tissue plasminogen activator (tPA). Hysteresis loops showed saturation magnetizations of 55.8, 44.1, and 43.0 emu/g for the naked nanoparticles, the surface coated nanoparticles, and the tPA-nanoparticle conjugates, respectively. The hemolytic activity of the nanoparticles in blood was negligible. An initial in vivo biocompatibility test in pig, carried out by intravascular injection of the nanoparticles in a stented brachial artery, showed no short-term adverse effects. In vitro evaluation in a flow-through model proved that the nanoparticles were captured efficiently to the surface of a ferromagnetic coiled wire at the fluid velocities typical for human arteries. A preliminary test of the tPA-nanoparticle conjugates in a pig model suggested that the conjugates may be used for treatment of in-stent thrombosis in coronary arteries.

Introduction of molecularly imprinted polymers as recognition elements in conductometric chemical sensors

The construction and demonstration of a conductometric chemical sensor based on a molecularly imprinted polymer (MIP) is reported. Benzyltriphenylphosphonium ions, chosen as a model, were used as the analyte. The MIP based sensors gave, when exposed to the analyte, a significantly higher conductivity reading than the reference sensors. Furthermore, the use of molecularly imprinted polymers as artificial recognition systems in sensor technology is discussed.

Receptor binding mimetics: a novel molecularly imprinted polymer

A novel molecularly imprinted polymer was prepared by copolymerization of trimethylolpropane trimethacrylate (1) and methacrylic acid (3) in the presence of a dipeptide acting as the template. The recognition capability of the synthetic receptor-like binding sites produced in the polymer network for the peptide was demonstrated by using the polymer as a chiral stationary phase in HPLC. The polymer was superior to previously reported molecularly imprinted polymers in that unusually high racemic resolution and load capacity were demonstrated.

Influence of salt ions on binding to molecularly imprinted polymers

AbstractSalt ions were found to have an influence on template binding to two model molecularly imprinted polymers (MIPs), targeted to penicillin G and propranolol, respectively, in water–acetonitrile mixtures. Water was detrimental to rebinding of penicillin G whereas propranolol bound in the entire water–acetonitrile range tested. In 100% aqueous solution, 3-M salt solutions augmented the binding of both templates. The effects followed the Hofmeister series with kosmotropic ions promoting the largest increase. Binding was mainly of a non-specific nature under these conditions. In acetonitrile containing low amounts of water, the specific binding to the MIPs increased with the addition of salts. Binding of penicillin G followed the Hofmeister series while an ion-exchange mechanism was observed for propranolol. The results suggest that hydration of kosmotropic ions reduces the water activity in water-poor media providing a stabilizing effect on water-sensitive MIP–template interactions. The effects were utilized to develop a procedure for molecularly imprinted solid-phase extraction (MISPE) of penicillin G from milk with a recovery of 87%. FigureBinding augmentation to a penicillin G imprinted MIP at the addition of kosmotropic ions.

Nanomedicine’s promising therapy: magnetic drug targeting

Magnetic drug targeting is a promising therapy that can benefit patients, as well as provide novel opportunities for pharmaceutical and medical technology/device industries.

QSRR analysis of β-lactam antibiotics on a penicillin G targeted MIP stationary phase

The imprinting factors of the β-lactam antibiotics penicillin V, methicillin, nafcillin, oxacillin, cloxacillin, dicloxacillin, and piperacillin on a poly(methacrylic acid-co-trimethylolpropane trimethacrylate) molecularly imprinted stationary phase targeted for penicillin G were correlated with molecular descriptors obtained by molecular computation. One-parameter linear regression and multivariate data analysis by principal component analysis and partial least square regression indicated that descriptors associated with molecular topology, shape, size, and volume were highly correlated with the imprinting factor and influential on the derived models.