Stefan Löfås

A novel hydrogel matrix on gold surfaces in surface plasmon resonance sensors for fast and efficient covalent immobilization of ligands

Gold surfaces intended for surface plasmon resonance sensors have been derivatized with a flexible matrix composed of carboxymethylated dextran to provide fast and efficient coupling of proteins and other ligands at low concentrations using the principles of ionic pre-concentration; these hydrophilic and protein compatible hydrogel surfaces allow increased immobilization capacity as compared to monolayer based coatings, for applications in biospecific interaction analysis.

Dextran modified gold surfaces for surface plasmon resonance sensors: immunoreactivity of immobilized antibodies and antibody-surface interaction studies

Abstract Recently, the modification of gold surfaces with covalently bound carboxylated dextran was described, for use in biospecific interaction studies in an analytical system based on surface plasmon resonance (SPR). In this study, the antigen binding immunoreactivity of antibodies immobilized on the modified surfaces was investigated with the SPR-based system. Four different monoclonal antibodies specific against the antigens β 2 -microglobulin, luteinizing hormone, human transferrin, and immunoglobulin E, were covalently attached by amine coupling to the dextran layer and the antigen binding capacities were evaluated for different amounts of bound antibody. High immunoreactivities were obtained with molar activities ranging from 0.6 to 1.5 over a wide range of surface concentrations. Interaction studies between carboxymethylated dextran surfaces and antibodies showed that, in comparison with unmodified gold surfaces, the modified surface had low nonspecific adsorption and high capacity for antibody immobilization.

Label-free kinetic binding data as a decisive element in drug discovery.

The emerging possibilities to obtain label-free, kinetic-based binding data for drug–target and drug absorption, distribution, metabolism and excretion (ADME)–marker interactions have proven useful in many drug discovery related issues. Multiple reports have demonstrated that the common use of affinity as an early measure of drug potency may be directly misleading. This review summarises findings in the literature related to compound selection in the drug discovery process. It is important to understand the different properties of association and dissociation rates, the former being related to both structure and dosage and the latter depending solely on molecular structure. By performing parallel optimisations of association and dissociation rates, compounds with desirable kinetic profiles for target binding may be generated. In addition, compound selection may also consider the kinetic properties of the drug–ADME–marker binding profiles, further refining the quality of compounds early in the drug discovery process. The promising results found in the literature indicate that kinetic data on drug–protein interactions may soon become a crucial decisive element in modern drug discovery.

α-Chlorination with carbon tetrachloride and α-1H/2H exchange with [2H]chloroform of amidines

The bicyclic amidines (1)–(4) have been found to be α-chlorinated with carbon tetrachloride at room temperature in darkness under nitrogen, (1) and (3) also undergo 1H–2H exchange in the α-position with [2H]-chloroform.

Solvent- and reagent-induced change of rate-limiting step in acid-catalysed α-halogenation of amidines with tetrahalogenomethanes

The acid-catalysed α-halogenation of amidines with tetrahalogenomethanes involves the intermediate formation of the ketene aminal tautomer, which then reacts with the tetrahalogenomethane. The kinetics of the acid-catalysed reaction of 2,10-diazabicyclo[4.4.0]dec-1-ene (1) with CCl4 in benzene, methylene dichloride, and DMF, and with CBrCl3 in DMF, respectively, have been investigated. The kinetics of the reaction of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)(5) with CCl4 in DMF and DMSO has also been studied. The reaction of amidine (1) with CCl4 in DMF is first-order in [(1)], close to zero-order in [CCl4], and close to pseudo-first-order in [acid], indicating rate-limiting formation of the ketene aminal (2). In contrast, in the non-polar solvents the rate of reaction is found to be limited by the reaction of the tautomer (2) with CCl4, which is much slower than in DMF. This change of rate-limiting step is also observed for the reaction of (1) in benzene when CBrCl3 is exchanged for CCl4, and is most likely induced by a much faster reaction of tautomer (2) with CBrCl3 than with CCl4. The present results support a non-chain one-electron-transfer mechanism for the halogenation step, with formation of an intermediate radical-ion pair. A pKa difference of 2.9 between amidine (1) and the α-chlorinated product (4) has also been determined using an appropriate 13C n.m.r. method.

The intermediacy of trichloromethyl anions in the reaction of enamines with bromotrichloromethane

Reaction of N-(cyclohex-1-enyl)pyrrolidine with bromotrichloromethane in dimethyl sulphoxide generates trichloromethyl anions which have been trapped by addition to iminium cations or converted into chloroform in the presence of a hydrogen ion source.