Microwave-assisted decarboxylation of bicyclic 2-pyridone scaffolds and identification of Abeta-peptide aggregation inhibitors

A reagent-free microwave-assisted decarboxylation procedure for carboxylic acid functionalized bicyclic 2-pyridones has been developed. This new method, based on microwave heating at 220 degrees C for 600 seconds in N-methyl pyrrolidone (NMP), proved to be practical and very efficient, resulting in decarboxylated 2-pyridones in near-quantitative yields. The decarboxylated products and the intermediate 2-pyridones in the form of carboxylic acid methyl esters and carboxylic acids were screened for their effect on Abeta-peptide aggregation. Two out of the 21 2-pyridones described in this study inhibited amyloid formation of the Alzheimer Abeta(1-40) peptide. The effect was seen even at a 4 : 1 ratio of 2-pyridone and monomeric Abeta-peptide.     

Neighboring Group Participation in a Regio- and Stereoselective Chlorination of a Bicyclo[2.2.2]octanone

The zinc chloride-mediated acetylation of the optically active silyl enol ether 2a gave the beta-diketone 3a (48%) together with the regio- and stereoselectively chlorinated compound 4 (27%). The yield of 4 increased to 70% by starting from the O-acetyl derivative 2c. The chlorination most likely occurs via neighboring group participation by the endo acetoxy group.     

Interfacial dynamics and structure of surfactant layers

The present article provides current opinion on studies of the interfacial dynamics, adsorption, and structure of surfactant layers. The physical principles and applications of physicochemical methods such as tensiometry, ellipsometry, photon correlation spectroscopy, and neutron reflectivity techniques, as well as relevant theoretical aspects related to the adsorption and desorption kinetics, interfacial structure development, wetting enhancement, and the effect of adsorbed surfactant films of the interfacial dynamics, are covered in detail. In order to make the text as self-contained as possible, essential mathematical derivations are given demonstrating how raw data, such as ellipsometric angles or neutron reflectivity, are transformed into sought layer characteristics, such as thickness or density.     

Bioactive heparin immobilized onto microfluidic channels in poly(dimethylsiloxane) results in hydrophilic surface properties

A new composition of heparin coating for microfluidic systems made out of poly(dimethylsiloxane) (PDMS) was developed and evaluated. The coating that consists of a conditioning polyamine layer followed by two heparin/glutaraldehyde layers, resulted in channel surfaces with sufficient wettability to obtain flow of human normal plasma by capillary force alone. Hydrophilic channel walls are a desirable characteristic in microfluidic devices, since alternative pumping mechanisms must otherwise be included into the system. The immobilized heparin showed high antithrombin-binding capacity and a low degree of blood–material interaction. Plasma in contact with heparin-coated PDMS formed no detectable fibrin in a spectrophotometric assay by which plasma in contact with non-treated PDMS showed complete coagulation. The quartz crystal microbalance technique with energy dissipation monitoring (QCM-D) was utilized to obtain detailed information regarding adsorption kinetics and structural properties of the different layers composing the heparin coating.     

Mechanism for catechol ring-cleavage by non-heme iron extradiol dioxygenases

The catalytic mechanism of the non-heme iron extradiol dioxygenases has been studied using hybrid density functional theory. These enzymes cleave a C-C bond outside the two hydroxyl groups of catechols, in contrast to the intradiol enzymes which cleave the C-C bond between these two groups. The chemical models used comprise about 70 atoms and include the first-shell ligands, two histidines, one glutamate, and one water, as well as some second-shell ligands, two histidines, one aspartate, and one tyrosine. Catechol is found to bind as a monoanion in agreement with experiments, while dioxygen is found to replace the water ligand. A spin-transition from the initial septet to a quintet state prepares the system for formation of a bridging peroxide with the catechol substrate. When the O-O bond is cleaved in the suggested rate-limiting step, a key substrate intermediate with partly radical and partly anionic character is formed. The partly anionic character is found to determine the selectivity of the enzyme. The results are compared to available experimental information and to previous studies.     

Extraction of clenbuterol from calf urine using a molecularly imprinted polymer followed by quantitation by high-performance liquid chromatography with UV detection

A method for the extraction of clenbuterol from calf urine samples using a molecularly imprinted polymer (MIP) has been developed. The aim was that the final extracts from the MIP should allow quantitation of clenbuterol down to 0.5 ng/mL urine using HPLC with UV detection. The MIP was produced using brombuterol as a template and the selectivity of the MIP, for clenbuterol, was tested against a non-imprinted polymer (produced without template) and was found to be high. After loading of 5 mL diluted centrifuged urine, selective binding was established in acetonitrile-acetic acid (98:2). For further elution of interferences, 0.5 M ammonium acetate buffer pH 5 and 70% acetonitrile in water was used. Clenbuterol was eluted using 1% trifluoroacetic acid in methanol, which was evaporated and reconstituted in buffer. Results from the HPLC analyses showed that the extraction of clenbuterol using MIP is linear in the range 0.5-100 ng/mL with good precision (4.3% for 0.6 ng/mL and 2.1% for 6.0 ng/mL) and accuracy (96.7% for 0.6 ng/mL and 96.7% for 6.0 ng/mL). The recoveries were 75%. The results show that the method offers a selectivity and sensitivity that make the quantitation of 0.5 ng clenbuterol/mL urine by HPLC-UV possible and a competitive alternative to state-of-the-art routine analytical methods.     

Conical intersection in a bilirubin model – A possible pathway for phototherapy of neonatal jaundice

Phototherapy of neonatal jaundice involves Z–E-isomerisation around an exocyclic double bond in bilirubin. Our results of a CASSCF study on dipyrrinone, a bilirubin model, show a conical intersection between the ground and first excited singlet states associated with the Z–E-isomerisation. The conical intersection, located ca. 50 kJ/mol below the Franck–Condon-point, together with the S₁ minimum, ca. 50 kJ/mol below the conical intersection, are able to explain the available time-resolved spectroscopic data (the very short lifetime of the initially excited state and transient ‘dark state’ intermediate) as well as bilirubin’s very low fluorescence quantum yield and the medium-efficient photoisomerisation reaction.     

Crack formation in α-alumina supported MFI zeolite membranes studied by in situ high temperature synchrotron powder diffraction

Cracks are frequently formed in α-alumina supported MFI membranes during calcination. To better understand crack formation, in situ powder diffraction data were collected during calcination of a type of MFI membrane (ca. 1800 nm thick) which is known to crack reproducibly. In addition, data for MFI powder and a blank support were also collected. Both a synchrotron radiation facility and an in-house instrument were used. The unit cell parameters were determined with the Rietveld method, and the strain in the direction perpendicular to the film surface was calculated for the film as well as for the support. The microstrain in the support was also estimated. Based on the results obtained here, a model for crack formation in this type of MFI membrane was proposed. The lack of cracks in other types of MFI membranes (ca. 500 nm) prepared in our laboratory is also explained by the model. In thicker MFI films, the crystals are well intergrown. During heating, the MFI crystals contract and the α-alumina support expands. Consequently, a thermal stress develops in the composite which eventually leads to formation of cracks in the film and structural defects in the support. In thinner films, the crystals are less well intergrown and the thermal expansion mismatch leads to opening of grain boundaries rather than cracks.     

Supported liquid membrane enrichment using an organophosphorus extractant for analytical trace metal determinations in river waters

Metal ions were preconcentrated from water samples using supported liquid membranes containing 40% w/w di-2-ethylhexyl phosphoric acid (DEHPA) dissolved in kerosene as the membrane liquid. The driving force for the mass transport of analytes in this system is the pH gradient across the membrane. The effect of the carrier concentration on the extraction efficiency was studied. The mechanism for the mass transport in the system was investigated by measuring changes in pH and analyte ion concentration as well as changes in the concentration of other interfering metal ions present in large excess during the enrichment. The extraction efficiency was found to be unchanged as long as the pH difference across the membrane was more than 2 pH units. The long-term stability of the system was investigated at different pHs in the donor solution. Under optimal conditions, the membrane was stable for at least 200 h with reagent water samples and at least 80 h for river water samples. Enrichment factors of approximately 15 times could be obtained. The corresponding extraction efficiencies were over 80% for some of the investigated metal ions. The detection limits of blank samples for Cu²⁺, Cd²⁺ and Pb²⁺ using 120 min processing time were 0.19, 0.024 and 0.09 ng/mL, respectively. Received: 29 October 1996 / Revised: 17 February 1997 / Accepted: 23 February 1997     

Chemoselective Reduction of Tertiary Amides under Thermal Control: Formation of either Aldehydes or Amines

The chemoselective reduction of amides in the presence of other more reactive reducible functional groups is a highly challenging transformation, and successful examples thereof are most valuable in synthetic organic chemistry. Only a limited number of systems have demonstrated the chemoselective reduction of amides over ketones. Until now, the aldehyde functionality has not been shown to be compatible in any catalytic reduction protocol. Described herein is a [Mo(CO)₆]‐catalyzed protocol with an unprecedented chemoselectivity and allows for the reduction of amides in the presence of aldehydes and imines. Furthermore, the system proved to be tunable by variation of the temperature, which enabled for either C?O or C?N bond cleavage that ultimately led to the isolation of both amines and aldehydes, respectively, in high chemical yields.