Estimation of the particle-wall interaction energy in sedimentation field flow fractionation

A new sedimentation field flow fractionation (SdFFF) method is presented for the estimation of the total potential energy of interaction between colloidal particles and the channel wall. The method is based on the variation of the mean cloud thickness in SdFFF due to the variation of the suspension's ionic strength. It requires only two SdFFF experiments at two different ionic strengths and at a constant acceleration field. The found values are compatible with those calculated from the various forms of equations of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory.     

Rhenium and technetium complexes bearing quinazoline derivatives: progress towards a 99mTc biomarker for EGFR-TK imaging

The quinazoline derivatives (3-chloro-4-fluorophenyl)quinazoline-4,6-diamine (2) and (3-bromophenyl)quinazoline-4,6-diamine (3) were labelled with (99m)Tc using the "4 + 1" mixed-ligand system [Tc(NS3)(CN-R)] and the tricarbonyl moiety fac-[Tc(CO)3]+. In the "4 + 1" approach the technetium(iii) is stabilized by a monodentate isocyanide bearing a quinazoline fragment (L1,L2 ) and by the tetradentate tripodal ligand tris(2-mercaptoethyl)-amine (NS3). In the "4 + 1" approach, 99mTc-labelling was performed in a two-step procedure, the complexes [Tc(NS3)(L1)] (7a) and [Tc(NS3)(L2)] (8a) being obtained in about 50-70% yield. In the tricarbonyl approach, the fac-[Tc(CO)3]+ unit is anchored by two different monoanionic chelators bearing the quinazoline derivatives (3-chloro-4-fluorophenyl)quinazoline-4,6-diamine (2) and (3-bromophenyl)quinazoline-4,6-diamine (3). Both chelators have a N2O donor atom set, but one contains a pyrazolyl ring (L5H) and the other contains a pyridine unit (L6H). In both cases the conjugation of the quinazoline to the chelator was done through the secondary amine of the potentially tridentate and monoanionic chelators, the corresponding 99mTc-complexes (10a, 11a) being obtained in quantitative yield. The identities of the 99mTc-labelled quinazolines (7a, 8a, 10a, 11a) were confirmed by comparison with the HPLC profiles of the analogous Re compounds (7, 8, 10, 11). All these Re complexes were characterized by NMR and IR spectroscopy, elemental analysis and in some cases by MS and X-ray diffraction analysis. In vitro studies indicate that the quinazoline fragments, after conjugation to the cyano group (L1, L2) or to the pyrazolyl containing chelator (L5H), as well as the corresponding Re complexes (7, 8, 10) inhibit significantly the EGFR autophosphorylation and also inhibit A431 cell growth. These two effects were also found for the pyridine-containing chelator (L6H) and corresponding Re complex (11), although to a lesser extent.     

Dual-cardiac marker capillary waveguide fluoroimmunosensor based on tyramide signal amplification

The early diagnosis of acute myocardial infarction requires the determination of several markers in serum shortly after its incidence. The markers most widely employed are the isoenzyme MB of creatine kinase (CK-MB) and the cardiac troponin I (cTnI). In the present work, a capillary waveguide fluoroimmunosensor for fast and highly sensitive simultaneous determination of these markers in serum samples is demonstrated. The dual-analyte immunosensor was realized using glass capillaries internally modified with an ultrathin poly(dimethylsiloxane) film by creating discrete bands of analyte-specific antibodies. The capillary was then filled with a mixture of sample and biotinylated detection antibodies followed by reaction with streptavidin–horseradish peroxidase and incubation with a fluorescently labeled tyramide derivative to accumulate fluorescent labels onto immunoreaction bands. Upon scanning the capillary with a laser beam, part of the emitted fluorescence is trapped and waveguided through the capillary wall to a photomultiplier placed on one of its ends. The employment of tyramide signal amplification provided detection limits of 0.2 and 0.5 ng/mL for cTnI and CK-MB, respectively, in a total assay time of 30 min compared to 0.8 and 0.6 ng/mL obtained for the corresponding assays when the conventional fluorescent label R-phycoerythrin was used in a 65-min assay. In addition, the proposed immunosensor provided accurate and repeatable measurements (intra-assay and interassay coefficients of variation lower than 10%), and the values determined in serum samples were in good agreement with those obtained with commercially available enzyme immunoassays. Thus, the proposed capillary waveguide fluoroimmunosensor has all the required characteristics for fast and reliable diagnosis of acute myocardial infarction.      

Derivatives of 5‐Oxy‐pyrido[2,3‐b]quinoxaline‐9‐carboxylic acid: A tricyclic system useful for the synthesis of potential intercalators

The synthesis of a new series of 5‐oxy‐pyrido[2,3‐b]quinoxaline‐9‐carboxamides 4a‐i and N¹,N²‐Bis(5‐oxy‐pyrido[2,3‐b]quinoxaline‐9‐benzoyl)ethylenediamine ( 5 ) is reported starting from 2‐chloro‐3‐nitropyri‐dine. Fundamental steps of the synthetic pathway are i) preparation of 2‐(3‐nitro‐pyridin‐2‐ylamino)benzoic acid ( 1 ) via copper‐catalyzed condensation of 2‐chloro‐3‐nitropyridine with o‐anthranilic acid, ii) intramolecular cyclization of the acid 1 to 5‐oxy‐pyrido[2,3‐b]quinoxaline‐9‐carboxylic acid ( 2b ) upon treatment with concentrated sulfuric acid and oleum and iii) conversion of the acid 2 to the desired amides 4a‐i and 5 . Compounds 4a‐i and 5 are oxygenated azaanalogs of phenazines, a wellknown series of intercalators with cytotoxic activity.     

Kinetic Study of the Alcoholic Fermentation Process, in the Presence of Free and Immobilized Saccharomyces Cerevisiae Cells, at Different Initial Glucose Concentrations by Reversed Flow GC

Reversed flow gas chromatography (RFGC) was applied for the kinetic study of the alcoholic fermentation processes conducted with cells of the alcohol-resistant and psychrophilic Saccharomyces cerevisiae AXAZ-1 yeast strain, either free or immobilized on wheat, barley and corn grains as well as on potato pieces. Repeated alcoholic fermentations with must of varying initial glucose concentrations were performed in order to estimate the catalytic efficiency of the biocatalysts used in the present study. With the RFGC method, the distinction of the duration of alcoholic fermentation phases was achieved, which may be correlated to the phases of AXAZ-1 cells growth cycle. The rate constants of ethanol production for each phase of the alcoholic fermentations, conducted with free and immobilized cells, were also determined with the aid of RFGC, confirming the predominance of the immobilized against free cells in the fermentation process. Comparing the supports used for immobilization, wheat and barley grains seemed to be more efficient than corn grains and potato pieces, as they provided a higher number of immobilized cells and rate constant values.     

Laboratory soft-x-ray microscope for cryotomography of biological specimens

Soft-x-ray cryotomography allows quantitative and high-resolution three-dimensional imaging of intact unstained cells. To date, the method relies on synchrotron-radiation sources, which limits accessibility for researchers. Here we present a laboratory water-window microscope for cryotomography. It is based on a λ=2.48 nm liquid-jet laser-plasma source, a normal-incidence multilayer condenser, a 30 nm zone-plate objective, and a cryotilt sample holder. We demonstrate high-resolution imaging, as well as quantitative tomographic imaging, of frozen intact cells. The reconstructed tomogram of the intracellular local absorption coefficient shows details down to ～100 nm.     

Synthesis and characterisation of benzyl phosphino-thioether and -thiolato Pd(II) complexes and their applications in Suzuki coupling reactions

The synthesis of the benzyl phosphinothioether derivatives Ph(2)PCH(2)CH(Et)SR and their corresponding palladium complexes are reported, where R = CH(2)Ph, R = CH(2)-3,5-Me-C(6)H(3) and R = 1-CH(2)C(10)H(7)(5). Crystallographic data obtained for the complexes Pd(3)Cl(2) and Pd(4)Cl(2) show intra- and inter-molecular pi-pi interactions between the aromatic rings on the P and S substituents, and NOE experiments for Pd(4)Cl(2) show that these interactions persist in solution. The performance of the phosphinothioether palladium complexes in aryl-aryl cross-coupling reactions is compared with that of the corresponding complex of the parent phosphinothiolato ligand Ph(2)PCH(2)CH(Et)S(-)(1). High turnover numbers up to 2000000 are reported for the coupling of bromobenzene, using the palladium dimer [Pd(1)I](2) as the catalyst precursor. Kinetic studies show a linear dependence of the reaction on catalyst loading. The effect of other variables on the cross-coupling reaction, such as temperature, solvent and base, is also reported.     

Estimation of the Hamaker constants by sedimentation field-flow fractionation

van der Waals forces are one of several forces that control the adhesion between two materials. These forces are important to quantify in adhesion studies because they are always present and are always attractive. The major problem in calculating the van der Waals interaction between colloidal particles is that of evaluating the Hamaker constant. Hence, an accurately determined Hamaker constant for a given material is needed when interfacial phenomena such as adhesion are discussed in terms of the total potential energy between a particle and a substrate. In this paper, a new simple and accurate methodology for the estimation of the Hamaker constant is introduced. The results are in good agreement with those values found in literature.