Application of screen printed electrodes in biochemical analysis

Screen printing technology has been used for the production of amperometric devices. The materials chosen were conventional thick film materials, (i.e. Al₂O₃-ceramic substrates and pastes of different composition, fired at 850°C). The working and the auxiliary electrodes were made by screen printing Pt paste, the connecting lines and reference electrodes in the three electrode system by printing AgPd paste. Enzymes were immobilised on the working electrodes either by cross-linking with glutaraldehyde or by adsorption in a screen printable graphite based paste. For both procedures the composition of the immobilisation matrix had to be optimised for each enzyme. It was observed that the achievable lower detection limits and standard deviations between different enzyme electrodes were lower when the enzymes were cross linked with glutaraldehyde, whereas the sensitivities were comparable for both immobilisation techniques and were improved further by the application of additional membranes acting as diffusion barriers. Stabilities of the enzyme electrodes were improved by electrode treatment (such as silanisation of the electrodes), optimisation of the measuring conditions and composition of the storage buffer.     

An efficient synthesis of β-ketosilanes

The reaction of α-silyl esters with an excess of a Grignard reagent leads to β-ketosilanes in good yield.     

Magnetic pseudo-differential Weyl calculus on nilpotent Lie groups

We develop a pseudo-differential Weyl calculus on nilpotent Lie groups, which allows one to deal with magnetic perturbations of right invariant vector fields. For this purpose, we investigate an infinite-dimensional Lie group constructed as the semidirect product of a nilpotent Lie group and an appropriate function space thereon. We single out an appropriate coadjoint orbit in the semidirect product and construct our pseudo-differential calculus as a Weyl quantization of that orbit.     

Labeling of macrophages using bacterial magnetosomes and their characterization by magnetic resonance imaging

This work investigated macrophages labeled with magnetosomes for the possible detection of inflammations by MR molecular imaging. Pure magnetosomes and macrophages containing magnetosomes were analyzed using a clinical 1.5 T MR-scanner. Relaxivities of magnetosomes and relaxation rates of cells containing magnetosomes were determined. Peritonitis was induced in two mice. T₁, T₂ and T₂* weighted images were acquired following injection of the probes. Pure magnetosomes and labeled cells showed slight effects on T₁, but strong effects on T₂ and T₂* images. Labeled macrophages were located with magnetic resonance imaging (MRI) in the colon area, thus demonstrating the feasibility of the proposed approach.     

Constrained nucleic acids (CNA). Part 2. Synthesis of conformationally restricted dinucleotide units featuring noncanonical alpha/beta/gamma or delta/epsilon/zeta torsion angle combinations

Four dinucleotide building units of nucleic acids in which three out of six backbone torsion angles are included in a dioxaphosphorinane ring structure (D-CNA family) have been synthesized: two diastereoisomeric alpha,beta,gamma-D-CNA {cis and trans} and two diastereoisomeric delta,epsilon,zeta-D-CNA {(S(C4'),R(P)) and (S(C4'),S(P))}. The structural analysis of these conformationally restricted dinucleotides, using NMR spectroscopy and X-ray crystallography, shows that these D-CNA structural elements allow the stabilization of torsion angle combinations, alpha/beta/gamma and delta/epsilon/zeta, that are significantly different from those typically observed in canonical A- or B-form duplexes.     

pH-sensitive paramagnetic liposomes for MRI: assessment of stability in blood

The pH-dependent stability of dipalmitoyl phosphatidyl ethanolamine/palmitic acid (DPPE/PA) liposomal GdDTPA-BMA was investigated in human blood and after exposure to selected blood components. Relaxometry, visual observations and cryo-transmission electron microscopy (cryo-TEM) were employed for the assessment of stability. The liposomes were stable in buffer at physiological pH and the T(1)-relaxivity (r(1)) of the system was significantly lowered compared to that of non-liposomal GdDTPA-BMA, which could be explained by an exchange limited relaxation process. Lowering the pH, however, gave a marked increase in r(1), due to liposome aggregation and subsequent leakage of GdDTPA-BMA. After a few minutes incubation in human blood the liposomes were destabilised and leaky at both high and low pH, and blood components likely to cause the instability were studied. Physiological level of Na(+) (150 mM) did not affect the relaxometric behavior of the liposomes at pH 7.4, but shifted the pH-r(1) profile laterally to higher pH-values compared to a level of 50 mM Na(+). Increased screening of the surface charges and, concomitantly, a lowering of the energy-barrier against aggregation is a plausible explanation for this phenomenon. In contrast, both Ca(2+) and Mg(2+) (physiological level, both 2 mM) caused massive aggregation of the liposomes and leakage of contents, and were therefore much more detrimental to the stability of the liposomes than a physiological level of Na(+). This could be due to the higher screening ability of divalent cations, but aggregation could also be induced through an inter-liposomal "bridging" effect. Physiological level of both Na(+) and Ca(2+) caused less leakage than for lower Na(+) concentration (50 mM Na(+) and 2 mM Ca(2+)), probably due to competition for the negative surface charges. Albumin also destabilised the liposomes, and it was shown to be due to an interaction between albumin and PA in the liposomal membrane.