Thermo-reversible sol–gel transition of TiO2 nanoparticles with surface modified by p-toluene sulfonic acid

In this paper an unprecedent thermo-reversible sol–gel transition for titania nanoparticles dispersed in a solution of p-toluene sulfonic acid (PTSH) in isopropanol is reported. The sol formed by the thermo-hydrolysis at 60 °C of titanium tetraisopropoxide (Ti(OⁱPr)₄) reversibly changes into a turbid gel upon cooling to room temperature. Turbidimetric measurements performed for samples containing different nominal acidity ratios (A = [PTSH]/[Ti]) have evidenced that the gel transformation temperature increases from 20 to 35 °C as the [PTSH]/[Ti] ratio increases from 0.2 to 2.0. SAXS results indicate that the thermo-reversible gelation is associated to a reversible aggregation of a monodisperse set of titania nanoparticles with average gyration radius of ≈2 nm. From the different PTSH species evidenced by Raman spectroscopy and TG/DTA of dried gels we proposed that the thermo-reversible gelation in this systems is induced by the formation of a supramolecular network, in which the protonated surface of nanoparticles is interconnected through cooperative hydrogen bonds between –SO₃ groups of p-toluene sulfonic acid.     

Elongational creep experiments - A new method for investigations of morphology development in polymer blends

This work is focused on the changes of phase structure in polystyrene/polyethylene blends with up to 15 wt.% of dispersed phase during elongational experiments in creep. In the first part, features of the experiments at constant stress with a special attention to morphology development in polymer blends are discussed. In the second part of the paper the deformation behavior of the dispersed droplets in dependence on applied stress and total strain is studied. It was found that with increasing the initial particle size the formation of homogeneously deformed long fibrils is preferred during the elongation. A maximum deformability of the droplets was observed, which cannot be increased by applying higher stresses, although the affine deformation of the droplets was not reached.     

Interaction of CO dehydrogenase with the cytoplasmic membrane monitored by fluorescence correlation spectroscopy

We have investigated the interaction of carbon monoxide dehydrogenase (CODH), an enzyme that catalyses the oxidation of CO in the aerobic eubacterium Oligotropha carboxidovorans, with the cytoplasmic membrane by using fluorescence correlation spectroscopy (FCS). Our results reveal that in vitro this interaction of CODH is specific for cytoplasmic membranes from CO-grown bacteria.     

Influence of motion correction on the visual analysis of cardiac magnetic resonance stress perfusion imaging

Objective

Image post-processing corrects for cardiac and respiratory motion (MoCo) during cardiovascular magnetic resonance (CMR) stress perfusion. The study analyzed its influence on visual image evaluation.

Materials and methods

Sixty-two patients with (suspected) coronary artery disease underwent a standard CMR stress perfusion exam during free-breathing. Image post-processing was performed without (non-MoCo) and with MoCo (image intensity normalization; motion extraction with iterative non-rigid registration; motion warping with the combined displacement field). Images were evaluated regarding the perfusion pattern (perfusion deficit, dark rim artifact, uncertain signal loss, and normal perfusion), the general image quality (non-diagnostic, imperfect, good, and excellent), and the reader’s subjective confidence to assess the images (not confident, confident, very confident).

Results

Fifty-three (non-MoCo) and 52 (MoCo) myocardial segments were rated as ‘perfusion deficit’, 113 vs. 109 as ‘dark rim artifacts’, 9 vs. 7 as ‘uncertain signal loss’, and 817 vs. 824 as ‘normal’. Agreement between non-MoCo and MoCo was high with no diagnostic difference per-patient. The image quality of MoCo was rated more often as ‘good’ or ‘excellent’ (92 vs. 63%), and the diagnostic confidence more often as “very confident” (71 vs. 45%) compared to non-MoCo.

Conclusions

The comparison of perfusion images acquired during free-breathing and post-processed with and without motion correction demonstrated that both methods led to a consistent evaluation of the perfusion pattern, while the image quality and the reader’s subjective confidence to assess the images were rated more favorably for MoCo.

     

Involvement of residues 296-299 in the enzymatic activity of tissue-type plasminogen activator

The tetra-alanine substitution variant KHRR 296–299 AAAAof tissue-type plasminogen activator (t-PA) was previously shownto have enhanced fibrin specificity and enhanced activity inthe presence of fibrin compared with the wild-type form of themolecule. The structural requirements for these alterationsin enzymatic activity were investigated by constructing severalamino acid substitution variants at each of the positions from296 to 299 and evaluating their activities under a variety ofconditions. Effects on plasminogen activator activity were commonamong the point mutants at positions 296–299; nearly allhad a phenotype similar to the KHRR 296–299 AAAA variant.The greatest effects on enzymatic function were found with multiplesubstitution variants, but some single charge reversals andproline substitutions had substantial effects. The enhancedfibrin specificity of KHRR 296–299 AAAA t-PA results inless fibrinogenolysis than seen with wild-type t-PA. Approximatelyfour times greater concentration of KHRR 296–299 AAAAcompared with wild-type t-PA was required to consume 50% ofthe fibrinogen in human plasma.