Enhancement of fluorescence in thin-layer chromatography induced by the interaction between n-alkanes and an organic cation

Fluorescence enhancement of a broad variety of solutes has been used extensively in TLC although no thorough explanation has been proposed. In this work, we try to understand it and explore new applications to which it can be put. In this way, alkanes can be quantitatively determined by fluorescence scanning densitometry using silica gel plates impregnated with berberine sulfate. Molecular simulation and analysis of molecular orbitals allows this phenomenon to be explained in this case and lays the groundwork to explain fluorescence enhancements produced by other molecules. A ion-molecule interaction between alkanes and berberine sulfate is responsible for the enhancement of fluorescence produced by alkanes. Computational results suggest that the surrounding alkane molecules provide an apolar environment to the berberine cation, thus enhancing the intensity of the fluorescence signal. This proposed explanation has been tested by extending the fluorescence determination to other compounds. These include biologically interesting saturated and unsaturated fatty acids, steroids and derivatives, prostaglandins, ceramides, galactocerebrosides, as well as terpenes, and polypropylene glycols. In addition, according to the proposed explanation, the properties required for alternative impregnants to berberine are discussed.     

WINGLET-TYPE VORTEX GENERATORS FOR PLATE-FIN HEAT EXCHANGERS USING TRIANGULAR FINS

Vortex generators in the form of delta winglet pairs have already been proposed by many researchers for enhancement of the heat transfer rate in plate-fin heat exchangers. In this work, the enhancement potential of triangular fins (which are widely used inserts between the plates of the plate-fin heat exchanger) having delta winglets mounted on their slant surfaces has been computed. The performance of this combination is evaluated for varying angles of attack of the winglet and different thermal boundary conditions. The performance of the combination of triangular fins and winglets with stamping on the slant surfaces also has been evaluated.     

Real-time fetal heart monitoring in biomagnetic measurements using adaptive real-time ICA

Electrophysiological signals of the developing fetal brain and heart can be investigated by fetal magnetoencephalography (fMEG). During such investigations, the fetal heart activity and that of the mother should be monitored continuously to provide an important indication of current well-being. Due to physical constraints of an fMEG system, it is not possible to use clinically established heart monitors for this purpose. Considering this constraint, we developed a real-time heart monitoring system for biomagnetic measurements and showed its reliability and applicability in research and for clinical examinations. The developed system consists of real-time access to fMEG data, an algorithm based on Independent Component Analysis (ICA), and a graphical user interface (GUI). The algorithm extracts the current fetal and maternal heart signal from a noisy and artifact-contaminated data stream in real-time and is able to adapt automatically to continuously varying environmental parameters. This algorithm has been named Adaptive Real-time ICA (ARICA) and is applicable to real-time artifact removal as well as to related blind signal separation problems.     

Droplet vaporization modeling of rapeseed and sunflower methyl esters

For numerical simulations of the combustion of liquid fuels, a thoroughly validated and verified quantitative model for droplet evaporation is necessary. In this work a simple single droplet infinite conductivity model is simulated for low pressure (0.1 MPa) and various temperatures (550–1050 K) using a chosen property rule (see Eq. (7)) and five convection correlations (C1, C2, C3, C4, and C5, see (Table 1) to obtain the temporal evolution of droplet diameter squared, droplet surface temperature and average evaporation rates of vegetable oil derived biofuels – rapeseed methyl ester (RME) and sunflower methyl ester (SME) – under near-quiescent conditions. The predictions are compared with the experimental and analytical results of Morin et al. [1]. The model uses an effective Reynolds number to conflate the effects of forced and natural convection. It is observed that the predicted temporal history of droplet diameter for RME droplet matches more closely with correlation C1 for T_amb ? 748 K and correlation C2 for T_amb ? 803 K at various ambient temperatures (i.e., from low to high evaporation rate). The correct droplet lifetime is predicted best by C1 for all temperatures. For average evaporation rates for SME, C1 best fits the experimental data. For the average evaporation rate of RME, the present model with C1 gives a better prediction than the theoretical, and corrected theoretical results of Morin et al. [1], and is observed to match closely with their experimental results. The present results using C2 are also found close to the experimental results for RME and SME. It is observed that the oxidation of RME/SME is similar to n-decane – a pure component fuel.     

Protein quantification by isotope dilution mass spectrometry of proteolytic fragments: cleavage rate and accuracy

The practice of quantifying proteins by peptide fragments from enzymatic proteolysis (digestion) was assessed regarding accuracy, reliability, and uncertainty of the results attainable. Purified recombinant growth hormone (rhGH, 22 kDa isoform) was used as a model analyte. Two tryptic peptides from hGH, T6 and T12, were chosen to determine the amount of the protein in the original sample. Reference solutions of T6 and T12 (isotopically labeled forms), value assigned by quantitative amino acid analysis (AAA) after complete hydrolysis, were used as internal standards. The accuracy of protein quantification by fragments T6 and T12 was evaluated by comparison of peptide results to those obtained for the same rhGH sample by AAA. The rate of cleavage (and thus the experimental protocol used) turned out to be crucial to the quality of results in protein quantification using enzymatic fragments. Applying a protocol customarily found in (qualitative) bottom-up proteomics gave results significantly higher than the target value from AAA (+11% with T6 and +6% with T12). In contrast, using a modified protocol optimized for fast and complete hydrolysis, results were unbiased within the limits of uncertainty, while the time needed for completion of proteolysis was considerably reduced (30 min as compared to 1080-1200 min). The method assessed highlighted three important criteria deemed necessary for successful protein quantification using proteolysis-based mass spectrometry methods. These are the following: the requirement for both the selected peptides and labeled internal standard to be stable throughout digestion; the correct purity assignment to the selected peptide standards; the proof of equimolar release of the selected peptides. The combined (overall) uncertainty for protein quantification was established by combination of estimates obtained for individual components and found to be U = 4% for this example. This uncertainty is of the same order as that typically attainable in quantification of "small" organic molecules using liquid chromatography/isotope dilution mass spectrometry.