Prediction of the evolution of the dispersed phase in bubbly flow problems

For modeling multi-phase where the dispersed phase plays a major role in determining the flow structure and inter phase transfer quantities, the size distribution of the bubbles has to be considered. This can be done by extension of the mass balance equation to a population balance equation. In this work, a least squares spectral method is tested for predicting the evolution of the dispersed phase in a vertical two-phase bubbly flow. The least squares spectral method consists in minimizing the L² norm of the residual over the simulation domain. The results are compared with experimental data obtained for two different initial bubble distributions.     

A natural abundance 15N NMR investigation of bilirubin IX-α

Natural abundance ¹⁵N NMR spectra have been obtained for bilirubin IX-α using polarization transfer via the INEPT and SINEPT-2 techniques. The resonances for all four nitrogens are clearly resolved. ¹⁵N chemical shifts and ¹⁵N? ¹H coupling constants over one and three bonds are reported. Heteronuclear chemical shift correlation between ¹⁵N and ¹H for the four NH groups has been established by means of the SINEPT-2 pulse sequence.     

Al Chemical Shielding Anisotropy

Accurate values for the²⁷Al chemical shielding anisotropy (CSA) are reported for sapphire (α-Al₂O₃). The values (δ_σ= −17.3 ± 0.6 ppm, η_σ= 0.03 ± 0.06) are obtained from single-crystal²⁷Al NMR and appear to be the first convincing determination of an²⁷Al CSA.     

DNA-controlled assembly of soft nanoparticles

Immobilization of DNA (encoding) on solid nanoparticles requires surface chemistry, which is well established for gold surfaces but often tedious and not generally applicable for many other inorganic surface materials. While substantial effort has been devoted to expanding surface chemistry techniques for solid nanoparticles, considerably less attention has been given to the development of noncovalent attachment of DNA to soft nanoparticles, like liposomes. Here we report a DNA-controlled assembly of liposomes in solution and on solid supported membranes, this process displays remarkably sharp thermal transitions from an assembled to a disassembled state, allowing application of DNA-controlled liposome assembly for the detection of polynucleotides (e.g., DNA) with single mismatch discrimination power. The method is based on a single DNA strand (contains two lipid membrane anchors), which is able to noncovalently attach to a liposome surface. This design enables detection of biological polynucleotide targets as the complementary strand can be unmodified DNA and RNA strands.     

Photochemical modification and patterning of SU-8 using anthraquinone photolinkers

Bioactive protein patterns and microarrays achieved by selective localization of biomolecules find various applications in biosensors, bio-microelectromechanical systems (bio-MEMS), and in basic protein studies. In this paper we describe simple photochemical methods to fabricate two-dimensional patterns on a Novolac A derivative polymer (SU-8) and, subsequently, their functionalization with biomolecules. Anthraquinone (AQ) derivatives are used to chemically modify and pattern SU-8 surfaces. Features as small as 20 mum are obtained when using uncollimated light. The X-Y spatial resolution of micropatterned AQ molecules is improved to 1.5 mum when a collimated light source is used. This micropatterning process will be important for the functionalization of MEMS-based biosensors. The method saves several processing steps and can be integrated in cleanroom fabrication thus avoiding contamination of the sensor surfaces.     

Long-term stability of rotor-controlled MAS frequencies to 0.1 Hz proved by 14N MAS NMR experiments and simulations

Experimental and simulated 14N MAS NMR spectra of the NH4+ ions in the two polymorphs, mS60 and mP60, of (NH4)2MoO4 are used to illustrate that a long-term stability of rotor-controlled MAS frequencies to 0.1 Hz can be achieved using commercial instrumentation (MAS speed controller and 7.5 mm MAS probe with a single marked rotor) attached to a highly pressure-stabilized air supply. A new modification of the STARS simulation software employs a Gaussian distribution for the experimental spinning frequency around the frequency set for the MAS speed controller. A simulated spectrum is then obtained by summation of several calculated spectra for evenly spaced spinning frequencies around the set frequency with relative weight factors corresponding to the Gaussian distribution.     

Synthesis and biological evaluation of new dipicolylamine zinc chelators as metallo-β-lactamase inhibitors

Antibiotics are key drugs in modern healthcare, especially in hospitals, where multiresistant bacteria resides and is a potential threat to human health. In the present work, a new series of adjuvants working synergistically with the carbapenem meropenem, in which a selective zinc-chelating agent was covalently linked to the small bacterial peptide D-Ala-D-Ala, was synthesized and tested against VIM-2 and NDM-1 metallo-β-lactamases (MBLs). The nature of the linker was modified in a structure-activity relationship study. Compound 1i, having an ethyl piperidine linker, lowered the MIC of meropenem from 32 to 64?mg/L to 2 and 1–2?mg/L against VIM-2- and NDM-1-producing clinical isolates, respectively. The IC₅₀ value of 1i against VIM-2 was 9.8 and 2.2?μM after 5 and 20?min, respectively. Compound 1i also showed intrinsic toxicity against three eukaryotic human tumoral cell lines between 50 and 120?μM.     

Revealing the mechanisms behind SnO2 nanoparticle formation and growth during hydrothermal synthesis: an in situ total scattering study

The formation and growth mechanisms in the hydrothermal synthesis of SnO(2) nanoparticles from aqueous solutions of SnCl(4)·5H(2)O have been elucidated by means of in situ X-ray total scattering (PDF) measurements. The analysis of the data reveals that when the tin(IV) chloride precursor is dissolved, chloride ions and water coordinate octahedrally to tin(IV), forming aquachlorotin(IV) complexes of the form [SnCl(x)(H(2)O)(6-x)]((4-x)+) as well as hexaaquatin(IV) complexes [Sn(H(2)O)(6-y)(OH)(y)]((4-y)+). Upon heating, ellipsoidal SnO(2) nanoparticles are formed uniquely from hexaaquatin(IV). The nanoparticle size and morphology (aspect ratio) are dependent on both the reaction temperature and the precursor concentration, and particles as small as ~2 nm can be synthesized. Analysis of the growth curves shows that Ostwald ripening only takes place above 200 °C, and in general the growth is limited by diffusion of precursor species to the growing particle. The c-parameter in the tetragonal lattice is observed to expand up to 0.5% for particle sizes down to 2-3 nm as compared to the bulk value. SnO(2) nanoparticles below 3-4 nm do not form in the bulk rutile structure, but as an orthorhombic structural modification, which previously has only been reported at pressures above 5 GPa. Thus, adjustment of the synthesis temperature and precursor concentration not only allows control over nanoparticle size and morphology but also the structure.     

First nucleophilic aromatic substitution of annelated pyrazole.

3-Chloropyrazolo[3,4-c]quinoline 5, 3-chloropyrazolo[3,4-c]isoquinoline 6, 1,2-dihydro-1,2-dimethylpyrazolo[3,4-c]quinolin-3-one 8, and 1,2-dihydro-1,2-dimethylpyrazolo[3,4-c]isoquinolin-3-one 10 were obtained by acid-induced nucleophilic aromatic substitution (S(N)H) of H-3 in N-hydroxypyrazolo[3,4-c]quinoline 1b and in N-hydroxy pyrazolo[3,4-c]isoquinoline 3b. In the acid-induced chlorination, 3b was far more reactive than 1b, whereas the related N-hydroxypyrazolo[4,3-c]quinoline 2b and N-hydroxypyrazolo[4,3-c]isoquinoline 4b were completely unreactive toward S(N)H under identical conditions.     

Determination of the enantiomer fraction of PBB 149 by gas chromatography/electron capture negative ionization tandem mass spectrometry in the selected reaction monitoring mode

Enantioselective determination of the atropisomers of 2,2',3,4',5',6-hexabromobiphenyl (PBB 149) in a purified sample from a bird egg was attempted in this work. By application of the classic method for PBB determination, i.e. gas chromatography coupled to electron capture negative ionization mass spectrometry (GC/ECNI-MS) using the bromide ions, the enantiomers interfered with another brominated compound. Subsequent measurements clarified that this interference did not occur in the mass chromatogram of the molecular ion of PBB 149. Therefore, a GC/ECNI tandem mass spectrometry (MS/MS) method was developed, based on the fragmentation of [M]-. A suitable precursor-product ion transition was found for m/z 627.5 --> 80 +/- 1.5, representing the most abundant ion trace of the molecular ion and the bromide ions. Optimization of the ion source temperature, the methane gas pressure, and the collision voltages resulted in a robust method that could solve the problem. Subsequent injections of a technical PBB product (Firemaster BP-6) resulted in the anticipated racemic proportion (enantiomer fraction (EF) = 0.50 +/- 0.02 (n = 8)). By contrast, the EF in the purified extract of a bird egg was found to be 0.42 +/- 0.02 (n = 10), indicative of a significant enantioenrichment of the second eluting atropisomer. Additional measurements were performed on a non-chiral column. These measurements allowed for the detection of 16 hexabromobiphenyls (hexa-BBs) in Firemaster BP-6. These comparisons verified that PBB 149 enantiomers did not interfere with an isomer that could falsify the enantiomer fraction in the sample. The novel method using GC/ECNI-MS/MS in the selected reaction monitoring (SRM) mode was eight times more sensitive than application of conventional GC/ECNI-MS selected ion monitoring (SIM) analysis of the molecular ion.