The Storage and Handling of Polymer Latices Used as Particle Standards

Latices of 2, 4 and 9 μm diameter intended for use a particle standard have been examined under a variety of storage and handling conditions. The effects of light exposure, temperature variation and storage in isotonic saline were studied as well as the handling conditions, such as multiple sampling, dispersion technique and effects of foaming. Particle sizes and particle number densities were remarkably constant, even under the most extreme conditions investigated.     

Redoxindicatoren in der indirekten volumetrischen Anionenbestimmung

Zusammenfassung Es wurde eine indirekte volumetrische Methode zur Bestimmung der Sulfationen (2–100 mg) durch Fällung mit einer Bleinitratlösung und Abtitrieren der überschüssigen Bleiionen mit Kaliumhexacyanoferrat(II)-lösung in 75% igen Methanollösungen gegen den Redoxindicator Variaminblau ausgearbeitet.Natrium-, Kalium- und Ammoniumionen können ohne zu stören in bis zu 5fachem Überschuß im Verhältnis zu den abtitrierten Bleiionen zugegen sein. Die Ionen der 2- und 3 wertigen Metalle werden durch Fällung mit Kaliumcarbonatlösung entfernt. Das Verfahren wurde mit Erfolg zur Sulfatbestimmung in Wässern und Metallsulfaten angewandt.Gewidmet Herrn Prof. Dr. W.Jakób aus der Jagiellonischen Universität in Kraków.     

The photolysis of 1-(4,5-dihydro-1H-imidazol-2-yl)benzotriazole

1-(4,5-Dihydro-1H-imidazolo-2-yl)benzotriazole was photolyzed at 254 nm yielding 1,2-dihydro-4H-imidazo-[1,2-a]benzimidazole.     

Cinnamates. III. The light sensitive polymers: Cinnamates with internal charge-transfer spectroscopic properties

In this paper, we outline the photochemical and spectroscopic properties of a new light-sensitive polymer obtained as a result of polystyrene modification by attachment of a pendant 4-dimethylamino-cinnamate ester group. This specific cinnamate displays typical charge-transfer character in the absorption and emission spectra. The photochemical and photophysical properties of photopolymer are compared with the monomeric model photochemistry and photophysics.     

Bestimmung von Cyanidspuren in Alkalisulfiden

Zusammenfassung Es wird eine photometrische Methode zur Bestimmung von Cyanidspuren in Alkalisulfiden beschrieben. Das Sulfidion wird mit einem kleinen überschu\ an Zinknitrat als ZnS gefÄllt, das Cyanidion wird dann aus der stark verdünnten Lösung in Form von HCN langsam abdestilliert, in 0,01 n Natronlauge absorbiert und in dieser Lösung auf Grund der Farbreaktion mit Variaminblau und Kupfersulfat gemessen. 5 g CN^– sind neben der 1600 fachen Menge Sulfidion mit guter Genauigkeit zu bestimmen.     

High performance capillary electrophoresis method for determination of ibuprofen enantiomers in human serum and urine

A direct and stereospecific capillary zone electrophoresis (CZE) method for quantification ibuprofen enantiomers in biological matrices: human serum and urine, has been developed. Chiral separation of the enantiomers of ibuprofen and (+)-S-indobufen [(+)-S-INDB, internal standard, IS] was obtained in an uncoated silica capillary filled with a background electrolyte (BGE), consisted of heptakis 2,3,6-tri-O-methyl-β-cyclodextrin (TM-β-CD) in buffer of pH 5.0. The complete enantioselective analysis of ibuprofen and its 1-hydroxy metabolite confirmed appropriate specificity of the method. The electrophoretic parameters: electroosmotic (μ_EOF) and electrophoretic (μ_ep) mobility and resolution factor (R_s) were determined. Extraction procedures with organic solvent and solid phase extraction (SPE) with C₁₈ stationary phase for isolation of enantiomers from biological fluids were compared. SPE method for further studies was chosen. Stereoselective extraction of IBP enantiomers from serum at basic pH has been discovered. Validation of the method was carried out. Calibration curves of ibuprofen enantiomers were linear in the range of 0.1-25.0 μg/ml in serum and of 0.5-250.0 μg/ml in urine. Recovery of both enantiomers from serum and urine amounted 74-86 and 90-98%, respectively. Intra- and inter-day measurement precision and accuracy were below 15%. Limits of detection for IBP enantiomers amounted 0.05 and 0.25 μg/ml in samples of serum and urine, respectively. Limit of quantitation was also estimated. IBP enantiomers proved to be stable following three freeze and thaw cycles and during storage in autosampler at ambient temperature. The validated methods enable pharmacokinetic studies of enantiomers in both media. The elaborated HPCE method can be alternative to HPLC.     

The synthesis and conformational analysis of optical isomers of 4-phenyl-perhydropyrido[1,2-a]pyrazine-1,3-dione: an example of ‘solid state–frozen’ dynamics in nitrogen-bridged bicyclic 2,6-diketopiperazines

The synthesis, chemical properties, and conformational analysis of enantiopure (4R,9aS)-, (4S,9aR)-, (4S,9aS)-, and (4R,9aR)-4-phenyl-perhydropyrido[1,2-a]pyrazine-1,3-diones having potential biological activity are described. An interesting example of the coexistence of two invertomers of the (4R,9aR)-diastereomer in a single crystal unit cell is reported. The invertomers differ in the cis/trans-relationship between the fused rings and in the absolute configuration at the chiral nitrogen atom. The structure and equilibrium distributions of the respective conformers have been determined by NMR spectroscopy in both polar and non-polar solvents at various temperatures. The NMR spectra show that dynamic processes in the imide parts of the interconverting species are restrained by self-aggregation. The (4S,9aR)-diastereomer exists in a single conformation with insignificant dynamic effects.     

A model of influenza virus spread as a function of temperature and humidity

The influence that atmospheric conditions might have on the efficiency of the spread of influenza virus is important for epidemiological and evolutionary research. However, it has not been satisfactorily recognized and quantified so far. Here we provide a statistical model of influenza transmission between individuals. It has been derived from the results of recent experiments, which involved infecting guinea pigs with influenza at various temperatures and relative air humidity levels. The wide range of transmission rates in those experiments reflects the ensemble-independent phenomena. The correlation between most of our simulations and the experimental results is satisfactory. For several different conditions, we obtained transmissibility values which seem to be sufficiently accurate to provide partial input for an intended large-scale epidemiological study in the near future.     

Molecular dynamics with the united-residue model of polypeptide chains. I. Lagrange equations of motion and tests of numerical stability in the microcanonical mode

The Lagrange formalism was implemented to derive the equations of motion for the physics-based united-residue (UNRES) force field developed in our laboratory. The C(alpha)...C(alpha) and C(alpha)...SC (SC denoting a side-chain center) virtual-bond vectors were chosen as variables. The velocity Verlet algorithm was adopted to integrate the equations of motion. Tests on the unblocked Ala(10) polypeptide showed that the algorithm is stable in short periods of time up to the time step of 1.467 fs; however, even with the shorter time step of 0.489 fs, some drift of the total energy occurs because of momentary jumps of the acceleration. These jumps are caused by numerical instability of the forces arising from the U(rot) component of UNRES that describes the energetics of side-chain-rotameric states. Test runs on the Gly(10) sequence (in which U(rot) is not present) and on the Ala(10) sequence with U(rot) replaced by a simple numerically stable harmonic potential confirmed this observation; oscillations of the total energy were observed only up to the time step of 7.335 fs, and some drift in the total energy or instability of the trajectories started to appear in long-time (2 ns and longer) trajectories only for the time step of 9.78 fs. These results demonstrate that the present U(rot) components (which are statistical potentials derived from the Protein Data Bank) must be replaced with more numerically stable functions; this work is under way in our laboratory. For the purpose of our present work, a nonsymplectic variable-time-step algorithm was introduced to reduce the energy drift for regular polypeptide sequences. The algorithm scales down the time step at a given point of a trajectory if the maximum change of acceleration exceeds a selected cutoff value. With this algorithm, the total energy is reasonably conserved up to a time step of 2.445 fs, as tested on the unblocked Ala(10) polypeptide. We also tried a symplectic multiple-time-step reversible RESPA algorithm and achieved satisfactory energy conservation for time steps up to 7.335 fs. However, at present, it appears that the reversible RESPA algorithm is several times more expensive than the variable-time-step algorithm because of the necessity to perform additional matrix multiplications. We also observed that, because Ala(10) folds and unfolds within picoseconds in the microcanonical mode, this suggests that the effective (event-based) time unit in UNRES dynamics is much larger than that of all-atom dynamics because of averaging over the fast-moving degrees of freedom in deriving the UNRES potential.