Self-assembly of poly(allylamine hydrochloride) through electrostatic interaction with sodium dodecyl sulfate

The self-assembly of poly(allylamine hydrochloride) (PAH) through an electrostatic interaction with sodium dodecyl sulfate (SDS) was explored. PAH itself showed no self-assembly in water. A light scattering study demonstrated that PAH formed monodispersed spherical aggregates in water in the presence of SDS. The hydrodynamic diameter of the aggregates was estimated to be ca. 170 nm based on the cumulant analysis. The scattering intensity and UV absorbance at 258 nm based on the aggregation increased with an increase in the molar ratio of SDS to the allylamine hydrochloride unit (SDS/AH), indicating an increase in the number of aggregates. On the other hand, the hydrodynamic diameter of aggregates was constant, i.e., independent of the SDS/AH ratio. The constant size of the aggregates in spite of the increase in the number of aggregates suggests the formation of the micellar aggregates by the intramolecular association through an electrostatic interaction.     

Nitroxide-mediated photo-living radical polymerization of vinyl acetate

The photoradical polymerization of vinyl acetate was performed using 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (MTEMPO) as the mediator in the presence of bis(alkylphenyl)iodonium hexafluorophosphate (BAI). The MTEMPO/BAI system using 2,2’-azobis(isobutyronitrile) or 2,2’-azobis(4-methoxy-2,4-dimethylvaleronitrile) as the initiator did not succeed in controlling the molecular weight and produced polymers that showed a bimodal gel permeation chromatography with the broad molecular weight distribution. On the other hand, the polymerization using 1-(cyano-1-methylethoxy)-4-methoxy-2,2,6,6-tetramethylpiperidine and BAI proceeded by the living mechanism based on linear increases in the first order time–conversion and conversion–molecular weight plots. The molecular weight distribution also increased with the increasing conversion due to cloudiness of the solution as the polymerization proceeded. It was found that the polymerization had a photolatency because the propagation stopped by interruption of the irradiation and was restarted by further irradiation.     

Physical properties of the probe electrospray ionization (PESI) needle applied to the biological samples

Probe electrospray ionization (PESI) is a recently developed technique that uses a fine solid needle as a probe for sampling biological materials. In this study, we quantified the volume of liquid sample picked up by the solid needle with the tip diameter of ～700 nm and the apex angle of ～60°. The amounts of low‐viscosity samples (rat urine) loaded on the tip of the needle by a single stroke were 0.35 ± 0.09 pl. Interestingly, the amount of liquid adhered to the tip did not significantly depend on the protein concentration, but viscosity and surface tension of the sample. Under these conditions, we successfully obtained mass spectra for each biological sample. Copyright © 2009 John Wiley & Sons, Ltd.     

Surface-deformation characteristics of uniaxially oriented poly(ethylene terephthalate) film as evaluated from nanoscratch tests with scanning probe microscopy

The surface-deformation characteristics of uniaxially drawn poly(ethylene terephthalate) (PET) film were successfully evaluated with multiline scratch tests using scanning probe microscopy (SPM) on a nanometer scale. The PET film was prepared by compression molding from the melt, followed by quenching in ice water. The obtained amorphous film was drawn uniaxially below its glass-transition temperature, and the resultant surface roughness could be reduced to within 5 nm. A multiline scratch with the Si(3)N(4) tip of an SPM on the oriented PET surface was made parallel and perpendicular to the drawing axis under applied loads of 5-30 nN. The perpendicular scratching generated a characteristic periodic pattern on the film surface, but the parallel scratching induced a tearing of the surface. These results suggest that surface-deformation mechanisms were dominated by molecular anisotropy. The surface-deformation properties, as evaluated from scratch-angle dependences on morphological changes on a nanometer scale, were similar to the mechanical properties of the bulk.     

Fundamental aspects of electrospray droplet impact/SIMS

A new ionization method, electrospray droplet impact ionization (EDI), has been developed for matrix-free secondary-ion mass spectrometry (SIMS). The charged droplets formed by electrospraying 1 M acetic acid aqueous solution are sampled through an orifice with a diameter of 400 microm into the first vacuum chamber, transported into a quadrupole ion guide, and accelerated by 10 kV after exiting the ion guide. The droplets impact on a dry solid sample (no matrix used) deposited on a stainless steel substrate. The secondary ions formed by the impact are transported to a second quadrupole ion guide and mass-analyzed by an orthogonal time-of-flight mass spectrometer (TOF-MS). Ten pmol of gramicidin S could be detected with the presence of as much as 10 nmol of NaCl. The ion signal for arginine disappeared with decrease in the substrate temperature below 150 K owing to the formation of ice film over the sample surface. While 10 fmol of gramicidin S could be detected for 30 min, the ionization/desorption efficiency for EDI becomes smaller with an increase in the molecular weight (MW) of a biological sample. The largest protein samples detected to date are cytochrome c and lysozyme. The high sensitivity for EDI is due to the fact that samples only a few monolayers thick are subject to desorption/ionization by EDI, with little fragmentation. A coherent phonon excitation may be the main mechanism for the desorption/ionization of the solid sample.     

Aqueous chromatography system using pH- and temperature-responsive stationary phase with ion-exchange groups

We report on the development of a novel analytical HPLC technique of nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, ketoprofen and naproxen, with an isocratic aqueous mobile phase. In this study, we designed a new pH- and temperature-responsive copolymer of N-isopropylacrylamide (NIPAAm), butyl methacrylate (BMA) and N,N-dimethylaminopropylacrylamide (DMAPAAm). The copolymer was modified with cross-linked poly(NIPAAm-co-BMA-co-DMAPAAm) (IBD) hydrogel on to aminopropyl silica beads, and the products were evaluated as HPLC packing materials for an ion-exchange- and temperature-responsive chromatography. The property of the surface of the stationary phase was altered from hydrophilic to hydrophobic, and from charged to non-charged by changes in the temperature and pH. In addition, it is possible that ion-exchange groups can appear or be hidden on the polymer chain surface by temperature changes. The interactions of NSAIDs with this stationary phase were controlled by the temperature and the pH with a constant aqueous mobile phase. PH- and temperature-responsive chromatography is expected to be useful for the separation of pharmaceuticals and biomolecules.     

Development of a large-volume, membrane-based injection system for gradient elution micro-liquid chromatography

A membrane unit which can be used to inject a large volume of sample solution was developed to facilitate reproducible and accurate gradient elution in micro-high-performance liquid chromatography (micro-HPLC). Since the membrane unit has a very low void volume, it facilitates the effective concentration of analytes in large sample volumes. Gradient elution micro-HPLC with the membrane unit allowed the efficient separation of n-alkyl benzoates, used as test samples, in a short time without marked gradient delay. In this study, the membrane unit could be loaded with up to 50 microg of n-hexyl benzoate, and more than 500 microL of sample solution could be applied. In about 50 chromatographic runs, the relative standard deviation (RSD) of the relative retention time of n-hexyl benzoate with respect to methyl benzoate was 0.530%.     

Aqueous chromatography system using temperature-responsive polymer-modified stationary phases

Extensive research has been carried out on functional polymers which are currently playing important roles in various fields such as medicine and engineering. Such functional polymers which respond to various kinds of stimuli are termed 'intelligent materials'. Poly(N-isopropylacrylamide) (PNIPAAm), a temperature-responsive polymer, was utilized as a chromatography column matrix modifier for a novel chromatographic approach in which only aqueous media are used as a mobile phase. The ability of the developed temperature-responsive chromatography system to separate solutes without using an organic solvent is advantageous from the point of view of maintaining the structure and activity of bioactive compounds. Recently, we designed and synthesized a new pH- and temperature-responsive copolymer as a representative of such environment-responsive polymers and grafted it onto aminopropyl silica beads. The products were evaluated as HPLC packing materials for separation systems based on a new concept, according to which the properties of the stationary phase surface are altered by external stimuli such as pH and temperature. This chromatography system utilizing the PNIPAAm copolymer is very useful for the separation of bioactive substances, such as proteins and peptides, because separation in the aqueous mobile phase is controlled solely by changing the temperature. This analytical system reduces organic waste because no organic solvent is used to separate the solutes and can therefore be classified as environmentally friendly. Future medical and pharmaceutical applications are expected.     

Agesamides A and B, bromopyrrole alkaloids from sponge Agelas species: application of DOSY for chemical screening of new metabolites

Diffusion-ordered NMR spectroscopy (DOSY) is a versatile and powerful NMR technique and a noninvasive analytical method for mixture analysis that does not require prior physical separation of the analytes. In our search for new metabolites from natural resources, DOSY was applied for constituent analysis of crude bromopyrrole fractions separated from an Okinawan marine sponge Agelas sp. so that two new bromopyrrole alkaloids, agesamides A (1) and B (2), have been isolated. The structures and relative stereochemistry of 1 and 2 were elucidated from spectroscopic data.     

Anomalous viscosity of an expanding quark-gluon plasma

We argue that an expanding quark-gluon plasma has an anomalous viscosity, which arises from interactions with dynamically generated color fields. We derive an expression for the anomalous viscosity in the turbulent plasma domain and apply it to the hydrodynamic expansion phase, when the quark-gluon plasma is near equilibrium. The anomalous viscosity dominates over the collisional viscosity for weak coupling and not too late times. This effect may provide an explanation for the apparent "nearly perfect" liquidity of the matter produced in nuclear collisions at the Relativistic Heavy Ion Collider without the assumption that it is a strongly coupled state.