Electron spin resonance study of γ-irradiated nylon 6

The free radicals trapped in oriented nylon 6 filaments after γ-irradiation under vacuum at room temperature were studied by ESR spectroscopy. The ESR spectrum measured after irradiation gradually changed to a broad singlet spectrum with decrease in the intensity. The ESR spectrum consisted of radicals with different orientation effects with respect to the outer magnetic field, and saturation effects in reference to microwave power. The simulation of the ESR spectrum from a Gaussian function gave a better fit to the observed spectrum than the calculation from a Lorentzian function. From the resolution of the spectrum from a Gaussian function, the observed spectrum is generated from three kinds of radicals: The relative radical concentration for the first, second, and third radical is about 75%, 6%, and 19% of the total radical concentration, respectively. With regard to the stability of the radicals, the third radical shows a comparatively long lifetime. The first and second radicals show almost identical lifetime, and their concentrations reduce to about 40% of the initial value during the 2 days at room temperature.     

Change in GPC elution volume of polymers by adsorption onto porous glass as column packing

The elution volume of polystyrene or of poly(ethylene glycol) of various molecular weights was measured in both tetrahydrofuran and benzene at 40 or 60°C by means of gel permeation chromatography utilizing columns packed with crosslinked polystyrene gel or porous glass. When the polystyrene gel was used as the column packing, a relationship between log [η]M and the peak elution volume for polystyrene agreed with that for poly(ethylene glycol). Using columns packed with glass, however, the elution volume of polystyrene was smaller than that of poly(ethylene glycol) at the same log [η]M. The results are considered to be attributable to the adsorption of poly(ethylene glycol) onto the glass. The effect of the adsorption on the elution volume was evaluated by assuming a universal calibration for columns containing porous glass; the deviation of the elution volume from the universal calibration curve increased with increase in molecular weight. At lower temperatures, even polystyrene was adsorbed onto the glass. Therefore, to reduce the adsorption of polymers on glass, it is necessary to increase the temperature or use surface treatment when porous glass is used as a GPC column packing.     

Novel Enantiocomplementary C2‐Symmetric Chiral Bis(imidazoline) Ligands: Highly Enantioselective Friedel–Crafts Alkylation of Indoles with Ethyl 3,3,3‐Trifluoropyruvate

Enantioselective Friedel–Crafts alkylations of a variety of indoles with ethyl 3,3,3‐trifluoropyruvate catalyzed by novel chiral m‐phenylenebis(imidazoline)‐copper(II) complexes or the bis(imidazoline)‐achiral acid combination afforded products with high enantioselectivity. Both enantiomers of indole derivatives can be prepared with high enantioselectivities by tuning the N‐substituents of the imidazoline.     

The Influences of Chain Length of Amylopectin on Resistant Starch in Rice (Oryza sativa L.)

Amylopectin is the principle component of starch. To elucidate the relationships between amylopectin and resistant starch content, six rice mutants with altered fine structure of amylopectin were selected for comparative studies with the primary wild type and two types of amylose‐extender (ae) mutants. Significant differences in resistant starch content were observed among mutants with similarity or differences in amylose levels. Mutants high in resistant starch had significantly increased proportions of short amylopectin chains with DP≤12, decreased levels of intermediate chains with size of 13≤DP≤36, and decreased fractions of long chains with DP≥37. Additionally, there was a mutant different to ae, which was characterized by an increased level of short chains with 8≤DP≤12 and 13≤DP≤24, and a decreased proportion of long chains with DP≥37. The increased contents of short chains with 8≤DP≤12 and decreased of intermediate and long chains with 24≤DP were clearly associated with the increase of resistant starch in rice.     

Facile Preparation of an Enzyme‐Immobilized Microreactor using a Cross‐Linking Enzyme Membrane on a Microchannel Surface

The enzyme microreactor has considerable potential for use in biotechnological syntheses and analytical studies. Simplifying the procedure of enzyme immobilization in a microreactor is attractive, and it is achievable by utilizing enzyme immobilization techniques and taking advantage of the characteristics of microfluidics. We previously developed a facile and inexpensive preparation method for an enzyme‐immobilized microreactor. The immobilization of enzymes can be achieved by the formation of an enzyme‐polymeric membrane on the inner wall of the microchannel through cross‐linking polymerization in a laminar flow. However, this method is unsuitable for use in conjunction with electronegative enzymes. Therefore, a novel preparation method using poly‐L ‐lysine [poly(Lys)] as a booster and an adjunct for the effective polymerization of electronegative enzymes was developed in this study. Using aminoacylase as a model for an electronegative enzyme, the reaction conditions for the enzyme‐cross‐linked aggregation were optimized. On the basis of the determined conditions, an acylase‐immobilized tubing microreactor was successfully prepared by cross‐linking polymerization in a concentric laminar flow. The resulting microreactor showed a higher stability against heat and organic solvents compared to those of the free enzyme. The developed method using poly(Lys) was applicable to various enzymes with low isoelectric points, suggesting that this microreactor preparation utilizing a cross‐linked enzyme in a laminar flow could be expanded to microreactors in which a broad range of functional proteins are employed.     

Enhancement of bonding strength by graded structure at interface between apatite layer and bioactive tantalum metal

Tantalum metal is a candidate for use as an implant material in high load-bearing bony defects, due to its attractive features such as high fracture toughness and high workability. This metal, however, does not have bone-bonding ability, i.e. bioactivity, and therefore the development of bioactive tantalum metal is highly desirable. It is known that the essential prerequisite for an artificial material to show bioactivity is to form a bonelike apatite layer on its surface in the body environment. The same type of apatite layer is formed in a simulated body fluid (SBF) with inorganic ion concentrations nearly equal to those of human blood plasma. The present authors previously showed that the apatite formation on tantalum metal in SBF was remarkably accelerated by treatment with 0.5 M-NaOH aqueous solution and subsequent firing at 300 °C, while untreated tantalum metal spontaneously formed the same apatite after a long soaking period. In the present study, the bonding strength of the apatite layer to the substrate was quantitatively evaluated in comparison with that to the untreated tantalum metal. Adhesive strength was measured as an estimation of bonding strength, and the surface microstructure of both the substrates was characterized in order to discuss the difference in the bonding strength in terms of surface structure. The apatite layer formed on the NaOH- and heat-treated tantalum metal shows higher adhesive strength than that formed on the untreated metal. The amorphous sodium tantalate layer formed on the tantalum metal by NaOH and heat treatments, has a smooth graded structure where its concentration gradually changes from the surface into the interior metal. Smooth graded structure with complex of apatite is constructed after soaking in SBF. The higher bonding strength of the apatite layer formed on the treated metal is attributed to its smooth graded structure.     

Autonomic control of heart rate during physical exercise and fractal dimension of heart rate variability

The objectives of the present study were to investigate autonomic nervous system influence on heart rate during physical exercise and to examine the relationship between the fractal component in heart rate variability (HRV) and the system's response. Ten subjects performed incremental exercise on a cycle ergometer, consisting of a 5-min warm-up period followed by a ramp protocol, with work rate increasing at a rate of 2.0 W/min until exhaustion. During exercise, alveolar gas exchange, plasma norepinephrine (NE) and epinephrine (E) responses, and beat-to-beat HRV were monitored. HRV data were analyzed by "coarse-graining spectral analysis" (Y. Yamamoto and R. L. Hughson. J. Appl. Physiol. 71: 1143-1150, 1991) to break down their total power (Pt) into harmonic and nonharmonic (fractal) components. The harmonic component was further divided into low-frequency (0.0-0.15 Hz) and high-frequency (0.15-0.8 Hz) components, from which low-frequency and high-frequency power (Pl and Ph, respectively) were calculated. Parasympathetic (PNS) and sympathetic (SNS) nervous system activity indicators were evaluated by Ph/Pt and Pl/Ph, respectively. From the fractal component, the fractal dimension (DF) and the spectral exponent (beta) were calculated. The PNS indicator decreased significantly (P < 0.05) when exercise intensity exceeded 50% of peak oxygen uptake (VO2 peak). Conversely, the SNS indicator initially increased at 50-60% VO2peak (P < 0.05) and further increased significantly (P < 0.05) at > 60% VO2peak when there were also more pronounced increases in NE and E.(ABSTRACT TRUNCATED AT 250 WORDS)     

Image contrast enhancement for two-photon fluorescence microscopy in a turbid medium

Image contrast enhancement is investigated for two-photon excitation fluorescence images of a microscopic sample that is buried underneath a turbid medium. The image contrast, which deteriorates rapidly with sample depth because of scattering loss, is enhanced by an increase in the average excitation power of the focused Gaussian (the TEM(00) mode) beam according to a compensation relation that has been derived by use of a Monte Carlo analysis of the scattering problem. A correct increase in the excitation power results in a detected fluorescence signal that remains invariant with sample depth. The scheme is demonstrated on images of DAPI-stained nuclei cells viewed underneath a suspension of 0.105-mum-diameter polystyrene spheres.