Polymer scrambling: macromolecular radical crossover reaction between the main chains of alkoxyamine-based dynamic covalent polymers

A novel polymer hybridization method, "polymer scrambling", was developed on the basis of the macromolecular radical crossover reaction between the main chains of dynamic covalent polymers. The macromolecular crossover reaction was successfully monitored by GPC and NMR measurements. The present methodology is innovative for the preparation of novel polymer hybrid materials at the nanometer scale.     

Simultaneous determination of water-soluble vitamins in a vitamin-enriched drink by an in-capillary enzyme reaction method

The in-capillary enzyme reaction method was used to determine riboflavin phosphate in a vitamin-enriched drink based on its conversion to riboflavin (vitamin B2) with alkaline phosphatase. Simultaneously, three water-soluble vitamins [thiamine nitrate (vitamin B2 mononitrate), pyridoxine hydrochloride (vitamin B6 hydrochloride) and nicotinamide (vitamin PP)] and anhydrous caffeine in the drink were subjected to quantitative analysis. In the system, electrophoretic migration was used to mix zones containing the substrate (riboflavin phosphate) and the enzyme (alkaline phosphatase). The reaction was then allowed to proceed in the presence of a weak electric field and, finally, the product (riboflavin) of enzyme reaction and other water-soluble vitamins migrated under the influence of an applied electric field to the detector. All the active ingredients and the formulation excipients were successfully separated by micellar electrokinetic chromatography with 135 mM sodium dodecyl sulfate. To prevent inhibition of enzyme reaction by the addition of sodium dodecyl sulfate to the reaction zone, sandwich mode injection, in which plugs of sandwich solution without sodium dodecyl sulfate were introduced into the capillary on both sides of the reaction zone, was utilized as a barrier to protect the enzyme reaction from the inhibitor. The relationship between the peak area of the product and the concentration of the substrate was calculated in the in-capillary enzyme reaction method. Excellent linearity was obtained, with correlation coefficients of 0.9999. The established method was validated and demonstrated to be applicable to the determination of the five active ingredients, including riboflavin phosphate, in a commercial vitamin-enriched drink. No interference from the formulation excipients was observed. Good linearities were obtained, with correlation coefficients above 0.999. Recoveries and precisions ranged from 99.3 to 101.8%, and from 0.1 to 2.5% RSD, respectively. Good agreement was obtained between the established method and traditional high-performance liquid chromatographic methods. These results suggest that the in-capillary enzyme reaction method can be used for the simultaneous determination of riboflavin phosphate and other water-soluble vitamins in pharmaceuticals.     

On the dispersion managed soliton

We review various methods used to study the dispersion managed soliton for nonlinear return-to-zero pulse propagation in optical fibers. A numerical averaging method, the guiding center soliton, the variational method both with a simple and with an extended ansatz, as well as the multiscale theory are discussed and numerically compared, allowing us to show their domains of applicability. Their relative merits and demerits are then exposed. (c) 2000 American Institute of Physics.     

Bifurcation analysis of the motion of an asymmetric double pendulum subjected to a follower force: Codimension three problem

Local and global bifurcations in the motion of a double pendulum subjected to a follower force have been studied when the follower force and the springs at the joints have structural asymmetries. The bifurcations of the system are examined in the neighborhood of double zero eigenvalues. Applying the center manifold and the normal form theorem to a four-dimensional governing equation, we finally obtain a two-dimensional equation with three unfolding parameters. The local bifurcation boundaries can be obtained for the criteria for the pitchfork and the Hopf bifurcation. The Melnikov theorem is used to find the global bifurcation boundaries for appearance of a homoclinic orbit and coalescence of two limit cycles. Numerical simulation was performed using the original four-dimensional equation to confirm the analytical prediction.     

Electronic stress tensor analysis of molecules in gas phase of CVD process for gesbte alloy

We analyze the electronic structure of molecules which may exist in gas phase of chemical vapor deposition process for GeSbTe alloy using the electronic stress tensor, with special focus on the chemical bonds between Ge, Sb, and Te atoms. We find that, from the viewpoint of the electronic stress tensor, they have intermediate properties between alkali metals and hydrocarbon molecules. We also study the correlation between the bond order which is defined based on the electronic stress tensor, and energy‐related quantities. We find that the correlation with the bond dissociation energy is not so strong while one with the force constant is very strong. We interpret these results in terms of the energy density on the “Lagrange surface,” which is considered to define the boundary surface of atoms in a molecule in the framework of the electronic stress tensor analysis. © 2015 Wiley Periodicals, Inc.     

Replica state exchange metadynamics for improving the convergence of free energy estimates

Metadynamics (MTD) is a powerful enhanced sampling method for systems with rugged energy landscapes. It constructs a bias potential in a predefined collective variable (CV) space to overcome barriers between metastable states. In bias‐exchange MTD (BE‐MTD), multiple replicas approximate the CV space by exchanging bias potentials (replica conditions) with the Metropolis–Hastings (MH) algorithm. We demonstrate that the replica‐exchange rates and the convergence of free energy estimates of BE‐MTD are improved by introducing the infinite swapping (IS) or the Suwa‐Todo (ST) algorithms. Conceptually, IS and ST perform transitions in a replica state space rather than exchanges in a replica condition space. To emphasize this, the proposed scheme is called the replica state exchange MTD (RSE‐MTD). Benchmarks were performed with alanine polypeptides in vacuum and water. For the systems tested in this work, there is no significant performance difference between IS and ST. © 2015 Wiley Periodicals, Inc.     

The Evaluation of Noninvasive Measurements of Erythema as a Potential Surrogate for DNA Damage in Repetitively UV‐exposed Human Skin

Erythema (i.e. visible redness) and DNA damage caused by ultraviolet radiation (UVR) in human skin have similar action spectra and show good correlation after a single exposure to UVR. We explored the potential to use instrumental assessments of erythema as a surrogate for DNA damage after repeated exposures to UVR. We exposed 40 human subjects to three different exposure schedules using two different UVR sources. Cyclobutane‐pyrimidine dimers (CPDs) in skin biopsies were measured by immunofluorescence, and erythema was assessed by both the Erythemal Index (EI) and the Oxy‐hemoglobin (Oxy‐Hb) content. Surprisingly, the skin with the highest cumulative dose ended up with the lowest level of DNA damage, and with the least erythema, as assessed by Oxy‐Hb (but not EI) 24 h after the last UV exposure. Although the level of CPDs, on average, paralleled Oxy‐Hb (R² = 0.80–0.94, P = 0.03–0.11), the correlation did not hold for the pooled individual measurements (R² = 0.009, P = 0.37) due to potential individual differences in UV‐induced photoadaptation. We suggest that the methodology may be optimized to improve the correlation between DNA damage level and erythema to enable noninvasive risk assessment based on erythema/Oxy‐Hb content for individual human subjects.     

A 1-hydroxy-2,3,1-benzodiazaborine-containing π-conjugated system: Synthesis,optical properties and solvent-dependent response toward anions

Our interest in the functionalization of OH-substituted azaborines prompted us to synthesize a 1-hydroxy-2,3,1-benzodiazaborine conjugated with 1,8-naphthalimide 1. Its fluorescence was dramatically affected by the nature of the solvent. In particular, the use of DMSO, which has a relatively high donor number (DN = 29.8), led to a remarkable decrease in the fluorescence intensity (Φ_F = 0.0014), possibly due to intermolecular hydrogen-bonding interactions (Me₂SO?HOB). The presence of the hydroxyl group on boron led to a solvent-driven colorimetric response towards anions; high selectivity for F^? over other anions in DMSO, and responded to AcO^? and F^? in THF, as shown by UV/vis titrations, NMR, and mass spectroscopic analysis. The nucleus-independent chemical shift (NICS) indices suggested that hydrogen bonding interactions between Me₂SO and HOB reduced the aromaticity of the benzodiazaborine macrocycle, causing an increase in the negative character of the boron. The increase in the polarity of the BN bond may prevent acetate-binding of 1 in DMSO.     

Asymmetric conjugate addition of 5-benzylfurfurals to nitroalkenes using a diaminomethylenemalononitrile organocatalyst

A pyrrolidine–diaminomethylenemalononitrile organocatalyst efficiently promotes the asymmetric direct bisvinylogous Michael addition of 5-benzylfurfural derivatives to nitroalkenes, affording the corresponding ε-regioselective addition products in high yields with up to 86% ee.