An Unusual Terpene Cyclization Mechanism Involving a Carbon–Carbon Bond Rearrangement

Terpene cyclization reactions are fascinating owing to the precise control of connectivity and stereochemistry during the catalytic process. Cyclooctat‐9‐en‐7‐ol synthase (CotB2) synthesizes an unusual 5‐8‐5 fused‐ring structure with six chiral centers from the universal diterpene precursor, the achiral C₂₀ geranylgeranyl diphosphate substrate. An unusual new mechanism for the exquisite CotB2‐catalyzed cyclization that involves a carbon–carbon backbone rearrangement and three long‐range hydride shifts is proposed, based on a powerful combination of in vivo studies using uniformly ¹³C‐labeled glucose and in vitro reactions of regiospecifically deuterium‐substituted geranylgeranyl diphosphate substrates. This study shows that CotB2 elegantly demonstrates the synthetic virtuosity and stereochemical control that evolution has conferred on terpene synthases.     

Solution properties of cellulose tris(3,5-dimethyl-phenylcarbamate)

The dilute-solution behavior and liquid crystal formation of cellulose tris(3,5-dimethylphenylcarbamate) (CTDC) in 1-methyl-2-pyrrolidone (NMP) at 25°C are discussed by summarizing our recent studies, and its molecular characteristics are compared with those of cellulose tris(phenylcarbamate) (CTC) in the same solvent. The molecular weight dependences of optical anisotropy factor, radius of gyration, intrinsic viscosity ([η]), and isotropic-cholesteric phase boundary concentration for CTDC are explained consistently by current theories based on the wormlike chain. An analysis of the newly measured [η] for CTC shows that the backbone conformation and chain stiffness are substantially the same for the two cellulose derivatives in NMP. However, a distinct difference in optical anisotropy is found and briefly discussed in relation to the higher optical resolution capacity of CTDC than that of CTC in chromatographic separation of racemic compounds.     

Photochemically-induced refractive index and fluoresence patterning on polymer films

The molecular design for large photo-induced refractive index changes in transparent visible light region was proposed and realized with norbornadiene polymers and poly(vinyl cinnamate). The patterning of pure refractive-index contract on their transparent films was made with near-field scanning optical microscopy (NSOM). Reversible fluorescence patterning on polymer films is also presented by using controlled energy transfer from a fluorescent pyromethene to a photochromic diarylethene.     

How does a choice of Markov partition affect the resultant symbolic dynamics?

The mutual relationship among Markov partitions is investigated for one-dimensional piecewise monotonic map. It is shown that if a Markov partition is regarded as a map-refinement of the other Markov partition, that is, a concept we newly introduce in this article, one can uniquely translate a set of symbolic sequences by one Markov partition to those by the other or vice versa. However, the set of symbolic sequences constructed using Markov partitions is not necessarily translated with each other if there exists no map-refinement relation among them. By using a roof map we demonstrate how the resultant symbolic sequences depend on the choice of Markov partitions.     

A semiclassical theory for nonseparable rovibrational motions in curved space and its application to energy quantization of nonrigid molecules

The nonseparability of vibrational and rotational motions of a nonrigid molecule placed in the rotationally isotropic space induces several important effects on the dynamics of intramolecular energy flow and chemical reaction. However, most of these studies have been performed within the framework of classical mechanics. We present a semiclassical theory for the motions of such nonrigid molecules and apply to the energy quantization of three body atomic cluster. It is shown numerically that the semiclassical spectum given without the correct account of the rotational symmetry suffers from unnecessary broadening of the resultant spectral lines and moreover from spurious peaks.     

On the spectrum for the artificial compressible system

Stability of stationary solutions of the incompressible Navier–Stokes system and the corresponding artificial compressible system is considered. Both systems have the same sets of stationary solutions and the incompressible system is obtained from the artificial compressible one in the zero limit of the artificial Mach number ? which is a singular limit. It is proved that if a stationary solution of the incompressible system is asymptotically stable and the velocity field of the stationary solution satisfies an energy-type stability criterion by variational method with admissible functions being only potential flow parts of velocity fields, then it is also stable as a solution of the artificial compressible one for sufficiently small ?. The result is applied to the Taylor problem.     

Development of a rapid process monitoring method for dry-coated tableting process by using near-infrared spectroscopy

A nondestructive transmittance near-infrared (NIR) method for detecting off-centered cores in dry-coated (DC) tablets was developed as a monitoring system in the DC tableting process. Caffeine anhydrate was used as a core active pharmaceutical ingredient (API), and DC tablets were made by the direct compression method. NIR spectra were obtained from these intact DC tablets using the transmittance method. The reference assay was performed with HPLC. Calibration models were generated by partial least squares (PLS) regression and principal component regression (PCR) utilizing external validations. Hierarchical cluster analysis (HCA) of the results confirmed that NIR spectroscopy correctly detected off-centered cores in DC tablets. We formulated and used the Centering Index (CI) to evaluate the precision of core alignment and generated an NIR calibration model that could correctly predict this index. The principal component (PC) 1 loading vector of the final calibration model indicated that it could specifically detect the misalignment of tablet cores. The model also had good linearity and accuracy. The CIs of unknown sample tablets predicted by the final calibration model and those calculated through the HPLC analysis were closely parallel with each other. These results demonstrate the validity of the final calibration model and the utility of the transmittance NIR spectroscopic method developed in this study as a monitoring system in DC tableting process.     

Bio‐based nanocomposites composed of photo‐cured epoxidized soybean oil and supramolecular hydroxystearic acid nanofibers

A mixture of epoxidized soybean oil (ESO), (R)‐12‐hydroxystrearic acid (HSA) and a photoinitiator for cationic polymerization in the ESO/HSA weight ratio 10/1 was heated to 100 °C and gradually cooled to room temperature to give bio‐based gelatinous material. The photo‐curing of the gel afforded a nanocomposite composed of crosslinked ESO and supramolecular HSA nanofibers. The transmission electron microscopy observation of the photo‐cured ESO/HSA revealed that dendritic clusters of HSA nanofibers are formed in the crosslinked ESO matrix. In the differential scanning calorimetry chart of the ESO/HSA, a thermal transition from the mesophase composed of supramolecular nanofibers to isotropic state was observed at 67 °C (ΔH = 22.6 J/g‐HSA), while the T_m of crystalline HSA is 77.7 °C (ΔH_m = 159 J/g‐HSA). Tensile strength at 20 °C of the ESO‐HSA was ～80% higher than that of photo‐cured ESO without HSA. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 669–673, 2009