Optical resolution by preferential crystallization of (1RS,3RS)-1,2,3,4-tetrahydro-6,7-dihydroxy-1-methyl-3-isoquinolinecarboxylic acid

The racemic structure of (1RS,3RS)-1,2,3,4-tetrahydro-6,7-dihydroxy-1-methyl-3-isoquinolinecarboxylic acid [(1RS,3RS)-1] was examined based on the melting point, solubility, and IR spectrum, with the aim of optical resolution by preferential crystallization. (1RS,3RS)-1 was indicated from these results to exist as a conglomerate. The successive optical resolution by preferential crystallization of (1RS,3RS)-1 yielded (1S,3S)- and (1R,3R)-1 with optical purities of 85--95% at 66--81% degrees of resolution, which were fully purified by recrystallization.     

The use of synchrotron radiation for study of structural changes in polymers during phase transition and deformation

An experimental method using monochromatized synchrotron radiation for a wide-angle x-ray scattering study of polymers during phase transition and deformation is described. Results obtained on low-density and high-density polyethylenes and on polypropylene are given. Melting processes could be studied conveniently by making exposures during a temperature scan; a few seconds were found sufficient to obtain a diffraction spectrum. This way relatively fast crystallization processes and the structural change accompanying stress relaxation could be followed easily. The crystalline-amorphous ratio was found to decrease continuously much below the melting temperature measured dilatometrically and by DSC, implying that in the α_c-relaxation transition region of polyethylene and polypropylene a structural change takes place. At the initial state of crystallization the 040 reflection in polypropylene was found to be stronger than the 110 one, while after crystallization has been completed this ratio was inverted. Equatorial spectra made after rapid uniaxial stretching of polypropylene sheet were found to exhibit a slight time dependence demonstrating that orientation went on after stretching had been stopped.     

Crystallization kinetics and excess free energy of H2O and D2O nanoscale films of amorphous solid water

Temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS) are used to investigate the crystallization kinetics and measure the excess free energy of metastable amorphous solid water films (ASW) of H(2)O and D(2)O grown using molecular beams. The desorption rates from the amorphous and crystalline phases of ASW are distinct, and as such, crystallization manifests can be observed in the TPD spectrum. The crystallization kinetics were studied by varying the TPD heating rate from 0.001 to 3 K/s. A coupled desorption-crystallization kinetic model accurately simulates the desorption spectra and accurately predicts the observed temperature shifts in the crystallization. Isothermal crystallization studies using RAIRS are in agreement with the TPD results. Furthermore, highly sensitive measurements of the desorption rates were used to determine the excess free energy of ASW near 150 K. The excess entropy obtained from these data is consistent with there being a thermodynamic continuity between ASW and supercooled liquid water.     

Preparation of optically active (2RS,3SR)-2-amino-3-hydroxy-3-phenylpropanoic acid (threo-beta-phenylserine) via optical resolutions by replacing and preferential crystallization

To obtain optically active threo-2-amino-3-hydroxy-3-phenylpropanoic acid (1) via optical resolutions by replacing and preferential crystallization, the racemic structure of (2RS,3SR)-1 hydrochloride [(2RS,3SR)-1.HCl] was examined based on the melting point, solubility, and infrared spectrum. (2RS,3SR)-1.HCl was indicated to exist as a conglomerate at room temperature, although it forms a racemic compound at the melting point. When, in optical resolution by replacing crystallization, L-phenylalanine methyl ester hydrochloride (L-2) was used as the optically active co-solute, (2R,3S)-1.HCl was preferentially crystallized from the supersaturated racemic solution; the use of D-2 as the co-solute afforded (2S,3R)-1.HCl with an optical purity of 95%. In addition, optical resolution by preferential crystallization was successfully achieved to give successively (2R,3S)- and (2S,3R)-1.HCl with optical purities of 90-92%. The (2R,3S)- and (2S,3R)-1.HCl purified by recrystallization from 1-propanol were treated with triethylamine in methanol to give optically pure (2R,3S)- and (2S,3R)-1.     

Preparation of optically active threo-2-amino-3-hydroxy-3-phenylpropanoic acid (threo-beta-phenylserine) via optical resolution

To obtain optically active threo-2-amino-3-hydroxy-3-phenylpropanoic acid (1), (2RS,3SR)-2-benzoylamino-3-hydroxy-3-phenylpropanoic acid [(2RS,3SR)-2] was first optically resolved using (1S,2S)- and (1R,2R)-2-amino-1-(4-nitrophenyl)-1,3-propanediol as the resolving agents to afford (2R,3S)- and (2S,3R)-2 in yields of 73% and 66%, based on half of the starting amount of (2RS,3SR)-2. Next, the racemic structures of ammonium and some organic ammonium salts of (2RS,3SR)-2 were examined based on melting point, solubility, and infrared spectrum, with the aim of optical resolution by preferential crystallization. The benzylammonium salt of (2RS,3SR)-2 was suggested to exist as a conglomerate at room temperature, although it forms a racemic compound at the melting point. The optical resolution by preferential crystallization of the racemic salt afforded the (2R,3S)- and (2S,3R)-salts with optical purities of 90-97%. The (2R,3S)- and (2S,3R)-2 obtained from the purified salts were hydrolyzed by reflux in hydrochloric acid to give (2R,3S)- and (2S,3R)-1.     

Optical resolution by preferential crystallization of (RS)-2-benzoylamino-2-benzyl-3-hydroxypropanoic acid and its use in synthesizing optically active 2-amino-2-methyl-3-phenylpropanoic acid

To synthesize optically active 2-amino-2-methyl-3-phenylpropanoic acid (1), (RS)-2-benzoylamino-2-benzyl-3-hydroxypropanoic acid [(RS)-2] was first optically resolved using cinchonidine as a resolving agent to yield optically pure (S)- and (R)-2 in yields of about 70%, based on half of the starting amount of (RS)-2. Next, the racemic structure of (RS)-2 was examined based on melting point, solubility, IR spectrum, and binary and ternary phase diagrams, with the aim of optical resolution by preferential crystallization of (RS)-2. Results indicated that the (RS)-2 exists as a conglomerate at room temperature, although it forms a racemic compound at the melting point. The optical resolution by preferential crystallization yielded (S)- and (R)-2 with optical purities of about 90%, which were fully purified by recrystallization. After O-tosylation of (S)- and (R)-2, reduction by zinc powder and sodium iodide gave (R)- and (S)-1, respectively.     

Molecular mobility and crystallinity in polytetramethylene ether glycol in the bulk and as soft component in polyurethanes

We revisit molecular mobility and crystallinity in a series of Polyurethanes prepared with polytetramethylene ether glycol (PTMEG) with varying molecular weights as soft component, methylene diisocyanate (MDI) as diisocyanate component and butanediol as chain extender in close comparison to the properties of the respective macrodiols used as soft segments. Modulated differential scanning calorimetry (MDSC) was utilized to study the glass transition and in detail crystallization and melting. Thermally stimulated depolarization currents (TSDC), and dielectric relaxation spectroscopy (DRS) were used to investigate local dynamics, dynamic glass transition and indirectly, crystallinity and morphology. The dielectric data were evaluated through representation by contour plots in the Arrhenius plane. Glass transition temperature of the diols is practically unaffected by molecular weight due to H-bonding effect, while for the PUs it showed a decreasing dependence due to higher microphase separation. Results are also discussed in terms of fragility. Crystallization of PTMEG becomes more intense and stable with increasing molecular weight, while the reflection of its melting process on its dielectric response was also observed. A weak crystallization process in the Polyurethane with long soft segments was well resolved using MDSC. Evidence for the occurrence of spinodal decomposition before this crystallization was observed by means of DRS.     

Roles of deeply supercooled ethanol in crystallization and solvation of LiI

The mechanisms of glass-liquid transition and crystallization of amorphous solid ethanol were investigated through detailed analyses of the interaction with LiI using time-of-flight secondary ion mass spectrometry and reflection absorption infrared spectroscopy. The LiI species adsorbed on the surface are incorporated into the bulk of ethanol at temperatures higher than 100 K, concomitantly with the reorganization of the ethanol molecules at the surface. This behavior is explicable by self-diffusion of the ethanol molecules as a consequence of the glass-liquid transition. The resulting liquid is a distinct phase, as revealed from the similarity of the IR absorption band to that of amorphous solid ethanol rather than liquid ethanol. The liquid-liquid phase transition occurs at 130 K, and a supercooled liquid ethanol is formed, as evidenced by formation of a metastable LiI solution when ethanol is deposited on the LiI film. The supercooled liquid ethanol is unstable, so that it crystallizes immediately at 130 K on the Ni(111) substrate. The film morphology changes continuously, even after crystallization, and the film abruptly becomes smoother before film evaporation. This behavior implies that crystallization is not completed and that a liquidlike phase coexists.     

Charge-transfer exciton transitions in anthracene-PMDA crystal

The reflection spectrum of the first singlet charge transfer transition of anthracene-PMDA (pyromellitic dianhydride) crystal has been obtained at temperatures close to 2 K. The spectrum is polarized along the stack axis and consists of a series of vibronic bands, approximately 500 cm^?1 wide, with impressed fine structure arising from intermolecular phonon modes. This fine structure is particularly prominent for the 00 band which starts with a zero-phonon line which is the most dominant feature of the entire spectrum. The zero-phonon line has a reflectivity of approximately 0.37 and a line width less than 5 cm^?1. This is the first time that an absolute reflection spectrum of a charge transfer transition with such vibronic details has been obtained. A preliminary discussion of the nature of the transition is presented.     

Two liquid phases of water in the deeply supercooled region and their roles in crystallization and formation of LiCl solution

The properties of supercooled liquid water and the mechanism of crystallization in it were investigated using time-of-flight secondary ion mass spectrometry and reflection absorption infrared spectroscopy. The self-diffusion of the water molecules commences at 136 K, and then the liquid-liquid phase transition occurs at 160-165 K. The latter is evidenced not only by the occurrence of fluidity but also by the formation of a LiCl solution. The infrared absorption band also changes drastically above 160 K due to crystallization of water (on the Au film) and the formation of LiCl solution (on the LiCl film). The immediate crystallization and dissolution of LiCl are thought to be characteristic of normal water that is created in a deeply supercooled region, indicating that viscous liquid water (T > 136 K) is transformed into supercooled liquid water at around 160 K. The crystallization kinetics is different between these two phases because the former (latter) involves nuclear growth (spontaneous nucleation). Without nuclei, crystallization is quenched below 160 K in the present experiment. It is suggested that the viscous liquid phase coexists at the surface or grain boundaries of metastable ice Ic.     

Crystallization and morphology of polymerized cyclic butylene terephthalate

The crystallization behavior and morphology of polymerized cyclic butylene terephthalate (pCBT) were investigated by thermal differential scanning calorimetry (DSC) and polarized light microscopy (PLM). The spherulite growth rate was analyzed based on the Hoffman and Lauritzen theory to better understand the crystallization behavior. We found four typical morphologic features of pCBT corresponding to the crystallization temperature spectrum: usual negative spherulite, unusual spherulite, mixed birefringence spherulite coexisting with boundary crystals, and highly disordered spherulitic crystallites. The Avrami crystallization kinetics confirmed the occurrence of combined heterogeneous nucleation accompanied by a change in the spherulitic shape of pCBT, which also agreed with the PLM results. The equilibrium melting temperature and glass transition temperature of pCBT were 257.8 °C and 41.1 °C, respectively. A regime II–III transition occurred at 200.9 °C, which was 10 °C lower than that reported for poly(butylene terephthalate) (PBT). Coinciding with and attributed to the regime transition, the boundary crystal disappeared at temperatures above 200 °C and the morphology changed from the mixed type to highly disordered spherulitic crystallites. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1127–1134, 2010     

负载激光染料香豆素151的MCM-41粉体及其纤维的光学性质研究

通过结晶包覆的方法将激光染料香豆素151成功地负载到具有介孔结构的MCM-41粉体和纤维中,制备了具有光致发光特性的MCM-41粉体和纤维材料,并通过SEM,SAXRD,UV-Vis和PL进行了表征.     

Induction and inhibition of preferential enrichment by controlling the mode of the polymorphic transition with seed crystals

Both induction and inhibition of "preferential enrichment", an unusual symmetry-breaking enantiomeric-resolution phenomenon observed upon simple recrystallization of a certain kind of racemic crystals from organic solvents, have been successfully achieved by controlling the mode of the polymorphic transition during crystallization with appropriate seed crystals. Such control of the polymorphic transition can be interpreted in terms of a novel phenomenon consisting of 1) the adsorption of prenucleation aggregates, 2) the heterogeneous nucleation and crystal growth of a metastable crystalline form, and 3) the subsequent polymorphic transition into the more stable form; these three processes occur on the same surface of a seed crystal. We refer to this phenomenon as an "epitaxial transition", which has been confirmed by means of in situ attenuated total reflection (ATR) FTIR spectroscopy in solution and the solid state, differential scanning calorimetry (DSC) measurements of the deposited crystals, and X-ray crystallographic analysis of the single crystals or the direct-space approach employing the Monte Carlo method with the Rietveld refinement for the structure solution from the powder X-ray diffraction data.     

Histogram Monte Carlo simulation on phase transitions in single‐polymer systems

Applying the histogram Monte Carlo simulation method and the bond‐fluctuation model, various phase transitions in single‐polymer systems were investigated. The critical transition temperature (Θ point) in the coil‐globule collapse transition of a macromolecular chain is accurately determined. Finite‐size scaling results near the transition point are verified. The first‐order transition associated with the freezing/crystallization of a polymer at a temperature below the Θ point is also observed. The free energy profiles associated with these two transitions are explicitly computed. Furthermore, the unfolding phase transition associated with stretching a collapsed polymer chain is investigated. The free energy profile associated with the transition is explicitly computed. Results on the energy cumulants and free energy profiles provide direct evidences for the first‐order nature of the unfolding phase transition.     

Isothermal crystallization kinetics of polypropylene latex–based nanocomposites with organo‐modified clay

The effect of organo‐modified clay (Cloisite 93A) on the crystal structure and isothermal crystallization behavior of isotactic polypropylene (iPP) in iPP/clay nanocomposites prepared by latex technology was investigated by wide angle X‐ray diffraction, differential scanning calorimetry and polarized optical microscopy. The X‐ray diffraction results indicated that the higher clay loading promotes the formation of the β‐phase crystallites, as evidenced by the appearance of a new peak corresponding to the (300) reflection of β‐iPP. Analysis of the isothermal crystallization showed that the PP nanocomposite (1% C93A) exhibited higher crystallization rates than the neat PP. The unfilled iPP matrix and nanocomposites clearly shows double melting behavior; the shape of the melting transition progressively changes toward single melting with increasing crystallization temperature. The fold surface free energy (σ_e) of polymer chains in the nanocomposites was lower than that in the PP latex (PPL). It should be reasonable to treat C93A as a good nucleating agent for the crystallization of PPL, which plays a determinant effect on the reduction in σ_e during the isothermal crystallization of the nanocomposites. The activation energy, ΔE_a, decreased with the incorporation of clay nanoparticles into the matrix, which in turn indicates that the nucleation process is facilitated by the presence of clay. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1927–1938, 2010     

Lithium analysis in Li-ion battery materials via a scanning electron microscopy-based approach

We performed Li analysis by reflection electron energy loss spectroscopy (REELS) with a scanning electron microscopy-based apparatus. It was possible to distinguish between Li compounds containing different transition metal elements spatially, via the spectrum imaging scheme of REELS spectra. We also acquired the Li spectrum for an Li-inserted graphite negative electrode. REELS measurements with hemispherical analyzer were performed to obtain high-quality spectra with sufficient energy resolution and compared with those from cylindrical mirror analyzer measurements; the former provided a more detailed chemical state evaluation of Li.     

Configurational studies on 2-[∝-(2-ethoxyphenoxy)benzyl] morpholine fce 20124

The relative configuration of the two diastereoisomers of (±)2-[?-(2-ethoxyphenoxy)benzyl] morpholine is determined by a synthesis involving regio and stereo specific reactions. (RS,RS) diastereoisomer FCE 20124 was separated into its (+) and (-) enantiomers both by crystallization of the optically active mandelate salt and by a multi-step synthesis from (+)-(2S,3R)-3-phenylglycidic acid.     

Can theory quantitatively model stratospheric photolysis? Ab initio estimate of absolute absorption cross sections of ClOOCl

We have calculated the absorption spectrum of dichlorine peroxide (ClOOCl) in the spectral range 250-400 nm. We have employed five different approaches to quantitatively model the absorption cross section (empirical broadening scheme, linearized harmonic reflection principle and full reflection principle with ground state density calculated using harmonic approximation, classical molecular dynamics, and path-integral molecular dynamics). We have also tested various single and multireference methods. We found that (i) the excitation characteristics of ClOOCl are sensitive on molecular geometries and therefore the ground state density has to be properly sampled and that (ii) single-reference methods tend to overestimate the absorption cross section and lead to a blueshift in the absorption maximum. The absorption spectrum calculated at the CASPT2 level with complete active space-configuration interaction (CAS-SCF) transition dipole moment with the ground state sampled via path-integral molecular dynamics is in a good agreement with the experiment. We, however, did not reach full agreement in the atmospherically relevant low-energy tail of the spectrum. The general message is that quantitative predictions are difficult even for a relatively small molecule as ClOOCl and the convergence, with respect to the electronic structure method, basis set used, and ground state sampling, needs to be carefully examined.     

On the possibility of exciton site splitting in PTS polydiacetylene crystal spectra

It is proposed that the splitting observed in the low temperature reflection spectrum of bis-paratoluene sulfonate diacetylene polymer single crystals is a manifestation of site splitting in a Frenkel exciton transition. Possible origins of the site splitting energy are discussed.