Polycondensation of activated L‐valine and L‐leucine esters with various lewis acids

To develop a novel polycondensation method for the preparation of poly (amino acid)s, we screened a transition metal or a rare‐earth triflate as a Lewis acid for the polycondensation of activated amino acid esters in N,N‐dimethylformamide solutions at room temperature. The polymerizations of 4‐nitrophenyl L ‐leucinate ( 1a ) and 4‐nitrophenyl L ‐valinate ( 1b ) scarcely proceeded without any Lewis acid at room temperature. In the presence of 5 mol % metal triflates, especially scandium(III) trifluoromethanesulfonate, the polymerizations of both monomers were promoted effectively. The products, which were collected by the reaction mixture being poured into water, were recognized as poly(L ‐valine)s by Fourier transform infrared spectroscopy, gel permeation chromatography analysis, and ¹H NMR spectroscopy. These results showed that a metal triflate as a Lewis acid could coordinate to a carbonyl oxygen of activated L ‐valinate and L ‐leucinate even in a highly polar solvent, such as N,N‐dimethylformamide; therefore, the polymerizations of activated L ‐valinate and L ‐leucinate were promoted. Because steric hindrance derived from the isobutyl group in 1b was less than that of the isopropyl unit in 1a , the effect of the metals was not as sensitive for the polymerization of 1b . © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 543–547, 2007     

Optical Perfect Shuffle Interconnection Using Computer-Generated Blazed Grating Array

In this paper a new type element that can implement perfect shuffle (PS) network of free spatial optical interconnection is presented. It is a microoptics array element consisting of a series of sub-blazed gratings with different spatial frequency. The array has highly efficient light energy and a very simple setup. It can realize 1-D, 2-D PS networks and their inverse transforms. Also, the array can conveniently realize microminiaturization and multilevel interconnection and other forms of interconnections.Presented at the International Commission for Optics Topical Meeting, Kyoto, 1994.     

Divergent synthesis of L-sugars and L-iminosugars from D-sugars

An efficient divergent synthesis of L-sugars and L-iminosugars from D-sugars is described. The important intermediate, delta-hydroxyalkoxamate, prepared from D-glucono-/galactono-1,5-lactone, was cyclized under Mitsunobu conditions to give the O-cyclized oxime compound and the N-cyclized lactam compound as mixtures. A more detailed investigation revealed that the appropriate protecting groups and solvents controlled the specificity for the O-/N-cyclization of the delta-hydroxyalkoxamate. Suitable protection at the 6-position of delta-hydroxyalkoxamate, derived from D-glucono-1,5-lactone, afforded the corresponding O-alkylation product alone. Thus we succeeded in applying this to the total synthesis of L-iduronic acid. In contrast, with both TBDMS as the protecting group and RCN as the solvent the efficient conversion of D-glucono/galactono-1,5-lactone into the corresponding L-iminosugars (L-idonolactam and L-altronolactam) was achieved.     

NMR on short-lived beta-emitter43Ti using new fragment separator at LBL

The lifetime and magnetic moment of⁴³Ti (I^π-7/2⁻, T_1/2=0.50 sec), one of the mirror beta-radioactive nuclei in the f_7/2-shell, have been measured with a fragment separator built at the Bevalac of the LBL. By means of the beta-NMR method on⁴³Ti, a preliminary value of the magnetic moment of⁴³Ti was determined to be μ=(0.70±0.07) μ_π.     

Crystal and molecular structure of 10,20-epoxy-grayanotoxin-II

The photooxidation with HgO in benzene and the hydrolysis with 2%-KOH in methanol of the grayanotoxin (GTX) derivative (4) gave a 10,20-epoxy-grayanotoxin-II(5). The crystal structure of (5) has been determined by X-ray diffraction at room temperature. The crystal is monoclinic, space group P2₁, with a = 14.248(10) Å, b = 6.670(10) Å, c = 9.990(10) Å, = 105.507(8)°, V = 914.9(2) ų, Z = 2. The structure was solved by direct methods and refined by full-matrix least squares methods to a final R1 = 0.046 (wR2 = 0.0833) for 1161 independent reflections. The molecule has a pentacyclic structure consisting of two five-membered, one six-membered, one seven-membered, and one three-membered rings. The three-membered ring is connected with the seven-membered ring by spiro-type bond.     

Deeply bound hole states and isobaric analog states observed by neutron pickup reactions on even tin isotopes

Deeply bound hole states in the odd tin isotopes ^{115, 117, 119, 123}Sn were investigated by using 81 MeV (³He, α) and 52 MeV (p, d) reactions. Excitation of low-spin states was largely suppressed in (³He, α) reactions due to the angular-momentum mismatch so that the excitation energies and widths of the $\text{1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ states have been clearly determined. DWBA analyses showed that the deeply bound hole states have spectroscopic factors less than 20% of the sum-rule limit. Isobaric analog states $\text{1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{, 2}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{and}\text{2}\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ corresponding to the ground and two lowest excited states of In isotopes were investigated in ^{115, 117, 119, 121, 123}Sn isotopes. Coulomb displacement energies were deduced. DWBA analyses of these states were used to check the calculations for the deeply bound states. The spectroscopic factors of the analog states are in good agreement with the sum-rule prediction.     

Quasi-gamma bands in even-mass Xe AND Ba nuclei

Low-lying excited states of ^124,126Xe and ¹³²Ba have been studied by means of in-beam γ-ray spectroscopy in (p, xny) reactions. Excitation functions, angular distributions and γ-γ coincidence spectra were obtained. The 2₂⁺ , 3⁺, 4₂⁺ and 5⁺ levels were observed at the following excitation energies in keV: 846.4(2₂⁺), 1247.5(3⁺), 1437.3 (4₂⁺), 1836.6(5⁺) in ¹²⁴Xe, 879.7(2₂⁺), 1317.3(3 ⁺), 1488.2(4₂⁺), 1903.1(5 ⁺) in ¹²⁶Xe and 1032.1(2₂⁺), 1511.3(3⁺), 1729.9(4₂⁺) in ¹³²Ba. The 2214.3 and 2561.7 keV levels in ¹²⁶Xe were tentatively assigned as the 6₂⁺ and 7⁺ levels, respectively. These 2₂⁺, 3 ⁺, 4₂⁺, 5⁺, 6₂⁺and 7⁺ levels are interpreted as members of a quasi-γ band. The E2/M1 mixing ratios of the 2₂⁺ → 2₁⁺ transitions in ^124,126Xe and ¹³²Ba were obtained as + 6.3^+5.3_?2.0 + 10.8^7.8_?3.2 and + 8.3^+4.9_?2.2, respectively.     

Effect of long-chain branching on the relation between steady-flow and dynamic viscosity of polyethylene melts

The steady-state viscosity η, the dynamic viscosity η′, and the storage modulus G′ of several high-density and low-density polyethylene melts were investigated by using the Instron rheometer and the Weissenberg rheogoniometer. The theoretical relation between the two viscosities as proposed earlier is:\documentclass{article}\pagestyle{empty}\begin{document}$ \eta \left( {\dot \gamma } \right){\rm } = {\rm }\int {H\left( {\ln {\rm }\tau } \right)} {\rm }h\left( \theta \right)g\left( \theta \right)^{{\raise0.7ex\hbox{$3$} \!\mathord{\left/ {\vphantom {3 2}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$2$}}} \tau {\rm }d{\rm }\ln {\rm }\tau $\end{document}, where \documentclass{article}\pagestyle{empty}\begin{document}$ \theta {\rm } = {\rm }{{\dot \gamma \tau } \mathord{\left/ {\vphantom {{\dot \gamma \tau } 2}} \right. \kern-\nulldelimiterspace} 2} $\end{document}; \documentclass{article}\pagestyle{empty}\begin{document}$ {\dot \gamma } $\end{document} is the shear rate, H is the relaxation spectrum, τ is the relaxation time, \documentclass{article}\pagestyle{empty}\begin{document}$ g\left( \theta \right){\rm } = {\rm }\left( {{2 \mathord{\left/ {\vphantom {2 \pi }} \right. \kern-\nulldelimiterspace} \pi }} \right)\left[ {\cot ^{ - 1} \theta {\rm } + {\rm }{\theta \mathord{\left/ {\vphantom {\theta {\left( {1 + \theta ^2 } \right)}}} \right. \kern-\nulldelimiterspace} {\left( {1 + \theta ^2 } \right)}}} \right] $\end{document}, and \documentclass{article}\pagestyle{empty}\begin{document}$ h\left( \theta \right){\rm } = {\rm }\left( {{2 \mathord{\left/ {\vphantom {2 \pi }} \right. \kern-\nulldelimiterspace} \pi }} \right)\left[ {\cot ^{ - 1} \theta {\rm } + {\rm }{{\theta \left( {1{\rm } - {\rm }\theta ^2 } \right)} \mathord{\left/ {\vphantom {{\theta \left( {1{\rm } - {\rm }\theta ^2 } \right)} {\left( {1{\rm } + {\rm }\theta ^2 } \right)^2 }}} \right. \kern-\nulldelimiterspace} {\left( {1{\rm } + {\rm }\theta ^2 } \right)^2 }}} \right] $\end{document}. Good agreement between the experimental and calculated values was obtained, without any coordinate shift, for high-density polyethylenes as well as for a low density sample with low n_w, the weight-average number of branch points per molecule. The correlation, however, was poor with low-density samples with large values of the long-chain branching index n_w. This lack of coordination can be related to n_w. The empirical relation of Cox and Merz failed in a similar way.