High pressure FTIR study of intramolecular hydrogen bonding and conformation of a small peptide in solution

Effect of pressure on conformational equilibria of a small peptide N-acetyl-l-Pro-l-Leu-Gly-NH₂ in a chloroform solution has been studied by FTIR spectroscopy. Absorption in the NH stretching region was measured at pressures in the 1–1080 bar range and at 296 K, and decomposed into component bands by least-squares fitting. Intensity ratios of bands which were assigned to a hydrogen-bond-free conformer and intramolecularly hydrogen-bonded conformers with 10- and 13-membered hydrogen bonded rings, respectively, were examined as a function of pressure. It was found that the conformer with the 13-membered ring has definitely smaller partial molar volume than the other two conformers which have nearly the same volume with each other. On the basis of a simple dielectric model, we have shown that the conformer with the 13-membered hydrogen-bonded ring has a considerably large dipole moment which is consistent with the α-helical structure suggested by the previous variable-temperature FTIR study.     

A New Approach to the Construction of BEDT-TTF Derivatives Condensed with Heterocycles via BF3-promoted Reactions of Organotin Thiolates

The synthesis of BEDT-TTF derivatives fused with heterocycles (3–7) has been accomplished via the BF₃-promoted reaction of organotin thiolates (8 and 9) with electrophiles (10 and 11). Electrical conductivities of radical cation salts derived from some of them were also investigated.     

Stark and Zeeman spectroscopies of 4f 66s6p 7G1-6 levels in Sm I under external electric and magnetic fields

Systematic study of hyperfine structures, Zeeman and Stark effects in Sm I is performed for the lowest ⁷G_1-6 levels belonging to the configuration 4f ⁶6s6p by atomic-beam laser spectroscopy with fluorescence detection. The hyperfine coupling constants of ⁷G_2-6 levels are determined. From the Zeeman splittings for the 4f ⁶6s ^{2 7}F_2-6 ? 4f ⁶6s6p ⁷G_2-6 transitions, g-values are determined for the ⁷G_2.6 levels and the precision is improved by several orders of magnitude. From the Stark splittings for the ⁷F_0-3 ? ⁷G_1-3 transitions, tensor polarizabilities α ₂(J) are determined for the upper ⁷G_1-3 levels. Particularly for the ⁷G₁ level (15 650.55 cm^?1) which has close-lying opposite-parity level, the isotope dependence of α ₂(J) is clearly observed for the first time.     

GENERATION AND PARTICIPATION OF O-2 IN 2-NITROPROPANE DIOXYGENASE REACTION

Abstract— 2-Nitropropane dioxygenase (EC 1. 13. 11) of the yeast Hansenula mrakii catalyzes the oxygenative denitrification of 2-nitropropane as follows:

The enzyme is significantly inhibited by superoxide dismutase and various scavengers for superoxide such as cytochrome c , epinephrine, thiols and polyhydric phenols. The scavengers added to the reaction mixture were oxidized or reduced. The addition of superoxide dismutase and the omission of 2-nitropropane or oxygen prevented the oxidation and the reduction of the scavengers. The enzyme catalyzes the formation of nitrite from 2-nitropropane by KO₂ added anaerobically.
One mole of NADH is bound per mole of the enzyme and predominantly the pro-R hydrogen of bound NADH is transferred to superoxide formed enzymatically or provided externally. The enzyme shows incomplete stereospecificity for hydrogen transfer from NADH.     

Hydration structure around a non-electrolyte molecule as revealed by monte carlo calculation: have you seen the “iceberg”?

Monte Carlo calculations have been carried out for pure water and an infinitely dilute aqueous solution of methanol at 298.15 K at ordinary density by the Metropolis method in NTV ensemble. The hydration structure around methanol revealed by a graphic display technique indicates a structure-forming effect near the hydrophobic group.     

Synthesis of (−)-terrecyclic acid A. Absolute configuration of terrecyclic acid A and quadrone

(?)-Terrecyclic acid A ($\text{15}$) was synthesized from (+)-fenchone ($\text{1}$). The absolute configuration of terrecyclic acid A and quadrone was established.     

Photoelectron spectra and angular distribution in reson three-photon ionization of atomic iron: J dependence

Kenetic energies and angular distributions of photoelectrons emitted by three-photon ionization fo atomic iron through two-photon resonant state e⁷D_J and e⁵ D_J, were measured, by using visible lasers. J-resolved photoelectron bands attributab to the a⁶D_J and a⁴F_j ionic states are reported.     

Observation of magnetic order of Cu-moment aroundx=0.12 in La2−x Ba x CuO4 and La2−x sr x CuO4 by μ+SR

Zero field positive muon spin rotation method ( ⁺SR) is applied on La_2–x Sr _x CuO₄ around forx=0.12 at which the high-T _c superconductivity (SC) is suppressed. The magnetically ordered state of Cu-moments, which is not a spin glass state but an antiferromagnetic like state, appears below 15 K for 0.105x0.120. The magnetic phase boundary is very similar to the one of the La_2–x Ba _x CuO₄ in which the structural transition from the low temperature orthorhombic (LTO) phase to the low temperature tetragonal (LTT) phase is observed aroundx=0.12. The present study suggests that there is no big difference of the electronic state of the CuO₂ plane between the La-Ba system and the La-Sr system and that the magnetic ordering of Cu-moments plays an important role for the suppression of the high-T _c SC aroundx=0.12 in both of the systems, although the LTO-LTT structural transition has not been observed yet in the La-Sr system.