Radical alpha-C-H hydroxyalkylation of ethers and acetal

[reaction: see text] Epsilonthers and an acetal were found to undergo direct intermolecular addition to aldehydes under the Et(3)B/air conditions. This study presents a very unique and simple means for the radical alpha-C-H hydroxyalkylation of oxygen-containing compounds.     

Preparation of (Cyanomethylene)tributylphosphorane: a new mitsunobu-type reagent

(Cyanomethylene)tributylphosphorane (CMBP), which promoted the alkylation of various nucleophiles (HA) with alcohols (ROH) to give RA (Mitsunobu-type reaction), was prepared in two steps starting from chloroacetonitrile.     

Direct observation of rectified motion of vortices in a niobium superconductor

Using Lorentz microscopy to directly image vortices, we investigate vortex motion control and rectification in a niobium superconductor. We directly observe a net motion of vortices along microfabricated channels with a spatially asymmetric potential, even though the vortices were driven by an oscillatory field. By observing the individual motion of vortices, we clarify elementary processes involved in this rectification. To further demonstrate the ability to control the motion of vortices, we created a tiny vortex "racetrack" to monitor the motion of vortices in a closed circuit channel.     

Synthesis and characterization of fluorine‐containing polyesters by the polyaddition of bis(epoxide)s with active diesters

The synthesis and optical properties of polyesters with pendant fluorinated phenoxy groups were examined. The polyaddition of bisphenol AF diglycidyl ether ( 1 ) with fluorine‐containing terephtalates ( 2a–f ) was carried out with tetrabutylphosphonium chloride (TBPC) as the catalyst in chlorobenzene to afford the corresponding polyesters with number‐average molecular weights (M_n's) ranging from 15,200 to 30,000 in 88–96% yields. Furthermore, the polyaddition of 1 with isophthalate 2g and phthalate 2h also produced high‐molecular‐weight polyesters with M_n's = 22,700 and 22,600 in 88 and 84% yields, respectively. The linear relationship was observed between the fluorine contents and refractive indices of the obtained polyesters. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 213–222, 2003     

Measurements of exciton absorption with pico-second light pulses produced by a self-phase modulation technique

Time-resolved absorption spectra of the A exciton in CdSe are measured by using pico-second white-light pulses produced by a self-phase modulation technique. The absorption peak of the n = 1 A exciton shifts to the high-energy side due to the high-density effect. The magnitude of the shift reaches a maximum at 20 psec after the pulse excitation, which is considered to indicate that the time constant for the formation of the n = 1 excitons by band-to-band excitation is about 20 psec.     

Structural studies on C-amidated amino acids and peptides: function of amide group in molecular association in crystal structures of Val-Gly-NH2, Ser-Phe-NH2, Gly-Tyr-NH2 and Pro-Tyr-NH2 hydrochloride salts

As part of a series of elucidation of the structural features of peptides caused by C-terminal alpha-amidation, the crystal structures of H-Val-Gly-NH2, H-Ser-Phe-NH2, H-Gly-Tyr-NH2, and H-Pro-Tyr-NH2 hydrochloride salts were analyzed by the X-ray diffraction method. Although respective molecules take energetically allowable torsion angles concerning the backbone and side chains, their conformations are not necessarily the same as the corresponding unamidated ones. This results from the different molecular packing requirements, rather than from different conformational features inherent in the C-amidated and -unamidated peptides. As for the molecular packing feature, each peptide tended to form a repeated structure through those hydrogen bonds in which both amide NH and O=C groups participate. The chloride ions are located between the neighboring peptides and are hydrogen-bonded to the respective amide NHs, leading to the sheet structure. The hydrogen-bonding feature of the amide group and its function in molecular packing was discussed based on the results analyzed so far.