Synthetic procedure for N-fmoc amino acyl-N-sulfanylethylaniline linker as crypto-Peptide thioester precursor with application to native chemical ligation

N-Sulfanylethylanilide (SEAlide) peptides 1, obtainable using Fmoc-based solid-phase peptide synthesis (Fmoc SPPS), function as crypto-thioesters in native chemical ligation (NCL), yielding a wide variety of peptides/proteins. Their acylating potential with N-terminal cysteinyl peptides 2 can be tuned by the presence or absence of phosphate salts, leading to one-pot/multifragment ligation, operating under kinetically controlled conditions. SEAlide peptides have already been shown to be promising for use in protein synthesis; however, a widely applicable method for the synthesis of N-Fmoc amino acyl-N-sulfanylethylaniline linkers 4, required for the preparation of SEAlide peptides, is unavailable. The present study addresses the development of efficient condensation protocols of 20 naturally occurring amino acid derivatives to the N-sulfanylethylaniline linker 5. N-Fmoc amino acyl aniline linkers 4 of practical use in NCL chemistry, except in the case of the proline- or aspartic acid-containing linker, were successfully synthesized by coupling of POCl(3)- or SOCl(2)-activated Fmoc amino acid derivatives with sodium anilide species 6, without accompanying racemization and loss of side-chain protection. Furthermore, SEAlide peptides 7 possessing various C-terminal amino acids (Gly, His, Phe, Ala, Asn, Ser, Glu, and Val) were shown to be of practical use in NCL chemistry.     

Anomalous magnetic properties of tetraphenylporphinato Co(II) complex in the solid state

The α,β,γ,δ-tetraphenylporphinatocobalt(II) complex is found to exist in two distinct, but interconvertible, polycrystalline forms. The one with a tetragonal crystal symmetry (species B) gives the EPR spectrum which has been attributed to the low-spin electronic configuration of Co(II) ion in an axial crystal field. The other form (species A) having a triclinic crystal symmetry shows no easily detectable EPR signal even at liquid helium temperature.Magnetic susceptibility and magnetization meaurements demonstrated that the complex is paramagnetic in both forms, but the species (A) is characterized by ferromagnetic exchange coupling, while the species (B) behaves as a normal paramagnet.The experimental susceptibility versus 1/T curve can be reproduced quite well by using the Ising method. The g values thus obtained (g_| = 5.2,g_⊥ = 0) can not be explained by a low-spin electronic configuration, but are consistent with a high-spin ground state. Assigning a high-spin state to the species (A), the first such case in Co(II) porphine complexes, can not only explain the absence of EPR signal, but is also supported by the results of X-ray structural analyses.     

Preparation of cellulose nanofibers using green and sustainable chemistry

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Light‐Switchable Janus [2]Rotaxanes Based on α‐Cyclodextrin Derivatives Bearing Two Recognition Sites Linked with Oligo(ethylene glycol)

Two Janus [2]rotaxanes, 5a and 5b , with α‐cyclodextrin (α‐CD) derivatives substituted on the 6‐position with two recognition sites (azobenzene and heptamethylene (C7)) that were linked with linkers of different lengths (oligo(ethylene glycol) with a degree of polymerization equal to 2 or approximately 21) were synthesized and characterized. 2D ROESY NMR spectroscopy and circular dichroism (cd) spectra demonstrated that the recognition site of the α‐CD moiety was switched by photoisomerization of the azobenzene moiety in 5a and 5b . The different size changes of 5a and 5b in hydrodynamic radius (R_H) owing to the different length of linker between two recognition sites were observed by pulse‐field‐gradient spin‐echo NMR spectroscopy. The kinetic results indicated that the different length of linker had no or a weak effect for the photoisomerization process of 5a and 5b .     

A dinuclear MnIII-CuII single-molecule magnet

The reaction of 1/3 equivalent of CuCl2.2H2O with MnCl2.4H2O and 5-bromo-2-salicylideneamino-1-propanol (H(2)5-Br-sap) in methanol gave dark brown crystals of [MnIIICuIICl(5-Br-sap)2(MeOH)] (1). Complex 1 has an alkoxo-bridged dinuclear core of MnIII and CuII ions, which have elongated octahedral and square-planar coordination geometries, respectively. In dc magnetic susceptibility measurements, chi(m)T values increased as the temperature was lowered, followed by a sudden decrease below 20 K. This behavior is indicative of the occurrence of intramolecular ferromagnetic interactions, and fitting gave an S=5/2 spin ground state with an exchange coupling constant J(MnCu) of +78 cm(-1). Magnetization data collected as a function of temperature and applied magnetic field were analyzed by using a spin Hamiltonian with isotropic Zeeman and axial zero-field splitting (ZFS) terms, and a negative D(5/2) value (-1.86 cm(-1)) was obtained. A high-field EPR (HFEPR) spectrum (342.0 GHz) at 4.2 K was composed of four peaks, and two additional peaks at higher magnetic field appeared as the temperature was increased. The temperature dependences in the HFEPR spectra are indicative of a negative D(5/2) value, and fitting of the data gave D(5/2)=-1.81 cm(-1). In the ac magnetic susceptibility measurements, frequency dependent in-phase (chi(m)') and out-of-phase (chi(m)') signals with peak maxima at 0.7-1.5 K were observed and small peaks below 0.7 K appeared. The ac susceptibility data supports that 1 is a single-molecule magnet (SMM). Arrhenius plots for the chi(m)' peaks from 0.7-1.5 K gave the re-orientation energy barrier (DeltaE) of 10.5 K with a pre-exponential factor of 8.2x10(-8) s.     

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.     

Theory of the Half-integer Quantum Hall Effect in Graphene

The unusual quantum Hall effect (QHE) in graphene is described in terms of the composite (c-) bosons, which move with a linear dispersion relation. The “electron” (wave packet) moves easier in the direction [1 1 0 c-axis] ≡ [1 1 0] of the honeycomb lattice than perpendicular to it, while the “hole” moves easier in [0 0 1]. Since “electrons” and “holes” move in different channels, the particle densities can be high especially when the Fermi surface has “necks”. The strong QHE arises from the phonon exchange attraction in the neighborhood of the “neck” surfaces. The plateau observed for the Hall conductivity and the accompanied resistivity drop is due to the superconducting energy gap caused by the Bose-Einstein condensation of the c-bosons, each forming from a pair of one-electron–two-fluxons c-fermions by phonon-exchange attraction. The half-integer quantization rule for the Hall conductivity: (1/2)(2P?1)(4e²/h), P=1,2,..., is derived.     

Normal generation of line bundles of high degrees on smooth algebraic curves

We give necessary and sufficient conditions for non-special line bundles of degree2g — 2 and 2g — 3 being not normally generated. We also provide criteria for special line bundles of degreed > 2g — 6 being normally generated. This work was done under JSPS-KOSEF joint research program 1997. The first named author was partially supported by Grant-in-Aid for Scientific Research, the Ministry of Education, #10440051. The second named author was partially supported by BSRI(1998-015-D00023) and SNU(99-5-l-031). During the period when this paper was prepared for publication, the second named author was enjoying the hospitality of ICTP. The third named author was partially supported by Grant-in-Aid for Scientific Research, the Ministry of Education, #09640043.