Investigation of the electrospray response of lysine-, arginine-, and homoarginine-terminal peptide mixtures by liquid chromatography/mass spectrometry

Guanidination has been used to investigate how modification of the lysine eta-amino group into the corresponding guanidino group affects response in electrospray (ES) mass spectrometry (MS). Selected ion monitoring (SIM) analysis of equimolar mixtures containing arginine-, lysine- and the corresponding homoarginine-terminal peptides following liquid chromatography (LC) showed differences in ES response. The ionisation behaviour of the standard peptides is in accordance with the postulated higher stability of the guanidino group present on arginine- and homoarginine-terminal peptides. Modification of the separation conditions employed during LC demonstrates that relative abundances of electrosprayed peptides ions rely mostly on peptide structure.     

Synthesis and properties of noncyclic polyether compounds. Part V : The influence of acid and concentration of cations on the uphill transport rates of cations and selectivities through liquid membranes by synthetic,noncyclic polyether ionophores

The effects of acid and cation concentration on the uphill transport rates of cations and selectivities through chloroform liquid membrane by noncyclic polyether ionophores, which are pentaethylene glycol derivatives containing both 8-quinolyt and o-carboxylphenyl terminal groups, have been demonstrated. Using sulfuric, oxalic, or polyphosphoric acid in aqueous solution, the initial transport rates and the amount of cation transported by the ionophores after two days were larger than those using hydrochloric or nitric acid. Using picric acid, the amount of cation transported decreased greatly. It was confirmed that it decreased where an acid could easily be counter-transported by the ionophore through liquid membranes. On the other hand, it was found that the rates, amounts of cation transported, and selectivities, change with the changing of the cation concentration in the aqueous solutions. When the cation concentration in both aqueous solutions is high enough compared with the pH gradient between the two aqueous solutions, the rate, amount, and selectivity of the ionophore for potassium ion increases compared with when the cation concentration is low.     

Stereospecific photocyclization of α-bisulfenylated keto compounds. Cis-dihydrobenzothiophenes

Irradiation of α-bisulfenylated keto compounds in acetonitrile affords the cis-fused dihydrobenzothiophenes which are dehydrated to benzothiophenes in high yields.     

Substituent effect of the coordinated pyridine in a series of pyrazolato bridged dinuclear diiron(II) complexes on the spin-crossover behavior

Two series of pyrazolato bridged dinuclear NCS and NCBH3 diiron(II) complexes with various types of 3- or 4-substituted pyridines, [{Fe(NCS or NCBH3)(X-py)}2(mu-bpypz)2], were prepared and their variable-temperature magnetic susceptibilities were measured. There were found linear correlations of the spin-crossover temperatures Tc not only between the NCS and NCBH3 complexes with the corresponding substituted pyridines, but also between the Tc and the Hammett constants, supporting the electronic substituent effect of the coordinated pyridine rather than a steric effect. The ligand field and the interelectronic repulsion parameters together with the thermodynamic data and/or cooperativity factor were discussed in relation with their spin-crossover behavior.     

Direct imaging of the alkali metal site in K-doped fullerene peapods

The structure of K-doped fullerene peapods has been investigated by means of high-resolution transmission electron microscopy and electron energy-loss spectroscopy (EELS). It is proven that the potassium atoms can be doped at the intermolecular sites within C60 peapods. The EELS spectrum of potassium (K) L edge clearly exhibits the feature of K+ in the doped peapod and consequently suggests n-type doping. These results encourage the realization of a one-dimensional superconducting wire based on the nanotube peapods.     

Determination of optical isomers for left-handed or right-handed chiral double-wall carbon nanotubes

The handedness relationship between adjacent layers in nested double-wall carbon nanotubes (DWNTs) has been investigated for the first time. Our high-resolution electron microscopy analysis on a series of specimen tilts can successfully tell the handedness of each constituent nanotube in a DWNT, and therefore the chiral indices (n, m) including their optical isomers [(n, m) or (m, n)] of inner and outer nanotubes can be uniquely determined. It is shown that right-handed and left-handed nanotubes are equally distributed for both the inner and outer nanotubes in the examined specimens and a preferable handedness relationship between the adjacent layers in DWNT may exist.     

Direct two-step spin-crossover through [HS-HS]...[LS-LS] at the plateau in dinuclear diiron(II) complex [{Fe(NCBH3)(4phpy)}2(mu-bpypz)2

The variable temperature magnetic susceptibility, X-ray crystallography, and IR and Raman spectra of a new dinuclear complex [{Fe(II)(NCBH(3))(4-phpy)}(2) mu-bpypz)(2)] demonstrated the first two-step spin-crossover associated with a 1 : 1 mixture of high-spin pair [HS-HS] and low-spin pair [LS-LS] at the plateau.