Bulk and surface magnetization of Co atoms in rutile Ti(1-x)Co(x)O(2-δ) thin films revealed by x-ray magnetic circular dichroism.

We have studied magnetism in Ti(1-x)Co(x)O(2-δ) thin films with various x and δ by soft x-ray magnetic circular dichroism (XMCD) measurements at the Co L(2, 3) absorption edges. The estimated ferromagnetic moment by XMCD was 0.15-0.24 µ(B)/Co at the surface, while in the bulk it was 0.82-2.25 µ(B)/Co, which is in the same range as the saturation magnetization of 1.0-1.5 µ(B)/Co. These results suggest an intrinsic origin of the ferromagnetism. The smaller moment of the Co atom at the surface is an indication of a magnetically dead layer of a few nanometers thick at the surface of the thin films.

Signature of carrier-induced ferromagnetism in Ti(1-x)Co(x)O(2-delta): exchange interaction between high-spin Co2+ and the Ti 3d conduction band.

X-ray photoemission spectroscopy measurements were performed on thin-film samples of rutile Ti(1-x)Co(x)O(2-delta) to reveal the electronic structure. The Co 2p core-level spectra indicate that the Co ions take the high-spin Co2+ configuration, consistent with substitution on the Ti site. The high-spin state and the shift due to the exchange splitting of the conduction band suggest strong hybridization between carriers in the Ti 3d t(2g) band and the t(2g) states of the high-spin Co+2 . These observations support the argument that room temperature ferromagnetism in Ti(1-x)Co(x)O(2-delta) is intrinsic.

A convenient NMR method for in situ observation of aerobically cultured cells.

We observed P31-NMR signals of intracellular phosphorylated metabolites, i.e. ATP, NAD(H) and UDPG, in the aerobically cultured cells of AJ13375 (a derivative of E. coli K-12) without a cell culture circulating system, which needs much more cells. Each NMR spectrum of 40 ml cell-culture was obtained with a 25 mm Phi sample tube mini-fermenter equipped with a pH electrode and three supply routes for O2 gas, aqueous ammonia and glucose. Spectra were measured at 15-min intervals. When glucose in the culture medium was consumed, P31-NMR signals of ATP disappeared first and then those of ADP decreased to below the limit of detection. The intracellular concentration of ATP was estimated to be approximately 7 mM.

An atypical heme-binding structure of cytochrome c1 of Euglena gracilis mitochondrial complex III.

Complex III was purified from submitochondrial particles prepared from Euglena gracilis. The purified complex consisted of 10 subunits and lost antimycin sensitivity. The Euglena complex III showed an atypical difference absorption spectrum for cytochrome c1 with its alpha-band maximum at 561 nm. The pyridine ferrohemochrome prepared from covalently bound heme in the Euglena complex III had an alpha-peak at 553 nm. This wavelength is the same as that of pyridine ferrohemochrome prepared from Euglena mitochondrial cytochrome c (c-558), the heme of which is linked to only a single cysteine residue through a thioether bond. Cytochrome c1 which was a heme-stained subunit with a molecular mass of 32.5 kDa was isolated from the purified complex III and its N-terminal sequence of 46 amino acids was determined. On the basis of apparent homologies to cytochromes c1 from other sources, this sequence included the heme-binding region. However, the amino acid at position 36, corresponding to the first cysteine involved in heme linkage in other cytochromes c1, was phenylalanine. Position 39, corresponding to the second cysteine, was not identified despite the treatment for removal of the heme and carboxymethylation of the expected cysteine. The unidentified amino acid is assumed to be a derivative of cysteine to which the heme is linked through a single thioether bond. The histidine-40 corresponding to the probable fifth ligand for heme iron was conserved in Euglena cytochrome c1.