New plastoquinones isolated from the brown alga, Sargassum micracanthum

Four new plastoquinones were isolated from the methanolic extract of the brown alga, Sargassum micracanthum. Their structures were elucidated based on spectroscopic analysis and chemical conversions from 2-geranylgeranyl-6-methyl-1,4-benzohydroquinone. These plastoquinones exhibited significant antioxidant activities such as an inhibitory effect on lipid peroxidation and a radical scavenging effect on 1,1-diphenyl-2-picrylhydrazyl (DPPH). Some of the new plastoquiones showed cytotoxic activity against cancer cell line.     

Shallow donor state due to nitrogen-hydrogen complex in diamond

Based on an ab initio calculation, we propose a possible shallowing of a nitrogen (N) donor in diamond, in contrast to the traditional thinking that it is very deep. A complex defect of N and hydrogen (H), N-H-N, should be much shallower than an isolated N donor. A qualitative scenario for formation of the N-H-N defects is presented. The existence of this complex is strongly suggested by a recent discovery of a new muonium center in N-rich diamond.     

Determination of traces of ruthenium by addition of cerium(IV) and atomic absorption spectrometry

The sensitivity of the determination of ruthenium by flame atomic absorption spectrometry is increased 60 times by adding 1 × 10^?2 M cerium(IV). Calibration is linear over the range of 0.05–5 μg ml^?1 ruthenium. A method applicable to nitrosylruthenium complexes is described. The increased sensitivity results from formation of ruthenium tetroxide.     

Synthesis of new Galβ1→4Fuc segments useful for biological investigations

Useful segments (1, 2) for chemical probes embedded in a Galβ1→4Fuc unit were designed and prepared for characterizing sugar-binding proteins in Caenorhabditis elegans. Segment 1 with an amino group terminus was used as a recognition unit in affinity chromatography. It was revealed that some proteins (annexins and galectins) in C. elegans have an affinity for Galβ1→4Fuc.     

Isolation and characterization of atropisomers of seven-membered-ring benzolactams

The atropisomeric properties of seven-membered-ring benzolactams (7a-c and 8a) [1,5-benzodiazepin-2-one (a), 1,5-benzothiazepin-4-one (b), and 1-benzazepin-2-one (c)] were examined. The atropisomers were isolated as the diastereomers with an (S)-phenethylamide moiety, which were characterized by X-ray crystallography, and the barriers to their interconversion were clarified.     

2-universal -lattices over real quadratic fields

Let be a real quadratic field with m a square-free positive rational integer, and be the ring of integers in F. An -lattice L on a totally positive definite quadratic space V over F is called r-universal if L represents all totally positive definite -lattices l with rank r over . We prove that there exists no 2-universal -lattice over F with rank less than 6, and there exists a 2-universal -lattice over F with rank 6 if and only if m=2, 5. Moreover there exists only one 2-universal -lattice with rank 6, up to isometry, over .     

Quaternary universal forms over \mathbf{Q}(\sqrt{13})

Let be a real quadratic field over Q with m a square-free positive rational integer and be the integer ring in F. A totally positive definite integral n-ary quadratic form f=f(x ₁,…,x _n )=∑_1≤i,j≤n α _ij x _i x _j ( ) is called universal if f represents all totally positive integers in . Chan, Kim and Raghavan proved that ternary universal forms over F exist if and only if m=2,3,5 and determined all such forms. There exists no ternary universal form over real quadratic fields whose discriminants are greater than 12. In this paper we prove that there are only two quaternary universal forms (up to equivalence) over . For the proof of universality we apply the theory of quadratic lattices.