A constructive solution to a problem of ranking tournaments

A tournament is an oriented complete graph. The problem of ranking tournaments was firstly investigated by P. Erd?s and J. W. Moon. By probabilistic methods, the existence of ?? ?? unrankable” tournaments was proved. On the other hand, they also mentioned the problem of explicit constructions. However, there seems to be only a few of explicit constructions of such tournaments. In this note, we give a construction of many such tournaments by using skew Hadamard difference sets which have been investigated in combinatorial design theory.     

Interactions of counterions with dextran sulfate in aqueous solutions

Counterion activity coefficients in solutions of dextran sulfate with and without added salts were determined potentiometrically by using a cation-exchange membrane and a sodium glass electrode. Dextran sulfate was shown to interact with monovalent cations in the order of preference: K⁺ > Cs⁺ > Na⁺ > Li⁺, whereas no specificity was found for bivalent cations. On the basis of light-scattering measurements, the expansion of the dextran sulfate polyion in solutions of alkali metal salts was found to fall in the same order as the counterion activity coefficients in salt-free solutions. It was also shown that the dextran sulfate polyion assumes a more extended conformation in magnesium chloride solution than in calcium chloride. These results were substantiated by measurements of solution viscosities.     

Transmembrane nanopores from porphyrin supramolecules

A porphyrin-based nanopore was constructed through a bilayer lipid membrane (BLM). The macrocyclic porphyrin (the inner diameter = ca. 2.1 nm) having six carboxylic acid groups directed up and down was synthesized by self-assembly of three trisporphyrins, metathesis linking, and subsequent hydrolysis. The porphyrin was incorporated into soybean lecithin based BLM, and the ion currents through the nanopore were observed under 500 mM KCl, LiCl, CaCl2, and tetraalkylammonium chloride solutions, indicating formation of a large pore through BLM. Blocking of the ion current was achieved by addition of the polycationic fourth-generation PAMAM dendrimer.     

Yessotoxin analogues in several strains of Protoceratium reticulatum in Japan determined by liquid chromatography-hybrid triple quadrupole/linear ion trap mass spectrometry

Several strains of Protoceratium reticulatum, one of the dinoflagellates producing yessotoxins (YTXs), were collected from various shellfish producing areas in Japan. YTXs in the cultured strains were analyzed by liquid chromatography-mass spectrometry (LC-MS). Neutral loss scan monitoring, multiple reaction monitoring (MRM) for more than 20 YTX analogues, and full-scan MS/MS spectra obtained with a hybrid triple quadrupole/linear ion trap mass spectrometer showed that yessotoxin (YTX), 45,46,47-trinoryessotoxin (trinorYTX), 1-homoyessotoxin (homoYTX), and 45,46,47-trinor-1-homoyessotoxin (trinor-1-homoYTX) were the dominant toxins in these strains of P. reticulatum. Enone isomer of 42,43,44,45,46,47,55-heptanor-41-oxoyessotoxin (noroxoYTX enone) was also detected in some strains. Toxin profiles and contents were different among the strains. Some strains produced YTX, trinorYTX, 1-homoYTX, trinor-1-homoYTX, and noroxoYTX enone, whereas other strains produced only YTX or 1-homoYTX. This is the first identification of 1-homoYTX and noroxoYTX enone in P. reticulutum in Japan. Some strains did not produce any detectable YTX analogues.     

Internal-friction study of the interstitial–substitutional effect on the deformation behaviour of Nb–O,Nb–Ta–O and Nb–Mo–O single crystals

To investigate the interstitial-substitutional interaction in dislocations, the effect of 0 on the temperature, frequency and amplitude dependence of the internal friction Q ^?1 in Nb–O, Nb-20 mol% Ta–O and Nb-20 mol% Mo–O single crystals has been studied (f = 1.55–8.2 Hz) in the temperature range from 298 to 1473 K. In our previous study, Nb–Mo and Nb–Ta single crystals were found to be strengthened by solute O. It was also suggested that the interstitial–substitutional interaction in dislocations contributes to the increase in their critical resolved shear stress (CRSS). In this study, Snoek-type relaxation peaks due to O are observed between 500 and 700 K in all the single crystals. The Snoek peak of Nb-20mol% Mo–O consisting of several peaks is analysed. The activation energy of the Snoek peak in Nb-20mol% Mo–O is higher than that of Nb–O. These results are attributable to the existence of the interstitial–substitutional complexes. The amplitude dependence of Q ^?1 at intermediate and high temperatures decreases as the O content increases. Moreover, the breakaway stress of Nb-20 mol% Mo–O still has a high value at 1200K and does not decrease much even at 1473 K. This suggests that the formation of Mo–O complexes reduces the dislocation mobility at high temperatures. From the results, the effect of the interstitial-substitutional interaction on the CRSS was discussed.     

Total synthesis of (-)-brevisin: a concise synthesis of a new marine polycyclic ether

The first and highly efficient total synthesis of (-)-brevisin has been achieved. The title compound was synthesized in only 29 steps (longest linear sequence) from commercially available starting materials. The synthesis provided over 70 mg of a marine polycyclic ether compound.     

Fullerene- and pyromellitdiimide-appended tripodal ligands embedded in light-harvesting porphyrin macrorings

Three new tripyridyl tripodal ligands appended with either fullerene or pyromellitdiimide moieties, named C(60)-s-Tripod, C(60)-l-Tripod, and PI-Tripod, were synthesized and introduced into a porphyrin macroring N-(1-Zn)(3) (where 1-Zn = trisporphyrinatozinc(II)). From UV-vis absorption and fluorescence titration data, the binding constants of C(60)-s-Tripod, C(60)-l-Tripod, and PI-Tripod with N-(1-Zn)(3) in benzonitrile were estimated to be 3 × 10(8), 1 × 10(7), and 2 × 10(7) M(-1), respectively. These large binding constants denote multiple interactions of the ligands to N-(1-Zn)(3). The binding constants of the longer ligand (C(60)-l-Tripod) and the pyromellitdiimide ligand (PI-Tripod) are almost the same as those without the fullerene or pyromellitdiimide groups, indicating that they interact via three pyridyl groups to the porphyrinatozinc(II) coordination. In contrast, the larger binding constants and the almost complete fluorescence quenching in the case of the shorter ligand (C(60)-s-Tripod) indicate that the interaction with N-(1-Zn)(3) is via two pyridyl groups to the porphyrinatozinc(II) coordination and a π-π interaction of the fullerene to the porphyrin(s). The fluorescence of N-(1-Zn)(3) was quenched by up to 80% by the interaction of C(60)-l-Tripod. The nanosecond transient absorption spectra showed only the excited triplet peak of the fullerene on selective excitation of the macrocyclic porphyrins, indicating that energy transfer from the excited N-(1-Zn)(3) group to the fullerenyl moiety occurs in the C(60)-l-Tripod/N-(1-Zn)(3) composite. In the case of PI-Tripod, the fluorescence of N-(1-Zn)(3) was quenched by 45%. It seems that the fluorescence quenching probably originates from electron transfer from the excited N-(1-Zn)(3) group to the pyromellitdiimide moiety.     

An efficient approach for the characterization of mucin-type glycopeptides: the effect of O-glycosylation on the conformation of synthetic mucin peptides

Despite the growing importance of mucin core O-glycosylation in many biological processes including the protection of epithelial cell surfaces, the immune response, cell adhesion, inflammation, and tumorigenesis/metastasis, the regulation mechanism and conformational significance of the multiple introduction of α-GalNAc residues by UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferases (ppGalNAcTs) remains unclear. Here we report an efficient approach by combining MS and NMR spectroscopy that allows for the identification of O-glycosylation site(s) and the effect of O-glycosylation on the peptide backbone structures during enzymatic mucin domain assembly by using an isoform UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase-T2 (ppGalNAcT2) in vitro. An electron-capture dissociation device in a linear radio-frequency quadrupole ion trap (RFQ-ECD) combined with a time-of-flight (TOF) mass spectrometer was employed for the identification of Thr/Ser residues occupied by α-GalNAc branching among multiple and potential O-glycosylation sites in the tandem repeats of human mucin glycoproteins MUC4 (Thr-Ser-Ser-Ala-Ser-Thr-Gly-His-Ala-Thr-Pro-Leu-Pro-Val-Thr-Asp) and MUC5AC (Pro-Thr-Thr-Val-Gly-Ser-Thr-Thr-Val-Gly). In the present study, O-glycosylation was initiated specifically at Thr10 in naked MUC4 peptide and additional introduction of α-GalNAc proceeded preferentially but randomly at three other Thr residues to afford densely glycosylated MUC4 containing six α-GalNAc residues at Thr1, Ser2, Ser5, Thr6, Thr10, and Thr15. On the contrary, O-glycosylation of naked MUC5AC peptide occurred predominantly at consecutive Thr residues and led to MUC5AC with four α-GalNAc residues at Thr2, Thr3, Thr7, and Thr8. The solution structures determined by NMR spectroscopic studies elicited that the preferential introduction of α-GalNAc at Thr10 of MUC4 stabilizes specifically a β-like extended backbone structure at this area, whereas other synthetic models with a single α-GalNAc residue at Thr1, Thr6, or Thr15 did not exhibit any converged three-dimensional structure at the proximal peptide moiety. Such conformational impact on the underlying peptides was proved to be remarkable in the glycosylation at the consecutive Thr residues of MUC5AC.     

Molecular cable-like 1-D iodic spiral chains covered with triple helices stabilized in guest-included chiral porous framework

The supramolecular crystal {[Pr(DMFA)](3)[Ni(II)(Hbim)(3)](2)I}(n) with intricate chiral networks of [Ni(II)(Hbim)(3)](-) molecules is reported. It includes a cationic architecture as a guest, constructed from chiral nanotubes that penetrate I(-) chains with spiral channels wrapped by triple helices. The I(-) chains have AC conductivity in crystals like a molecular cable.