2‐connected 7‐coverings of 3‐connected graphs on surfaces

An m‐covering of a graph G is a spanning subgraph of G with maximum degree at most m. In this paper, we shall show that every 3‐connected graph on a surface with Euler genus k ≥ 2 with sufficiently large representativity has a 2‐connected 7‐covering with at most 6k ? 12 vertices of degree 7. We also construct, for every surface F² with Euler genus k ≥ 2, a 3‐connected graph G on F² with arbitrarily large representativity each of whose 2‐connected 7‐coverings contains at least 6k ? 12 vertices of degree 7. © 2003 Wiley Periodicals, Inc. J Graph Theory 43: 26–36, 2003     

Detection of a metallo-beta-lactamase (IMP-1) by fluorescent probes having dansyl and thiol groups

A fluorescent probe for the detection of a metallo-beta-lactamase (IMP-1), N-[2-(5-dimethylaminonaphthalen-1-ylsulfonylamino)ethyl]-3- mercaptopropionamide (Dansyl-C2SH), 1, was designed based on combining the inhibitory function of mercaptocarboxylate and a fluorophore. The binding of 1 to IMP-1 was investigated by fluorescence spectroscopy. Compound 1 can act as fluorescent probe for detecting IMP-1 selectively.     

Quantitative evaluation of stress distribution in bulk polymer samples through the comparison of mechanical behaviors between giant single‐crystal and semicrystalline samples of poly(trans‐1,4‐diethyl muconate)

The Raman shift and crystallite modulus were measured under the application of tensile force for a giant single crystal and a series of uniaxially oriented semicrystalline samples of poly(trans‐1,4‐diethyl muconate) (polyEMU). The apparent Raman shift factor α^app or a vibrational frequency shift per 1 GPa tensile stress was higher for the semicrystalline samples with lower crystallinity or lower bulk modulus. The apparent crystallite modulus E or Young's modulus along the chain axis in the crystalline region was not constant but varied remarkably between the giant single crystal and semicrystalline samples. A systematic change in α^app and E among the polyEMU samples with different preparation history could be interpreted quantitatively on the basis of a mechanical series parallel model consisting of crystalline and amorphous phases. The origin of different E and α^app was speculated to be a stress concentration on the taut‐tie chain contained as a parallel crystalline component in the mechanical model. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 444–453, 2003     

Biological activities of chemically synthesized derivatives of lipid A: tetraacetyl-monosaccharides linked to 2,3-acyloxyacylglucosamine-4-phosphate

The mitogenicity and lethal toxicity of chemically synthesized lipid A analogs, in which 2,3-acyloxyacylglucosamine-4-phosphate (acyl-GlcN-4P) is linked to a tetraacetyl (Ac4)-monosaccharide, i.e., Ac4-glucose (A-211), Ac4-mannose (A-212), Ac4-galactose (A-213) or Ac4-glucosamine (A-214), were compared with those of tetraacetyl-3-deoxy-D-manno-2-octulosonic acid (Ac4-KDO) linked to acyl-GlcN-4P (A-203). All the compounds were capable of increasing incorporation of 3H-thymidine into splenocytes of C57BL/6 mice at doses of 50 and 100 micrograms/ml, but the mitogenic activity of A-203 at these doses seems to be stronger than those of the analogs. Intravenous injection of A-203, A-211, and A-213 did not exhibit lethal toxicity even at a high dose (50 micrograms/mouse) in C57BL/6 mice loaded with D-galactosamine hydrochloride. However, A-212 and A-214 showed lethality at the doses of 10 and 50 micrograms/mouse, respectively. The findings indicate that the biological activity of these compounds is affected by the kind of monosaccharide linked to acyl-GlcN-4P.     

Photoinduced hydrogen production by direct electron transfer from photosystem I cross-linked with cytochrome c3 to [NiFe]-hydrogenase

The photosynthetic reaction center is an efficient molecular device for the conversion of light energy to chemical energy. In a previous study, we synthesized the hydrogenase/photosystem I (PSI) complex, in which Ralstonia hydrogenase was linked to the cytoplasmic side of Synechocystis PSI, to modify PSI so that it photoproduced molecular hydrogen (H2). In that study, hydrogenase was fused with a PSI subunit, PsaE, and the resulting hydrogenase-PsaE fusion protein was self-assembled with PsaE-free PSI to give the hydrogenase/PSI complex. Although the hydrogenase/PSI complex served as a direct light-to-H2 conversion system in vitro, the activity was totally suppressed by adding physiological PSI partners, ferredoxin (Fd) and ferredoxin-NADP+-reductase (FNR). In the present study, to establish an H2 photoproduction system in which the activity is not interrupted by Fd and FNR, position 40 of PsaE from Synechocystis sp. PCC6803, corresponding to the Fd-binding site on PSI, was selected and targeted for the cross-linking with cytochrome c3 (cytc3) from Desulfovibrio vulgaris. The covalent adduct of cytc3 and PsaE was stoichiometrically assembled with PsaE-free PSI to form the cytc3/PSI complex. The NADPH production by the cytc3/PSI complex coupled with Fd and FNR decreased to approximately 20% of the original activity, whereas the H2 production by the cytc3/PSI complex coupled with hydrogenase from Desulfovibrio vulgaris was enhanced 7-fold. Consequently, in the simultaneous presence of hydrogenase, Fd, and FNR, the light-driven H2 production by the hydrogenase/cytc3/PSI complex was observed (0.30 pmol Hz/mg chlorophyll/h). These results suggest that the cytc3/PSI complex may produce H2 in vivo.     

High-performance liquid chromatography of coenzyme Q-related compounds and its application to biological materials

A convenient and precise method for the separation and determination of coenzyme Q (CoQ)-related compounds (CoQ homologues, plastoquinone-9, ubichromenol-9, etc.) was developed using high-performance liquid chromatography (HPLC). All compounds tested were separated using a reverse-phase column with a suitable mobile phase and detected at a wavelength of 275 nm. CoQ extracts in plasma and erythrocytes were purified by thin-layer chromatography prior to HPLC analysis, but such purification was not necessary when determining CoQ in urine and tissues. Hydroquinone forms of CoQ existing in animal tissues were oxidized to the corresponding quinone forms with potassium hexacyanoferrate(III). This HPLC method was applied satisfactorily to the determination of the contents of CoQ homologues in human and animal samples. CoQ10 was the only homologue detected in human samples, and CoQ8, CoQ9 and CoQ10 were native homologues of CoQ in rat tissues. Ubichromenol-9 and plastoquinone-9 were not detected in these samples.     

Atoms-in-molecules analysis of extended hypervalent five-center, six-electron (5c-6e) C(2)Z(2)O interactions at the 1,8,9-positions of anthraquinone and 9-methoxyanthracene systems

To clarify the nature of five-center, six-electron (5c-6e) C(2)Z(2)O interactions, atoms-in-molecules (AIM) analysis has been applied to an anthraquinone, 1,8-(MeZ)(2)ATQ (1 (Z=Se), 2 (Z=S), and 3 (Z=O)), and a 9-methoxyanthracene system, 9-MeO-1,8-(MeZ)(2)ATC (4 (Z=Se), 5 (Z=S), and 6 (Z=O)), as well as 1-(MeZ)ATQ (7 (Z=Se), 8 (Z=S), and 9 (Z=O)) and 9-MeO-1-(MeZ)ATC (10 (Z=Se), 11 (Z=S), and 12 (Z=O)). The total electronic energy density (H(b)(r(c))) at the bond critical points (BCPs), an appropriate index for weak interactions, has been examined for 5c-6e C(2)Z(2)O and 3c-4e CZO interactions of the n(p)(O)sigma*(Z--C) type in 1-12. Some hydrogen-bonded adducts were also re-examined for convenience of comparison. The total electronic energy densities varied in the following order: OO (3: H(b)(r(c))=0.0028 au)=OO (6: 0.0028 au)>OO (9: 0.0025 au)> or =NNHF (0.0024 au)> or =OO (12: 0.0023 au)>H(2)OHOH (0.0015 au)>SO (8: 0.0013 au)=SO (2: 0.0013 au)> or =SO (11: 0.0012 au)=SO (5: 0.0012 au)>HFHF (0.0008 au)=SeO (10: 0.0008 au)=SeO (4: 0.0008 au)> or =SeO (1: 0.0007 au)> or =SeO (7: 0.0006 au)>HCNHF (-0.0013 au). H(b)(r(c)) values for SO were predicted to be smaller than the hydrogen bond of H(2)OHOH and H(b)(r(c)) values for SeO are very close to or slightly smaller than that for HFHF in both the ATQ and 9-MeOATC systems. In the case of Z=Se and S, H(b)(r(c)) values for 5c-6e C(2)Z(2)O interactions are essentially equal to those for 3c-4e CZO if Z is the same. The results demonstrate that two n(p)(O)sigma*(Z--C) 3c-4e interactions effectively connect through the central n(p)(O) orbital to form the extended hypervalent 5c-6e system of the sigma*(C--Z)n(p)(O)sigma*(Z--C) type for Z=Se and S in both systems. Natural bond orbital (NBO) analysis revealed that n(s)(O) also contributes to some extent. The electron charge densities at the BCPs, NBO analysis, and the total energies calculated for 1-12, together with the structural changes in the PhSe derivatives, support the above discussion.     

Molecular understanding of the adhesive interactions between silica surface and epoxy resin: Effects of interfacial water

The molecular mechanism of the adhesion between silica surface and epoxy resin under atmospheric conditions is investigated by periodic density-functional-theory (DFT) calculations. Slab models of the adhesion interface were built by integrating a fragment of epoxy resin and hydroxylated (0 0 1) surface of α-cristobalite in the presence of adsorbed water molecules. Effects of adsorbed water on the adhesion interaction are evaluated on the basis of geometry-optimized structures, adhesion energies, and forces. Calculated results demonstrate that adsorbed water molecules significantly reduce both the adhesion energies and forces of the silica surface–epoxy resin interface. The reduction of adhesion properties can be associated with structural deformation of water molecules confined in the tight space between the adhesive and adherend as well as structural flexibility of the hydrogen-bonding network in the interfacial region during detachment of the epoxy resin from the hydrophilic silica surface. © 2018 Wiley Periodicals, Inc.     

A convenient stereoselective synthesis of β-lactams from β-hydroxy-α-thioalkylesters prepared from Michael/aldol tandem reaction or stereoselective addition of thiols to the Baylis-Hillman adducts

A convenient stereoselective synthesis of β-lactams from thio-Michael/aldol tandem adduct is described. syn-Selective tandem reaction followed by amidation and intramolecular S_N2 reaction provided β-lactams in diastereomerically pure form. The tandem reaction with aliphatic aldehydes, on the other hand, afforded a mixture of diastereomers of corresponding tandem adducts in about 3:1 ratio so that the conversion to β-lactams afforded a diastereomeric mixture. As an alternative approach to prepare the tandem adducts, the stereoselective Michael addition of aliphatic thiols to Baylis-Hillman adduct was developed. The stereoselectivity was sensitive to the protective group at the hydroxyl group and TBS protection brought the most successful syn-selective formation of the tandem adducts. The procedure could be applied to the ketone derivatives of the Baylis-Hillman adduct but no selectivity was observed for the nitrile-Baylis-Hillman adducts. A similar conversion of the adduct provided desired β-lactams stereoselectively.     

Application of plug–plug technique to ACE experiments for discovery of peptides binding to a larger target protein: A model study of calmodulin‐binding fragments selected from a digested mixture of reduced BSA

To discover peptide ligands that bind to a target protein with a higher molecular mass, a concise screening methodology has been established, by applying a “plug–plug” technique to ACE experiments. Exploratory experiments using three mixed peptides, mastoparan‐X, β‐endorphin, and oxytocin, as candidates for calmodulin‐binding ligands, revealed that the technique not only reduces the consumption of the protein sample, but also increases the flexibility of the experimental conditions, by allowing the use of MS detection in the ACE experiments. With the plug–plug technique, the ACE–MS screening methodology successfully selected calmodulin‐binding peptides from a random library with diverse constituents, such as protease digests of BSA. Three peptides with K_d values between 8–147 μM for calmodulin were obtained from a Glu‐C endoprotease digest of reduced BSA, although the digest showed more than 70 peaks in its ACE–MS electropherogram. The method established here will be quite useful for the screening of peptide ligands, which have only low affinities due to their flexible chain structures but could potentially provide primary information for designing inhibitors against the target protein.