Intermolecular potential and second virial coefficient of the water-hydrogen complex

We construct a rigid-body (five-dimensional) potential-energy surface for the water-hydrogen complex using scaled perturbation theory (SPT). An analytic fit of this surface is obtained, and, using this, two minima are found. The global minimum has C2v symmetry, with the hydrogen molecule acting as a proton donor to the oxygen atom on water. A local minimum with Cs symmetry has the hydrogen molecule acting as a proton acceptor to one of the hydrogen atoms on water, where the OH bond and H2 are in a T-shaped configuration. The SPT global minimum is bound by 1097 microEh (Eh approximately 4.359744 x 10(-18) J). Our best estimate of the binding energy, from a complete basis set extrapolation of coupled-cluster calculations, is 1076.1 microEh. The fitted surface is used to calculate the second cross virial coefficient over a wide temperature range (100-3000 K). Three complementary methods are used to quantify quantum statistical mechanical effects that become significant at low temperatures. We compare our results with experimental data, which are available over a smaller temperature range (230-700 K). Generally good agreement is found, but the experimental data are subject to larger uncertainties.     

Development of delta(15)N stratification of NO(3)(-) in soil profiles

New evidence, obtained using a robust method for measuring the delta(15)N of NO(3)(-)-N in soil, is consistent with denitrification being the major determinant in the vertical distribution of NO(3)(-)-delta(15)N in soil profiles. These data also suggest that varying moisture regimes result in different effects of soil NO(3)(-)-N leaching on residual whole soil delta(15)N.     

Using flow injection analysis to time-resolve rhythmic and pulsatile signals

Continuous monitoring can be used to detect rhythms, an important aspect of biology. But peaks of concentration are broadened by dispersion so that they overlap their neighbours and obscure high frequency chemoperiodicities. In this study, flow injection was found experimentally to be useful in resolving these. A rhythmically varying pattern of permanganate concentration was measured spectrophotometrically. The rhythm (frequency 0.08 Hz) was observable at a dispersion coefficient of 3.0 but not at 3.9 (when only a single peak was recorded). It was again observable using the same high dispersion manifold but positioned after an injection valve that subsampled the stream at intervals. A design based on this work is proposed for an automated instrument that outputs a time series of concentration measures.     

Oxygen capture by lithiated organozinc reagents containing aromatic 2-pyridylamide ligands

The sequential reaction of ZnMe2 with a 2-pyridylamine (HN(2-C5H4N)R, R = Ph: 1; 3,5-Xy (=3,5-xylyl): 2; 2,6-Xy: 3; Bz (=benzyl): 4; Me: 5), tBuLi and thereafter with oxygen affords various lithium zincate species, the solid-state structures of which reveal a diversity of oxo-capture modes. Amine 1 reacts to give both dimeric THF [Li(Me)OZn[N(2-C5H4N)Ph]2] (6), wherein oxygen has inserted into the Zn-C bond of a [MeZn[N(2-C5H4N)-Ph]2] ion, and the trigonal Li2Zn complex, bis(OtBu)-capped (THF x Li)2-[[(mu3-O)tBu]2Zn[N(2-C5H4N)Ph]2] (7). The structural analogue of 6 (8) results from the employment of 2, while the use of more sterically congested 3 yields a pseudo-cubane dimer [(THF x [Li(tBu)OZn(OtBu)Me]]2] (9) notable for the retention of labile Zn-C(Me). Amines 4 and 5 afford the oxo-encapsulation products [mu4-O)Zn4[(2-C5H4N)-NBz]6] (10b), and [tBu(mu3-O)-Li3(mu6-O)Zn3[(2-C5H4N)NMe]6] (11), respectively, with concomitant oxo-insertion into a Li-C interaction resulting in capping of the fac-isomeric (mu6-O)M3M'3 distorted octahedral core of the latter complex by a tert-butoxide group.     

Mimicry of host-defense peptides by unnatural oligomers: antimicrobial beta-peptides

We have designed beta-amino acid oligomers that are helical, cationic, and amphiphilic with the intention of mimicking the biological activity of amphiphilic, cationic alpha-helical antimicrobial peptides found in nature (e.g., magainins). We have previously identified a 17-residue beta-peptide (called beta-17) with antibiotic activity similar to that of a magainin derivative against four bacterial species, including two clinical isolates that are resistant to common antibiotics. This beta-peptide displays very low hemolytic activity against human red blood cells, which indicates selectivity for bacterial cells over mammalian cells. Here we examine some of the factors important for activity in this class of beta-peptides. An amphiphilic helix is necessary, because a nonamphiphilic isomer proved to be inactive. The ratio of cationic to hydrophobic residues is also important. Active beta-peptides induce the leakage of beta-galactosidase from treated Bacillus subtilis cells, as do alpha-helical antibiotic peptides, and this similarity suggests that the beta-peptide mode of action involves disruption of microbial membranes. This class of beta-peptides is not degraded by proteases, which bodes well for biological applications.     

Temperature-sensitive polypeptide brushes-coated mesoporous silica nanoparticles for dual-responsive drug release

A multifunctional nanohybrid based on mesoporous silica nanoparticle and biocompatible polypeptide was fabricated for targeted and dual-responsive therapy of tumor cells.     

Efficient synthesis of trisubstituted alkenes in an aqueous-organic system using a versatile and recyclable Rh/m-TPPTC catalyst

We have found that the use of [Rh(cod)OH]₂ associated with the water-soluble ligand m-TPPTC was highly efficient for the Rh-catalyzed arylation of alkynes. Aryl and alkyl alkynes were transformed to alkenes using 3 mol % rhodium catalyst and 2.5 equiv of boronic acid at 100 °C in a biphasic water/toluene system in 80-99% yield. The reaction was found to be totally regioselective for alkyl arylalkynes and alkyl silylated alkynes. The Rh/m-TPPTC system was for the first time recycled with no loss of the activity and with excellent purity of the desired alkene.     

Application of recombinant phage display antibody system in study of Codakia orbicularis gill proteins

We used the recombinant phage display antibody system (RPAS) to obtain chimeric single-chain fragment variable (ScFv) antibodies to gill proteins of the white clam Codakia orbicularis (Linné, 1758). After three rounds of selection on immunotubes loaded with total gill protein extract, recombinant phages exhibiting antibodies to gill proteins were isolated and tested by enzyme-linked immunosorbent assay (ELISA). Clones exhibiting a high affinity for the mollusk proteins were selected for production of soluble ScFv antibodies, which were purified for subsequent analysis. ScFv antibodies exhibited a reaction specific for a protein whose molecular mass was about 15,000 Daltons and that was detected by the antigen capture technique followed by sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blotting.