Synthesis of Trilaurin by Developing Pisa Seeds (Actinodaphne hookeri)

The developing seeds of Actinodaphne hookeri were investigated to delineate their ability to synthesize large amounts of trilaurin. Until 88 days after flowering the embryos contained 71% neutral lipids (NL) and 29% phospholipids (PL) and both these components contained C-16:0, C-18:0, C-18:2, and C-18:3 as the major fatty acids (FA). At 102 days after flowering the seeds began to accumulate triacylglycerols (TAG) and to synthesize lauric acid (C-12:0). By 165 days after flowering, when the seeds were mature, they contained about 99% NL and 1% FL. At this stage the TAG contained exclusively C-12:0, while the PL consisted of long-chain fatty acids (LCFA) only. Leaf lipids in contrast did not contain any C-12:0. Experiments on [1-C-14]acetate incorporation into developing seed slices showed that at 88 days after flowering only 4% of the label was in TAG, 1% in diacylglycerols (DAG), and 87% in FL. One hundred two days after flowering seeds incorporated only 2% of the label into TAG, 30% into DAG, and 64% into FL. In contrast at 114 days after flowering 71% of the label was incorporated into TAG, 25% into DAG, and only 2% into FL. Analysis of labeled FA revealed that up to 102 days after flowering it was incorporated only into LCFA, whereas at 114 days after flowering it was incorporated exclusively into C-12:0. Furthermore, 67% of the label in PL at 114 days after flowering was found to be dilaurylglycerophosphate. Analysis of the label in DAG at this stage showed that it was essentially in dilaurin species. These observations indicate the induction of enzymes of Kennedy pathway for the specific synthesis of trilaurin at about 114 days after flowering, Homogenates of seeds (114 days after flowering) incubated with labeled FA in the presence of glycerol-3-phosphate and coenzymes A and ATP incorporated 84% of C-12:0 and 61% of C-14:0, but not C-16:0, C-18:2, and C-18:3, into TAG. In contrast the LCFA were incorporated preferentially into FL. It is concluded that, between 102 and 114 days after flowering, a switch occurs in A. hookeri for the synthesis of C-12:0 and trilaurin which is tissue specific. Since the seed synthesizes exclusively C-12:0 at 114 days after flowering onwards and incorporates specifically into TAG, this system appears to be ideal for identifying the enzymes responsible for medium-chain fatty acid as well as trilaurin synthesis and for exploiting them for genetic engineering. (C) 1994 Academic Press, Inc.

Electronic structure of early 3d-transition-metal oxides by analysis of the 2p core-level photoemission spectra

The electronic structures of a wide range of early transition-metal (TM) compounds, including Ti and V oxides with metal valences ranging from 2+ to 5+ and formal d-electron numbers ranging from 0 to 2, have been investigated by a configuration-interaction cluster model analysis of the core-level metal 2p x-ray photoemission spectra (XPS). Inelastic energy-loss backgrounds calculated from experimentally measured electron-energy-loss spectra (EELS) were subtracted from the XPS spectra to remove extrinsic loss features. Parameter values deduced for the charge-transfer energy Delta and the d-d Coulomb repulsion energy U are shown to continue the systematic trends established previously for the late TM compounds, giving support to a charge-transfer mechanism for the satellite structures. The early TM compounds are characterized by a large metal d-ligand p hybridization energy, resulting in strong covalency in these compounds. Values for Delta and U suggest that many early TM compounds should be reclassified as intermediate between the charge-transfer regime and the Mott-Hubbard regime.

Development of specific DNA probes and their usage in the detection of Plasmodium vivax infection in blood

The application of nucleic acid probes, in the detection of pathogenic micro-organisms, has become an integral part of diagnostic technologies. In this study, Plasmodium vivax-specific DNA probes have been identified by carrying out genomic subtractive hybridization. In this approach, the recombinant clones from a P. vivax genomic library are screened with radiolabelled human and P. falciparum DNA. The colonies which react with labelled P. falciparum and human DNA are eliminated and those which do not produce any autoradiographic signal have been subjected to further screening procedures. Three Fl vivax specific DNA probes have been obtained by these repeated screenings. Further analyses indicate that these probes are specific and sensitive enough to detect P. vivax infection in clinical blood samples when used in a non-radioactive DNA hybridization assay. (C) 1995 Academic Press Limited

Structure of Ethyl 5-Methoxy-3-phenyl-2-indolecarboxylate

C18H17NO3, M r = 295"34, monoclinic, C2/c, a = 11.689 (2), b = 22.934 (4), c = 11.592 (2) A, fl=100.16(3) ° , V =3058.8(8) A 3, Z=8, D,n= 1.30 (5), Dx = 1.28 Mg m -3, A(Mo Ka) = 0.7107 A, tz(Mo Ka) = 0.094 mm- 1, F(000) = 1248, T = 300 K, final R = 0.046 for 1849 observed reflections [I > 30"(/)]. The indole nucleus is slightly bent along the C(8)---C(9) bond. The phenyl ring connected to the indole moiety is rotated about the C(3)---C(10) bond by 45.8 (3) °. The carboxyl group makes a dihedral angle of 8.1 (4) ° with the mean plane of the indole moiety. Centrosymmetrically related pairs of molecules are linked through hydrogen bonds across the centre of symmetry and form dimers.

Local environmental structures of Mo in the superionic conducting glass (AgI)(0.6)(Ag2MoO4)(0.4) by anomalous X-ray scattering

The anomalous X-ray scattering (AXS) method using Mo K absorption edges has been employed for obtaining the local structural information of superionic conducting glass having the composition (AgI)(0.6)(Ag2MoO4)(0.4). The possible atomic arrangements in the near-neighbor region of this glass were estimated by coupling the results with the least-squares variational analysis so as to reproduce the differential intensity profile for Mo as well as the ordinary scattering profile. The coordination number of oxygen around Mo is found to be about 4 at the distance of 0.180 mn. This implies that the most probable structural entity in the glass is the MoO4 tetrahedral unit which has been proposed based on infrared spectroscopy. The value of the coordination number of I- around Ag+ is estimated as 4.4 at 0.287 nm, suggesting an arrangement similar to that of crystalline or molten AgI.

Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film

La0.67Ba0.33MnO3 (LBMO) thin film is deposited on a 36.7degrees SrTiO3 bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears at temperature T > 175 K. At low temperature, I-V characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic conductance-voltage characteristics of the bicrystal grain boundary indicates that at low temperatures (T < 175 K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese atoms and tunneling through disordered oxides. At higher temperatures (T > 175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance with the increase in temperature is due to enhanced spin-flip scattering process.

Conformational changes of the chaperone SecB upon binding to a model substrate - bovine pancreatic trypsin inhibitor (BPTI)

SecB is a homotetrameric cytosolic chaperone that forms part of the protein translocation machinery in E. coli. Due to SecB, nascent polypeptides are maintained in an unfolded translocation-competent state devoid of tertiary structure and thus are guided to the translocon. In vitro SecB rapidly binds to a variety of ligands in a non-native state. We have previously investigated the bound state conformation of the model substrate bovine pancreatic trypsin inhibitor (BPTI) as well as the conformation of SecB itself by using proximity relationships based on site-directed spin labeling and pyrene fluorescence methods. It was shown that SecB undergoes a conformational change during the process of substrate binding. Here, we generated SecB mutants containing but a single cysteine per subunit or an exposed highly reactive new cysteine after removal of the nearby intrinsic cysteines. Quantitative spin labeling was achieved with the methanethiosulfonate spin label (MTS) at positions C97 or E90C, respectively. Highfield (W-band) electron paramagnetic resonance (EPR) measurements revealed that with BPTI present the spin labels are exposed to a more polar/hydrophilic environment. Nanoscale distance measurements with double electron-electron resonance (DEER) were in excellent agreement with distances obtained by molecular modeling. Binding of BPTI also led to a slight change in distances between labels at C97 but not at E90C. While the shorter distance in the tetramer increased, the larger diagonal distance decreased. These findings can be explained by a widening of the tetrameric structure upon substrate binding much like the opening of two pairs of scissors.

Current views on microscopic thermodynamics of liquid alloys

An attempt has been made to review current information on the microscopic thermodynamics of liquid alloys. For complex alloys, and for alloys of simple metals with strong "compound-forming" tendencies, the fluctuation approach developed by Bhatia and his co-workers provides a useful link between the fluctuation in concentration and number density of atoms in the mixture on the one hand, and macroscopic thermodynamic properties on the other. Some selected examples of the application of structural data of liquid alloys to estimating macroscopic thermodynamic properties such as the Gibbs free energy of mixing, coupled with the fluctuation approach are given. The relevant thermodynamic quantities such as vapor pressure and entropy are also discussed, to facilitate the understanding of the present status of the fundamental and powerful links between macroscopic and microscopic (atomic scale) structure of liquid alloys (Mg--Sn, Li--Pb, Hg--K). 63 ref.--AA

Gibbs energy of formation of nickel orthosilicate (Ni2SiO4)

Two solid state galvanic cells:Pt, Ni + Ni2Si04 + Si02/(Y203)Zr02/Ni + + NiO, Pt (1) and Pt, Ni + NizSiOj + Si02/CaF2/Ni + + NiO, Pt (11) have been employed for the determination of the Gibbs' energy of formation of nickel orthosilicate(Ni2Si04) from nickel oxide and quartz. The emf of cell (I) was reversible and reproducible in the temperature range 925 to 1375K whereas emf of cell (11) drifted with time and changed polarity. From the results of cell (I), the Gibbs' energy of formation of nickel silicate is obtained as,2Ni0 (r.s.) + Si02 (quartz) + Ni2Si04 (olivine)Gibbs' energy of formation of the spinel form of Ni2Si04 is obtained by combining the data for olivine obtained in this study with high pressure data on olivine to spinel transition reported in the literature. The complex time dependence of the emf of cell (11) can be rationalised on the basis of formation of calcium silicates from calcium oxide, generally present as an impurity in the calcium fluoride electrolyte, and silica. The emf of cell (11) is shown to be the function of the activity of calcium oxide at the electrolyte/ electrode interface. The results provide strong evidence against the recent suggestion of mixed anionic conduction in calcium fluoride.

Physical chemistry of the reduction of calcium oxide with aluminium in vacuum

The physical chemistry of "aluminothermic" reduction of calcium oxide in vacuum is analyzed. Basic thermodynamic data required for the analysis have been generated by a variety of experiments. These include activity measurements in liquid AI-Ca alloys and determination of the Gibbs energies of formation of calcium aluminates. These data have been correlated with phase relations in the Ca-AI-0 system at 1373 K. The various stages of reduction, the end products and the corresponding equilibrium partial pressures of calcium have been established from thermodynamic considerations. In principle, the recovery of calcium can be improved by reducing the pressure in the reactor. However,, the cost of a high vacuum system and the enhanced time for reduction needed to achieve higher yields makes such a practice uneconomic. Aluminum contamination of calcium also increases at low pressures. The best compromise is to carry the reduction up to the stage where 3CaO-Al,O, is formed as the product. This corresponds to an equilibrium calcium partial pressure of 31.3 Pa at 1373 K and 91.6 Pa at 1460 K. Calcium can be extracted at this pressure using mechanical pumps in approximately 8 to 15 hr, depending on the size and the fill ratio of the retort and porosity of the charge briquettes.