ALBERT

Notes: The Raman spectrum of sodium tetrasilicate (Na2Si4O9) glass has been obtained as a function of pressure at 298 K to approximately 50 GPa. The scattering intensity of bands associated with silica tetrahedra containing nonbridging oxygens (Q3 species) decreases with increasing pressure and these bands are absent above 20 GPa. The spectral changes observed over this pressure interval are consistent with the formation of high-coordinate Si species at the expense of nonbridging oxygens. Above 33 GPa, the mode of change of the Raman spectrum with pressure changes abruptly. The main Raman band markedly broadens and weakens, accompanied by a twofold increase in the pressure derivative of the peak maximum. These spectral changes indicate the onset of a second densification mechanism operative at higher pressures. We conjecture that above 33 GPa, high coordinate silicon species are formed through the involvement of bridging oxygens (i.e., formation of IIIO species). The changes in the Raman spectrum associated with this latter mechanism are found to be reversible on decompression. However, spectral changes observed at lower pressures (〈20 GPa) are not fully reversible and decompressed glass samples do not completely relax to their normal 1 atm state. Although silica tetrahedral species containing nonbridging oxygens hysteretically reform at low pressures on the decompression path, a comparison of the Raman spectra of pressure-quenched glass samples with that of normal sodium tetrasilicate glass indicates a change in distribution of these species. In particular, there is an increase in the relative abundance of Q2 species (silica tetrahedra containing two non-bridging oxygens) in samples decompressed from high pressures. We emphasize that Q2 species are not formed under pressurization but are formed on the decompression path and may be due to the reversion of high-coordinate silicon species to tetrahedral species under pressure release.

Notes: The mid-, near-, and far-infrared (IR) spectra of synthetic, single-phase calcium silicate hydrates (C-S-H) with Ca/Si ratios (C/S) of 0.41–1.85, 1.4 nm tobermorite, 1.1 nm tobermorite, and jennite confirm the similarity of the structure of these phases and provide important new insight into their H2O and OH environments. The main mid-IR bands occur at 950–1100, 810–830, 660–670, and 440–450 cm−1, consistent with single silicate chain structures. For the C-S-H samples, the mid-IR bands change systematically with increasing C/S ratio, consistent with decreasing silicate polymerization and with an increasing content of jennite-like structural environments of C/S ratios 〉1.2. The 950–1100 cm−1 group of bands due to Si-O stretching shifts first to lower wave number due to decreasing polymerization and then to higher wave numbers, possibly reflecting an increase in jennite-like structural environments. Because IR spectroscopy is a local structural probe, the spatial distribution of the jennite-like domains cannot be determined from these data. A shoulder at ∼1200 cm−1 due to Si-O stretching vibrations in Q3 sites occurs only at C/S lessthan equal to 0.7. The 660–670 cm−1 band due to Si-O-Si bending broadens and decreases in intensity for samples with C/S 〉 0.88, consistent with depolymerization and decreased structural order. In the near-IR region, the combination band at 4567 cm−1 due to Si-OH stretching plus O-H stretching decreases in intensity and is absent at C/S greater than ∼1.2, indicating the absence of Si-OH linkages at C/S ratios greater than this. The primary Si-OH band at 3740 cm-1 decreases in a similar way. In the far-IR region, C-S-H samples with C/S ratio greater than ∼1.3 have increased absorption intensity at ∼300 cm−1, indicating the presence of CaOH environments, even though portlandite cannot be detected by X-ray diffraction for C/S ratios 〈1.5. These results, in combination with our previous NMR and Raman spectroscopic studies of the same samples, provide the basis for a more complete structural model for this type of C-S-H, which is described.

Notes: The Plasmodium falciparum genome contains genes encoding three α-ketoacid dehydrogenase multienzyme complexes (KADHs) that have central metabolic functions. The parasites possess two distinct genes encoding dihydrolipoamide dehydrogenases (LipDH), which are indispensable subunits of KADHs. This situation is reminiscent of that in plants, where two distinct LipDHs are found in mitochondria and chloroplasts, respectively, that are part of the organelle-specific KADHs. In this study, we show by reverse transcription polymerase chain reaction (RT-PCR) that the genes encoding subunits of all three KADHs, including both LipDHs, are transcribed during the erythrocytic development of P. falciparum. Protein expression of mitochondrial LipDH and mitochondrial branched chain α-ketoacid dihydrolipoamide transacylase in these parasite stages was confirmed by Western blotting. The localization of the two LipDHs to the parasite's apicoplast and mitochondrion, respectively, was shown by expressing the LipDH N-terminal presequences fused to green fluorescent protein in erythrocytic stages of P. falciparum and by immunofluorescent colocalization with organelle-specific markers. Biochemical characterization of recombinantly expressed mitochondrial LipDH revealed that the protein has kinetic and physicochemical characteristics typical of these flavo disulphide oxidoreductases. We propose that the mitochondrial LipDH is part of the mitochondrial α-ketoglutarate dehydrogenase and branched chain α-ketoacid dehydrogenase complexes and that the apicoplast LipDH is an integral part of the pyruvate dehydrogenase complex which occurs only in the apicoplast in P. falciparum.

Notes: We conducted a field experiment to examine how seeding method, soil ripping, and soil characteristics affected the initial establishment and growth of seeded species and if differences among treatments persisted into the second growing season. We planted seeds into a compacted field plot where most of the topsoil had been removed. The native seed mixture of Artemisia californica, Eschscholzia californica, Eriogonum fasciculatum, Lupinus succulentus, Nassella pulchra, and Vulpia microstachys represented different seed sizes and life histories. Three seeding methods (hydroseeding, imprinting, and drilling) and three ripping depths (0, 20, and 40 cm) were combined in a factorial experiment. Soil organic matter and NO3− were used as covariates. For two years, we measured density, percent cover, mean size, and flower production of the selected species, and weed emergence. Only seeding method and soil variation affected initial establishment of natives. Small-seeded species had higher density in imprinted and hydroseeded than drilled treatments, whereas large-seeded species had higher density in imprinted and drilled than hydroseeded treatments. These patterns persisted with only slight modification into the second year. Weed density in year 1 decreased with soil ripping. In year 1, Vulpia height and Lupinus height and flowering were greater with drilling or imprinting than hydroseeding but were not affected by ripping. Eschscholzia, Lupinus, and Vulpia produced seeds in the first year, but only Vulpia reestablished successfully in the second year. Vulpia had high cover in the second year that increased with increasing NO3−, but did not vary by treatment. In year 2 perennial Nassella, and to some extent Eriogonum, grew largest, produced more inflorescences, and had their highest percent cover in the 40-cm rip treatment. Size and inflorescence production also increased with increasing NO3−; sometimes this relationship was stronger than the effects of treatments. We found only positive associations between estimated biomass (density × height) of annuals and survival of shrubs. Potential for erosion control, as measured by total density in year 1 and total vegetative cover in year 2, was greatest in imprinted and hydroseeded treatments and increased with increasing NO3−. This relatively simple experiment yielded information critical to understanding optimum seeding methods and seedbed preparation and indicates that seeding method can be determined by seed size and germination biology. Although an experiment such as this enables some generalizations, it does not eliminate the need for site-specific experiments prior to restoration.

Notes: Abstract The vibrational frequencies of a series of splatquenched, olivine glasses spanning the compositional range from Mg2SiO4 to Mn2SiO4 have been determined using both infrared and Raman spectroscopies. The spectra of all glasses show evidence of tetrahedral coordination of silicon (possibly with some slight distortions), and largely octahedral coordination of magnesium. Spectra of Mn-rich glasses indicate that there is some manganese in 4 or 5-fold coordination. The frequencies observed for the fundamental vibrations of the silica tetrahedra are similar to those previously observed for SiO4 groups in both crystalline and glassy orthosilicates. Additionally, there is evidence for a small amount of silicate polymerization in all glasses characterized: vibrations attributable to Si2O7 groups are visible in both infrared and Raman spectra.

Notes: Abstract The enthalpies of transition at T= 298 K between zinc metasilicate assemblages, measured by molten oxide solution calorimetry, are: $$\begin{gathered} {1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2} Zn_2 SiO_4 (phen) + {1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2} SiO_2 (qz) \to ZnSiO_3 (cpx) \hfill \\ \Delta H = 10.4 \pm 2.4 kJ/mol \hfill \\ \end{gathered} $$ (1) 2 $$\begin{gathered} {\text{ZnSiO}}_{\text{3}} {\text{(cpx)}} \to {\text{ZnSiO}}_{\text{3}} {\text{(ilm)}} \hfill \\ \Delta H = {\text{52}}{\text{.4}} \pm {\text{2}}{\text{.7kJ/mol}} \hfill \\ \end{gathered}$$ (2) For reaction (1), the measured enthalpy is lower than the value 15.7±2.0 kJ/mol from the phase boundary of Syono et al. The P-T slope derived from the calorimetric data has a somewhat greater value than that of the line chosen by Syono et al., but is still consistent with the individual data points in that study. For reaction (2), the measured enthalpy of transformation is in close agreement with the value 54.0±5.1 kJ/mol estimated from the phase boundary of Akimoto et al, and with the value 50.9±3.2 kJ/mol from the phase boundary of Ohtani, which is parallel to and 0.6 GPa lower than Akimoto's. All estimates assume a pressure-independent volume of transition. For the zinc metagermanate composition, measured heats of transformation are: 3 $$\begin{gathered} {\text{1/2 Zn}}_{\text{2}} {\text{GeO}}_{\text{4}} {\text{(phen) + 1/2 GeO}}_{\text{2}} {\text{(qz)}} \hfill \\ \to {\text{1/2 Zn}}_{\text{2}} {\text{GeO}}_{\text{4}} {\text{(dist sp) + 1/2 GeO}}_{\text{2}} {\text{(rutile)}} \hfill \\ \Delta H = - {\text{17}}{\text{.7}} \pm {\text{3}}{\text{.8 kJ/mol}} \hfill \\ \end{gathered}$$ (3) 4 $$\begin{gathered} {\text{1/2 Zn}}_{\text{2}} {\text{GeO}}_{\text{4}} {\text{(dist sp) + 1/2 GeO}}_{\text{2}} {\text{(rutile)}} \to {\text{ZnGeO}}_{\text{3}} {\text{(lim)}} \hfill \\ \Delta H = {\text{14}}{\text{.3}} \pm {\text{5}}{\text{.9 kJ/mol}} \hfill \\ \end{gathered}$$ (4) Raman and infrared spectra of ZnSiO3 clinopyroxene and ilmenite are presented. The entropy change for the clinopyroxene → ilmenite transiton is calculated from the spectra and estimates for the directionally-averaged acoustic velocities, using the Kieffer model for the vibrational density of states. The value ΔS = −12±5 J/mol·K, calculated using a variety of plausible densities of states, agrees with the value from phase equilibria, ΔS = −12.7±6.0 J/mol·K.