Mechanism of the gas-phase decomposition of trifluoro-, trichloro-, and tribromomethanols in the presence of hydrogen halides

Ab initio calculations at the G2 level were used in a theoretical analysis of the kinetics of the decomposition of trifluoro-, trichloro-, and tribromomethanols. The high-pressure limiting rate coefficients k_diss,∞ for the thermal dissociation of CF₃OH, CCl₃OH, and CBr₃OH were calculated using the conventional transition state theory. The results of potential surface calculations show that in the presence of the hydrogen halides HX (X = F, Cl, and Br), considerably lower energy pathways are accessible for the decomposition of CF₃OH, CCl₃OH, and CBr₃OH. The mechanism of the reactions appears to be complex and consists of three consecutive elementary processes with the formation of pre- and post-reaction adducts. The presence of hydrogen halides considerably decreases the energy barrier for the bimolecular decomposition of the alcohols CF₃OH, CCl₃OH, and CBr₃OH. Results of this study indicate that hydrogen halides can considerably accelerate the homogeneous decomposition of perhalogenated methanols when they are present in the reaction area at sufficiently high concentrations. However, the atmospheric concentrations of hydrogen halides are too small for efficient removal of atmospheric CF₃OH, CCl₃OH, and CBr₃OH.     

Ab initio studies on the decomposition kinetics of CF<Subscript>3</Subscript>OCF<Subscript>2</Subscript>O radical

The present study deals with the decomposition of CF₃OCF₂O radical formed from a hydrofluoroether, CF₃OCHF₂ (HFE-125), in the atmosphere. The study is performed using ab initio quantum mechanical methods. Two plausible pathways of decomposition of the titled species have been considered, one involving C-O bond scission and the other occurring via F atom elimination. The geometries of the reactant, products and transition states involved in the decomposition pathways are optimized and characterized at DFT (B3LYP) level of theory using 6-311G(d,p) basis set. Single point energy calculations have been performed at G2M(CC,MP2) level of theory. Out of the two prominent decomposition channels considered, the C-O bond scission is found to be dominant involving a barrier height of 15.3 kcal mol⁻¹ whereas the F-elimination path proceeds with a barrier of 26.1 kcal mol⁻¹. The thermal rate constants for the above two decomposition pathways are evaluated using canonical transition state theory (CTST) and these are found to be 1.78 × 10⁶ s⁻¹ and 2.83 × 10⁻⁷ s⁻¹ for C-O bond scission and F-elimination respectively at 298 K and 1 atm pressure. Transition states are searched on the potential energy surfaces involved during the decomposition channels and each of the transition states is characterized. The existence of transition states on the corresponding potential energy surface is ascertained by performing intrinsic reaction coordinate (IRC) calculation.     

Ab initio studies on the reactivity of the CF3OCH2O radical: Thermal decomposition vs. reaction with O2

Hydrofluoroethers are being considered as potential candidates for third generation refrigerants. The present investigation involves the ab initio quantum mechanical study of the decomposition mechanism of CF₃OCH₂O radical formed from a hydrofluoroether, CF₃OCH₃ (HFE-143a) in the atmosphere. The geometries of the reactant, products and transition states involved in the decomposition pathways are optimized and characterized at the DFT (B3LYP) level of theory using 6-311G(d,p) basis set. Energy calculations have been performed at the G2(MP2) and G2M(CC,MP2) level of theory. Two prominent decomposition channels, C-O bond scission and reaction with atmospheric O₂ have been considered for detailed investigation. Studies performed at the G2(MP2) level reveals that the decomposition channel involving C-O bond scission occurs with a barrier height of 23.8 kcal mol⁻¹ whereas the oxidative pathway occurring with O₂ proceeds with an energy barrier of 7.2 kcal mol⁻¹. On the other hand the corresponding values at G2M(CC,MP2) are 24.5 and 5.9 kcal mol⁻¹ respectively. Using canonical transition state theory (CTST) rate constants for the two pathways considered are calculated at 298 K and 1 atm pressure and found to be 5.9 × 10⁻⁶ s⁻¹ and 2.3 × 10⁻⁵ s⁻¹ respectively. The present study concludes that reaction with O₂ is the dominant path for the consumption of CF₃OCH₂O in the atmosphere. Transition states are searched and characterized on the potential energy surfaces involved in both of the reaction channels. The existence of transition state on the corresponding potential energy surface is ascertained by performing intrinsic reaction coordinate (IRC) calculation.     

Microcalorimetric Study of <Emphasis Type="Italic">Tetrahymena</Emphasis> Growth Affected by Copper(II) Complexes

By means of microcalorimetry, the effect of four copper(II) complexes on Tetrahymena growth was investigated. The extent and duration of the inhibitory effect on the metabolism, judged by the rate constant, k, and the half inhibition concentration, IC₅₀, varied with the different complexes. The results showed that the half inhibition concentrations IC₅₀ of CuCl₂, (C₉H₆NO)₂Cu and [Cu(phen)₂]Cl₂⋅6H₂O were 9.9 × 10⁻⁴, 2.0 × 10⁻⁴, and 2.6 × 10⁻⁴ mol/L, respectively. The sequence of antibiotic activity of these three complexes was: (C₉H₆NO)₂Cu > [Cu(phen)₂]Cl₂⋅6H₂O > CuCl₂. The growth rate constants of [Cu(phen)₃]Cl₂⋅6H₂O did not change obviously with the increase of concentrations, but [Cu(phen)₃]Cl₂⋅6H₂O also can prolong the time of Tetrahymena growth.     

Hydroxylamine oxidation and subsequent nitrous oxide production by the heterotrophic ammonia oxidizer Alcaligenes faecalis

Nitrous oxide (N₂O), a greenhouse gas, is emitted during autotrophic and heterotrophic ammonia oxidation. This emission may result from either coupling to aerobic denitrification, or it may be formed in the oxidation of hydroxylamine (NH₂OH) to nitrite (NO₂ ⁻). Therefore, the N₂O production during NH₂OH oxidation was studied with Alcaligenes faecalis strain TUD. Continuous cultures of A. faecalis showed increased N₂O production when supplemented with increasing NH₂OH concentrations. ¹⁵N-labeling experiments showed that this N₂O production was not due to aerobic denitrification of NO₂ ⁻. Addition of ¹⁵N-labeled NH₂OH indicated that N₂O was a direct by-product of NH₂OH oxidation, which was subsequently reduced to N₂. These observations are sustained by the fact that NO₂ ⁻ production was low (0.23 mM maximum) and did not increase significantly with increasing NH₂OH concentration in the feed. The NH₂OH-oxidizing capacity increased with increasing NH₂OH concentrations. The apparent V _max and K _m were 31 nmol min⁻¹ mg dry weight⁻¹ and 1.5 mM respectively. The culture did not increase its growth yield and was not able to use NH₂OH as the sole N source. A non-haem hydroxylamine oxidoreductase was partially purified from A. faecalis strain TUD. The enzyme could only use K₃Fe(CN)₆ as an electron acceptor and reacted with antibodies raised against the hydroxylamine oxidoreductase of Thiosphaera pantotropha. Received: 1 September 1998 / Received revision: 5 November 1998 / Accepted: 7 November 1998     

Actual and potential rates of hydrogen photoproduction by continuous culture of the purple non-sulphur bacterium Rhodobacter capsulatus

The influence of (NH₄)₂SO₄ concentration and dilution rate (D) on actual and potential H₂ photoproduction has been studied in ammonium-limited chemostat cultures of Rhodobacter capsulatus B10. The actual H₂ production in a photobioreactor was maximal (approx. 80 ml h⁻¹l⁻¹) at D = 0.06 h⁻¹ and 4 mM (NH₄)₂SO₄. However, it was lower than the potential H₂ evolution (calculated from hydrogen evolution rates in incubation vials), which amounted to 100–120 ml h⁻¹ l⁻¹ at D = 0.03–0.08 h⁻¹. Taking into account the fact that H₂ production in the photobioreactor under these conditions was not limited by light or lactate, another limiting (inhibiting) factor should be sought. One possibility is an inhibition of H₂ production by the H₂ accumulated in the gas phase. This is apparent from the non-linear kinetics of H₂ evolution in the vials or from its inhibition by the addition of H₂; initial rates were restored in both cases after the vials had been refilled with argon. The actual H₂ production in the photobioreactor at D = 0.06 h⁻¹ was shown to increase from approximately 80 ml h⁻¹ l⁻¹ to approximately 100 ml h⁻¹ l⁻¹ under an argon flow at 100 ml min⁻¹. Under maximal H₂ production rates in the photobioreactor, up to 30% of the lactate feedstock was utilised for H₂ production and 50% for biomass synthesis. Received: 22 April 1997 / Received revision: 14 July 1997 / Accepted: 27 July 1997     

Protective effects of prostaglandins in the isolated gastric mucosa of the eel, Anguilla anguilla

The protective effect of endogenous prostaglandins on the fish gastric mucosa was evaluated by studying the effect of indomethacin and aspirin, known cyclooxigenase inhibitors, on the mucosal ulceration in the isolated gastric sacs of Anguilla anguilla. Gastric sacs devoid of muscle layers were incubated in the presence of indomethacin (10⁻⁴ mol · l⁻¹) or aspirin (10⁻⁴ mol · l⁻¹) in different experimental conditions. Both the anti-inflammatory drugs produced ulcers, but the effects were more severe in the presence of histamine and in the absence of HCO₃ ⁻ in the incubation bath. The effects of prostaglandin E₂ (PGE₂) on acid secretion rate (J_H) and on alkaline secretion rate (J_OH) were evaluated (with the aid of the pH stat method) in isolated gastric mucosa mounted in Ussing chambers. We found that PGE₂ (10⁻⁸–10⁻⁵ mol · l⁻¹) increased J_H in a dose-dependent manner. In tissues pretreated with luminal omeprazole (10⁻⁴ mol · l⁻¹), PGE₂ stimulated gastric alkaline secretion. It was nullified by serosal removal of HCO₃ ⁻ or Na⁺ and by serosal ouabain (10⁻⁴ mol · l⁻¹). These results suggested that prostaglandins also exert their protective effects in fish gastric mucosa. This protection seems partially due to a stimulation of exogenous HCO₃ ⁻ transport from the serosal to the mucosal side. It is likely that this transport is an active transcellular mechanism coupled to Na⁺ transport. Accepted: 14 April 2000     

Optimization of culture medium for the continuous cultivation of the microalga Haematococcus pluvialis

The freshwater microalga Haematococcus pluvialis is one of the best microbial sources of the carotenoid astaxanthin, but this microalga shows low growth rates and low final cell densities when cultured with traditional media. A single-variable optimization strategy was applied to 18 components of the culture media in order to maximize the productivity of vegetative cells of H. pluvialis in semicontinuous culture. The steady-state cell density obtained with the optimized culture medium at a daily volume exchange of 20% was 3.77 · 10⁵ cells ml⁻¹, three times higher than the cell density obtained with Bold basal medium and with the initial formulation. The formulation of the optimal Haematococcus medium (OHM) is (in g l⁻¹) KNO₃ 0.41, Na₂HPO₄ 0.03, MgSO₄ · 7H₂O 0.246, CaCl₂ · 2H₂O 0.11, (in mg l⁻¹) Fe(III)citrate · H₂O 2.62, CoCl₂ · 6H₂O 0.011, CuSO₄ · 5H₂O 0.012, Cr₂O₃ 0.075, MnCl₂ · 4H₂O 0.98, Na₂MoO₄ · 2H₂O 0.12, SeO₂ 0.005 and (in μg l⁻¹]) biotin 25, thiamine 17.5 and B₁₂ 15. Vanadium, iodine, boron and zinc were demonstrated to be non-essential for the growth of H. pluvialis. Higher steady-state cell densities were obtained by a three-fold increase of all nutrient concentrations but a high nitrate concentration remained in the culture medium under such conditions. The high cell productivities obtained with the new optimized medium can serve as a basis for the development of a two-stage technology for the production of astaxanthin from H. pluvialis. Received: 10 September 1999 / Received revision: 2 December 1999 / Accepted: 3 December 1999     

Metabolic rates in an anadromous clupeid, the American shad (Alosa sapidissima)

To assess the energetics of migration in an anadromous fish, adult American shad (Alosa sapidissima) were swum in a large respirometer at a range of speeds (1.0–2.3 body lengths (BL) s⁻¹, 13–24 °C). Metabolic rate (M_O2) was logarithmically related to swimming speed (Bl s⁻¹; r ² = 0.41, slope = 0.23 ± 0.037) and tailbeat frequency (beats × min⁻¹; r ² = 0.52, slope = 0.003 ± 0.0003). Temperature had a significant effect on metabolic rate (r ² = 0.41) with a Q₁₀ of 2.2. Standard metabolic rate (SMR), determined directly after immobilization with the neuroblocker gallamine triethiodide, ranged from 2.2–6.2 mmolO₂ kg⁻¹ h⁻¹ and scaled with mass (W) such that SMR = 4.0 (±0.03)W^{0.695(±0.15)}. Comparison of directly determined and extrapolated SMR suggests that swimming respirometry provides a good estimate of SMR in this species, given the differences in basal activity monitored by the two methods. Overall, American shad metabolic rates (M_O2 and SMR) were intermediate between salmonids and fast-swimming perciforms, including tunas, and may be a result of evolutionary adaptation to their active pelagic, schooling life history. This study demonstrates variability in metabolic strategy among anadromous fishes that may be important to understanding the relative success of different migratory species under varying environmental conditions. Accepted: 3 March 1999     

Effects of H2O2 on the growth, secretion, and metabolism of hybridoma cells in culture

Summary The effect of low concentrations of hydrogen peroxide (H₂O₂) (5 × 10⁻⁷−9.5 × 10⁻⁷ M) on cell growth and antibody production was investigated with murine hybridoma cells (Mark 3 and anti-hPL) in culture. Cell growth, measured by flow cytometry with morphological parameters, was significantly stimulated by H₂O₂ (8 × 10⁻⁷ M) but H₂O₂ concentration of 7 × 10⁻⁶ M and above increased cell death. H₂O₂ stimulation of antibody production was nonsignificant. The metabolism of cells treated with 8 × 10⁻⁷ or 1 × 10⁻⁵ M H₂O₂ was similar to that of the control in terms of glucose and glutamine consumption, lactate and ammonia production, and amino acid concentrations in the medium. The concentrations of lactate dehydrogenase, a marker of cell death, in test and control cells were similar. However, concentrations of intracellular free radicals measured by flow cytometry with dihydrorhodamine 123 (DHR 123) and dichlorofluorescein diacetate (DCFH-DA) as fluorochromes were different. The reactive oxygen species content of cells in 8 × 10⁻⁷ M H₂O₂ was similar to that of the controls, but there was a sudden, marked production of superoxide anions (detected with DHR 123) and H₂O₂ or peroxides (detected with DCFH-DA) by cells incubated with 1 × 10⁻⁵ M H₂O₂ which increased with increasing H₂O₂ until cell death.     

Geomicrobiological Properties of Ultra-Deep Granitic Groundwater from the Mizunami Underground Research Laboratory (MIU), Central Japan

Although deep subterranean crystalline rocks are known to harbor microbial ecosystems, geochemical factors that constrain the biomass, diversity, and metabolic activities of microorganisms remain to be clearly defined. To better understand the geochemical and microbiological relationships, we characterized granitic groundwater collected from a 1,148- to 1,169-m-deep borehole interval at the Mizunami Underground Research Laboratory site, Japan, in 2005 and 2008. Geochemical analyses of the groundwater samples indicated that major electron acceptors, such as NO₃⁻ and SO₄²⁻, were not abundant, while dissolved organic carbon (not including organic acids), CH₄ and H₂, was moderately rich in the groundwater sample collected in 2008. The total number of acridine orange-stained cells in groundwater samples collected in 2005 and 2008 were 1.1 × 10⁴ and 5.2 × 10⁴ cells/mL, respectively. In 2005 and 2008, the most common phylotypes determined by 16S rRNA gene sequence analysis were both related to Thauera spp., the cultivated members of which can utilize minor electron donors, such as aromatic and aliphatic hydrocarbons. After a 3–5-week incubation period with potential electron donors (organic acids or CH₄ + H₂) and with/without electron acceptors (O₂ or NO₃⁻), dominant microbial populations shifted to Brevundimonas spp. These geomicrobiological results suggest that deep granitic groundwater has been stably colonized by Thauera spp. probably owing to the limitation of O₂, NO₃⁻, and organic acids.     

In vitro studies on active calcium absorption from ovine rumen

From various in vivo and in vitro studies it has been shown that the rumen represents a significant site of Ca²⁺ absorption in sheep and goats. It was the aim of the present study to further characterize the underlying mechanisms. Unidirectional flux rates of Ca²⁺ across rumen wall epithelia of sheep were measured in vitro by applying the Ussing-chamber technique in the absence of electrochemical gradients. Under these conditions, significant Ca²⁺ net flux rates (J_net) clearly indicate the presence of active mechanisms for Ca²⁺ transport. Short chain fatty acids (SCFAs) caused highest stimulation of Ca²⁺ J_net (6.3 ± 1.9 nmol · cm⁻² · h⁻¹) when used as a mixture of acetate, proprionate and butyrate in physiological proportions (36, 15, 9 mmol · l⁻¹, respectively). The effect of 30 mmol · l⁻¹ butyrate (3.2 ± 0.6 nmol · cm⁻² · h⁻¹) was higher than respective amounts of propionate and acetate (0.6 ± 0.8 nmol · cm⁻² · h⁻¹ and 0.9 ± 0.8 nmol · cm⁻² · h⁻¹, respectively). Eliminating SCFAs resulted in Ca²⁺ J_net of 0.4 ± 1.1 nmol ^. cm^−2 .h⁻¹. Addition of Ca channel blocker verapamil (mucosal 1 mmol · l⁻¹) had no significant effect on SCFA-stimulated J_net of Ca²⁺, whereas application of Na⁺/H⁺ inhibitor amiloride (mucosal 1 mmol · l⁻¹) further enhanced the Ca²⁺ J_net by >65%. The Ca²⁺-pump inhibitor vanadate had no significant effect on J_net of Ca²⁺. Dietary Ca depletion enhanced calcitriol plasma concentrations but had no effect on active Ca²⁺ absorption across the rumen wall of sheep. In addition, no effect on active Ca²⁺ absorption could be observed during early lactation. In conclusion, there is clear evidence for the rumen as a main site for active Ca²⁺ absorption in sheep. Our results suggest the presence of a Ca²⁺/H⁺ exchange mechanism in the apical membrane of rumen epithelial cells which depends on SCFA absorption and which does not seem to be under the control of calcitriol. Basolateral Ca²⁺ extrusion occurs independently from Ca²⁺-pump activity and may be accomplished via Na⁺/Ca²⁺ exchange. Accepted: 29 June 1999     

Kinetics and thermodynamics of peroxidase- and laccase-catalyzed oxidation of N-substituted phenothiazines and phenoxazines

N -substituted phenothiazines (PTs) and phenoxazines (POs) catalyzed by fungal Coprinus cinereus peroxidase and Polyporus pinsitus laccase were investigated at pH 4–10. In the case of peroxidase, an apparent bimolecular rate constant (expressed as k _cat/K _m) varied from 1 ×10⁷M⁻¹s⁻¹to 2.6×10⁸M⁻¹s⁻¹ at pH 7.0. The constants for PO oxidation were higher in comparison to PT. pH dependence revealed two or three ionizable groups with pK _a values of 4.9–5.7 and 7.7–9.7 that significantly affected the activity of peroxidase. Single-turnover experiments showed that the limiting step of PT oxidation was reduction of compound II and second-order rate constants were obtained which were consistent with the constants at steady-state conditions. Laccase-catalyzed PT and PO oxidation rates were lower; apparent bimolecular rate constants varied from 1.8×10⁵M⁻¹s⁻¹ to 2.0×10⁷M⁻¹s⁻¹ at pH 5.3. PO constants were higher in comparison to PT, as was the case with peroxidase. The dependence of the apparent bimolecular constants of compound II or copper type 1 reduction, in the case of peroxidase or laccase, respectively, was analyzed in the framework of the Marcus outer-sphere electron-transfer theory. Peroxidase-catalyzed reactions with PT, as well as PO, fitted the same hyperbolic dependence with a maximal oxidation rate of 1.6×10⁸M⁻¹s⁻¹ and a reorganization energy of 0.30 eV. The respective parameters for laccase were 5.0×10⁷M⁻¹s⁻¹ and 0.29 eV. Received: 20 September 1999 / Accepted: 24 February 2000     

Complete degradation of tetrachloroethene in coupled anoxic and oxic chemostats

Anaerobic tetrachloroethene(C₂Cl₄)-dechlorinating bacteria were enriched in slurries from chloroethene-contaminated soil. With methanol as electron donor, C₂Cl₄ and trichloroethene (C₂HCl₃) were reductively dechlorinated to cis-1,2-dichloroethene (cis-C₂H₂Cl₂), whereas, with l-lactate or formate, complete dechlorination of C₂Cl₄ via C₂HCl₃, cis-C₂H₂Cl₂ and chloroethene (C₂H₃Cl) to ethene was obtained. In oxic soil slurries with methane as a substrate, complete co-metabolic degradation of cis-C₂H₂Cl₂ was obtained, whereas C₂HCl₃ was partially degraded. With toluene or phenol both of the above were readily co-metabolized. Complete degradation of C₂Cl₄ was obtained in sequentially coupled anoxic and oxic chemostats, which were inoculated with the slurry enrichments. Apparent steady states were obtained at various dilution rates (0.02–0.4 h⁻¹) and influent C₂Cl₄-concentrations (100–1000 μM). In anoxic chemostats with a mixture␣of␣formate and glucose as the carbon and electron source, C₂Cl₄ was transformed at high rates (above␣140 μmol l⁻¹ h⁻¹, corresponding to 145 nmol Cl⁻ min⁻¹ mg protein⁻¹) into cis-C₂H₂Cl₂ and C₂H₃Cl. Reductive dechlorination was not affected by addition of 5 mM sulphate, but strongly inhibited after addition of 5 mM nitrate. Our results (high specific dechlorination rates and loss of dechlorination capacity in the absence of C₂Cl₄) suggest that C₂Cl₄-dechlorination in the anoxic chemostat was catalysed by specialized dechlorinating bacteria. The partially dechlorinated intermediates, cis-C₂H₂Cl₂ and C₂H₃Cl, were further degraded by aerobic phenol-metabolizing bacteria. The maximum capacity for chloroethene (the sum of tri-, di- and monochloro derivatives removed) degradation in the oxic chemostat was 95 μmol l⁻¹ h⁻¹ (20 nmol min⁻¹ mg protein⁻¹), and that of the combined anoxic → oxic reactor system was 43.4 μmol l⁻¹ h⁻¹. This is significantly higher than reported thus far. Received: 17 April 1997 / Received revision: 6 June 1997 / Accepted: 7 June 1997     

Physiological and morphological variation in Metrosideros polymorpha, a dominant Hawaiian tree species, along an altitudinal gradient: the role of phenotypic plasticity

Metrosideros polymorpha, a dominant tree species in Hawaiian ecosystems, occupies a wide range of habitats. Complementary field and common-garden studies of M. polymorpha populations were conducted across an altitudinal gradient at two different substrate ages to ascertain if the large phenotypic variation of this species is determined by genetic differences or by phenotypic modifications resulting from environmental conditions. Several characteristics, including ecophysiological behavior and anatomical features, were largely induced by the environment. However, other characteristics, particularly leaf morphology, appeared to be mainly determined by genetic background. Common garden plants exhibited higher average rates of net assimilation (5.8 μmol CO₂ m⁻² s⁻¹) and higher average stomatal conductance (0.18 mol H₂O m⁻² s⁻¹) than their field counterparts (3.0 μmol CO₂ m⁻² s⁻¹, and 0.13 mol H₂O m⁻² s⁻¹ respectively). Foliar δ¹³C of most common-garden plants was similar among sites of origin with an average value of −26.9‰. In contrast, mean values of foliar δ¹³C in field plants increased substantially from −29.5‰ at low elevation to −24.8‰ at high elevation. Leaf mass per unit area increased significantly as a function of elevation in both field and common garden plants; however, the range of values was much narrower in common garden plants (211–308 g m⁻² for common garden versus 107–407 g m⁻² for field plants). Nitrogen content measured on a leaf area basis in common garden plants ranged from 1.4 g m⁻² to 2.4 g m⁻² and from 0.8 g m⁻² to 2.5 g m⁻² in field plants. Photosynthetic nitrogen use efficiency (PNUE) decreased 50% with increasing elevation in field plants and only 20% in plants from young substrates in the common garden. This was a result of higher rates of net CO₂ assimilation in the common garden plants. Leaf tissue and cell layer thickness, and degree of leaf pubescence increased significantly with elevation in field plants, whereas in common garden plants, variation with elevation of origin was much narrower, or was entirely absent. Morphological characteristics such as leaf size, petiole length, and internode length decreased with increasing elevation in the field and were retained when grown in the common garden, suggesting a potential genetic basis for these traits. The combination of environmentally induced variability in physiological and anatomical characteristics and genetically determined variation in morphological traits allows Hawaiian M. polymorpha to attain and dominate an extremely wide ecological distribution not observed in other tree species. Received: 12 March 1997 / Accepted: 27 August 1997     

FTIR, Raman, and UV-Vis spectroscopic and DFT investigations of the structure of iron-lead-tellurate glasses

In this work, the effects of iron ion intercalations on lead–tellurate glasses were investigated via FTIR, Raman and UV-Vis spectroscopies. This homogeneous glass system has compositions xFe₂O₃·(100−x)[4TeO₂·PbO₂], where x = 0–60 mol%. The presented observations in these mechanisms show that the lead ions have a pronounced affinity towards [TeO₃] structural units, resulting in the deformation of the Te–O–Te linkages, and leading to the intercalation of [PbO _n ] (n = 3, 4) and [FeO _n ] (n = 4, 6) entities in the [TeO₄] chain network. The formation of negatively charged [FeO₄]¹⁻ structural units implies the attraction of Pb²⁺ ions in order to compensate for this electrical charge. Upon increasing the Fe₂O₃ content to 60 mol%, the network can accommodate an excess of oxygen through the formation of [FeO₆] structural units and the conversion of [TeO₄] into [TeO₃] structural units. For even higher Fe₂O₃ contents, Raman spectra indicate a greater degree of depolymerization of the vitreous network than FTIR spectra do. The bands due to the Pb–O bond vibrations are very strongly polarized and the [TeO₄] structural units convert into [TeO₃] units via an intermediate coordination stage termed “[TeO₃₊₁]” structural units. Our UV-Vis spectroscopic data show two mechanisms: (i) the conversion of the Fe³⁺ to Fe²⁺ at the same time as the oxidation of Pb²⁺ to Pb⁺⁴ ions for samples with low Fe₂O₃ contents; (ii) when the Fe₂O₃ content is high (x ≥ 50 mol%), the Fe²⁺ ions capture positive holes and are transferred to Fe³⁺ ions through a photochemical reaction, while the Pb²⁺ ions are formed by the reduction of Pb⁴⁺ ions. DFT calculations show that the addition of Fe₂O₃ to lead–tellurate glasses seems to break the axial Te–O bonds, and the [TeO₄] structural units are gradually transformed into [TeO₃₊₁]- and [TeO₃]-type polyhedra. Analyzing these data further indicates a gradual conversion of the lead ions from covalent to ionic environment. There is then a charge transfer between the tri- and tetracoordinated tellurium atoms due to the capacity of the lead–tellurate network to form the appropriate coordination environments containing structural units of opposite charge, such as iron ions, [FeO₄]¹⁻.     

Effect of Mg2+ on the Structure and Function of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase

Mg²⁺ in various concentrations was added to purified Rubisco in vitro to gain insight into the mechanism of molecular interactions between Mg²⁺ and Rubisco. The enzyme activity assays showed that the reaction between Rubisco and Mg²⁺ was two order, which means that the enhancement of Rubisco activity was accelerated by low concentration of Mg²⁺ and slowed by high concentration of Mg²⁺. The kinetics constant (K _m) and V _max was 1.91 μM and 1.13 μmol CO₂ mg⁻¹ protein∙min⁻¹, respectively, at a low concentration of Mg²⁺, and 3.45 μM and 0.32 μmol CO₂∙mg⁻¹ protein∙min⁻¹, respectively, at a high concentration of Mg²⁺. By UV absorption and fluorescence spectroscopy assays, the Mg²⁺ was determined to be directly bound to Rubisco; the binding site of Mg²⁺ to Rubisco was 0.275, the binding constants (K _A) of the binding site were 6.33 × 10⁴ and 5.5 × 10⁴ l·mol⁻¹. Based on the analysis of the circular dichroism (CD) spectra, it was concluded that the binding of Mg²⁺ did not alter the secondary structure of Rubisco, suggesting that the observed enhancement of Rubisco carboxylase activity was caused by a subtle structural change in the active site through the formation of the complex with Mg²⁺.     

The Mechanism of CeCl<Subscript>3</Subscript> on the Activiation of Alanine Aminotransferase from Mice

The activity of alanine aminotransferase (ALT; E.C. 2.6.1.2) is often changed upon inflammatory responses in animals. Rare earths was shown to provoke various inflammatory responses both in rats and mice; however, the molecular mechanism by which rare earths exert its toxicity has not been completely understood, especially, we know little about the mechanism of the interaction between CeCl₃ and ALT. In this report, we investigated the mechanisms of CeCl₃ on ALT activity in vivo and in vitro. Our results showed that Ce³⁺ could significantly activate ALT in vivo and in vitro; the kinetics constant (Km) and Vmax were 0.018 μM and 1,380 unit mg⁻¹ protein min⁻¹, respectively, at a low concentration of Ce³⁺, and 0.027 μM and 624 unit mg⁻¹ protein min⁻¹, respectively, at a high concentration of Ce³⁺. By UV absorption and fluorescence spectroscopy assays, the Ce³⁺ was determined to be directly bound to ALT; the binding site of Ce³⁺ to ALT was 1.72, and the binding constants of the binding site were 4.82 × 10⁸ and 9.05 × 10⁷ L mol⁻¹. Based on the analysis of the circular dichroism spectra, it was concluded that the binding of Ce³⁺ altered the secondary structure of ALT, suggesting that the observed enhancement of ALT activity was caused by a subtle structural change in the active site through the formation of the complex with Ce³⁺.     

Protoplast ion fluxes: their measurement and variation with time, position and osmoticum

The ability to measure directly individual protoplast ion fluxes is a valuable addition to patch clamp and other techniques when using protoplasts to study membrane transporters. Before interpreting observations on protoplasts in terms of behaviour of intact cells and tissues, some methodological questions should be addressed. These include effects of space and time variations of transporter activities over the membrane, the osmotic dependence of specific ion transporters and the effect of the regenerating cell wall. In this study net H⁺ and Ca²⁺ fluxes were measured from individual corn (Zea mays L.) coleoptile protoplasts using a non-invasive microelectrode technique for ion flux measurements. For Ca²⁺, the flux distribution was almost symmetrical, ranging ±30 nmol · m⁻² · s⁻¹ around zero. For H⁺ it was skewed towards efflux ranging from −100 to +10 nmol · m⁻² · s⁻¹. The distribution of H⁺ fluxes through the protoplast surface was a complex mosaic which changed with time, sometimes showing oscillations. These flux variations with time and position around the surface, apparently driven by endogenous mechanisms, may be relevant to protoplast pH homeostasis. When the new cell wall was partially regenerated on the next day, the correlation between H⁺ and Ca²⁺ fluxes increased, which is consistent with the weak-acid Donnan-Manning model of cell wall ion exchange. Received: 11 June 1997 / Accepted: 10 July 1997     

Assessing the influence of the carbon oxidation-reduction state on organic pollutant biodegradation in algal-bacterial photobioreactors

The influence of the carbon oxidation–reduction state (CORS) of organic pollutants on their biodegradation in enclosed algal–bacterial photobioreactors was evaluated using a consortium of enriched wild-type methanotrophic bacteria and microalgae. Methane, methanol and glucose (with CORS −4, −2 and 0, respectively) were chosen as model organic pollutants. In the absence of external oxygen supply, microalgal photosynthesis was not capable of supporting a significant methane and methanol biodegradation due to their high oxygen demands per carbon unit, while glucose was fully oxidized by photosynthetic oxygenation. When bicarbonate was added, removal efficiencies of 37 ± 4% (20 days), 65 ± 4% (11 days) and 100% (2 days) were recorded for CH_4, CH₃OH and C₆H₁₂O₆, respectively due to the additional oxygen generated from photosynthetic bicarbonate assimilation. The use of NO₃⁻ instead of NH₄⁺ as nitrogen source (N oxidation–reduction state of +5 vs. −3) resulted in an increase in CH₄ degradation from 0 to 33 ± 3% in the absence of bicarbonate and from 37 ± 4% to 100% in the presence of bicarbonate, likely due to a decrease in the stoichiometric oxygen requirements and the higher photosynthetic oxygen production. Hypothetically, the CORS of the substrates might affect the CORS of the microalgal biomass composition (higher lipid content). However, the total lipid content of the algal–bacterial biomass was 19 ± 7% in the absence and 16 ± 2% in the presence of bicarbonate.