Synthesis and characterisation of the carboxylate linked osmium clusters [{Os3H(CO)10}2(CO2CH2CO2)], [{Os3H(CO)10}2(CO2C2H4CO2)], [{Os3H(CO)10}2(C4O4)] and [{Os3H(CO)10}2(C4O4){Co2(CO)6}]

Reactions between the activated cluster [Os₃(CO)₁₀(NCMe)₂] and malonic acid, succinic acid and dicarboxylic acetylene, respectively, lead to the formation of the linked cluster complexes [{Os₃H(CO)₁₀}₂(CO₂CH₂CO₂)] (1), [{Os₃H(CO)₁₀}₂(CO₂C₂H₄CO₂)] (2), and [{Os₃H(CO)₁₀}₂(C₄O₄)] (3) in good yield. Cluster 3 was subsequently treated with [Co₂(CO)₈] and this results in the addition of a “Co₂(CO)₆” group giving [{Os₃H(CO)₁₀}₂(C₂O₄){Co₂(CO)₆}] (4). The X-ray crystal structures are reported for 2–4. In each structure the two triangular triosmium units are linked by the carboxylate groups and within each complex the carboxylate groups are chelating and bridge two osmium atoms.     

Photochemical synthesis method of tungsten(II) complexes [WCl2(CO)3PPh3)2] and [WCl2(CO)2(dppe)]

The photochemical oxidation reaction of W(CO)₆ to [W(CO)₄Cl₂]₂ with CCl₄ was applied in the synthesis of [WCl₂(CO)₃(PPh₃)₂] and [WCl₂(CO)₂₋- (dppe)].     

Crystal structures of the dimeric cobalt compounds [Co(PPhMe2)(CO)3]2 and [Co2(PPhMe2)3(CO)5]

The molecular structures of the dimeric cobalt compounds [Co(PPhMe₂)(CO)₃]₂ and [Co₂(PPhMe₂)₃(CO)₅] have been characterised by X-ray crystallography. The compound [Co₂(PPhMe₂)₃(CO)₅] contains both bridging and terminal carbonyl groups in the solid state.     

Anapleurotic CO(2) Fixation by Phosphoenolpyruvate Carboxylase in C(3) Plants

The role of phosphoenolpyruvate carboxylase in photosynthesis in the C₃ plant Nicotiana tabacum has been probed by measurement of the ¹³C content of various materials. Whole leaf and purified ribulose bisphosphate carboxylase are within the range expected for C₃ plants. Aspartic acid purified following acid hydrolysis of this ribulose bisphosphate carboxylase is enriched in ¹³C compared to whole protein. Carbons 1-3 of this aspartic acid are in the normal C₃ range, but carbon-4 (obtained by treatment of the aspartic acid with aspartate β-decarboxylase) has an isotopic composition in the range expected for products of C₄ photosynthesis (−5‰), and it appears that more than half of the aspartic acid is synthesized by phosphoenolpyruvate carboxylase using atmospheric CO₂/HCO₃⁻. Thus, a primary role of phosphoenolpyruvate carboxylase in C₃ plants appears to be the anapleurotic synthesis of four-carbon acids.     

Quantum Yields for CO(2) Uptake in C(3) and C(4) Plants: Dependence on Temperature, CO(2), and O(2) Concentration

The quantum yields of C₃ and C₄ plants from a number of genera and families as well as from ecologically diverse habitats were measured in normal air of 21% O₂ and in 2% O₂. At 30 C, the quantum yields of C₃ plants averaged 0.0524 ± 0.0014 mol CO₂/absorbed einstein and 0.0733 ± 0.0008 mol CO₂/absorbed einstein under 21 and 2% O₂. At 30 C, the quantum yields of C₄ plants averaged 0.0534 ± 0.0009 mol CO₂/absorbed einstein and 0.0538 ± 0.0011 mol CO₂/absorbed einstein under 21 and 2% O₂. At 21% O₂, the quantum yield of a C₃ plant is shown to be strongly dependent on both the intercellular CO₂ concentration and leaf temperature. The quantum yield of a C₄ plant, which is independent of the intercellular CO₂ concentration, is shown to be independent of leaf temperature over the ranges measured. The changes in the quantum yields of C₃ plants are due to changes in the O₂ inhibition. The evolutionary significance of the CO₂ dependence of the quantum yield in C₃ plants and the ecological significance of the temperature effects on the quantum yields of C₃ and C₄ plants are discussed.     

Vibrational spectra and structure of M(CO2) and M2(CO2) molecules

Atomic Na, K and Cs were codeposited with CO₂ in excess of matrix gas at the temperature of 12 K. The IR spectra revealed the presence of ionic aggregates corresponding to the molecules M(CO)₂ and M₂(CO₂) (M=Na, K, Cs). Both molecular species have C_2v symmetry; M(CO₂) species have a planar ring structure while M₂(CO₂) have a W-shape structure. M₂(CO₂) molecules with C_s symmetry were also identified. The geometrical parameters of all the molecules were determined by ¹²C/¹³C and ¹⁶O/¹⁸O isotopic shifts. Raman spectra were also recorded and the results are reported in this study. The effect of photolysis on the structure of these molecules was examined. It was determined that photolysis promotes the formation of Na(CO₂) and transforms the M₂(CO₂) molecules with C_2v symmetry into C_s symmetry isomers.     

Acclimation of Photosynthesis to Elevated CO(2) in Five C(3) Species

The effect of long-term (weeks to months) CO₂ enhancement on (a) the gas-exchange characteristics, (b) the content and activation state of ribulose-1,5-bisphosphate carboxylase (rubisco), and (c) leaf nitrogen, chlorophyll, and dry weight per area were studied in five C₃ species (Chenopodium album, Phaseolus vulgaris, Solanum tuberosum, Solanum melongena, and Brassica oleracea) grown at CO₂ partial pressures of 300 or 900 to 1000 microbars. Long-term exposure to elevated CO₂ affected the CO₂ response of photosynthesis in one of three ways: (a) the initial slope of the CO₂ response was unaffected, but the photosynthetic rate at high CO₂ increased (S. tuberosum); (b) the initial slope decreased but the CO₂-saturated rate of photosynthesis was little affected (C. album, P. vulgaris); (c) both the initial slope and the CO₂-saturated rate of photosynthesis decreased (B. oleracea, S. melongena). In all five species, growth at high CO₂ increased the extent to which photosynthesis was stimulated following a decrease in the partial pressure of O₂ or an increase in measurement CO₂ above 600 microbars. This stimulation indicates that a limitation on photosynthesis by the capacity to regenerate orthophosphate was reduced or absent after acclimation to high CO₂. Leaf nitrogen per area either increased (S. tuberosum, S. melongena) or was little changed by CO₂ enhancement. The content of rubisco was lower in only two of the five species, yet its activation state was 19% to 48% lower in all five species following long-term exposure to high CO₂. These results indicate that during growth in CO₂-enriched air, leaf rubisco content remains in excess of that required to support the observed photosynthetic rates.     

Two-breath CO(2) test detects altered dynamic cerebrovascular autoregulation and CO(2) responsiveness with changes in arterial P(CO(2))

The new two-breath CO(2) method was employed to test the hypotheses that small alterations in arterial P(CO(2)) had an impact on the magnitude and dynamic response time of the CO(2) effect on cerebrovascular resistance (CVRi) and the dynamic autoregulatory response to fluctuations in arterial pressure. During a 10-min protocol, eight subjects inspired two breaths from a bag with elevated P(CO(2)), four different times, while end-tidal P(CO(2)) was maintained at three levels: hypocapnia (LoCO(2), 8 mmHg below resting values), normocapnia, and hypercapnia (HiCO(2), 8 mmHg above resting values). Continuous measurements were made of mean blood pressure corrected to the level of the middle cerebral artery (BP(MCA)), P(CO(2)) (estimated from expired CO(2)), and mean flow velocity (MFV, of the middle cerebral artery by Doppler ultrasound), with CVRi = BP(MCA)/MFV. Data were processed by a system identification technique (autoregressive moving average analysis) with gain and dynamic response time of adaptation estimated from the theoretical step responses. Consistent with our hypotheses, the magnitude of the P(CO(2))-CVRi response was reduced from LoCO(2) to HiCO(2) [from -0.04 (SD 0.02) to -0.01 (SD 0.01) (mmHg x cm(-1) x s) x mmHg Pco(2)(-1)] and the time to reach 95% of the step plateau increased from 12.0 +/- 4.9 to 20.5 +/- 10.6 s. Dynamic autoregulation was impaired with elevated P(CO(2)), as indicated by a reduction in gain from LoCO(2) to HiCO(2) [from 0.021 +/- 0.012 to 0.007 +/- 0.004 (mmHg x cm(-1) x s) x mmHg BP(MCA)(-1)], and time to reach 95% increased from 3.7 +/- 2.8 to 20.0 +/- 9.6 s. The two-breath technique detected dependence of the cerebrovascular CO(2) response on P(CO(2)) and changes in dynamic autoregulation with only small deviations in estimated arterial P(CO(2)).     

Infrared spectra and structure of bridging carbonyls in Fe2Ru(CO)12 and Fe3(CO)12

IR spectra of crystal, solution and pseudo-gas phases (argon and nitrogen matrices) of Fe₂Ru(CO)₁₂ and of crystal and solution phases of Fe₃(CO)₁₂ were recorded. By quantitative data-handling procedures, structures and bond angles for bridging carbonyls were estimated. Fe₂Ru(CO)₁₂ in crystal has a bridging structure analogous to that of Fe₃(CO)₁₂, with two bridged carbonyls and C_2v or pseudo-C_2v symmetry. In solution, both samples contain the same carbonyl bridged structure of C_2v symmetry,just as in pseudo- gas phase; the latter, however, contains other bridged molecules of unknown structures, too.     

Effects of O(2) Tension and Temperature during Light Uptake of CO(2) on the Dark Release of CO(2) by Excised C(3) and C(4) Leaves

A study was conducted on a C₄ (Panicum maximum) and a C₃ (Panicum bisulcatum) species to determine the nature of the dark release of ¹⁴CO₂ with respect to its responses to changes in temperature and O₂ tension during light CO₂ uptake of ¹⁴CO₂.     

Photosynthetic CO(2) Fixation at Air Levels of CO(2) by Isolated Spinach Chloroplasts

A system has been developed for the study of photosynthetic CO₂ fixation by isolated spinach chloroplasts at air levels of CO₂. Rates of CO₂ fixation were typically 20 to 60 micromoles/milligrams chlorophyll per hour. The rate of fixation was linear for 10 minutes but then declined to less than 10% of the initial value by 40 minutes. Ribulose 1,5-bisphosphate (RuBP) levels remained unchanged during this period, indicating that they were not the cause for the decline. The initial activity of the RuBP carboxylase in the chloroplast was high for 8 to 10 minutes and then declined similar to the rate of CO₂ fixation, suggesting that the decline in CO₂ fixation may have been caused by deactivation of the enzyme.     

Laboratory-Produced CO(2) Calibration Gases

A simple, inexpensive apparatus for making mixtures of accurately known amounts of CO₂ and CO₂-free atmospheric air is described. Calibration gases with CO₂ contents of 200 to 1500 microliters per liter produced with the apparatus had concentrations which were within 10 microliters per liter of the target concentration.     

C(3)-C(4) Intermediate Species in Alternanthera (Amaranthaceae) : Leaf Anatomy, CO(2) Compensation Point, Net CO(2) Exchange and Activities of Photosynthetic Enzymes

Two naturally occurring species of the genus Alternanthera, namely A. ficoides and A. tenella, were identified as C₃-C₄ intermediates based on leaf anatomy, photosynthetic CO₂ compensation point (Γ), O₂ response of г, light intensity response of г, and the activities of key enzymes of photosynthesis. A. ficoides and A. tenella exhibited a less distinct Kranz-like leaf anatomy with substantial accumulation of starch both in mesophyll and bundle sheath cells. Photosynthetic CO₂ compensation points of these two intermediate species at 29°C were much lower than in C₃ plants and ranged from 18 to 22 microliters per liter. Although A. ficoides and A. tenella exhibited similar intermediacy in г, the apparent photorespiratory component of O₂ inhibition in A. ficoides is lower than in A. tenella. The г progressively decreases from 35 microliters per liter at lowest light intensity to 18 microliters per liter at highest light intensity in A. tenella. It was, however, constant in A. ficoides at 20 to 25 microliters per liter between light intensities measured. The rates of net photosynthesis at 21% O₂ and 29°C by A. ficoides and A. tenella were 25 to 28 milligrams CO₂ per square decimeter per hour which are intermediate between values obtained for Tridax procumbens and A. pungens, C₃ and C₄ species, respectively. The activities of key enzymes of C₄ photosynthesis, phosphoenolpyruvate carboxylase, pyruvate Pi dikinase, NAD malic enzyme, NADP malic enzyme and phosphoenolpyruvate carboxykinase in the two intermediates, A. ficoides and A. tenella are very low or insignificant. Results indicated that the relatively low apparent photorespiratory component in these two species is presumably the basis for the C₃-C₄ intermediate photosynthesis.     

CO(2)-Enhanced Yield and Foliar Deformation among Tomato Genotypes in Elevated CO(2) Environments

Yield increases observed among eight genotypes of tomato (Lycopersicon esculentum Mill.) grown at ambient CO₂ (about 350) or 1000 microliters per liter CO₂ were not due to carbon exchange rate increases. Yield varied among genotypes while carbon exchange rate did not. Yield increases were due to a change in partitioning from root to fruit. Tomatoes grown with CO₂ enrichment exhibited nonepinastic foliar deformation similar to nutrient deficiency symptoms. Foliar deformation varied among genotypes, increased throughout the season, and became most severe at elevated CO₂. Foliar deformation was positively related to fruit yield. Foliage from the lower canopy was sampled throughout the growing season and analysed for starch, K, P, Ca, Mg, Fe, and Mn concentrations. Foliar K and Mn concentrations were the only elements correlated with deformation severity. Foliar K decreased while deformation increased. In another study, foliage of half the plants of one genotype received foliar applications of 7 millimolar KH₂PO₄. Untreated foliage showed significantly greater deformation than treated foliage. Reduced foliar K concentration may cause CO₂-enhanced foliar deformation. Reduced K may occur following decreased nutrient uptake resulting from reduced root mass due to the change in partitioning from root to fruit.     

Oscillations of the internal CO(2) concentration in tobacco leaves transferred to low CO(2)

Measurement of the internal CO(2) concentration (Ci) in tobacco leaves using a fast-response CO(2) exchange system showed that in the light, switching from 350 microLL(-1) to a low CO(2) concentration of 36.5 microLL(-1) (promoting high photorespiration) resulted in the Ci oscillating near the value of CO(2) compensation point (Gamma*). The oscillations are highly irregular, the range of Ci varying by 2-4 microLL(-1) in substomatal cavities with a period of a few seconds. The statistical properties of the time series became stationary after a transient of approximately 100s following transfer to low CO(2). Attractor reconstruction shows that the observed oscillations are not chaotic but exhibit stochastic behavior. The period of oscillations is consistent with the duration of photorespiratory post-illumination burst (PIB). We suggest that the observed oscillations may be due to a similar mechanism to that which leads to PIB, and may play a role in switching mitochondrial operation between oxidation of the photorespiratory glycine and of the tricarboxylic acid cycle substrates.     

Synthesis and characterization of two isomers of Os3(CO)10(C5H4N-2-C(H)NR) and the conversion to ortho-metallated HOs3(C5H3N-2-C(H)NR)(CO)9. Part III. X-ray Structure of HOs3(C5H3N-2-C(H)Ni-Pr)(CO)9

Os₃(CO)₁₀(MeCN)₂ reacts at room temperature in MeCN or toluene with R-Pyca2 to yield two isomers of Os₃(CO)₁₀(R-Pyca) that differ in the bonding of the R-Pyca ligand to the Os₃(CO)₁₀ unit. In all cases Os₃(CO)₁₀(R-Pyca(4e)) (isomer A; 4a: R = c-Pr, 4b: R = i-Pr, 4c: R = neo-Pent, 4d: R = t-Bu), containing a chelating 4e donating R-Pyca ligand and three OsS bonds, could be isolated. In the case of R = c-Pr and R = i-Pr Os₃(CO)₁₀(R-Pyca(6e)) (isomer B; 5a: R = c-Pr, 5b: R = i-Pr), in which only two OsS bonds are present and the R-Pyca ligand is bonded as a 6e donating ligand bridging two non-bonded Os atoms, could be isolated as a minor product.At 70 °C Os₃(CO)₁₀(R-Pyca(4e)) (4b and 4d) loses one carbonyl and the pyridine moiety of the R-Pyca ligand is ortho-metallated to form HOs₃(C₅H₃N-2-C(H)NR)(CO)₉ (6b: R = i-Pr and 6d: R = t-Bu). Under the same conditions Os₃(CO)₁₀(i-Pr-Pyca(6e)) (5b) reacts to Os₂(CO)₆(6e)) (7b) containing a bridging 6e donating ligands. The latter two reactions were followed with FT-IR spectroscopy in a high temperature IR cell.The structure of the complexes in solution have been studied by ¹H and ¹C NMR and IR spectroscopy. The stoichiometries of 4a and 5a were determined by FAB-mass spectrometry while an exact mass determination was carried out for 4a.The crystal structure of 6b has been determined. Crystal of 6b are monoclinic, space group P2₁/n, with a = 7.808(2),b = 17.613(3),c = 16.400(8)Å, β = 94.09(3)° and Z = 4. The structure was refined to R = 0.039. The molecule contains a triangular array of osmium atoms [Os(1)Os(2) = 2.898(2)Å, Os(1)Os(3) = 2.886(2)Åand Os(2)O(3) = 2.911(2)Å] and nine terminally bonded carbonyl ligands. The C₅H₃N-2-C(H)N-i-Pr ligand is chelate bonded to Os(2) with the pyridine and imine nitrogens atoms axially and equatorially coordinated respectively [Os(2)N(1) = 2.00(2)Åand Os(2)N(2) = 2.11(2)Å]. The i-Pr-Pyca ligand is ortho-metallated at C(1) and forms a four membered ring containing Os(2), Os(3), C(1) and N(1), the Os(3)C(1) distance being 2.12(2)Å. The hydride, which could not be located unequivocally from a difference Fourier map is proposed to bridge the Os(2)(3) bond on the basis of stereochemical considerations.     

Simultaneous Transport of CO(2) and HCO(3) by the Cyanobacterium Synechococcus UTEX 625

A mass spectrometer was used to simultaneously follow the time course of photosynthetic O₂ evolution and CO₂ depletion of the medium by cells of the cyanobacterium Synechococcus leopoliensis UTEX 625. Analysis of the data indicated that both CO₂ and HCO₃⁻ were simultaneously and continuously transported by the cells as a source of substrate for photosynthesis. Initiation of HCO₃⁻ transport by Na⁺ addition had no effect on ongoing CO₂ transport. This result is interpreted to indicate that the CO₂ and HCO₃⁻ transport systems are separate and distinctly different transport systems. Measurement of CO₂-dependent photosynthesis indicated that CO₂ uptake involved active transport and that diffusion played only a minor role in CO₂ acquisition in cyanobacteria.     

Internal conductance to CO(2) diffusion and C(18)OO discrimination in C(3) leaves

(18)O discrimination in CO(2) stems from the oxygen exchange between (18)O-enriched water and CO(2) in the chloroplast, a process catalyzed by carbonic anhydrase (CA). A proportion of this (18)O-labeled CO(2) escapes back to the atmosphere, resulting in an effective discrimination against C(18)OO during photosynthesis (Delta(18)O). By constraining the delta(18)O of chloroplast water (delta(e)) by analysis of transpired water and the extent of CO(2)-H(2)O isotopic equilibrium (theta(eq)) by measurements of CA activity (theta(eq) = 0.75-1.0 for tobacco, soybean, and oak), we could apply measured Delta(18)O in a leaf cuvette attached to a mass spectrometer to derive the CO(2) concentration at the physical limit of CA activity, i.e. the chloroplast surface (c(cs)). From the CO(2) drawdown sequence between stomatal cavities from gas exchange (c(i)), from Delta(18)O (c(cs)), and at Rubisco sites from Delta(13)C (c(c)), the internal CO(2) conductance (g(i)) was partitioned into cell wall (g(w)) and chloroplast (g(ch)) components. The results indicated that g(ch) is variable (0.42-1.13 mol m(-2) s(-1)) and proportional to CA activity. We suggest that the influence of CA activity on the CO(2) assimilation rate should be important mainly in plants with low internal conductances.