Myoglobin functions in the heart

The physiological role of myoglobin (Mb) within the heart depends on its oxygenation state. The myocardium exhibits a broad oxygen partial pressure (pO₂) spectrum with a transmural gradient from the epicardial to the subendocardial layer, ranging from arterial values to an average of 19.3 mm Hg down to 0 mm Hg. The function of Mb as an O₂ storage depot is well appreciated, especially during systolic compression. In addition, Mb controls myocardial nitric oxide (NO) homeostasis and thus modulates mitochondrial respiration under physiological and pathological conditions. We recently discovered the role of Mb as a myocardial O₂ sensor; in its oxygenated state Mb scavenges NO, protecting the heart from the deleterious effects of excessive NO. Under hypoxia, however, deoxygenated Mb changes its role from an NO scavenger to an NO producer. The NO produced protects the cell from short phases of hypoxia and from myocardial ischemia/reperfusion injury. In this review we summarize the traditional and novel aspects of Mb and its (patho)physiological role in the heart.     

The effects of feeding on the swimming performance and metabolic response of juvenile southern catfish,Silurus meridionalis,acclimated at different temperatures

To test whether the effects of feeding on swimming performance vary with acclimation temperature in juvenile southern catfish (Silurus meridionalis), we investigated the specific dynamic action (SDA) and swimming performance of fasting and feeding fish at acclimation temperatures of 15, 21, 27, and 33 °C. Feeding had no effect on the critical swimming speeding (U_crit) of fish acclimated at 15 °C (p = 0.66), whereas it elicited a 12.04, 18.70, and 20.98% decrease in U_crit for fish acclimated at 21, 27 and 33 °C, respectively (p < 0.05). Both the maximal postprandial oxygen consumption rate (VO_2peak) and the active metabolic rate (VO_2active, maximal aerobic sustainable metabolic rate of fasting fish) increased significantly with temperature (p < 0.05). The postprandial maximum oxygen consumption rates during swimming (VO_2max) were higher than the VO_2active of fasting fish at all temperature groups (p < 0.05). The VO_2max increased with increasing temperature, but the relative residual metabolic scope (VO_2max? VO_2peak) during swimming decreased with increasing in temperature. The present study showed that the impairment of postprandial swimming performance increased with increasing temperature due to the unparalleled changes in the catfish's central cardio-respiratory, peripheral digestive and locomotory capacities. The different metabolic strategies of juvenile southern catfish at different temperatures may relate to changes in oxygen demand, imbalances in ion fluxes and dissolved oxygen levels with changes in temperature.     

Decomposition processes in soil of a healthy and a declining Phragmites australis stand

Decomposition processes were investigated in the soil of a declining, more eutrophic and a healthy, less eutrophic freshwater reed (Phragmites australis (Cav.) Trin. ex Steudel) stand in the littoral zone of Rožmberk fishpond, Czech Republic. Soil and pore water were sampled five times from April to October 1998. Chemical properties, CO₂ production in oxic and anoxic conditions, CH₄ production, denitrifying enzyme activity (DEA) and bacterial biomass were measured under laboratory conditions in suspensions prepared from homogenised soil samples. The more eutrophic West stand was more anaerobic than the East stand, with lower redox potential, lower pH and with a higher amount of organic acids, mainly acetic and lactic acid. Mean seasonal concentrations of total nitrogen in pore water, nitrogen of amino acids and proteins, and reducing sugars were all higher in the soil at the more eutrophic stand. Higher nutrient status and more reduced conditions at the more eutrophic stand were accompanied by (i) a limitation of aerobic microbial activities (CO₂ production in oxic conditions: 0.35 versus 0.54 μmol CO₂ cm⁻³ h⁻¹); lower DEA (4.0 versus 20.2 nmol N₂O cm⁻³ h⁻¹) and a lower proportion of bacteria that were active in aerobic conditions; (ii) by a prevalence of anaerobic over aerobic microbial processes; (iii) by a higher rate of methanogenesis (15.0 versus 11.5 nmol CH₄ cm⁻³ h⁻¹) and (iv) by an overall lower rate of microbial processes as compared to less eutrophied stand. The shift from aerobic to anaerobic microbial metabolism, and a coinciding restriction of metabolic activities at the more eutrophic stand are indicative of an elevated oxygen stress in the soil, associated with accumulation of metabolites toxic to both the micro-organisms and the reed. Possible links between eutrophication, decomposition processes in the soil and reed decline are discussed.     

Investigation on the properties and kinetics of glucose-fed aerobic granular sludge

Aerobic granulation is a process in which suspended biomass aggregate and form discrete well-defined granules in aerobic systems. To investigate the properties and kinetics of aerobic granular sludge, aerobic granules were cultivated with glucose synthetic wastewater in a series of sequencing batch reactors (SBR). The spherical shaped granules were observed on 8th day with the mean diameter of 0.1 mm. With the organic loading rate (OLR) being increased to 4.0 g COD L⁻¹ d⁻¹, aerobic granules grew matured with spherical shape. The size of granules ranged from 1.2 to 1.8 mm, and the corresponding settling velocity of individual granule was 24.2–36.4 m h⁻¹. The oxygen utilization rate (OUR) of mature granules was 41.90 g O₂ kg MLSS⁻¹ h⁻¹, which was two times higher than that of activated sludge (18.32 g O₂ kg MLSS⁻¹ h⁻¹). The experimental data indicated that the substrate utilization and biomass growth kinetics generally followed Monod's kinetics model. The corresponding kinetic coefficients of k (maximum specific substrate utilization rate), K_s (half velocity coefficient), Y (growth yield coefficient) and K_d (decay coefficient) were determined as follows, k_c = 23.65 d⁻¹, K_c = 3367.05 mg L⁻¹, K_N = 0.038 d⁻¹, K_N = 29.65 mg L⁻¹, Y = 0.1927–0.2022 mg MMLS (mg COD)⁻¹ and K_d = 0.00845–0.0135 d⁻¹, respectively. Those properties of aerobic granules made aerobic granules system had a short setup period, high substrate utilization rate and low sludge production.     

Antioxidant response of a novel Streptomyces sp. M3004 isolated from legume rhizosphere to H2O2 and paraquat

This paper aims to investigate the effect of H₂O₂ and paraquat on the activities of superoxide dismutase (SOD) and catalase (CAT), and membrane lipid peroxidation (LPO) levels in newly isolated Streptomyces sp. M3004. SOD activities of Streptomyces sp. M3004, grown in 10 mM and 30 mM H₂O₂, were significantly lower than the control cultures. On the other hand, as an antioxidant enzyme, CAT activity in both H₂O₂ treatment conditions increased significantly compared with the control. These activity values in 10 mM and 30 mM H₂O₂ treatment on the 48th hour of incubation were 3.8- and 6.6-fold higher than the control, respectively. SOD activity decreased significantly with respect to paraquat concentration, which was added at the start of the incubation. CAT activities increased significantly in 1.0 mM and 3.0 mM paraquat treatments compared to control. As an indicative marker of membrane damage, LPO levels of the novel isolate Streptomyces sp. M3004 treated with H₂O₂, and paraquat stress conditions were significantly higher than the control. Nevertheless, compared with the 30 mM H₂O₂ in both treatment conditions, LPO levels in 10 mM H₂O₂ were significantly higher. The decreases in SOD activities in paraquat and H₂O₂ treatment conditions resulted in the increases in the LPO levels although it increases in CAT activities.     

Performance evaluation of various bioreactors for the removal of Cr(VI) and organic matter from industrial effluent

Performances of various bioreactors under different operating conditions were evaluated with respect to hexavalent chromium (Cr(VI)) reduction and COD removal. Continuous reactor studies were carried out with (i) aerobic suspended growth system, (ii) aerobic attached growth system, and (iii) anoxic attached growth system, using both synthetic and actual industrial wastewater. Arthrobacter rhombi-RE (MTCC7048), a Cr(VI) reducing strain enriched and isolated from chromium contaminated soil, was used in all the bioreactors for Cr(VI) biotransformation and COD removal. Aerobic and anoxic batch experiments were conducted to evaluate the bio-kinetic parameters. The bio-kinetic parameters for aerobic system were: μ_max = 2.34/d, K_s = 190 mg/L (as COD), K_i = 3.8 mg/L of Cr(VI), and Y_T = 0.377. These parameters for anoxic conditions were: μ_max = 0.57/d, K_s = 710 mg/L (as COD), K_i = 8.77 mg/L of Cr(VI), and Y_T = 0.13. Aerobic attached growth system, operated at a hydraulic retention time (HRT) of 24 h and an organic loading rate (OLR) of 3 kg/m³/d, performed better than aerobic suspended and the anoxic attached growth systems operated under identical conditions, while treating synthetic wastewater as well as industrial effluent.     

Aerobic Fitness and Glycemic Variability in Adolescents with Type 1 Diabetes

ObjectiveThis study examines the association of fitness on glycemic variability (GV) in adolescents with type 1 diabetes mellitus (T1DM). GV has been associated with high frequency of hyper-and hypoglycemia.MethodsNineteen adolescents with T1DM, ages 14 to 19 years, underwent aerobic fitness testing to determine their maximal aerobic capacity (VO₂ max). A continuous glucose monitoring (CGM) device was placed on each subject and worn for 3 to 5 days until a return visit when the subjects underwent a 1-hour treadmill exercise session. Mean amplitude of glycemic excursion (MAGE) was calculated from the CGM data collected between the 2 study visits. Metabolic equivalent (MET), a measure of accumulated metabolic workload during the exercise session, was also calculated.ResultsMean VO₂ max was 46.6 ± 6.8 mL/kg/min, with a range of 34.8 to 57.0 mL/kg/min. Mean MET during the exercise session was 577.2 ± 102.4 and ranged from 354.3 to 716.2 METs. There was an inverse association between VO₂ max and MAGE (r = − 0.46; 95% confidence interval [CI], − 0.01 to − 0.76; P = .048). MET load and MAGE also had an inverse relationship (r = − 0.48; 95% CI, − 0.03 to − 0.77; P = .037).ConclusionGV is inversely associated with fitness and MET load. Aerobic fitness should be promoted in adolescents with T1DM not only because of its multiple beneficial effects but also due to a possible association with GV, leading to fewer extremes in hypo-and hyperglycemia. (Endocr Pract. 2014;20:566-570)     

Comparative kinetic study between moving bed biofilm reactor-membrane bioreactor and membrane bioreactor systems and their influence on organic matter and nutrients removal

New technologies regarding wastewater treatment have been developed. Among these technologies, the moving bed biofilm reactor combined with membrane bioreactor (MBBR-MBR) is a recent solution alternative to conventional processes. This paper presents the results obtained from three wastewater treatment plants working in parallel. The first wastewater treatment plant consisted of a membrane bioreactor (MBR), the second one was a MBBR-MBR system containing carriers both in anoxic and aerobic zones, and the last one consisted of a MBBR-MBR system which contained carriers only in the aerobic zone. The reactors operated with a hydraulic retention time of 26.47 h. During the study, the difference between the experimental plants was not statistically significant concerning organic matter and nutrients removal. However, different tendencies regarding nutrients removal are shown by the three wastewater treatment plants. In this sense, the performances in terms of nitrogen and phosphorus removal of the MBBR-MBR system which contained carriers only in the aerobic zone (67.34 ± 11.22% and 50.65 ± 11.13%, respectively) were slightly better than those obtained from another experimental plants. As a whole, the pilot plant which consisted of a MBR showed better performance from the point of view of the kinetics of the heterotrophic and autotrophic biomass with values of μ_m,H = 0.00858 h⁻¹, μ_m,A = 0.07646 h⁻¹, K_M = 2.37 mg O₂ L⁻¹ and K_NH = 1.31 mg N L⁻¹.     

Response surface analysis for enzymatic decolorization of Congo red by manganese peroxidase

The enzymatic decolorization process of manganese peroxidase (MnP) is a complex system, which is greatly affected by the concentrations of H₂O₂, Mn²⁺, dye and enzyme. This work aimed to study these factors and investigate the combined interactions between them by applying response surface methodology (RSM) for decolorization of Congo red with MnP from Schizophyllum sp. F17, meanwhile conventional one-factor-at-a-time analysis was carried out. Through the one-factor-at-a-time analysis the optimized H₂O₂, Mn²⁺, Congo red and MnP extract was 0.2 mM, 0.5 mM, 50 mg/l and 0.8 ml, respectively, and the maximum decolorization attained under such conditions was 24.2%. Response surface analysis was conducted through Box–Behnken design and a second-order polynomial model (R² = 0.8565) was generated to describe the combined effect and the interactions quantificationally. ANOVA analysis indicated that the interactions between H₂O₂ and MnP, between dye and MnP were significant; the optimum condition through RSM was found to be 0.35 mM H₂O₂, 0.5 mM Mn²⁺, 75 mg/l Congo red and 1.4 ml MnP extract, for maximum decolorization of 30.8%.     

Thalassia testudinum response to the interactive stressors hypersalinity,sulfide and hypoxia

A large-scale mesocosm (sixteen 500 L tanks) experiment was conducted to investigate the effects of hypersalinity (45–65 psu), porewater sulfide (2–6 mM) and nighttime water column hypoxia (5–3 mg L⁻¹) on the tropical seagrass Thalassia testudinum Banks ex König. We examined stressor effects on growth, shoot survival, tissue sulfur (S⁰, TS, δ³⁴S) and leaf quantum efficiencies, as well as, porewater sulfides (∑TS_pw) and mesocosm water column O₂ dynamics. Sulfide was injected into intact seagrass cores of T. testudinum exposing below-ground tissues to 2, 4, and 6 mM S²⁻, but rapid oxidation resulted in ∑TS_pw < 1.5 mM. Hypersalinity at 65 psu lowered sulfide oxidation and significantly affected plant growth rates and quantum efficiencies (F_v/F_m < 0.70). The most depleted rhizome δ³⁴S signatures were also observed at 65 psu, suggesting increased sulfide exposure. Hypoxia did not influence ∑TS_pw and plant growth, but strengthened the hypersalinity response and decreased rhizome S⁰, indicating less efficient oxidation of ∑TS_pw. Following nighttime hypoxia treatments, ecosystem level metabolism responded to salinity treatments. When O₂ levels were reduced to 5 and 4 mg L⁻¹, daytime O₂ levels recovered to approximately 6 mg L⁻¹; however, this recovery was more limited when O₂ levels were lowered to 3 mg L⁻¹. Subsequent to O₂ reductions to 3 mg O₂ L⁻¹, nighttime O₂ levels rose in the 35 and 45 psu tanks, stayed the same in the 55 psu tanks, and declined in the 65 psu tanks. Thus, hypersalinity at 65 psu affects T. testudinum's oxidizing capacity and places subtle demands on the positive O₂ balance at an ecosystem level. This O₂ demand may influence T. testudinum die-off events, particularly after periods of high temperature and salinity. We hypothesize that the interaction between hypersalinity and sulfide toxicity in T. testudinum is their synergistic effect on the critical O₂ balance of the plant.     

Nutrient composition,digestion and rumen fermentation in sheep of wheat straw treated with calcium oxide,sodium hydroxide and alkaline hydrogen peroxide

This study tested the effect of calcium oxide (CaO), sodium hydroxide (NaOH) and NaOH plus hydrogen peroxide (H₂O₂; AHP) on cell wall composition, digestion and fermentation of wheat straw (straw) in sheep. Treated straws were prepared by mixing straw either with water followed by dusting with CaO at 160 g kg⁻¹ DM or with a NaOH solution alone at 3 l kg⁻¹ DM to supply 80 g NaOH kg⁻¹ DM (Na) or pre-soaked with Na exactly as in the previous treatment for 27 h followed by mixing with 130 g H₂O₂ kg⁻¹ DM (AHP) for 6 h. After 14 days of storage, the treated straws and an untreated straw (U) were fed automatically every 2 h to four individually housed sheep together with a supplement in a 4×4 latin square experiment. Each kilogram supplement DM contained 422 g CP and 10.8 MJ ME. NDF (p<0.001) and hemicellulose (p<0.01) contents were significantly reduced whereas cellulose was increased (p<0.001) in treated compared to untreated straw. ADL was reduced in Ca (p<0.05) but increased (p<0.05) in Na and AHP compared with U. The rumen and total tract digestibility were significantly (p<0.001) greater in sheep fed treated compared with untreated straw. Significant differences (p<0.05) between treatments for pH, NH₃ and VFA were also observed. All treatments improved the nutritive value of straws compared with untreated through modification of cell wall with a subsequent increase in digestibility by sheep. Although the digestibility for Ca was lower than that for Na despite reduction in cell wall, its use to treat straws may be more safe and cost effective than Na. AHP was the most effective and could also improve the energy value of other low quality forages for ruminants. However, the need of AHP for a large amount of NaOH to achieve highly alkaline pH limits its farm scale application. Therefore, further studies should either consider reducing the amount of NaOH or finding alternative alkalis that are cost effective and user-friendly.     

Seasonal variations in photosynthetic irradiance response curves of macrophytes from a Mediterranean coastal lagoon

The main photosynthesis and respiration parameters (dark respiration rate, light saturated production rate, saturation irradiance, photosynthetic efficiency) were measured on a total of 23 macrophytes of the Thau lagoon (2 Phanerogams, 5 Chlorophyceae, 10 Rhodophyceae and 6 Phaeophyceae). Those measurements were performed in vitro under controlled conditions, close to the natural ones, and at several seasons. Concomitantly, measurements of pigment concentrations, carbon, phosphorous and nitrogen contents in tissues were performed. Seasonal intra-specific variability of photosynthetic parameters was found very high, enlightening an important acclimatation capacity. The highest photosynthetic capacities were found for Chlorophyceae (e.g. Monostroma obscurum thalli at 17 °C, 982 μmol O₂ g⁻¹ dw h⁻¹ and 9.1 μmol O₂ g⁻¹ dw h⁻¹/μmol photons m⁻² s⁻¹, respectively for light saturated net production rate and photosynthetic efficiency) and Phanerogams (e.g. Nanozostera noltii leaves at 25 °C, 583 μmol O₂ g⁻¹ dw h⁻¹ and 2.6 μmol O₂ g⁻¹ dw h⁻¹/μmol photons m⁻² s⁻¹ respectively for light saturated net production rate and photosynthetic efficiency). As expected, species with a high surface/volume ratio were found to be more productive than coarsely branched thalli and thick blades shaped species. Contrary to R_d (ranging 6.7–794 μmol O₂ g⁻¹ dw h⁻¹, respectively for Rytiphlaea tinctoria at 7 °C and for Dasya sessilis at 25 °C) for which a positive relationship with water temperature was found whatever the species studied, the evolution of P/I curves with temperature exhibited different responses amongst the species. The results allowed to show summer nitrogen limitation for some species (Gracilaria bursa-pastoris and Ulva spp.) and to propose temperature preferences based on the photosynthetic parameters for some others (N. noltii, Zostera marina, Chaetomorpha linum).     

Synthesis and characterization of a pH-sensitive conjugate of isoniazid with Fe3O4@SiO2 magnetic nanoparticles

The Letter describes the preparation and characterization of a conjugate of isoniazid (INH) with magnetic nanoparticles Fe₃O₄@SiO₂ 115 ± 60 nm in size. The INH molecules were attached to the surface of nanoparticles by a covalent pH-sensitive amidine bond. The conjugate was characterized by X-ray diffraction, SEM, dynamic light scattering, IR spectroscopy and microanalysis. The conjugate released isoniazid under in vitro conditions (pH = 4; 37 °C; t_1/2 ≈ 115 s). In addition, the cytotoxicity of the Fe₃O₄@SiO₂–INH conjugate was evaluated in SK-BR-3 cells using the xCELLigence system.     

The effect of molecular packing on the occurrence of spin crossover phenomena in one-dimensional Fe(II)-bis-Schiff base complexes

Two new one-dimensional Fe(II)-bis-Schiff base complexes, [Fe(L1)(pyz)] · CH₂Cl₂ (1) and [Fe(L2)(pyz)] · 2CH₂Cl₂ (2) (H₂L1 = bis(O-vanillin)-O-phenylenediimine, H₂L2 = bis(O-vanillin)-2,3-naphthalenediimine, pyz = pyrazine) are reported with their crystal structures and magnetic property. Compound 1 shows a two-step SCO behavior while 2 shows HS at all the temperature range measured. Although the extension of aromatic moiety from benzene (L1) to naphthalene (L2) was introduced for the purpose of strengthening the cooperativity, it leads to the absence of SCO, due to the unanticipated π–π interaction, which leads to the longer Fe–N bond lengths and a weak ligand field around Fe(II) ion.     

Thermo- and mesophilic aerobic batch biodegradation of high-strength distillery wastewater (potato stillage) – Utilisation of main carbon sources

The aim of the study was to ascertain the extent to which temperature influences the utilisation of main carbon sources (reducing substances determined before and after hydrolysis, glycerol and organic acids) by a mixed culture of thermo- and mesophilic bacteria of the genus Bacillus in the course of aerobic batch biodegradation of potato stillage, a high-strength distillery effluent (COD = 51.88 g O₂/l). The experiments were performed at 20, 30, 35, 40, 45, 50, 55, 60 and 63 °C, at pH 7, in a 5 l working volume stirred-tank bioreactor (Biostat^®B, B. Braun Biotech International) with a stirrer speed of 550 rpm and aeration at 1.6 vvm. Particular consideration was given to the following issues: (1) the sequence in which the main carbon sources in the stillage were assimilated and (2) the extent of their assimilation achieved under these conditions.     

Flow velocity affects internal oxygen conditions in the seagrass Cymodocea nodosa

The internal oxygen status of seagrass tissues, which is believed to play an important role in events of seagrass die-off, is partly determined by the rates of gas exchange between leaves and water column. In this study, we examined whether water column flow velocity has an effect on gas exchange, and hence on internal oxygen partial pressures (pO₂) in the Mediterranean seagrass, Cymodocea nodosa. We measured the internal pO₂ in the horizontal rhizomes of C. nodosa in darkness at different mainstream flow velocities, combined with different levels of water column oxygen pO₂ using an experimental flume in the laboratory. Flow velocity clearly had an effect on the internal oxygen status. In stagnant, but fully aerated water the mean internal pO₂ was 6.9 kPa, corresponding to about 30% of air saturation. The internal pO₂ increased with increasing flow velocity reaching saturation of around 12.2 kPa (60% of air saturation) at flow velocities ≥7 cm s⁻¹. Flow had a relatively larger influence on internal pO₂ at lower water column oxygen concentrations. By extrapolating linear relationships between internal and water column pO₂ in this experimental setup, rhizomes would become anoxic at a water column oxygen pO₂ of 4–4.5 kPa (∼20% of air saturation) in flowing water, but already at 6.4 kPa (∼30% of air saturation) in stagnant water. Water flow may play an important role for seagrass performance and survival in areas with poor water column oxygen conditions and may, in general, be of importance for the distribution of submerged rooted plants.     

Dihydrochalcone glucosides and antioxidant activity from the roots of Anneslea fragrans var. lanceolata

Bioassay-guided fractionation of the roots of Anneslea fragrans var. lanceolata led to the isolation of four dihydrochalcone glucosides, davidigenin-2′-O-(6″-O-4″′-hydroxybenzoyl)-β-glucoside (1), davidigenin-2′-O-(2″-O-4″′-hydroxybenzoyl)-β-glucoside (2), davidigenin-2′-O-(3″-O-4″′-hydroxybenzoyl)-β-glucoside (3), and davidigenin-2′-O-(6″-O-syringoyl)-β-glucoside (4), and 13 known compounds. The structures were identified by means of spectroscopic analysis. Davidigenin-2′-O-(6″-O-syringoyl)-β-glucoside (4), 1-O-3,4-dimethoxy-5-hydroxyphenyl-6-O-(3,5-di-O-methylgalloyl)-β-glucopyranoside (5), lyoniresinol (10), and syringic acid (13) showed ABTS [2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid)] cation radical scavenging activity, with SC₅₀ values of 52.6 ± 5.5, 26.0 ± 0.7, 6.0 ± 0.2, and 27.5 ± 0.6 μg/mL in 20 min, respectively. Lyoniresinol (10), isofraxidin (12), and syringic acid (13) also showed DPPH [1,1-diphenyl-2-picrylhydrazyl] radical scavenging activity, with SC₅₀ values of 8.4 ± 1.8, 51.6 ± 2.2, and 4.3 ± 0.7 μg/mL in 30 min, respectively.     

Acetato complexes of molybdenum(V): A novel tetranuclear core based on the metal–metal bonded {Mo2O4}2+ units

A series of acetato complexes of molybdenum(V), based on the singly metal–metal bonded {Mo₂O₄}²⁺ structural fragment, has been prepared. A dinuclear (PyH)₃[Mo₂O₄Cl₄(OOCCH₃)] · CH₃CN (1) (PyH⁺ = pyridinium cation, C₅H₅NH⁺) was obtained upon the reaction of (PyH)₅[MoOCl₄(H₂O)]₃Cl₂ with the equimolar solution of pyridine and acetic acid in acetonitrile at ambient conditions. The acetato ligand in 1 is coordinated to a pair of molybdenum atoms in a syn–syn bidentate bridging manner. (PyH)_n[MoOBr₄]_n afforded in an analogous synthetic procedure a tetranuclear cluster, [Mo₄O₈(OOCCH₃)₃(OH)Py₄] · 1/2CH ₃CN · 1/2H₂O (3), with a novel core which may be envisioned as the acetate- and hydroxide-assisted assembly of {Mo₂O₄}²⁺ building blocks. Its structure is presented in terms of known tetranuclear clusters which are also composed of two {Mo₂O₄}²⁺ units. The acetato ligands in 3 adopted apart from bidentate bridging binding modes also a monodentate one. Partial substitution of chlorido ligands in (PyH)₃[Mo₂O₄Cl₄(OOCCH₃)] · CH₃CN (1) with pyridine resulted in a neutral [Mo₂O₄Cl(OOCCH₃)Py₃] · PrⁱOH · Py (2) which retained the original acetate coordination. The title compounds were fully characterized by X-ray diffraction studies and infrared vibrational spectroscopy.     

PSII photochemistry and carboxylation efficiency in Liriodendron tulipifera under ozone exposure

Liriodendron tulipifera is an important forest plant which is commonly used in urban environments as a shade tree. Young plants have been exposed (under controlled conditions) to 120 ppb of O₃ for 45 consecutive days (5 h d⁻¹). The aim of this investigation was to clarify if O₃ limits the physiological performance of L. tulipifera. In treated plants, dynamics related to membrane injury, gas exchange and chlorophyll a fluorescence leads to: (i) increase in lipid peroxidation (maximum value of +78% 15 days after the fumigation, compared to controls); (ii) reduction of photosynthetic activity (up to 66% 28 days after the exposure), twinned with a partial stomatal closure and a store of CO₂ in substomatal chambers; (iii) reduction in carboxylation efficiency (−11% at the end of exposure); (iv) damage to PSII, as demonstrated by the increase in the PSII excitation pressure (−57% 28 days after the treatment). On this basis, O₃ should be considered very harmful to L. tulipifera, although the reduction of total chlorophylls content and the activation of xanthophyll cycle take place in order to attempt to regulate light absorbed energy limiting oxidative damage.