Starch grain morphology of the seagrasses Halodule wrightii, Ruppia maritima, Syringodium filiforme, and Thalassia testudinum

Starch grains are a ubiquitous component of plants that have been used in tandem with phytoliths, pollen, and macrofossils to reconstruct past floral diversity. This tool has yet to be fully explored for aquatic plants, specifically seagrasses, which lack phytoliths and are rarely preserved as macrofossils or pollen. If starch grains in seagrasses are morphologically distinct, this method has the potential to improve seagrass identification in the fossil record in such cases where its starch is preserved (e.g. scratches and occlusal surfaces of tooth enamel from seagrass consumers). The goals of this study were twofold: (1) to determine if starch is present in seagrass material and (2) to assess how starch grain morphology differs between different seagrasses.This study focused on four abundant and ecologically distinct seagrasses from the Caribbean: Halodule wrightii, Ruppia maritima, Syringodium filiforme, and Thalassia testudinum. Starch grains were observed in all species except S. filiforme. Grains from H. wrightii are typically observed in side-on orientation, are sub-round to angular, and are fairly small (3-19 μm, end-on). Grains of R. maritima are small spherical grains (4-8 μm) that have a centric hilum and a straight extinction cross with a median angle between the arms of 90°. Grains from T. testudinum are large (9-31 μm, end-on), conical in side-on and round/sub-round in end-on orientation, have a slightly eccentric hilum with an obvious particle, and prominent lamellae.Visual assessment and comparative statistics demonstrate that the morphology of starch grains from T. testudinum, R. maritima, and H. wrightii are significantly different. With more extensive research, there is potential for the positive identification of starch grains from an unknown seagrass. The ability to identify seagrass from starch grains could facilitate the identification of seagrasses in the fossil record and supply information on seagrass evolution and distribution, climate effects on seagrass distribution, and the diets of seagrass consumers.     

Synergistic effects of high temperature and sulfide on tropical seagrass

To examine the synergism of high temperature and sulfide on two dominant tropical seagrass species, a large-scale mesocosm experiment was conducted in which sulfide accumulation rates (SAR) were increased by adding labile carbon (glucose) to intact seagrass sediment cores across a range of temperatures. During the initial 10 d of the 38 d experiment, porewater SAR in cores increased 2- to 3-fold from 44 and 136 μmol L^− 1 d^− 1 at 28-29 °C to 80 and 308 μmol L^− 1 d^− 1 at 34-35 °C in Halodule wrightii and Thalassia testudinum cores, respectively. Labile C additions to the sediment resulted in SAR of 443 and 601 μmol L^− 1 d^− 1 at 28-29 °C and 758 to 1,557 μmol L^− 1 d^− 1 at 34-35 °C in H. wrightii and T. testudinum cores, respectively. Both T. testudinum and H. wrightii were highly thermal tolerant, demonstrating their tropical affinities and potential to adapt to high temperatures. While plants survived the 38 d temperature treatments, there was a clear thermal threshold above 33 °C where T. testudinum growth declined and leaf quantum efficiencies (Fv/Fm) fell below 0.7. At this threshold temperature, H. wrightii maintained shoot densities and leaf quantum efficiencies. Although H. wrightii showed a greater tolerance to high temperature, T. testudinum had a greater capacity to sustain biomass and short shoots under thermal stress with labile C enrichment, regardless of the fact that sulfide levels in the T. testudinum cores were 2 times higher than in the H. wrightii cores. Tropical seagrass tolerance to elevated temperatures, predicted in the future with global warming, should be considered in the context of the sediment-plant complex which incorporates the synergism of plant physiological responses and shifts in sulfur biogeochemistry leading to increased plant exposure to sulfides, a known toxin.     

Uptake and resource allocation of inorganic carbon by the temperate seagrasses Posidonia and Amphibolis

Productivity measurements from carbon uptake have been suggested as good indicators of the physiological health of seagrasses. As seagrasses acquire carbon from the surrounding water, the rate of uptake often provide a good measure of the efficiency at which seagrasses meet their resource demands for growth. This rate is often used to assess the photosynthetic efficiency of the plants, a proxy for the physiological status of seagrass. This has special relevance to the Adelaide region as over 5000 ha of seagrasses have been lost from Adelaide coastal waters over the last 70 years, with much of this loss attributed to nutrient inputs from wastewater, industrial and stormwater discharges. This study used an in-situ inorganic carbon isotope-labelling and spike approach to obtain ecologically relevant estimates of seasonal variability in carbon uptake and its allocation in two species of temperate seagrass common to this coast (Amphibolis antarctica and Posidonia angustifolia). Uptake of carbon by the seagrass complex (leaves, roots, phytoplankton and epiphytes) was affected by both season and species. Carbon uptake rates of phytoplankton were generally higher than other components of the system. Uptake rates ranged from 0.01 mg C g^− 1 DW h^− 1 (summer) to 0.61 mg C g^− 1 DW h^− 1 (spring) in Posidonia and 0.02 mg C g^− 1 DW h^− 1 (summer) to 0.93 mg C g^− 1 DW h^− 1 (winter) in Amphibolis. Carbon uptake by the Amphibolis complex was higher than in the Posidonia complex. The Amphibolis complex had higher uptake rates in summer whereas the Posidonia complex was higher in spring. Fine sediments probably from a nearby dredging operation, are likely to have resulted in lower carbon uptake and a reduction in the above-ground and below-ground biomass in summer.     

Environmental variables explaining structural and functional diversity of seagrass macrofauna in an archipelago landscape

Thirteen seagrass beds located over a 80-km range in the brackish waters of SW, Finland, northern Baltic Sea were investigated in order to determine the environmental variables important for univariate community measures and for number, composition and redundancy of functional groups of benthic macrofauna. For species assemblages, fetch and shore angle were the best explanatory variables, followed by sediment granulometry (fine gravel) and then sediment organics. Similarly, fetch, shore angle and Zostera marina shoot density were the best explanatory variables for functional group patterns. Small (< 50 m²) inner-archipelago beds were functionally and structurally equal to the most extensive (500 to > 1000 m²) seagrass beds in the study area. Community measures (density, number of species and diversity) and functional diversity (number of functional groups) equalled or exceeded levels previously recorded in deeper, non-vegetated communities in the northern Baltic Sea. In comparison with marine seagrass assemblages, the total number of species and number of species per function were low. However, species density and derived diversity measures (Shannon-Wieners index H′) equalled or exceeded those reported for other seagrass ecosystems. It is concluded that in terms of seagrass infauna, the Baltic Sea should not be regarded species poor, as is often generally stated, and that conservation initiatives and management strategies should consider both minor as well as more extensive occurrences of seagrasses in coastal waters.     

Chemiluminescent determination of H2O2 using 4-(1,2,4-triazol-1-yl)phenol as an enhancer based on the immobilization of horseradish peroxidase onto magnetic beads

This article describes the employment of a novel p-phenol derivative, 4-(1,2,4-triazol-1-yl)phenol (TRP), as a highly potent signal enhancer of the luminol-hydrogen peroxide (H₂O₂)-horseradish peroxidase (HRP) chemiluminescence (CL) system. The CL reaction conditions were optimized, and the enhancement characteristics of TRP were compared with those of p-iodophenol (PIP). TRP produced a strong enhancement of the CL with the effect of prolonging the light emission. The developed system was then applied to the determination of H₂O₂ with immobilized HRP using magnetic beads as a solid support. The linear range for H₂O₂ was 2.0 × 10⁻⁶ to 1.0 × 10⁻³ M. The detection limit for H₂O₂ was 2.0 × 10⁻⁶ M. The proposed sensor was applied successfully to the determination of H₂O₂ in rainwater.     

Hydrogen peroxide targets the cysteine at the active site and irreversibly inactivates creatine kinase

In our study, we showed that at a relatively low concentration, H₂O₂ can irreversibly inactivate the human brain type of creatine kinase (HBCK) and that HBCK is inactivated in an H₂O₂ concentration-dependent manner. HBCK is completely inactivated when incubated with 2 mM H₂O₂ for 1 h (pH 8.0, 25 °C). Inactivation of HBCK is a two-stage process with a fast stage (k₁ = 0.050 ± 0.002 min⁻¹) and a slow (k₂ = 0.022 ± 0.003 min⁻¹) stage. HBCK inactivation by H₂O₂ was affected by pH and therefore we determined the pH profile of HBCK inactivation by H₂O₂. H₂O₂-induced inactivation could not be recovered by reducing agents such as dl-dithiothreitol, N-acetyl-l-cysteine, and l-glutathione reduced. When HBCK was treated with DTNB, an enzyme substrate that reacts specifically with active site cysteines, the enzyme became resistant to H₂O₂. HBCK binding to Mg²⁺ATP and creatine can also prevent H₂O₂ inactivation. Intrinsic and 1-anilinonaphthalene-8-sulfonate-binding fluorescence data showed no tertiary structure changes after H₂O₂ treatment. The thiol group content of H₂O₂-treated HBCK was reduced by 13% (approximately 1 thiol group per HBCK dimer, theoretically). For further insight, we performed a simulation of HBCK and H₂O₂ docking that suggested the CYS283 residue could interact with H₂O₂. Considering these results and the asymmetrical structure of HBCK, we propose that H₂O₂ specifically targets the active site cysteine of HBCK to inactivate HBCK, but that substrate-bound HBCK is resistant to H₂O₂. Our findings suggest the existence of a previously unknown negative form of regulation of HBCK via reactive oxygen species.     

Differentiation of benthic marine primary producers using stable isotopes and fatty acids: Implications to food web studies

A two-dimensional biomarker approach, using stable isotopes (δ¹³C, δ¹⁵N) and fatty acids, was used to evaluate differences both amongst and within benthic primary producer types (seagrass, fleshy red algae, calcareous red algae, brown algae, and seagrass periphyton) that are typical of the nearshore, temperate Australian region. The primary source of variance (as examined by permutational ANOVA) for all biomarkers examined was amongst primary producer types, as opposed to amongst species within type. δ¹³C showed a clear separation (Monte Carlo p < 0.05) between seagrass (range of means = −10.1 to −14.0‰) and macroalgae (−14.6 to −25.2‰), but could not differentiate amongst the algal types examined. Similarly, distinct δ¹⁵N signatures (p < 0.05) were found only for seagrass (range of means = 3.6-4.1‰) versus calcareous red algae (4.6-5.5‰), with all other types overlapping in their mean δ¹⁵N values. In contrast, multivariate analysis of fatty acid data (using Canonical Analysis of Principal coordinates; CAP) distinguished not only between seagrass and macroalgae, but also between red and brown algae (and to a limited extent between the calcareous and fleshy red algal types). The principal unsaturated fatty acids in the samples were C₂₀ polyunsaturates (found primarily in the macroalgae and periphyton), and C₁₈ mono- and polyunsaturates, with high proportions of 18:2n-6 and 18:3n-3 typical of the seagrasses. The C₁₈ monounsaturate 18:1n-7 was one of the most diagnostic compounds for the red algae examined, being present in very low amounts in seagrass and virtually absent in the brown algae. Conversely, brown algae were high in 18:4n-3, with 20:4n-3 particularly diagnostic of the kelp Ecklonia radiata. In contrast to stable isotopes, fatty acids helped distinguish different algal groups, thereby providing support that a two-dimensional approach using stable isotopes and fatty acids is likely to provide the most useful tool to distinguish primary producers in food web structure.     

Cyclic and acyclic compartmental Schiff bases, their reduced analogues and related mononuclear and heterodinuclear complexes

[1+1] macrocyclic and [1+2] macroacyclic compartmental ligands (H₂L), containing one N₂O₂, N₃O₂, N₂O₃, N₄O₂ or O₂N₂O₂ Schiff base site and one O₂O_n (n=3, 4) crown-ether like site, have been prepared by self-condensation of the appropriate formyl- and amine precursors. The template procedure in the presence of sodium ion afforded Na₂(L) or Na(HL) · nH₂O. When reacted with the appropriate transition metal acetate hydrate, H₂L form M(L) · nH₂O, M(HL)(CH₃COO) · nH₂O, M(H₂L)(X)₂ · nH₂O (M=Cu²⁺, Co²⁺, Ni²⁺; X=CH₃COO⁻, Cl⁻) or Mn(L)(CH₃COO) · nH₂O according to the experimental conditions used. The same complexes have been prepared by condensation of the appropriate precursors in the presence of the desired metal ion. The Schiff bases H₂L have been reduced by NaBH₄ to the related polyamine derivatives H₂R, which form, when reacted with the appropriate metal ions, M(H₂R)(X)₂ (M= Co²⁺, Ni²⁺; X=CH₃COO⁻, Cl⁻), Cu(R) · nH₂O and Mn(R)(CH₃COO) · nH₂O. The prepared ligands and related complexes have been characterized by IR, NMR and mass spectrometry. The [1+1] cyclic nature of the macrocyclic polyamine systems and the site occupancy of sodium ion have been ascertained, at least for the sodium (I) complex with the macrocyclic ligand containing one N₃O₂ Schiff base and one O₂O₃ crown-ether like coordination chamber, by an X-ray structural determination. In this complex the asymmetric unit consists of one cyclic molecule of the ligand coordinated to a sodium ion by the five oxygen atoms of the ligand. The coordination geometry of the sodium ion can be described as a pentagonal pyramid with the metal ion occupying the vertex. In the mononuclear complexes with H₂L or H₂R the transition metal ion invariantly occupies the Schiff base site; the sodium ion, on the contrary, prefers the crown-ether like site. Accordingly, the heterodinuclear complexes [MNa(L)(CH₃COO)_x] (M=Cu²⁺, Co²⁺, Ni², x=1; M=Mn³⁺, x=2) have been synthesised by reacting the appropriate formyl and amine precursors in the presence of M(CH₃COO)_n · nH₂O and NaOH in a 1:1:1:2 molar ratio. The reaction of the mononuclear transition metal complexes with Na(CH₃COO) · nH₂O gives rise to the same heterodinuclear complexes. Similarly [MNa(R)(CH₃COO)_x] have been prepared by reaction of the appropriate polyamine ligand H₂R with the desired metal acetate hydrate and NaOH in 1:1:2 molar ratio.     

Antioxidant metabolism of grapefruit infected with Xanthomonas axonopodis pv. citri

Grapefruit is one of the most susceptible citrus genotypes to Asiatic Citrus Canker, caused by Xanthomonas axonopodis pv. citri (Xac), that can cause severe losses in citrus yield and quality. Although much is known about citrus response to Xac, little is known of the role of antioxidant metabolism. Grapefruit leaves were artificially injected with a strain of Xac obtained from a commercial grove in Florida and components of oxidative metabolism were measured. Symptoms observed included water soaking (2 dai; days after inoculation), raised and ruptured epidermis (6-8 dai), formation of necrotic lesions (16 dai), and leaf abscission (21 dai). The Xac population increased to a maximum (≈10⁹ CFU/cm²) 8 dai and then declined to ≈10⁷ CFU/cm² by 20 dai. Lipid peroxidation was higher in infected leaves than uninoculated controls from 4 to 21 dai indicating greater oxidative stress. H₂O₂ concentration demonstrated a biphasic pattern with peak concentrations at 4 and 13 dai and minimum concentrations that were lower than the controls at 10 and 20 dai. The H₂O₂ concentration somewhat corresponded with superoxide dismutase (SOD) activity, which generates H₂O₂ via dismutase of superoxide ions. Total SOD activity in Xac-infected leaves increased to a maximum at 4 dai, the day of highest H₂O₂ concentration, and then declined and remained at or below controls. Mn-SOD and Fe-SOD activities both increased to maximum activities at 4 dai. Mn-SOD had four isoforms in Xac-infected leaves but only three in the controls. Fe-SOD had three isoforms in both infected and control plants. Suppression of H₂O₂ in Xac-infected leaves also corresponded to higher activities of the H₂O₂ catabolising enzymes catalase (CAT), ascorbate peroxidase (APOD), and peroxidase (POD). Two additional CAT isoforms were detected in infected leaves and not the controls. Three POD isoforms were detected in both control and infected leaves. Previous research has shown that Xac is sensitive to intraplant H₂O₂ concentration, however, the pattern of Xac in this study did not correspond to H₂O₂ concentration, which initially increased due to enhanced SOD activity, but was later suppressed apparently with the aid of peroxidases. In conclusion, Xac infection altered H₂O₂ metabolism in grapefruit leaves by changes in the activities and isoforms of SODs, CATs, PODs and APOD.     

Analysis of peroxidase activity of rice (Oryza sativa) recombinant hemoglobin 1: Implications for in vivo function of hexacoordinate non-symbiotic hemoglobins in plants

In plants, it has been proposed that hexacoordinate (class 1) non-symbiotic Hbs (nsHb-1) function in vivo as peroxidases. However, little is known about peroxidase activity of nsHb-1. We evaluated the peroxidase activity of rice recombinant Hb1 (a nsHb-1) by using the guaiacol/H₂O₂ system at pH 6.0 and compared it to that from horseradish peroxidase (HRP). Results showed that the affinity of rice Hb1 for H₂O₂ was 86-times lower than that of HRP (K_m = 23.3 and 0.27 mM, respectively) and that the catalytic efficiency of rice Hb1 for the oxidation of guaiacol using H₂O₂ as electron donor was 2838-times lower than that of HRP (k_cat/K_m = 15.8 and 44 833 mM⁻¹ min⁻¹, respectively). Also, results from this work showed that rice Hb1 is not chemically modified and binds CO after incubation with high H₂O₂ concentration, and that it poorly protects recombinant Escherichia coli from H₂O₂ stress. These observations indicate that rice Hb1 inefficiently scavenges H₂O₂ as compared to a typical plant peroxidase, thus indicating that non-symbiotic Hbs are unlikely to function as peroxidases in planta.     

Protonated N-heterocycle-templated supramolecular frameworks built of triangular molybdenum(IV) clusters

A series of porous supramolecular complexes (Hoxine)₂ · [Mo₃O₄(C₂O₄)₃(H₂O)₃] · 5H₂O (1),(Hphen)₂ · [Mo₃O₄(C₂O₄)₃(H₂)₃]  · 0.5C₂H₅OH · 7H₂O (2), H₂bpy · [Mo₃O₄(C₂O₄)₃(H₂O)₃] · 2.5H₂O (3), H₂TTD · [Mo₃O₄(C₂O₄)₃(H₂O)₃] · C₂H₅OH · 3H₂O (4), (oxine = 8-hydroxyquinoline, phen = 1,10-phenanthroline, bpy = 4,4′-bipyridine, TTD = triethylene diamine) have been prepared and characterized by single-crystal X-ray crystallography, elemental analysis and infrared spectroscopy. Self-assembly of [Mo₃O₄(C₂O₄)₃(H₂O)₃]²⁻ directed by H-bonding association between the coordination water molecules and oxalate groups forms 2-D host H-bonded single layer in 1, double layer in 2 and 3, and undulated layer in 4 depending on the nature of the guest protonated N-heterocycles. Unlike cis-Hoxine⁺ or Hphen⁺ that employs lattice water molecules H-bonded to them to interconnect the host layers, trans-H₂bpy²⁺ or H₂TTD²⁺ acts a linker between the neighboring host layers to form 3-D supramolecular frameworks with channeled structures wherein the guest protonated cations are located.     

Antioxidant defenses and oxidative stress parameters in tissues of mud crab (Scylla serrata) with reference to changing salinity

The effects of salinity (10, 17 and 35 ppt) on O₂ consumption, CO₂ release and NH₃ excretion by crabs and oxidative stress parameters and antioxidant defenses of its tissues were reported. An increase in salinity caused a decrease in O₂ consumption and CO₂ release and an increase in ammonia excretion by crabs. Lipid peroxidation, protein carbonyl, H₂O₂ levels and total antioxidant capacity of the tissues elevated significantly at 35 ppt salinity except in abdominal muscle where H₂O₂ content was low. Ascorbic acid content of tissues was higher at 17 ppt salinity than at 10 and 35 ppt salinities. With increasing salinity, a gradual decrease in SOD, an increase in catalase, no change in GPx and a decrease followed by an increase in GR activities were recorded for abdominal muscle. While for hepatopancreas, an increase followed by a decrease in SOD and catalase, decrease in GPx and GR activities were noticed with increasing salinity. In the case of gills, a decrease followed by an increase in SOD, a decrease in catalase and GPx and an increase in GR activities were noted when the salinity increased from 10 ppt to 35 ppt. These results suggest that salinity modulation of oxidative stress and antioxidant defenses in Scylla serrata is tissue specific.     

Clonal diversity and structure related to habitat of the marine angiosperm Thalassia testudinum along the Atlantic coast of Mexico

The clonal structure of the tropical seagrass Thalassia testudinum was studied at 16 sites along the Mexican Atlantic coast, situated in back-reef, shallow coastal and lagoon habitats. Thalassia testudinum was highly clonal, with an overall average clonal richness (R) of 0.55. The largest genet found in this study extended throughout the sampling area (∼230 m), with an estimated max age almost reaching 600 years. Lagoons with higher nutrient availability reflected by nutrient content of leaves (mean leaf C:N ratio 11.4) and lower hydrodynamic regimes reflected by the percentage of fine sediments (on average 23%), sustained larger genets of T. testudinum (mean of the largest genets over populations was 167.3 m) than the shallow coastal areas (C:N 12.3, 6.2% fine sediment, mean largest genet 10.3 m) and the more oligotrophic back-reefs (C:N 16.3, 2.7% fine sediment, mean largest genet 6.5 m). Population genetic analysis showed different levels of clonality, genotypic diversity and spatial genetic relatedness for this seagrass per habitat, with the lagoons presenting much lower levels of clonal diversity than the other two habitats.     

Bio-oil from hydro-liquefaction of Dunaliella salina over Ni/REHY catalyst

The hydro-liquefaction of Dunaliella salina over solid acid catalyst was examined under moderate conditions (200 °C, 2.0 MPa, 60 min). The significant increment of bio-oil yield was obtained over Ni/REHY catalyst, increasing about 20% compared without modified REHY. H₂-temperature-programmed desorption (H₂-TPD) and X-ray powder diffraction (XRD) demonstrated that Ni/REHY as bifunctional catalyst played roles in hydrogenation and cracking, and further achieved the deoxygenation and desulfurization of D. salina under hydrogen gas. The oxygen and sulfur contents of bio-oils decreased relative to D. salina, and the higher heating value (HHV) significantly increased to 30.11 MJ/kg. From gas chromatography/mass spectrometry (GC/MS), the dominant compounds of the bio-oils were found to be esters, glycerins. The qualities of bio-oils were greatly improved. Hydro-liquefaction was beneficial to the exploration of bio-oils from microalgae.     

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.     

Bidentate palladium(II) chelation by the common aldoses

The [Pd^II{(R,R)-chxn}(OH)₂] reagent (chxn = 1,2-diaminocyclohexane) is introduced as a metal probe for the detection of the bidentate chelating sites of a glycose. Two moles of hydroxide per mole palladium support double deprotonation of potentially chelating diol functions at a glycose’s backbone. The individual chelating sites are detected using one- and two-dimensional NMR techniques. At equimolar amounts of palladium(II) and aldose, the metal-binding sites include mostly the hydroxy function at the anomeric carbon atom. Chelators are derived from both the pyranose and the furanose isomers. Most pyranose-based chelators form five-membered chelate rings by using their 1,2-diol function. Though 1,2-diolate bonding is also common to the furanoses, the formation of six-membered chelate rings by 1,3-bonding is more significant for them. Metal-excess conditions provoke mostly bis-bidentate 1,2;3,4-chelation but unusual isomers form also: thus d-xylose is dimetallated in its all-axial β-pyranose form, and erythrose’s dimetallation results in the formation of two isomers of a metal derivative of the open-chain hydrate. The spectroscopic results are supported by crystal-structure determinations on [Pd{(R,R)-chxn}(α-d-Xylp1,2H₋₂-κO^1,2)]·H₂O (Xyl = xylose), [Pd{(R,R)-chxn}(α-d-Ribp1,2H₋₂-κO^1,2)]·2.25H₂O (Rib = ribose), [Pd{(R,R)-chxn}(α-l-Thrf1,3H₋₂-κO^1,3)]·2H₂O (Thr = threose) and [Pd{(R,R)-chxn}(α-d-Eryf1,3H₋₂-κO^1,3)]·3H₂O (Ery = erythrose).     

Kinetic studies on the first dihydrogen aquacomplex, [Ru(H2)(H2O)5]: Formation under H2 pressure and catalytic H/D isotope exchange in water

The ruthenium(II) hexaaqua complex [Ru(H₂O)₆]²⁺ reacts with dihydrogen under pressure to give the η²-dihydrogen ruthenium(II) pentaaqua complex [Ru(H₂)(H₂O)₅]²⁺.The complex was characterized by ¹H, ²H and ¹⁷O NMR: δ_H = −7.65 ppm, J_HD = 31.2 Hz, δ_O = −80.4 ppm (trans to H₂) and δ_O = −177.4 ppm (cis to H₂).The H-H distance in coordinated dihydrogen was estimated to 0.889 Å from J_HD, which is close to the value obtained from DFT calculations (0.940 Å).Kinetic studies were performed by ¹H and ²H NMR as well as by UV-Vis spectroscopy, yielding the complex formation rate and equilibrium constants: k_f = (1.7 ± 0.2) × 10⁻³ kg mol⁻¹ s⁻¹ and K_eq = 4.0 ± 0.5 mol kg⁻¹.The complex formation rate with dihydrogen is close to values reported for other ligands and thus it is assumed that the reaction with dihydrogen follows the same mechanisn (I_d).In deuterated water, one can observe that [Ru(H₂)(H₂O)₅]²⁺ catalyses the hydrogen exchange between the solvent and the dissolved dihydrogen.A hydride is proposed as the intermediate for this exchange.Using isotope labeling, the rate constant for the hydrogen exchange on the η²-dihydrogen ligand was determined as k₁ = (0.24 ± 0.04) × 10⁻³ s⁻¹.The upper and lower limits of the pK_a of the coordinated dihydrogen ligand have been estimated:3 < pK_a < 14.     

Tropical seagrass species tolerance to hypersalinity stress

The long-term sustainability of seagrasses in the subtropics and tropics depends on their ability to adapt to shifts in salinity regimes, particularly in light of present increases in coastal freshwater extractions and future climate change scenarios. Although there are major concerns world-wide on increased salinity in coastal estuaries, there is little quantitative information on the specific upper salinity tolerance of tropical and subtropical seagrass species. We examined seagrass hypersalinity tolerance under two scenarios: (1) when salinity is raised rapidly simulating a pulsed event, such as exposure to brine effluent, and (2) when salinity is raised slowly, characteristic of field conditions in shallow evaporative basins; the first in hydroponics (Experiments I and II) and the second in large mesocosms using intact sediment cores from the field (Experiment III). The three tropical seagrass species investigated in this study were highly tolerant of hypersaline conditions with a slow rate of salinity increase (1 psu d⁻¹). None of the three species elicited total shoot mortality across the range of salinities examined (35–70 psu over 30 days exposures); representing in situ exposure ranges in Florida Bay, a shallow semi-enclosed subtropical lagoon with restricted circulation. Based on stress indicators, shoot decline, growth rates, and PAM florescence, all three species were able to tolerate salinities up to 55 psu, with Thalassia testudinum (60 psu) and Halodule wrightii (65 psu) eliciting a slightly higher salinity threshold than Ruppia maritima (55 psu). However, when salinity was pulsed, without a slow osmotic adjustment period, threshold levels dropped 20 psu to approximately 45 psu for T. testudinum. While we found these three seagrass species to be highly tolerant of high salinity, and conclude that hypersalinity probably does not solely cause seagrass dieoff events in Florida Bay, high salinity can modify carbon and O₂ balance in the plant, potentially affecting the long-term health of the seagrass community.