Leaf chlorophyll fluorescence, reflectance, and physiological response to freshwater and saltwater flooding in the evergreen shrub, Myrica cerifera

Photosynthesis, water relations, chlorophyll fluorescence, and leaf reflectance were used to evaluate stress due to freshwater and saltwater flooding in the evergreen coastal shrub, Myrica cerifera, under controlled conditions. M. cerifera forms large monospecific thickets that facilitate scaling up from leaf-level measurements to the landscape. Based on physiological responses, stress began by day 3 in flooded plants treated with 5, 10, and 15 g L⁻¹ salinity, as seen by significant decreases in stomatal conductance and net photosynthesis relative to control plants. Decreases in physiological measurements occurred by day 9 in freshwater flooded plants. Visible signs of stress occurred by day 5 for plants treated with 15 g L⁻¹, day 8 for flooded plants exposed to 10 g L⁻¹, and day 10 for those treated with 5 g L⁻¹ salinity. Significant differences in light-adapted fluorescence yield () were observed by day 3 in plants flooded with 5, 10, and 15 g L⁻¹ salinity and day 6 in freshwater flooded plants. Non-photochemical quenching (Φ_NPQ) increased with decreasing . In comparison, statistical differences in dark-adapted fluorescence yield (F_v/F_m) were observed by day 12 in plants flooded with 5, 10, and 15 g L⁻¹ salinity, well after visible signs of stress were apparent. Fluorescence parameters were successful at detecting and distinguishing both freshwater and saltwater flooding stress. A positive, linear correlation (r² = 0.80) was observed between and the physiological reflectance index (PRI). Xanthophyll-cycle dependent energy dissipation appears to be the underlying mechanism in protecting photosystem II from excess energy in saltwater flooded plants. was useful in detecting stress-induced changes in the photosystem before any visible signs of damage were evident at the leaf-level. This parameter may be linked to hyperspectral reflectance data for rapid detection of stress at the canopy-level.     

Mutations at position 1122 in the catalytic domain of the mouse ras-specific guanine nucleotide exchange factor CDC25 originate both loss-of-function and gain-of-function proteins

The role of two residues within the catalytic domain of CDC25^Mm, a mouse ras-specific guanine nucleotide exchange factor (GEF), was investigated by site-directed mutagenesis. The function of the mutant proteins was tested in vivo in both a Saccharomyces cerevisiae cdc25 complementation assay and in a mammalian fos-luciferase assay, and in in vitro assays on human and yeast Ras proteins. Mutants CDC25 and CDC25 were shown to be (partly) inactive proteins, similar to their yeast homologs. Mutant CDC25 showed higher nucleotide exchange activity than the wild type protein on the basis of both in vitro and in vivo assays. Thus, alanine and valine substitutions at position 1122 within the GEF catalytic domain originate mutations with opposite biological properties, indicating an important role for position 1122 in GEF function.     

A multishear microfluidic device for quantitative analysis of calcium dynamics in osteoblasts

Reactive oxygen species (ROS) are an important factor in the development of skin lesions in diabetes. A new antioxidant, hydrogen, can selectively neutralize hydroxyl radicals (OH) and peroxynitrite (ONOO⁻) in cell-free systems, whereas it seldom reacts with other ROS. Fibroblasts are a key component of skin. In the present study, we investigated the protective effects of hydrogen-rich medium on human skin fibroblasts (HSFs) under oxidative stress. Confocal microscopy was used to assay both the intracellular superoxide anion () concentration and the mitochondrial membrane potential (ΔΨ). Cell viability was determined using the Cell Counting Kit-8 (CCK-8). The concentrations of cellular malonaldehyde (MDA), superoxide dismutase (SOD), glutathione (GSH), 8-hydroxy-2′-deoxyguanosine (8-OHdG) and 3-nitrotyrosine (3-NT) were also measured. The results revealed that both mannitol and high glucose could cause oxidative stress in HSFs. Interestingly, the use of a hydrogen-rich medium significantly reduced the level of intracellular , stabilized the ΔΨ and attenuated production of MDA, 8-OHdG and 3-NT which efficiently enhanced the antioxidative defense system and protected the HSFs from subsequent oxidative stress damage. In other words, hydrogen decreased the excessive generation of intracellular and elevated the cellular antioxidative defense. Based on our results, hydrogen may have applications in the treatment of skin diseases caused by diabetes.     

Activity of Debaryomyces hansenii UFV-1 α-galactosidases against α-d-galactopyranoside derivatives

α-d-Galactopyranosides were synthesized and their inhibitory activities toward the Debaryomyces hansenii UFV-1 extracellular and intracellular α-galactosidases were evaluated. Methyl α-d-galactopyranoside was the most potent inhibitor compared to the others tested, with values of 0.82 and 1.12 mmol L⁻¹, for extracellular and intracellular enzymes, respectively. These results indicate that the presence of a hydroxyl group in the C-6 position of α-d-galactopyranoside derivatives is important for the recognition by D. hansenii UFV-1 α-galactosidases.     

Reactive oxygen and nitrogen species regulate inducible nitric oxide synthase function shifting the balance of nitric oxide and superoxide production

Inducible NOS (iNOS) is induced in diseases associated with inflammation and oxidative stress, and questions remain regarding its regulation. We demonstrate that reactive oxygen/nitrogen species (ROS/RNS) dose-dependently regulate iNOS function. Tetrahydrobiopterin (BH₄)-replete iNOS was exposed to increasing concentrations of ROS/RNS and activity was measured with and without subsequent BH₄ addition. Peroxynitrite (ONOO⁻) produced the greatest change in NO generation rate, ∼95% decrease, and BH₄ only partially restored this loss of activity. Superoxide () greatly decreased NO generation, however, BH₄ addition restored this activity. Hydroxyl radical (OH) mildly decreases NO generation in a BH₄-dependent manner. iNOS was resistant to H₂O₂ with only slightly decreased NO generation with up to millimolar concentrations. In contrast to the inhibition of NO generation, ROS enhanced production from iNOS, while ONOO⁻ had the opposite effect. Thus, ROS promote reversible iNOS uncoupling, while ONOO⁻ induces irreversible enzyme inactivation and decreases both NO and production.     

Forest structure of a subtropical mangrove along a river inferred from potential tree height and biomass

The hypothesis was tested that potential tree height and biomass in mangroves decrease downstream with the tidal gradient along the Okukubi River in Okinawa Island, Japan. The mangrove stands consisted of Bruguiera gymnorrhiza (L.) Lamk. and Kandelia obovata (S., L.) Yong (Rhizophoraceae). Four sites were selected considering the distance from the mouth of the river. Soil salinity increased downstream, while soil total nitrogen content decreased. The soil redox potential did not vary along the river. Maximum gross photosynthesis and tree height for each species decreased downstream. The potential tree height (H_max) inferred from the stem diameter (D_0.1)–tree height (H) relationship ( a, h, coefficient) in each species decreased downstream. The tree density (ρ)–mean tree size () relationships ( K, α, coefficient) determined for four sites revealed that the mean tree size at any given tree density decreased downstream, which indicates the decrease of potential biomass. Furthermore, an index for biomass () was homogeneous within a site regardless of tree density, i.e. the value of α at each site did not differ significantly from 1.0 (p > 0.05). The decreases in potential tree height and biomass may be partially ascribed to the stressful environments at the downstream sites characterized by high salinity (>2.6%) and nitrogen-poor soils (<0.25 ppt) in our study area.     

New applications of ruthenium solar cell sensitizers N3 and N719 as luminescence turn-on anion sensors

Optical sensing of F⁻, Cl⁻, Br⁻, I⁻, OAc⁻, , , and by cis-dithiocyanatobis(2,2′-bipyridyl-4,4′-dicarboxylic acid)ruthenium(II) (N3) and bis(tetrabutylammonium) cis-dithiocyanatobis(2,2′-bipyridine-4-COOH,4′-COO⁻)ruthenium(II) (N719) have been investigated in dimethyl sulfoxide (DMSO), by means of UV-Vis absorption and emission spectrophotometric titrations. Additions of F⁻, OAc⁻, and in DMSO solution caused obvious UV-Vis spectral changes with appearance of several isosbestic points, and remarkable emission enhancements along with large blue shifts in emission bands. The values of F⁻-induced emission intensity enhancement factor (emission quantum yield enhancement factor), I/I₀ (φ/φ₀), were found to be 40 (86) and 38 (58) for N3 and N719, respectively. No obvious spectral changes were observed upon addition of Cl⁻, Br⁻, I⁻, and in DMSO solutions. Luminescent F⁻ sensing in DMSO/H₂O (4:1, v/v) has also been demonstrated to be operative with a luminescence enhancement factor of 12, indicating that N3 is very potential for practical application as fluorescent anion sensor in aqueous solution. An interaction mechanism of anion-induced deprotonation of N3 and N719 was confirmed, and the deprotonation reaction equilibrium constants of N3 and N719 were derived as well.     

Anation kinetics of pentacyanoaquachromate(III) by thiocyanate and azide

The kinetics of the reaction of Cr(CN)₅(H₂O)²⁻ with NCS⁻ and were studied at pH 5.0 and at pH 6.3-7.0, respectively, as a function of the temperature between 25.0 and 55.0 °C, and at various ionic strengths. Anation occurs in competition with aquation of CN⁻, with rate constants that exhibit less-than-first-order dependence on the concentration of the entering anions. The results are interpreted in terms of ligand interchange in a context of association of the two reacting anions mediated by the Na⁺ or Ca²⁺ counterions. The degree of aggregation depends mainly on the total cationic charge rather than on the ionic strength, and is ca. 2-fold larger for than for NCS⁻. Within the associated species, is a better entering ligand than NCS⁻ by a factor of 4.5. The Cr(CN)₅(NCS)³⁻ and Cr(CN)₅(N₃)³⁻ complexes were also synthesized, and the rates of aquation of NCS⁻ and were measured at pH 5.0 and between 55.0 and 80.0 °C, over the same range of ionic strengths. The ionic strength enhances the anation rates but has little effect on the aquation rates. The average activation enthalpies of the interchange step are 80 ± 3 and 76 ± 3 kJ mol⁻¹ for entry of NCS⁻ and , respectively. Those of the corresponding aquation reactions are 94 ± 4 and 107 ± 4 kJ mol⁻¹. Within error limits, all ΔH^‡ values are independent of the ionic strength. The results are consistent with an I_d mechanism for substitution in Cr(CN)₅X^z− complexes.     

Photocatalysis of chloroform degradation by μ-dichlorotetrachlorodipalladate(II)

Unlike other chlorometallate complexes that catalyze the photodecomposition of haloalkanes through photodissociation of a chlorine atom, both and catalyze chloroform decomposition through a process that appears to involve C-H bond breakage from an excited state association complex with chloroform. This would account for the greatly retarded rate of decomposition in CDCl₃ and for the generation of CCl₄ as a side product. In chloroform, and are in slow equilibrium with each other. The rate for the conversion of - in chloroform at 23 °C obeys the expression (0.03 M⁻¹ s⁻¹) [][Cl⁻]. The equilibrium constant, K = [][Cl⁻]²/[]², was estimated to be 3 × 10⁻³ M in CHCl₃.     

Kinetics and mechanism of the oxidation of oxalic acid by tetrachloroaurate(III) ion

The oxidation of oxalic acid by tetrachloroaurate(III) ion in 0.005 ? [HClO₄] ? 0.5 mol dm⁻³ is first order in and a fractional order in [oxalic acid], the reactive entities being AuCl₃(OH)⁻ and ions. The pseudo first-order rate, k_obs, with respect to [Au(III)], is retarded by increasing [H⁺] and [Cl⁻]. The retardation by H⁺ ion is caused by the dissociation equilibrium . A mechanism in which a substitution complex, is formed from AuCl₃(OH)⁻ and ions prior to its rate limiting disproportionation into products is suggested. The rate limiting constant, k, has been evaluated and its activation parameters are reported. The equilibrium constant K₁ for the formation of the substitution complex and its thermodynamic parameters are also reported.     

Luminescent metalloreceptors with pendant macrocyclic ionophore: Synthesis, characterization, electrochemistry and ion-binding study

Metalloreceptors containing ruthenium(II) bipyridine unit as fluorophore and pendant macrocyclic units as ionophore have been synthesized and their luminescence and electrochemical properties have been investigated. Ion-binding study of these fluoroionophore with the anions F⁻, Cl⁻, Br⁻, I⁻, , , , , CH₃COO⁻, and and cations Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺, Ba²⁺, Sr²⁺ Cd²⁺, Hg²⁺, Pb²⁺ and Cu²⁺, monitored by luminescence and ¹H NMR spectral changes, reveal strong interactions of and F⁻ for 2 and 3 and of Cu²⁺ only for 3. Luminescence titrations for 2 and 3 have been carried out to determine binding constants (K_s), and the calculated values are in the range 2.85 × 10² to 4.48 × 10⁴ M⁻¹. The ¹H NMR spectral changes for 2 and 3 with the addition of increasing concentration of F⁻ and exhibit substantial low-field shift of the CONH proton indicating its involvement in complex formation with the anions. The adduct of 2 and 3 have been isolated and characterized by ¹H and ³¹P NMR, mass and IR spectroscopy. The results are discussed in light of selectivity, structures of the anion bound complexes and their luminescence property.     

Rationalizing 5000-fold differences in receptor-binding rate constants of four cytokines

The four cytokines erythropoietin (EPO), interleukin-4 (IL4), human growth hormone (hGH), and prolactin (PRL) all form four-helix bundles and bind to type I cytokine receptors. However, their receptor-binding rate constants span a 5000-fold range. Here, we quantitatively rationalize these vast differences in rate constants by our transient-complex theory for protein-protein association. In the transient complex, the two proteins have near-native separation and relative orientation, but have yet to form the short-range specific interactions of the native complex. The theory predicts the association rate constant as where k_a0 is the basal rate constant for reaching the transient complex by random diffusion, and the Boltzmann factor captures the rate enhancement due to electrostatic attraction. We found that the vast differences in receptor-binding rate constants of the four cytokines arise mostly from the differences in charge complementarity among the four cytokine-receptor complexes. The basal rate constants (k_a0) of EPO, IL4, hGH, and PRL were similar (5.2 × 10⁵ M⁻¹s⁻¹, 2.4 × 10⁵ M⁻¹s⁻¹, 1.7 × 10⁵ M⁻¹s⁻¹, and 1.7 × 10⁵ M⁻¹s⁻¹, respectively). However, the average electrostatic free energies () were very different (−4.2 kcal/mol, −2.4 kcal/mol, −0.1 kcal/mol, and −0.5 kcal/mol, respectively, at ionic strength = 160 mM). The receptor-binding rate constants predicted without adjusting any parameters, 6.2 × 10⁸ M⁻¹s⁻¹, 1.3 × 10⁷ M⁻¹s⁻¹, 2.0 × 10⁵ M⁻¹s⁻¹, and 7.6 × 10⁴ M⁻¹s⁻¹, respectively, for EPO, IL4, hGH, and PRL agree well with experimental results. We uncover that these diverse rate constants are anticorrelated with the circulation concentrations of the cytokines, with the resulting cytokine-receptor binding rates very close to the limits set by the half-lives of the receptors, suggesting that these binding rates are functionally relevant and perhaps evolutionarily tuned. Our calculations also reproduced well-observed effects of mutations and ionic strength on the rate constants and produced a set of mutations on the complex of hGH with its receptor that putatively enhances the rate constant by nearly 100-fold through increasing charge complementarity. To quantify charge complementarity, we propose a simple index based on the charge distribution within the binding interface, which shows good correlation with . Together these results suggest that protein charges can be manipulated to tune k_a and control biological function.     

Anions induced structural variety of macrocycles containing imidazolium cations

Six compounds including macrocyclic imidazolium cations ([H₂L^I]²⁺, [H₂L^II]²⁺ or [H₂L^III]²⁺) and anions such as Cl⁻, SCN⁻ and have been synthesized and characterized, in which different anions were introduced to the macrocyclic skeleton and the interactions of anions with the macrocycle have been investigated. Single-crystal X-ray analyses indicated that the macrocyclic configuration changed from a boat-like configuration to a chair-like configuration with the geometric variety of anions from spherical (Cl⁻) to linear (SCN⁻) or trigonal planner . Meanwhile, hydrogen bonding interactions between the macrocycle and anions were also studied.     

Synthesis, spectroscopy, computational evaluation and first X-ray structural characterization of a primary amine containing boronium ion

Stable (CF₃SO₂)₂N⁻, I⁻ and salts of the boronium ion [(tert-butylamine)(1-methylimidazole)BH₂]⁺ have been isolated and characterized. A single-crystal X-ray structure of the salt provides the first unambiguous proof for a boronium ion supported by a primary amine ligand.     

Layered iron(II) spin crossover complex constructed by NH?Br hydrogen bonds with 2 K wide thermal hysteresis, [FeH3L]Br·CF3SO3 (H3L = tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine)

A series of compounds [Fe^IIH₃L^Me]Br·Y·nMeOH ( (1), (2), (3), (4); n = 0 or 1) were synthesized, where H₃L^Me is a hexadentate N₆ tripodal ligand of the neutral form, tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine, and their structures and magnetic properties were investigated. The compounds 1−3 with counter anions , , and contain methanol as a crystal solvent, and show no SCO behaviors, while the corresponding Cl⁻ compounds have no crystal solvent and show a variety of SCO behaviors. The compound [Fe^IIH₃L^Me]Br·CF₃SO₃ (4) has no crystal solvent and has isomorphous structure to the Cl⁻ compounds, and shows an abrupt spin transition between the HS (S = 2) and LS (S = 0) states with a hysteresis about 2 K and large frozen-in effect below 72 K. The T_1/2↑ and T_1/2↓ values are 98 and 96 K, whose values are higher than those of corresponding Cl⁻ compound about 15 K and the width of hysteresis is narrower than that of corresponding Cl⁻ compound about 2 K. The crystal structures of 4 were determined at 296 and 93 K, where the crystal system and space group showed no change between these temperatures. The structures at both temperatures have a same 2D layered structure, which is composed of NH?Br⁻ hydrogen bonds between the Br⁻ ion and the imidazole NH groups of three neighboring cations [Fe^IIH₃L^Me]²⁺. This network structure is the same as that of corresponding Cl⁻ compound. The 600 nm light irradiation at 5 K induced the LIESST effect.