Measuring Ca binding to short chain fatty acids and gluconate with a Ca electrode: Role of the reference electrode

Many organic anions bind free Ca²⁺, the total concentration of which must be adjusted in experimental solutions. Because published values for the apparent dissociation constant (K_app) describing the Ca²⁺ affinity of short chain fatty acids (SCFAs) and gluconate are highly variable, Ca²⁺ electrodes coupled to either a 3 M KCl or a Na⁺ selective electrode were used to redetermine K_app. All solutions contained 130 mM Na⁺, whereas the concentration of the studied anion was varied from 15 to 120 mM, replacing Cl⁻ that was decreased concomitantly to maintain osmolarity. This induces changes in the liquid junction potential (LJP) at the 3 M KCl reference electrode, leading to a systematic underestimation of K_app if left uncorrected. Because the Na⁺ concentration in all solutions was constant, a Na⁺ electrode was used to directly measure the changes in the LJP at the 3 M KCl reference, which were under 5 mV but twice those predicted by the Henderson equation. Determination of K_app either after correction for these LJP changes or via direct reference to a Na⁺ electrode showed that SCFAs do not bind Ca²⁺ and that the K_app for the binding of Ca²⁺ to gluconate at pH 7.4, ionic strength 0.15 M, and 23 °C was 52.7 mM.     

[H,N] NMR studies of the aquation of cis-diamine platinum(II) complexes

Two ¹⁵N-labelled cis-Pt(II) diamine complexes with dimethylamine (¹⁵N-dma) and isopropylamine (¹⁵N-ipa) ligands have been prepared and characterised. [¹H,¹⁵N] HSQC NMR spectroscopy is used to obtain the rate and equilibrium constants for the aquation of cis-[PtCl₂(¹⁵N-dma)₂] at 298 K in 0.1 M NaClO₄ and to determine the pK_a values of cis-[PtCl(H₂O)(¹⁵N-dma)₂]⁺ (6.37) and cis-[Pt(H₂O)₂(¹⁵N-dma)₂]²⁺ (pK_a1 = 5.17, pK_a2 = 6.47). The rate constants for the first and second aquation steps (k₁ = (2.12 ± 0.01) × 10⁻⁵ s⁻¹, k₂ = (8.7 ± 0.7) × 10⁻⁶ s⁻¹) and anation steps (k₋₁ = (6.7 ± 0.8) × 10⁻³ M⁻¹ s⁻¹, k₋₂ = 0.043 ± 0.004 M⁻¹ s⁻¹) are very similar to those reported for cisplatin under similar conditions, and a minor difference is that slow formation of the hydroxo-bridged dimer is observed. Aquation studies of cis-[PtCl₂(¹⁵N-ipa)₂] were precluded by the close proximity of the NH proton signal to the ¹H₂O resonance.     

Multinuclear NMR and molecular modelling investigations on the structure and equilibria of complexes that form in aqueous solutions of Ca and gluconate

Complexation of d-gluconate (Gluc⁻) with Ca²⁺ has been investigated via ¹H, ¹³C and ⁴³Ca NMR spectroscopy in aqueous solutions in the presence of high concentration background electrolytes (1 M ? I ? 4 M (NaCl) ionic strength). From the ionic strength dependence of its formation constant, the stability constant at 6 ? pH ? 11 and at I → 0 M has been derived (). The protonation constant of Gluc⁻ at I = 1 M (NaCl) ionic strength was also determined and was found to be log K_a = 3.24 ± 0.01 (¹³C NMR) and log K_a = 3.23 ± 0.01 (¹H NMR). It was found that ¹H and ¹³C NMR chemical shifts upon complexation (both with H⁺ and with Ca²⁺) do not vary in an unchanging way with the distance from the Ca²⁺/H⁺ binding site. From 2D ¹H-⁴³Ca NMR spectra, simultaneous binding of Ca²⁺ to the alcoholic OH on C2 and C3 was deduced. Molecular modelling results modulated this picture by revealing structures in which the Gluc⁻ behaves as a multidentate ligand. The five-membered chelated initial structure was found to be thermodynamically more stable than that derived from a six-membered chelated initial structure.     

Survival,osmoregulation and ammonia-N excretion of blue swimmer crab, Portunus pelagicus, juveniles exposed to different ammonia-N and salinity combinations

Ammonia-N toxicity to early Portunus pelagicus juveniles at different salinities was investigated along with changes to haemolymph osmolality, Na⁺, K⁺, Ca²⁺ and ammonia-N levels, ammonia-N excretion and gill Na⁺/K⁺-ATPase activity. Experimental crabs were acclimated to salinities 15, 30 and 45‰ for one week and 25 replicate crabs were subsequently exposed to 0, 20, 40, 60, 80, 100 and 120 mg L^− 1 ammonia-N for 96-h, respectively. High ammonia-N concentrations were used to determine LC₅₀ values while physiological measurements were conducted at lower concentrations. When crabs were exposed to ammonia-N, anterior gill Na⁺/K⁺-ATPase activity significantly increased (p < 0.05) at all salinities, while this only occurred on the posterior gills at 30‰. For crabs exposed to 20 and 40 mg L^− 1 ammonia-N, both posterior gill Na⁺/K⁺-ATPase activity and ammonia-N excretion were significantly higher at 15‰ than those at 45‰. Despite this trend, the 96-h LC₅₀ value at 15‰ (43.4 mg L^− 1) was significantly lower (p < 0.05) than at both 30‰ and 45‰ (65.8 and 75.2 mg L^− 1, respectively). This may be due to significantly higher (p < 0.05) haemolymph ammonia-N levels of crabs at low salinities and may similarly explain the general ammonia-N toxicity pattern to other crustacean species.     

Hemolymph ion regulation and kinetic characteristics of the gill (Na⁺, K⁺)-ATPase in the hermit crab Clibanarius vittatus (Decapoda, Anomura) acclimated to high salinity

We examine hemolymph ion regulation and the kinetic properties of a gill microsomal (Na⁺, K⁺)-ATPase from the intertidal hermit crab, Clibanarius vittatus, acclimated to 45‰ salinity for 10 days. Hemolymph osmolality is hypo-regulated (1102.5 ± 22.1 mOsm kg⁻¹ H₂O) at 45‰ but elevated compared to fresh-caught crabs (801.0 ± 40.1 mOsm kg⁻¹ H₂O). Hemolymph [Na⁺] (323.0 ± 2.5 mmol L⁻¹) and [Mg²⁺] (34.6 ± 1.0 mmol L⁻¹) are hypo-regulated while [Ca²⁺] (22.5 ± 0.7 mmol L⁻¹) is hyper-regulated; [K⁺] is hyper-regulated in fresh-caught crabs (17.4 ± 0.5 mmol L⁻¹) but hypo-regulated (6.2 ± 0.7 mmol L⁻¹) at 45‰. Protein expression patterns are altered in the 45‰-acclimated crabs, although Western blot analyses reveal just a single immunoreactive band, suggesting a single (Na⁺, K⁺)-ATPase α-subunit isoform, distributed in different density membrane fractions. A high-affinity (Vm = 46.5 ± 3.5 U mg⁻¹; K_0.5 = 7.07 ± 0.01 μmol L⁻¹) and a low-affinity ATP binding site (Vm = 108.1 ± 2.5 U mg⁻¹; K_0.5 = 0.11 ± 0.3 mmol L⁻¹), both obeying cooperative kinetics, were disclosed. Modulation of (Na⁺, K⁺)-ATPase activity by Mg²⁺, K⁺ and NH₄⁺ also exhibits site-site interactions, but modulation by Na⁺ shows Michaelis-Menten kinetics. (Na⁺, K⁺)-ATPase activity is synergistically stimulated up to 45% by NH₄⁺ plus K⁺. Enzyme catalytic efficiency for variable [K⁺] and fixed [NH₄⁺] is 10-fold greater than for variable [NH₄⁺] and fixed [K⁺]. Ouabain inhibited ≈80% of total ATPase activity (K_I = 464.7 ± 23.2 μmol L⁻¹), suggesting that ATPases other than (Na⁺, K⁺)-ATPase are present. While (Na⁺, K⁺)-ATPase activities are similar in fresh-caught (around 142 nmol Pi min⁻¹ mg⁻¹) and 45‰-acclimated crabs (around 154 nmol Pi min⁻¹ mg⁻¹), ATP affinity decreases 110-fold and Na⁺ and K⁺ affinities increase 2-3-fold in 45‰-acclimated crabs.     

Oxidation of thiocyanate by iron(V) in alkaline medium

The oxidation of thiocyanate by iron(V) (Fe(V)) was studied as a function of pH in alkaline solutions by a premix pulse radiolysis technique. The rates decrease with an increase in pH. The rate law for the oxidation of SCN⁻ by Fe(V) was obtained as −d[Fe(V)]/dt = k₁₀{[H⁺]²/([H⁺]² + K₂[H⁺] + K₂K₃)}[Fe(V)][SCN⁻], where k₁₀ = 5.72 ± 0.19 × 10⁶ M⁻¹ s⁻¹, pK₂ = 7.2, and pK₃ = 10.1. The reaction precedes via a two-electron oxidation, which converts Fe(V) to Fe(III). Thiocyanate reacts approximately 10³× faster with iron(V) than does with iron(VI).     

Aqueous solution chemistry of dichloro[S-methylcysteine(N,S)]platinum(II) isomers and their hydrolysis products

Rate and equilibrium constants at 25 °C, pH ∼ 1, and ionic strength 0.10 for hydrolysis of the two non-equivalent chlorides of dichloro[S-methyl-l-cysteine(N,S)]platinum(II) isomers, denoted [PtCl₂(SmecysH)], and the resultant chloro-aqua species have been determined by NMR, potentiometric, and spectrophotometric methods. Though hydrolysis constants, K_h, for the two chlorides are similar (pK_h = 4-5), the rate of hydrolysis of the chloride trans to coordinated S, k_h = 3.4 × 10⁻³ s⁻¹, is 2-3 orders of magnitude faster than the k_h for the other chloride, 2.3 × 10⁻⁶ s⁻¹, and for the cancer drug cisplatin, cis-[PtCl₂(NH₃)₂], 5.2 × 10⁻⁵ s⁻¹. Relative rates of hydrolysis determined under three different experimental conditions (pH ∼ 1 in 0.10 M HNO₃, high pH in 0.10 M NaOH, and at low pH with Ag⁺ assistance) are consistent: the Cl trans to S is 100-1000 times more labile than the Cl cis to S. Potentiometric and NMR methods were also used to estimate pK_a values of all aqua species, which are comparable to values reported for corresponding aqua species derived from cisplatin.     

K homeostasis and central pattern generation in the metathoracic ganglion of the locust

Stress-induced arrest of ventilatory motor pattern generation is tightly correlated with an abrupt increase in extracellular potassium concentration ([K⁺]_o) within the metathoracic neuropil of the locust, Locusta migratoria. Na⁺/K⁺-ATPase inhibition with ouabain elicits repetitive surges of [K⁺]_o that coincide with arrest and recovery of motor activity. Here we show that ouabain induces repetitive [K⁺]_o events in a concentration-dependent manner. 10⁻⁵ M, 10⁻⁴ M, and 10⁻³ M ouabain was bath-applied in semi-intact locust preparations. 10⁻⁴ M and 10⁻³ M ouabain reliably induced repetitive [K⁺]_o events whereas 10⁻⁵ M ouabain had no significant effect. In comparison to 10⁻⁴ M ouabain, 10⁻³ M ouabain increased the number and hastened the time to onset of repetitive [K⁺]_o waves, prolonged [K⁺]_o event duration, increased resting [K⁺]_o, and diminished the absolute value of [K⁺]_o waves. Recovery of motor patterning following [K⁺]_o events was less likely in 10⁻³ M ouabain. In addition, we show that K⁺ channel inhibition using TEA suppressed the onset and decreased the amplitude of ouabain-induced repetitive [K⁺]_o waves. Our results demonstrate that ventilatory circuit function in the locust CNS is dependent on the balance between mechanisms of [K⁺] accumulation and [K⁺] clearance. We suggest that with an imbalance in favour of accumulation the system tends towards a bistable state with transitions mediated by positive feedback involving voltage-dependent K⁺ channels.     

Polynuclear complex formation of trivalent lanthanides by 5-sulfosalicylate in an aqueous system—potentiometric, H NMR, and TRLIFS studies

The complex formation between several trivalent lanthanides (Ln) and 5-sulfosalicylate, (SSA)³⁻, was investigated by potentiometry, ¹H NMR, and time resolved laser-induced fluorescence spectroscopy (TRLIFS). The potentiometric data were used to deduce the stoichiometry and equilibrium constants for the reactions pLn³⁺ + rL ? Ln_pH_−qL_r + qH⁺ at 298 K in an ionic medium with a constant concentration of Na⁺ equal to 1.00 M. Note that “L” denotes the SSA ligand where all protons are dissociated. Two mononuclear chelating complexes, LnL(aq) and , were identified. Their stability constants obtained by least-squares refinement of the potentiometric data agree well with previously published information. In addition, two additional dinuclear complexes, and , which have very different ¹H NMR and fluorescence characteristics, were identified by least-squares refinement in the −log[H⁺] range of 6.0-10.0. ¹H NMR spectra from the ligand in the complex showed separate peaks having two different rates of exchange with free ligand in the bulk solution besides a signal from the free and carboxylate-coordinated ligands. This indicates that the dinuclear complex, , consists of two different types of chelating ligands: μ-{OR}-type chelating ligands between metals to form the {Ln₂L₂}-type core structure and the bidentate ligands outside the {Ln₂L₂}-type core. This core structure is different from the An(IV)-SSA case (An(IV): tetravalent actinide), in which hydroxides play the role of forming the {An₂(OH)₂}-type core structure. TRLIFS measurement gave further information about the dynamics and molecular structures of the complexes.     

Kinetics of the Ca, H, and Mg Interaction with the Ion-Binding Sites of the SR Ca-ATPase

Electrochromic styryl dyes were used to investigate mutually antagonistic effects of Ca²⁺ and H⁺ on binding of the other ion in the E₁ and P-E₂ states of the SR Ca-ATPase. On the cytoplasmic side of the protein in the absence of Mg²⁺ a strictly competitive binding sequence, H₂E₁?HE₁?E₁?CaE₁?Ca₂E₁, was found with two Ca²⁺ ions bound cooperatively. The apparent equilibrium dissociation constants were in the order of K_1/2(2 Ca) = 34 nM, K_1/2(H) = 1 nM and K_1/2(H₂) = 1.32 μM. Up to 2 Mg²⁺ ions were also able to enter the binding sites electrogenically and to compete with the transported substrate ions (K_1/2(Mg) = 165 μM, K_1/2(Mg₂) = 7.4 mM). In the P-E₂ state, with binding sites facing the lumen of the sarcoplasmatic reticulum, the measured concentration dependence of Ca²⁺ and H⁺ binding could be described satisfactorily only with a branched reaction scheme in which a mixed state, P-E₂CaH, exists. From numerical simulations, equilibrium dissociation constants could be determined for Ca²⁺ (0.4 mM and 25 mM) and H⁺ (2 μM and 10 μM). These simulations reproduced all observed antagonistic concentration dependences. The comparison of the dielectric ion binding in the E₁ and P-E₂ conformations indicates that the transition between both conformations is accompanied by a shift of their (dielectric) position.     

A reverse method for diversity introduction of benzimidazole to synthesize H(+)/K(+)-ATP enzyme inhibitors

A series of 2-[(2-pyridylmethyl)sulfinyl]benzimidazole derivatives were synthesized via a solution phase synthetic route using a reversal method of diversity introduction. Using this synthetic strategy, we obtained two key intermediates (4-A and 4-B) simultaneously, which allows us to introduce diversity points onto the benzimidazole part of the final product under reliable reaction conditions to identify potent H⁺/K⁺-ATP enzyme inhibitors. Compound 14l (IC₅₀ = 1.6 × 10⁻⁵ M) was comparable with H⁺/K⁺-ATP enzyme inhibitor in vitro.     

The kinetics of the complex formation between iron(III)-ethylenediaminetetraacetate and hydrogen peroxide in aqueous solution

The kinetics of the formation of the purple complex [Fe^III(EDTA)O₂]³⁻, between Fe^III-EDTA and hydrogen peroxide was studied as a function of pH (8.22-11.44) and temperature (10-40 °C) in aqueous solutions using a stopped-flow method. The reaction was first-order with respect to both reactants. The observed second-order rate constants decrease with an increase in pH and appear to be related to deprotonation of Fe^III-EDTA ([Fe(EDTA)H₂O]⁻ ⇔ Fe(EDTA)OH]²⁻ + H⁺). The rate law for the formation of the complex was found to be d[Fe^IIIEDTAO₂]³⁻/dt=[(k₄[H⁺]/([H⁺] + K₁)][Fe^III-EDTA][H₂O₂], where k₄=8.15±0.05×10⁴ M⁻¹ s⁻¹ and pK₁=7.3. The steps involved in the formation of [Fe(EDTA)O₂]³⁻ are briefly discussed.     

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.     

Extraction properties for alkali metal picrates of macrocyclic trinuclear (p-cymene)ruthenium(II) and (pentamethylcyclopentadienyl)rhodium(III) complexes

The solvent extraction properties of macrocyclic trinuclear organometallic complexes, [(p-cymene)Ru(pyO₂)]₃ and [Cp^∗Rh(pyO₂)]₃, for Li⁺, Na⁺, and K⁺ picrates have been investigated in a dichloromethane-water system at 25 °C. The extraction rates of the alkali metal picrates with these macrocyclic complex ligands are unusually slow; the shaking times required to attain equilibrium are at least 1 h for [(p-cymene)Ru(pyO₂)]₃ and 20-40 h for [Cp^∗Rh(pyO₂)]₃. From analysis of the equilibrium data, the extraction constants (K_ex = [ML⁺A⁻]_o/[M⁺][L]_o[A⁻]; M⁺ = alkali metal ion, L = macrocyclic ligand, A⁻ = picrate ion, o = organic phase) have been determined. The log K_ex value varies in the sequences, Li⁺ (5.72) > Na⁺ (4.50) > K⁺ (2.88) for [(p-cymene)Ru(pyO₂)]₃ and Li⁺ (4.79) > Na⁺ (2.70) ≈ K⁺ (2.69) for [Cp^∗Rh(pyO₂)]₃. The K_ex values of 6,6-dibenzyl-14-crown-4 (DBz14C4), which is one of the best Li⁺-selective crown ethers, have also been determined for comparison. It is revealed that [Cp^∗Rh(pyO₂)]₃ is much superior to DBz14C4 both in the extractability for Li⁺ and the selectivity for Li⁺ over Na⁺.     

The aluminium(III)-sialic acid interaction: A potential role in aluminium-induced cellular membrane degeneration

The coordination between Al(III) and sialic acid (N-acetylneuraminic acid, HL, pK_a = 2.58 ± 0.01) was studied by potentiometric titrations at 25 °C in aqueous 0.2 M KCl, by ¹H NMR, and by electrospray ionization mass spectrometry (ESI-MS). The potentiometric measurements gave the following aluminium complex stoichiometries and stability constants: , log β(AlLH₋₂) = −6.34 ± 0.02, and log β(AlL₂H₋₁) = −1.14 ± 0.04. The ¹H NMR spectra yielded structural information on species . The ESI-MS data confirmed the metal-ligand stoichiometry of the complexes.The metal-ligand speciation at micromolar Al(III) concentrations (i.e., under in vivo conditions) at physiological pH values reveals that considerable amount of Al(III) is complexed. This suggests that the toxic effect of Al(III) towards cellular membranes might be due to its coordination by protein-bound sialic acid.     

(E)-2-(2-(2-hydroxyphenyl)hydrazono)-1-phenylbutane-1,3-dione: Tautomery and coordination to copper(II)

(E)-2-(2-(2-hydroxyphenyl)hydrazono)-1-phenylbutane-1,3-dione (H₂L) was synthesized by azocoupling of diazonium salt of 2-hydroxyaniline with 1-phenylbutane-1,3-dione and characterized by IR, ¹H and ¹³C NMR spectroscopies and X-ray diffraction analysis. In solution, H₂L exists as a mixture of the enol-azo and hydrazone tautomeric forms and a decrease of temperature and of solvent polarity shifts the tautomeric balance to the hydrazone form. In the solid state, H₂L crystallizes from ethanol-water in the monohydrate hydrazone form, as shown by X-ray analysis. The dissociation constants of H₂L (pK₁ = 5.98 ± 0.04, pK₂ = 9.72 ± 0.03) and the stability constants of its copper(II) complex (log β₁ = 11.01 ± 0.07, log β₂ = 20.19 ± 0.08) were determined by the potentiometric method in aqueous-ethanol solution. The copper(II) complex [Cu₂(μ-L)₂]_n was isolated in the solid state and found by X-rays to be a coordination polymer of a binuclear core with a distorted square pyramidal metal coordination geometry.     

Synthesis and characterization of silver(I) derivatives containing acylpyrazolonate and phosphino ligands: X-ray crystal structures of monomeric [Ag(Q)(PPh3)2] and of dimeric [{Ag(Q)(PiBu3)}2] (Q = 1-phenyl-3-methyl-4-tert-butylacetylpyrazolon-5-ato)

New silver(I) acylpyrazolonate derivatives [Ag(Q)], [Ag(Q)(PR₃)]₂ and [Ag(Q)(PR₃)₂] (HQ = 1-R¹-3-methyl-4-R²(CO)pyrazol-5-one, HQ^Bn = R¹ = C₆H₅, R² = CH₂C₆H₅; HQ^CHPh2 = R¹ = C₆H₅, R² = CH(C₆H₅)₂; HQ^nPe = R¹ = C₆H₅, R² = CH₂C(CH₃)₃; HQ^tBu = R¹ = C₆H₅, R² = C(CH₃)₃; HQ^fMe = R¹ = C₆H₄-p-CF₃, R² = CF₃; HQ^fEt = R¹ = C₆H₅, R² = CF₂CF₃; R = Ph or iBu) have been synthesized and characterized in the solid state and solution. The crystal structure of 1-(4-trifluoromethylphenyl)-3-methyl-5-pyrazolone, the precursor of proligand HQ^fMe and of derivatives [Ag(Q^nPe)(PPh₃)₂] and [Ag(Q^nPe)(PiBu₃)]₂ have been investigated. [Ag(Q^nPe)(PPh₃)₂] is a mononuclear compound with a silver atom in a tetrahedrally distorted AgO₂P₂ environment, whereas [Ag(Q^nPe)(PiBu₃)]₂ is a dinuclear compound with two O₂N-exotridentate bridging acylpyrazolonate ligands connecting both silver atoms, their coordination environment being completed by a phosphine ligand.     

Different sensitivity of Phragmites australis and Glyceria maxima to high availability of ammonium-N

The ability to cope with NH₄⁺-N was studied in the littoral helophytes Phragmites australis and Glyceria maxima, species commonly occupying fertile habitats rich in NH₄⁺ and often used in artificial wetlands. In the present study, Glyceria growth rate was reduced by 16% at 179 μM NH₄⁺-N, and the biomass production was reduced by 47% at 3700 μM NH₄⁺-N compared to NO₃⁻-N. Similar responses were not found in Phragmites. The amounts (mg g⁻¹ dry wt) of starch and total non-structural carbohydrates (TNC) in rhizomes were significantly lower in NH₄⁺ (8.9; 12.2 starch; 20.1; 41.9 TNC) compared to NO₃⁻ treated plants (28.0; 15.6 starch; 58.5; 56.3 TNC) in Phragmites and Glyceria, respectively. In addition, Glyceria showed lower amounts (mg g⁻¹ dry wt) of soluble sugars, TNC, K⁺, and Mg²⁺ in roots under NH₄⁺ (5.6; 14.3; 20.6; 1.9) compared to NO₃⁻ nutrition (11.6; 19.9; 37.9; 2.9, for soluble sugars, TNC, K⁺, and Mg²⁺, respectively), while root internal levels of NH₄⁺ and Ca²⁺ (0.29; 4.6 mg g⁻¹ dry wt, mean of both treatments) were only slightly affected. In Phragmites, no changes in soluble sugars, TNC, Ca²⁺, K⁺, and Mg²⁺ contents of roots (7.3; 14.9; 5.1; 17.3; 2.6 mg g⁻¹ dry wt, means of both treatments) were found in response to treatments. The results, therefore, indicate a more pronounced tolerance towards high NH₄⁺ supply in Phragmites compared to Glyceria, although the former may be susceptible to starch exhaustion in NH₄⁺-N nutrition. In contrast, Glyceria's ability to colonize fertile habitats rich in NH₄⁺ is probably related to the avoidance strategy due to shallow rooting or to the previously described ability to cope with high NH₄⁺ levels when P availability is high and NO₃⁻ is also provided.     

Complexation of Group IIIA metals with asymmetric tridentate ligands: Synthesis, characterization, formation constants and cytotoxicity

A series of new aluminum(III), gallium(III) and indium(III) complexes with some tridentate Schiff base, viz., N-{pyridine-2-ylmethyl}-2-hydroxy-5-methoxy-benzylideneamine [HL¹], N-{pyridine-2-ylmethyl}-2-hydroxy-benzylideneamine [HL²], N-{pyridine-2-ylmethyl}-2-hydroxy-5-nitro-benzylideneamine [HL³], N-{pyridine-2-ylmethyl}-2-hydroxy-5-bromo-benzylideneamine [HL⁴], N-{pyridine-2-ylethyl}-2-hydroxy-5-methoxy-benzylideneamine [HL⁵], N-{pyridine-2-ylethyl}-2-hydroxy-benzylideneamine [HL⁶], N-{pyridine-2-ylethyl}-2-hydroxy-5-nitro-benzylideneamine [HL⁷], N-{pyridine-2-ylethyl}-2-hydroxy-5-bromo-benzylideneamine [HL⁸], with the general formula [ML₂][Y] (M = Al³⁺, Ga³⁺, In³⁺; Y = NO₃⁻, ClO₄⁻) were synthesised and characterized by elemental analysis, ¹H NMR, FT-IR, UV-Vis spectrophotometry and mass spectrometry. The thermodynamic formation constants of the complexes were determined spectrophotometrically at constant ionic strength (I = 0.10 M NaClO₄) and at 25 °C in methanol. The trend of formation constants of the complexes are as follow:

Al<Ga<In