Photosynthetic responses of a wheat (Asakaze)–barley (Manas) 7H addition line to salt stress

The photosynthetic responses to salt stress were examined in a wheat (Triticum aestivum L. cv. Asakaze)–barley (Hordeum vulgare L. cv. Manas) 7H addition line having elevated salt tolerance and compared to the parental wheat genotype. For this purpose, increasing NaCl concentrations up to 300 mM were applied and followed by a 7-day recovery period. Up to moderate salt stress (200 mM NaCl), forcible stomatal closure, parallel with a reduction in the net assimilation rate (P _N), was only observed in wheat, but not in the 7H addition line or barley. Since the photosynthetic electron transport processes of wheat were not affected by NaCl, the impairment in P _N could largely be accounted for the salt-induced decline in stomatal conductance (g _s), accompanied by depressed intercellular CO₂ concentration and carboxylation efficiency. Both, P _N and nonstomatal limitation factors (L_ns) were practically unaffected by moderate salt stress in barley and in the 7H addition line due to the sustained g _s, which might be an efficient strategy to maintain the efficient photosynthetic activity and biomass production. At 300 mM NaCl, both P _N and g _s decreased significantly in all the genotypes, but the changes in P _N and L_ns in the 7H addition line were more favourable similar to those in wheat. The downregulation of photosynthetic electron transport processes around PSII, accompanied by increases in the quantum yield of regulated energy dissipation and of the donor side limitation of PSI without damage to PSII, was observed in the addition line and barley during severe stress. Incomplete recovery of P _N was observed in the 7H addition line as a result of declined PSII activity probably caused by enhanced cyclic electron flow around PSI. These results suggest that the better photosynthetic tolerance to moderate salt stress of barley can be manifested in the 7H addition line which may be a suitable candidate for improving salt tolerance of wheat.     

Kinetics and mechanism of the oxidative addition of iodomethane to β-diketonatobis(triphenylphosphite)rhodium(I) complexes

The kinetics and mechanism of the oxidative addition of CH₃I to [Rh(β-diketone)(P(OPh)₃)₂] complexes was studied in acetone medium at various temperatures. The experimental rate law is R = k[Rh(β-diketone)(P(OPh₃)₂][CH₃I]. The order of the effect of the β-diketone on the reactivity of the complexes is acac >; BA >; DBM >; TFAA >; TFBA >; HFAA indicating that electronegative substituents of the β-diketone decrease the reactivity of the complexes towards oxidative addition reactions. The volume of activation for some of the reactions was determined in various solvents. The large negative values of the volume and entropy of the activation indicated a mechanism which occurs via a polar transition state.     

Computer-augmented modeling studies of Pb(II) and Cd(II) complexes with maleic acid in ethylene glycol–water mixture

Chemical speciation of binary complexes of Pb(II) and Cd(II) ions with maleic acid have been studied pH metrically in the concentration range of 0–50% v/v ethylene glycol (EG)–water mixtures maintaining an ionic strength of 0.16 molL^?1 at 303 K. Alkalimetric titrations were carried out in different relative concentrations of metal and maleic acid. Stability constants of various models of binary complexes were refined with MINIQUAD75. The best-fit chemical models were selected based on statistical parameters and residual analysis. The species detected are ML₂, ML₃, and ML₂H for Pb(II) and Cd(II). The chemical speciation, metal bioavailability, and transportation are explained based on the distribution diagrams.     

New thiocyanato and azido adducts of the redox-active Fe(η-C5Me5)(η-dppe) center: Synthesis and study of the Fe(II) and Fe(III) complexes

The new thiocyanato- (5) and azido- (6) complexes were synthesized and studied under their Fe(II) and Fe(III) redox states. For the first time among the various [Fe(η⁵-C₅Me₅)(η²-dppe)]-based cationic radicals studied so far, the magnitude and spatial orientation of the g-tensor diagonal values were experimentally determined for 5[PF₆]. These data are in good agreement with those issued from a DFT modelization. The changes experienced by the electronic structure of the Fe(II) complexes subsequent to oxidation are reminiscent of these previously observed for the known arylalkynyl analogues, albeit some differences can be pointed out. Thus, the differences observed in the ¹H NMR spectra of 5[PF₆] and 6[PF₆] are attributed to a slower electronic spin relaxation and to the differently oriented magnetic anisotropy. The sizeable spin density evidenced by DFT on the terminal atom of the ligands of the Fe(III) complexes renders these new paramagnetic metallo-ligands quite appealing for accessing larger polynuclear molecular assemblies with magnetically interacting centers.     

Determination of the equilibrium constant for binding hydroxide to tetraazamacrocyclic—Nickel(II) complexes

The pK_b for the equilibria NiL(OH)⁺ ⇄ NiL²⁺ + OH⁻ for L1,4,7,10-tetraazacyclotridecane, 1,4,8, 12-tetraazacyclopentadecane, C-β-racemic-5,7,7,12, 14,14-hexamethyl-l,4,8,11-tetraazacyclotetradecane and C-β-racemic-1,4,5,7,7,8,11,12,14,14,-decamethyl- 1,4,8,112-tetraazacyclotetradecane are 0.95, 1.9, 0.2 and 0.65 respectively. The results are compared with data for analogous complexes reported earlier. The results indicate that the main factors affecting these equilibrium constants are the in plane ligand field strengths of the square planar complexes and steric factors.     

Stabilities of lead(II) complexes formed in aqueous solution with methyl thiophosphate (MeOPS2–), uridine 5'-O-thiomonophosphate (UMPS2–) or adenosine 5'-O-thiomonophosphate (AMPS2–)

The acidity constants of twofold protonated methyl thiophosphate (MeOPS(2-)) and of monoprotonated uridine 5'- O-thiomonophosphate (UMPS(2-)) have been determined in aqueous solution (25 degrees C; I= 0.1 M, NaNO(3)) by potentiometric pH titration. The stability constants of their 1:1 complexes formed with Pb(2+), i.e. Pb(MeOPS) and Pb(UMPS), have also been measured. The results show that replacement of a phosphate oxygen by a sulfur atom increases the acidity by about 1.4 p K units. On the basis of recently established log versus plots ( = simple phosphate or phosphonate ligands where R is a non-coordinating residue), it is shown that the stability of the Pb(thiophosphate) complexes is by log Delta= 2.43+/-0.09 larger than expected for a Pb(2+)-phosphate interaction. The identity of the stability increase (log Delta) observed for Pb(MeOPS) and Pb(UMPS) shows that the nucleobase residue in the Pb(UMPS) complex has no influence on complex formation. To be able to carry out the mentioned comparisons, we have also determined the stability constant of the complex formed between Pb(2+) and methyl phosphate; the corresponding data for Pb(UMP) were already known from our earlier studies. The present results allow an evaluation of other Pb(2+) complexes formed with thiophosphate derivatives and they are applied now to the Pb(2+) complexes of adenosine 5'- O-thiomonophosphate (AMPS(2-)). The stability constants of the Pb(H;AMPS)(+) and Pb(AMPS) complexes were measured and it is shown that, within the error limits, the stability of the Pb(AMPS) complex is determined by the basicity of the thiophosphate group of AMPS(2-); in other words, no hint for macrochelate formation involving N7 was observed. More important, with the aid of micro-stability-constant considerations it is concluded that the structure of the dominating isomer of the Pb(H;AMPS)(+) species is the one where the proton is located at the N1 site of the adenine residue and Pb(2+) is coordinated to the deprotonated thiophosphate group. The insights gained from this study with regard to thiophosphate-altered single-stranded nucleic acids and their affinity towards Pb(2+) are discussed.     

Synthesis and structure of an unusual di-rhodium diarylbutadiyne π-complex featuring a μ-(1,2-η2):(3,4-η2)-p-CF3C6H4–CC–CC–C6H4-p-CF3 moiety

Reaction of the salt [Rh(PMe₃)₄]Cl (1) with p-F₃C–C₆H₄–CC–CC–C₆H₄-p-CF₃ (2) in THF gives a mixture of two related neutral π-bound diyne complexes of [Rh(PMe₃)₃Cl], each having two distinct CF₃ resonances of equal intensity in the in situ ¹⁹F{¹H} NMR spectrum. The ratio of the two products can be varied by varying the stoichiometry of the reagents. On the basis of the spectroscopic data and literature precedent, we propose Rh(PMe₃)₃(Cl)((1,2-η²)-p-F₃C–C₆H₄–CC–CC–C₆H₄-p-CF₃) (3a) and [Rh(PMe₃)₃(Cl)]₂(μ-(1,2-η²):(1,2-η²)-p-F₃C–C₆H₄–CC–CC–C₆H₄-p-CF₃) (3b) as the most likely structures of the species in solution. However, upon standing overnight, single crystals of the unusual, dinuclear complex [Rh(PMe₃)₃(Cl)]₂(μ-(1,2-η²):(3,4-η²)-p-F₃C–C₆H₄–CC–CC–C₆H₄-p-CF₃) (4), an isomer of 3b, form reproducibly and in good yield as two different solvates from THF/C₆D₆ solution. The centrosymmetric structure of 4, obtained from single-crystal X-ray diffraction data, displays a transoid orientation of the bridging diarylbutadiyne ligand.     

DFT study on the reactions of ClO–/BrO– with RCl (R = CH3, C2H5, and C3H7) in gas phase

Gas-phase reactions of ClO^–/BrO^– with RCl (R = CH₃, C₂H₅, and C₃H₇) have been investigated in detail using the popular DFT functional BHandHLYP/aug-cc-pVDZ level of theory. As a result, our findings strongly suggest that the type of reaction is firstly initiated by a typical S_N2 fashion. Subsequently, two competitive substitution steps, named as S_N2-induced substitution and S_N2-induced elimination, respectively, would proceed before the initial S_N2 product ion-dipole complex separates, in which the former exhibits less reactivity than the latter. Those are consistent with relevant experimental results. Moreover, we have also explored reactivity difference for the title reactions in term of some factors derived from methyl group, p-π electronic conjugation, ionization energy (IE), as well as molecular orbital (MO) analysis.

Further studies on the copper(II) complexes of lysine: [Cu(II)(H3N·C5H10·CH·NH2·COO)2] [HgI3]2

Spontaneous resolution in the formation of the [HgI₃]⁻ salts of the copper complex of racemic lysine was previously reported. X-ray and IR studies were used to support this conclusion. Gas chromatographic studies using a chiral phase on the crystals originally studied, and on newly formed crystals using D,L-lysine, do not substantiate the suggestion that spontaneous resolution occurs.     

Spectroscopic studies of metal complexes containing π-delocalized sulfur ligands. The pre-resonance Raman spectra of the antitumor agent 2-formylpyridine thiosemicarbazone and its Cu(II) and Zn(II) complexes

The pre-resonance Raman spectra of 2-formylpyridine thiosemicarbazone have been measured at three pH values corresponding to the fully protonated (H₂FPT⁺), half protonated (HFPT) and deprotonated (FPT⁻) forms of the ligand. Assignments of the vibrations coupled with the π→π^* transition have been made by comparison with the spectrum of the deuterated form (DFPT). The pre-resonance Raman spectra of the Zn(II) and Cu(II) complexes, [ZnFPT]⁺, [CuFPT]⁺ and [CuHFPT]²⁺, have also been measured. The spectral pattern of the Cu(II) complexes shows resonance enhancement of vibrations coupled with the π→π^*, as well as with the ligand to metal charge transfer transitions. In addition, it is consistent with coordination through thiolate sulfur in [CuFPT]⁺ and thione sulfur in [CuHFPT]²⁺.     

Mössbauer and spectroscopic studies on substituted tetraphenylporphyrinato iron(III) complexes in aqueous solutions and the formation of the μ-oxo-bridged species

Electronic and ⁵⁷Fe Mössbauer spectra are reported for two new water-soluble porphyrinato iron(III) complexes. Equilibrium constants for μ-oxo bishaem formation are calculated assuming two protons are released.Comparisons are made of the data with other porphyrinato iron(III) systems and it is shown that, in the absence of well-defined fifth ligands, the mononuclear species in acidic solution probably contain two axial water ligands. The μ-oxo bishaems do not contain water or hydroxide coordinated to iron but may hold water by hydrogen-bonding to the oxygen bridge or possibly by aquation of the porphyrin ligands.μ-Oxo bridge formation is controlled by the acid strength of the water coordinated to the iron in the mononuclear species, low pK_a values assisting oxo-bridge formation. Such low pK_a values are assisted by electron-attracting substituents on the porphyrin periphery. It is noted that this same property assists the stabilisation of iron(II) complexes. Steric inhibition of oxo-bridge formation requires large substituents, unsubstituted phenyl groups being apparently not large enough.     

Cyclopentadienyl iron xanthate complexes. Crystal and molecular structure and electrochemical reduction of η-C5R5Fe(CO)2(η1-SC(S)OEt) (RH or CH3)

Complexes η-C₅R₅Fe(CO)₂(η¹-SC(S)OEt) (RH, (1) and RCH₃ (2)) have been analysed by X-ray diffraction techniques. 1: P2₁2₁2₁ 11.3560(5), 10.8595(4), 10.1158(3) Å, Z=4; 1023 observed reflexions, R and R_w 0.069 and 0.073. 2: Pbca, 15.6907(11), 15.4566(13), 14.3083(11) Å, Z=8; 2271 observed reflexions, R and R_w being 0.071, 0.073. The coordination is quite similar for both compounds with the xanthate monodentate ligand almost perpendicular to the ring planes and a relative twist, one from each other of about 10°. The reductive electrochemistry of both complexes has been examined by cyclic voltammetry and coulometry. In a carbon electrode the first-one electron reduction step can be ascribed to the formation of corresponding carbonyl dimers. In a mercury electrode, the first reduction step of 1 leads to a bond rupture process with formation of a mercury compound [CpFe(CO)₂]₂Hg and further reduction to the anion CpFe(CO)₂⁻. However, the behaviour of the pentamethylcyclopentadienyl complex (2) is quite different, and it is reduced in a three step process.     

New synthesis of seven-coordinate complexes of molybdenum(II) and tungsten(II) containing bidentate phosphorus ligands, [MI2(CO)3{Ph2P(CH2)nPPh2}] (n = 1–6)

A new high yielding synthesis of the seven-coordinate complexes [MI₂(CO)₃{Ph₂P(CH₂)_nPPh₂}] (M = Mo and W; n = 1–6) is described. The procedure involves reacting the complexes [MI₂(CO)₃(NCMe)₂] in CH₂Cl₂ with an equimolar amount of the bidentate phosphorus ligand. The low temperature (−70 °C) ¹³C NMR spectra of the complexes [Wl₂(CO)₃{Ph₂P(CH₂)_nPPh₂}] (n = 3 and 5) indicates that the geometry is capped octahedral with a carbonyl ligand in the unique capping position.     

Synthesis of heterodinuclear FeRu(CO)6(R-DAB(6e))(R-DABRNC(H)C(H)NR) Part XV. Comparison of the reactivities of heterodinuclear FeRu(CO)6(R-DAB(6e)) and homodinuclear analogues M2(CO)6(R-DAB(6e)) (M = Fe,Ru). Single-crystal x-ray structures of FeRu(CO)6(i-Pr-DAB(6e)) and FeRu(CO)5(i-Pr-DAB(4e))(C3H4)

The reactions of Fe(CO)₃(R-DAB; R¹, H(4e)) (1a: R = i-Pr, R¹ = H; 1b: R = t-Bu, R¹ = H; 1c: R = c-Hex, R¹ = H; 1e: R = p-Tol, R¹ = H; 1f: R = i-Pr, R¹ = Me) with Ru₃(CO)₁₂ and of Ru(CO)₃(R-DAB; R¹, H(4e)) (2a: R = i-Pr, R¹ = H; 2d: R = CH(i-Pr)₂, R¹ = H) with Fe₂(CO)₉ in refluxing heptane both afforded FeRu(CO)₆(R-DAB; R¹, H(6e)) (3) in yields between 50 and 65%.The coordination mode of the ligand has been studied by a single crystal X-ray structure determination of FeRu(CO)₆(i-Pr-DAB(6e)) (3a). Crystals of 3a are monoclinic, space group P2₁/a, with four molecules in a unit cell of dimensions: a = 22.436(3), b = 8.136(3), c = 10.266(1) Å and β = 99.57(1)°. The structure was refined to R = 0.049 and R_w = 0.052 using 3045 reflections above the 2.5σ(I) level. The molecule contains an FeRu bond of 2.6602(9) Å, three terminally bonded carbonyls to Fe, three terminally bonded carbonyls to Ru and bridging 6e donating i-Pr-DAB ligand. The i-Pr-DAB ligand is coordinated to Ru via N(1) and N(2) occupying an apical and equatorial site respectively (RuN(1) = 2.138(4) RuN(2) = 2.102(3) Å). The C(2)N(2) moiety of the ligand is η²-coordinated to Fe with C(2) in an apical and N(2) in an equatorial site (FeC(2) = 2.070(5) and FeN(2) = 1.942(3) Å).The ¹H and ¹³C NMR data indicate that in all FeRu(CO)₆(R-DAB(6e)) complexes (3a to 3f) exclusively η²-CN coordination to the Fe atom and not to the Ru atom is present irrespective of whether 3 was prepared by reaction of Fe(CO)₃(R-DAB(4e)) (1) with Ru₃(CO)₁₂ or by reaction of Ru(CO)₃(R-DAB(4e)) (2) with Fe₂(CO)₉. In the case of FeRu(CO)₆(i-Pr-DAB; Me, H(6e)) (3f) the NMR data show that only the complex with the C(Me)N moiety of the ligand σ-N coordinated to the Ru atom and the C(H)N moiety η²-coordinated to the Fe atom was formed. Variable temperature NMR experiments up to 140 °C showed that the α-diimine ligand in 3a is stereochemically rigid bonded.FeRu(CO)₆(R-DAB(6e)) (3a and 3e) reacted with allene to give FeRu(CO)₅(R-DAB(4e))(C₃H₄) (4a and 4e). A single crystal X-ray structure determination of FeRu(CO)₅(i-Pr-DAB(4e))(C₃H₄) (4a) was performed. Crystals of 4a are triclinic, space group P1, with two molecules in a unit cell of dimensions: a = 9.7882(7), b = 12.2609(9), c = 8.3343(7) Å, α = 99.77(1)°, β = 91.47(1)° and γ = 86.00(1)°. The structure was refined to R = 0.028 and R_w = 0.043 using 4598 reflections above the 2σ(I) level. The molecule contains an FeRu bond of 2.7405(7) Å and three terminally bonded carbonyls to iron. Two carbonyls are terminally bonded to the Ru atom together with a chelating 4e donating i-Pr-DAB ligand [RuN = 2.110(1) (mean)]. The allene ligand is coordinated in an η³-allylic fashion to the Fe atom while the central carbon of the allene moiety is σ-bonded to the Ru atom (FeC(14) = 2.166(3), FeC(15) = 1.970(2), FeC(16) = 2.127(3) and RuC(15) = 2.075(2) Å). The ¹H and ¹³C NMR data show that in solution the coordination modes of the R-DAB and the allene ligands are the same as in the solid state.Thermolysis reactions of 3a with R-DAB or carbodiimides gave decomposition and did not afford C(imine)C(reactant) coupling products. Thermolysis reactions of 3a with M₃(CO)₁₂ (M = Ru, Os) and Me₃NO gave decomposition. When the reaction of 3a with Me₃NO was performed in the presence of dimethylacetylenedicarboxylate (DMADC) the known complex FeRu(CO)₄(i-Pr-DAB(8e))(DMADC) (5a) was formed in low yield. In 5a the R-DAB ligand is in the 8e coordination mode with both the imine bonds η²-coordinated to iron. The acetylene ligand is coordinated in a bridging fashion, parallel with the FeRu bond.     

The effects of structural variations of thiophene-containing Ru(II) complexes on the acid–base and DNA binding properties

A phenylthiophenyl-bearing Ru(II) complex of [Ru(bpy)₂(Hbptip)](PF₆)₂ {bpy?=?2,2′-bipyridine, Hbptip?=?2-(4-phenylthiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline} was synthesized and characterized by elemental analysis, ¹H NMR spectroscopy, and electrospray ionization mass spectrometry. The ground- and excited-state acid–base properties of the complex were studied by UV–visible absorption and photoluminescence spectrophotometric pH titrations and the negative logarithm values of the ground-state acid ionization constants were derived to be pK _a1?=?1.31?±?0.09 and pK _a2?=?5.71?±?0.11 with the pK _a2 associated deprotonation/protonation process occurring over 3 pK _a units more acidic than thiophenyl-free parent complex of [Ru(bpy)₂(Hpip)]²⁺ {Hpip?=?2-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline}. The calf thymus DNA-binding properties of [Ru(bpy)₂(Hbptip)]²⁺ in Tris–HCl buffer (pH 7.1 and 50?mM NaCl) were investigated by DNA viscosities and density functional theoretical calculations as well as UV–visible and emission spectroscopy techniques of UV–visible and luminescence titrations, steady-state emission quenching by [Fe(CN)₆]^4?, DNA competitive binding with ethidium bromide, DNA melting experiments, and reverse salt effects. The complex was evidenced to bind to the DNA intercalatively with binding affinity being greater than those for previously reported analogs of [Ru(bpy)₂(Hip)]²⁺, [Ru(bpy)₂(Htip)]²⁺, and [Ru(bpy)₂(Haptip)]²⁺ {Hip?=?1H-imidazo[4,5-f][1,10]phenanthroline, Htip?=?2-thiophenimidazo[4,5-f][1,10]phenanthroline, Haptip?=?2-(5-phenylthiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline}.