Formation constants (log K1) for TPTZ (2,4,6-tris(2-pyridyl)-1,3,5-triazine) with a variety of metal ions in aqueous solution are reported at ionic strength 0.1 and at 25 °C. The Ln(III) series with log K1(TPTZ) plotted against ionic radius (r+) in reverse order shows a novel set of log K1 values with log K1 rising from La(III) to peak at Sm(III) and then dropping down steadily to Lu(III) with log K1 lower than for La(III). Y(III) and Am(III) show log K1 values relative to their Ln(III) size analogues, with a small drop for Y(III) and little difference in log K1 for Am(III). The variation of log K1 along the Ln(III) series, as well as log K1 for Am(III) and Y(III) compared to their Ln(III) size analogues, is discussed for several ligands. The patterns in variation of log K1 along the Ln(III) series depend on increasing covalence, which contributes to a rise in log K1 toward Lu(III). The coordinating nitrogen of the triazine moiety of TPTZ is shown by density functional theory calculation to be of very low basicity and therefore unable to cause a rise in log K1 to Lu(III), resulting in the unusual log K1 vs r+ diagram for the Ln(III) cations with TPTZ.

The blackening of cut carrots decreases their shelf life and causes severe economic losses but the molecular and metabolic mechanisms that underpin this phenomenon remain poorly characterized. Studies were therefore undertaken to determine the molecular and metabolic causes of the blackening. The susceptibility of blackening was dependent on the period of time that the crop was stored underground prior to harvest. The structure of the cell walls in the black regions was substantially changed compared to the orange regions. The black regions of carrot batons had decreased immunodetection of xyloglucan, HG-pectin, RG-I pectin, galactan and arabinan but had higher levels of lignin and phenolic compounds compared to the orange regions. Transcript profiling analysis revealed that phytohormone signalling processes were activated in the black regions. Transcripts associated with auxin signalling and ethylene-responsive transcription factors were increased in the black regions. In contrast, the levels of transcripts encoding proteins associated with secondary metabolism were decreased in the black regions. These findings implicate ethylene and auxin-related processes in the control of the primary to secondary metabolism shift that results in lignification and cell wall disruption that underpin the blackening process.

Additional file 2 Table S1. Two-way analysis of variance (ANOVA) table with p values (those less than 5% are highlighted in bold) and means squares (in italics) for response variables in two Brassica oleracea accessions (C6 and F103) grown hydroponically for 2 weeks in solutions containing 0.025 mM P (Low P) or 0.25 mM P (High P); Zn, zinc. Table S2. Relative concentration of polar metabolites detected in root exudates of two Brassica oleracea accessions (C6 and F103) grown hydroponically for 2 weeks in solutions containing 0.025 mM P (Low P) or 0.25 mM P (High P). * indicates metabolites for which fold change could not be calculated, as it was not detected in one of the treatments in both accessions. Table S3. Two-way analysis of variance (ANOVA) table with p values (those less than 5% are highlighted in bold) and means squares (in italics) for main root length and ANOVA on Ranks for lateral root length along the main root length, divided into quartiles, in two Brassica oleracea accessions (C6 and F103) grown in the high throughput root phenotyping system with Low phosphorus (P) and High P treatments (four groups in total) for 2 weeks. Table S4. All differentially expressed P-responsive genes and their expression in FPKM, in roots of two Brassica oleracea accessions (C6 and F103) grown hydroponically for 2 weeks in solutions containing 0.025 mM P (Low P; LP) and 0.25 mM P (High P; HP). Differentially expressed genes were defined by comparing the gene expression in the Low P treatment with the gene expression in the High P treatment for each of the B. oleracea accession. Table S5. Gene ontology enrichment analysis for all differentially expressed genes in roots of two Brassica oleracea accessions (the C6 and the F103) grown in solutions containing 0.025 mM P (Low P) and 0.25 mM P (High P) for 2 weeks (n = 3 for each accession and each treatment). Bonferroni corrected p-values were used to determine significantly enriched categories and a corrected p-value of 0.05 was used as a cut-off. Table S6. P-responsive genes with orthologues in Arabidopsis thaliana. The table shows the gene expression of all P-responsive genes in the roots of two Brassica oleracea accessions (C6 and F103) grown hydroponically for 2 weeks in solutions containing 0.025 mM P (Low P) and 0.25 mM P (High P) which have A. thaliana ortholouges. Table S7. Shoot fresh weight, phosphorus (P) and zinc (Zn) concentrations and P efficiency ratio (calculated as Yieldlow / (Plow × Yieldlow) or Yieldhigh / (Phigh × Yieldhigh)) of the two Brassica oleracea accessions (C6 and F103) grown in a peat-based compost amended with Low P (5.25 mg L− 1) and High P (15.75 mg L− 1) used in the experiments. Data for fresh weight, shoot P concentration and P efficiency ratio are from [1] and shoot Zn concentrations are from [2]; DM, dry matter.

Studies of the complexation of new promising ligands with uranyl (UO22+) and other seawater cations can aid the development of more efficient, selective, and robust sorbents for the recovery of uranium from seawater. In this work, we propose that the ligand design principles based on structural preorganization can be successfully applied to obtain a dramatic enhancement in UO22+ ion binding affinity and selectivity. This concept is exemplified through the investigation of the complexes of UO22+, VO2+, and VO2+ with the highly preorganized ligand 1,10-phenanthroline-2,9-dicarboxylic acid (PDA) using a combination of fluorescence and absorbance techniques, along with density functional theory (DFT) calculations. The measured stability constant value, log K1, of 16.5 for the UO22+/PDA complex is very high compared to uranyl complexes with other dicarboxylic ligands. Moreover, PDA exhibits strong selectivity for uranyl over vanadium ions, since the determined stability constant values of the PDA complexes of the vanadium ions are quite low (V(IV) log K1 = 7.4, V(V) = 7.3). The structures of the corresponding UO22+, VO2+, and VO2+ complexes with PDA were identified by systematic DFT calculations and helped to interpret the stronger binding affinity for uranium over the vanadium ions. Because of its high chemical stability, selectivity, and structural preorganization for UO22+ complexation, PDA is a very promising candidate that can be potentially used in the development of novel adsorbent materials for the selective extraction of uranium from seawater.

Sensory differentiation of blueberries from eight highbush cultivars grown in the UK was related to flavor volatile composition. A two-phase descriptive sensory analysis was used: initial FCP to understand the range of descriptors used by consumers to differentiate the fruit and a subsequent conventional profiling by trained assessors using a consensus vocabulary to generate a multivariate product space describing relationships between the cultivars. A generalized Procrustes analysis product was obtained for aroma volatiles, extracted by headspace solid-phase microextraction (HS-SPME), and analyzed by gas chromatography linked mass spectrometry (GC/MS). Sensory information on cultivar aroma characters could be correlated with differences in aroma volatiles.

The Cd(II) complex of adpa (N-(9-anthracenylmethyl)-N,N-di-(picolyl)amine) in MeOH-H2O has increased fluorescence intensity with [Cl(-)], a new type of anion sensor. The structure of [Cd(adpa)(NO3)2] has a proposed fluorescence-quenching π-contact between Cd and the fluorophore, while the Cl in [Cd(adpa)Cl2] disrupts the π-contact, restoring fluorescence.

Factors in polypyridyl ligands that control their thermodynamic metal ion selectivity in aqueous solution, and their use in selective fluorescent sensing, are examined. Preorganization of polypyridyl ligands ranging from bidentate to tetradentate by bridging benzo groups, as are present in 1,10-phenanthroline (phen) compared to 2,2'-bipyridyl (bpy), is discussed. The role of solvation is considered in relation to the relative affinity of ligands containing pyridyl groups for divalent and trivalent metal ions in aqueous solution. The effects of steric clashes between H atoms on polypyridyl ligands in decreasing complex stability are evaluated, as well as the effect of chelate ring size on metal ion selectivity. Phen ligands with other donor groups present at the 2 and 9 positions, such as alcohols, amides, carboxylates, and oximes are discussed. The design of pyridyl-based ligands for the separation of Am(III) from lanthanide(III) ions is considered, as well as ligands for the removal of metal ions such as Cu(II) or Zn(II) in neurological diseases such as Alzheimer's. The design of pyridyl-based fluorescent sensors for selective sensing of metal ions is examined in terms of the role of spin-orbit coupling constants (ζ), paramagnetism, and steric effects in the development of selective fluorescent sensors that operate via chelation enhanced fluorescence (CHEF). It is concluded that for lighter metal ions with smaller ζ values such as Zn(II) and Ca(II), and to a lesser extent Cd(II), that the CHEF effect can be achieved with pyridyl-containing fluorophores that coordinate directly to the metal ion. The way in which steric effects can be used to decrease the CHEF effect in Zn(II) relative to Cd(II) to enable selective sensing of the latter is analyzed. For heavier metal ions such as Hg(II) and Pb(II), because of their large ζ values which quench fluorescence, it is concluded that the fluorophore should be tethered to the metal-binding part of the sensor, and prevented from binding to the metal ion by steric and electronic factors. How Hg(II) can quench the CHEF effect by π-contact with fluorophores such as the anthracenyl group, which at first sight might not seem able to bond with metal ions, is examined.

DPA (dipyrido[4,3-b;5,6-b]acridine) may be considered as a tridentate homologue of phen (1,10-phenanthroline). In this paper some of the metal ion complexing properties of DPA in aqueous solution are reported. Using UV-visible spectroscopy to follow the intense π-π* transitions of DPA as a function of pH gave protonation constants at ionic strength (μ) = 0 and 25 °C of pK(1) = 4.57(3) and pK(2) = 2.90(3). Titration of 10(-5) M solutions of DPA with a variety of metal ions gave log K(1) values as follows: Zn(II), 7.9(1); Cd(II), 8.1(1); Pb(II), 8.3(1); La(III), 5.23(7); Gd(III), 5.7(1); Ca(II), 3.68; all at 25 °C and μ = 0. Log K(1) values at μ = 0.1 were obtained for Mg(II), 0.7(1); Sr(II), 2.20(1); Ba(II), 1.5(1). The log K(1) values show that the high level of preorganization of DPA leads to complexes 3 log units more stable than the corresponding terpyridyl complexes for large metal ions such as La(III) or Ca(II), but that for small metal ions such as Mg(II) and Zn(II) such stabilization is minimal. Molecular mechanics calculations (MM) are used to show that the best-fit M-N length for coordination with DPA is 2.60 Å, accounting for the high stability of Ca(II) or La(III) complexes of DPA, which are found to have close to this M-N bond length in their phen complexes.

Some metal-ion-complexing properties of the ligand 2,2',6',2''-terpyridyl (terpy) in aqueous solution are determined by following the π-π* transitions of 2 × 10(-5) M terpy by UV-visible spectroscopy. It is found that terpy forms precipitates when present as the neutral ligand above pH ∼5, in the presence of electrolytes such as NaClO(4) or NaCl added to control the ionic strength, as evidenced by large light-scattering peaks. The protonation constants of terpy are thus determined at the ionic strength (μ) = 0 to avoid precipitation and found to be 4.32(3) and 3.27(3). The log K(1) values were determined for terpy with alkali-earth metal ions Mg(II), Ca(II), Sr(II), and Ba(II) and Ln(III) (Ln = lanthanide) ions La(III), Gd(III), and Lu(III) by titration of 2 × 10(-5) M free terpy at pH >5.0 with solutions of the metal ion. Log K(1)(terpy) was determined for Zn(II), Cd(II), and Pb(II) by following the competition between the metal ions and protons as a function of the pH. Complex formation for all of these metal ions was accompanied by marked sharpening of the broad π-π* transitions of free terpy, which was attributed to complex formation affecting ligand vibrations, which in the free ligand are coupled to the π-π* transitions and thus broaden them. It is shown that log K(1)(terpy) for a wide variety of metal ions correlates well with log K(1)(NH(3)) values for the metal ions. The latter include both experimental log K(1)(NH(3)) values and log K(1)(NH(3)) values predicted previously by density functional theory calculation. The structure of [Ni(terpy)(2)][Ni(CN)(4)]·CH(3)CH(2)OH·H(2)O (1) is reported as follows: triclinic, P1, a = 8.644(3) Å, b = 9.840(3) Å, c = 20.162(6) Å, α = 97.355(5)°, β = 97.100(5)°, γ = 98.606(5)°, V = 1663.8(9) Å(3), Z = 4, and final R = 0.0319. The two Ni-N bonds to the central N donors of the terpy ligands in 1 average 1.990(2) Å, while the four peripheral Ni-N bonds average 2.107(10) Å. This difference in the M-N bond length for terpy complexes is typical of the complexes of smaller metal ions, while for larger metal ions, the difference is reversed. The significance of the metal-ion size dependence of the selectivity of polypyridyl ligands, and the greater rigidity of ligands based on aromatic groups such as pyridyl groups, is discussed.

Blackcurrant (Ribes nigrum L.) is a widely grown commercial crop valued for its high ascorbic acid content. In the present study we report large year-to-year variation in the ascorbic acid content of four different blackcurrant cultivars grown at the same site demonstrating strong environmental influence on fruit ascorbic acid concentration. All cultivars examined showed the same trend in ascorbic acid concentration on a year-to-year basis and cultivar hierarchy in fruit ascorbic acid was generally maintained. These data suggest strong underlying genetic determinants for fruit vitamin C concentration and demonstrate that different blackcurrant cultivars show similar responses to prevailing environmental conditions. Linear regression analysis of fruit ascorbic acid content versus several environmental parameters (total solar radiation, total precipitation and average air temperature) suggested a complex environmental interaction with multiple environmental parameters affecting fruit ascorbate. However, pre-harvest solar radiation showed the strongest correlation and data from fruit grown on north or south facing slopes further highlighted the importance of irradiation. Expression analysis of four genes encoding ascorbate biosynthetic enzymes failed to identify any correlations between gene expression and fruit ascorbate content although specific alleles of the gene encoding GDP-D-mannose 3,5-epimerase (E.C. 5.1.3.18) were associated with high fruit ascorbate. _____________________________________________________________________________________________________________

The hydrothermal synthesis and structures of [UO2(PDA)] (1) and [Th(PDA)2(H2O)2].H2O (2) (PDA = 1,10-phenanthroline-2,9-dicarboxylic acid) are reported. 1 is orthorhombic, Pnma, a = 11.1318(7) A, b = 6.6926(4) A, c = 17.3114(12) A, V = 1289.71(14), Z = 4, R = 0.0313; 2 is triclinic, P1, a = 7.6190(15) A, b = 10.423(2) A, c = 17.367(4) A, alpha = 94.93(3) degrees , beta = 97.57(3) degrees , gamma = 109.26(3) degrees , V = 1278.3(4) A (3), Z = 2, R = 0.0654. The local geometry around the U in 1 is a pentagonal bipyramid with the two uranyl oxygens occupying the apical positions. The donor atoms in the plane comprise the four donor atoms from the PDA ligand (average U-N = 2.558 and U-O = 2.351 A) with the fifth site occupied by a bridging carboxylate oxygen from a neighboring UO2/PDA individual. The PDA ligand in 1 is exactly planar, with the U lying in the plane of the ligand. The latter planarity, as well as the near-ideal U-O and U-N bond lengths, and O-U-N and N-U-N bond angles within the chelate rings of 1 suggest that PDA binds to the uranyl cation in a low-strain manner. In 2, there are two PDA ligands bound to the Th (average Th-N = 2.694 and Th-O = 2.430 A) as well as two water molecules (Th-O = 2.473 and 2.532 A) to give the Th a coordination number of 10. The PDA ligands in 2 are bowed, with the Th lying out of the plane of the ligand. Molecular mechanics calculations suggest that the distortion of the PDA ligands in 2 arises because of steric crowding. UV spectroscopic studies of solutions containing 1:1 ratios of PDA and Th(4+) in 0.1 M NaClO4 at 25 degrees C indicate that log K1 for the Th(4+)/PDA complex is 25.7(9). The latter result confirms the previous prediction that complexes of PDA with metal ions of higher charge and an ionic radius of about 1.0 A such as Th(IV) would have remarkably high log K1 values with PDA. The origins of this very high stability are discussed in terms of a synergy between the pyridyl and the carboxylate donor groups of PDA. Metal ions of high charge normally bond poorly with pyridyl donors in aqueous solution because such metal ions require donor groups that are able to disperse charge to the solvent via hydrogen-bonding, which pyridyl groups are unable to do. In PDA, the carboxylates fulfill this need and so enable the high donor strength of the pyridyl groups of PDA to become apparent in the high log K1 for Th(IV) with PDA.

The metal ion complexing properties of highly preorganized non-macrocyclic ligands in aqueous solution are discussed and contrasted with those of less preorganized analogues that have simple ethylene bridges between the donor atoms. High levels of preorganization can be achieved using cyclohexenyl bridges between ligand donor atoms, use of reinforced bridges such us bispidines, or by use of extended aromatic systems as bridges, such as those found in 1,10-phenanthroline (1,10-phen). Cyclohexenyl groups increase thermodynamic stability of metal ion complexes, as indicated by logK1 values (formation constants), that increase by between 1 and 5log units compared to less preorganized analogues. The way in which such bridges alter selectivity in the direction of smaller metal ions is discussed. Rigid bridges such as those provided by bispidine are discussed in terms of increased logK1 values, and sharply increased selectivity for smaller metal ions. Ligands derived from 1,10-phen by placing donor groups at the 2- and 9-positions are discussed, including examples with acetates (PDA), pyridyls (DPP) and phenolates (DPHP). The five-membered chelate rings of PDA lead to strong selectivity for larger metal ions, including Cd(II), La(III), and Gd(III). Possible uses of PDA type ligands for Gd(III)-based MRI agents are discussed. The remarkably high stability of complexes of PDA is discussed in terms of the role of H-bonding with the solvent in stabilizing complexes with metal ions, and the very high level of preorganization of the ligand.