Molecule-based magnets with TC above room temperature: Improved synthesis of vanadium–chromium Prussian blue analogues with inserted alkali cations

We report the synthesis of several new vanadium–chromium Prussian blue analogues with a Curie temperature above room temperature. A catalytic amount of vanadium(III) during the synthesis allows to get improved magnetic properties, stable Curie temperatures (T_C) and a magnetisation at saturation in satisfying agreement with the stoichiometry. The insertion of alkali cations (potassium, rubidium, caesium) allows to reach a V:Cr stoichiometry close to 6:5, hence to enhance the number of magnetic neighbours compared to the usual V:Cr 3:2 stoichiometry and to increase accordingly the Curie temperature. For the same stoichiometry, the ferrimagnetic ordering temperature varies slightly with the nature of the inserted alkali cation (T_C/K = 360, 346 and 340 K for the potassium, rubidium and caesium derivatives, respectively). X-ray absorption spectroscopy allows to characterise the local surroundings of the chromium and vanadium ions and to propose an explanation of the magnetic properties.     

Caesium,potassium and ammonium distributions in different organs of tropical plants

In the present work the distribution of ions in aboveground plant parts was studied in order to establish the suitability of using radiocaesium as a tracer for the plant absorption of nutrients, such as potassium (K⁺) and ammonium (NH₄⁺). We present the results for the distributions of ¹³⁷Cs, ⁴⁰K and NH₄⁺ from four tropical plant species: lemon (Citrus aurantifolia), orange (Citrus sinensis), guava (Psidium guajava) and chili pepper (Capsicum frutescens). Activity concentrations of ¹³⁷Cs and ⁴⁰K were measured by gamma spectrometry and concentrations of free NH₄⁺ ions by a colorimetric method. Similarly to potassium and ammonium, caesium showed a high mobility within the plants, exhibiting the highest values of concentration in the growing parts of the tree (fruits, new leaves, twigs, and barks). A significant correlation between activity concentrations of ¹³⁷Cs and ⁴⁰K was observed in these tropical plants. The K/Cs discrimination ratios were approximately equal to unity in different compartments of each individual plant, suggesting that caesium could be a good tracer for ⁴⁰K in tropical woody fruit species. Despite the similarity observed for the behaviour of caesium and ammonium in the newly grown plant compartments, ¹³⁷Cs was not well correlated with NH₄⁺. Significant temporal changes in the NH₄⁺ concentrations were observed during the development of fruits, while the ¹³⁷Cs activity concentration alterations were not of great importance, indicating, therefore, that Cs⁺ and free NH₄⁺ ions could have distinct concentration ratios for each particular plant organ.     

Complexation of a four-strand tetraalcohol with labile metal ions probed by electrospray mass spectrometry

The saturated, stereodefined tetraalcohol 2,3,5,6-endo,endo,endo,endo-tetrakis(hydroxymethyl)bicyclo[2.2.1]heptane (tetol, L¹) and the simple alcohol butane-1,3-diol (L²) form complexes with alkali metal ions (lithium, sodium, potassium, rubidium and caesium), alkali earth cations (magnesium, calcium, strontium and barium) and Ga(III) and Ce(IV) in aqueous solution, characterised by electrospray ionisation mass spectrometry (ESMS). Metal ion exchange between the Li⁺ complex of L¹ and the other metal ions is rapid, with a range of M(L¹)_n ^m+ species detected, in addition to solvated species. With the alkal metal ions, M(L¹)⁺ and M(L¹)₂ ⁺ are dominant, although speciation varies with metal ion size. For the alkaline earth ions, a range of complex ions up to n=8 are observed, although n=1-3 dominate. A preference for M(L¹)₂ ²⁺ with Mg²⁺ versus M(L¹)₃ ²⁺ with Ca²⁺ may again relate to a larger ion size. For the higher-charged Ga(III) and Ce(IV), hydroxo species M(OH)(L¹)_n ^(m−1)+ are dominant reflecting bulk solution behaviour, which the ESMS studies appear to map generally.     

水文过程对缙云山径流盐基离子变化特征的影响

通过选取缙云山针阔混交林(马尾松×四川大头茶)和常绿阔叶林(四川大头茶×四川山矾)内2个标准径流小区,结合野外观测和室内分析研究降雨及径流的化学性质径流盐基离子变化特征,为该地区水环境保护提供依据。结果表明:1)针阔混交林与常绿阔叶林中p H值变化趋势相同均为:地表径流壤中流大气降水。p H与降雨量之间存在显著相关关系。2)在大气降雨-地表径流-壤中流过程中,NH+4的地表径流及壤中流输出总量小于降雨输入量,表明了土壤对NH+4有一定的吸附持留能力。其他盐基离子径流输出量均高于大气降雨的输入量,且主要以壤中流输出为主,元素发生流失。从盐基离子总量来看,径流输出量均增加:针阔混交林(2.86 kg/hm2),常绿阔叶林(2.47 kg/hm2),说明在两种林分内养分均流失。(3)K+、Ca2+、Mg2+和Na+盐基离子输出量与径流量之间存在相关关系,随着径流量的增大径流输出量增加。而NH+4输出量与径流量之间的相关性不明显,说明了NH+4的变化除受径流量的影响外,可能还受微生物、季节等其他因素的影响。     

Similar structural feature observed in the crystal packing of [Ni(dmit)2] salts of geometrical isomer of methoxycarbonyl pyridinium

The crystal structures of the C-H?O hydrogen-bonded, 1:1 complex salts of with [Ni(dmit)₂]⁻ 2MMP, 3MMP and 4MMP (ortho-, meta-, and para-methoxycarbonyl N-methyl-pyridinium, respectively) cations with have been investigated. All complex salts formed non-segregated stacks with the anions being sandwiched between layers or dimers of cations. Within these salts, the arrangement of the counter cations are structurally modulated by two weak intermolecular hydrogen bonds between the hydrogen of the pyridinium ring, methyl group or one of the two and the CO group of the cations. The alignment of Ni(dmit)₂ molecules is found to be mainly governed by the attached position of methoxycarbonyl group. Powders of (2MMP)[Ni(dmit)₂], (3MMP)[Ni(dmit)₂] and (4MMP)[Ni(dmit)₂] salts exhibited room temperature conductivities of 4.33 × 10⁻¹⁰, 1.80 × 10⁻⁶ and 5.60 × 10⁻⁶ S cm⁻¹, respectively.     

A Calcium-Activated Phytase from Pollen of Lilium longiflorum

A phytase was isolated and partially purified from the pollen of Lilium longiflorum Thumb. Optimum activity was at pH 8.0. The phytase was activated by Ca²⁺ and Sr²⁺ but not by the other divalent cations tested. Activity was inhibited by ethylenediaminetetraacetate. The phytase had a temperature optimum of 55 to 60°C and an activation energy of about 12,700 calories/mole. Extraction of L. longiflorum pollen with 0.1% Triton X-100 increased recovery of the phytase by nearly 4-fold. The phytase had a molecular weight of about 88,000 as determined by gel filtration chromatography and a K_m value of 7.2 micromolar for phytic acid in the presence of Ca²⁺.     

Low field electric birefringence study of monovalent cation-DNA interactions

The effects of monovalent cations on DNA have been studied using static and dynamic electric birefringence. Kerr's law is obeyed in a limited E range (<30 Vcm_?1) and the steady state birefringence values are close for the different cations. The birefringence kinetics have been analysed in terms of three relaxation times. On a semilogarithmice plot of Δn(t), the tail of the curve is linear over a wide range of time for Na⁺, K⁺, NH₄⁺ and Li⁺. Only for Cs⁺ solution is no linear part found and a much longer relaxation time is determined. This only contributes a small part of the total birefringence. With Cs⁺ this contribution is more field-dependent than for the other cations and we observe a larger molecular flexibility. On the other hand, with Li⁺ a greater stiffness of the DNA molecule appears. The electrical polarizabilities anisotropies decrease in the order: Cs⁺ >NH⁺₄ >K⁺ >Na⁺ >Li⁺. There are no significant differences in the optical anisotropy factors.     

Crystal structure of bis(N-methylethylenediammonium) hexabromodicuprate(I)

The crystal structure of the title compound (C₃H₁₂N₂)₂Cu₂Br₆, is monoclinic, space group P2₁/n, with lattice constants a=8.222(2), b=11.214(2), c=10.646(2) Å, β=91.97(1)° and V=981.0(3) ų. The structure contains anionic Cu₂Br₆²⁻ dimers and N-methylethylenediammonium (henceforth MEDA²⁺) cations. The centrosymmetric dimer units are composed of two edge-shared CuBr₄ tetrahedra, with bridging Cu-Br distances 0.08 Å longer than the terminal distances. A pair of MEDA²⁺ cations hydrogen bond to each dimer via two of the -NH₃⁺ hydrogen atoms and one of the -NH₂⁺- hydrogen atoms. Additional hydrogen bonding between the cations and anions tie the structure together in a complex supramolecular network.     

Translocation and plant availability of radio caesium in an organic soil

¹³⁴Caesium chloride solution was injected into the surface of a peaty podzol at 3 cm depth with 5 cm spacing over a M² at two upland sites, one of which had been fertilized and reseeded. The movement of radio caesium in the soil was subsequently followed by coring and/or taking out 10-cm square blocks at monthly intervals over a period of 2 years. There was very little movement of the caesium down the profile, with more than 95% remaining at the point of application. Lateral movement was also minimal. The caesium did not concentrate in the roots. Samples of herbage collected from the surface during the growing season showed a progressively decreasing concentration of caesium over the period. Total caesium removed in herbage amounted to 3.5 and 0.6% of the original present for the improved and umimproved soils, respectively.The extractability of the caesium from the ¹³⁴Cs-amended peaty soil was compared with that from a low-ash peat which had been treated with the radionuclide for 2 months. Initially 1 M ammonium acetate (pH 7.2) extracted 30 and 56% of the Cs from 0–3 and 3–6 horizous of the improved peaty podzol, respectively. After 5 months only about 12 and 7% of the Cs was extracted by 1 M ammonium acetate and 4 and 1% by 0.1 M sodium pyrophosphate from the 0–3 and 3–6 cm horizons, respectively. After 24 months 1 M ammonium acetate extracted 1.6 and 3.3% of the Cs from the 0–3 and 3–6 cm horizons, respectively. In contrast, the values for the peat after 2 months were 100 and 80% for 1 M ammonium acetate and 0.1 M pyrophosphate, respectively.     

An Improved Diluent for Rubella Hemagglutination and Hemagglutination-Inhibition Tests

Rubella hemagglutinating (HA) antigen was prepared in BHK-21 tissue as 5% cell suspensions and from unconcentrated and 20× concentrated infected supernatant fluids. In some instances, unconcentrated fluids were treated with Tween 80 and ether; cell suspensions were treated with ether alone. Preparations were tested for HA activity in dextrose-gelatin-Veronal (DGV) buffer solutions; 0.85% NaCl; Sorenson's phosphate-buffered saline, pH 7.2; and a diluent of 0.9% NaCl, 0.1% CaCl₂ (anhydrous), and 0.1% MgSO₄·7H₂O. HA titers were consistently two- to fourfold higher in the saline with added Ca⁺⁺ and Mg⁺⁺ than in DGV. Hemagglutination-inhibition titers of paired human sera were the same in either diluent. It is suggested that the interaction between rubella HA antigen and the red cells of young (less than 1-day-old) chicks may be at least partially ion dependent and that titers are enhanced by increased quantities of divalent cations.     

Affinity for phosphatidylinositol 4,5-bisphosphate determines muscarinic agonist sensitivity of Kv7 K+ channels

Kv7 K⁺-channel subunits differ in their apparent affinity for PIP₂ and are differentially expressed in nerve, muscle, and epithelia in accord with their physiological roles in those tissues. To investigate how PIP₂ affinity affects the response to physiological stimuli such as receptor stimulation, we exposed homomeric and heteromeric Kv7.2, 7.3, and 7.4 channels to a range of concentrations of the muscarinic receptor agonist oxotremorine-M (oxo-M) in a heterologous expression system. Activation of M₁ receptors by oxo-M leads to PIP₂ depletion through G_q and phospholipase C (PLC). Chinese hamster ovary cells were transiently transfected with Kv7 subunits and M₁ receptors and studied under perforated-patch voltage clamp. For Kv7.2/7.3 heteromers, the EC₅₀ for current suppression was 0.44 ± 0.08 µM, and the maximal inhibition (Inhib_max) was 74 ± 3% (n = 5–7). When tonic PIP₂ abundance was increased by overexpression of PIP 5-kinase, the EC₅₀ was shifted threefold to the right (1.2 ± 0.1 µM), but without a significant change in Inhib_max (73 ± 4%, n = 5). To investigate the muscarinic sensitivity of Kv7.3 homomers, we used the A315T pore mutant (Kv7.3^T) that increases whole-cell currents by 30-fold without any change in apparent PIP₂ affinity. Kv7.3^T currents had a slightly right-shifted EC₅₀ as compared with Kv7.2/7.3 heteromers (1.0 ± 0.8 µM) and a strongly reduced Inhib_max (39 ± 3%). In contrast, the dose–response curve of homomeric Kv7.4 channels was shifted considerably to the left (66 ± 8 nM), and Inhib_max was slightly increased (81 ± 6%, n = 3–4). We then studied several Kv7.2 mutants with altered apparent affinities for PIP₂ by coexpressing them with Kv7.3^T subunits to boost current amplitudes. For the lower affinity (Kv7.2 (R463Q)/Kv7.3^T) or higher affinity (Kv7.2 (R463E)/Kv7.3^T) channels, the EC₅₀ and Inhib_max were similar to Kv7.4 or Kv7.3^T homomers (0.12 ± 0.08 µM and 79 ± 6% [n = 3–4] and 0.58 ± 0.07 µM and 27 ± 3% [n = 3–4], respectively). The very low-affinity Kv7.2 (R452E, R459E, and R461E) triple mutant was also coexpressed with Kv7.3^T. The resulting heteromer displayed a very low EC₅₀ for inhibition (32 ± 8 nM) and a slightly increased Inhib_max (83 ± 3%, n = 3–4). We then constructed a cellular model that incorporates PLC activation by oxo-M, PIP₂ hydrolysis, PIP₂ binding to Kv7-channel subunits, and K⁺ current through Kv7 tetramers. We were able to fully reproduce our data and extract a consistent set of PIP₂ affinities.     

Effect of adsorbed cations on phosphorus uptake by excised roots

Pretreatment of excised roots of Hordeum vulgare, Zea mays, and Glycine max with various salt solutions affected their subsequent rate of phosphorus absorption from 2 × 10⁻⁵m KH₂PO₄. The rate of absorption was greatest for roots pretreated with trivalent cations, intermediate with divalent cations and lowest with monovalent cations. It appeared that the pretreatment involved a rapid exchange reaction at the root surface which was reversible. A 1 min pretreatment was effective for more than 20 min. The acceleration of phosphorus uptake by roots produced by polyvalent cations may be due partly or entirely to a greater reduction in the electrical potential at the root surface or within the pores of the negatively charged cell wall by polyvalent cations than by monovalent cations.     

f-Element/crown ether complexes. 16. Synthesis,crystallization and crystal structure of [Dy(OH2)8]Cl3·18-crown-6·4H2O

When crystals of [Dy(OH₂)₇(OHMe)] [DyCl(OH₂)₂(18- crown-6)]₂Cl₇·2H₂O [1] are allowed to warm from 5 °C to ambient temperature (22 °C) under the original solvent mixture (1:3 CH₃OH: CH₃CN), they redissolve and the title complex can be isolated by slow evaporation of the resulting solution. The crystal structure of this complex, [Dy(OH₂)₈]Cl₃·18-crown-₆·4H₂O, has been determined. It crystallizes in the monoclinic space group, P2₁/c, with a = 10.395(1), b = 18.684(1), c = 16.259- (3) Å, β= 102.56(1)°, and D_calc = 1.61 g cm⁻³ for Z = 4. A final conventional R value of 0.041 was obtained by least-squares refinement using 3453 independent observed [F_o⩾5σ(F_o)] reflections. The [Dy(OH₂)₈]³⁺ cations and crown ether molecules are hydrogen bonded in a polymeric chain with the crown molecules separating the cations and a total of seven DyOH₂···O(crown ether) hydrogen bonds. The chains are connected by a hydrogen bonding network consisting of the cations, chloride ions, and uncoordinated water molecules. The geometry of the cation is best described as a bicapped trigonal prism with distortions on the reaction pathway toward dodecahedral symmetry. The two capping atoms average 2.41(1) Å from Dy, the remaining DyO distances average 2.38(2) Å. The 18-crown-6 molecule has the D_3d conformation normally observed except for a distortion of one OCCO unit containing the oxygen atom accepting two hydrogen bonds.     

An improved synthesis, crystal structures, and metallochromism of salts of [Ru(tolyl-terpy)(CN)3]

The previously reported complex [Ru(ttpy)(CN)₃]⁻ [ttpy = 4′(p-tolyl)-2,2′:6′,2″-terpyridine] is conveniently synthesised by reaction of ttpy with Ru(dmso)₄Cl₂ to give [Ru(ttpy)(dmso)Cl₂], which reacts in turn with KCN in aqueous ethanol to afford [Ru(ttpy)(CN)₃]⁻ which was isolated and crystallographically characterised as both its (PPN)⁺ and K⁺ salts. The K⁺ salt contains clusters containing three complex anions and three K⁺ cations connected by end-on and side-on cyanide ligation to the K⁺ ions. The solution speciation behaviour of [Ru(ttpy)(CN)₃]⁻ was investigated with both Zn²⁺ and K⁺ salts in MeCN, a solvent sufficiently non-competitive to allow the added metal cations to associate with the complex anion via the externally-directed cyanide lone pairs. UV-Vis spectroscopic titration of (PPN)[Ru(ttpy)(CN)₃] with Zn(ClO₄)₂ showed a blue shift of 2900 cm⁻¹ in the ¹MLCT absorption manifold due to the ‘metallochromism’ effect; a series of distinct binding events could be discerned corresponding to formation of 4:1, 1:1 and then 1:3 anion:cation adducts, all with high formation constants, as the titration proceeded. In contrast titration of (PPN)[Ru(ttpy)(CN)₃] with the more weakly Lewis-acidic KPF₆ resulted in a much smaller blue-shift of the ¹MLCT absorptions, and the titration data corresponded to formation of 1:1 and then 2:1 cation:anion adducts with weaker stepwise association constants of the order of 10⁴ and then 10³ M⁻¹. Although association of [Ru(ttpy)(CN)₃]⁻ resulted in a blue-shift of the ¹MLCT absorptions, the luminescence was steadily quenched, as raising the ³MLCT level makes radiationless decay via a low-lying ³MC state possible.     

Hexa-coordinated aluminum and gallium cations derived from indazole

trans-Dichloro-tetrakis-(indazole)aluminum(III) tetrachloroaluminate(III) 1 and trans-dichloro-tetrakis-(indazole)gallium(III) tetrachlorogallate(III) 3 were obtained by the asymmetric cleavage of the chloride-bridged dimers [AlCl₃]₂ and [GaCl₃]₂ with two moles of indazole and characterized by NMR, X-ray diffraction, EA and IR. The synthesis of 3[1] was improved (yield 86%) using methylene chloride at room temperature. The addition of THF to a solution of 1/CH₂Cl₂ afforded in good yield complex 2 {[AlCl₂(IndH)₄]⁺[AlCl₄]⁻·4THF}. The crystal structures of these complexes are monoclinic in the space groups P2(1)/n (1), C2/c (2) and P2(1)/n (3). The unit cells of 1-3 contain ion pairs [ECl₂(IndH)₄]⁺ [ECl₄]⁻ (E = Al and Ga) with multiple hydrogen interactions (Cl?H 2.434-2.925 Å, O?H 1.984-2.665 Å, C?H 2.769-2.888 Å). The [ECl₂(IndH)₄]⁺ cations show hexa-coordinated octahedral aluminum and gallium atoms with two chlorine atoms in anti positions and four coplanar nitrogen atoms from the indazole ligands. The [ECl₄]⁻ anions have a tetrahedral coordination geometry around the central atom. In the lattice, the presence of THF molecules simplifies the weak interactions network in 2, so one anion interacts with two [MCl₂(Ind-H)₄]⁺ cations and two THF molecules through Cl?H intermolecular interactions (2.855-2.922 Å) and one [MCl₂(Ind-H)₄]⁺ cation interacts with two cations through ClL₄MCl?H interactions (2.922 Å). Whereas in 1 and 3, six anions interact through Cl?H intermolecular interactions (2.795-2.925 Å) with one [MCl₂(Ind-H)₄]⁺ cation and this latter interacts with other three [MCl₂(Ind-H)₄]⁺ cations through C?H interactions (2.769-2.888 Å). Additionally, every chlorine atom in the [MCl₂(Ind-H)₄]⁺ cationic moieties is bounded by NCH?ClM or NH?ClM intramolecular-tetrafurcated hydrogen bonds (2.434-2.907 Å).     

The kinetics of the reaction of nitrogen dioxide with iron(II)- and iron(III) cytochrome c

The reactions of NO₂ with both oxidized and reduced cytochrome c at pH 7.2 and 7.4, respectively, and with N-acetyltyrosine amide and N-acetyltryptophan amide at pH 7.3 were studied by pulse radiolysis at 23 °C. NO₂ oxidizes N-acetyltyrosine amide and N-acetyltryptophan amide with rate constants of (3.1±0.3)×10⁵ and (1.1±0.1)×10⁶ M⁻¹ s⁻¹, respectively. With iron(III)cytochrome c, the reaction involves only its amino acids, because no changes in the visible spectrum of cytochrome c are observed. The second-order rate constant is (5.8±0.7)×10⁶ M⁻¹ s⁻¹ at pH 7.2. NO₂ oxidizes iron(II)cytochrome c with a second-order rate constant of (6.6±0.5)×10⁷ M⁻¹ s⁻¹ at pH 7.4; formation of iron(III)cytochrome c is quantitative. Based on these rate constants, we propose that the reaction with iron(II)cytochrome c proceeds via a mechanism in which 90% of NO₂ oxidizes the iron center directly—most probably via reaction at the solvent-accessible heme edge—whereas 10% oxidizes the amino acid residues to the corresponding radicals, which, in turn, oxidize iron(II). Iron(II)cytochrome c is also oxidized by peroxynitrite in the presence of CO₂ to iron(III)cytochrome c, with a yield of ~60% relative to peroxynitrite. Our results indicate that, in vivo, NO₂ will attack preferentially the reduced form of cytochrome c; protein damage is expected to be marginal, the consequence of formation of amino acid radicals on iron(III)cytochrome c.     

BEDT-TTF salts of the unsymmetrical [M(tfadt)2] dithiolene complexes (M = Ni, Au; tfadt = S2C2(CN)(CF3))

Two closely related 1:1 salts are obtained upon electrocrystallization of BEDT-TTF (BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene) in the presence of the isosteric [M(tfadt)₂]⁻ dithiolene complexes (tfadt: 1-trifluoromethyl-2-cyano-1,2-dithiolato), which essentially differ by their spin state, S = 0 in [Au(tfadt)₂]⁻, S = 1/2 in [Ni(tfadt)₂]⁻. In both [BEDT-TTF][M(tfadt)₂] salts, the BEDT-TTF radical cations form chains with a strong lateral overlap and strong antiferromagnetic interactions while the paramagnetic anions in the nickel-containing salt [BEDT-TTF][Ni(tfadt)₂] are essentially non-interacting. The structural differences between the nickel and gold complexes are analyzed and discussed.     

Ionic microenvironmental effects on triplex DNA stabilization: Cationic counterion effects on poly(dT)·poly(dA)·poly(dT)

The structure and conformation of nucleic acids are influenced by metal ions, polyamines, and the microenvironment. In poly(purine) · poly(pyrimidine) sequences, triplex DNA formation is facilitated by metal ions, polyamines and other ligands. We studied the effects of mono- and di-valent metal ions, and ammonium salts on the stability of triple- and double-stranded structures formed from poly(dA) and poly(dT) by measuring their respective melting temperatures. In the presence of metal ions, the absorbance versus temperature profile showed two transitions: T_m1 for triplex to duplex and single stranded DNA, and T_m2 for duplex DNA melting to single stranded DNA. Monovalent cations (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺ and ₄NH⁺${{\text{NH}}_4}^{+}$) promoted triplex DNA at concentrations ≥150 mM. T_m1 varied from 49.8 °C in the presence of 150 mM Li⁺ to 30.6 °C in the presence of 150 mM K⁺. ₄NH⁺${{\text{NH}}_4}^{+}$ was very effective in stabilizing triplex DNA and its efficacy decreased with increasing substitution of the hydrogen atoms with methyl, ethyl, propyl and butyl groups. As in the case of monovalent cations, a concentration-dependent increase in T_m1 was observed with divalent ions and triplex DNA stabilization decreased in the order: Mg²⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺. All positively charged cations increased the melting temperature of duplex DNA. Values of Δn (number of ions released) on triplex DNA melting were 0.46 ± 0.06 and 0.18 ± 0.02, respectively, for mono- and di-valent cations, as calculated from 1/T_m1 versus ln[M^+,2+] plots. The corresponding values for duplex DNA were 0.25 ± 0.02 and 0.12 ± 0.02, respectively, for mono- and di-valent cations. Circular dichroism spectroscopic studies showed distinct conformational changes in triplex DNA stabilized by alkali metal and ammonium ions. Our results might be useful in developing triplex forming oligonucleotide based gene silencing techniques.     

Purification and properties of ginger chlorotic fleck virus

A previously undescribed isometric virus, named ginger chlorotic fleck virus (GCFV), was detected in ginger (Zingiber officinale) imported into Australia from a number of countries. The geographical distribution of the virus is uncertain, but is thought to include India, Malaysia and Mauritius. The virus apparently does not occur in Australian commercial ginger plantings. The virus has isometric particles c. 30 nm in diameter, with a sedimentation coefficient of 111 S, and was readily purified from infected ginger with yields of 50–90 mg/kg leaf tissue. Purified preparations contained a major species of single-stranded RNA of mol. wt 1.50 × 10⁶ and a major coat protein species of mol. wt 29.0 × 10³. At pH 7, the particles formed a single zone in both caesium chloride and caesium sulphate gradients, with buoyant densities of 1.355 g cm^-3 (fixed virus) and 1. 297 g cm^-3 (unfixed virus), respectively. The virus particles migrated as two electrophoretic components and were labile when treated with 10 mM EDTA, 1 M NaCI, 10 mM tris pH 8.25 or when negatively stained with potassium phosphotungstate. GCFV was mechanically transmitted only to ginger, and was not transmitted by the aphids Myzus persicae. Pentalonia nigronervosa, Rhopalosiphum maidis or R. padi. Possible affinities of GCFV with the sobemo-virus group are discussed. The present cryptogram of GCFV is ^R/_l: ^1.5/₂₀: ^S/_S: ^S/_*.