The pH-specific synthesis,spectroscopic, structural,and magnetic properties of a new Ni(II) species containing the plant physiological binder d-(−)-quinic acid: Association with the aqueous speciation of the binary Ni(II)–quinate system

Nickel is an element present in the abiotic and biological world. In its capacity to promote chemistry at the cellular level, Ni(II) interacts with physiological ligands, thus influencing physiological or pathological conditions. Efforts to comprehend the underlying chemistries led to the investigation of Ni(II) reactivity toward the physiological d-(−)-quinic acid, under pH-specific conditions, facilitating the isolation of a new species Na[Ni(C₇H₁₁O₆)₃] · 2.75H₂O (1). Compound 1 was characterized by elemental analysis, spectroscopic techniques (FT-IR, UV–Visible), magnetic susceptibility studies, and X-ray crystallography. The lattice of 1 reveals the presence of an octahedral Ni(II) complex bound to three quinate ligands through the α-hydroxycarboxylate group, thus projecting a stable entity. Concurrent aqueous speciation studies on the Ni(II)–quinate binary system unravel the nature and properties of species arising from Ni(II)–quinate interactions. To this end, the structural and spectroscopic properties of 1, in the solid state and in solution, are in line with the aqueous speciation, exemplifying key features of Ni(II) interactions with the low molecular mass quinic acid in biologically relevant fluids. The overall physicochemical profile of 1 projects well-defined soluble and potentially bioavailable Ni(II) species that could be involved in specific chemical processes and (bio)chemical reactivity patterns at the physiological or molecular toxicity level.     

Active Thermochemical Tables: accurate enthalpy of formation of hydroperoxyl radical, HO2

Through the use of the Active Thermochemical Tables approach, the best currently available enthalpy of formation of HO2 has been obtained as delta(f)H(o)298 (HO2) = 2.94 +/- 0.06 kcal mol(-1) (3.64 +/- 0.06 kcal mol(-1) at 0 K). The related enthalpy of formation of the positive ion, HO2+, within the stationary electron convention is delta(f)H(o)298 (HO2+) = 264.71 +/- 0.14 kcal mol(-1) (265.41 +/- 0.14 kcal mol(-1) at 0 K), while that for the negative ion, HO2- (within the same convention), is delta(f)H(o)298 (HO2-) = -21.86 +/- 0.11 kcal mol(-1) (-21.22 +/- 0.11 kcal mol(-1) at 0 K). The related proton affinity of molecular oxygen is PA298(O2) = 100.98 +/- 0.14 kcal mol(-1) (99.81 +/- 0.14 kcal mol(-1) at 0 K), while the gas-phase acidity of H2O2 is delta(acid)G(o)298 (H2O2) = 369.08 +/- 0.11 kcal mol(-1), with the corresponding enthalpy of deprotonation of H2O2 of delta(acid)H(o)298 (H2O2) = 376.27 +/- 0.11 kcal mol(-1) (375.02 +/- 0.11 kcal mol(-1) at 0 K). In addition, a further improved enthalpy of formation of OH is briefly outlined, delta(f)H(o)298 (OH) = 8.93 +/- 0.03 kcal mol(-1) (8.87 +/- 0.03 kcal mol(-1) at 0 K), together with new and more accurate enthalpies of formation of NO, delta(f)H(o)298 (NO) = 21.76 +/- 0.02 kcal mol(-1) (21.64 +/- 0.02 kcal mol(-1) at 0 K) and NO2, delta(f)H(o)298 (NO2) = 8.12 +/- 0.02 kcal mol(-1) (8.79 +/- 0.02 kcal mol(-1) at 0 K), as well as H(2)O(2) in the gas phase, delta(f)H(o)298 (H2O2) = -32.45 +/- 0.04 kcal mol(-1) (-31.01 +/- 0.04 kcal mol(-1) at 0 K). The new thermochemistry of HO2, together with other arguments given in the present work, suggests that the previous equilibrium constant for NO + HO2 --> OH + NO2 was underestimated by a factor of approximately 2, implicating that the OH + NO2 rate was overestimated by the same factor. This point is experimentally explored in the companion paper of Srinivasan et al. (next paper in this issue).     

Development of an inorganic cations retention model in ion chromatography by means of artificial neural networks with different two-phase training algorithms

This paper describes development of artificial neural network (ANN) retention model, which can be used for method development in variety of ion chromatographic applications. By using developed retention model it is possible both to improve performance characteristic of developed method and to speed up new method development by reducing unnecessary experimentation. Multilayered feed forward neural network has been used to model retention behaviour of void peak, lithium, sodium, ammonium, potassium, magnesium, calcium, strontium and barium in relation with the eluent flow rate and concentration of methasulphonic acid (MSA) in eluent. The probability of finding the global minimum and fast convergence at the same time were enhanced by applying a two-phase training procedure. The developed two-phase training procedure consists of both first and second order training. Several training algorithms were applied and compared, namely: back propagation (BP), delta-bar-delta, quick propagation, conjugate gradient, quasi Newton and Levenberg-Marquardt. It is shown that the optimized two-phase training procedure enables fast convergence and avoids problems arisen from the fact that every new weight initialization can be regarded as a new starting position and yield irreproducible neural network if only second order training is applied. Activation function, number of hidden layer neurons and number of experimental data points used for training set were optimized in order to insure good predictive ability with respect to speeding up retention modelling procedure by reducing unnecessary experimental work. The predictive ability of optimized neural networks retention model was tested by using several statistical tests. This study shows that developed artificial neural network are very accurate and fast retention modelling tool applied to model varied inherent non-linear relationship of retention behaviour with respect to mobile phase parameters.     

Lanthanide Contraction within a Series of Asymmetric Dinuclear [Ln2] Complexes

A complete isostructural series of dinuclear asymmetric lanthanide complexes has been synthesized by using the ligand 6‐[3‐oxo‐3‐(2‐hydroxyphenyl)propionyl]pyridine‐2‐carboxylic acid (H₃ L ). All complexes have the formula [Ln₂(H L )₂(H₂ L )(NO₃)(py)(H₂O)] (Ln=La ( 1 ), Ce ( 2 ), Pr ( 3 ), Nd ( 4 ), Sm ( 5 ), Eu ( 6 ), Gd ( 7 ), Tb ( 8 ), Dy ( 9 ), Ho ( 10 ), Er ( 11 ), Tm ( 12 ), Yb ( 13 ), Lu ( 14 ), Y ( 15 ); py=pyridine). Complexes of La to Yb and Y have been crystallographically characterized to reveal that the two metal ions are encapsulated within two distinct coordination environments of differing size. Whereas one site maintains the coordination number (nine) through the whole series, the other one increases from nine to ten owing to a change in the coordination mode of an NO₃^? ligand. This series offers a unique opportunity to study in detail the lanthanide contraction within complexes of more than one metal. This analysis shows that various representative parameters proportional to this contraction follow a quadratic decay as a function of the number n of f electrons. Slater’s model for the atomic radii has been used to extract, from these decays, the shielding constant of 4f electrons. The average of O???O distances within the coordination polyhedra shared by both metals and of the Ln???Ln separations follow also a quadratic decay, therefore showing that such dependence holds also for parameters that receive the contribution of two lanthanide ions simultaneously. The magnetic behavior has been studied for all nondiamagnetic complexes. It reveals the effect of the spin–orbit coupling and a weak antiferromagnetic interaction between both metals. Photoluminescent studies of all the complexes in the series reveal a single broad emission band in the visible region, which is related to the coordinated ligand. On the other hand, the Nd, Er, and Yb complexes show features in the near‐IR region due to metal‐based transitions.     

NMR Spectral Data of Benzofurans and Bithiophenes from Hairy Root Cultures of Tagetes Patula Andthe Molecular Structure of Isoeuparin

In the course of our biosynthetic studies of constituents of hairy root cultures of Tagetes patula, we isolated four bithiophenes,[5-(3-buten-1-yny1)]-2,2′-bithiophenes(BBT),5-(4-acetoxy-1-butyny1)-2,2′-bithiophenes (BBTOAc),5-(4-hydroxy-1-butyny1)-2,2′bithiophenes (BBTOH) and 5-(3,4-diacetoxy-1-butyny1)-2,2′-bithiophenes [BBT(OAc)2]. In addition, stigmasterol, α-farnesene, three known benzofurans, of which only one was previouly isolated from T.patula, as well as a new benzofuran were obtained. The structures of the componds were determined by spectral analysis and comparison with published data. The molecular structure of the benzofuran isoeuparin was established by single crystal x-ray diffraction.     

HF molecules and poly(hydrogen fluoride) anions as ligands to metal centers

The paper is dealing with the two sets of the coordination compounds:

• (a) 

  the coordination compounds in which anhydrous HF is acting as a ligand to the metal ions

• (b) 

  the compounds in which poly(hydrogen–fluoride) anions of the type HnFn+1− (n = 1, 2, 3) are coordinated to the metal centers and connecting them in the 3D structures.

The main purpose of this work is the review of the above mentioned compounds which were recently isolated in our laboratory. The coordination of the metal centers and their connection in the three-dimensional network are illustrated with their crystal structures. A very brief review of the achievements of some other groups is also mentioned where it is appropriate.