Low temperature heat capacity of the coordination compound: Nickel(II) nitrate with 4-amine-1,2,4-triazole at temperatures from 11 to 317 K

Low-temperature heat capacity of the coordination compound of nickel(II) nitrate with 4-amine-1,2,4-triazole was measured in the temperature range from 11 to 317 K using a computerized vacuum adiabatic calorimeter. The thermodynamic functions have been derived from the smoothed experimental data over the whole temperature interval covered and at standard conditions. At 298.15 K, the heat capacity is 574.7±1.2 J K^-1 mol^-1, the entropy is 599.2±1.2 J K^-1 mol^-1, the enthalpy is 91070±200 J mol^-1, and the reduced Gibbs energy is 293.7±1.2 J K^-1 mol^-1. The results on C_p(T) were compared with those for Cu(NH₂trz)₃(NO₃)₂·0.5H₂O. It was revealed that the slope of the curve dC_p/dT (T) changes essentially for both compounds at 110-120 K. It implies that additional degrees of freedom appear in the heat capacity at these temperatures.This revised version was published online in November 2005 with corrections to the Cover Date.     

Conformational fluxionality in a palladium(II) complex of flexible click chelator 4-phenyl-1-(2-picolyl)-1,2,3-triazole: A dynamic NMR and DFT study

An experimental and theoretical DFT study was carried out on the solution behavior in [D₇]DMF for bis-chelate complex [Pd(L)₂](BF₄)₂·2CH₃CN (L = 4-phenyl-1-(2-picolyl)-1,2,3-triazole). In structure of [Pd(L)₂]²⁺, the central square-planar palladium(II) cation is trans-chelated by two L substrates, each through the pyridine and the triazole N2 nitrogen atoms, forming two six-membered metallacycles. These can adopt boat-like conformations anti-trans-[Pd(L)₂]²⁺ and syn-trans-[Pd(L)₂]²⁺ in which the picolyl methylene carbons are anti or syn, respectively, relative to the palladium coordination plane. In solution, the boat-to-boat inversion at both metallacycles takes place. The conformers are in a dynamic equilibrium, which was monitored by variable-temperature (VT) ¹H NMR spectroscopy in the temperature range of 223-353 K. The equilibrium lies on the side of the anti-trans-[Pd(L)₂]²⁺ conformer and the corresponding reaction enthalpy and entropy is estimated to be 0.6 ± 0.5 kcal mol⁻¹ and 0.8 ± 1 cal mol⁻¹ K⁻¹, respectively. From the full-line-shape analysis of resonances in the VT ¹H NMR spectra, the activation enthalpy and activation entropy was determined to be 13.0 ± 0.4 kcal mol⁻¹ and 2.7 ± 1.6 cal mol⁻¹ K⁻¹, respectively. The activation entropy close to zero suggests a nondissociative mechanism for the isomerisation. DFT investigation revealed that the isomerisation proceeds through a one step mechanism with a barrier of 11.40 kcal mol⁻¹. The structures of the syn and anti conformers as well as that of the transition state were characterized. Energy decomposition analysis was carried out in order to explore the origins of the stability difference between the syn and anti isomers.     

Complexation of tetrandrine with calcium ion probed by various spectroscopic methods and molecular modeling

The formation of the complex between tetrandrine and the calcium ion, in solution, was studied using FTIR, UV-Vis, ¹H NMR, ¹³C NMR and electrospray mass spectroscopy spectroscopic methods and molecular modeling. The calcium salts used were: Ca(ClO₄)₂·4H₂O and Ca(Picrate)₂ in the solvents: acetonitrile (CH₃CN), deuterated acetonitrile (CD₃CN) and tetrahydrofurane (THF). The determined complex stability constant was: 20277±67 dm³ mol⁻¹ and corresponding free energy ΔG₀=−5.820±0.002 kcal mol⁻¹. The molecular simulation of the complex formation with the MM3 Augmented force field integrated in CAChe provided useful data about its energy. Combining the experimental results and molecular modeling we propose a model for the structure of tetrandrine-Ca complex with an eight coordinated geometry.     

Simultaneous determination of Mn(II), Cu(II) and Fe(III) as 2-(5′-bromo-2′-pyridylazo)-5-diethylaminophenol complexes by adsorptive cathodic stripping voltammetry at a carbon paste electrode

A simple and precise square-wave adsorptive cathodic stripping voltammetry (SW-AdCSV) method has been described for simultaneous determination of Mn(II), Cu(II) and Fe(III) in water samples using a carbon paste electrode. In 0.1 mol L⁻¹ acetate buffer (pH 5) containing 50 μmol L⁻¹ of 2-(5′-bromo-2′-pyridylazo)-5-diethylaminophenol (5-Br-PADAP), Mn(II), Cu(II) and Fe(III) were simultaneously determined as metal-complexes with 5-Br-PADAP following preconcentration onto the carbon paste electrode by adsorptive accumulation at +1.0 V (vs. Ag/AgCl/3 M KCl). Insignificant interference from various cations (K⁺, Na⁺, Mg²⁺, Ca²⁺, Al³⁺, Bi³⁺, Sb³⁺, Se⁴⁺, Zn²⁺, Ni²⁺, Co²⁺, Cd²⁺, Pb²⁺, V⁵⁺, Ti⁴⁺ and NH₄⁺), anions (HCO₃⁻, Cl⁻, NO³⁻, SO₄²⁻ and PO₄³⁻) and ascorbic acid was noticed. Limits of detection of 0.066, 0.108 and 0.093 μg L⁻¹ and limits of quantitation of 0.22, 0.36 and 0.31 μg L⁻¹ Mn(II), Cu(II) and Fe(III), respectively, were achieved by the described method. The described stripping voltammetry method was successfully applied for simultaneous determination of Mn(II), Cu(II) and Fe(III) in ground, tap and bottled natural water samples.     

Thermodynamic properties of BaCeO3 and BaZrO3 at low temperatures

Specific heat capacities (C_p) of polycrystalline samples of BaCeO₃ and BaZrO₃ have been measured from about 1.6 K up to room temperature by means of adiabatic calorimetry. We provide corrected experimental data for the heat capacity of BaCeO₃ in the range T < 10 K and, for the first time, contribute experimental data below 53 K for BaZrO₃. Applying Debye's T³-law for T → 0 K, thermodynamic functions as molar entropy and enthalpy are derived by integration. We obtain C_p = 114.8 (±1.0) J mol⁻¹ K⁻¹, S° = 145.8 (±0.7) J mol⁻¹ K⁻¹ for BaCeO₃ and C_p = 107.0 (±1.0) J mol⁻¹ K⁻¹, S° = 125.5 (±0.6) J mol⁻¹ K⁻¹ for BaZrO₃ at 298.15 K. These results are in overall agreement with previously reported studies but slightly deviating, in both cases. Evaluations of C_p(T) yield Debye temperatures and identify deviations from the simple Debye-theory due to extra vibrational modes as well as anharmonicity. The anharmonicity turns out to be more pronounced at elevated temperatures for BaCeO₃. The characteristic Debye temperatures determined at T = 0 K are Θ₀ = 365 (±6) K for BaCeO₃ and Θ₀ = 402 (±9) K for BaZrO₃.     

Combined cation-exchange and extraction chromatographic method of pre-concentration and concomitant separation of Cu(II) with high molecular mass liquid cation exchanger after its online detection

A selective method has been developed for the extraction chromatographic trace level separation of Cu(II) with Versatic 10 (liquid cation exchanger) coated on silanised silica gel (SSG-V10). Cu(II) has been extracted from 0.1 M acetate buffer at the range of pH 4.0–5.5. The effects of foreign ions, pH, flow-rate, stripping agents on extraction and elution have been investigated. Exchange capacity of the prepared exchanger at different temperatures with respect to Cu(II) has been determined. The extraction equilibrium constant (K_ex) and different standard thermodynamic parameters have also been calculated by temperature variation method. Positive value of ΔH (7.98 kJ mol⁻¹) and ΔS (0.1916 kJ mol⁻¹) and negative value of ΔG (−49.16 kJ mol⁻¹) indicated that the process was endothermic, entropy gaining and spontaneous. Preconcentration factor was optimized at 74.7 ± 0.2 and the desorption constants K_desorption¹(1.4 × 10⁻²) and K_desorption²(9.8 × 10⁻²) were determined. The effect of pH on R_f values in ion exchange paper chromatography has been investigated. In order to investigate the sorption isotherm, two equilibrium models, the Freundlich and Langmuir isotherms, were analyzed. Cu(II) has been separated from synthetic binary and multi-component mixtures containing various metal ions associated with it in ores and alloy samples. The method effectively permits sequential separation of Cu(II) from synthetic quaternary mixture containing its congeners Bi(III), Sn(II), Hg(II) and Cu(II), Cd(II), Pb(II) of same analytical group. The method was found effective for the selective detection, removal and recovery of Cu(II) from industrial waste and standard alloy samples following its preconcentration on the column. A plausible mechanism for the extraction of Cu(II) has been suggested.     

Tetramidocavitand: strong anion receptor by well-organized four -(CO)N-H?X interactions

Resorcin[4]arene-based tetramidocavitands containing four secondary amide groups on their upper rim showed strong (R = methyl or ethyl) binding properties. The caviplex formation through hydrogen bonds of -(CO)N-H?X⁻ was supported by ¹H NMR and crystal structure analyses. In a mixture of C₂D₂Cl₄/DMSO/D₂O = 5:15:2 at 25 °C, the thermodynamic parameters for caviplex @1, ΔG (kcal mol⁻¹), ΔH (kcal mol⁻¹), and ΔS (cal K⁻¹ mol⁻¹), are −3.7, −8.6, and −16.7, respectively.     

Heat capacity, enthalpy and entropy of ternary bismuth tantalum oxides

Heat capacity and enthalpy increments of ternary bismuth tantalum oxides Bi₄Ta₂O₁₁, Bi₇Ta₃O₁₈ and Bi₃TaO₇ were measured by the relaxation time method (2-280 K), DSC (265-353 K) and drop calorimetry (622-1322 K). Temperature dependencies of the molar heat capacity in the form C_pm=445.8+0.005451T−7.489×10⁶/T² J K⁻¹ mol⁻¹, C_pm=699.0+0.05276T−9.956×10⁶/T² J K⁻¹ mol⁻¹ and C_pm=251.6+0.06705T−3.237×10⁶/T² J K⁻¹ mol⁻¹ for Bi₃TaO₇, Bi₄Ta₂O₁₁ and for Bi₇Ta₃O₁₈, respectively, were derived by the least-squares method from the experimental data. The molar entropies at 298.15 K, S°_m(298.15 K)=449.6±2.3 J K⁻¹ mol⁻¹ for Bi₄Ta₂O₁₁, S°_m(298.15 K)=743.0±3.8 J K⁻¹ mol⁻¹ for Bi₇Ta₃O₁₈ and S°_m(298.15 K)=304.3±1.6 J K⁻¹ mol⁻¹ for Bi₃TaO₇, were evaluated from the low-temperature heat capacity measurements.     

Heat capacity at constant pressure and thermodynamic properties of phase transitions in PbMO<Subscript>3</Subscript> (<Emphasis Type="Italic">M</Emphasis>=Ti,Zr and Hf)

The heat capacity of PbMO₃ (M=Ti, Zr and Hf) at constant pressure was measured using a differential scanning calorimeter (DSC) from room temperature up to 870 K. Large anomalies were found in the heat capacity curves, corresponding to the ferroelectricparaelectric phase transition in PbTiO₃ (PT), the antiferroelectric-paraelectric phase transitions in PbZrO₃ (PZ) and PbHfO₃ (PH). The transition entropies were estimated as 7.3 J K⁻¹ mol⁻¹ (PT), 9.9 J K⁻¹ mol⁻¹ (PZ) and 9.3 J K⁻¹ mol⁻¹ (PH). These values of transition entropies are much larger than that of a typical displacive-type phase transition.     

Study of the binding equilibrium between Zn(II) and HSA by capillary electrophoresis-inductively coupled plasma optical emission spectrometry

A new method has been developed for following the interaction between zinc ion and human serum albumin (HSA) by capillary electrophoresis-inductively coupled plasma optical emission spectrometry. Under optimized experimental conditions, the detection limit (3σ) for free Zn²⁺ ion was found to be 1.34 μM by running 11 replicates of the reagent blank. The RSD was less than 3% and the recovery was more than 98.13%. The linear range of zinc ion concentration was between 5.1 μM and 0.3 M. The measured Zn(II)-HSA combination values of n₁ and K₁ for primary binding of Zn²⁺ to HSA were 1.09 and 2.29 × 10⁵ L mol⁻¹, respectively. The measured values of n₂ and K₂ for the non-specific binding of Zn²⁺ to HSA were 8.96 and 6.65 × 10³ L mol⁻¹, respectively. This new method allows rapid analysis of a small amount of sample, simple operation, while avoiding long periods of dialysis and eliminating interference from other metal ions. This method provides a reliable and convenient new way for studying interactions between metal ions and biomolecules.     

Spectroscopic study of protonation of oligonucleotides containing adenine and cytosine

Acidobasic properties of purine and pyrimidine bases (adenine, cytosine) and relevant nucleosides (adenosine, cytidine) were studied by means of glass-electrode potentiometry and the respective dissociation constants were determined under given experimental conditions (I = 0.1 M (NaCl), t = (25.0 ± 0.1) °C): adenine (pK _HL = 9.65 ± 0.04, pK _H2L = 4.18 ± 0.04), adenosine (pK _H2L = 3.59 ± 0.05), cytosine (pK _H2L = 4.56 ± 0.01), cytidine (pK _H2L = 4.16 ± 0.02). In addition, thermodynamic parameters for bases: adenine (ΔH ⁰ = (−17 ± 4) kJ mol⁻¹, ΔS ⁰ = (23 ± 13) J K⁻¹ mol⁻¹), cytosine (ΔH ⁰ = (−22 ± 1) kJ mol⁻¹, ΔS ⁰ = (13 ± 5) J K⁻¹ mol⁻¹) were calculated. Acidobasic behavior of oligonucleotides (5′CAC-CAC-CAC3′ = (CAC)₃, 5′AAA-CCC-CCC3′ = A₃C₆, 5′CCC-AAA-CCC3′ = C₃A₃C₃) was studied under the same experimental conditions by molecular absorption spectroscopy. pH-dependent spectral datasets were analyzed by means of advanced chemometric techniques (EFA, MCR-ALS) and the presence of hemiprotonated species concerning (C⁺-C) a non-canonical pair (i-motif) in titled oligonucleotides was proposed in order to explain experimental data obtained according to literature.     

Synthesis of some fluorine-containing pyridinealdoximes of potential use for the treatment of organophosphorus nerve-agent poisoning

Fluoroheterocyclic aldoximes were screened as therapeutic agents for the treatment of anticholinesterase poisoning. 2-Fluoropyridine-3- and -6-aldoxime, and 3-fluoropyridine-2- and -4-aldoxime, were synthesised. Attempts to obtain 3,5,6-trifluoropyridine-2,4-bis(aldoxime) and -2-aldoxime, however, proved unsuccessful. Pentafluorobenzaldoxime was prepared by oximation of pentafluorobenzaldehyde. Acid dissociation constants (pK_a) and second-order rate constants (k_ox−) of the fluorinated pyridinealdoximes towards sarin were measured. 2,3,5,6-Tetrafluoropyridine-4-aldoxime had the best profile: its k_ox− approached that of the therapeutic oxime P2S (310 vs. 120 l mol⁻¹ min⁻¹), but its higher pK_a (9.1 vs. 7.8) fell short of the target figure of 8 required for reactivation of inhibited acetylcholinesterase in vivo. N-alkylation of the fluorinated pyridine-aldoximes may reduce their pK_a nearer to 8 and enhance their therapeutic potential.     

Heat capacities and absolute entropies of UTi<Subscript>2</Subscript>O<Subscript>6</Subscript> and CeTi<Subscript>2</Subscript>O<Subscript>6</Subscript>

Summary As part of a larger study of the physical properties of potential ceramic hosts for nuclear wastes, we report the molar heat capacity of brannerite (UTi₂O₆) and its cerium analog (CeTi₂O₆) from 10 to 400 K using an adiabatic calorimeter. At 298.15 K the standard molar heat capacities are (179.46±0.18) J K^-1 mol^-1 for UTi₂O₆ and (172.78±0.17) J K^-1 mol^-1 for CeTi₂O₆. Entropies were calculated from smooth fits of the experimental data and were found to be (175.56±0.35) J K^-1 mol^-1 and (171.63±0.34) J K^-1 mol^-1 for UTi₂O₆ and CeTi₂O₆, respectively. Using these entropies and enthalpy of formation data reported in the literature, Gibb’s free energies of formation from the elements and constituent oxides were calculated. Standard free energies of formation from the elements are (-2814.7±5.6) kJ mol^-1 for UTi₂O₆ and (-2786.3±5.6) kJ mol^-1 for CeTi₂O₆. The free energy of formation from the oxides at T=298.15 K are (-5.31±0.01) kJ mol^-1 and (15.88±0.03) kJ mol^-1 for UTi₂O₆ and CeTi₂O₆, respectively.     

Thermodynamic properties of hydrated sodium l-threonate Na(C4H7O5)·H2O(s)

Low-temperature heat capacities of the compound Na(C₄H₇O₅)·H₂O(s) have been measured with an automated adiabatic calorimeter. A solid-solid phase transition and dehydration occur at 290-318 K and 367-373 K, respectively. The enthalpy and entropy of the solid-solid transition are Δ_transH_m = (5.75 ± 0.01) kJ mol⁻¹ and Δ_transS_m = (18.47 ± 0.02) J K⁻¹ mol⁻¹. The enthalpy and entropy of the dehydration are Δ_dH_m = (15.35 ± 0.03) kJ mol⁻¹ and Δ_dS_m = (41.35 ± 0.08) J K⁻¹ mol⁻¹. Experimental values of heat capacities for the solids (I and II) and the solid-liquid mixture (III) have been fitted to polynomial equations.     

Heat capacity, enthalpy and entropy of bismuth niobate and bismuth tantalate

The heat capacity and the heat content of bismuth niobate BiNbO₄ and bismuth tantalate BiTaO₄ were measured by the relaxation method and Calvet-type heat flux calorimetry. The temperature dependencies of the heat capacities in the form C_pm=128.628+0.03340 T−1991055/T²+136273131/T³ (J K^-1 mol^-1) and 133.594+0.02539 T−2734386/T²+235597393/T³ (J K^-1 mol^-1) were derived for BiNbO₄ and BiTaO₄, respectively, by the least-squares method from the experimental data. Furthermore, the standard molar entropies at 298.15 K S_m(BiNbO₄)=147.86 J K^-1 mol^-1 and S_m(BiTaO₄)=149.11 J K^-1 mol^-1 were assessed from the low temperature heat capacity measurements. To complete a set of thermodynamic data of these mixed oxides an attempt was made to estimate the values of the heat of formation from the constituent binary oxides.     

A calorimetric contribution to the study of polymorphism in tetramethylammonium chloride

The heat capacity of tetramethylammonium chloride has been measured from 115 to 498 K, both for the thermodynamically stable modifications and for the form II, which is metastable below 407 K. The entropy gains at the IV → III λ-transition and at the III → II first-order transition are estimated to be 1.19 J K⁻¹ mol⁻¹ and 4.16 J K⁻¹ mol⁻¹, respectively. At 125 K, the entropy of the metastable phase II exceeds that of the stable modification IV by only 1.76 J K⁻¹ mol⁻¹. If, as has been suggested, each cation in phase II has two possible orientations, it would seem that at 125 K this disorder in phase II is largely, if not wholly, suppressed, without the appearance of any transition or thermal anomaly.Results are also recorded of test measurements of the heat capacity of the NBS sample of synthetic sapphire (α-Al₂O₃) from 138 to 515 K.     

Reflections on the journey: six short stories

The low-temperature heat capacities of nickel titanate (NiTiO₃), cobalt titanate (CoTiO₃), and cobalt carbonate (CoCO₃) were measured between 2 and 300 K, and thermochemical functions were derived from the results. Our new data show previously unknown low-temperature lambda-shaped heat capacity anomalies peaking at 37 K for CoTiO₃ and 26 K for NiTiO₃. From our data we calculate standard molar entropies (298.15 K) for NiTiO₃ of 90.9 ± 0.7 J mol^-1 K^-1 and for CoTiO₃ of 94.4 ± 0.8 J mol^-1 K^-1. For CoCO₃, we find only a small broad heat capacity anomaly, peaking at about 31 K. From our data, we suggest a new standard entropy (298.15 K) for CoCO₃ of 88.9 ± 0.7 J mol^-1 K^-1.     

Heat capacity and thermodynamic functions of LuPO4 in the range 0-320 K

The heat capacity of LuPO₄ was measured in the temperature range 6.51-318.03 K. Smoothed experimental values of the heat capacity were used to calculate the entropy, enthalpy and Gibbs free energy from 0 to 320 K. Under standard conditions these thermodynamic values are: (298.15 K) = 100.0 ± 0.1 J K⁻¹ mol⁻¹, S⁰(298.15 K) = 99.74 ± 0.32 J K⁻¹ mol⁻¹, H⁰(298.15 K) − H⁰(0) = 16.43 ± 0.02 kJ mol⁻¹, −[G⁰(298.15 K) − H⁰(0)]/T = 44.62 ± 0.33 J K⁻¹ mol⁻¹. The standard Gibbs free energy of formation of LuPO₄ from elements Δ_fG⁰(298.15 K) = −1835.4 ± 4.2 kJ mol⁻¹ was calculated based on obtained and literature data.     

Heat-capacity measurements and thermodynamic functions of crystalline adenine; revised thermodynamic properties of aqueous adenine

The standard molar heat capacity C^°_p,m of adenine(cr) has been measured using adiabatic calorimetry over the range 6<(T/K)<310 and the results used to derive thermodynamic functions for adenine(cr) at smoothed temperatures. At T=298.15 K, C^°_p,m=(142.67±0.29) J · K⁻¹ · mol⁻¹ and the third law entropy S^°_m=(145.62±0.29) J · K⁻¹ · mol⁻¹. The standard molar Gibbs free energy of formation Δ_fG^°_m at T=298.15 K for crystalline adenine was calculated, using the standard molar enthalpy of formation for the compound and entropies of the elements from the literature, and found to be Δ_fG^°_m=(301.4±1.0) kJ · mol⁻¹. The results were combined with solution calorimetry and solubility measurements from the literature to yield revised values for the standard molar thermodynamic properties of aqueous adenine at T=298.15 K: Δ_fG^°_m=(313.4±1.0) kJ · mol⁻¹, Δ_fH^°_m=(129.5±1.4) kJ · mol⁻¹, and S_m^°=(217.68±0.44) J · K⁻¹ · mol⁻¹.     

Synthesis, heat capacity and enthalpy of formation of [Ho2(l-Glu)2(H2O)8](ClO4)4·H2O

A complex of holmium perchlorate coordinated with l-glutamic acid, [Ho₂(l-Glu)₂(H₂O)₈](ClO₄)₄·H₂O, was prepared with a purity of 98.96%. The compound was characterized by chemical, elemental and thermal analysis. Heat capacities of the compound were determined by automated adiabatic calorimetry from 78 to 370 K. The dehydration temperature is 350 K. The dehydration enthalpy and entropy are 16.34 kJ mol⁻¹ and 16.67 J K⁻¹ mol⁻¹, respectively. The standard enthalpy of formation is −6474.6 kJ mol⁻¹ from reaction calorimetry at 298.15 K.