A Preliminary Investigation of the Solution Complexation of 4-Sulphonic calix[n]arenes with Testosterone

The complexation between water soluble calixarenes and testosterone has been studied. Stability constants of the host guest complexes of 4-sulphonic calix[n]arenes (n = 4, 6 and 8) with testosterone in water and buffers (pH 5.8, 7.3 and 10.0) were determined from phase solubility curves. These solubility curves indicated that the complexes were all of the A_L type. The constants were in the range 26–341 M^-1, dependent on the size of the calixarene and the pH of the solutions.     

Sorption of radiocobalt(II) onto Ca-montmorillonite: effect of contact time, solid content, pH, ionic strength and temperature

In this paper, the sorption of Co(II) from aqueous solution to Ca-montmorillonite was studied under ambient conditions by using batch technique. The effects of contact time, solid content, pH, ionic strength and temperature on the sorption of Co(II) to Ca-montmorillonite was also investigated. The results indicated that the sorption of Co(II) was strongly dependent on pH values. The sorption was dependent on ionic strength at low pH values, but independent of ionic strength at high pH values. Outer-sphere surface complexes were formed on the surface of Ca-montmorillonite at low pH values, whereas inner-sphere surface complexes were formed at high pH values. The Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were used to simulate the sorption isotherms of Co(II) at three different temperatures. The thermodynamic parameters (ΔH ⁰, ΔS ⁰ and ΔG ⁰) were calculated from the temperature dependent sorption isotherms, and the results indicated that the sorption reaction of Co(II) to Ca-montmorillonite was an endothermic and spontaneous process. The high sorption capacity of Co(II) on Ca-montmorillonite suggests that the Ca-montmorillonite is a suitable material for the preconcentration and solidification of radiocobalt from aqueous solutions.     

Photophysics and Acid‐Base Chemistry of Re(CH3bpyCOOH)(CO)3X (X=Cl−, and Imidazole) Complexes

Rheniumtricarbonyl(4′‐methyl‐2,2′‐bipyridine‐4‐carboxylic acid)X (where X is Cl^? and imidazole) complexes have been prepared. These two complexes exhibit similar spectroscopic properties. The metal‐ to‐ligand charge‐transfer (MLCT) absorption and the corresponding emission are observed. This charge transfer band is highly solvent dependent. Due to the stronger electron‐withdrawing ability of the ‐COOH (in comparison to the ‐COO^? group), the MLCT band has red‐shifted during protonation. Emission quantum yields are dramatically reduced while life time remains similar upon protonation. These behaviors are typical in static quenching mechanism by protons. The ground state pK_a of Re(CO)₃ (CH₃bpyCOOH)Cl obtained from the pH titration curve of the complex absorption at 409 nm was 2.5.     

Fluorescence Sensitization of Aqueous Terbium and Europium Ions Without Aromatic Donors or Synergistic Agents

Abstract

EDTA and DTPA complexes of terbium and europium are excited at wavelengths below 250 nm. producing the typical lanthanide emission through energy transfer from the complex to the coordinated metal. This allows determination of these rare earth ions in water without solvent extraction, the use of synergistic agents, or aromatic sensitizers. Terbium-EDTA has the most efficient energy transfer, 31%, giving a 165-fold emission enhancement and a limit of detection of 6 × 10^?7 M. Calibration curves are linear over a concentration range spanning three orders of magnitude. The characteristic lanthanide ion emission is obtained in all cases, but the excitation of the complexes is pH dependent, showing intensity increases up to pH 12. Mild interference by alkali and alkaline earth metals was overcome by increasing the ligand concentration, but transition metal interference was more severe. Only minor enhancement was observed at higher ligand/metal ratios.     

Dependence on pH of the Luminescent Properties of Metal Ion Complexes of 5-Chloro-8-hydroxyquinoline Appended Diaza-18-Crown-6

Luminescent properties of 5-chloro-8-hydroxyquinoline (CHQ) free and appended tothe amines in diaza-18-crown-6 (A₂18C6) were determined. These propertieswere compared to those of bivalent alkaline earth and post-transition metal ioncomplexes of the appended macrocycle (CHQ-A218C6). The luminescent properties were foundto be pH dependent. In the pH range 3 to 7, CHQ-A₂18C6 forms luminescent complexes withonly Zn²⁺ and Cd²⁺. At higher pH values, luminescent complexes wereformed with Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺. No luminescent complex was formed by Hg²⁺ over the pH range studied. This lariat macrocycle could findapplication as a chemosensor for several of the metal ions studied.     

The sorption of Eu(III) on calcareous soil: effects of pH,ionic strength,temperature, foreign ions and humic acid

The sorption of Eu(III) on calcareous soil as a function of pH, humic acid (HA), temperature and foreign ions was investigated under ambient conditions. Eu(III) sorption on soil was strongly pH dependent in the observed pH range. The effect of ionic strength was significant at pH < 7, and not obvious at pH > 8. The type of salt cation used had no visible influence on Eu(III) uptake on soil, however at low pH values, the influence of anions was following the order: Cl⁻ ≈ NO₃ ⁻ > ClO₄ ⁻. In the presence of HA, the sorption edge obviously shifted about two pH units to the lower pH, whilst in range of pH 6–7, the sorption of Eu(III) decreased with increasing pH because a considerable amount of Eu(III) was present as humate complexes in aqueous phase, then increased again at pH > 11. The results indicated that the sorption of Eu(III) on soil mainly formed outer-sphere complexes and/or ion exchange below pH ~7; whereas inner-sphere complexes and precipitation of Eu(OH)₃(s) may play main role above pH ~8.     

Importance of Outer‐Sphere and Aggregation Phenomena in the Relaxation Properties of Phosphonated Gadolinium Complexes with Potential Applications as MRI Contrast Agents

A series composed of a tetra‐, a tris‐ and a bisphosphonated ligand based on a pyridine scaffold ( L⁴ , L³ and L² , respectively) was studied within the frame of lanthanide (Ln) coordination. The stability constants of the complexes formed with lanthanide cations (Ln=La, Nd, Eu, Gd, Tb, Er and Lu) were determined by potentiometry in aqueous solutions (25.0 °C, 0.1 M NaClO₄), showing that the tetraphosphonated complexes are among the most stable Ln^III complexes reported in the literature. The complexation of L⁴ was further studied by different titration experiments using mass spectrometry and various spectroscopic techniques including UV/Vis absorption, and steady state and time‐resolved luminescence (Ln=Eu and Tb). Titration experiments confirmed the formation of highly stable [Ln L⁴ ] complexes. ³¹P NMR experiments of the Lu L⁴ complex revealed an intramolecular interconversion process which was studied at different temperatures and was rationalized by DFT modelling. The relaxivity properties of the Gd^III complexes were studied by recording their ¹H NMRD profiles at various temperatures, by temperature dependent ¹⁷O NMR experiments (Gd L⁴ ) and by pH dependent relaxivity measurements at 0.47 T (Gd L³ and Gd L² ). In addition to the high relaxivity values observed for all complexes, the results showed an important second‐sphere contribution to relaxivity and pH dependent variations associated with the formation of aggregates for Gd L² and Gd L³ . Finally, intravenous injection of Gd L⁴ to a mouse was followed by dynamic MRI imaging at 1.5 T, which showed that the complex can be immediately found in the blood stream and rapidly eliminated through the liver and in large part through the kidneys.     

Probing the Coordination Environment of the Human Copper Chaperone HAH1: Characterization of HgII‐Bridged Homodimeric Species in Solution

Although metal ion homeostasis in cells is often mediated through metallochaperones, there are opportunities for toxic metals to be sequestered through the existing transport apparatus. Proper trafficking of Cu^I in human cells is partially achieved through complexation by HAH1, the human metallochaperone responsible for copper delivery to the Wilson and Menkes ATPase located in the trans‐Golgi apparatus. In addition to binding copper, HAH1 strongly complexes Hg^II, with the X‐ray structure of this complex previously described. It is important to clarify the solution behavior of these systems and, therefore, the binding of Hg^II to HAH1 was probed over the pH range 7.5 to 9.4 using ¹⁹⁹Hg NMR, ^199mHg PAC and UV–visible spectroscopies. The metal‐dependent protein association over this pH range was examined using analytical gel‐filtration. It can be concluded that at pH 7.5, Hg^II is bound to a monomeric HAH1 as a two coordinate, linear complex (HgS₂), like the Hg^II–Atx1 X‐ray structure (PDB ID: 1CC8). At pH 9.4, Hg^II promotes HAH1 association, leading to formation of HgS₃ and HgS₄ complexes, which are in exchange on the μs–ns time scale. Thus, structures that may represent central intermediates in the process of metal ion transfer, as well as their exchange kinetics have been characterized.     

Comprehensive Evaluation of the Physicochemical Properties of LnIII Complexes of Aminoethyl‐DO3A as pH‐Responsive T1‐MRI Contrast Agents

N‐Substituted aminoethyl groups were attached to 1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acid (DO3A) with the aim to design pH‐responsive Ln^III complexes based on the pH‐dependent on/off ligation of the amine nitrogen to the metal ion. The following ligands were synthesized: AE ‐ DO3A (aminoethyl‐DO3A), MAE ‐ DO3A (N‐methylaminoethyl‐DO3A), DMAE ‐ DO3A (N,N‐dimethylaminoethyl‐DO3A) and MEM ‐ AE ‐ DO3A (N‐methoxyethyl‐N‐methylaminoethyl‐DO3A). The physicochemical properties of the Ln^III complexes were investigated for the evaluation of their potential applicability as magnetic resonance imaging (MRI) contrast agents. In particular, a ¹H and ¹⁷O NMR relaxometric study was carried out for these Gd^III complexes at two different pH values: at basic pH (pendant amino group coordinated to the metal centre) and at acidic pH (protonated amine, not interacting with the metal ion). Eu^III complexes allow one to estimate the number of inner‐sphere water molecules through luminescence lifetime measurements and obtain some structural information through variable‐temperature (VT) high‐resolution ¹H NMR studies. Equilibria between differently hydrated species were found for most of the complexes at both acidic and basic pH. The thermodynamic stability of Ca^II, Zn^II, Cu^II and Ln^III complexes and kinetics of formation and dissociation reactions of Ln^III complexes of AE ‐ DO3A and DMAE ‐ DO3A were investigated showing stabilities comparable to currently approved Gd^III‐based CAs. In detail, higher total basicity (Σlog K_i^H) and higher stability constants of Ln^III complexes were found for AE ‐ DO3A with respect to DMAE ‐ DO3A (i.e., log K_{Gd‐ AE‐DO3A} =22.40 and log K_{Gd‐ DMAE‐DO3A} =20.56). The transmetallation reactions of Gd^III complexes are very slow (Gd‐ AE ‐ DO3A : t_1/2=2.7×10⁴ h; Gd‐ DMAE ‐ DO3A : 1.1×10⁵ h at pH 7.4 and 298 K) and occur through proton‐assisted dissociation.     

Electron transfer reactions of tris(1,10-phenanthroline)cobalt(II) with copper(III) imine-oxime complexes

Summary The kinetics of oxidation of [Co^II(phen)₃]²⁺ (phen = 1,10-phenanthroline) by copper(III) imine-oxime complexes are first-order in each reactant. All reactions proceed via two parallel pathways; one pH independent, the other pH dependent. The second-order rate constant varies with [H⁺] as k₂ = k _inf2 ^supo + k _inf2 ^supH [H⁺]. The rapidity of the electron transfer step, coupled with the relative inertness of [Co^II(phen)₃]²⁺ over the pH range studied and the absence of a bridging atom on the phen ligand, supports an outer-sphere mechanism for this process. Reasonably good agreement between the experimental rate constants and those calculated using the Marcus equation has been obtained.     

Voltammetric Behavior of Antileukemia Drug Glivec. Part I – Electrochemical Study of Glivec

The electrochemical behavior of the antileukemia drug glivec was investigated at a glassy carbon electrode (GCE). The oxidation is a complex, pH‐dependent, irreversible electrode process involving the transfer of 2 electrons and 2 protons and the formation of an electroactive product, P_glivec, which strongly adsorbs on the GCE surface and undergoes reversible oxidation. The adsorption of P_glivec at the GCE surface yields a compact monolayer that inhibits further oxidation of glivec. The electrochemical reduction is a simple pH dependent irreversible process involving the transfer of 2 electrons and 2 protons and occurs with the formation of a nonelectroactive product. The diffusion coefficient of glivec was calculated to be D_O=7.35×10^?6 cm² s^?1 in pH 4.5 0.1 M acetate buffer.     

FT‐IR and Isotherm Study on Anion Adsorption onto Novel Chelating Fibers

A new chelating fiber, poly(acrylo‐amidino diethylenediamine), was synthesized based on polyacrylonitrile fibers in diethylenetriamine with the aid of AlCl₃. Complex formation with CrO₄^2– was strongly pH‐dependent, as complexes formed only in the presence of NH₃⁺ and NH₂⁺. In the medium pH region, both ionic and hydrogen bonds were formed between poly(acrylo‐amidino diethylenediamine) and the chromate ion, as was confirmed by means of FT‐IR spectroscopy.     

Serum Albumin Targeted,pH‐Dependent Magnetic Resonance Relaxation Agents

The objective of this work was the synthesis of serum albumin targeted, Gd^III‐based magnetic resonance imaging (MRI) contrast agents exhibiting a strong pH‐dependent relaxivity. Two new complexes ( Gd‐glu and Gd‐bbu ) were synthesized based on the DO3A macrocycle modified with three carboxyalkyl substituents α to the three ring nitrogen atoms, and a biphenylsulfonamide arm. The sulfonamide nitrogen coordinates the Gd in a pH‐dependent fashion, resulting in a decrease in the hydration state, q, as pH is increased and a resultant decrease in relaxivity (r₁). In the absence of human serum albumin (HSA), r₁ increases from 2.0 to 6.0 mM ^?1 s^?1 for Gd‐glu and from 2.4 to 9.0 mM ^?1 s^?1 for Gd‐bbu from pH 5 to 8.5 at 37 °C, 0.47 T, respectively. These complexes (0.2 mM ) are bound (>98.9 %) to HSA (0.69 mM ) over the pH range 5–8.5. Binding to albumin increases the rotational correlation time and results in higher relaxivity. The r₁ increased 120 % (pH 5) and 550 % (pH 8.5) for Gd‐glu and 42 % (pH 5) and 260 % (pH 8.5) for Gd‐bbu . The increases in r₁ at pH 5 were unexpectedly low for a putative slow tumbling q=2 complex. The Gd‐bbu system was investigated further. At pH 5, it binds in a stepwise fashion to HSA with dissociation constants K_d1=0.65, K_d2=18, K_d3=1360 μM . The relaxivity at each binding site was constant. Luminescence lifetime titration experiments with the Eu^III analogue revealed that the inner‐sphere water ligands are displaced when the complex binds to HSA resulting in lower than expected r₁ at pH 5. Variable pH and temperature nuclear magnetic relaxation dispersion (NMRD) studies showed that the increased r₁ of the albumin‐bound q=0 complexes is due to the presence of a nearby water molecule with a long residency time (1–2 ns). The distance between this water molecule and the Gd ion changes with pH resulting in albumin‐bound pH‐dependent relaxivity.     

Responses of Metalloporphyrin‐Based Ion‐Selective Electrodes to pH

The ISEs based on [M(tpp)Cl] (M: Al, Ga, In, Mn, Fe; H₂tpp: tetraphenylporphin) had pH responses across their respective pH ranges, which had some correlation with the pH ranges of the two‐phase hydrolysis. Such pH responses are ascribed to the phase boundary potentials relating to the acid‐base pairs of [M(tpp)(H₂O)]⁺ and [M(tpp)(OH)] and/or [M₂(tpp)₂O]. The potential responses of the In and Fe complexes had the upper limitation to pH of 90 % hydrolysis, whereas those of the Al and Ga complexes had the extension to at least pH 12, indicating stable existence of [M(tpp)(H₂O)]⁺ even in contact with strongly alkaline solutions.     

Investigation of the stereodynamics of tris‐(α‐diimine)–transition metal complexes by enantioselective dynamic MEKC

Enantiomerization of octahedral tris(α‐diimine)–transition metal complexes was investigated by enantioselective dynamic MEKC. Varying both the transition metal ion (Fe²⁺, Fe³⁺, and Ni²⁺) and the bidentate diimine ligand (1,10‐phenanthroline and 2,2′‐bipyridyl), the enantiomer separations were performed either in a 100 mM sodium tetraborate buffer (pH 9.3) or in a 100 mM sodium tetraborate/sodium dihydrogenphosphate buffer (pH 8.0) both containing sodium cholate as chiral surfactant. The unified equation of dynamic chromatography was employed to determine apparent reaction rate constants from the electropherograms showing distinct plateau formation. Apparent activation parameters ΔH^? and ΔS^? were calculated from temperature‐dependent measurements between 10.0 and 35.0°C in 2.5 K steps. It was found that the nature of the central metal ion and the ligand strongly influence the enantiomerization barrier. Surprisingly, complexes containing the 2,2′‐bipyridyl ligand show highly negative activation entropies between ?103 and ?116 J (K mol)^?1 while the activation entropy of tris(1,10‐phenanthroline) complexes is positive indicating a different mechanism of interconversion. Furthermore, it was found that the Ni²⁺ complexes are stereostable under the conditions investigated here making them a lucent target as enantioselective catalysts.     

Electrochemical Oxidation at a Glassy Carbon Electrode of the Anti‐Arrhythmia Drug Disopyramide

Abstract

A voltammetric study of the oxidation of disopyramide has been carried out using a glassy carbon electrode. The electrochemical oxidation of disopyramide was investigated by cyclic, differential pulse, and square wave voltammetry. The oxidation of disopyramide is an irreversible, diffusion‐controlled process. The diffusion coefficient of disopyramide was calculated in pH 7.0 phosphate buffer to be D _disopyramide=3.8×10^?6 cm² s^?1. The oxidation of disopyramide is also pH dependent and for electrolytes with pH between 4 and 7 occurs with the transfer of one electron and one proton. In alkaline electrolytes, two consecutive charge transfer reactions are observed: both oxidation reactions involve the transfer of two electrons but only the first also involves the transfer of two protons. Two procedures for the analytical determination of disopyramide in pH 7.0 phosphate buffer were developed and compared and a detection limit LOD=1.27 µM was obtained.     

Unusual deactivation in the asymmetric hydrogenation of itaconic acid

The formation of unusual Rh(III) substrate complexes from [Rh(DIPAMP)(MeOH)₂]BF₄ and itaconic acid has been detected which leads to the deactivation of the catalyst. The influence of different parameters on the formation of such complexes, namely substrate concentration, reaction time, temperature, acidic and basic additives, was investigated with different NMR methods. Two different Rh(III) substrate complexes are formed whose ratio is strongly dependent on substrate concentration and reaction time. The pH value of the solution shows a strong influence on the chemical shifts of the ³¹P NMR signals of such complexes. A catalyst-mediated esterification of itaconic acid in methanol was detected. Extended investigations provide detailed ¹H, ¹³C and ³¹P NMR data for the Rh(III) complexes and information about their stability in solution.     

Pyrazole‐substituted Near‐infrared Cyanine Dyes Exhibit pH‐dependent Fluorescence Lifetime Properties

Near‐infrared heptamethine cyanine dye is functionalized with pyrazole derivatives at the meso‐position to induce pH‐dependent photophysical properties. The presence of pyrazole unsubstituted at ¹N‐position is essential to induce pH‐dependent fluorescence intensity and lifetime changes in these dyes. Replacement of meso‐chloro group of cyanine dye IR820 with ¹N‐unsubstituted pyrazole resulted in the pH‐dependent fluorescence lifetime changes from 0.93 ns in neutral media to 1.27 ns in acidic media in DMSO. Time‐resolved emission spectra (TRES) revealed that at lower pH, the pyrazole consists of fluorophores with two distinct lifetimes, which cor‐responds to pH‐sensitive and non‐pH‐sensitive species. In contrast, ¹N‐substituted pyrazoles do not exhibit pH response, suggesting excited state electron transfer as the mechanism of pH‐dependent fluorescence lifetime sensitivity for this class of compounds.     

胶束及反胶束微环境中的槲皮素金属配合物

无机金属元素可与中药活性有机化合物通过配位键结合形成配合物,进而影响药物的生理活性[1]。但配合物的形成往往改变了原有机成分的溶解性能(如水溶性或脂溶性),而表面活性胶束体系可使金属有机配合物的水溶性或脂溶性得到明显改善,从而提高药物的生物利用度和改善药物的吸收。然而,胶束体系中已有的研究多是针对单纯的有机化合物[2]或生物分子如蛋白质[3]等,而涉及金属配合物胶束溶液的则很少,尤其是反胶束微环境中的中药金属配合物。反胶束亦称W/O型微乳液,是双亲物质在非极性有机溶剂中自发形成的具有纳米尺寸的含有水核的微小胶团聚集…