Large Formation Constants Research Articles

Colloidal titration: from the perspective of stability constants between oppositely charged polyelectrolytes

Abstract Colloidal titration is a unique method to measure the concentration of charged groups based on the association between cationic and anionic colloids. Titrimetry must involve a unidirectional reaction with a large formation constant. However, the underlying polyelectrolyte complex (PEC) for colloidal titration lacks sufficient data regarding the stability constants (KI). To date, the stoichiometry of colloidal titration has not been discussed in relation to KI. Thus, in this paper, we reviewed PEC studies by focusing on KI and discuss colloidal titration comprehensively. The topics include the history of its establishment, the method to calculate KI, and the special characteristics of PEC compared with ion association reactions, the practical use of colloid titration, and the condition by which the stability constant can be increased. In terms of analytical reagents, polyelectrolytes are similar to (but positioned as a subspecies of) ion association reagents. Ionic strength strongly affects KIs values. Excluding coaggregation effects, the maximum values of log10 KI obtained from reliable data were found to decrease linearly as ionic strength increases logarithmically. The critical line connected with the maximum KI value at each ionic strength can be used as an empirical reference value and facilitate the analytical design of colloidal titration.

Asymmetrical Platinum and Rhodium Dinuclear Complex Strongly Bound to Filled d Complexes by Unbridged Pt-Metal Bonds: Toward Heterometallic-Extended Metal Atom Chains.

Heterometallic extended metal atom chains (EMACs) aligned with three types of metal were rationally synthesized by forming unbridged metal-metal bonds based on the interactions between highest occupied and lowest unoccupied molecular orbitals at the d orbital. These chains form pentanuclear structures aligned as Rh-Pt-M-Pt-Rh with relatively large formation constants of 5.0×1013 M-2 for M=Pt and 6.3×1011 M-2 for M=Pd, while retaining their backbones in solution. In the case of M=Cu, the original Cu(+2) atoms were reduced to Cu(+1) during the synthetic process. Cu(+1) has an unprecedented trigonal bipyramidal coordination geometry. The reported synthesis based on asymmetrical dinuclear complexes provides a guideline for the synthesis of hetero-EMACs to allow several analogs through judicious combinations realized by tuning the number of metal nuclei and metal species.

5-ACETYL-8-HYDROXYQUINOLINE AND 5-FORMYL-8- HYDROXYQUINOLINE: CHELATING AGENTS FOR COMPLEXOMETRIC TITRATIONS

Metal–organic ligand complexes are essential to many technological developments from protein supramolecular assemblies to solvent extraction, complexometric titrations, and environmental remediation. We studied the chelating and acid-base properties in ethanol of two derivatives of 8-hydroxyquinoline (Q), 5-acetyl-8-hydroxyquinoline (A) and 5-formyl-8-hydroxyquinoline (F), of which applications as chelators are unknown. The ligands acidity followed the order F (pKa1 2.9; pKa2 9.5)> A (pKa1 4.8; pKa2 9.6)> Q (pKa1 5.3; pKa2 10.0) due to inductive effects of electronegative groups, formyl in F and acetyl in A. The higher acidity of F with respect to A was due to the higher electronegativity of the formyl group in F. This acidity order was reflected in larger formation constants of F-metal complexes with pKf values of 32 (Fe3+), 27.1 (Cu2+), 26.2 (Cu2+), and 24.9 (Pb2+), than with A, with pKf values of 31, 22.5, 21.4 and 21.2 with these metals, or the pKf values in the literature for Q. In summary, A and F resulted excellent chelators for metals in complexometric titrations with large formation constants; these large formation constants recommend the application of these compounds in masking, preconcentration, and titration of metals by complexation and oxidation-reduction reactions.

(Invited) Synthesis and Photophysical Properties of Photofunctional Porphyrin Supramolecular Assemblies

The self-assembled formation of dye molecules to form ordered nanoarchitectures is currently receiving great interest as a means of constructing well-defined superstructures. The possibility for controlling macroscopic structures through a proper choice of the molecular components paves a way to design and synthesize materials with specific properties and functions. One of the main challenges is the consturction of highly organized supramolecular multicomponent nanostructures in a well-controlled manner, which is very related to the molecular systems of natural photosynthesis. Therefore, utilization of electron donor (D) and acceptor (A) molecules such as porphyrins and polycyclic aromatic hydrocarbon derivatives (PAHs) for controlled assembly has stimulated the related research fields such as molecular electronics and solar energy conversion.1-4 In this work, one-dimensional supramolecular hexagonal columnar phases composed of porphyrins (electron donor: D) and benzo[ghi]perylenetriimides (electron acceptor: A) through triple hydrogen bonds have been successfully constructed to perform sequential light-harvesting and electron-transfer processes. In the steady-state spectroscopic measurements, the spectra of benzo[ghi]perylenetriimides became significantly red-shifted and broadened, whereas the successive positive shifts of first reduction potentials were observed with increasing the number of electron-deficient substituents. These are consistent with the results of DFT calculations. Then, formation of the 1 : 1 supramolecular complex between zinc porphyrin and benzo[ghi]perylenetriimide derivatives through triple hydrogen bonds was confirmed by job’s plot of 1H NMR titration. The large formation constant (~104 M–1) measured by the 1H NMR titration agreed with the values estimated from the UV-vis and fluorescence titration. Then, the one-dimensional supramolecular nanoarrays were successfully prepared in a mixed solvent of benzonitrile and methylcyclohexane. X-ray diffraction (XRD) measurement, polarization optical microscopy (POM) and differential scanning calorimetry (DSC) suggested that these nanoarrays contained one-dimensional hexagonal columnar phases composed of stacked donor and acceptor layers. Finally, femtosecond transient absorption and electron spin resonance (ESR) measurements clearly indicated that photoinduced electron transfer occurred via the singlet excited states in the supramolecular columns. References (1) Aoki, T.; Sakai, H.; Ohkubo, K.; Sakanoue, T.; Takenobu, T.; Fukuzumi, S.; Hasobe, T. Chem. Sci. 2015, 6, 1498. (2) Hasobe, T.; Ida, K.; Sakai, H.; Ohkubo, K.; Fukuzumi, S. Chem. Eur. J. 2015, 21, 11196. (3) Hirayama, S.; Sakai, H.; Araki, Y.; Tanaka, M.; Imakawa, M.; Wada, T.; Takenobu, T.; Hasobe, T. Chem. Eur. J. 2014, 20, 9081. (4) Ida, K.; Sakai, H.; Ohkubo, K.; Araki, Y.; Wada, T.; Sakanoue, T.; Takenobu, T.; Fukuzumi, S.; Hasobe, T. J. Phys. Chem. C 2014, 118, 7710. (5) Sakai, H.; Shinto, S.; Araki, Y.; Wada, T.; Sakanoue, T.; Takenobu, T.; Hasobe, T. Chem. Eur. J. 2014, 20, 10099.

The Dissolution of Amorphous Silica in the Presence of Tropolone Under Acidic Conditions

AbstractDissolution of amorphous silica or silicate is an important reaction to release silicic acid in natural water and this reaction is affected by several factors. The existence of a natural organic compound, tropolone, because of its abundance, is of particular importance. In the present study, the dissolution of amorphous silica in the presence of tropolone (HL) was investigated in an aqueous solution under acidic conditions. The dissolution is controlled by the reaction between silicic acid and tropolone (Si(OH)4 + 3HL + H+ ⇌ SiL3+ + 4H2O), where the conditional formation constant K = [SiL3+]/[Si(OH)4][HL]3[H+]). The solubility of amorphous silica in the presence of tropolone was significantly greater than that in pure water due to the formation of the Si-tropolonate complex in the solution. The acceleration of silica dissolution by tropolone depends on the reaction pH and tropolone concentration. The solubility of the amorphous silica in the tropolone solution at pH 1 was approximately ten times greater than in the 0.1 mol/dm3 HCl used as a reference. This increase in the solubility correlates to a K value of the Si-tropolone complex at each pH. From the solubility experiments, the conditional formation constants (log K) of the Si-tropolonate complex at each reaction pH 1, 2, and 3 were 6.39, 5.88, and 5.77, respectively. The significant acceleration of the dissolution of amorphous silica by tropolone at pH 1 can be attributed to the large formation constant of the Si-tropolonate complex.

Inclusion of potassium 4,4′-biphenyldicarboxylate into β-cyclodextrin: the design and synthesis of an organic secondary building unit

The paper describes a design strategy for the preparation of a novel inclusion compound (potassium 4,4′-biphenyldicarboxylate⊂β-CD) suitable for use in supramolecular chemistry. In the first step the chemical feasibility of such an inclusion compound was evaluated by DFT calculations. Preliminary results revealed that two types of adducts are energetically favourable: 1 ∶ 1 and 2 ∶ 1 (host ∶ guest). The stability in aqueous solution of the prepared inclusion compounds, a strict requirement for their use as Secondary Building Units in supramolecular chemistry, was investigated by means of liquid NMR (Job plot) and computational resolution of the equilibrium equations. As predicted by the theoretical calculations, it was found that two types of inclusion compounds were formed. The 1 ∶ 1 adduct has a large formation constant. Synthesis led to the preparation of two unusual crystalline products depending on the pH. Compound 1 (formed at pH = 7.5) is truly unprecedented and comprises a 1 ∶ 1 inclusion compound with a large water layer. Because it is highly stable in the liquid state this novel inclusion compound is a good candidate to be employed as a rigid organic Secondary Building Units in the construction of modular coordination polymers. Compound 2 (formed at pH = 10) comprises a mixture of the same two adducts predicted by the theoretical calculations and detected by liquid NMR, and its crystal structure exhibits a rare proportion between the host and the guest (4 ∶ 3).

Flow Injection Spectrophotometric Determination of Sub-mg dm-3 Silver(I) in a Strongly Acidic Solution Containing Concentrated Copper(II) Using a Pyridylazo Reagent

A novel spectrophotometric flow injection method for determination of silver(I) in a strongly acidic solution containing concentrated copper(II) was developed using a coloring ligand, 4-(3,5-dibromo-2-pyridylazo)-N-ethyl-N-(3-sulfopropyl)aniline (3,5-diBr-PAESA). The method was first investigated by batch method. The interference from copper(II) chelate could be eliminated by the masking effect of EDTA. By utilizing the large formation constant (K = 12.3) of AgBr, one could determine silver(I) as a decrease of absorption by silver(I) chelate due to formation of AgBr by addition of KBr. Based on the results of batch experiments, two types of flow injection analysis (FIA) systems were constructed. Sub-mg dm(-3) determination of silver(I) was attained without interference from excess copper(II). The proposed method was successfully applied to determination of silver in a copper plating solution used in a plant to manufacture copper printed circuit boards, where the concentration of silver was critically important in the process control.

Catching CO2 in a Bowl

Increased concentrations of CO(2) in the atmosphere contribute to global climate change. Improved methods are needed for removing CO(2) from the flue gas of power plants and/or directly from the atmosphere. A macrocyclic amidourea recently synthesized by Brooks et al., when dissolved in DMSO along with tetrabutyl ammonium fluoride, removes CO(2) from the atmosphere to form a complex in which a CO(3) group is held by a number of O-H-N bonds within the bowl-shaped cavity of the macrocycle. We have calculated the structure, stability, and vibrational spectra of this complex, using density functional techniques and polarized double-zeta basis sets. Both basis set superposition errors and polarizable continuum effects on the complex geometry and stability have been evaluated. The calculated structure is in good agreement with experiment. We predict that this CO(3)(-2) complex (and its HCO(3)(-) analogue) have larger formation constants by several orders of magnitude than the analogue complex of the amidourea macrocycle with Cl(-) (particularly in DMSO solution compared to aqueous solution). Our calculations also indicate that the CO(3)(-2) and HCO(3)(-) complexes can be distinguished by (13)C NMR. The CO(3)(-2) complex also has a distinctive H-N stretch, perturbed by the H-bonding to the CO(3) group. We also calculate the CO(3)(-2) complex to absorb within the visible region, unlike the free macrocycle or typical metal carbonates. Macrocycles of this type may provide a useful route to the absorption of atmospheric CO(2). Our calculations also indicate that changing the solvent from DMSO to water and/or heating the complex will be an efficient way to decompose it to release CO(2).

LSP spectral changes correlating with SERS activation and quenching for R6G on immobilized Ag nanoparticles

In terms of chemical enhancement in Surface Enhanced Raman Scattering (SERS), we investigated the effect of halide and other anions to rhodamine 6G (R6G) adsorbed Ag particles that were immobilized on the substrates. The residual species on chemically prepared Ag particles such as citrate or a-carbon were thoroughly substituted by various anions, e.g., Cl−, Br−, I−, SCN−, CN−, or S2O3 2− anions, whose adsorption features are elucidated by the formation constants for AgX2 (m−1)−, here X denotes the above anions. In particular, Cl−, Br−, or SCN− ions activated SERS of R6G via intrinsic electronic interaction with Ag, whereas CN−, S2O3 2−, or I− anions quenched it due to their exclusive adsorption onto the Ag surfaces. We found that the activation process with the anions commonly yields a marked blue-shift of the coupled plasmon peak from ca. 650–700 to 500–550 nm in elastic scattering. It is rationalized by slight increase of the gap size between adjacent Ag nanoparticles by only ca. 1 nm based on theoretical simulations. This is probably caused by slight dissolution, oxidative etching, of the particles according to large formation constants of the complexes. Consequently, partly remaining negative charges on the Ag surface, and a slight increase in the gap size, providing huge electric field, facilitated R6G cations to adsorb on the nanoparticles, especially at the junction.

Curium(III) Complexation with Desferrioxamine B (DFO) Investigated Using Fluorescence Spectroscopy

Abstract Hydroxamate-type siderophores like desferrioxamine B (DFO) are the most common siderophores ubiquitously found in the environment. These naturally occurring chelating substances have the potential to enhance the solubility and mobility of actinides by forming soluble complexes. The unknown interaction between curium(III) and aqueous DFO species is the subject of this paper. The reactions between soluble species of curium(III) and DFO were studied at trace curium(III) concentrations (3×10−7 M) in 0.1 M NaClO4 using time-resolved laser-induced fluorescence spectroscopy (TRLFS). Three Cm3+–DFO species, MpHqLr, could be identified from the luminescence spectra, CmH2DFO2+, CmHDFO+, and CmDFO, having emission maxima at 599, 611, and 614 nm, respectively. The large formation constants, logβ121=31.62±0.23, logβ111=25.70±0.17, and logβ101=16.80±0.40, compared to those of other chelating agents illustrate the unique complexation properties of hydroxamate-type siderophores. An indirect excitation mechanism for the curium(III) luminescence was observed in the presence of the DFO molecules.

Curium(III) complexation with pyoverdins secreted by a groundwater strain of Pseudomonas fluorescens

Pyoverdins, bacterial siderophores produced by ubiquitous fluorescent Pseudomonas species, have great potential to bind and thus transport actinides in the environment. Therefore, the influence of pyoverdins secreted by microbes on the migration processes of actinides must be taken into account in strategies for the risk assessment of potential nuclear waste disposal sites. The unknown interaction between curium(III) and the pyoverdins released by Pseudomonas fluorescens (CCUG 32456) isolated from the granitic rock aquifers at the Aspö Hard Rock Laboratory (Aspö HRL), Sweden, is the subject of this paper. The interaction between soluble species of curium(III) and pyoverdins was studied at trace curium(III) concentrations (3 x 10(-7)M) using time-resolved laser-induced fluorescence spectroscopy (TRLFS). Three Cm(3+)-P. fluorescens (CCUG 32456) pyoverdin species, M(p)H(q)L(r), could be identified from the fluorescence emission spectra, CmH(2)L(+), CmHL, and CmL(-), having peak maxima at 601, 607, and 611 nm, respectively. The large formation constants, log beta(121 )= 32.50 +/- 0.06, log beta(111) = 27.40 +/- 0.11, and log beta(101) = 19.30 +/- 0.17, compared to those of other chelating agents illustrate the unique complexation properties of pyoverdin-type siderophores. An indirect excitation mechanism for the curium(III) fluorescence was observed in the presence of the pyoverdin molecules.

Selective detection of copper ions in aqueous solution based on an evanescent wave infrared absorption spectroscopic method.

A new infrared sensing scheme based on an evanescent wave was proposed in this work for selective detection of copper ion in aqueous solutions. This sensing scheme is based on the band-shifting technique to overcome the limitation that metal ions do not absorb IR radiation. To demonstrate that the proposed mechanism is feasible, both theoretical considerations and practical examination of copper ions in aqueous solutions were investigated. The IR sensor was constructed by surface modification with L-(-)proline to selectively interact with copper ions by formation of stable square-planar complexes. After complexation, the absorption bands of the immobilized L-(-)proline exhibits a band shift and could be used to monitor the quantity of metal ions in aqueous solutions. To immobilize L-(-)proline on the surface of a sensing element and increase the stability of the modified phase in aqueous solutions, poly(vinylbenzyl chloride) was coated onto the sensing element for further immobilization of L-(-)proline. A sensitive and a water-stable L-(-)proline phase was obtained. This sensing phase is selective and sensitive to copper ions due to the large formation constant between the copper ions and L-(-)proline. Factors, such as the copper ion concentration, response time, solution pH, long-term stability, regeneration efficiency, and the matrix effect, were investigated. Results indicated that the pH effect was significant but could be controlled by buffering the sample solutions. Using the optimal conditions found in this work, the detection limit could be lower than 0.7 microM and the linear regression coefficients in standard curves could be higher than 0.99 for a concentration range from 5 to 200 microM.

Fiber-Optic Evanescent-Wave Absorption Copper(II) Sensor Based on Sol-Gel-Derived Organofunctionalized Silica Cladding

A fiber-optic evanescent-wave absorption sensor was constructed on the basis of an organofunctionalized silica cladding. The cladding material was prepared by the sol-gel processing of an organofunctional silicon alkoxide, which contains a propyl-ethylenediamine triacetate (PEDTA) group. The PEDTA group can chelate with a Cu(II) ion to form a colored complex. Because of the large formation constant of the complexation reaction, a kinetic approach was used to quantify the Cu(II) content in samples. The sensor has a dynamic range of 0.5–100 ppm and a detection limit of 56 ppb. The measurement of the Cu(II) content in a scattering medium has also been demonstrated.

Intramolecular hydrogen bonding in hydroxylated semiquinones inhibits semiquinone–Mg2+ complex formation

Complex formation between the semiquinones of 5,8-dihydroxynaphtho-1,4-quinone, NZQ˙−, 1,4-dihydroxyanthracene-9,10-dione, QNZ˙−, benzo-1,4-quinone, BQ˙−, and phenanthraquinone, PHQ˙−, and Mg2+ was studied utilizing EPR spectroscopy. Weighted average EPR spectra between those corresponding to the uncomplexed and complexed semiquinones were observed for NZQ˙−, QNZ˙− and BQ˙− while these species were observed simultaneously for PHQ˙−. The semiquinones NZQ˙−, QNZ˙− and BQ˙− behave as weak Mg2+ chelators while PHQ˙− chelates this cation much more strongly (binding constant = (1.1 ± 0.5) × 103 dm3 mol−1). The weak binding of Mg2+ by NZQ˙− and QNZ˙− is in contrast with the large complex formation constants between the parent quinones NZQ and QNZ and different metal cations. This apparent paradox is explained by the strong intramolecular hydrogen bonding existing in NZQ˙− and QNZ˙−.

Triple-ion formation and acid–base strength of ions in protophobic aprotic solvents

The formation of symmetrical triple ions [2M++ X–⇌ M2X+, (K2); M++ 2X–⇌ MX–2, (K3); K2=K3] and the quadrupole [M2X++ X–⇌ M2X2, (K4); M++ MX–2⇌ M2X2, (K5); K4=K5], in addition to ion-pair formation [M++ X–⇌ MX, (K1)] from various uni–univalent salts were examined by means of conductometry in acetonitrile, benzonitrile and propylene carbonate. The salts are made from bases (B) and acids (HX) of varying strength. For diethylcyclohexylammonium chloride [(0.4–6.0)× 10–3 mol dm–3 in benzonitrile], the calculated molar conductivities (Λ/S cm2 mol–1) were fitted to the observed ones within 0.36% of the standard deviation of the relative error, considering the symmetrical formation of the triple ions. In the higher concentration range [(0.4–12.0)× 10–2 mol dm–3] of the salt a minimum was observed in the relation between Λ and C1/2. The observed minimum could be reproduced in terms of the large formation constants of the triple ions and the quadrupole complex by computer simulations. However, a larger formation constant of the quadrupole above the critical value caused the minimum to disappear. Weaker basicities of amines tended to give higher formation constants of the triple ion; however a levelling-off was observed below pKBH+= 18 in acetonitrile. On the other hand, the formation constants for the ion pair and the triple ions from salts with different anion basicities (from perchlorate to 3,5-dinitrobenzoate) were proportional to the acidities of the corresponding acids.

Effect of Substituents on the Triple Ion Formation from Various Ammonium or Guanidium Chlorides

Abstract The triple ion formation from various ammonium or guanidium chlorides has been examined by conductometry in acetonitrile, benzonitrile, and propylene carbonate. The observed minimum in the Λ−C1/2 curve of diethylcyclohexylammonium chloride in benzonitrile could be reproduced in terms of a large formation constant of quadrupole complexes by computer simulations.

Ordered Ionic Liquids: Chloroaluminates and Silicates

Ordering in NaCl--AlCl{sub 3} melts leads to sharp minima in the solubility of divalent chlorides MCl{sub 2} (e.g., CoCl{sub 2}, and NiCl{sub 2}) near the 50-50 mole % composition. The composition dependence of these solubilities in acids melts can be described by using either the coordination cluster theory or the solubility product principle. The magnitudes of the solubility products are largely related to the fact the standard free energy of formation of 2NaNlCl{sub 4} form 2NaCl and 2AlCl{sub 3} is considerably more negative that the corresponding free energy for N (AlCl{sub 4}){sub 2}. In basic melts solubilities are largely related to the formation of the associated species MCI{sup +}, MCI{sup 2}, MCI {sup {minus}3} and MCI {sub 4}{sup {minus}2}, which appear to have very large formation constants. 15 refs., 3 figs.

Complexation of gadolinium ion with poly(methacrylic acid)s and magnetic properties of the complexes

The complexation of gadolinium (Gd 3+) ion with poly(methacrylic acid) and its copolymers was studied. Poly(methacrylic acid-co-acrylamide) formed the tris(carboxylate)-coordinate gadolinium complex with an extra large complex formation constant, while poly(methacrylic acid) formed the biscoordinate complex. Transparent and flexible film containing a high proportion of Gd ion was prepared by casting the complex solution of poly(methacrylic acid-co-methylacrylate). The complexed Gd ion was uniformly dispersed in the film and showed paramagnetism. The formation and magnetic properties of the polymer—Gd complexes are discussed in comparison with those of the corresponding iron complexes.

ChemInform Abstract: Cobalt(II) Bis(1,4,7‐trithiacyclononane): A Low‐Spin Octahedral Complex.

AbstractCobalt(II) forms a cationic 1:2 complex with 1,4,7‐trithiacyclononane with an unprecedentedly large overall formation constant.

The reactivity of Cu(tim)2+(tim = 2,3,9,10-tetramethyl-1,4,8,11-tetra-azacyclotetradeca-1,3,8,10-tetraene) with chloride ion: an unusually large formation constant

The reaction of Cu(tim)2+(tim = 2,3,9,10-tetramethyl-1,4,8,11-tetra-azacyclotetradeca-1,3,8,10-tetraene) with Cl– ion was studied by cyclic voltammetry; the formation constant for the Cu(tim)Cl+ adduct was determined by a computer simulated cyclic voltammogram and found to be unusually large: β1= 2 × 107 dm3 mol–1.