Formation Constants Of Complexes Research Articles

Equilibrium studies of binary and mixed-ligand dimethyltin(IV) complexes involving homopiperazine and DNA constituents with reference to the antitumor activity

ABSTRACT The reaction of dimethyltin(IV) dichloride (DMT) with homopiperazine (HPIP) was studied. The equilibria of the complexes formed in solution were investigated. The complexes detected are of 1:1 stoichiometry in addition to the protonated and hydrolysed species. The complex formation constants were determined by the use of potentiometric technique and the non-linear computer program Miniquad-75. The dielectric constant effect of the reaction medium on the formation of the complexes was investigated. Formation constants of the complexes were determined at different temperatures and the thermodynamic parameters as ΔH° and ΔS° were estimated and discussed. The ternary complexes of dimethyltin(IV) with HPIP and DNA constituents are formed by a simultaneous mechanism. Their formation constants were determined. The speciation diagrams of the binary and mixed-ligand complexes were evaluated.

Chromatographic study of four sesquiterpenoids in volatile oil of Curcumae Rhizoma on reverse phase stationary phase with methyl-β-cyclodextrin as mobile additive

The elution behavior of four sesquiterpenoids in volatile oil of Curcumae Rhizoma on reverse-phase high-performance liquid chromatography with methyl-β-cyclodextrin as mobile phase additive was studied, including germacrone, curzerene, furanodiene, and β-elemene. Stoichiometric ratio and apparent formation constants of inclusion complex formed by methyl-β-cyclodextrin and each analyte were calculated by varying the concentration of the additive in the mobile phase composed of methanol and water (90:10, v/v), in which the association constant for inclusion complex formed by the organic modifier methanol and methyl-β-cyclodextrin was also determined. Results showed that the stoichiometric ratio of all the inclusion complex was 1:1 when 0–9 mmol L−1 of methyl-β-cyclodextrin was added in the mobile phase. Unusual retention behavior of the analyte germacrone was found, which was further investigated by the calculation of thermodynamic parameters. Meanwhile, enthalpy and entropy of the inclusion complexes and solute-stationary phase interactions were determined by linear van’t Hoff plots.

Interaction between 2-pyrrolidine-1-hydroxymethane-1,1-diphosphonic acid and palladium(II) in aqueous solutions

The structure of the 2-pyrrolidine-l-hydroxymethane-l,l-diphosphonic acid (PyrHMDP, H4L) has been determined by X-ray crystallography. Formation of the complexes between K2[PdCl4] and PyrHMDP was studied by pH-potentiometry, UV–Vis spectrophotometry and 31P, 13C and 1H NMR spectroscopy in aqueous solutions containing CKCl = 0.15 mol L−1, which corresponds to the concentration of chloride ions in intercellular fluid. The formation constants were calculated for the protonated forms of the PyrHMDP and for the [PdHLCl2]3− and [PdLCl2]4− complexes. The equilibrium concentration distribution diagram for the complexes of different composition was drawn using the formation constants of the Pd chloro-aqua complexes and the chloride concentration. In equimolar palladium complexes with PyrHMDP the ligand was coordinated in a bidentate manner via the nitrogen atom of the pyrrolidine ring and the oxygen atom of the phosphonic group forming a six-membered chelate ring.

Understanding the Solution Behavior of Epinephrine in the Presence of Toxic Cations: A Thermodynamic Investigation in Different Experimental Conditions.

The interactions of epinephrine ((R)-(−)-3,4-dihydroxy-α-(methylaminomethyl)benzyl alcohol; Eph−) with different toxic cations (methylmercury(II): CH3Hg+; dimethyltin(IV): (CH3)2Sn2+; dioxouranium(VI): UO22+) were studied in NaClaq at different ionic strengths and at T = 298.15 K (T = 310.15 K for (CH3)2Sn2+). The enthalpy changes for the protonation of epinephrine and its complex formation with UO22+ were also determined using isoperibolic titration calorimetry: ΔHHL = −39 ± 1 kJ mol−1, ΔHH2L = −67 ± 1 kJ mol−1 (overall reaction), ΔHML = −26 ± 4 kJ mol−1, and ΔHM2L2(OH)2 = 39 ± 2 kJ mol−1. The results were that UO22+ complexation by Eph− was an entropy-driven process. The dependence on the ionic strength of protonation and the complex formation constants was modeled using the extended Debye–Hückel, specific ion interaction theory (SIT), and Pitzer approaches. The sequestering ability of adrenaline toward the investigated cations was evaluated using the calculation of pL0.5 parameters. The sequestering ability trend resulted in the following: UO22+ >> (CH3)2Sn2+ > CH3Hg+. For example, at I = 0.15 mol dm−3 and pH = 7.4 (pH = 9.5 for CH3Hg+), pL0.5 = 7.68, 5.64, and 2.40 for UO22+, (CH3)2Sn2+, and CH3Hg+, respectively. Here, the pH is with respect to ionic strength in terms of sequestration.

Complementary Effect of Intra- and Intermolecular Hydrogen Bonds on Electron Transfer in β-Hydroxy-Anthraquinone Derivatives.

We have carried out an electrochemical and theoretical study on the relationship between electron transfer (ET) and hydrogen bonding in 11 different 9,10-anthraquinone (AQ) derivatives, including β-hydroxy AQs and their methoxylated analogs, in the presence of hydrogen donors in acetonitrile (ACN). The complementary effects of the intra- and intermolecular hydrogen bonds (HBs) on ET were studied by analyzing the complex formation constants derived from the intermolecular HB. Our results revealed that the inductive effect of the β substituent that indirectly controls the charge distribution on the AQ carbonyl oxygen, and steric hindrance at the β position, affect the complex formation constants. Furthermore, the analysis of ET in different isomeric dihydroxy AQs suggested that the position of the hydroxy groups affects the charge distribution and stabilizes structures through conjugation of the quinone moiety including the ipso ring, controlling the intra- and intermolecular HBs complementarily.

Analysis of Solvent Effect on Formation Constants and Speciation of Cobalt(II), Copper(II) and Lead(II) Complexes of L-Methionine and Uracil

The analysis of coordination of chelating agents to metal ions in the formation of complexes under different experimental conditions provide information on the effects of the conditions on the extent of the coordination of the ligands to the metal ions for potential applications in bioinorganic and environmental Inorganic Chemistry. The effect of solvent on the coordination of L-methionine (primary ligand) and uracil (secondary ligand) to Co(II), Cu(II) and Pb(II) ions in the formation of binary and ternary complexes have been potentiometrically investigated in water and 40% (v/v) ethanol- water media at 27 °C and ionic strength of 0.02 mol dm–3was maintained by using NaNO3. The proton-ligand stability constants and formation constants of the binary and ternary systems were established under the experimental conditions. The formation constants of the ternary complexes were numerically compared with the corresponding binary complexes in terms of Δ log K and percentage relative stabilization (%RS). Speciation of the metal ions, binary and ternary complexes as a function of pH in the solutions was investigated by using HYSS program. The ligands were observed to form more stable ternary complexes than binary complexes. The proton-ligand stability constants the ligands and the formation constants of the metal complexes were found to be higher in 40% (v/v) ethanol-water than water. The distribution of the species revealed a decrease in the metal ion concentrations with increase in the concentrations of the binary and ternary as pH increased. The chelating agents interacted strongly with the metal ions and showed different selectivity towards the metals ions. These properties can be exploited in combating metal poisoning, separating the metals and expounding the bioinorganic chemistry of the metal ions and the ligands.

Enantioseparation of acetyltropic acid by countercurrent chromatography with sulfobutyl ether-β-cyclodextrin as chiral selector.

Acetyltropic acid is an important synthetic intermediate for preparation of tropane alkaloid derivatives, which can be used as anticholinergic drugs, deliriants, and stimulants. In the present work, acetyltropic acid was successfully enantioseparated by countercurrent chromatography using sulfobutyl ether-β-cyclodextrin as chiral selector. A biphasic solvent system composed of n-butyl acetate/n-hexane/0.1mol/L citrate buffer at pH=2.2 containing 0.1mol/L of sulfobutyl ether-β-cyclodextrin (7:3:10, v/v) was selected, which produced a suitable distribution ratio DS =1.14, DR =2.31 and a high enantioseparation factor α=2.03. Baseline separation was achieved for preparative enantioseparation of 50mg of racemic acetyltropic acid. A method for chiral analysis of acetyltropic acid by conventional reverse phase liquid chromatography with hydroxylpropyl-β-cyclodextrin as mobile phase additive was established, and formation constants of inclusion complex were determined. It was found that different substituted β-cyclodextrin should be selected for enantioseparation of acetyltropic acid by countercurrent chromatography and reverse phase liquid chromatography.

An Experimental Study to Synthesize and Characterize Host–Guest Encapsulation of Anthracene, and the Quenching Effects of Co and Ni

A complex of anthracene with methyl-beta-cyclodextrin (A-Me-β-CD) having fluorophoric characteristics was obtained in aqueous medium. Spectroscopic and thermal analyses of the complex were performed by Fourier transform infrared spectroscopy and differential scanning calorimetry-thermogravimetry. The interaction of Me-β-CD and anthracene was also analyzed by means of spectrometry by a UV–Vis spectrophotometer. The stoichiometry of the complex was determined by the Benesi–Hildebrand method. The complex formation constant was found to be (42 ± 3) × 103 L·mol−1. The Gibbs energy and excited singlet state energy were calculated. The mechanism of the quenching effect of Co(II) and Ni(II) metals in the inclusion complex was studied. The Stern–Volmer constant, bimolecular quenching rate constant, lifetime and approximate activation energy values were determined, and the quenching was found to be diffusion controlled dynamic quenching. In addition, with the energy band calculations made, it was shown by means of Taug curves that electron transfer was made to Ni and Co metals from the complex fluorophore group in the quenching mechanism.

Formation Constants of Mixed Ligand Complexes of Anti-Inflammatory Drug Piroxicam and Some Bioligands with Copper(II)

The formation constants of various complexes of copper(II) with anti-inflammatory drug piroxicam (P) as primary ligand and some bioligands such as L-serine, L-tyrosine, L-threonine as secondary ligand have been determined pH metrically at 25 ºC and I = 0.1 M NaNO3. The results suggest that the formation of Cu(P)L and Cu(P)(LH-1) species in the pH range of 5-12. The values of Δ log10 K, percentage of relative stabilization and log X were evaluated and discussed.

X-ray crystal structure, spectroscopic and DFT computational studies of H-bonded charge transfer complexes of tris (hydroxymethyl)aminomethane (THAM) with chloranilic acid (CLA)

The crystal and molecular structures of two new synthesized charge transfer complexes produced from the reaction of tris(hydroxymethyl)aminomethane, THAM and 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid, CLA) in the mole ratios (2:1) [I] and (1:1) [II], have been studied. The; FT-IR and 1H NMR spectral data of the complexes are confirmed by single-crystal X-ray crystallography. The single-crystal X-ray crystallography, indicated the formation of both inter- and intra-molecular hydrogen bonding as well as the proton transfer from CLA to THAM. The electronic transition spectra of these two complexes as acetonitrile (AN), methanol (MeOH), ethanol (EtOH) solutions are recorded. The molecular compositions of the formed complexes in the three solvents determined by Job's method, support 1:1 mol ratio complex, whatever the polarity of the solvent. The high values of charge transfer complex formation constants, KCT determined by applying the minimum–maximum absorbance method, indicated the formation of stable CT-complexes, with the order Ethanol > Methanol ≫ Acetonitrile. Computational study incorporated the use of TD-DFT with PCM as solvation model are applied for energy minimization and estimation of the stabilization energy for the produced complexes. The geometrical parameters (bond lengths and angles) of the formed CT complexes are computed and analyzed. Furthermore, Mulliken atomic charges, molecular potential energy surface, HOMO and LUMO molecular orbitals of the formed complexes are presented. A good agreement between experimental and DFT computational analysis has been found.

Gold Plate Electrodes Functionalized by Multiwall Carbon Nanotube Film for Potentiometric Thallium(I) Detection.

Solid-contact potentiometric ion-selective electrodes (SC-ISEs) for thallium determination have been designed using multiwall carbon nanotubes (MWCNTs) as the ion-to-electron transducer. Dispersed MWCNTs were drop-casted over a gold plate electrode. Two different crown ethers were used in the sensing membrane for the recognition of thallium (I). Sensorsbased on dibenzo-18-crown-6 (DB18C6) as a neutral carrier and NaTPB as an anionic additive exhibited a near Nernstian response of 57.3 mV/decade towards Tl+ ions over the activity range 4.5 × 10−6–7.0 × 10−4 M, with a limit of detection of 3.2 × 10−7 M. The time required to achieve 95% of the steadyequilibrium potential was <10 s. The complex formation constant (log βML) between dibenzo-18-crown-6 and thallium (I) (i.e., 5.99) was measured using the sandwich membrane technique. The potential response was pH independent over the range 3.0–9.5. The introduction of MWCNTs as an electron-ion-transducer layer between gold plate and the sensing membrane lead to a smaller membrane resistance and a large double layer capacitance, which was proven using impedance spectra and chronopotentiometry (i.e., 114.9 ± 12 kΩ, 52.1 ± 3.3 pF, 200 ± 13.2 kΩ, and 50 ± 4.2 µF). Additionally, reduction ofthe water layer between the sensing membrane and the underlying conductor wastested. Thus, it is clear that MWCNTs can be used as a transducing layer in SC-ISEs. The proposed sensor was introduced as an indicator electrode for potentiometric titration of single and ternary mixtures of I−, Br−, and S2− anions.

A Stand‐Alone Module for Solar‐Driven H2 Production Coupled with Redox‐Mediated Sulfide Remediation

Efficient electrochemical devices are required to convert electric power by intermittent renewable energy sources into a chemical form. The choice of combination in reduction–oxidation reactions can vary depending on the target, which provides different thermodynamics and kinetics. A promising approach for H2 production coupled with sulfide remediation is demonstrated to utilize the intermediate redox media. H2 is produced on the cathode, and soluble redox ions in a reduced form are oxidized on the anode. The ions are then transferred to a separate reactor to oxidize the sulfide ions via a homogeneous reaction, and the reduced redox ions are recirculated. A solar‐driven redox photovoltaic‐electrochemical (PV‐EC) system is operated as a stand‐alone module and is composed of Cu(In,Ga)(S,Se)2 (CIGS) PVs and EC cells in series and operated under natural solar irradiation. A unique EC cell is established in an aqueous‐phase membraneless configuration at ambient temperature, and a cathode is decorated with a semipermeable CrOx‐based nanomembrane. This allows for selective H2 evolution without causing Fe redox reduction. Remaining issues associated with the stability of the CrOx permselective layer on the cathode are also discussed, which are associated with the formation constant of a soluble metal complex in the presence of ligand counterions.

Chelator-assisted washing for the extraction of lead, copper, and zinc from contaminated soils: A remediation approach

Chelators have proven to be effective extractants in soil washing and represent a suitable remediation technology for potentially toxic elements (PTEs) from contaminated sites. In this paper, the extraction of lead (Pb), copper (Cu), and zinc (Zn) from contaminated real and reference soils using both biodegradable (EDDS and HIDS) and persistent (EDTA and DTPA) chelators was investigated. Different metal–chelator complex formation constants, pH, extraction temperature, and mechanochemical energy were tested. The PTEs were extracted at a relatively higher rate under acidic to neutral conditions (pH 5 and 7), with the greatest extraction being observed at pH 5. The metal extraction efficiencies of the chelators for the real sample at pH 5 were as follows: Pb – EDTA > DTPA > EDDS > HIDS; Cu – DTPA > EDTA > EDDS > HIDS; and Zn – DTPA > EDTA > HIDS > EDDS. The data suggested that EDDS was more effective than HIDS for Cu and Zn extraction in neutral to slightly alkaline solutions, as well as at raised temperature. Furthermore, EDTA washing using mechanochemical agitation was found to enhance the removal efficiency of Cu and Zn. Sequential chemical extraction showed that the apparent metal mobilities were reduced by soil washing. EDTA and DTPA appeared to offer greater potential than the biodegradable chelators in extracting metals from the relatively mobile carbonate- and Fe–Mn oxide-bound fractions. The residual fraction of Pb displayed considerable stability (≥70%), and was not entirely amenable under washing treatments, and hence could be considered non-bioavailable and non-toxic.

Investigation of Uranyl Sulfate Complexation under Hydrothermal Conditions by Quantitative Raman Spectroscopy and Density Functional Theory

Quantitative first and second formation constants of aqueous uranyl sulfate complexes were obtained from Raman spectra of solutions in fused silica capillary cells at 25 MPa, at temperatures ranging from 25 to 375 °C. Temperature-dependent values of the symmetric O-U-O vibrational frequencies of UO22+(aq), UO2SO40(aq), and UO2(SO4)22-(aq) were determined from the high-temperature spectra. Temperature-independent Raman scattering coefficients of UO22+(aq) were calculated directly from uranyl triflate spectra from 25 to 300 °C, while those of UO2SO40(aq) and UO2(SO4)22-(aq) were derived from spectroscopic data at 25 °C and concentrations calculated using the formation constants of Tian and Rao ( J. Chem. Thermodyn. 2009 , 41 , 569 - 574 ), together with the Specific Ion Interaction Theory (SIT) activity coefficient model. Chemical structures and vibrational frequencies predicted from Density Functional Theory (Gaussian 09) were employed to interpret the Raman spectra. Values of the cumulative formation constants ranged from log β1 = 3.23 ± 0.08 and log β2 = 4.22 ± 0.15 at 25 °C, to log β1 = 12.35 ± 0.22 and log β2 = 14.97 ± 0.02 at 350 °C. This is the first reported use of high-pressure fused silica capillary cells to determine formation constants of metal ligand complexes from their reduced isotropic Raman spectra under hydrothermal conditions.

An experimental and computational study on naphthylideneimine based pH sensitive fluorescence probe for zinc.

Rational design chelating fluorescent sensors probing metal ions in biological system are continuously hot essays nowadays, especially for zinc detection. Herein, a naphthylideneimine based zinc fluorescence probe (3) was prepared and characterized in this work. Structural features and optical properties of 3 and its metallic complexes were characterized. Fluorescent experiment indicates 3 is extremely sensitive and selective for Zn2+ with a strong fluorescence enhancement (∼34 folds) in aqueous buffer solution with a limit of detection (LOD) of 3.78 × 10-7 mol L-1. Formation constant (logKa) of the chelating complex of 3 and Zn2+ ion was determined to be 4.45. Theoretical studies were carried out to get deep insight into the response mechanism in the sensing process. Density functional theory (DFT) methods calculated formation Gibbs free energy (ΔrGmө) of the deprotonated complexes model (32- ⊃ Zn) is-2.9 kcal/mol, which is in good agreement with the experimental result. The calculation results show that the low excitation states can be ascribe to S0 → T2 and S0 → S1 at 390-430 nm and 310-330 nm, respectively, due to the π → π∗ transition. Finally, yeast cell imaging experiments indicate that 3 can monitor intracellular Zn2+ as well. These findings would enable this fluorescent probe to be used as a Zinc sensor.

Chemical Thermodynamics and Calculation of Parameters of Ionic Equilibria of Indium(III) in Perchlorate, Chloride and Sulphate Aqueous Solutions

The problem of activity coefficients dependence of indium(In)-containing complex species and of corresponding concentration formation constants from qualitative and quantitative composition of aqueous solutions is discussed. The Bmnsted-Guggenheim-Scatchard’s model (Specific ion Interaction Theory, SIT), basing on extended semi-empirical Debye-Huckel equation in third approximation is supplied. The checking of data for formation constants of complexes on comparability and consistency, including for different background electrolytes can be done using this model. The survey of basic specific interaction coefficients (SIC) is done. The constancy of this coefficients is permissible in the definite ionic strengths ranges, or it’s necessary using two-parameters coefficients fitting. The classical SIT model is modified by the introduction of mixing parameters (SIC of same charge ion). On the basis of the numerical critical analysis of the available literature experimental data, with employment of the SIT, thermodynamic formation (stability) constants of chloro-, sulfato-aqua-complexes and hydrolysis constants of indiumfII) and related specific interaction coefficients (“non-ideality” parameters) in acidic aqueous solutions (pH < 5.5) at ambient temperature (20-25 °C) are calculated. The quotients of cationic and anionic complexes parts in SIC are separated according to empiric Ciavatta’s approach. Discrepancies of published «thermodynamic» constants may be caused by evidencing methodological and calculated errors (essential change of activity factors in series of experiments or various competing ion equilibria are neglected), as well as inaccuracies of extrapolation methods and choice of conditional standard state or erroneous evaluation of formal and standard potentials, but with the exception of alternative Baes-Mesmer’s nonlinear regression procedure. The job’s results could be used for modeling of the indium(III) state in some aqueous solutions and for study of indium and other metal ions complexation or prediction of their electrochemical and geochemical behaviour.

Studies on Pd(1,4-bis(2-hydroxyethyl)piperazine)-dicarboxylic acid complexes as models for carboplatin with structural features enhancing the interaction with DNA

[Pd(BHEP)Cl2] and [Pd(BHEP)(CBDA)] complexes, where BHEP = 1,4-bis(2-hydroxyethyl)piperazine and CBDA = cyclobutanedicarboxylate, were synthesized and characterized. [Pd(BHEP) (CBDA)] crystallizes in space group P21, a = 9.5740(8) Å, b = 9.4700(7) Å, c = 9.7890(10) Å, α = 90.00°, β = 113.360(5)°, γ = 90.00°, V = 814.78(13) Å3, Z = 2. The palladium center has a typical square planar geometry with tetrahedral distortion. DFT calculations show good agreement between theoretical and X-ray data. The stability constants and stoichiometry of the complexes formed between various dicarboxylic acids and [Pd(BHEP)(H2O)2]2+ were studied. Dicarboxylic acids form 1:1 and protonated complexes. Inosine forms 1:1, 1:2 and the protonated form of 1:1 complexes. The temperature effect on the formation constant of the cyclobutanedicarboxylate complex was investigated. The hydrolysis of [Pd(BHEP)(H2O)2]2+ and complex formation with cyclobutanedicarboxylic acid are exothermic processes.

Determination of complex formation constants of neptunium(V) with propionate and lactate in 0.5–2.6 m NaCl solutions at 22–60°C using a solvent extraction technique

Abstract Natural clay rocks like Opalinus (OPA) and Callovo-Oxfordian (COx) clay rock are considered as potential host rocks for deep geological disposal of nuclear waste. However, small organic molecules such as propionate and lactate exist in clay rock pore water and might enhance Np mobility through a complexation process. Therefore, reliable complex formation data are required in the frame of the Safety Case for a nuclear waste repository. A solvent extraction technique was applied for the determination of NpO 2 + ${\rm{NpO}}_2^ + $ complexation with propionate and lactate. Extraction was conducted from isoamyl alcohol solution containing 10−3 M TTA and 5 · 10−4 M 1,10-phenanthroline. Experiments were performed in 0.5–2.6 m NaCl solutions at temperatures ranging from 22 to 60 °C. Formation of 1:1 Np(V) complexes for propionate and lactate was found under the studied conditions. The SIT approach was applied to calculate equilibrium constants β°(T) at zero ionic strength from the experimental data. Log β°(T) is found linearly correlated to 1/T for propionate and lactate, evidencing that heat capacity change is near 0. Molal reaction enthalpy and entropy ( Δ r H m ∘ ${\Delta _{\rm{r}}}H_{\rm{m}}^ \circ $ and Δ r S m ∘ ${\Delta _{\rm{r}}}S_{\rm{m}}^ \circ $ ) could therefore be derived from the integrated van’t Hoff equation. Data for log β° (298.15 K) are in agreement with literature values for propionate and lactate. Np(V) speciation was calculated for concentrations of acetate, propionate and lactate measured in clay pore waters of COx. In addition, the two site protolysis non-electrostatic surface complexation and cation exchange (2SPNE SC/CE) model was applied to quantitatively describe the influence of Np(V) complexation on its uptake on Na-illite, a relevant clay mineral of OPA and COx.

Thermoreversible gelation with ion-binding cross-links of variable multiplicity.

Thermoreversible gelation and liquid-liquid phase separation are theoretically studied for the gels of polyfunctional molecules (polymers) whose network junctions are formed by complexation of functional groups on the polymer chains with added metal ions. Phase diagrams on the polymer/ion/solvent concentration plane, including both sol-gel transition lines and liquid-liquid phase separation lines (spinodals), are derived as functions of the polymer functionality, molecular weight, maximum coordination number of ions, and temperature. Binding isotherms of ions are also calculated as functions of the ion concentration. Results of the calculated sol-gel transition lines are compared with our recent experimental data on gelation of star block and telechelic, acrylic copolymers cross-linked by iron ions. It is shown that, owing to reaction stoichiometry, there is an optimal ion concentration at which the solution gels for the lowest polymer concentration and also that a re-entrant sol phase appears in the ion concentrations higher than the optimal one. The effect of stepwise complex formation constants on the re-entrant phase is studied in detail.

2+2] Photocycloaddition of Styryl Dyes in the Cucurbit[8]uril Cavity and Its Ultrafast Dynamics

[2+2] Photocycloaddition of a series of styryl dyes (a, b, and c, see text) in the cavity of cucurbit[8]uril (CB8) in aqueous solutions has been studied by optical spectroscopy. The complex formation constants were calculated for the 1 : 1 and 2 : 1 complexes of the styryl dyes with CB8. The optimal CB8 to dye molar ratios that correspond to the highest concentrations of the 2 : 1 complexes in the solution have been determined as 0.5, 0.3, and 1 for dyes a, b, and c, respectively. The quantum yields of photocycloaddition have been calculated from the results of dye photolysis in the presence of CB8: 0.06, 0.02, and 0.04 for a, b, and c, respectively. The fluorescence decay kinetics has been studied on the picosecond timescale. The lifetimes found are 1–2 ps, which correspond to the characteristic time of the solvation shell effect on the redistribution of the dye charge in the excited state. The long component of the fluorescence decay on the order of tens of picosecond is also observed. This component decreases in the presence of CB8, indicating the formation of dimeric state.