Complexation in aqueous solutions of lignosulfonates

The capability of lignosulfonates for donor-acceptor interaction with d-metal cations in aqueous solutions was studied. A quantitative estimation of the complexing properties of lignosulfonates was made.     

Diffusion of cyclodextrins in aqueous polymer solutions

Diffusion of α and β cyclodextrin (α-CD and β-CD, respectively) has been studied in aqueous solutions of poly(methacrylic acid), sodium poly(styrene sulfonate), having three different degrees of sulfonation (DS), and copoly(styrene-methacrylic acid) containing three different amounts of styrene. N-Acetylglucosamine and raffinose were included as reference diffusants. It was found that a decrease of the diffusion coefficients of the CD's in these polymer solutions is characteristically dependent on the polymer concentration, DS, Styrene content, and the degree of neutralization. The results were interpreted by assuming a 1:1 complex formation between CD and an appropriate residue in the polymer. The complex diffusion behavior of CD in the copolymer solutions suggested that the ability of the polymer residue to form complexes with the CD is lost when the polymer chain dimensions are reduced with decreasing neutralization.     

Complexation of tyrosol with cyclodextrins

Tyrosol (TY), 4-(2-hydroxyethyl)phenol, is an olive oil biophenol with antioxidant activity and positive effects on human health. This study has investigated the interactions of TY with cyclodextrins (CD) and a CD polymer. Complexation of TY with β-CD, hydroxypropyl-β-CD (HP-β-CD), and methyl-β-CD (Me-β-CD) has been evaluated both in aqueous solution and in the solid state. The techniques employed in solution to determine the apparent stability constants of the respective complexes were fluorescence and UV–visible spectroscopies. Complexation with β-CD and its derivatives involved an increase of both the UV absorbance and the intrinsic fluorescence of TY; a bathochromic shift of the UV spectrum was detected as well. The apparent stability constants obtained with native β-CD, Me-β-CD and HP-β-CD presented similar values. Complexes in the solid state were obtained by coevaporation and kneading. They were characterised by X-ray diffraction analysis and differential thermal analysis. The interaction of TY with β-CD led to a crystalline complex; the same diffraction pattern was obtained by coevaporation and kneading. The complexes obtained with methyl- and HP-β-CD were amorphous irrespective of the preparation method. In addition, the retention of TY in an insoluble polymer of CD crosslinked with epichlorohydrin has been quantified. In approximately 20 min, 1 mg of TY per gram of polymer was retained.     

Inclusion complexes of spin-labeled indoles with cyclodextrins in aqueous solutions

Guest-host complexes of β- and γ-cyclodextrins (CDs) with two spin-labeled indole derivatives having the same molecular weights but different structures were studied by EPR spectroscopy in aqueous solutions and semiempirical quantum-chemical calculations of these systems were carried out. In the presence of CD the polarity of the NO group environment decreases and the rotational correlation time (τ) of guest molecules increases. Both indole derivatives form 1 : 1 complexes with γ-CD, the binding constants of the complexes being different more than twice. Simulation of EPR spectra made it possible to determine the indole ring orientation relative to the plane of the host molecule (at angles in the range 30–60°) and the rotational diffusion coefficients of the complexes, which corresponded to the hydrodynamic volume of one γ-CD molecule. In contrast to the complexes with γ-CD the rotational correlation times, τ, of the complexes with β-CD correspond to a hydrodynamic volume which much exceeds the volume of a single β-CD molecule. The complexes with β-CD are also characterized by more hydrophobic environment for guest molecules and absence of spin exchange with Ni²⁺ ions in the aqueous solution. There results are consistent with a dimeric structure of β-CD in the complex and with the orientation of the long axis of the guest molecule along the dimer axis. The energies and geometric parameters were calculated for all complexes by the PM3 method with a conventional set of parameters. The optimized energetically stable structures of the 1 : 1 complexes with γ-CD and of the 1 : 2 complexes with β-CD are consistent with experimental data. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1139–1147, May, 2005.     

Complexation of cyclodextrins with nicotinamide and N-(hydroxymethyl)nicotinamide in aqueous solution

Complex formation of α- and β-cyclodextrins with biologically active nicotinamide and Nhydroxymethylnicotinamide (nicodine) was studied by calorimetry and ¹H NMR spectroscopy. Cyclodextrins showed a weak complexing ability toward nicotinamide and nicodine: 1: 1 enthalpy-stabilized host-guest complexes were formed in aqueous solution at 298.15 K. Nicotinamide and nicodine molecules appeared inside the macrocycle cavity of cyclodextrins, but interaction between their polar side-chain groups with the outer surface of cyclodextrins cannot be ruled out. Thermodynamic parameters of the complexation process were calculated, and a mechanism was proposed for the observed interaction. The results were compared with those obtained previously for the complexation of cyclodextrins with nicotinic acid.     

Interactions of xanthine and its derivatives with cyclodextrins in aqueous solutions

Using calorimetry, ¹H NMR, UV spectroscopy, and solubility methods, the interactions of natural and hydroxypropylated 6h-, β-, and γ-cyclodextrins with xanthine and its methylated derivatives (theophylline, theobromine, and caffeine) were studied in aqueous solutions at 298.15 K. Cyclodextrins revealed low complexation ability toward xanthine and its methylated derivatives. Hydroxypropyl-γ-cyclodextrin with the largest internal cavity is the most effective solubilizing agent for this type of compounds. The calculated thermodynamic parameters are discussed in terms of structural effects of cyclodextrins and purine alkaloids on the character of their intermolecular interactions in aqueous medium.     

Complexation properties of phosphonocarboxylic acids in aqueous solutions

The concentration formation constants of phosphonoacetic acid (PAA) complexes with the Ca²⁺ and Mg²⁺ ions were determined in aqueous solution at 25°C by potentiometric and coulometric titrations at different ionic strengths and were extrapolated to I=0 in order to obtain thermodynamic values of the formation constants. Complexes were formed by the completely deprotonated K _f (ML) and monoprotonated K _f (MHL) forms of the PAA anion. The respective values for the complexes are: log K _f (CaL)=4.68±0.03, log K _f (CaHL)=2.61±0.08; log K _f (MgL)=5.58±0.09, log K _f (MgHL)=3.0±0.3. The enthalpy and entropy of complexation for the deprotonated Ca²⁺ and Mg²⁺ PAA species, determined from the temperature dependence of the log K _f (ML), are: H⁰(Ca) =0.6±0.2 kcal-mol^–1, S⁰(Ca)=21.4±0.6 cal-mol^–1-K^–1, H⁰(Mg)=3.0±0.7 kcal-mol^–1, and S⁰(Mg)=35±2 cal-mol^–1-K^–1. It is seen there-fore, that the complexes are entropy stabilized but enthalpy destabilized. Formation constants were also determined for Ca²⁺ and Mg²⁺ complexes with PAA analogs, phosphonoformic and 3-phosphonopropionic acids and the complexation of PAA was also studied at a single ionic strength, with Na⁺, Ag⁺, Tl⁺, Sr²⁺, Ba²⁺, Cd²⁺, Cu²⁺, and Pb²⁺ ions.     

Solubilization of lanthanide ions by cyclodextrins in basic aqueous solutions

Cyclodextrins form complexes with lanthanide ions in basic aqueous solutions. This complex formation in basic solution dramatically enhances the solubility of lanthanide ions, which are otherwise insoluble due to the formation of hydroxide gels. Solutions of the -cyclodextrin-Ce³⁺ complex effectively hydrolyze 2-deoxyadenosine-5-monophosphate to 2-deoxyadenosine.     

Inclusion complexation of volatile chlorinated hydrocarbons in aqueous solutions of branched cyclodextrins

The inclusion complexation of five volatile chlorinated hydrocarbons, i.e., chloroform, carbon tetrachloride, trichloroethylene, tetrachloroethylene, and monochlorobenzene, with branched cyclodextrins (CDs) such as monoglucosyl--CD and monomaltosyl--CD in aqueous solutions was examined. Their inclusion complexes were found to be very water soluble and the solubilities of the chlorinated hydrocarbons in aqueous solutions increased almost linearly or gradually with increasing concentration of the branched CDs. The amounts of the chlorinated hydrocarbons included in the branched CDs were well related to their molecular size and shape. In addition, the viability of application to pollution prevention is discussed.     

Spectroscopic and electrochemical study of Rose Bengal in aqueous solutions of cyclodextrins

The interaction of Rose Bengal (RB) in aqueous solution of LiClO4 0.1 M with alpha-cyclodextrin (alpha-CD), hydroxypropyl-beta-cyclodextrins (HP-beta-CD) and hydroxypropyl-gamma-cyclodextrins (HP-gamma-CD) were studied by spectrophotometric measurements. The presence of Induced Circular Signals and the results of the analysis of the modifications in the absorbance spectra of RB produced by the presence of CDs in solution indicate that RB forms inclusion complexes only with HP-beta-CD and with HP-gamma-CD.     

Capture of volatile chlorinated hydrocarbons by aqueous solutions of branched cyclodextrins

The use of aqueous solutions of branched cyclodextrins was examined in order to develop an effective method of capturing toxic volatile chlorinated hydrocarbons such as trichloroethylene and monochlorobenzene. From the experiments in which trichloroethylene diluted with nitrogen gas came into contact with aqueous solutions of branched cyclodextrin mixtures, it was found that absorption could be performed without the formation of inclusion complex solids, which should simplify the whole process of absorption and recovery.     

Complexation of the potassium ion by diaza crown compounds in aqueous solutions

The conductance behavior of potassium nitrate in water with and without 1,7,10,16-tetraoxa-4,13-diazacyclooctandecane[2.2] and 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo-8.8.8-exacosane[2.2.2] macrocyclic ligands have been studied in order to analyze the complexation behavior of potassium cations in water. The absence of the complexation found in the [2.2] system is discussed in terms of the ligand structural features (presence of hydrogen bond donor and acceptor sites). The ion pair association constant of potassium cryptate as obtained from conductance measurements is also reported and discussed.     

Complexation of thallium(I) with adenosine 5'-monophosphate in aqueous methanol solutions.

The formation constants of the species formed in the systems H+ + thallium(I) + AMP and H+ + AMP have been determined in aqueous solutions of methanol at 25 degrees C and constant ionic strength 0.1 mol dm(-3) sodium perchlorate, using spectrophotometric and potentiometric techniques. Thallium(I) forms two mononuclear 1:1 complexes with AMP of the type TlHL and TlL- in the pH range of study (1-11), where L2- represents the fully dissociated ligand. The formation constants in various media were analyzed in terms of Kamlet and Taft's parameters. Single-parameter correlation of the formation constants, beta111, and beta101, versus alpha (hydrogen-bond donor acidity), beta (hydrogen-bond accepter basicity), and for pi* (dipolarity/polarizability) are relatively poor in all solutions, but multi-parameter correlation represents significant improvement with regard to the single-parameter models. Finally, the results are discussed in terms of the effect of the solvent on complexation.     

Calorimetric study of the complex formation of cyclodextrins with nicotinic and niflumic acids in aqueous solutions

Russian Journal of General Chemistry - Thermodynamic parameters of the inclusion complex formation of native and hydroxypropylated cyclodextrins with pharmacologically active niflumic and nicotinic...     

Interactions of cholesterol with cyclodextrins in aqueous solution

The interaction of cholesterol with several cyclodextrins (CDs) was investigated in water using solubility method. It was found that heptakis (2,6-di-O-methyl)-beta-CD (DOM-beta-CD) forms two types of soluble complex, with molar ratios of 1 : 1 and 1 : 2 (cholesterol : DOM-beta-CD), and neither a soluble nor insoluble complex is formed between cholesterol and alpha-CD, beta-CD, and gamma-CD, although a minor soluble complex formation was observed between cholesterol and 2-hydroxylpropyl-beta-CD. The thermodynamic parameters for 1 : 1 and 1 : 2 complex formation of cholesterol with DOM-beta-CD obtained from the changes in K with temperature are as follows: DeltaG degrees (1 : 1)=-11.6 kJ/mol at 25 degrees C (K(1 : 1)=1.09x10(2) M(-1)); DeltaH degrees (1 : 1)=-3.38 kJ/mol; TDeltaS degrees (1 : 1)=8.25 kJ/mol; DeltaG degrees (1 : 2)=-27.1 kJ/mol at 25 degrees C (K(1 : 2)=5.68x10(4) M(-1)); DeltaH degrees (1 : 2)=-3.96 kJ/mol; and TDeltaS degrees (1 : 2)=23.2 kJ/mol. The formation of the 1 : 2 complex occurred much more easily than that of the 1 : 1 complex. The driving force for 1 : 1 and 1 : 2 complex formation was considered to be mainly hydrophobic interaction. Also, based on the measurements of proton nuclear magnetic resonance spectra and studies with Corey-Pauling-Koltun atomic models, the probable structutures of the 1 : 2 complex were estimated.     

Formation of poly(ethylene glycol) inclusion complexes in aqueous solutions of mixed cyclodextrins

Even though the addition of modified cyclodextrins (modified CDs) accelerates the precipitation in aqueous solutions of poly(ethylene glycol) (PEG) and α-cyclodextrin (α-CD) the final amount of formed solid complex remains unchanged, with no significant presence of modified CDs detected by MALDI-TOF mass spectrometry. Thus unsuitability of kinetic turbidity measurements for determination of binding parameters was confirmed. On the other hand, theoretical calculations based on a model of a chain of freely accessible binding sites demonstrated that the results do not necessarily contradict the finding that individual modified CD molecules can thread onto PEG chains with the efficiency comparable to that of natural (unmodified) α-CD.     

Complexation of quercetin with three kinds of cyclodextrins: an antioxidant study

The slightly water-soluble flavonoid quercetin (QUE) and its inclusion with either beta-cyclodextrin (betaCD), hydroxypropyl-beta-cyclodextrin (HP-betaCD) or sulfobutyl ether-beta-cyclodextrin (SBE-betaCD) were investigated. The stoichiometric ratios and stability constants describing the extent of formation of the complexes have been determined by phase-solubility measurements; in all cases type-A(L) diagrams have been obtained (soluble 1:1 complexes). The results showed that the inclusion ability of betaCD and its derivatives was the order: SBE-betaCD>HP-betaCD>betaCD. Kinetic studies of DPPH with QUE and CDs complexes were done. The results obtained indicated that the QUE-SBE-betaCD complex was the most reactive form. The scavenging capability of QUE and CDs complexes with DPPH and galvinoxyl was studied using ESR spectroscopy. All complexes showed a higher scavenging capability with both radicals, compare quercetin in water. Beside, these results indicated that the complexes formed maintained the quercetin antioxidant activity.     

Interaction of bovine serum albumin with nonionic surfactant Tween 80 in aqueous solutions: Complexation and association

It is shown by the methods of precision tensiometry, quasi-elastic light scattering, and UV, IR, and fluorescent spectroscopies that the properties of binary aqueous solutions with a constant concentration of bovine serum albumin and different concentrations of the nonionic surfactant Tween 80 (1 × 10^–7−6 × 10⁻² M) are determined mainly by the complexation and formation of a new phase. The complexation occurs owing to specific interactions (hydrogen bonding) between polar groups of Tween 80 and protein molecules. The solubility in water and surface activity of a 1: 1 Tween 80-protein complex are determined. At the concentrations above the break point on surface tension isotherms (conditionally corresponding to critical association concentration), the particles are formed with radii varying from 16 to 350 nm. At a molar nonionic surfactant/protein ratio in the range of 6–10, the additional binding of Tween 80 molecules by the particles of the new phase due to hydrophobic interactions is observed. Original Russian Text ? N.M. Zadymova, G.P. Yampol’skaya, L.Yu. Filatova, 2006, published in Kolloidnyi Zhurnal, 2006, Vol. 68, No. 2, pp. 187–197.     

Use of water spin-spin relaxation rate to probe the solvation of cyclodextrins in aqueous solutions

1H spin-spin relaxation rate constant, R2, of water was measured by using the Carr-Purcell-Meiboom-Gill sequence in aqueous solutions of native cyclodextrins (alpha, beta, and gamma-CD) and chemically modified CDs in order to probe the structuring of the water surrounding these cyclic carbohydrate molecules. R2 values for water in solutions containing glucose and dextran were also measured for comparison. A two-site model for bonded and free water molecules was used to fit the results for the dependence of R2 on the solute concentrations. The order of relaxation rates for water in aqueous solution at a fixed specific hydroxyl group concentration is glucose>dextran congruent with CDs. No significant difference was observed for R2 of water in solutions containing native CDs, which indicates that the size and nature of the cavity has a small effect on the spin-spin relaxation times of water. The lower relaxation rate for water in CD solutions was attributed to the intramolecular hydrogen bonding formed between the secondary hydroxyl groups that line the rim of the CDs. For comparison, the relaxation rates for water in solutions of two chemically modified CDs were also studied.