Hydrodynamic properties of cyclodextrin molecules in dilute solutions (original) (raw)
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Some Transport Properties of γ-Cyclodextrin Aqueous Solutions at (298.15 and 310.15) K
Journal of Chemical & Engineering Data, 2008
Values of binary mutual diffusion (interdiffusion) coefficients, obtained by using the Taylor dispersion method, for aqueous solutions of γ-cyclodextrin in the concentration range from (0.002 to 0.010) mol · dm -3 and temperatures (298.15 and 310.15) K are reported. From these experimental results, the hydrodynamic radius values for the γ-cyclodextrin are estimated. Also, the measured diffusion coefficients are used with both Hartley's and Gordon's equations to estimate activity coefficients for aqueous γ-cyclodextrin. These studies are complemented by some density and viscosity measurements, carried out at the same range of concentrations and temperatures. The effect of both the viscosity of the medium and the formation of γ-cyclodextrin dimers on the estimated hydrodynamic radius is discussed.
Characterization and control of the aggregation behavior of cyclodextrins
Photon correlation spectroscopy has been employed for the purpose of characterizing the aggregation behavior of cyclodextrin molecules in aqueous solutions. This optical method is generally intended to study particle size distribution of colloidal particles, associates and macromolecules. Herein we report on some general methodological issues of photon correlation spectroscopy aiming to illustrate aggregated and non-aggregated state of parent cyclodextrins and cyclodextrin derivatives, such as (2-hydroxy)propyl-b-cyclodextrin and tetraamino rhodaminyl (2-hydroxypropyl)-b-cyclodextrin in different aqueous media. Based on particle size analysis data we have demonstrated that the tendency of cyclodextrin molecules to form aggregates may be controlled by temperature and by various additives, e.g. urea, citric acid and polyvinylpyrrolidone. In the case of (2-hydroxypropyl)-b-cyclodextrin the effect of degree of substitution was also studied.
A thermodynamic study of a gemini type surfactant, bis(dodecyl dimethylammonium)diethyl ether dibromide (12-EO 1 -12), has been carried out in water and in the presence of b-cyclodextrin (b-CD) at 298 K. Density and sound velocity data for the aqueous solution of the gemini in both systems were analyzed to calculate the molar apparent and partial volumes and adiabatic compressibilities. For the ternary system, the shift of the critical micelle concentration and the values of the transfer properties prove the formation of a molecular complex with a predominantly 1:2 stoichiometry (one surfactant molecule per two CDs).
Langmuir, 2017
The aggregation of the most common natural cyclodextrins (α-, βand γ-) in aqueous 28 solutions is addressed by studying the CD-CD interactions using deuterium relaxation 29 rates for deuterium labelled CDs. Relaxation times (T 1) and its corresponding relaxation rates (R 1 =1/T 1) provide information about the rotational correlation times of CDs and 31 serve as a proxy for solute-solute interactions. Measured T 1 's for α-, β-, and γ-CD at the 32 lowest CD concentrations were in agreement with predictions of a hydrodynamic model 33 for toroids, in particular with regard to the dependence of T 1 on CD size. On the other 34 hand, the dependence of T 1 's with respect to the increase in CD concentration could not 35 be explained by hydrodynamic or direct interaction between CD molecules, and it is 36 suggested that there is an equilibrium between monomeric and dimeric CD to account 37 for the observed concentration dependence. No evidence in favor of large aggregates of 38 CD involving a non-negligible fraction was found for the investigated CDs.
Negative solubility coefficient of methylated cyclodextrins in water: A theoretical study
Molecular dynamics and Monte Carlo simulations of b-cyclodextrin and its per-dimethylated derivative hepta-kis(2,6-di-O-methyl)-b-cyclodextrin have been carried out in water solutions at two temperatures, 25°C and 70°C. The structure of the hydration shells, as well as the solute±solvent and solvent±solvent correlations have been analyzed. The negative solubility coecient of heptakis(2,6-di-O-methyl)-b-cyclodextrin is conditioned ®rst of all by progressive destruction of the hydration shells around its methyl groups with temperature increase, whereas for b-cyclodextrin with positive temperature coecient, solution is comparable at 25°C and 70°C.
Negative solubility coecient of methylated cyclodextrins in water: A theoretical study
Molecular dynamics and Monte Carlo simulations of b-cyclodextrin and its per-dimethylated derivative heptakis(2,6-di-O-methyl)-b-cyclodextrin have been carried out in water solutions at two temperatures, 25°C and 70°C. The structure of the hydration shells, as well as the solute±solvent and solvent±solvent correlations have been analyzed. The negative solubility coecient of heptakis(2,6-di-O-methyl)-b-cyclodextrin is conditioned ®rst of all by progressive destruction of the hydration shells around its methyl groups with temperature increase, whereas for b-cyclodextrin with positive temperature coecient, solution is comparable at 25°C and 70°C. Ó
Theoretical Study of the α-Cyclodextrin Dimer
Journal of Physical Chemistry A, 2005
The molecular structure, stabilization energy, and thermodynamic properties of the plausible modes of the interaction for the three possible R-cyclodextrin (R-CD) dimers (head-to-head, tail-to-tail, and head-to-tail) with a water cluster were obtained using quantum chemical methods for the first time. Nine distinct spatial arrangements were investigated. The head-to-head mode of interaction with water is preferred by more than 10 kcal‚mol -1 (BLYP/6-31G(d,p)//PM3 Gibbs free energy difference value at room temperature) in relation to the next stable structure, with a water dimer structure placed inside each cavity and cyclic water tetramers surrounding each tail end. The inter R-CD hydrogen bonds play a major role to stabilize the dimeric structures, with no water tetramer being found between the two R-CD subunits for the preferred global minimum structure. Therefore, a theoretical model aimed to describe the behavior of R-CD dimer, or their inclusion complexes, in the aqueous media should take into account this preference for binding of the water molecules.