Investigation of the Complexation between 4-Aminoazobenzene and Cucurbit[7]uril through a Combined Spectroscopic, Nuclear Magnetic Resonance, and Molecular Simulation Studies.

Cucurbiturils are well known for their ability to form supramolecular systems with ultrahigh affinities binding. Inclusion complex between 4-aminoazobenzene and cucurbit[7]uril has been investigated in aqueous solution by ultraviolet (UV)-spectroscopy, 1H NMR, and molecular simulations. 4-aminoazobenzene shows high affinity in acidic solutions while no association was detected in neutral solutions. The thermodynamic properties of complex formation are investigated using both UV spectroscopy and nuclear magnetic resonance (NMR) measurements. Our results highlight that the high binding constant between CB7 and 4AA (log K = 4.9) is the result of a large negative change in Δr H° (-19 kJ/mol) and a small positive change in TΔr S° (9 kJ/mol). The analysis of the experimental data lead to hypothesis on the structure of the complex. We have used molecular dynamics simulation to interpret experiments. Interestingly, the cis-trans isomerization of aminoazobenzene is considered. All the results are discussed and compared with those previously obtained with other host molecules.

Associations of Water-Soluble Macrocyclic Hosts with 4-Aminoazobenzene: Impact of pH.

An investigation of the pH effect on the inclusion complexes of ß-cyclodextrins and calixarenesulfonates with 4-aminoazobenzene was conducted both by experiments and molecular simulations. The whole thermodynamic characterizations of the association between hosts and 4-aminoazobenzene ( K, Δr G0, Δr H0, and TΔr S0) were determined by UV-visible spectroscopy. ß-Cyclodextrin inclusion complexes are not affected by pH change unlike those obtained with calixarenes. All the studied systems were enthalpically favored. Nevertheless, the entropic behavior is different depending on the host. In order to interpret these experimental results, molecular simulations were used to calculate the number of atoms inserted into the cage-like host compounds and the number of water molecules expelled from the cavity.

Polarity, viscosity, and ionic conductivity of liquid mixtures containing [C4C1im][Ntf2] and a molecular component.

In this study, we have focused on binary mixtures composed of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)-imide, [C(4)C(1)im][Ntf(2)], and a selection of six molecular components (acetonitrile, dichloromethane, methanol, 1-butanol, t-butanol, and water) varying in polarity, size, and isomerism. Two Kamlet-Taft parameters, the polarizability π* and the hydrogen bond acceptor ß coefficient were determined by spectroscopic measurements. In most cases, the solvent power (dipolarity/polarizability) of the ionic liquid is only slightly modified by the presence of the molecular component unless large quantities of this component are present. The viscosity and electrical conductivity of these mixtures were measured as a function of composition and the relationship between these two properties were studied through Walden plot curves. The viscosity of the ionic liquid dramatically decreases with the addition of the molecular component. This decrease is not directly related to the volumetric properties of each mixture or its interactions. The conductivity presents a maximum as a function of the composition and, except for the case of water, the conductivity maxima decrease for more viscous systems. The Walden plots indicate enhanced ionic association as the ionic liquid gets more diluted, a situation that is the inverse of that usually found for conventional electrolyte solutions.

Vapour pressures, aqueous solubility, Henry's law constants and air/water partition coefficients of 1,8-dichlorooctane and 1,8-dibromooctane.

New data on the vapour pressures and aqueous solubility of 1,8-dichlorooctane and 1,8-dibromooctane are reported as a function of temperature between 20 degrees C and 80 degrees C and 1 degrees C and 40 degrees C, respectively. For the vapour pressures, a static method was used during the measurements which have an estimated uncertainty between 3% and 5%. The aqueous solubilities were determined using a dynamic saturation column method and the values are accurate to within +/-10%. 1,8-Dichlorooctane is more volatile than 1,8-dibromooctane in the temperature range covered (p(sat) varies from 3 to 250 Pa and from 0.53 to 62 Pa, respectively) and is also approximately three times more soluble in water (mole fraction solubilities at 25 degrees C of 5.95 x 10(-7) and 1.92 x 10(-7), respectively). A combination of the two sets of data allowed the calculation of the Henry's law constants and the air water partition coefficients. A simple group contribution concept was used to rationalize the data obtained.