The X-ray patterns of lithium (LiDC) and potassium (KDC) deoxycholate fibers, drawn from aqueous micellar solutions, have been interpreted by means of a packing of 8/1 helices formed by trimers. Previously, these helices satisfactorily represented the structure of the sodium (NaDC) and rubidium (RbDC) deoxycholate micellar aggregates. Dielectric measurements show that the trend of the average electric dipole moment µ of a NaDC monomer as a function of temperature and concentration supports a two-structure equilibrium. The high µ values (32-58 D) can be explained by the remarkable hydration of the NaDC micellar aggregates. The µ moderate decrease when the size of the aggregates increases can agree with the presence of small helices but disagrees with the existence of aggregates that are disordered or have a center (or a pseudocenter) of symmetry. Formerly, it was observed that sodium taurodeoxycholate (NaTDC) micellar aggregates, represented by 7/1 helices, formed by trimers, behave similarly. The contribution to the electrical conductivity of NaDC and NaTDC in aqueous solutions containing NaCl tends to zero by increasing the NaCl concentration, denoting strong interactions between Na + ions and anion aggregates. According to the similar 7/1 and 8/1 helices, which have the Na + ions in their inner part, the micellar size and the fraction of Na + ions trapped inside the helices increase together. The aggregate apparent hydrodynamic radius (R h ) increases by increasing the ionic strength in the order LiDC > NaDC > KDC > RbDC. Fibers drawn from solutions containing two cations at the same concentration show that the affinity for the anionic structure seems to follow the order Li + > Na + > K + > Rb + at high ionic strength. The R h values vs the mole fractions of Li + and Rb + or Na + and K + at lower ionic strength are fitted by straight lines. Probably, the free energy gains, associated with the cation and anion transfer from the bulk solution to the micellar aggregates, are almost equal for the four salts at lower ionic strength.

Previously, structural models, observed in fibers and crystals, were proposed for sodium deoxycholate (NaDC), glycodeoxycholate (NaGDC), taurodeoxycholate (NaTDC), and taurocholate (NaTC) micellar aggregates, and were verified in aqueous solutions by means of several techniques. Here we report the X-ray analysis of sodium glycocholate (NaGC) fibers, which indicates that NaGC micellar aggregates could be formed by dimers and octamers as in the case of NaTC. Moreover, we present electrolytic conductance and dielectric measurements on NaGDC, NaTC, and NaGC aqueous micellar solutions to verify our micellar aggregate models. Specific conductance values of 0.1 mol dm-3 NaDC, NaTDC, NaGDC, NaTC, and NaGC solutions containing NaCl at concentration ranging from 0 to 0.8 mol dm-3 practically do not depend on the particular bile salt. Comparison with NaCl values shows that bile salt contribution to conductance decreases by increasing NaCl concentration, is nearly zero around the concentration range 0.5−0.6 mol dm-3, and becomes negative at higher concentration. This behavior can be explained if Na+ ions strongly interact with bile salt anions and reinforce their interaction when micellar size increases. Even the inclusion of Na+ and Cl- ions, coming from NaCl, into micellar aggregates cannot be excluded, especially at high ionic strength. NaDC, NaTDC, NaGDC, NaTC, and NaGC present high values of the average electric dipole moment per monomer μ that can be justified by a remarkable hydration of their micellar aggregates. Reasonably, micellar aggregate composition and population change very slightly or do not change at all within the temperature range 15−45 °C, because μ is nearly constant in this interval. Results also suggest that Na+ ions are anchored to anions in dilute solution, thus forming ion pairs in the case of NaTC and NaGC, at least. Dihydroxy and trihydroxy bile salts are characterized by very similar cation−anion interaction strengths, even though their structures are different. The trend of μ, which moderately decreases by increasing bile salt concentration, agrees with our structural models and can be due to coexistence of two structures, at least.

A combination of experimental (XRPD) and computational (MD-simulation) techniques was used for a detailed study of the structural, dynamic and hydration properties of the ZnAl layered double hydroxides (LDHs) of formula [Zn 0.65 , with y = 0.35 and 0.69, respectively. Our approach was based on a direct comparison made, for the first time, between the observed XRPD diffraction pattern and the MD-simulated pattern of each model that was considered. The XRPD curve is affected (reflection angles and line shapes) by dynamic and structural factors, and the interlayer distribution of the water content. Accordingly, its reproduction through MD modelling is the most suitable means of monitoring these properties of the material. Molecular modelling was performed by MD simulations of models of I and II built up through appropriate modifications of their interlayer total water contents and related distribution. The validated models, namely those that provided the best MD-simulated pattern of I and II, were then used to determine structures

This contribution explores the effect of the bridging diamine upon the aggregation properties of a Zn(II) Schiff-base complex, , both in the solid state and in solution. The X-ray structure of , resulting from the harvest of good quality crystals using chloroform and diethyl ether as solvents, shows the presence of a densely packed dimer in the solid state which pentacoordinates two Zn atoms involved in a μ-phenoxo bridge. Detailed studies in solution, through (1)H NMR, DOSY NMR, and optical spectroscopic investigations, indicate the typical aggregation/deaggregation behaviour on switching from non-coordinating to coordinating solvents, in relation to the Lewis acidic character of such Zn(II) complexes. Thus, while in DMSO-d6 both (1)H NMR and DOSY studies suggest the existence of monomeric species, in chloroform solution experimental data support the existence of aggregates. However, unlike our previous studies, (1)H NMR data in chloroform solution indicate the existence of an asymmetric dimer, as observed in the X-ray crystal structure. This further evidences a very rigid backbone of the dimeric aggregate and can be related to the defined stereochemistry of the chelate cis-1,2-diaminocyclohexane bridge.