Self-Diffusion, Dynamical Molecular Conformation, and Liquid Structures of n-Saturated and Unsaturated Fatty Acids

Abstract

The translational movement, the dynamical molecular conformation, and the aggregate structure in the liquid state for three kinds of cis-type unsaturated fatty acids (cis-6-, cis-9-, and cis-11-octadecenoic acids), transtype unsaturated acid (trans-9-octadecenoic acid), and n-saturated acid (octadecanoic acid) have been studied through the measurements of density, self-diffusion coefficient, 13 C NMR spin-lattice relaxation time, and X-ray diffraction. The magnitude of the self-diffusion coefficient, D, fell in sequence of cis-type unsaturated acids > trans-type acid > saturated acid below 350 K. Above 350 K the value of D for the trans-type acid rose to those for the cis-type acids. On the other hand, the density F for the acids also fell in the order of cis-type acids > trans-type acid > saturated acid; the order of the density is just opposite to that expected from the results of the self-diffusion coefficient and other physical properties such as melting point and heat of fusion. This discrepancy between D and F values for the acids is well explained by the models of the clusters in their liquids.

Dynamic Molecular Behavior of Semi-Fluorinated Oleic, Elaidic and Stearic Acids in the Liquid State

“…As represented in a previous paper 9,10 , the value of 1/τ c for each carbon atom of oleic acid, elaidic acid, or stearic acid obviously increases with increasing temperature. At any temperature, rotational movements for carbon atoms at the second position attached to the dimerized carboxyl group are considerably restricted, while those for other carbon atoms increase toward the end of the hydrocarbon chain.…”

The oleic acid-ozone heterogeneous reaction system: products, kinetics, secondary chemistry, and atmospheric implications of a model system – a review

“…They attribute this to the lower degree of order in MOL compared to OL. Under ambient conditions OL is an ordered liquid (Iwahashi et al, 2000(Iwahashi et al, , 1995(Iwahashi et al, , 1991 (Fig. 9), while MOL is probably an isotropic liquid under these conditions.…”

On the microstructure of organic solutions of mono-carboxylic acids: Combined study by infrared spectroscopy, small-angle neutron scattering and molecular dynamics simulations

“…Moreover, the diffraction peaks corresponding to the formation of the ordered structures of the liquid crystal type are observed at about q c = 2.12(1) and 1.65(1) nm À1 , which according to the equation L c = 2p/q c gives 2.96 and 3.81 nm for the correlation length in the MA and SA solutions, respectively. Such kind of ordering is typical for fatty acids and takes place in neat liquids of these molecules [56]. Both the effective size of the aggregates and the order parameter (correlation length) correlate with the effective acid lengths and are greater in the solutions of longer SA molecules.…”