Siporska Agnieszka, Makowska Anna, Szydłowski Jerzy
Faculty of Chemistry, University of Warsaw, Zwirki Wigury 101, 02-089, Warsaw, Poland.
J Phys Chem B. 2007 Oct 11;111(40):11632-4. doi: 10.1021/jp074792w. Epub 2007 Sep 18.
The miscibility of isobutyric acid with water and the influence of the isotope substitution of oxygen (16O/18O) in water over a broad concentration range are reported. The system exhibits a phase diagram with an upper critical solution temperature (UCST) and a visible isotope effect thereon. The oxygen isotope substitution decreases the UCST, leading to better miscibility of isobutyric acid with water. The isotope shift, DeltaTc = Tc(18O) - Tc(16O), extrapolated to the 100% enrichment in 18O, is equal to -1.15 K; hence it is much smaller and opposite to that found for deuterium substitution. The origin of the observed miscibility isotope effect has been qualitatively discussed in terms of the condensed-phase isotope effect theory.
报道了异丁酸与水的混溶性以及在较宽浓度范围内水中氧同位素取代（(^{16}O/^{18}O)）的影响。该体系呈现出具有上临界溶液温度（UCST）的相图，并且在其上存在明显的同位素效应。氧同位素取代降低了UCST，导致异丁酸与水具有更好的混溶性。同位素位移(\Delta T_c = T_c(^{18}O) - T_c(^{16}O))，外推到(^{18}O)的100%富集时，等于 -1.15 K；因此它比氘取代时发现的同位素位移小得多且方向相反。已根据凝聚相同位素效应理论对观察到的混溶性同位素效应的起源进行了定性讨论。
