Partitioning of ABA into Bilayers of Di-Saturated Phosphatidylcholines as Measured by DSC

Abstract

Using differential scanning calorimetry, we have investigated partitioning of the plant hormone abscisic acid into a homologous series of di-saturated phosphatidylcholines increasing in chain length from C(14) to C(19). Partition coefficients calculated from the shift in T(m) range from 1280 for DiC(14)PC to 480 for DiC(19)PC. The free energy of transfer is chain-length independent with a value of DeltaG = -17.4 kJ/mol and an enthalpic contribution of DeltaH = -22.6 kJ/mol. The low net entropic contribution of -TDeltaS = -5.2 J/mol agrees with the concept of the bilayer effect, but differs from that of the entropy-driven classic hydrophobic effect valid for partitioning between bulk solvents. Preferential location of the hormone in the outer region of the membrane is indicated by characteristic changes in the transition profiles and by comparison with partitioning into organic solvents whose dielectric constants model the interior and exterior regions of the bilayer. Differences in partitioning and surface pKa between the biologically active ct-ABA and the inactive tt-isomer are discussed for biological relevance.

Interaction of articaine hydrochloride with prokaryotic membrane lipids

“…In our study, the DSC results demonstrated a concentration-dependent change. A comparable change of the DSC thermogram has been revealed by the addition of compounds such as tocopherol [24], abscisic acid [25], cholesterol [26], and cholesterol/vinblastine [27]. A decreased main transition temperature of di-saturated palmitoyl-phosphatidyl-choline bilayer membranes has previously been found from LAs [22].…”

Thermodynamics of Indomethacin Adsorption to Phospholipid Membranes

“…Negative Δ ads S values were previously determined for adsorption of aromatic molecules such as estrone and 4-phenyl phenol to POPC lipid bilayers and for tetracaine adsorbed to SLBs composed of DOPC, DOPC + 28% CHO, and SOPC . In the current studies, adsorption of indomethacin to DOPC resulted in |Δ ads H | > | T Δ ads S | and suggests that indomethacin may behave like abscisic acid, which adsorbed to DOPC through an enthalpically driven process . Similar to the results reported here, adsorption of endocrine-disrupting chemicals from the aqueous phase to saturated, gel-phase DPPC lipids was driven by increased entropy, whereas adsorption from aqueous phase to fluid-phase lipids (DOPC and DMPC) was driven by enthalpic forces …”

“…Following the precedent set in previous publications 33,53,58,77 and because K eq is not always measured at standard conditions, we use the term Δ ads G instead of Δ ads G 0 to represent the Gibbs energies determined experimentally from eq 6. For aqueousphase indomethacin adsorbed to lipid bilayers composed of DOPC at 25 °C, Δ ads G is 9.8 kJ/mol higher than the Δ ads G for the anesthetic tetracaine 9 (Δ ads G = −23.6 kJ/mol) and 16 kJ/ mol higher than the plant hormone, abscisic acid 72 (Δ ads G = −17.4 kJ/mol) adsorbed to DOPC. Indomethacin is about 1.4 times larger in molecular weight compared to that of either tetracaine or abscisic acid.…”

“…Kwon and co-workers also observed negative Δ ads H values for adsorption of endocrine-disrupting small molecules to fluid-phase 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid vesicles and positive Δ ads H values for adsorption to gel phase DPPC lipid vesicles. 53 Indomethacin adsorption to DOPC resulted in higher Δ ads H values compared to the Δ ads H for abscisic acid to DOPC (Δ ads H = −22.6 kJ/ mol) 72 or the adsorption of estrone to fluid-phase POPC liposomes (Δ ads H = −42.6 ± 18.8 kJ/mol). 53 Δ ads H values determined for indomethacin adsorbed to DMPC at 25 °C are intermediate between Δ ads H for tetracaine adsorbed to SLBs composed of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC) (Δ ads H = −31.9 ± 10.5 kJ/mol) and to SOPC + 28% CHO (Δ ads H = −4.58 ± 0.89 kJ/mol).…”

Folding is not required for bilayer insertion: Replica exchange simulations of an α‐helical peptide with an explicit lipid bilayer

“…Similar results were found the COX IV peptide 49 and for several Trp derivatives 50 . In contrast, many aromatic amphiphiles have negative enthalpy changes upon binding to lipid bilayers 3,[51][52][53] . DeVido et al 54 suggest that negative enthalpic changes are generic for spontaneous binding of small molecules to ordered lipid chain phases.…”