The Structural and Dynamical Effects of Monolignol Coniferyl Alcohol on Biomembranes

Monolignols are lignin precursors that must cross the plasma membrane before polymerization in the cell wall, but their interaction with lipid membranes remains poorly defined experimentally. In this work, we used Neutron Membrane Diffraction (NMD), Small-Angle Neutron Scattering (SANS), Neutron Spin Echo (NSE), and Quasi-Elastic Neutron Scattering (QENS) to examine the structural and dynamical effects of coniferyl alcohol (CA) in a DOPC/DOPE model membrane. Partially deuterated coniferyl alcohol (CA-D5) provided enhanced neutron contrast for probing changes in the trans-bilayer structure and possible distribution within the bilayer. NMD did not resolve CA-D5 at a specific bilayer depth over the nominal concentration range studied. Both NMD measurements of substrate-supported multilamellar bilayers and SANS measurements of unilamellar vesicles in solution revealed a small but clearly resolved bilayer thinning of approximately 1–2 Å, while the overall membrane architecture remained intact. Dynamically, CA-D5 softens the membrane at the collective length scale, as shown by a reduced effective bending modulus from NSE. At the molecular scale, QENS showed no systematic change in lipid lateral diffusivity, although the characteristic microscopic displacement length increased at higher CA-D5 concentrations. These cross-scale measurements show that CA produces measurable but limited changes in membrane structure and dynamics without major membrane reorganization. This membrane-compatible response is consistent with various proposed monolignol transport pathways, including passive permeation and vesicle-associated transport.