Water Isotope Effect on the Phosphatidylcholine Bilayer Properties: A Molecular Dynamics Simulation Study
Bibliographic record
Abstract
Physicochemical properties of heavy water (D2O) differ to some extent from those of normal water. Substituting D2O for H2O has been shown to affect the structural and dynamic properties of proteins, but studies of its effects on lipid bilayers are scarce. In this paper, the atomic level molecular dynamics (MD) simulation method was used to determine the effects of this substitution on the properties of a dipalmitoylphosphatidylcholine (DPPC) bilayer and its hydrating water. MD simulations of two DPPC bilayers, one fully hydrated with H2O and the other with D2O, were carried out for over 50 ns. For H2O, the simple point charge (SPC) model was used, and for D2O, the extended SPC-HW model was employed. Analyses of the simulation trajectories indicate that several properties of the membrane core and the membrane/water interface are affected by replacing H2O by D2O. However, the time-averaged properties, such as membrane compactness, acyl chain order, and numbers of PC-water H (D)-bonds and PC-PC water bridges, are much less affected than time-resolved properties. In particular, the lifetimes of these interactions are much longer for D2O molecules than for H2O ones. These longer lifetimes results in a slightly better ordering of the D2O molecules and average self-diffusion, which is 50% slower compared with the H2O molecules. This large isotope effect has been assigned to the repercussions of the longer lived D-bonding to DPPC headgroups insofar as all water molecules sense the presence of the DPPC bilayer.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".