Research method
Molecular Dynamics Simulation
Molecular dynamics integrates Newton's equations (classically, or with forces from DFT/QM/MM) to generate a trajectory of nuclear positions. Averages of distances, proton-transfer events, or metadynamics barriers are statistics of that trajectory at a chosen temperature and Hamiltonian — not a diffracted intensity or a measured rate. In this library MD ranges from AIMD of a MOF defect and of GFP's proton shuttle, through neural-network potentials trained on DFT water–gold data, to short classical MD of a calixarene–lysozyme crystal.
Chemists reach for MD when an experiment averages away the motion that might matter: a proton hopping on a missing linker, an excited-state shuttle in GFP, or an associative ORR path in water. It answers 'what does this model do over picoseconds to nanoseconds?' Its main limitation is that the dynamics are computed: they can be faster than femtosecond Raman, invisible to time-averaged XRD, and unable to rank binding sites even when a crystal structure exists.
Evidence
What the evidence shows
Drawn from 8 studies in this library. Each finding starts with a plain-language takeaway, then the denser detail. Supports means evidence for a finding; Challenges means evidence against a stated position; Qualifies marks scope with a short note on each study’s contribution. Challenged positions are labeled — they are not findings.
AIMD of defective UiO-66 makes a proton shuttle that diffraction cannot see. Average Zr⋯O = 2.23 Å matches 300 K experiment, but a direct O0–O1 proton-transfer barrier is only 6.5 kJ mol⁻¹ versus 27.5 kJ mol⁻¹ for an O3-mediated path. NH₃ binds 110.1 versus 75.8 kJ mol⁻¹ at defect versus perfect regions; water can leave, exposing frustrated-Lewis-pair-like Zr. The dynamics are computed, not a measured catalytic turnover.
A learned potential can push DFT-quality forces into nanosecond metadynamics. A PaiNN ensemble trained on PBE-D3 Au(100)–water data, then 2.5 ns path-CV metadynamics at 350 K, finds associative ORR: O₂ is hydrogenated toward *OOH, which is reduced to two *OH with neighbouring water rather than splitting into *OH + *O. The O₂-to-hydroxyl barrier is about 0.3 eV. The model is Au(100) in pure water without explicit cations or applied potential; the barrier is from the NNP landscape, not a measured Tafel slope.
QM/MM AIMD of wtGFP in S₁ transfers a proton in four of five runs within 1 ps (720 fs in TRJI; 350, 380 and 980 fs in II–IV). O–O contacts shorten in 15–20 fs; twist modes drop from 146 to 101 cm⁻¹. Those computed times are faster than the experimental FSRS 3/10 ps phases (DFT barrier underestimation, no MM polarisation); nonadiabatic hops at longer times are omitted.
MD plus docking can design peptides that then meet a wet IC₅₀, which is a stronger claim than MD that cannot rank sites. SARS-CoV-2 Mpro peptides p12–p16 have IC₅₀ 3.11–5.36 μM; at 8-fold excess they cut s01 depletion from >98% to 70–95%; the ion-pair dyad lies 28.5 kJ mol⁻¹ above the neutral state. On dimethylated lysozyme, short MD at each Lys-Me₂ and a crystal of sclx4 encapsulating Lys116-Me₂ still left MM-PBSA unable to rank sites; precipitation limited solution stoichiometry.
Study Role Design N Population Outcome Modelled peptides inhibit SARS-CoV-2 main protease Supports OtherComputational design plus biochemical IC50 assays of Mpro peptide inhibitors Four designed peptides assayed in vitro — no sample cohort N SARS-CoV-2 main protease with designed peptide inhibitors Peptide IC50 values and substrate-depletion inhibition of Mpro Calixarene docks dimethyllysine on lysozyme Supports OtherCrystal and NMR study of p-sulfonatocalix[4]arene bound to dimethylated lysozyme lysines Protein–small-molecule structural study — no cohort N Dimethylated hen egg-white lysozyme with sclx4 Site-selective Lys-Me2 encapsulation by the calixarene TDDFT spectra computed on MD snapshots can assign a surprising UV-vis tail. Protein α3C (54% charged residues) has ε ≈ 7338 M⁻¹ cm⁻¹ at 250 nm and ε ≈ 964 and 501 M⁻¹ cm⁻¹ at 450 and 800 nm; 4–6 Å Lys–Glu contacts modulate ProCharTS charge-transfer bands. Computed CT energies inherit both the TDDFT functional and the MD ensemble.
Open questions
Tensions and limits
Some items are genuine disagreements on the same question. Others mark different assays, populations, or outcomes — limits on how far one study travels — not a forced fight between papers.
MD that is later tested in a cuvette is not the same deliverable as MD that stays inside the computer. Mpro peptides have micromolar IC₅₀ values; GFP AIMD proton-transfer times disagree with 3/10 ps FSRS phases; UiO-66 proton hops are invisible to time-averaged XRD. A student who says 'MD showed the mechanism' must say whether a wet observable confirmed it.
- Modelled peptides inhibit SARS-CoV-2 main protease
- AIMD maps GFP's excited-state proton shuttle
- Defect hydroxides in UiO-66 shuttle protons
Study Role Design N Population Outcome Modelled peptides inhibit SARS-CoV-2 main protease Supports OtherComputational design plus biochemical IC50 assays of Mpro peptide inhibitors Four designed peptides assayed in vitro — no sample cohort N SARS-CoV-2 main protease with designed peptide inhibitors Peptide IC50 values and substrate-depletion inhibition of Mpro AIMD maps GFP's excited-state proton shuttle Supports Computational / modellingONIOM QM/MM AIMD of wtGFP excited-state proton transfer with wavelet spectral analysis Five S1 trajectories; ESPT within ~1 ps in four runs — no experimental sample N Wild-type green fluorescent protein chromophore environment Excited-state proton-transfer timing and vibrational signatures Defect hydroxides in UiO-66 shuttle protons Supports Computational / modellingPBE0+D3 and AIMD of defective UiO-66 proton transfer and NH3 binding Periodic DFT/AIMD study of MOF defects — no sample N Defective UiO-66 zirconium MOF models Dynamic Brønsted acidity and proton-transfer barriers at defect sites A short classical MD on a crystal pose can fail at ranking, while a neural-network AIMD-quality trajectory can propose a path. MM-PBSA could not rank lysozyme Lys-Me₂ sites; the Au(100) NNP metadynamics did propose an associative 0.3 eV ORR path — still without cations or bias. Success is Hamiltonian- and question-specific, not a property of 'having run MD'.
Study Role Design N Population Outcome Calixarene docks dimethyllysine on lysozyme Supports OtherCrystal and NMR study of p-sulfonatocalix[4]arene bound to dimethylated lysozyme lysines Protein–small-molecule structural study — no cohort N Dimethylated hen egg-white lysozyme with sclx4 Site-selective Lys-Me2 encapsulation by the calixarene NN potentials map gold–water ORR paths Supports Computational / modellingPaiNN active-learning NNPs enabling path-CV metadynamics of ORR on Au(100)–water 2.5 ns production metadynamics after AIMD active learning — no sample N Au(100)–water models with O2/OH adsorbates Associative ORR pathway and ~0.3 eV O2-to-hydroxyl barrier
Common misconceptions
Molecular dynamics is a measurement of the real barrier or lifetime.
GFP S₁ transfers in <1 ps in four trajectories, faster than 3/10 ps FSRS phases because DFT barriers are underestimated and MM is not polarisable. The Au ORR 0.3 eV barrier is an NNP/metadynamics landscape. UiO-66 6.5 kJ mol⁻¹ is a computed proton-transfer barrier, not a turnover frequency.
If the average MD distance matches XRD, the trajectory's proton hops are also experimentally established.
UiO-66's 2.23 Å Zr⋯O matches 300 K diffraction; the 6.5 versus 27.5 kJ mol⁻¹ proton paths and NH₃ 110.1 versus 75.8 kJ mol⁻¹ binding are computed. Time-averaged XRD cannot see those hops.
Docking plus MD that produces an IC₅₀ means the computed protonation state is proven.
Peptides p12–p16 inhibit at 3.11–5.36 μM; the 28.5 kJ mol⁻¹ ion-pair-over-neutral dyad preference remains a computed free energy. These are micromolar peptides, not oral antivirals.
Exam-style questions
Short-answer questions that ask you to explain or compare, not recall.
Defective UiO-66 has Zr⋯O = 2.23 Å, matching experiment, and a 6.5 kJ mol⁻¹ direct proton-transfer barrier. Which number is an MD/DFT prediction that XRD cannot confirm?
The 6.5 kJ mol⁻¹ (versus 27.5 kJ mol⁻¹ O3-mediated) barrier and the NH₃ 110.1 versus 75.8 kJ mol⁻¹ defect/perfect contrast. XRD agrees with the average Zr–O distance; it does not time-resolve proton shuttling.
Why must you not quote the Au(100) O₂-to-hydroxyl barrier of ~0.3 eV as an experimental Tafel slope?
It comes from 2.5 ns path-CV metadynamics on a PaiNN potential trained on PBE-D3 data in pure water at 350 K, without explicit cations or applied potential. Gold's high experimental ORR activity is cited as qualitative consistency, not as the same observable.
Four of five GFP S₁ AIMD runs transfer a proton within 1 ps, yet FSRS reports 3 and 10 ps phases. Give two reasons the paper offers for the mismatch.
DFT underestimates the barrier, and the MM region is not polarisable; nonadiabatic hops at longer times are also omitted. The trajectory set is small (four successful S₁ runs).
Mpro peptides reach IC₅₀ 3.11–5.36 μM, but MM-PBSA could not rank calixarene sites on lysozyme. What is different about what MD was asked to do?
The protease work used docking/MD/QM/MM to design sequences that were then synthesised and assayed. The lysozyme work ran short MD on crystal poses and asked MM-PBSA to rank Lys-Me₂ sites — a scoring problem it failed, while crystallography/NMR still identified Lys116-Me₂ encapsulation.
The studies
8 studies in this library bear on Molecular Dynamics Simulation, ordered by citations.
- Charged amino acids absorb past 250 nm
A 67-residue protein with no aromatic side chains still absorbs from 250 to 800 nm because Lys/Glu charge-transfer transitions create Protein Charge Transfer Spectra.
- Defect hydroxides in UiO-66 shuttle protons
Simulations of missing-linker UiO-66 put charge-balancing OH on under-coordinated Zr and show those sites swap between hydroxide and water by rapid proton transfer with extra-framework water.
- Modelled peptides inhibit SARS-CoV-2 main protease
Simulations prefer a neutral His41/Cys145 dyad and guided four designed peptides that bind the Mpro dimer and inhibit substrate cleavage with IC50 values of 3–5 μM.
- Calixarene docks dimethyllysine on lysozyme
p-Sulfonatocalix[4]arene selectively encapsulates Lys116-Me2 on dimethylated lysozyme, mimicking an aromatic cage.
- AIMD maps GFP's excited-state proton shuttle
TD-DFT AIMD and wavelet spectra show GFP ESPT is concerted once low-frequency chromophore modes planarize the H-bond wire.
- 2D IR indexing maps hIAPP helix-to-sheet kinetics
Paired 13C18O labels report dihedral angles: monomeric hIAPP is partly helical at L12A13, then oligomers lose helix and fibers form β-sheets.
- NN potentials map gold–water ORR paths
Equivariant neural-network potentials drive nanosecond metadynamics showing associative ORR on Au(100) in which *OOH is reduced to two *OH, with a ~0.3 eV barrier.
- PROTAC THNAN69 degrades LIMK2, not LIMK1
A cereblon-recruiting degrader based on LIMKi3 and a phenyl dihydrouracil ligand wipes out LIMK2 at nanomolar DC50 while leaving LIMK1 and phospho-cofilin largely intact.
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