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Ordinary vesicle budding and fusion preserve which side of a membrane a protein domain faces: a cytoplasmic domain remains cytoplasmic, and a luminal domain remains luminal. Invagination can enclose previously external space without transporting its contents through a bilayer. The endoplasmic reticulum lumen is continuous with the space between the two nuclear envelope membranes; it is not the chromosome-containing nucleoplasm. Any proposed evolutionary remodelling must account for these distinct spaces and the membrane connections between them.

The E blastomere produces the intestinal lineage. Maternal SKN-1 and the P2-to-EMS inductive interaction converge on an endoderm gene regulatory network with parallel inputs and partly redundant GATA transcription factors. Loss of one late marker does not establish loss of the lineage.^[ref]

The embryonic endoderm population specified during gastrulation, distinguished from earlier extraembryonic primitive endoderm. In mouse, resulting gut endoderm can include intercalated cells from distinct histories.

An iminium intermediate can lose a proton at either adjacent carbon, generating different enamine double-bond positions. Reaction selectivity can depend on which regioisomer is populated.

A porous gel changes the electrophoretic mobility of charged synthetic polymers through confinement, deformation and pore-to-pore dynamics. Free-draining charge and friction can both grow proportionally to chain length, leaving free-solution mobility nearly length independent; matrix obstruction adds size sensitivity. reptation supplies one weak-field long-chain regime, not a universal calibration. Matrix concentration, effective charge, solvent conditions, conformation, topology, adsorption, electro-osmotic drift and heating can all alter migration. Size standards should match the relevant chemistry and operating regime.

Electronic excitation occurs rapidly compared with nuclear motion. In the Condon approximation, vibronic intensities are proportional to squared overlaps of initial and final vibrational wavefunctions; vertical arrows on a potential diagram summarize this overlap rather than a nuclear trajectory.

A sequence of vibronic transitions sharing a lower vibrational level and reaching successive vibrational levels of another electronic state. frequency differences remove the common electronic origin and reveal vibrational spacings.

A two-index arrangement of vibronic transition wavenumbers. Differences along rows isolate lower-state spacings; differences down columns isolate upper-state spacings. Deviations from exact separability can expose measurement uncertainty, rotational structure or incorrect assignments.

A scale proportional to the average spectroscopic one-electron binding energy of a free ground-state atom’s valence electrons. For an s,p atom, $\chi =C(n_s{\epsilon }_s+n_p{\epsilon }_p)/(n_s+n_p)$, with positive binding energies and a scale constant $C$. It distinguishes s and p binding rather than assigning both one Slater charge.^[ref]

Electron transfer through a ligand shared by two metal centres. Bridge formation, electron transfer and bridge cleavage can leave transferred-ligand connectivity in a substitution-inert product.

electron transfer made favorable by photoexcitation of a donor or acceptor.

Measurement of the energy lost by transmitted electrons to electronic, vibrational or other excitations.

Elemental analysis using Characteristic X-rays, commonly excited by an electron beam.

The 18-electron rule is a useful closed-shell guideline for many low-valent transition-metal complexes, filling nine valence orbitals. It is not universal: many early-metal $d^0$ complexes have fewer electrons, while stable square-planar $d^8$ complexes are often 16-electron.

An orbital- and model-dependent parameter representing nuclear attraction after electronic screening. A screening construction writes $Z_{\mathrm{eff}}=Z-S$; a binding-energy construction requires an additional orbital-energy model.

Atoms, molecules or ions with the same electron count, often compared because their orbital occupations or bonding patterns are related. Equal electron counts do not guarantee identical energies or geometry.

An excess electron stabilized by its surrounding solvent. It can be a highly reactive reducing species.

Motion driven by the force on induced polarization in a nonuniform electric field. In the dipole regime its sign depends on the particle–medium polarizability contrast and its magnitude scales with particle volume.

With interface normal from medium 1 to medium 2, Ampère's boundary condition is $\hat{\mathbf{n}}\times ({\mathbf{H}}_2-{\mathbf{H}}_1)={\mathbf{K}}_f$. With no free surface current, tangential $H$ is continuous. Normal $B$ is continuous independently because magnetic monopoles are absent.